U.S. patent application number 14/300915 was filed with the patent office on 2014-12-04 for high-density polydicyclopentadiene.
The applicant listed for this patent is University of Iowa Research Foundation. Invention is credited to Ned B. Bowden, Abhinaba Gupta, Tyler R. Long.
Application Number | 20140353254 14/300915 |
Document ID | / |
Family ID | 47555053 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140353254 |
Kind Code |
A1 |
Bowden; Ned B. ; et
al. |
December 4, 2014 |
HIGH-DENSITY POLYDICYCLOPENTADIENE
Abstract
The invention provides highly cross-linked polydicyclopentadiene
matrices and methods for using such matrices to separate components
having varying cross-sectional areas.
Inventors: |
Bowden; Ned B.; (Iowa City,
IA) ; Gupta; Abhinaba; (Iowa City, IA) ; Long;
Tyler R.; (Iowa City, IA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Iowa Research Foundation |
Iowa City |
IA |
US |
|
|
Family ID: |
47555053 |
Appl. No.: |
14/300915 |
Filed: |
June 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13546252 |
Jul 11, 2012 |
8778186 |
|
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14300915 |
|
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61506528 |
Jul 11, 2011 |
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Current U.S.
Class: |
210/650 ;
210/489; 525/55; 526/171; 526/340.2 |
Current CPC
Class: |
B01D 2323/30 20130101;
B01D 71/44 20130101; B01D 71/26 20130101; C08F 132/06 20130101;
B01D 67/0006 20130101 |
Class at
Publication: |
210/650 ;
210/489; 526/340.2; 526/171; 525/55 |
International
Class: |
B01D 71/26 20060101
B01D071/26; C08F 132/06 20060101 C08F132/06 |
Goverment Interests
GOVERNMENT FUNDING
[0002] This invention was made with government support under Grant
CHE-0848162 awarded by the National Science Foundation. The
government has certain rights in the invention.
Claims
1. A method comprising contacting a membrane comprising a highly
cross-linked polydicyclopentyldiene matrix with a feed solution
comprising a) a first component having a molecular weight in the
range of from about 100 g mol.sup.-1 to about 600 g mol.sup.-1 and
a cross-sectional area of less than about 0.40 nm.sup.2 and b) a
second component having a molecular weight in the range of from
about 100 to about 600 grams g mol.sup.-1 and a cross-sectional
area of greater than about 0.50 nm.sup.2 so that the feed solution
is fractionated into a permeate comprising the first component and
a retentate enriched in the second component.
2. The method of claim 1 wherein the ratio of crosslinked double
bonds to uncrosslinked double bonds in the highly cross-linked
polydicyclopentyldiene matrix is at least about 3:2.
3. The method of claim 1 wherein the ratio of crosslinked double
bonds to uncrosslinked double bonds in the highly cross-linked
polydicyclopentyldiene matrix is at least about 4:1.
4. The method of claim 1 wherein the first component is an organic
compound.
5. The method of claim 1 wherein the first component is a
catalyst.
6. The method of claim 1 wherein the second component is an organic
compound.
7. The method of claim 1 wherein the second component is a
catalyst.
8. The method of claim 1 wherein the feed solution comprises an
organic solvent.
9. The method of claim 1 wherein the feed solution comprises an
aprotic organic solvent.
10. The method of claim 1 wherein the feed solution comprises
water.
11. A method for preparing a highly cross-linked
polydicyclopentdiene matrix comprising polymerizing cyclopentadiene
in the presence of a catalyst to provide a highly cross-linked
polydicyclopentdiene matrix wherein the ratio of crosslinked double
bonds to uncrosslinked double bonds is at least about 3:2.
12. The method of claim 11 wherein the catalyst is Grubb's
catalyst.
13. The method of claim 12 wherein the monomer to catalyst ratio is
at least about 4000.
14. The method of claim 13 wherein the monomer to catalyst ratio is
at less than about 50,000.
15. The method of claim 11 wherein the ratio of crosslinked double
bonds to uncrosslinked double bonds is at least about 7:3.
16. The method of claim 11 wherein the ratio of crosslinked double
bonds to uncrosslinked double bonds is at least about 4:1.
17. A method for preparing a highly cross-linked
polydicyclopentdiene matrix comprising, contacting a starting
cyclopentadiene matrix wherein the ratio of crosslinked double
bonds to uncrosslinked double bonds is less than about 3:2 with an
organic solvent under conditions which yield the highly
cross-linked polydicyclopentdiene matrix wherein the ratio of
crosslinked double bonds to uncrosslinked double bonds increases to
at least about 3:2.
18. A method for preparing a highly cross-linked
polydicyclopentdiene matrix comprising, a) polymerizing
cyclopentadiene in the presence of a catalyst to provide an
intermediate polydicyclopentdiene matrix, and b) contacting the
intermediate cyclopentadiene matrix with an organic solvent under
conditions which yield the highly cross-linked polydicyclopentdiene
matrix wherein the ratio of crosslinked double bonds to
uncrosslinked double bonds increases to at least about 3:2.
19. A highly cross-linked polydicyclopentdiene matrix prepared
according to the method of claim 11.
20. A composite membrane comprising a highly crosslinked
polydicyclopentyldiene matrix on a porous support backing material.
Description
RELATED APPLICATION
[0001] This application is a continuation application of U.S.
application Ser. No. 13/546,252, which was filed on Jul. 11, 2012,
which claims the benefit of priority of U.S. Provisional
Application Ser. No. 61/506,528 filed on Jul. 11, 2011, which
applications are herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0003] Semipermeable membranes play an important part in industrial
processing technology and other commercial and consumer
applications. Examples of their applications include, among others,
biosensors, transport membranes, drug delivery systems, water
purification systems, optical absorbers, and selective separation
systems for aqueous and organic liquids carrying dissolved or
suspended components.
[0004] Generally, semipermeable membranes operate in separation
devices by allowing only certain components of a solution or
dispersion to preferentially pass through the membrane. The fluid
that is passed through the membrane is termed the permeate and
comprises a solvent alone or in combination with one or more of the
other agents in solution. The components that do not pass through
the membrane are usually termed the retentate. The permeate and/or
retentate may provide desired product.
[0005] Membranes are one of the most common and economically
efficient methods to purify active pharmaceutical ingredients (API)
in industry and provide a critical alternative to distillations,
recrystallizations, and column chromatography (B. Schmidt, et al.,
Org. Process Res. Dev. 2004, 8, 998-1008; and S. Muller, et al.,
Eur. J. Org. Chem. 2005, 1082-1096). Distillations require that an
API be stable to elevated temperatures and require significant
amounts of energy to complete. Recrystallizations often result in
APIs with high purities, but not every molecule can be
recrystallized and the recyrstallization conditions are often
difficult to optimize and scale up to an appropriate level. In
addition, the formation of multiple crystalline isomorphs is poorly
understood and results in APIs with different delivery
characteristics in the body. Column chromatography is often used in
the early discovery and development of APIs due to its simplicity
and success, but it is not widely used for large scale production
of APIs due in part to the large volumes of solvents that are used
which necessitate further purification.
[0006] In contrast, the use of nanoporous membranes to purify APIs
can be readily scaled up to purify large quantities of product, use
little energy, and does not require large amounts of solvent (H. P.
Dijkstra, et al., Acc. Chem. Res. 2002, 35, 798-810; M. F. J.
Dijkstra, et al., J Mem. Sci. 2006, 286, 60-68; J. Geens, et al.,
Sep. Sci. Technol 0.2007, 42, 2435-2449; C. J. Pink, et al., Org.
Proc. Res. Dev. 2008, 12, 589-595; and P. Silva, et al., Adv.
Membr. Technol. Appl. 2008, 451-467). The use of nanoporous
membranes in industry is common in aqueous separations or to purify
gasses by pervaporation, but nanoporous membranes are used less
commonly with organic solvents. A breakthrough was realized in 1990
when nanoporous membranes based on "organic solvent nanofiltration"
(OSN) membranes were used in an ExxonMobil refinery to separate oil
from dewaxing solvents (R. M. Gould, et al., Environ. Prog. 2001,
20, 12-16). The next generation of OSN membranes based on
cross-linked polyaniline, polyimides, and other polymers and sold
as StarMem.TM., Duramem.TM., and PuraMem.TM. have been developed
that function in a wide range of organic solvents and separate
organic molecules dissolved in organic solvents (D. A. Patterson,
et al., Desalination 2008, 218, 248-256; Y. H. See-Toh, et al., J.
Mem. Sci. 2008, 324, 220-232; Y. H. S. Toh, et al., J. Mem. Sci.
2007, 291, 120-125; and L. G. Peeva, et al., In Comprehensive
membrane science and engineering; Drioli, E., Giorno, L., Eds.;
Elsevier: Boston, 2010; Vol. 2, p 91-111).
[0007] All OSN membranes report values for the "molecular weight
cutoff" (MWCO) that correspond to the molecular weight where
molecules transition from having high to low values of permeation
(Y. H. S. Toh, et al., J. Mem. Sci. 2007, 291, 120-125; and L. G.
Peeva, et al., In Comprehensive membrane science and engineering;
Drioli, E., Giorno, L., Eds.; Elsevier: Boston, 2010; Vol. 2, p
91-111). Simply, molecules below the MWCO permeate the membranes
but molecules above the MWCO have significantly reduced permeation
and are retained. The use of membranes that feature a MWCO has
limitations for the separation of catalysts from APIs because the
ligands on a catalyst often have molecular weights that are similar
to that of the product. Thus, ligands such as PPh.sub.3 (MW: 262 g
mol.sup.-), PCy.sub.3 (MW: 280 g mol.sup.-1), and binol (MW: 286 g
mol.sup.-1) can be very challenging to separate from APIs with
similar molecular weights or impossible to separate if an API has a
higher molecular weight.
[0008] The state-of-the-art membranes to separate catalysts from
the products of reactions are based on highly cross-linked organic
polymers that function in a range of organic solvents. For instance
RuBINAP catalyst (molecular weight 795 g mot) was retained by OSN
membranes at levels of approximately 98% for multiple cycles and
was active for long periods of time (D. Nair, et al., Org. Proc.
Res. Dev. 2009, 13, 863-869). The product was allowed to permeate
the membranes and was isolated on the side of the membrane opposite
of the catalyst. Part of the success of this project was the high
molecular weight of the catalyst compared to the product (molecular
weight 160 g mol.sup.-1) which allowed the catalyst to have a
molecular weight significantly higher than the MWCO of the membrane
(220 g mol.sup.-1).
[0009] In other work, the flux of trialkylamines (i.e. NR.sub.3
where R is methyl, ethyl, propyl, etc) through commercially
available OSN membranes (StarMem.TM. membranes) were studied (D. A.
Patterson, et al., Desalination 2008, 218, 248-256). This study
described perplexing results because even though the molecular
weight cutoff was 220 g mol.sup.-1, only 19% of tridodecylamine
(molecular weight 522 g mol.sup.-1) was retained (81% permeated the
membrane). Also, when the system was studied using cross-flow, the
rejection rate for all of the trialkylamines was much poorer than
expected. The authors concluded that the use of a molecular weight
cutoff for trialkylamines and the StarMem membranes was not useful
and gave misleading predictions.
[0010] OSN membranes have an important role in the chemical
industry, but they have two limitations that hinder applications in
many commercial syntheses of small molecules. First, to be
effective there must be a large difference between the molecular
weight of the catalyst and the organic product. The molecular
weights of many common ligands range from a couple to several
hundred grams per mole and would not provide enough difference in
molecular weight to separate them from products with similar or
higher molecular weights. Second, the MWCO of a membrane is defined
as the molecular weight at which 90 to 98% of the solute is
rejected; thus, significant amounts of a molecule may pass through
these membranes even if the molecular weight is larger than the
cutoff.
[0011] Other membranes composed of nanopores etched in
polycarbonate, zeolites, and metal-organic frameworks have been
fabricated by others that can separate organic molecules. Zeolites
are well known for distinguishing molecules based on size, but they
are not used as membranes for molecules with the dimensions
described in this proposal. Nanopores etched in polycarbonates have
found some success, but the molecular size cutoffs are typically
not sharp and the membranes suffer from low flux, fouling, and
degradation with time (A. Asatekin and K. K. Gleason Nano Lett.
2011, 11, 677-686; K. B. Jirage, et al., Science 1997, 278,
655-658; C. R. Martin, et al., J. Phys. Chem. B 2005, 105,
1925-1934; and M. Wirtz, et al., Chem. Rec. 2002, 2, 112-117).
Metal-organic frameworks have been developed that use porphyrins to
define pores, but all of these examples require either water as the
solvent or only separate gasses (J. T. Hupp, et al., Langmuir 2006,
22, 1804-1809; R. Q. Snurr, et al., AIChE Journal 2004, 50,
1090-1095, B. Chen, et al., Acc. Chem. Res. 2010, 43, 1115-1124;
D.-H. Liu and C.-L. Zhong J. Mater. Chem. 2010, 20, 10308-10318; U.
Mueller, et al., J. Mater. Chem. 2006, 16, 626-636; K. M. Thomas
Dalton Tran. 2009, 1487-1505; D. Zhao, et al., Acc. Chem. Res.
2011, 44, 123-133; and R. Zou, et al., Cryst Eng Comm 2010, 12,
1337-1353).
[0012] PDCPD synthesized from the polymerization of commercially
available dicyclopentadiene and the Grubbs catalyst is a relatively
new material (M. Perring and N. B. Bowden Langmuir 2008, 24,
10480-10487; J. K. Lee, et al., J Polym. Sci., Part B: Polym. Phys
2007, 45, 1771-1780; L. M. Bellan, et al., Macromol. Rap. Comm.
2006, 27, 511-515; A. D. Martina, et al., J. Appl. Polym. Sci.
2005, 96, 407-415; and J. D. Rule and J. S. Moore Macromolecules
2002, 35, 7878-7882). This polymer is cross-linked and forms a
solid, hard material that, when synthesized by other catalysts, is
used in the fabrication of the hoods of semitrucks and
snowmobiles.
SUMMARY OF THE INVENTION
[0013] Although PCPDCD is a hard polymer, it will readily swell in
organic solvents and allow molecules to pass through it. Applicant
has discovered a highly cross-linked PDCPD that can be used for
liquid separations. It has been determined that molecules with a
variety of polar functional groups and differing molecular weights
permeate PDCPD membranes while other molecules do not. The
difference in permeation is based on cross-sectional area of each
molecule. Molecules that have cross-sectional areas larger than a
critical value do not permeate the membranes while those below the
critical value do permeate them (T. E. Balmer, et al., Langmuir
2005, 21, 622-632; M. R. Shah, et al., J. Mem. Sci. 2007, 287,
111-118; J. A. Cowen, et al., Rev. Sci. Instr. 2003, 74, 764-776;
J. M. Watson, et al., J. Mem. Sci. 1992, 73, 55-71; S. Banerjee, et
al., J. Appl. Polym. Sci. 1997, 65, 1789-1794; J. Du Pleiss, et
al., Eur. J. Pharm. Sci. 2002, 15, 63-69; W. A. Philip, et al., ACS
Appl. Mater. Inter. 2009, 1, 472-480; V. Sarveiya; J. F. Templeton
and H. A. E. Benson Eur. J. Pharm. Sci. 2005, 26, 39-46; Y. Tamai,
et al., Macromolecules 1994, 27, 4498-4508; Y. Tamai, et al.,
Macromolecules 1995, 28, 2544-2554; and J. Crank The mathematics of
diffusion; Clarendon Press: Oxford, 1970).
[0014] Both polar and apolar molecules permeate if their
cross-sectional area is below the critical value. This criterion
for separation is based on the highly cross-linked matrix of PDCPD
that results in a set of pores that allow the polymer to have
unique properties for molecules with molecular weights between
100-600 g mol.sup.-1.
[0015] The highly cross-linked PDCPD described herein are the first
membranes to separate organic molecules with these molecular
weights based on cross-sectional areas. Molecules with a
cross-sectional area of 0.50 nm.sup.2 or higher do not permeate the
membranes and molecules with cross-sectional areas of 0.40 nm.sup.2
do permeate them. Notably, many common ligands for metals have
cross-sectional areas above 0.50 nm.sup.2 and products of reactions
with these ligands have cross-sectional areas 0.40 nm.sup.2 or
lower.
[0016] Accordingly, Applicant has discovered the first nanoporous
membranes that separate many common ligands for metals from other
molecules that possess molecular weights lower and higher than
those of the ligands. The separation is due to the large
cross-sectional area of ligands which hinders their diffusion
through highly cross-linked PDCPD. In contrast to the ligands which
do not permeate these membranes at any level, molecules with low to
high molecular weights permeate them if their cross-sectional areas
are below a critical threshold. Thus, the PDCPD materials of the
invention retain key molecules that are common ligands for metals
while allowing molecules with molecular weights over three times as
high to permeate. Existing OSN membranes do not have this property
for molecules with molecular weights of 100-600 g mol.sup.-1.
[0017] In one embodiment the invention provides a method
comprising, contacting a membrane comprising a highly cross-linked
polydicyclopentyldiene matrix with a feed solution comprising a) a
first component having a molecular weight in the range of from
about 100 g mol.sup.-1 to about 600 g mol.sup.-1 and a
cross-sectional area of less than about 0.40 nm.sup.2 and b) a
second component having a molecular weight in the range of from
about 100 to about 600 g mol.sup.-1 and a cross-sectional area of
greater than about 0.50 nm.sup.2 so that the feed solution is
fractionated into a permeate comprising the first component and a
retentate enriched in the second component.
[0018] In another embodiment the invention provides a method for
preparing a highly cross-linked polydicyclopentdiene matrix
comprising polymerizing cyclopentadiene in the presence of a
catalyst to provide the highly cross-linked polydicyclopentdiene
matrix.
[0019] In another embodiment the invention provides a method for
preparing a highly cross-linked polydicyclopentdiene matrix
comprising, contacting a starting cyclopentadiene matrix wherein
the ratio of crosslinked double bonds to uncrosslinked double bonds
is less than about 3:2 with an organic solvent under conditions
which yield the highly cross-linked polydicyclopentdiene matrix
wherein the ratio of crosslinked double bonds to uncrosslinked
double bonds increases to at least about 3:2.
[0020] In another embodiment the invention provides a method for
preparing a highly cross-linked polydicyclopentdiene matrix
comprising, a) polymerizing cyclopentadiene in the presence of a
catalyst to provide an intermediate polydicyclopentdiene matrix,
and b) contacting the intermediate cyclopentadiene matrix with an
organic solvent under conditions which yield the highly
cross-linked polydicyclopentdiene matrix wherein the ratio of
crosslinked double bonds to uncrosslinked double bonds increases to
at least about 3:2.
[0021] In another embodiment the invention provides a method
comprising contacting a membrane comprising a highly cross-linked
polydicyclopentyldiene matrix of the invention with a feed solution
comprising a) a first component having a molecular weight in the
range of from about 100 to about 600 g mol.sup.-1 and a
cross-sectional area of less than about 0.40 nm.sup.2 and b) a
second component having a molecular weight in the range of from
about 100 to about 600 g mol.sup.-1 and a cross-sectional area of
greater than about 0.50 nm.sup.2 so that the feed solution is
fractionated into a permeate comprising the first component and a
retentate enriched in the second component.
[0022] In another embodiment the invention provides a highly
cross-linked polydicyclopentdiene matrix prepared according to a
method of the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0023] FIG. 1. Illustrates a cross-sectional schematic of an
apparatus that can be used to measure permeation through PDCPD
membranes.
[0024] FIG. 2. Illustrates, a) The unreacted five membered ring of
cyclopentadiene that is responsible for the infrared absorption
peak at 704 cm.sup.-1 and b) The infrared spectrum of PDCPD in a
region of interest.
[0025] FIG. 3. Is a graphic representation of the amount of
hexadecane (in mmol) that was downstream of a membrane as a
function of time. The solvent was a) CH.sub.2Cl.sub.2 and b)
toluene.
[0026] FIG. 4. Shows the molecules that were studied for their
permeation through PDCPD membranes hereinbelow.
DETAILED DESCRIPTION
[0027] As used herein, the term "membrane" means a semipermeable
material which can be used to separate components of a feed fluid
into a permeate that passes through the membrane and a retentate
that is rejected or retained by the membrane.
[0028] As used herein, the term "matrix" means a regular, irregular
and/or random arrangement of polymer molecules such that on a
macromolecular scale the arrangements of molecules may show
repeating patterns, or may show series of patterns that sometimes
repeat and sometimes display irregularities, or may show no
pattern. On a scale such as would be obtained from SEM, X-Ray or
FTNMR, the molecular arrangement may show a physical configuration
in three dimensions like those of networks, meshes, arrays,
frameworks, scaffoldings, three dimensional nets or three
dimensional entanglements of molecules. The matrix may be non-self
supporting. Preferably, the matrix is in the form of a thin film
with an average thickness from about 5 nm to about 10000 nm, and
more preferably about 5 to about 400 nm. In usual practice, the
matrix is grossly configured as an ultrathin film or sheet.
[0029] As used herein the term "highly crosslinked" as applied to a
polydicyclopentyldiene matrix includes martices wherein the ratio
of crosslinked double bonds to uncrosslinked double bonds is at
least about 3:2. In one embodiment of the invention the ratio of
crosslinked double bonds to uncrosslinked double bonds is at least
about 7:3. In another embodiment of the invention the ratio of
crosslinked double bonds to uncrosslinked double bonds is at least
about 4:1.
[0030] In one embodiment the invention provides a composite
membrane comprising a highly crosslinked polydicyclopentyldiene
matrix on a porous support backing material. The porous support
backing material can comprise a polymeric material containing pore
sizes which are of sufficient size to permit the passage of
permeate therethrough. Examples of porous support backing materials
which may be used to prepare composite membranes of the invention
include polymers such as polysulfones, polycarbonates, microporous
polypropylenes, polyamides, polyimines, polyphenylene ethers, and
various halogenated polymers such as polyvinylidine fluoride.
[0031] The membranes of the invention can be used to separate
molecules having molecular weights in the range of from about 100
to about 600 g mol.sup.-1. Molecules that can be separated include
organic compounds, such as synthetic intermediates, pharmaceutical
agents, catalysts, dyes, food additives, low molecular weight
polymers (oligomers), some ligands for metals, and inorganic
compounds such as those that bind to low molecular weight organic
ligands or no organic ligands.
[0032] The feed solutions of the methods of the invention can
comprise catalyst as components which are to be separated from
other components in the feed solution. Such catalysts include
palladium chloride, osmium dihydroxylation catalysts, acids, bases,
hydrogenation catalysts (e.g. Wilkinson's catalyst), oxidation
catalysts or reagents, nanocolloids of any one or combination of
different elements, catalysts based on transition metals that spend
part or all of their catalytic cycle in the homogeneous phase,
catalysts based on copper or other metals that catalyze
enantioselective Diels-Alder reactions or aldol reactions,
catalysts based on Pd that are applied in Buchwald-Hartwig or
Suzuki or Sonogashira or other coupling reaction. Additionally, the
ligands to many metals can be considered a component of a
catalyst.
[0033] The feed solutions can comprises a broad range of polar and
non-polar solvents. For example, suitable solvents include
paraffins (e.g. n-pentane, n-hexane, hexanes, n-heptane,
cyclopentane, cyclohexane, methylcyclopentane, and naphtha),
isopars, halogenated hydrocarbons (e.g. chloroform, methylene
chloride, carbontetrachloride, and the Freon class of halogenated
solvents), ethers (e.g., tetrahydrofuran and di(C1-C6)alkylethers),
water, other ionic liquids (e.g. 1-butyl-3-methylimidazolium
hexafluorophosphate), and other polar solvents. In one embodiment
of the invention the feed solution comprises an aprotic organic
solvent. In one embodiment of the invention the feed solution
comprises a protic organic solvent. In one embodiment of the
invention the feed solution comprises water. In one embodiment of
the invention the feed solution comprises methylene chloride,
toluene, tetrahydrofuran, methanol, ethyl acetate, chloroform,
benzene, DMF, DMSO, or other organic solvent.
[0034] In one embodiment the invention provides a method for
preparing a highly cross-linked polydicyclopentdiene matrix
comprising polymerizing cyclopentadiene in the presence of a
catalyst. Suitable catalysts include Grubb's catalyst. In one
embodiment of the invention the monomer to Grubb's catalyst ratio
is at least about 4000. In another embodiment the monomer to
Grubb's catalyst ratio is at less than about 50,000.
[0035] In one embodiment the invention provides a method for
preparing a highly cross-linked polydicyclopentdiene matrix
comprising, contacting a starting cyclopentadiene matrix wherein
the ratio of crosslinked double bonds to uncrosslinked double bonds
is less than about 3:2 with an organic solvent under conditions
which yield the highly cross-linked polydicyclopentdiene matrix.
Any suitable organic solvent can be used. For example, suitable
solvents may include aprotic organic solvents (e.g. benzene,
toluene, methylene chloride, chloroform, carbontetrachloride,
tetrahydrofuran, pentane, or hexanes, or a mixture thereof). In one
embodiment the solvent comprises toluene or methylene chloride, or
a mixture thereof.
[0036] The invention will now be illustrated by the following
non-limiting Examples.
EXPERIMENTAL
Characterization and Measurements
[0037] .sup.1H NMR spectra were acquired on a Bruker DPZ-300 NMR at
300 MHz or a Bruker DRX-400 NMR at 400 MHz and referenced to TMS.
The concentration of Co(salen) was acquired on a Varian Cary 100
Scan UV-Visible spectrophotometer and Varian 720-ES ICP-OES
(inductively coupled plasma-optical emission spectrometer). The
thicknesses of the membranes were determined using a Micromaster
microscope at the highest magnification. Infrared spectra were
acquired on a Bruker Tensor 27. A room temperature DTGS (deuterated
triglycine sulfate) detector was used. All chemicals were purchased
at their highest purity from Aldrich or Acros and used as
received.
[0038] Calibration of UV-VIS Spectrophotometer.
[0039] Co.sup.II(salen) (23 mg, 0.039 mmol) was dissolved in
toluene (0.5 mL) prior to the addition acetic acid (0.01 mL, 0.18
mmol). The mixture was stirred at room temperature for 1 h to yield
Co.sup.II(salen) with an acetate counterion. Here
Co.sup.III(salen)OAc is referred to as Co(salen) for the rest of
this report. Toluene and the excess acetic acid were removed under
vacuum. The Co(salen) was dissolved in CH.sub.2Cl.sub.2 (10 mL) and
stirred at room temperature for 24 h. The solvent was removed and
Co(salen) was redissolved in CH.sub.2Cl.sub.2 (10 mL) to yield a
0.00386 M solution. This solution was diluted to make standard
solutions to calibrate the instrument. The intensity of the peak at
410 nm in each of the spectra was measured and plotted against
concentration to create a calibration curve.
[0040] Calibration of ICP-OES.
[0041] Standards for Co were made by diluting a standard solution
containing 9908 ppm of Co in 1-2 wt. % of HNO.sub.3 with water. The
concentrations of the standards were 0.248 ppm, 0.495 ppm 0.990
ppm, 1.99 ppm, 4.95 ppm, 7.93 ppm, 15.8 ppm, and 39.6 ppm. The
standards were used to calibrate the ICP-OES before running the
samples for Table 2. A 1 ppm solution of was Y used as an internal
standard.
[0042] Optical Spectroscopy.
[0043] The thickness of a membrane was determined by cutting a
section of a membrane and placing it under the microscope. The
section of membrane was held vertically with tweezers and the edge
was imaged at the highest magnification. An optical micrograph was
taken and the thickness was measured.
[0044] Synthesis of PDCPD Membranes at a 5,000:1
Dicyclopentadiene:Grubbs Catalyst Ratio.
[0045] A 20 mg/mL solution of Grubbs first generation catalyst was
made using 1,2-dichloroethane. A sample of this solution (0.246 mL,
6.0.times.10.sup.-3 mmol of catalyst) was added to 4 mL of
dicyclopentadiene heated to 40.degree. C. to melt it. The melting
point of dicyclopentadiene is 33.degree. C. This solution was
immediately placed between two glass slides with 100 .mu.m thick
paper as spacers along the edges. The sample was heated to
50.degree. C. for 2 h and then removed from the glass slides.
[0046] Synthesis of PDMS Membrane.
[0047] These membranes were fabricated similar to methods described
in prior work. Sylgard 184 was mixed with a curing agent in a 10:1
ratio and degassed. The PDMS was poured over a flat glass slide
while allowing any excess to flow over the side. The glass had been
coated with a monolayer of trichloro(1H, 1H, 2H,
2H-perfluoroctyl)silane prior to its use. The PDMS was cured in a
65.degree. C. oven for 24 h. The PDMS membrane was delaminated from
the glass side by swelling in dichloromethane.
[0048] Permeation of Co(Salen) Through PDCPD Membranes (Table
2).
[0049] Co(salen) was synthesized with acetic acid and toluene as
described before. A PDCPD membrane was added to the glass apparatus
to study permeation. CH.sub.2Cl.sub.2 (25 mL) was added to the
downstream side of the membrane. CH.sub.2Cl.sub.2 (25 mL) with
Co(salen) (0.038 mmol) was added to the upstream side of the
membrane. Both sides of the membrane were stirred continuously at
room temperature. Aliquots (4 mL) were removed from both sides of
the membrane at 24 and 48 h.
[0050] The concentration of Co(salen) was determined by UV-Vis
spectroscopy or ICP-OES using the calibration curves that were
determined as previously described. Samples for ICP-OES were
prepared by first drying each aliquot and burning off all the
organic materials with a Bunsen burner. The Co was dissolved in 1
mL of a 3:1 solution of concentrated HCl and concentrated
HNO.sub.3. The aliquot from upstream side of the membrane was
diluted with 10 mL of water. The aliquot from the downstream side
of the membrane was diluted with 5 mL of water. The samples were
run through ICP-OES after it was calibrated on the same day as the
measurements.
[0051] Permeation of Co(Salen) Through PDCPD Membranes Treated with
Ethyl Vinyl Ether (Table 2 Entries 6-8).
[0052] Co(salen) was synthesized with acetic acid and toluene as
described before. CH.sub.2Cl.sub.2 (25 mL) and ethyl vinyl ether (5
mL, 52 mmol) were added to the downstream side of the membrane and
CH.sub.2Cl.sub.2 (25 mL) and ethyl vinyl ether (5 mL, 52 mmol) with
Co(salen) (0.038 mmol) were added to the upstream side of the
membrane. Both sides of the membrane were stirred continuously at
room temperature. At 24 and 48 h aliquots (4 mL) of solvent were
removed from both sides of the membrane. The aliquots were used to
determine the concentration of Co(salen) by UV-Vis spectroscopy as
previously described.
[0053] Permeation of Co(Salen) Through a PDMS Membrane (Table
1).
[0054] Co(salen) was synthesized with acetic acid and toluene. A
PDMS membrane was added to the apparatus to study permeation.
CH.sub.2Cl.sub.2 (25 mL) was added to the downstream side of the
membrane. CH.sub.2Cl.sub.2 (25 mL) with Co(salen) (0.038 mmol) were
added to the upstream side of the membrane. Both sides of the
membrane were stirred continuously at room temperature. At 2, 4,
and 6 h aliquots (4 mL) were removed from both sides of the
membrane. The aliquots were used to determine the concentration of
Co(salen) by UV-Vis spectroscopy as previously described.
[0055] Swelling of PDCPD by Various Solvents (Table 3).
[0056] Commercially available dicyclopentadiene (24 mL, 0.177 mol)
was heated in a glass vial at 35.degree. C. for 10 minutes to melt
it. The Grubbs catalyst (15 mg, 0.017 mmol) was mixed with
dichloromethane (0.5 mL), added to the dicyclopentadiene, and
thoroughly mixed. The solution was heated in a water bath at
50.degree. C. for 1.5 h. The slab of PDCPD was removed from the
vial and swelled in dichloromethane mixed with ethyl vinyl ether.
The slab of PDCPD was cut into 12 small cubes. All the cubes were
dried in air and then under vacuum.
[0057] The weights of cubes of PDCPD were measured. Each cube was
placed in a glass vial with 10 mL of solvent to completely immerse
the cube for 24 h. Next, the cubes were removed from the vials and
briefly wiped with kimwipes to remove solvent from their surfaces.
The weights of the swollen PDCPD cubes were measured. The swollen
weight was divided by the dry weight of PDCPD to calculate how well
each solvent swells PDCPD.
[0058] Permeation of Organic Molecules Through PDCPD Membranes with
Different Solvents (Tables 4 and 5).
[0059] A membrane--made with a monomer:catalyst loading of
5000:1--was added to the apparatus to study permeation.
CH.sub.2Cl.sub.2, toluene, or THF (25 mL) was added to the
downstream side of the membrane and 25 mL of the same solvent was
added to the upstream side of the membrane with 3 mmol of the
substrate and 1 mmol hexadecane as an internal standard. Both sides
of the membrane were stirred continuously at room temperature. At
24 and 48 h a 1 mL aliquot was removed from both sides. The aliquot
was used to determine the concentration of the substrate and
hexadecane by .sup.1H NMR spectroscopy. The concentrations were
found by the addition of known amounts of tetraethylene glycol to
each aliquot and comparing the known concentration of tetraethylene
glycol with the concentration of the molecule of interest.
[0060] Rate of Flux of Hexadecane Through a 5000/1 PDCPD
Membrane.
[0061] A membrane--made with a monomer:catalyst loading of
5000:1--was added to the apparatus to study permeation.
CH.sub.2Cl.sub.2 (20 mL) was added to the upstream and downstream
sides of the membrane. The membrane was allowed to equilibrate for
30 min. CH.sub.2Cl.sub.2 (5 mL) was added to the downstream side of
the membrane and CH.sub.2Cl.sub.2 (5 mL) was added to the upstream
side of the membrane with hexadecane (1 mmol). Both sides of the
membrane were stirred continuously at room temperature. At 1, 2,
and 3 h a 1 mL aliquot was removed from both sides. An .sup.1H NMR
spectrum was taken of each aliquot using tetraethylene glycol as an
internal standard as described previously.
[0062] Flux is the amount of material in moles that progress
through a unit area of a membrane per unit time. The mmole of
hexadecane on the downstream side as determined by .sup.1H NMR
spectroscopy was plotted against time. The slope of the graph was
divided by the area of the membrane (7.07 cm.sup.2) resulting in
the flux of hexadecane. The aliquots were obtained early when flux
can be approximated as unidirectional.
[0063] Density of Cross-Links of PDCPD Membranes.
[0064] IR spectroscopy was used to determine the density of
cross-links in PDCPD. Dicyclopentadiene (5%, 10%, 15% and 20% by
volume solutions) in dioxane was used to find a calibration curve.
The IR spectrum of each solution was measured using a cell with a
fixed pathlength of 100 .mu.m. The intensity of the peak at 704
cm.sup.-1 in each of the IR spectra was measured and plotted
against concentration to yield the calibration curve.
[0065] A 20 mg/mL solution of the Grubbs first generation catalyst
in 1,2-dichloroethane was made. Commercially available
dicyclopentadiene (4 mL, 0.029 mmol) was heated to 40.degree. C.
The catalyst solution (0.246 mL, 6.0.times.10.sup.-3 mmol of
catalyst) was added to dicyclopentadiene. A sample of this solution
was added to the top of a glass slide and was pressed by down by
another glass slide. This set up was heated to 50.degree. C. for 2
h. The glass slides were removed from the PDCPD membranes and the
thicknesses were measured using an optical microscope as described
previously.
[0066] Eleven PDCPD membranes were fabricated and the IR spectrum
of each was obtained. The intensity of the peak at 704 cm.sup.-1
for each of the membranes was fitted to the calibration curve and
the density of unreacted cyclic olefin in PDCPD was calculated. The
membranes were immersed in methylene chloride in glass vials for an
hour. The dichloromethane was decanted off and any remaining
solvent in the membrane was removed in vacuo for 12 h. The IR
spectra were measured for all of the membranes. The intensity of
the peak at 704 cm.sup.-1 for each of these membranes was fitted to
the calibration curve and the density of unreacted cyclic olefin in
PDCPD was calculated.
[0067] Isolation of Cholesterol from Tricyclohexylphosphine,
Triphenylphosphine, and Tributylamine.
[0068] A membrane--made with a monomer:catalyst loading of
5000:1--was added to the apparatus to study permeation.
CH.sub.2Cl.sub.2 (23 mL) was added to the downstream side of the
membrane and CH.sub.2Cl.sub.2 (25 mL) was added to the upstream
side of the membrane with cholesterol (3 mmol),
tricyclohexylphosphine (2 mmol), triphenylphosphine (2 mmol), and
tributylamine (3 mmol). The solutions on the downstream and
upstream sides of the membranes were continuously stirred. A 2 mL
aliquot was removed from the upstream side immediately after it was
added to the apparatus. The solvent was removed and a .sup.1H NMR
spectrum was obtained. At 48 h aliquots (5 mL) were removed from
both sides of the membrane. The solvent was removed and .sup.1H NMR
spectra were obtained.
[0069] Isolation of Nitrobenzaldehyde from Binol.
[0070] A membrane--made with a monomer:catalyst loading of
5000:1--was added to the apparatus to study permeation.
CH.sub.2Cl.sub.2 (50 mL) was added to the downstream side of the
membrane and CH.sub.2Cl.sub.2 (25 mL) was added to the upstream
side of the membrane with binol (0.264 g) and nitrobenzaldehyde
(0.484 g). The solvent on both sides of the membrane was stirred
continuously at room temperature. At 24 h the solvent from the
downstream side was removed and evaporated to recover
nitrobenzaldehyde (0.249 g). The solvent was replaced with
CH.sub.2Cl.sub.2 (50 mL). At 48 h the solvent was removed from the
downstream side and evaporated recover nitrobenzaldehyde (0.186 g).
Also at 48 h, the solvent from the upstream side was removed and
evaporated to recover nitrobenzaldehyde (50 mg) and binol (0.046
g). CH.sub.2Cl.sub.2 (25 mL) was added the upstream side and
stirred for 24 h. The solvent was removed and evaporated to yield
0.103 g of binol. The membrane was removed from the apparatus, cut
into pieces, and placed into a flask with CH.sub.2Cl.sub.2 (50 mL)
for 24 h. The CH.sub.2Cl.sub.2 was evaporated to yield an
additional 0.033 g of binol. The total recovery of
nitrobenzaldehyde from solvent downstream of the membrane was 90%
with <3% binol contamination. The total recovery of binol from
solvent upstream of the membrane was 69%.
[0071] Recycling of a PDCPD Membrane.
[0072] A PDCPD membrane was added to the apparatus to study
permeation. CH.sub.2Cl.sub.2 (50 mL) was added to the downstream
side of the membrane and CH.sub.2Cl.sub.2 (15 mL) was added to the
upstream side of the membrane with binol (0.286 g, 1 mmol) and
nitrobenzaldehyde (0.151 g, 1 mmol). At 24 and 48 h the solvent
from the downstream side was removed and evaporated to recover
nitrobenzaldehyde. The solvent was replaced with fresh
CH.sub.2Cl.sub.2 (50 mL). At 72 h the solvent on the upstream and
downstream sides of the membrane were remove and evaporated to
recover binol and nitrobenzaldehyde. Fresh CH.sub.2Cl.sub.2 (30 mL)
was added upstream of the membrane to extract binol from the
membrane. At 84 h solvent upstream of the membrane was removed and
evaporated to recover binol. This completed cycle 1 and cycles 2
and 3 were completed with the same PDCPD membrane. In cycle 1 99%
of the nitrobenzaldehyde and 40% of the binol were recovered, in
cycle 2 79% of the nitrobenzaldehyde and 4% of the binol were
recovered, and in cycle 3 72% of the nitrobenzaldehyde and 82% of
the binol were recovered.
[0073] Measurement of the Critical Dimension and Critical Area.
[0074] The software used for these measurements was Spartan '08
V1.2.0. Each molecule was drawn in the software using a ball and
spoke representation and its energy was minimized by finding the
equilibrium geometry at ground state with a semi-empirical method
using AM1 parameters. The surface area and molecular volume were
calculated based on a space filling model. The space filling model
chosen was a 3D molecular model with atoms represented by spheres
whose radius is assumed to be the Van der Waals radius determined
by the electron density cut-off at 0.002 electrons/.ANG..sup.3.
[0075] Each molecule was analyzed to find the conformation with the
lowest rectangular, cross-sectional area. The two dimensions of the
rectangle were measured and the longer dimension was labeled the
critical dimension and the area was labeled as the critical
area.
Results and Discussion
Fabrication of PDCPD Membranes and the Apparatus to Measure
Permeation.
[0076] Membranes composed of PDCPD were readily fabricated by the
polymerization of commercially available dicyclopentadiene using
the Grubbs first generation catalyst at molar ratios of >4,000:1
dicyclopentadiene:Grubbs catalyst. The Grubbs catalyst was added to
dicyclopentadiene, mixed thoroughly, and placed between two glass
slides separated by approximately 100 microns. These membranes were
robust and could be manipulated by hand.
[0077] In the experiments described in this report, the membranes
were placed in an apparatus between two reservoirs of solvent. The
membranes were kept in place using O-rings on either side and held
in place using a clamp. The solvent on either side of the membrane
was agitated using stir bars and a magnetic stir plate to eliminate
any boundary effects that might influence these experiments. In
most experiments the permeation of a molecule through the membrane
was studied by adding it to solvent on only one side of the
membrane. This was called the "upstream" side of the membrane. Many
molecules permeated through the membranes and were also found in
the solvent "downstream" of the membrane.
Permeation of Co(Salen) Using Membranes Composed of PDCPD or
Polydimethylsiloxane.
[0078] Preliminary work indicated that membranes composed of PDCPD
would not allow molecules above a critical cross-sectional area to
permeate. To investigate the composition of PDCPD membranes that
would retain selected molecules based on their cross-sectional
area, the permeation of Co(salen) was studied due to its large
cross-sectional area of 1.15 nm.sup.2. To contrast the results with
PDCPD membranes, the permeation of Co(salen) and hexadecane through
membranes composed of polydimethylsiloxane (PDMS) were also
studied. PDMS was chosen based on our prior work to site-isolate
water, Grignard reagents, butyl lithium, PdCl.sub.2, and other
catalysts and reagents..sup.20,21 In this prior work, PDMS
successfully retained a wide variety of reagents and catalysts
based on their low solubility in hydrophobic PDMS.
[0079] A membrane composed of PDMS was fabricated with a thickness
of 450 microns and equilibrated with CH.sub.2Cl.sub.2 on both sides
of the membrane. Co(salen) and hexadecane were added upstream of
the membrane and the concentration of Co(salen) and hexadecane
upstream (S.sub.u) and downstream (S.sub.d) of the membrane were
measured at 2, 4, and 6 h (Table 1). In prior work little evidence
was observed for the ability of PDMS membranes to distinguish
molecules based on their cross-sectional areas, and in experiments
with Co(salen) and hexadecane, both molecules permeated the
membranes at similar rates.
TABLE-US-00001 TABLE 1 Permeation of Co(salen) and hexadecane using
PDMS membranes and CH.sub.2Cl.sub.2 as the solvent. S.sub.d/S.sub.u
S.sub.d/S.sub.u S.sub.d/S.sub.u Molecule at 2 h at 4 h at 6 h
Co(salen) 0.03 0.07 0.13 hexadecane 0.17 0.52 0.61
[0080] PDCPD membranes were fabricated with different loadings of
dicyclopentadiene:Grubbs catalyst as shown in Table 2 to determine
the ratio that led to retention of Co(salen). In all of these
experiments the concentration of Co(salen) was studied by UV-VIS
spectroscopy rather than .sup.1H NMR spectroscopy because the
UV-VIS spectrometer allowed lower concentrations of Co(salen) to be
measured and because Co(salen) was paramagnetic. At high loadings
of 50,000:1 dicyclopentadiene:Grubbs catalyst the polymerization
was incomplete and the polymer membrane was tacky and not robust.
At loadings of dicyclopentadiene:Grubbs catalyst below 4,000:1 the
polymerization was too rapid and the solution hardened before it
could be cast into a thin film.
TABLE-US-00002 TABLE 2 Permeation of Co(salen) using PDCPD
membranes fabricated with different catalyst loadings.
Dicyclopenta- Ethyl diene:Grubbs vinyl .sup.aThickness
.sup.bS.sub.d/S.sub.u .sup.bS.sub.d/S.sub.u Entry catalyst ether
(.mu.m) at 24 h at 48 h 1 .sup.c50000/1.sup. .sup.dnone.sup. Na Na
Na 2 20000/1 none 110 .ltoreq.0.004.sup.e .ltoreq.0.005.sup.e 3
10000/1 none 110 .ltoreq.0.005.sup.e .ltoreq.0.006.sup.e 4 5000/1
none 110 .ltoreq.0.006.sup.e .ltoreq.0.007.sup.e 5 4000/1 none 100
.ltoreq.0.005.sup.e .ltoreq.0.007.sup.e 6 10000/1 .sup.f10 mL 120
0.49 0.35 7 5000/1 .sup.f10 mL 88 0.05 0.06 8 4000/1 .sup.f10 mL
110 0.04 0.08 9 5000/1 .sup.gnone.sup. 98 .ltoreq.0.006.sup.e
.ltoreq.0.009.sup.e .sup.aThe thickness of the membrane. .sup.bThe
ratio of the downstream (S.sub.d) concentration of Co(salen) to the
upstream (S.sub.u) concentration. .sup.cIncomplete polymerization
after 47 h at 50.degree. C. .sup.dNo ethyl vinyl ether was added to
the solvent on either side of the membrane. .sup.eNo Co(salen) was
detected in the solvent downstream of the membrane. .sup.fEthyl
vinyl ether was added to the solvent on each side of the membrane.
.sup.gTHF was added to the solvent on either side of the membrane
in the same concentration as ethyl vinyl ether from entries
6-8.
[0081] PDCPD membranes synthesized with molar ratios of 4,000 to
20,000 dicyclopentadiene to one Grubbs catalyst resulted in
controlled polymerizations and well-defined membranes. These
membranes were used to study whether Co(salen) permeated them using
CH.sub.2Cl.sub.2 as the solvent. In each of these experiments
Co(salen) was not detected by UV-VIS spectroscopy downstream of the
membrane at 24 or 48 h (Table 2). To provide further evidence for
the retention of Co(salen), the concentration of Co downstream and
upstream of the membranes were measured by ICP-OES at 48 h for
entries 4 and 5. In these experiments, <0.5% of the Co was found
downstream of the membrane which demonstrated that it did not
permeate.
[0082] In entries 2-5 in Table 2 less than 30% of the Co(salen)
permeated into the PDCPD matrix after 48 h, the remainder was found
in the solvent upstream of the membrane. Thus, the Co(salen) was
soluble in the PDCPD membrane and readily partitioned into it, so
its slow permeation through the membrane was due to a very low rate
of diffusion in the PDCPD matrix. In a later section it will be
shown that molecules can be extracted from the PDCPD membrane and
do not remain "trapped" in the PDCPD matrix.
[0083] These membranes were futher studied for the effect of ethyl
vinyl ether on the permeation of Co(salen). When dicyclopentadiene
is polymerized with the Grubbs catalyst, the strained bicylic
olefin reacts rapidly to yield a polymer and the other olefin
reacts at a slower rate to yield cross-links in the PDCPD matrix.
We hypothesized that the membranes underwent further cross-linking
when swollen in organic solvent prior to being used as membranes
because they were fabricated in the absence of solvent and
initially yielded hard, solid materials that hindered the diffusion
of the Grubbs catalyst. To investigate whether the Grubbs catalyst
reacted when the membranes were swollen in organic solvents, they
were swollen in CH.sub.2Cl.sub.2 with ethyl vinyl ether to
terminate the Grubbs catalyst. If the Grubbs catalyst was inactive
when the membranes were swollen in CH.sub.2Cl.sub.2, membranes
treated with ethyl vinyl ether would have similar properties for
the permeation of Co(salen) as those not exposed to ethyl vinyl
ether. If the Grubbs catalyst was dormant in the solid PDCPD and
further cross-linked PDCPD when swollen in CH.sub.2Cl.sub.2, the
addition of ethyl vinyl ether would stop any further cross-linking
and affect the permeation of Co(salen). When these membranes were
studied for their ability to resist the permeation of Co(salen),
all of them allowed Co(salen) to permeate (entries 6-8 in Table 2).
In a control experiment to study whether the addition of ethyl
vinyl ether resulted in different permeation rates due to a change
in solvent polarity, THF was added to CH.sub.2Cl.sub.2 rather than
ethyl vinyl ether (entry 9 in Table 2). In this experiment
Co(salen) did not permeate the membrane which demonstrated that the
effect of ethyl vinyl ether could not be explained by a change in
solvent polarity.
[0084] These experiments provided evidence that the cross-linking
of the PDCPD matrix is incomplete when a solid polymer matrix is
formed and the membranes must be swollen in organic solvents to
have the desired properties to retain Co(salen). In the next
section of this report, the density of cross-links in PDCPD before
and after swelling in CH.sub.2Cl.sub.2 will be reported that
provide further evidence that the Grubbs catalyst is dormant in
PDCPD and reacts to form more cross-links when the polymer is
swollen in organic solvents.
Measurement of Density of Cross-Links in PDCPD.
[0085] The density of cross-links in PDCP was measured using IR
spectroscopy. It important to understand that when
dicyclopentadiene is polymerized it yields a hard, solid material
that lacks well-defined, empty pores such as those found for
zeolites or other nanoporous membranes. PDCPD was studied by
scanning electron microscopy to reveal a flat, featureless surface.
The surface of PDCPD was investigated by x-ray photoelectron
spectroscopy and grazing angle total reflection-infrared (GATR-IR)
spectroscopy in prior work. The surface of PDCPD had little surface
oxidation and its GATR-IR spectrum did not possess any unexplained
peaks. Typical methods to characterize the distribution of empty
pores were not attempted because of the lack of empty pores within
PDCPD.
[0086] The most important characteristic of PDCPD is the density of
cross-links within the matrix that occur when the five membered
ring in the monomer reacts with another polymer chain. The degree
of cross-linking of PDCPD was measured using IR spectroscopy by
investigating the peak at 704 cm.sup.-1 that was assigned to the
cis oops bending of the unreacted olefin in PDCPD (FIG. 2). Opening
of this ring by the Grubbs catalyst led to cross-links in PDCPD;
thus, measurement of the concentration of the unreacted cyclic
olefin in a PDCPD matrix gave an approximate concentration of
cross-links. The peak at 704 cm.sup.-1 was assigned to the cis oops
of the unreacted olefin based on literature precedent for peaks in
this area. Olefins that reacted with the Grubbs catalyst were no
longer part of medium sized rings and their values for the oops
peak appeared at higher wavenumbers based on analogy to linear
molecules. For instance, the oops peak for cis-3 heptene was at 714
cm.sup.-1 and for cyclopentene it was at 697 cm.sup.-1. Trans oops
peak typically have values above 720 cm.sup.-1. Thus, the peak at
704 cm.sup.-1 was used to find the concentration of uncross-linked
monomer in PDCPD.
[0087] A calibration curve for the cis oops peak was obtained by
measuring the intensity of the peak for dicyclopentadiene dissolved
in dioxane. Dioxane was chosen due to its low dielectric constant
and absence of peaks in the area of interest. Briefly, an IR flow
cell with 100 micron spacings between the plates was filled with
solutions of dicyclopentadiene in dioxane. The IR spectra were
obtained for different concentrations and a calibration curve was
measured.
[0088] Eleven PDCPD membranes were fabricated with molar ratios of
dicyclopentadiene to Grubbs catalyst of 5,000:1 and their IR
spectra were measured. Next, the membranes were swelled in
CH.sub.2Cl.sub.2 for an hour, dried under N.sub.2, and the solvent
was completely removed by placing the membranes under vacuum for 12
h. The IR spectra were again measured for the membranes. The
average density of unreacted cyclic olefin as shown by the peak at
704 cm.sup.-1 was only 47% (.+-.19%) before swelling in
CH.sub.2Cl.sub.2. Thus, approximately 53% (.+-.19%) of the cyclic
olefins had reacted to form cross-links. From the prior experiments
with Co(salen) and PDCPD membranes that had been exposed to ethyl
vinyl ether (Table 2), it was known that the Grubbs catalyst was
reactive and would further cross-link the membranes when swollen in
organic solvent. This conclusion was supported by the IR spectrum
of the membranes after swelling in CH.sub.2Cl.sub.2 which showed
that approximately 84% (.+-.12%) of the cyclic olefins had reacted.
Clearly, the Grubbs catalyst was able to react further when the
hard, solid PDCPD membranes were swollen in CH.sub.2Cl.sub.2 for an
hour. This result is understandable because of the stability of the
Grubbs catalyst in air (particularly when it is embedded in a solid
matrix), and the extent that the PDCPD membranes swell in
CH.sub.2Cl.sub.2.
Flux of Organic Molecules Through PDCPD Membranes
[0089] PDCPD is significantly swollen by organic solvents (Table
3). To quantify the ability of solvents to swell PDCPD a series of
dry slabs of PDCPD were weighed, immersed in a solvent for 24 h,
removed from the solvent, briefly dried of any solvent on the
exterior of the slab, and weighed. The data in Table 3 demonstrated
that apolar solvents swelled PDCPD the best which was reasonable
considering apolar structure of PDCPD. In addition, PDCPD adsorbed
more than its weight in selected solvents.
TABLE-US-00003 TABLE 3 How solvents swell PDCPD. Weight of swollen
Solvent PDCPD/weight of PDCPD (g/g) chloroform 3.38 dichloromethane
2.46 toluene 2.23 tetrahydrofuran 2.06 ethyl acetate 1.35 diethyl
ether 1.34 hexanes 1.32 petroleum ether 1.27 dioxane 1.26 acetone
1.14 methanol 1.12
[0090] The flux of hexadecane through PDCPD membranes was
quantified with CH.sub.2Cl.sub.2 and toluene as the solvents. The
membranes were fabricated as before with a molar ratio of 5,000:1
dicyclopentadiene to Grubbs catalyst. The membranes were placed
into the apparatus to measure flux and were equilibrated for 30 min
with solvent on both sides. After this time period, 1 mmol of
hexadecane was added to solvent on one side of the membrane (the
upstream side) and aliquots upstream and downstream of the
membranes were periodically removed to quantify the concentration
of hexadecane. In FIG. 3 the amount of hexadecane--measured in
mmoles--downstream of the membranes as a function of time is shown.
The values for the flux of hexadecane were calculated to be
1.02.times.10.sup.-5 mol cm.sup.-2 h.sup.-1 with CH.sub.2Cl.sub.2
as solvent and 6.53.times.10.sup.-6 mol cm.sup.-2 h.sup.-1 with
toluene as solvent. Although these values are lower than those
reported for other membranes, such as the OSN membranes used in the
chemical industry, the PDCPD membranes were not optimized for their
flux. The flux can be increased by using thinner membranes and by
applying external pressure.
[0091] For comparison, the upper limit for the flux of Co(salen) in
entry 4 of Table 2 with CH.sub.2Cl.sub.2 as the solvent was
approximately 4.times.10.sup.-10 mol cm.sup.-2 h.sup.-1. Thus, the
difference for flux of hexadecane and Co(salen) was at least four
to five orders of magnitude.
[0092] The ability of hexadecane, nitrobenzaldehyde, cholesterol,
hexanoic acid, and 1,6-diaminohexane to permeate PDCPD membranes
with CH.sub.2Cl.sub.2, toluene, and THF as solvents was studied. In
these experiments, each of the molecules and hexadecane were added
to solvent on one side of the membrane and the concentrations
upstream and downstream were found after 24 and 48 h (Table 4).
Hexadecane was added as an internal control to ensure that each
membrane had similar properties and that permeation was measured
consistently. Each of these molecules had reasonable rates of
permeation through the membranes and, except for cholesterol, the
concentrations on either side of the membrane had mostly
equilibrated at 48 h.
TABLE-US-00004 TABLE 4 Flux of five organic molecules through PDCPD
membranes .sup.aThickness .sup.bS.sub.d/S.sub.u
.sup.bS.sub.d/S.sub.u Molecule Solvent (.mu.m) at 24 h at 48 h
hexadecane CH.sub.2Cl.sub.2 100 0.68 0.95 hexadecane Toluene 110
0.82 0.86 hexadecane THF 100 0.66 0.98 nitrobenzaldehyde
CH.sub.2Cl.sub.2 100 0.82 1.0 nitrobenzaldehyde Toluene 110 0.96
0.98 nitrobenzaldehyde THF 100 0.66 1.0 cholesterol
CH.sub.2Cl.sub.2 100 0.44 0.69 cholesterol Toluene 110 0.54 0.58
cholesterol THF 100 0.54 0.82 hexanoic acid CH.sub.2Cl.sub.2 99
0.88 0.94 hexanoic acid Toluene 110 0.55 0.82 hexanoic acid THF 89
0.69 1.0 1,6-diaminohexane CH.sub.2Cl.sub.2 80 0.81 0.93
1,6-diaminohexane Toluene 98 0.95 0.97 1,6-diaminohexane THF 120
1.0 1.0 .sup.aThe thickness of the PDCPD membrane that was prepared
at a molar ratio of dicyclopentadiene:Grubbs catalyst of 5,000:1.
.sup.bThe ratio of the concentration downstream to the
concentration upstream for each molecule.
[0093] The permeation of a molecule through a membrane is dependent
on the rate of diffusion of that molecule within a membrane
multiplied by its solubility in the membrane according to the well
known equation P=DS. Each of the five molecules shown in Table 4
permeated the membranes at appreciable rates which demonstrated
that they were soluble and possessed reasonable rates of diffusion
within the PDCPD matrix. What is notable is that both polar and
apolar molecules permeated at similar rates through the
hydrophobic, but swollen, PDCPD membranes.
[0094] The ability of 14 additional molecules to permeate PDCPD
membranes fabricated from a dicyclopentadiene to Grubbs catalyst
ratio of 5,000:1 were measured with CH.sub.2Cl.sub.2 as the solvent
(FIG. 4 and Table 5). Similar to other experiments, the molecule of
interest and hexadecane were added to solvent upstream of the
membranes. The internal control of adding hexadecane to each
experiment ensured that the flux was similar for each membrane and
that a lack of flux of a molecule through the membrane was not due
to a faulty membrane, but rather it was due to an intrinsic
property of the membrane.
TABLE-US-00005 TABLE 5 Permeation of organic molecules using PDCPD
membranes and CH.sub.2Cl.sub.2 as the solvent. Molecular weight
.sup.aThickness .sup.bS.sub.d/S.sub.u .sup.bS.sub.d/S.sub.u
Molecule (g mol.sup.-1) (.mu.m) at 24 h at 48 h quinuclidine 111
100 0.81 0.93 triethylamine 101 97 1.0 0.98 tripropylamine 143 100
0.67 0.87 tributlyamine 185 96 .ltoreq.0.02.sup.c
.ltoreq.0.03.sup.c triisobutylamine 185 100 0.88 1.0
triphenylmethane 244 90 .ltoreq.0.01.sup.c .ltoreq.0.01.sup.c
MacMillan organocatalyst 246 120 0.32 0.70 triphenylphosphine 262
100 .ltoreq.0.02.sup.c .ltoreq.0.03.sup.c triphenylphosphine oxide
278 84 .ltoreq.0.02.sup.c .ltoreq.0.03.sup.c
.sup.dtricyclohexylphosphine 280 100 .ltoreq.0.01.sup.c
.ltoreq.0.02.sup.c binol 286 96 .ltoreq.0.01.sup.c
.ltoreq.0.02.sup.c salen 492 100 .ltoreq.0.01.sup.c
.ltoreq.0.01.sup.c methyl 528 98 0.85 0.94 nonadecafluorodecanoate
nonaethylene glycol 583 130 0.04 0.33 monododecyl ether .sup.aThe
thickness of the membrane. .sup.bThe ratio of the concentration of
a molecule downstream to its concentration upstream. .sup.cThe
molecule was not observed downstream of the membrane. .sup.dLess
than 10% of the tricyclohexylphosphine oxidized during these
experiments.
[0095] Several conclusions can be drawn from the experiments in
Table 5 and those presented earlier in this article. Whether a
molecule will permeate PDCPD is clearly not dependent on molecular
weight because the two molecules (MW: 528 and 583 g mol.sup.-1)
with highest molecular weights permeated the membranes but
tributylamine (MW: 185 g mol.sup.-1) and triphenylphospine (MW: 262
g mol.sup.-1) did not permeate it. Both hydrophobic and hydrophilic
molecules permeated the membranes and failed to permeate them. For
instance, apolar molecules such as hexadecane, cholesterol, and
tripropylamine permeated the membranes but tributylamine,
triphenylphosphine, and tricyclohexylphosphine did not permeate
them. Triphenylphosphine oxide was choosen because it is more polar
than triphenylphosphine due to the presence of a polar P.dbd.O bond
but possessed a similar shape. Triphenylphosphine oxide did not
permeate the membranes at any detectable amount. The presence of
amines or phoshines was not a distinguishing factor for whether a
molecule would not permeate a membrane because triphenylmethane did
not permeate it also.
Reason for the Retention of Selected Molecules by PDCPD
Membranes
[0096] The flux of molecules through cross-linked polymeric
membranes has been described theoretically by others through
competing models. A general description that is agreed upon is that
the diffusion, D, of a molecule to move from point to point in a
polymer matrix depends exponentially on energy of activation,
E.sub.a, according to the equation D=D.sub.oexp(-E.sub.a/RT). In a
highly cross-linked polymer matrix, small molecules can diffuse
with little or no rearrangement of the polymer and the value for
E.sub.a is small. Molecules with cross-sectional areas that are
comparable or larger than the pores in a cross-linked polymer
require substantial rearrangement of the polymer matrix that lead
to high values for E.sub.a and low values for diffusion. Thus, the
theoretical descriptions of flux and rates of diffusion make
extensive use of cross-sectional areas to make predictions or to
rationalize observed results. For instance, in a classic paper in
1982 by Berens and Hopfenberg the log of diffusion versus diameter
and the square of diameter was plotted for 18 molecules that
permeated polystyrene, polymethylmethacrylate, and polyvinyl
chloride..sup.24 Neither plot was superior to the other due to
scatter in the data, but it was clear that flux strongly depended
on molecular diameter. In fact, the difference in flux for He
(diameter=0.258 nm) and neopentane (diameter 0.580 nm) was
approximately ten orders of magnitude. Unfortunately, this
difference in flux was not studied for molecules larger than
hexanes because of the vanishingly slow values for diffusion. At
the other end of the molecular weight spectrum, the separation of
polymers from small molecules using porous polymeric membranes is
well known and used in applications such as to dialyze proteins
from small molecules.
[0097] Most prior membranes to separate organic molecules used
molecular weight or hydrophobic/hydrophilic effects to distinguish
between molecules. For instance, ionic liquids will not partition
into PDMS (a hydrophobic polymer) so they have no measurable flux
through membranes composed of PDMS. Membranes that separate organic
molecules possessing molecular weights from 100 to 600 g mol.sup.-1
use molecular weight as the criterion for separation rather than
cross-sectional area for two reasons. First, molecular weight is
straightforward and easy to define but cross-sectional area is a
more challenging concept to quantify. Second, separations based on
molecular weight are successful and no allowances must be made for
molecular size. Molecules below a MWCO permeate the membranes but
molecules above the MWCO do not permeate and no exceptions are
needed for effects based on cross-sectional area. The use of
molecular weight as the criterion for separation does not imply any
underlying importance to molecular weight in the mechanisms by
which molecules are separated.
[0098] In Table 6 the molecular sizes of molecules that permeated
or did not permeate PDCPD membranes are described. The surface
area, molecular volume, critical dimension, and critical area were
calculated by first minimizing the energy for each molecule using
Spartan '08 V1.2.0. Next, the surface area and molecular volume
were calculated from space filling models as described in the
experimental section. The critical area was defined as the smallest
rectangular cross-sectional area of a molecule that must be met for
it to pass through a pore. For instance, a penny would be viewed on
its side such that its cross-sectional area is a thin rectangle and
distinctly smaller than the cross-sectional area for a sphere with
the same radius as a penny. This rectangular cross-sectional area
was determined using Sparan '08 V1.2.0 for each molecule as
described in the experimental section. The critical dimension was
the larger of the two distances used to find the critical area.
TABLE-US-00006 TABLE 6 The chemical and physical sizes of molecules
that did or did not permeate PDCPD membranes. Molecular Surface
Molecular Critical Critical Measurable weight area volume dimension
area Molecule flux (g mol.sup.-1) (nm.sup.2) (nm.sup.3) (nm)
(nm.sup.2) triethylamine Yes 101 1.64 0.138 0.67 0.18 quinuclidine
Yes 111 1.46 0.131 0.42 0.21 hexanoic acid Yes 116 1.65 0.135 0.28
0.067 1,6-diaminohexane Yes 116 1.80 0.146 0.28 0.067
tripropylamine Yes 143 2.20 0.193 0.79 0.32 nitrobenzaldehyde Yes
151 1.64 0.142 0.43 0.060 tributlyamine No 185 2.86 0.249 0.92 0.50
triisobutylamine Yes 185 2.82 0.248 0.80 0.38 hexadecane Yes 226
3.52 0.307 0.28 0.067 triphenylmethane No 244 2.92 0.285 0.95 0.51
MacMillan organocatalyst Yes 246 2.96 0.279 0.62 0.36
triphenylphosphine No 262 2.92 0.286 0.95 0.61 triphenylphosphine
oxide No 278 3.11 0.299 0.95 0.61 tricyclohexylphosphine No 280
3.24 0.323 0.92 0.57 binol No 286 2.99 0.298 0.72 0.51 cholesterol
Yes 387 4.49 0.454 0.55 0.28 salen No 492 6.36 0.630 1.22 0.79
methyl Yes 528 3.39 0.312 0.43 0.14 nonadecafluorodecanoate
nonaethylene glycol Yes 583 7.37 0.640 0.28 0.067 monododecyl ether
Co(salen) No 662 7.06 0.699 1.22 1.15
[0099] It is clear from Table 6 that the critical dimension and
area both correlate to whether a molecule will permeate PDCPD.
Molecules that permeated through PDCPD membranes had critical
dimensions and areas of less than 0.80 nm and 0.38 nm.sup.2, but
molecules that did not flux through the membranes had critical
dimensions and areas of at least 0.92 nm and 0.50 nm.sup.2.
Surprisingly, a difference in critical dimension or area
significantly less than a factor of two had a substantial impact on
the flux of molecules through PDCPD. The difference in permeation
was striking. Molecules with no measurable flux through the
membranes were not detected in the solvent downstream of the
membrane and possessed values for flux 10.sup.4 to 10.sup.5 times
slower than the molecules that did permeate the membranes.
[0100] The difference in permeation of tripropylamine,
triisobutylamine, and tributylamine illustrates the importance of
cross-sectional area (Table 6). Triisobutylamine and tributylamine
are constitutional isomers that possess the same molecular weight
and similar surface areas and volumes. The major difference between
triisobutylamine and tributylamine are their cross-sectional areas,
triisobutylamine (0.38 nm.sup.2) has a similar cross-sectional area
to tripropylamine (0.32 nm.sup.2), but the cross-sectional area of
tributylamine (0.50 nm.sup.2) is larger. In flux experiments
tripropylamine and triisobutylamine permeated the membranes but
tributylamine did not permeate. These experiments demonstrate the
selectivity of the membranes and the need to consider
cross-sectional area as the important parameter for the flux of
molecules.
Extraction of Nitrobenzaldehyde from Binol.
[0101] The ability to efficiently extract a molecule through a
PDCPD membrane while retaining a second molecule was studied using
nitrobenzaldehyde and binol. It is important that a high yield of a
molecule be obtained after permeation through a membrane, and it is
also important that molecules that are retained by a membrane do
not remain embedded with the PDCPD matrix. In some applications it
will also be important that molecules that are retained be recycled
and accessible after separations. These issues were initially
addressed by studying the extraction of nitrobenzaldehyde from
binol.
[0102] In these experiments, a mixture of nitrobenzaldehyde (484
mg) and binol (264 mg) were added upstream of a membrane in
CH.sub.2Cl.sub.2 and extracted downstream using CH.sub.2Cl.sub.2.
After 24 h, the solvent downstream was removed from the apparatus
and fresh CH.sub.2Cl.sub.2 was added downstream. After an
additional 24 h, the solvent downstream was removed and the
extracted yield of nitrobenzaldehyde through two cycles calculated
to be 90% with no detectable level of binol contamination. The
solvent upstream was also removed from the apparatus and the amount
of binol in solution was only 17% of the original amount of binol
added to the apparatus. The remainder of the binol was in the PDCPD
matrix and had to extracted. A fresh aliquot of CH.sub.2Cl.sub.2
was added on the upstream side of the membrane and allowed to sit
for 24 h. The CH.sub.2Cl.sub.2 was removed from the apparatus to
yield an additional 39% of the original amount of binol. The
membrane was cut into pieces and immersed in CH.sub.2Cl.sub.2 to
further extract binol. After 24 h an additional 13% of the original
amount of binol was isolated which yielded a total isolation of 69%
of the original amount of binol. When this experiment was repeated
the amount of nitrobenzaldehyde that was isolated downstream of the
membrane was 87% and the amount of binol that was isolated was
72%.
[0103] These experiments demonstrated that high yields of clean
nitrobenzaldehyde could be isolated from significant quantities of
binol. Furthermore, most of the binol partitioned into the PDCPD
membranes during these experiments, but it was readily extracted
into fresh solvent where it was isolated and characterized. The
partitioning of binol from solvent into the membranes was a
reversible process that allowed much of the binol to be isolated at
the end of these experiments.
Extraction of Cholesterol from Triphenylphosphine,
Tricyclohexylphosphine, and Tributylamine Using a PDCPD
Membrane
[0104] To demonstrate the selective permeation of a high molecular
weight compound from low molecular weight compounds based on their
different cross-sectional areas, the extraction of cholesterol (3
mmol) from a mixture of triphenylphosphine (2 mmol),
tricyclohexylphosphine (2 mmol), and tributylamine (3 mmol) was
investigated. These four molecules were dissolved in 25 mL of
CH.sub.2Cl.sub.2 and added to one side of a membrane and 23 mL of
CH.sub.2Cl.sub.2 was added downstream of the membrane. A 2 mL
aliquot was immediately removed from the upstream side and
characterized by .sup.1H NMR spectroscopy to show the initial
mixture of molecules. After 48 h aliquots were removed from both
sides of the membrane and characterized by .sup.1H NMR
spectroscopy.
[0105] The .sup.1H NMR spectra demonstrated that cholesterol was
selectively extracted from the solvent mixture. The .sup.1H NMR
spectra of the initial mixture of the four molecules, the organic
molecules upstream of the membrane after 48 h, the organic
molecules downstream of the membrane after 48 h, and a sample of
pure cholesterol are all shown. Some oxidation of the PCy.sub.3
occurred during the extraction, but the OPCy.sub.3 was also
retained by the membrane. The .sup.1H NMR spectrum of the organic
product downstream of the membrane after 48 h matched the .sup.1H
NMR spectrum of cholesterol and no evidence of PCy.sub.3,
OPCy.sub.3, PPh.sub.3, or NBu.sub.3 were seen downstream of the
membrane. This result was remarkable considering that the molecular
weight of cholesterol (MW: 387 g mol.sup.-1) was much higher than
the other molecules (185-296 g mol.sup.-1).
Recycling of PDCPD Membranes
[0106] The ability to recycle PDCPD membranes was studied using
nitrobenzaldehyde and binol. In this experiment both
nitrobenzaldehyde and binol were added upstream of a membrane and
nitrobenzaldehyde was isolated downstream of the membrane.
Nitrobenzaldehyde was extracted three times with fresh solvent over
72 h. After 72 h the binol that had permeated into the PDCPD matrix
was extracted by the addition of fresh solvent upstream of the
membrane. After the first cycle was complete, fresh
nitrobenzaldehyde and binol were added upstream of the membrane and
the process was repeated with the same membrane.
[0107] A total of three cycles were completed and the extraction of
nitrobenzaldehyde was high for each cycle. In the three cycles
nitrobenzaldehyde was isolated in 99%, 79%, and 72% yield and the
binol was isolated in 40%, 4%, and 82% yield. The fourth cycle was
not finished because binol began to permeate the membrane. Notably,
nitrobenzaldehyde was isolated as a clean product without any
impurities from binol. The binol contained some nitrobenzaldehyde
as an impurity and had to be extracted from the PDCPD membrane.
This experiment demonstrates that the membranes can be recycled
over several cycles, and future work will study how to optimize
this process.
CONCLUSIONS
[0108] New technologies originate from new materials. Most past
examples of membranes that separate organic molecules with
molecular weights from 100-600 g mol.sup.-1 use the concept of a
molecular weight cutoff that hinder the use of these membranes to
separate catalysts from products of a reaction. Many catalysts and
ligands for metals have modest molecular weights that place a real
limitation on what molecules they can be separated from. The
problem that PDCPD membranes solve is that they are the first
membranes that separate molecules with molecular weights between
100 and 600 g mol.sup.-1 based on the concept of a cross-sectional
area cutoff rather than a molecular weight cutoff. These membranes
are significant because of the large number and importance of
molecules within this range of molecular weights and the need to
separate them in the chemical industry. For instance, many
reactions require metal catalysts with ligands such as phosphines.
It is important that the final product be clean of all but ppm
levels of impurities of metal and phosphines so several
purification steps are often required to clean the product. PDCPD
membranes offer a new solution to cleaning the products and
recycling the catalysts.
[0109] The surprising aspect of PDCPD membranes is not that they
separate molecules based on cross-sectional area because
cross-sectional area is well known as a critical parameter that
affects flux. Rather, it was surprising that these membranes were
the first to have a critical importance of cross-sectional area for
the flux of molecules within this range of molecular weights. In
addition, the difference in permeation was very large; molecules
that did not permeate the membranes were undetected in the solvent
downstream of the membrane and possessed values for flux that were
10.sup.4 to 10.sup.5 times slower than molecules that permeated the
membranes. The origins of the selectivity of these membranes lies
in the size and distribution of pore sizes that result when the
polymer is cross-linked, and these materials properties will be
studied in more detail in future work. An understanding of what
makes PDCPD so unique may allow the design of more membranes with
similar separations but faster flux.
[0110] All publications, patents, and patent documents discussed
herein are incorporated by reference herein, as though individually
incorporated by reference. The invention has been described with
reference to various specific and preferred embodiments and
techniques. However, it should be understood that many variations
and modifications may be made while remaining within the spirit and
scope of the invention.
* * * * *