U.S. patent application number 14/495029 was filed with the patent office on 2015-01-08 for ethylene-based interpolymers and processes to make the same.
The applicant listed for this patent is Dow Global Technologies LLC. Invention is credited to Otto J. Berbee, Roger G. Gagnon, Bryan Gutermuth, Mark Jasek, Laura Nunez.
Application Number | 20150011708 14/495029 |
Document ID | / |
Family ID | 44678094 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150011708 |
Kind Code |
A1 |
Berbee; Otto J. ; et
al. |
January 8, 2015 |
Ethylene-Based Interpolymers and Processes to Make the Same
Abstract
Ethylene-based interpolymers, e.g., ethylene-acrylic acid
copolymers, are made by a process comprising the steps of: A.
Injecting a first feed comprising a chain transfer agent system
(CTA system) and ethylene into a first autoclave reactor zone to
produce a first zone reaction product, the CTA system of the first
reactor zone having a transfer activity Z1; and B. (1) Transferring
at least part of the first zone reaction product to a second
reactor zone selected from a second autoclave reactor zone or a
tubular reactor zone, and (2) at least one of transferring or
freshly injecting a feed comprising a CTA system into the second
reactor zone to produce a second zone reaction product, the CTA
system of the second reactor zone having a transfer activity of Z2;
and with the proviso that the ratio of Z1:Z2 is greater than 1. The
comonomer comprises at least one carboxylic acid group or an
anhydride group.
Inventors: |
Berbee; Otto J.; (Hulst,
NL) ; Gagnon; Roger G.; (Clute, TX) ; Jasek;
Mark; (Clute, TX) ; Nunez; Laura; (Lake
Jackson, TX) ; Gutermuth; Bryan; (Angleton,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dow Global Technologies LLC |
Midland |
MI |
US |
|
|
Family ID: |
44678094 |
Appl. No.: |
14/495029 |
Filed: |
September 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13876280 |
Mar 27, 2013 |
8871876 |
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PCT/US11/52509 |
Sep 21, 2011 |
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14495029 |
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61388214 |
Sep 30, 2010 |
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Current U.S.
Class: |
525/221 ;
526/318.6 |
Current CPC
Class: |
C08F 110/02 20130101;
C08J 2423/06 20130101; C08F 110/02 20130101; C08L 2205/02 20130101;
C08F 210/02 20130101; C08F 210/02 20130101; C08F 2/01 20130101;
C08F 210/02 20130101; C08J 5/18 20130101; C08F 2500/11 20130101;
C08J 2323/08 20130101; C08F 2500/12 20130101; C08F 2/38 20130101;
C08F 220/06 20130101; C08F 218/08 20130101; C08F 210/02 20130101;
C08F 2/001 20130101; C08L 23/08 20130101; C08F 210/02 20130101 |
Class at
Publication: |
525/221 ;
526/318.6 |
International
Class: |
C08F 210/02 20060101
C08F210/02; C08L 23/08 20060101 C08L023/08; C08J 5/18 20060101
C08J005/18 |
Claims
1-15. (canceled)
16. An ethylene-based interpolymer comprising at least one
comonomer that comprises at least one ethylenic unsaturation and at
least one carbonyl group, and wherein the interpolymer comprises at
least one the following properties: A. An average small gel count
per 50,000 square inches (in.sup.2) of less than or equal to 600;
and B. An average micro gel count per 50,000 in.sup.2 of less than
or equal to 3,500.
17. The ethylene-based interpolymer of claim 16 having a percent by
weight of acid comonomer units in the polymer chain from 2 to
30.
18. The ethylene-based interpolymer of claim 16 having a molecular
weight distribution (MWD, Mw/Mn) from 3 to 20.
19. The ethylene-based interpolymer of claim 17 having a molecular
weight distribution (MWD, Mw/Mn) from 3 to 20.
20. The ethylene-based interpolymer of claim 16 wherein the
ethylenic unsaturation of the comonomer is conjugated with the
carbonyl group.
21. The ethylene-based interpolymer of claim 16 wherein the
comonomer is at least one of an ethylenically unsaturated
carboxylic acid, anhydride, or ester or its salt.
22. The ethylene-based interpolymer of claim 16 wherein the
comonomer is acrylic acid or methacrylic acid.
23. The ethylene-based interpolymer of claim 16 wherein the average
small gel count per 50,000 square inches (in.sup.2) of less than or
equal to 300.
24. The ethylene-based interpolymer of claim 16 wherein the average
micro gel count per 50,000 in.sup.2 of less than or equal to
1,500.
25. The ethylene-based interpolymer of claim 16 wherein the percent
by weight of acid comonomer units in the interpolymer chain is from
4 to 15.
26. The ethylene-based interpolymer of claim 16 wherein the
molecular weight distribution (MWD, Mw/Mn) from 5 to 12.
27. The ethylene-based interpolymer of claim 16 comprising greater
than, or equal to, 1 weight percent of the comonomer based on the
weight of the interpolymer.
28. A composition comprising the ethylene-based interpolymer of
claim 16.
29. The composition of claim 28 comprising at least one other
ethylene-based polymer.
30. An article comprising the composition of claim 29.
31. A film comprising the composition of claim 29.
Description
FIELD OF THE INVENTION
[0001] This invention relates new polymerization processes to make
ethylene-based interpolymers, and to such interpolymers. Notably,
the polymerization process involves one or more autoclave reactors,
optionally operated with one or more tubular reactors.
BACKGROUND OF THE INVENTION
[0002] High molecular weight, normally solid copolymers of ethylene
and unsaturated carboxylic acids, such as acrylic acid and
methacrylic acid, are well known. However, there is a need for new
ethylene copolymers which have improved film optics, while
maintaining other performance attributes.
[0003] There are two main reactor types to produce high pressure
free radical copolymers of ethylene and unsaturated carboxylic
acids, namely the autoclave reactor and the tubular reactor.
Generally a tubular reactor is more advantaged for making narrow
molecular weight distribution (MWD) polyethylene due the uniform
residence time in tubular reaction zones; however in case of the
manufacturing of ethylenic-carboxylic acid copolymer a tubular
reactor is less suited as a first reaction zone due to the
following. [0004] 1. The requirement to preheat the reactor feed to
a minimum start temperature to avoid phase separation. [0005] 2.
The risk of premature carboxylic acid comonomer polymerization and
consequently gel formation in the heating step of the reactor feed.
[0006] 3. The high inlet acid comonomer concentration in a tubular
reactor enhances the risk of phase separation. For these reasons an
autoclave or a hybrid autoclave-tubular reactor system is preferred
for the production of acid high pressure copolymers. However due to
broadening of the MWD by the residence time distribution in an
autoclave reactor, this reactor type is less suited for making
narrow MWD copolymer products.
[0007] Good optical properties are achieved by making a narrow MWD
polymer. The MWD can be narrowed by polymerizing at lower
temperatures and or higher operating pressure. Typically the
maximum operating pressure is limited by the design of the
compression and/or reaction section. In practice the MWD of a
copolymer is narrowed by lowering polymerization temperature
conditions. However lowering the polymerization temperature
increases the risk of inducing phase separation conditions.
[0008] There remains a need for the production of narrow MWD
ethylenic-carboxylic acid copolymer products with low gel levels,
by suppressing phase separation and or hydrogen bonding of the
carboxylic acid groups in the reactor. These needs and others have
been met by the following invention.
SUMMARY OF THE INVENTION
[0009] In one embodiment, the invention is a high pressure
polymerization process to form an ethylene-based interpolymer, the
process comprising the steps of: [0010] A. Injecting a first feed
comprising a chain transfer agent system (CTA system) and ethylene
into a first autoclave reactor zone operating at polymerization
conditions to produce a first zone reaction product, the CTA system
of the first reactor zone having a transfer activity Z1; and [0011]
B. (1) Transferring at least part of the first zone reaction
product to a second reactor zone selected from a second autoclave
reactor zone or a tubular reactor zone and operating at
polymerization conditions, and, optionally, (2) freshly injecting,
a feed into the second reactor zone to produce a second zone
reaction product, with the proviso that at least one of the first
reactor zone product and the freshly injected feed comprises a CTA
system with a transfer activity of Z2; and with the proviso that
the ratio of Z1:Z2 is greater than 1, and
[0012] wherein at least one comonomer is injected into the
polymerization process at one or more of the flowing locations: at
a suction to a hyper compressor, at a hyper compressor discharge,
directly into a autoclave reactor at one or more zones, or directly
into a tubular reactor at one or more zones, and
[0013] wherein the at least one comonomer comprises at least one
carboxylic acid group or an anhydride group.
[0014] In one embodiment, the high pressure polymerization process
further comprises one or more steps of transferring a zone reaction
product produced in an (ith-1) reaction zone to an (ith) reaction
zone, where 3.ltoreq.i.ltoreq.n, and n.gtoreq.3, each zone
operating at polymerization conditions, and optionally adding an
(ith) feed comprising a CTA system into the (ith) reaction zone,
the CTA system of the (ith) reaction zone having a transfer
activity of Zi with the proviso that the ratio of Z1/Zi is greater
than 1.
[0015] The invention also provides an ethylene-based interpolymer
comprising at least one comonomer that comprises at least one
carboxylic acid group or an anhydride group, and wherein the
polymer comprises at least one, preferably at least two, more
preferably at least three, and even more preferably all of the
following properties:
[0016] A. An average small gel count per 50,000 square inches
(in.sup.2) of less than or equal to 600, or 500, or 400, or
300;
[0017] B. An average micro gel count per 50,000 in2 of less than or
equal to 3,500, or 3,000, or 2,500, or 2,000, or 1,500;
[0018] C. A percent by weight of acid comonomer units in the
polymer chain from 2 to 30, or from 3 to 20, or from 4 to 15;
and
[0019] D. A molecular weight distribution (MWD, Mw/Mn) from 3 to
20, or from 4 to 16, or from 5 to 12.
DETAILED DESCRIPTION
Overview
[0020] As discussed above, the invention provides a high pressure
polymerization process to form an ethylene-based interpolymer, the
process comprising the steps of: [0021] A. Injecting a first feed
comprising a chain transfer agent system (CTA system) and ethylene
into a first autoclave reactor zone operating at polymerization
conditions to produce a first zone reaction product, the CTA system
of the first reactor zone having a transfer activity Z1; and [0022]
B. (1) Transferring at least part of the first zone reaction
product to a second reactor zone selected from a second autoclave
reactor zone or a tubular reactor zone and operating at
polymerization conditions, and, optionally, (2) freshly injecting,
a feed into the second reactor zone to produce a second zone
reaction product, with the proviso that at least one of the first
reactor zone product and the freshly injected feed comprises a CTA
system with a transfer activity of Z2; with the provisos that:
[0023] the ratio of Z1:Z2 is greater than 1, and [0024] at least
one comonomer is injected into the polymerization process at one or
more of the flowing locations: at a suction to a hyper compressor,
at a hyper compressor discharge, directly into a autoclave reactor
at one or more zones, or directly into a tubular reactor at one or
more zones, and [0025] the at least one comonomer comprises at
least one carboxylic acid group or an anhydride group.
[0026] In one embodiment, the process further comprises one or more
steps of transferring a zone reaction product produced in an
(ith-1) reaction zone to an (ith) reaction zone, where
3.ltoreq.i.ltoreq.n, and n.gtoreq.3, each zone operating at
polymerization conditions, and injecting an (ith) feed comprising a
CTA system into the (ith) reaction zone, the CTA system of the
(ith) reaction zone having a transfer activity of Zi; and with the
proviso that the ratio of Z1/Zi is greater than 1.
[0027] In one embodiment, a second feed is injected into the second
reactor zone, and the second feed comprises ethylene.
[0028] In one embodiment, the second feed of the preceding
embodiment further comprises a CTA system.
[0029] In one embodiment, the second feed is injected into the
second reactor zone, and the second feed comprises ethylene but
does not comprise a CTA system.
[0030] In one embodiment, the second feed of any of the preceding
embodiments further comprises at least one comonomer.
[0031] In one embodiment, the ith feed of any of the preceding
embodiments further comprises ethylene.
[0032] In one embodiment, the ith feed of any of the preceding
claims further comprises at least one comonomer.
[0033] In one embodiment, the at least one comonomer of any of the
preceding claims is selected from acrylic acid, methacrylic acid,
or a combination thereof.
[0034] In one embodiment of any of the preceding embodiments, steps
(B)(1) and (B)(2) are conducted simultaneously.
[0035] In one embodiment of any of the preceding embodiments, steps
(B)(1) and (B)(2) are conducted at different times.
[0036] In one embodiment of any of the preceding embodiments, at
least part of the first zone reaction product is transferred to a
second autoclave reactor zone.
[0037] In one embodiment of any of the preceding embodiments, the
second autoclave reactor zone is adjacent to the first autoclave
reactor zone.
[0038] In one embodiment of any of the preceding embodiments, the
second autoclave reactor zone is separated from the first autoclave
reactor zone by one or more reactor zones.
[0039] In one embodiment of any of the preceding embodiments, at
least part of the first zone reaction product is transferred to a
tubular reactor zone.
[0040] In one embodiment of any of the preceding embodiments, the
tubular reactor zone is adjacent to the first autoclave reactor
zone.
[0041] In one embodiment of any of the preceding embodiments, the
tubular reactor zone is separated from the first autoclave reactor
zone by one or more reactor zones.
[0042] In one embodiment of any of the preceding embodiments, each
feed to each reactor zone contains the same CTA system. In a
further embodiment each CTA system comprises a single CTA.
[0043] In one embodiment of any of the preceding embodiments, at
least one of the feeds to at least one of the reactor zones
contains a CTA that is different from at least one of the CTAs to
the other reactor zones. In a further embodiment at least one of
the CTA systems comprises a single CTA.
[0044] In one embodiment of any of the preceding embodiments, each
CTA is independently one of an olefin, an aldehyde, a ketone, an
alcohol, a saturated hydrocarbon, an ether, a thiol, a phosphine,
an amino, an amine, an amide, an ester, and an isocyanate.
[0045] In one embodiment of any of the preceding embodiments, each
CTA is independently selected from an aldehyde, a ketone, or an
alcohol.
[0046] In one embodiment of any of the preceding embodiments, the
cloud point pressure of the polymerization is lowered more than the
cloud point pressure of a similar polymerization that has the same
process conditions except that the ratio of Z1:Z2 and/or Z1:Zi is
less than or equal to 1.
[0047] In one embodiment of any of the preceding embodiments, the
CTA prevents phase separation of the polymerization mixture.
[0048] In one embodiment of any of the preceding embodiments, at
least one CTA has a chain transfer constant Cs greater than
0.002.
[0049] In one embodiment of any of the preceding embodiments, all
autoclave zones are located in the same autoclave reactor.
[0050] In one embodiment of any of the preceding embodiments, the
autoclave zones are located in two or more different autoclave
reactors.
[0051] In one embodiment of any of the preceding embodiments, the
autoclave zones are of about the same size.
[0052] In one embodiment of any of the preceding embodiments, two
or more of the autoclave zones are of different sizes.
[0053] In one embodiment of any of the preceding embodiments, the
polymerization conditions in each reactor zone are operated at the
same temperature and same pressure.
[0054] In one embodiment of any of the preceding embodiments, at
least one polymerization condition in at least one reactor zone is
different from the other polymerization conditions.
[0055] In one embodiment of any of the preceding embodiments, each
of the polymerization conditions in the reactor zones,
independently, comprises a temperature greater than, or equal to,
100.degree. C., and a pressure greater than, or equal to, 100
MPa.
[0056] In one embodiment of any of the preceding embodiments, each
of the polymerization conditions in the reactor zones,
independently, comprises a temperature less than 400.degree. C.,
and a pressure less than 500 MPa.
[0057] In one embodiment of any of the preceding embodiments, the
ratio Z1/Z2 and each ratio Z1/Zi are greater than 1.03.
[0058] In one embodiment of any of the preceding embodiments, the
ratio Z1/Z2 and each ratio Z1/Zi are greater than 1.1.
[0059] In one embodiment of any of the preceding embodiments, the
ratio Z1/Z2 and each ratio Z1/Zi are less than 10.
[0060] In one embodiment, an ethylene-based interpolymer is made by
a process of any of the previous process embodiments.
[0061] In one embodiment the ethylene-based interpolymer comprises
at least one comonomer that comprises at least one carboxylic acid
group or an anhydride group, and wherein the interpolymer has an
average small gel count per 50,000 square inches (in.sup.2) of less
than or equal to 600, or 500, or 400, or 300.
[0062] In one embodiment the ethylene-based interpolymer comprises
at least one comonomer that comprises at least one carboxylic acid
group or an anhydride group, and wherein the interpolymer has an
average micro gel count per 50,000 square inches (in.sup.2) of less
than or equal to 3,500, or 3,000, or 2,500, or 2,000, or 1,500.
[0063] In one embodiment the ethylene-based interpolymer comprises
at least one comonomer that comprises at least one carboxylic acid
group or an anhydride group, and wherein the interpolymer has a
percent by weight of acid comonomer units in the polymer chain from
2 to 30, or from 3 to 20, or from 4 to 15.
[0064] In one embodiment the ethylene-based interpolymer comprises
at least one comonomer that comprises at least one carboxylic acid
group or an anhydride group, and wherein the interpolymer has a
molecular weight distribution (MWD, Mw/Mn) from 3 to 20, or from 4
to 16, or from 5 to 12.
[0065] In one embodiment of any of the preceding ethylene-based
interpolymer embodiments, the interpolymer comprises at least two,
or at least three, or all of the average small gel count, average
micro gel count, acid content and MWD properties.
[0066] In one embodiment of any of the preceding interpolymer
embodiments, the interpolymer comprises greater than, or equal to,
1 weight percent of a comonomer, based on the weight of the
interpolymer.
[0067] In one embodiment the invention is a composition comprising
the ethylene-based interpolymer of any of interpolymer
embodiments.
[0068] In one embodiment the composition of the previous
composition embodiment further comprises another ethylene-based
polymer.
[0069] In one embodiment the invention is an article comprising at
least one component formed from the ethylene-based interpolymer of
any of the interpolymer embodiments.
[0070] In one embodiment the invention is an article comprising at
least one component formed from a composition of any one of the
preceding composition embodiments.
[0071] In one embodiment the article is a film comprising at least
one polymer of any of the preceding polymer embodiments.
[0072] In one embodiment the article is a film comprising at least
one component formed from a composition of any of the preceding
composition embodiments.
Polymerizations
[0073] For a high pressure, free radical initiated polymerization
process, two basic types of reactors are known. In the first type,
an agitated autoclave vessel having one or more reaction zones is
used. In the second type, a jacketed tube is used as reactor, which
tube has one or more reaction zones. The high pressure process of
the present invention to produce ethylene-based interpolymers
comprising an acid group can be carried out in an autoclave reactor
having at least two reaction zones or in a combination of an
autoclave and a tubular reactor. The process of this invention,
i.e., the separate introduction of the CTA system at different
locations in the reactor system and maintaining a Z1:Z2 ratio
greater than 1, prevents phase separation and, this in turn,
reduces gel formation by reducing the cloud point pressure of the
polymerization system. Moreover, the CTA can act as a co-solvent
for the system.
[0074] The temperature in each autoclave and tubular reactor zone
of the process is typically from 100 to 400, more typically from
150 to 350 and even more typically from 160 to 320, .degree. C. The
pressure in each autoclave and tubular reactor zone of the process
is typically from 100 to 400, more typically from 120 to 360 and
even more typically from 150 to 320, MPa. The high pressure values
used in the process of the invention have a direct effect on the
amount of chain transfer agent, for example acetone, methyl ethyl
ketone (MEK) or propionaldehyde, incorporated in the polymer. The
higher the reaction pressure is, the more chain transfer agent
derived units are incorporated in the product.
[0075] In one embodiment of the process of the invention, a
combination of an autoclave comprising at least two reaction zones
and a conventional tubular reactor having at least one reaction
zone is used. In a further embodiment, such a conventional tubular
reactor is cooled by an external water jacket and has at least one
injection point for initiator and/or monomer. Suitable, but not
limiting, reactor lengths can be between 500 and 1500 meters. The
autoclave reactor normally has several injection points for
initiator and/or monomer. The particular reactor combination used
allows conversion rates of above 20 percent, which is significantly
higher than the conversion rates obtained for standard autoclave
reactors, which allow conversion rates of about 16-18 percent,
expressed as ethylene conversion, for the production of low density
type of polymers.
[0076] Examples of suitable reactor systems are described in U.S.
Pat. Nos. 3,913,698 and 6,407,191.
Monomers and Comonomers
[0077] The term ethylene copolymer as used in the present
description and the claims refers to polymers of ethylene and one
or more comonomers. Suitable comonomers to be used in the ethylene
polymers of the present invention include, but are not limited to,
any unsaturated organic compound containing at least one ethylenic
unsaturation (e.g. at least one double bond), and at least one
carbonyl group (--C.dbd.O). Representative unsaturated organic
compounds that contain at least one carbonyl group are the
ethylenically unsaturated carboxylic acids, anhydrides, esters and
their salts, both metallic and nonmetallic. Preferably, the organic
compound contains ethylenic unsaturation conjugated with the
carbonyl group. Representative compounds include maleic, fumaric,
acrylic, methacrylic, itaconic, crotonic, .alpha.-methyl crotonic,
cinnamic, and the like, acids and their anhydride, ester and salt
derivatives, if any. Acrylic acid and methacrylic acid are the
preferred unsaturated organic compounds containing at least one
ethylenic unsaturation and at least one carbonyl group.
Initiators
[0078] The process of the present invention is a free radical
polymerization process. The type of free radical initiator to be
used in the present process is not critical. Free radical
initiators that are generally used for such processes are oxygen,
which is usable in tubular reactors in conventional amounts of
between 0.0001 and 0.005 weight percent (wt %) based on the weight
of polymerizable monomer, and organic peroxides. Typical and
preferred initiators are the organic peroxides such as peresters,
perketals, peroxy ketones and percarbonates, di-tert-butyl
peroxide, cumyl perneodecanoate, and tert-amyl perpivalate. Other
suitable initiators include azodicarboxylic esters, azodicarboxylic
dinitriles and 1,1,2,2-tetramethylethane derivatives. These organic
peroxy initiators are used in conventional amounts of between 0.005
and 0.2 wt % based on the weight of polymerizable monomers.
Chain Transfer Agents
[0079] Chain transfer agents or telogens are used to control the
melt flow index in a polymerization process. Chain transfer
involves the termination of growing polymer chains, thus limiting
the ultimate molecular weight of the polymer material. Chain
transfer agents are typically hydrogen atom donors that will react
with a growing polymer chain and stop the polymerization reaction
of the chain. These agents can be of many different types, from
saturated hydrocarbons or unsaturated hydrocarbons to aldehydes,
ketones or alcohols. By controlling the concentration of the
selected chain transfer agent, one can control the length of
polymer chains, and, hence, the weight average molecular weight, M.
The melt flow index (MFI or I.sub.2) of a polymer, which is related
to M.sub.w, is controlled in the same way.
[0080] The chain transfer agents used in the process of this
invention include, but are not limited to, aliphatic and olefinic
hydrocarbons, such as saturated hydrocarbons of six or more carbon
atoms (e.g., hexane, cyclohexane, octane, etc.), propene, pentene
or hexene; ketones such as acetone, diethyl ketone or diamyl
ketone; aldehydes such as formaldehyde or acetaldehyde; and
saturated aliphatic aldehyde alcohols such as methanol, ethanol,
propanol or butanol. Preferred chain transfer agents are those with
a chain transfer constant (Cs) not in excess of 0.1 (e.g., MEK,
propionaldehyde, tert-butanethiol), more preferably from 0.02 to
0.05 (e.g., propylene, isopropanol, 1-butene), and even more
preferably from 0.002 to 0.02 (e.g., methanol, ethanol,
isopropanol, acetone). The Cs is calculated as described by
Mortimer at 130.degree. C. and 1360 atmospheres (Ref. No. 1-4). The
top Cs value typically does not exceed 25, more typically it does
not exceed 21.
[0081] In one embodiment, the amount of chain transfer agent used
in the process of the present invention is from 0.3 to 15 percent
by weight, preferably from 1 to 10 percent by weight based on the
amount of monomer introduced in the reactor system.
[0082] The manner and timing of the introduction of the CTA into
the process of the invention can vary widely as long as the CTA
and/or ethylene are freshly injected into at least two reaction
zones. Typically the CTA is fed to the first reaction zone along
with ethylene and other reaction components, e.g., comonomers,
initiator, additives, etc., and make-up CTA, i.e., CTA replacement
for the CTA consumed in the first reactor zone, is fed to a down
stream (2.sup.nd, 3.sup.rd, 4.sup.th, etc) reaction zone. The first
reaction zone is an autoclave.
[0083] In one embodiment, additional (fresh) CTA is fed together
with fresh ethylene through direct injection and/or along with the
injected peroxide solution.
[0084] In one embodiment, additional (fresh) ethylene without CTA
is fed as a make up flow for ethylene consumed in the first
reaction zone either to the first autoclave reaction zone and/or to
one or more down stream reaction zones.
[0085] In one embodiment, the fresh CTA is a CTA with a Cs higher
than the Cs of the CTA fed to the first reaction zone.
[0086] In one embodiment, the CTA comprises a monomeric group, like
propylene, butene-1, etc. The monomeric group enhances reactor
conversion (it increases the consumption of comonomer).
[0087] In one embodiment, the CTA and/or operating conditions in
the recycle sections are selected such that the CTA will condense
and/or separate from the polymer product resulting in less CTA
recycled back to the reactor inlet.
[0088] In one embodiment, CTA is purged from the reactor system in
a downstream reaction zone.
[0089] In one embodiment, the reactor system comprises two
autoclave reaction zones followed by two reaction tubular zones,
and ethylene monomer and CTA are fed to both autoclave reaction
zones but not to either tubular reaction zone.
[0090] In one embodiment, the reactor system comprises two
autoclave reaction zones followed by two reaction tubular zones,
and ethylene monomer and CTA are fed to both autoclave reaction
zones but not to either tubular reaction zone, but initiator is fed
to one or both tubular reaction zones.
[0091] In one embodiment, the CTA is the components injected to
control molecular weight and melt-index of the product. Process
impurities, such as peroxide dissociation products and peroxide
diluent solvent, and comonomers are not CTA's, although their level
in the process will influence the level of CTA system needed to
control molecular weight and melt-index of the product.
Polymers
[0092] The ethylene-based polymers made according to the process of
this invention can vary from film grade, with a very narrow
molecular weight distribution (MWD), to coating type resins having
a much broader MWD, by enhancing the production in the tube or in
the autoclave when either a minor or a large degree of back mixing
is needed. By polymerizing ethylene and comonomers in an autoclave
reactor, one will get a polymer product having a broad molecular
weight distribution, while the polymerization in a tubular reactor
will give a polymer product having a narrow molecular weight
distribution. Surprisingly, however, by using the split CTA
addition process of this invention, the polymers can be prepared
with high amounts of branching and a MWD narrower than polymers
produced in a conventional autoclave polymerization but broader
than polymers produced in a conventional tube reactor
polymerization. In this way the molecular weight distribution of
ethylene-based interpolymers can be adjusted with more flexibility
than in a conventional autoclave reactor or in a conventional
tubular reactor.
[0093] Representative of the interpolymers of ethylene and an
alpha,beta-unsaturated carbonyl comonomer that can be made by the
process of this invention are copolymers of ethylene and acrylic
acid or methacrylic acid (EAA or EMAA) and their ionomers (e.g.
their metal salts), ethylene and vinyl acetate (EVA) and its
derivative ethylene vinyl alcohol (EVOH), ethylene and carbon
monoxide (ECO), ethylene/propylene and carbon monoxide (EPCO),
ethylene/carbon monoxide/acrylic acid terpolymer (ECOAA), and the
like. With respect to EAA and EMAA (and their derivatives), these
materials have carboxylic acid groups along the backbone and/or
side chains of the copolymer which in the case of their ionomers,
can be subsequently neutralized or partially neutralized with a
base. Typically, these copolymers contain from 2 to 30, or from 3
to 20, or from 4 to 15, percent by weight of acid comonomer units
in the polymer chain. The melt index of these copolymers is
typically from 0.5 to 1500, or from 2 to 300, or from 5 to 50.
[0094] The ethylene-based interpolymers made according to this
invention have the benefits of conversion as mentioned above. This
distinguishes them from other ways of making similar ethylene
polymers, being in a tubular process. In one aspect the polymer of
this invention has a narrower MWD than other polymers made in
similar reactors that do not use the split CTA concept (Z1/Zi=1).
This exemplified and quantified with the melt elasticity-melt index
balance, which is a sensitive method to show these differences as
shown by the examples and comparative examples. It is also
exemplified by the improvement in film optics associated narrow
MWD.
[0095] In one embodiment, the ethylene-based interpolymers of this
invention have a typical density from 0.920 to 0.960 grams per
cubic centimeter (g/cc or g/cm.sup.3).
Blends
[0096] The inventive interpolymers can be blended with one or more
other polymers such as, but not limited to, other polyolefins.
Additives
[0097] One or more additives may be added to a composition
comprising an inventive polymer. Suitable additives include, but
are not limited to, stabilizers.
Uses
[0098] The polymer of this invention may be employed in a variety
of conventional thermoplastic fabrication processes to produce
useful articles, including objects comprising at least one film
layer, such as a monolayer film, or at least one layer in a
multilayer film prepared by cast, blown, calendered, or extrusion
coating processes; molded articles, such as blow molded, injection
molded, rotomolded or vacuum formed articles; extrusions (e.g.,
wire and cable coating); and woven or non-woven fabrics. Film uses
include, but are not limited to, adhesive films, clarity shrink
films, collation shrink films, cast stretch films, silage films,
stretch hood, sealants and diaper backsheets. Other uses include in
coatings for metal (especially aluminum), as a sealing layer, and
in dispersions and extrusion coatings. Compositions comprising the
inventive polymer can also be formed into fabricated articles using
conventional polyolefin processing techniques.
[0099] Other suitable applications for the inventive polymer
include elastic films; soft touch goods, such as tooth brush
handles and appliance handles; gaskets and profiles; adhesives
(including hot melt adhesives and pressure sensitive adhesives);
footwear (including shoe soles and shoe liners); auto interior
parts and profiles; foam goods (both open and closed cell); impact
modifiers for other thermoplastic polymers such as high density
polyethylene, isotactic polypropylene, or other olefin polymers;
coated fabrics; flooring; and viscosity index modifiers, also known
as pour point modifiers, for lubricants.
[0100] Further treatment of the polymer of this invention may be
performed for application to other end uses. For example,
dispersions (both aqueous and non-aqueous) can also be formed using
the present polymers or formulations comprising the same. Frothed
foams comprising the inventive polymer can also be formed. The
inventive polymer may also be crosslinked by any known means, such
as the use of peroxide, electron beam, silane, azide, or other
cross-linking technique. The inventive polymers can be further
modified to form ionomers, such as reaction with sodium hydroxide
or zinc oxide.
DEFINITIONS
[0101] Unless stated to the contrary, implicit from the context, or
customary in the art, all parts and percents are based on weight
and all test methods are current as of the filing date of this
disclosure. For purposes of United States patent practice, the
contents of any referenced patent, patent application or
publication are incorporated by reference in their entirety (or its
equivalent US version is so incorporated by reference) especially
with respect to the disclosure of definitions (to the extent not
inconsistent with any definitions specifically provided in this
disclosure) and general knowledge in the art.
[0102] The numerical ranges in this disclosure are approximate, and
thus may include values outside of the range unless otherwise
indicated. Numerical ranges include all values from and including
the lower and the upper values, in increments of one unit, provided
that there is a separation of at least two units between any lower
value and any higher value. As an example, if a compositional,
physical or other property, such as, for example, molecular weight,
viscosity, melt index, etc., is from 100 to 1,000, it is intended
that all individual values, such as 100, 101, 102, etc., and sub
ranges, such as 100 to 144, 155 to 170, 197 to 200, etc., are
expressly enumerated. For ranges containing values which are less
than one or containing fractional numbers greater than one (e.g.,
1.1, 1.5, etc.), one unit is considered to be 0.0001, 0.001, 0.01
or 0.1, as appropriate. For ranges containing single digit numbers
less than ten (e.g., 1 to 5), one unit is typically considered to
be 0.1. These are only examples of what is specifically intended,
and all possible combinations of numerical values between the
lowest value and the highest value enumerated, are to be considered
to be expressly stated in this disclosure. Numerical ranges are
provided within this disclosure for, among other things, density,
melt index, molecular weight, reagent amounts and process
conditions.
[0103] The term "composition," as here used means a combination of
two or more materials. With the respective to the inventive
polymer, a composition is the inventive polymer in combination with
at least one other material, e.g., an additive, filler, another
polymer, catalyst, etc.
[0104] The terms "blend" or "polymer blend," as used, mean an
intimate physical mixture (that is, without reaction) of two or
more polymers. A blend may or may not be miscible (not phase
separated at molecular level). A blend may or may not be phase
separated. A blend may or may not contain one or more domain
configurations, as determined from transmission electron
spectroscopy, light scattering, x-ray scattering, and other methods
known in the art. The blend may be effected by physically mixing
the two or more polymers on the macro level (for example, melt
blending resins or compounding) or the micro level (for example,
simultaneous forming within the same reactor).
[0105] The term "polymer" refers to a compound prepared by
polymerizing monomers, whether of the same or a different type. The
generic term polymer thus embraces the term homopolymer (which
refers to polymers prepared from only one type of monomer with the
understanding that trace amounts of impurities can be incorporated
into the polymer structure), and the term "interpolymer" as defined
below. The term "interpolymer" refers to polymers prepared by the
polymerization of at least two different types of monomers. The
generic term interpolymer includes copolymers (which refers to
polymers prepared from two different monomers), and polymers
prepared from more than two different types of monomers.
[0106] The term "ethylene-based polymer" or "ethylene polymer"
refers to a polymer that comprises a majority amount of polymerized
ethylene based on the weight of the polymer and, optionally, may
comprise at least one comonomer.
[0107] The term "ethylene-based interpolymer" or "ethylene
interpolymer" refers to an interpolymer that comprises a majority
amount of polymerized ethylene based on the weight of the
interpolymer, and comprises at least one comonomer.
[0108] The term "acid comonomer units in the polymer chain" refers
to units within a polymer chain derived from a comonomer containing
at least one ethylenic unsaturation (e.g. at least one double
bond), and at least one carbonyl group (--C.dbd.O).
[0109] The term "reactor zone," refers to a section of a reactor
where a free radical polymerization reaction takes place by
injecting an initiator system, which is able to decompose to
radicals at the conditions within the zone. A reactor zone can be a
separate reactor unit or a part of a larger reactor unit. In a
tubular plug flow reactor unit, each zone begins where fresh
initiator is injected. In an autoclave reactor unit, zones are
formed by a separation device, e.g., a baffle, preventing back
mixing. Each reactor zone may have its own initiator feed, while
feeds of ethylene, comonomer, chain transfer agent and other
components can be transferred from a previous reaction zone, and/or
freshly injected (mixed or as separate components).
[0110] The term "zone reaction product" refers to the
ethylene-based polymer made under high-pressure conditions (e.g., a
reaction pressure greater than 100 MPa) through a free radical
polymerization mechanism. This product typically includes not only
the polymer molecules formed by the polymerization of the monomers
and, optionally, comonomers, but also unreacted monomer and
comonomer, CTA system, by-products and any other compounds or
materials introduced or made in the reaction zone. Due to
intermolecular hydrogen transfer, existing dead polymer molecules
can be reinitiated, resulting in the formation of long chain
branches (LCB) on the original (linear) polymer backbone. In a
reactor zone, new polymer molecules are initiated, and a part of
the polymer formed will be grafted on existing polymer molecules to
form long chain branches.
[0111] The term "polymerization conditions" refers to process
parameters under which the initiator entering the reactor zone will
at least partly decompose into radicals, initiating the
polymerization. Polymerization conditions include, for example,
pressure, temperature, concentrations of reagents and polymer,
residence time and distribution. The influence of polymerization
conditions on the polymer product is well described and modeled in
S. Goto et al, Ref No. 1.
[0112] The term "CTA system" includes a single CTA or a mixture of
CTAs. A CTA system includes a molecule able to transfer a hydrogen
radical to a growing polymer molecule containing a radical by which
the radical is transferred to the CTA molecule, which can then
initiate the start of a new polymer chain. CTA is also known as
telogen or telomer. In a preferred embodiment of the invention,
each CTA system comprises a single CTA.
[0113] The term "fresh CTA" refers to CTA fed to a reaction zone
other than reaction zone 1.
[0114] The term "suction to a hyper compressor" refers to the final
compressor prior to the reactor that brings one or more feed flows
to reactor pressure from a lower pressure. The suction to a hyper
compressor is the inlet configuration of this compressor.
[0115] The term "hyper compressor discharge" refers to the outlet
configuration of the hyper compressor.
[0116] The term "cloud point pressure" is used herein, refers to
the pressure, below which, the polymer solution of a fixed
composition at a fixed temperature, separates into two liquid
phases. Above this pressure, the polymer solution is a single
liquid phase.
Test Methods
[0117] Polymer Testing Methods
[0118] Density:
[0119] Samples for density measurement are prepared according to
ASTM D 1928. Samples are pressed at 190.degree. C. and 30,000 psi
for 3 minutes, and then at (21.degree. C.) and 207 MPa for 1
minute. Measurements are made within one hour of sample pressing
using ASTM D792, Method B.
[0120] Melt Index:
[0121] Melt index, or I.sub.2, (grams/10 minutes) is measured in
accordance with ASTM D 1238, Condition 190.degree. C./2.16 kg.
I.sub.to is measured with ASTM D 1238, Condition 190.degree. C./10
kg.
[0122] Triple Detector Gel Permeation Chromatography (TDGPC):
[0123] High temperature 3Det-GPC analysis is performed on an
Alliance GPCV2000 instrument (Waters Corp.) set at 145.degree. C.
The flow rate for the GPC is 1 mL/min. The injection volume is
218.5 .mu.L. The column set consists of four Mixed-A columns
(20-.mu.m particles; 7.5.times.300 mm; Polymer Laboratories
Ltd).
[0124] Detection is achieved by using an IR4 detector from Polymer
ChAR, equipped with a CH-sensor; a Wyatt Technology Dawn DSP MALS
detector (Wyatt Technology Corp., Santa Barbara, Calif., USA),
equipped with a 30-mW argon-ion laser operating at .lamda.=488 nm;
and a Waters three-capillary viscosity detector. The MALS detector
is calibrated by measuring the scattering intensity of the TCB
solvent. Normalization of the photodiodes is done by injecting SRM
1483, a high density polyethylene with weight-average molecular
weight (Mw) of 32,100 and polydispersity of 1.11. A specific
refractive index increment (dn/dc) of -0.104 mL/mg, for
polyethylene in TCB, is used.
[0125] The conventional GPC calibration is done with 20 narrow PS
standards (Polymer Laboratories Ltd.) with molecular weights in the
range 580-7,500,000 g/mol. The polystyrene standard peak molecular
weights are converted to polyethylene molecular weights using
M.sub.polyethylene=A.times.(M.sub.polystyrene).sup.B
with A.apprxeq.0.39, B=1. The value of A is determined by using
HDPE Dow 53494-38-4, a linear polyethylene homopolymer with Mw of
115,000 g/mol. The HDPE reference material is also used to
calibrate the IR detector and viscometer by assuming 100% mass
recovery and an intrinsic viscosity of 1.873 dL/g. The acid group
is neutralized, e.g., silylated, prior to analysis.
[0126] Distilled "Baker Analyzed"-grade 1,2,4-trichlorobenzene (J.
T. Baker, Deventer, The Netherlands), containing 200 ppm of
2,6-di-tert-butyl-4-methylphenol (Merck, Hohenbrunn, Germany), is
used as the solvent for sample preparation, as well as for the
3Det-GPC experiments. HDPE SRM 1483 is obtained from the U.S.
National Institute of Standards and Technology (Gaithersburg, Md.,
USA).
[0127] LDPE solutions are prepared by dissolving the samples under
gentle stirring for three hours at 160.degree. C. The PS standards
are dissolved under the same conditions for 30 minutes. The sample
concentration for the 3Det-GPC experiments is 1.5 mg/mL and the
polystyrene concentrations 0.2 mg/mL.
[0128] A MALS detector measures the scattered signal from polymers
or particles in a sample under different scattering angles 0. The
basic light scattering equation (from M. Andersson, B. Wittgren,
K.-G. Wahlund, Anal. Chem. 75, 4279 (2003)) can be written as
Kc R .theta. = 1 M + 16 .pi. 2 3 .lamda. 2 1 M Rg 2 sin 2 ( .theta.
2 ) ( 2 ) ##EQU00001##
where R.sub..theta. is the excess Rayleigh ratio, K is an optical
constant, which is, among other things, dependent on the specific
refractive index increment (dn/dc), c is the concentration of the
solute, M is the molecular weight, R.sub.g is the radius of
gyration, and .lamda. is the wavelength of the incident light.
Calculation of the molecular weight and radius of gyration from the
light scattering data require extrapolation to zero angle (see also
P. J. Wyatt, Anal. Chim. Acta 272, 1 (1993)). This is done by
plotting (Kc/R.sub..theta.).sup.1/2 as a function of
sin.sup.2(.theta./2) in the so-called Debye plot. The molecular
weight can be calculated from the intercept with the ordinate, and
the radius of gyration from initial slope of the curve. The Zimm
and Berry methods are used for all data. The second virial
coefficient is assumed to be negligible. The intrinsic viscosity
numbers are calculated from both the viscosity and concentration
detector signals by taking the ratio of the specific viscosity and
the concentration at each elution slice.
[0129] ASTRA 4.72 (Wyatt Technology Corp.) software is used to
collect the signals from the IR detector, the viscometer, and the
MALS detector. Data processing is done with in house-written
Microsoft EXCEL macros.
[0130] The calculated molecular weights, and molecular weight
distributions (?) are obtained using a light scattering constant
derived from one or more of the polyethylene standards mentioned
and a refractive index concentration coefficient, dn/dc, of 0.104.
Generally, the mass detector response and the light scattering
constant should be determined from a linear standard with a
molecular weight in excess of about 50,000 daltons. The viscometer
calibration can be accomplished using the methods described by the
manufacturer or alternatively by using the published values of
suitable linear standards such as Standard Reference Materials
(SRM) 1475a, 1482a, 1483, or 1484a. The chromatographic
concentrations are assumed low enough to eliminate addressing 2''
viral coefficient effects (concentration effects on molecular
weight).
[0131] Cloud Point Measurement
[0132] Cloud point measurement is described in Loos et al., "Fluid
Phase Equilibria in the System Polyethylene and Ethylene. Systems
of Linear Polyethylene and Ethylene at High Pressures,"
Macromolecules 16 (1983), 111-117.
[0133] Gel Measurement
[0134] Gels are defects in the film, and can be formed by a number
of different factors, e.g., by phase separation in the reactor, or
by extrusion, or from impurities, etc.). Reactor gels typically are
not crosslinked or oxidized, and they have a different viscosity
and/or acid content than the film in which they are carried. With
EAA products, reactor gels are typically rich in the dimer of the
acid (a Michael addition product). Gels give a grainy structure to
the film, and are typically analyzed as large, medium, small and
very small (micro) gels.
[0135] Gels are characterized by analyzing a film sample produced
using an extruder equipped with an FTIR that has a microscope
attachment. A camera gives a first crude number (total gel count),
and FTIR analysis can distinguish between reactor gels and other
gels formed from impurities, equipment, oxidization, thermal
degradation, etc. One extruder for producing the film for analysis
is a Model OCS ME 20 available from OCS Optical Control Systems
GmbH, Wullener Feld 36, 58454 Witten, Germany equipped with a
parameter standard screw, L/D 25/1, with a chrome coating. The
extruder is operated at a compression ratio of 3/1. The feed zone
is 10D, the transition zone is 3D and the metering zone is 12D. The
cast film die is a ribbon die, 150.times.0.5 mm. An air knife is
used to pin the film on the chill roll. The die, knife, chill rolls
and winding unit are also available from OCS Optical. The gel
counter is an OCS FS-3 or OCS FS-5 line gel counter consisting of a
lighting unit, a CCD detector and an image processor with a gel
counter software version 3.65e 1991-1999, all too available from
OCS.
[0136] Gels are measured continuously by taking a stream of pellets
from the process and transferring them to the cast film line. The
film line uses a set temperature profile by product family (melt
index). One analysis cycle inspects 24.6 cm.sup.3 of film. The
corresponding area is 0.324 m.sup.2 for a film thickness of 76
microns and 0.647 m.sup.2 for a film thickness of 38 microns. The
gels are reported by size per 50,000 square inches of film. The gel
classifications are as follows: [0137] Large gel: >1600 microns
in size [0138] Medium gel: 800 to 1600 microns [0139] Small gel:
400 to 800 microns [0140] Very small (micro) gels: 200 to 400
microns
[0141] Acid Content
[0142] The percent by weight of acid comonomer units in the polymer
chain may be analyzed by titration or using an FTNIR technique.
EXPERIMENTAL
Calculations for Z1, Z2 and Zi
[0143] The "reactor zone molar concentration of a CTA j in a
reactor zone i ([CTA]ji)" is defined as the "total molar amount of
that CTA freshly injected to reactor zones 1 to i" divided by the
"total molar amount of ethylene freshly injected to reactor zones 1
to i." This relationship is shown below in Equation A.
[ CTA ] j i = k = 1 i n CTA , j k k = 1 i n eth k ( Eqn . A )
##EQU00002##
[0144] In Equation A, j.gtoreq.1, n.sub.CTA,j.sub.i is the "amount
of moles of the jth CTA freshly injected to the ith reactor zone,"
and n.sub.eth.sub.i is the "amount of moles of ethylene freshly
injected to the ith reactor zone."
[0145] The "transfer activity of a CTA (system) in a reactor zone
i" is defined as the "sum of the reactor zone molar concentration
of each CTA in the reactor zone" multiplied with its chain transfer
activity constant (Cs). The chain transfer activity constant (Cs)
the ratio of reaction rates Ks/Kp, at a reference pressure (1360
atm) and a reference temperature (130.degree. C.). This
relationship is shown below in Equation B, where n.sub.compi is the
total number of CTAs in reactor zone i.
Z i = j i = 1 n comp , i [ CTA ] j i C s , j ( Eqn . B )
##EQU00003##
[0146] Thus, the ratio Z1/Zi is shown below in Equation C.
Z 1 Z i = j 1 = 1 n comp , 1 [ CTA ] j 1 C s , j j i = 1 n comp , i
[ CTA ] j i C s , j ( Eqn . C ) ##EQU00004##
The chain transfer constant (Cs) values for some chain transfer
agents are shown below in Table 1., showing chain transfer
constants (Cs) derived by Mortimer at 130.degree. C. and 1360 atm
for example chain transfer agents.
TABLE-US-00001 TABLE 1 Cs-Values as Measured by Mortimer at
130.degree. C. and 1360 atm in References 2 and 3 Cs at 130.degree.
C. and CTA 1360 atm propane 0.0030 iso-butane 0.0072 propylene
0.0122 iso-propanol 0.0144 acetone 0.0168 1-butene 0.047 methyl
ethyl ketone 0.060 propionaldehyde 0.33 tert-butanthiol 15
[0147] 1. G. Mortimer; Journal of Polymer Science: Part A-1; Chain
transfer in ethylene polymerization; vol 4, p 881-900 (1966) [0148]
2. G. Mortimer; Journal of Polymer Science: Part A-1; Chain
transfer in ethylene polymerization. Part Iv. Additional study at
1360 atm and 130.degree. C.; vol 8, p 1513-1523 (1970) [0149] 3. G.
Mortimer; Journal of Polymer Science: Part A-1; Chain transfer in
ethylene polymerization. Part V, The effect of temperature; vol 8,
p 1535-1542 (1970) [0150] 4. G. Mortimer; Journal of Polymer
Science: Part A-1; Chain transfer in ethylene polymerization. Part
VII. Very reactive and depletable transfer agents; vol 10, p
163-168 (1972)
[0151] When only one CTA is used in the total reactor system,
Equations B and C simplify to Equations D and E, respectively.
Z i = [ CTA ] i C s ( Eqn . D ) Z 1 Z i = [ CTA ] 1 C s [ CTA ] i C
s = [ CTA ] 1 [ CTA ] i ( Eqn . E ) ##EQU00005##
[0152] Although all the examples reported below use two-zone
autoclave reactors, those skilled in the art understand that
multi-zone reactor systems comprising a first zone of an autoclave
reactor followed by a single or multiple zone autoclave or tube
reactor, or combinations of the two reactors, can also be
employed.
[0153] For the four polymerizations (two inventive, two
comparative) discussed below, only one CTA was used. Four reactor
zones are used configured as A A T T. Reactor zone 1 is A, reactor
zone 2 is A, reactor zone 3 is T, reactor zone 4 is T. CTA is
injected into zones 1 and 2, only initiator is injected into zones
3 and 4, however typically some CTA is carried over into zones 3
and 4 from zones 1 and 2. No CTA is added to reactor zones 3 and
4.
[0154] Only one CTA implies that Cs drops out of equations, and
thus, Equation E is used for all examples, as shown below.
Z 1 Z 2 = [ CTA ] 1 C s [ CTA ] 2 C s = [ CTA ] 1 [ CTA ] 2 = k = 1
1 n CTA k k = 1 1 n eth k k = 1 2 n eth k k = 1 2 n CTA k = k = 1 2
n eth k k = 1 1 n eth k k = 1 1 n CTA k k = 1 2 n CTA k = n eth 1 +
n eth 2 n eth 1 n CTA 1 n CTA 1 + n CTA 2 ##EQU00006##
[0155] In addition, the tubular part of the AC/tube reactor system
(which is the system used to generate all examples) can be
considered as reactor zones 3 and 4, where both zones do not
receive any additional freshly injected ethylene or CTA. This means
that Equation E becomes as shown below. So Z1/Z4=Z1/Z3=Z1/Z2.
Z 1 Z 2 = [ CTA ] 1 C s [ CTA ] i C s = [ CTA ] 1 [ CTA ] i = k = 1
1 n CTA k k = 1 1 n eth k k = 1 i n eth k k = 1 i n CTA k = k = 1 i
n eth k k = 1 1 n eth k k = 1 1 n CTA k k = 1 i n CTA k = k = 1 2 n
eth k k = 1 1 n eth k k = 1 1 n CTA k k = 1 2 n CTA k = Z 1 Z 2 , i
.gtoreq. 3 ##EQU00007##
[0156] In addition, for all examples:
n.sub.eth.sub.1=n.sub.eth.sub.2 and thus, the relationship is
further simplified as shown below.
Z 1 Z 2 = n eth 1 + n eth 2 n eth 1 n CTA 1 n CTA 1 + n CTA 2 = n
eth 1 + n eth 1 n eth 1 n CTA 1 n CTA 1 + n CTA 2 = 2 n CTA 1 n CTA
1 + n CTA 2 ##EQU00008##
Conditions in an Autoclave Top Zone
[0157] The typical autoclave top zone conditions for EAA 3440 are
2137 bar and 215.degree. C. The polymer made in the first zone has
on average 11 wt % acrylic acid (AA). Non-perfect mixing in the
autoclave top zone results in a colder subzone near the cold
ethylene/AA inlet. This colder subzone is characterized by lower
temperature, lower polymer concentration, higher AA concentration,
and polymer with a higher AA content (>11 wt % AA). These
conditions promote local occurrence of phase separation in the top
zone. Phase separation is indicated by the gel level to solvent
concentration, temperature and/or pressure conditions. The agitator
shows deposits of solid EAA in the upper part of the top zone of
the autoclave, where the Ethylene/AA entry is located.
Characterization of this material using FTIR technique described
above shows that this material is also present in gels.
Ethylene/EAA Phase Separation Data (Cloud Point) from External
Literature [0158] Literature reference: Carsten Beyer and Lothar R.
Oellrich, "Solvent studies with the system
Ethylene/Poly(ethylene-co-acrylic acid): Effects of solvent,
density, hydrogen bonding, and copolymer composition," Helvetica
Chimica Acta; Vol. 85 (2002); pp 659-670.
[0159] Table 2 shows the impact of AA content in the polymer on
cloud point pressure for ethylene/polyethylene (95/5 wt %) systems.
A solvent was not used in these systems of Table 2.
TABLE-US-00002 TABLE 2 Impact of AA Content in Polymer on Cloud
Point Pressure EAA, wt % 0 5 5 5 5 5 5 AA content in 0 6 7.5 8 9 11
15 EAA, wt % LDPE, wt % 5 Ethylene, wt % 95 95 95 95 95 95 95
Temperature, .degree. C. Cloud point pressure, bar 150.5 .+-. 0.5
1529 2153 174.5 .+-. 300.6 1421 1779 1946 2037 2209 200.5.5 .+-. 2
1341 1539 1637 1692 1779 2104 2647 224.5 .+-. 0.5 1272 1394 1442
1469 1521 1686 2066 249.5 .+-. 1 1221 1302 1340 1349 1390 1484
1732
[0160] As seen from Table 2, cloud point pressure increases
strongly with decreasing temperature and/or increasing AA content
in polymer.
Additional Ethylene/EAA Phase Separation Data
[0161] The properties of the EAA copolymer are shown in Table 3.
Cloud point pressure as a function of solvent is shown in Table
4.
TABLE-US-00003 TABLE 3 Properties of Investigated Polymer EAA
Copolymer 10 30 40 60 04 AA content wt % 9.7 9.7 9.7 9.7 9.7 Melt
gr/10 1.8 4.8 10.0 19.5 8.5 index min
TABLE-US-00004 TABLE 4 Cloud Point Pressure as a Function of
Solvent 1 2 3 4 System w % w % w % w % EAA 10 15 15 16 16 AA
content in 9.7 EAA 10, wt % Ethylene 85 75 75 75 Isobutane 0 10
Ethanol 9 Acetone 9 Cloud point data Temperature Pressure (.degree.
C.) (bar) 180 .+-. 1.55 1990 2066 1356 1434 197.5 .+-. 1.5 1688
1744 1252 1323
[0162] Table 4 shows the impact of a solvent on cloud point
pressure. The conditions shown in Table 4 are the closest to the
conditions in the autoclave top zone. Although the AA content is
still a little lower (9.7 versus 11 wt % AA), the EAA concentration
is at the high side (15-16 wt % versus 13.5 wt %), and there is no
AA monomer present. Furthermore, in plant systems low levels of
solvent (diluent for peroxides) and isobutane (CTA) are
present.
[0163] Cloud point pressure as a function of AA comonomer is shown
in Table 5. As shown in Table 5, the "3 wt % iso-octane"
neutralizes the negative impact of "4 wt % AA" on cloud point
pressure.
TABLE-US-00005 TABLE 5 Impact of Solvent and AA on Cloud Point
Pressure System w % w % w % EAA 10, wt % 10.1 10 10 AA content in
9.7 9.7 9.7 EAA, wt % Ethylene, wt % 89.9 86.6 89.9 2,2,4 0 3.4 2.8
trimethylpentane, wt % Acrylic acid, wt % 0 0 4.2 Cloud point data
Temperature Pressure Pressure Pressure (.degree. C.) (bar) (bar)
(bar) 220 .+-. 0.5 1920 1815 1924
[0164] Some solvents and their properties are shown in Table 6.
TABLE-US-00006 TABLE 6 Properties and Compositions of Selected
Solvents Boiling Density range at 15.degree. C. (.degree. C.)
(kg/dm3) Major components 2,2,4- 99.3 0.688 2,2,4 trimethylpentane
trimethylpentane (iso-octane) Isopar-C 98-104 0.698 >80% 2,2,4
trimethylpentane plus other C6-C9 isoparaffins Isopar-H 179-188
0.758 C11-C13 isoparaffins
[0165] The solvent type was changed at an EAA polymerization from
Isopar-C (mainly 2,2,4-trimethylpentane) to Isopar-H, as peroxide
dilution solvent. Isopar-H, being a heavier boiling solvent, will
more easily condense and remove from the polymerization system as
compared to Isopar-C. Thus, a lower level of Isopar-H will build up
in the polymerization process. The lower amount of Isopar-H, means
that a higher amount of isobutane (CTA) is needed to control the
melt-index of the polymer product.
[0166] Isobutane will compensate for the lower solvent content in
the polymerization process. Isobutane will replace the condensed
solvent (Isopar-H) as CTA. The reduced solvent level, the in case
of Isopar-H, results in a critical cloud point pressure increase,
by which phase separation conditions are reached in the top zone.
The consequence is an increased gel level in the polymer product.
In Tables 7 and 8, the impact of the solvent change on CTA amount
and gel levels, respectively, is shown.
TABLE-US-00007 TABLE 7 Process Conditions and CTA Content for
Various Products (ISOPAR C and H) Control temperature MI AA AC- AC-
CTA EAA g/10 content Pressure zone 1 zone 2 Isobutane name min. wt.
% Solvent bar .degree. C. .degree. C. vol % 40 10.0 9.7 Isopar 2137
215 233 1.9 C 40 10.0 9.7 Isopar 2137 215 233 2.4 H 30 4.8 9.7
Isopar 2137 210 240 1.1 C 30 4.8 9.7 Isopar 2137 210 240 1.5 H 04
8.5 9.7 Isopar 2137 215 233 1.7 C 04 8.5 9.7 Isopar 2137 215 233
2.3 H
[0167] Table 7 shows that the polymer MI is control by isobutane
content in case of solvent change from Isopar C to Isopar H. As
shown in Table 7, on average the increase in isobutane level was
0.5 vol %, when the solvent is changed from Isopar C to Isopar H.
As shown in table 8, Isopar C gave lower small and micro gel levels
as compared with the polymerization using Isopar H. This indicates
that the use of Isopar C, as a peroxide diluent solvent, reduces CP
pressure.
TABLE-US-00008 TABLE 8 Zone 1 Temperature Profile and Product Gel
Count Zone 1 temperature profile, C. Top of Top Middle Average gel
count per 50,000 square inches EAA Solvent zone middle bottom
Bottom Large Medium Small Micro 40 Isopar 211.6 212.6 212.1 215.0
0.3 8.7 405 19893 C 40 Isopar 212.0 213.1 212.8 215.0 0.3 14.7 544
22203 H 30 Isopar 206.7 207.7 207.2 210.9 0.3 32.8 347 11995 C 30
Isopar 206.4 208.0 208.0 211.0 0.6 34.4 473 30541 H 04 Isopar 212.1
212.8 212.0 214.9 0.1 14.4 280 15734 C 04 Isopar 211.8 213.1 212.7
215.0 0.6 22.9 600 28310 H
The top of zone 1 is a cold spot that is several degrees colder
than the control temperature.
[0168] Table 9 shows the effect of solvent change on cloud point
pressure using Mortimer chain transfer data from Table 10. The
increase in isobutane demand as CTA can be assigned to a loss in
solvent build up level. The increase in isobutane level is
calculated in Table 9 as a loss in 2,2,4-trimethylpentane. In the
calculation it is assumed that "1 wt % Isopar-C" and "1 wt %
Isopar-H" have the same impact on cloud point pressure, and have
the same chain transfer activity. The increase on cloud point
pressure of 41 bar is calculated by taking into consideration the
impact of isobutane and the loss in solvent concentration on the
cloud point pressure.
TABLE-US-00009 TABLE 9 Calculated Impact of Solvent Change on Cloud
Point pressure Equivalent CTA CP Activity to Isobutane CP Increase
by Iso- 2,2,4- Increase by Solvent butane trimethylpentane
Isobutane Change vol % vol %* wt % bar/wt %** bar Delta iso- 0.5
0.56 1.11 37 41 butane Note*: Using Cs values of Mortimer Note**:
Combined effect of iso-octane (31 bar/wt %) and isobutane (-6
bar/wt %)
TABLE-US-00010 TABLE 10 Chain Transfer Data by Mortimer Cs at
130.degree. C. Chain transfer agent &1360 atm Ethyl acetate
0.0045 2,4,4Trimethylpentane 0.0064 iso-butane 0.0072 ethanol
0.0075 iso-propanol 0.0144 acetone 0.0168 methyl ethyl ketone
0.06
Polymerization Simulations
[0169] Polymerization simulations were achieved with Goto LDPE
simulation model as described in: S. Goto et al; Journal of Applied
Polymer Science: Applied Polymer Symposium, 36, 21-40, 1981 (Title:
Computer model for commercial high pressure polyethylene reactor
based on elementary reaction rates obtained experimentally).
[0170] The chain transfer activity data is from Mortimer, as
described in the following references: [0171] 1. G. Mortimer;
Journal of Polymer Science: Part A-1; Chain transfer in ethylene
polymerization; vol. 4, p 881-900 (1966), and [0172] 2. G.
Mortimer; Journal of Polymer Science: Part A-1; Chain transfer in
ethylene polymerization. Part V. The effect of Temperature; vol. 8,
p 1535-1542 (1970).
[0173] A two zone high pressure autoclave reactor using
respectively isobutane, ethanol, acetone and methyl ethyl ketone as
chain transfer agent is employed.
TABLE-US-00011 Residence time: 1.sup.st AC zone: 26 sec 2.sup.nd AC
zone: 27 sec
[0174] Ratio 1.sup.st AC zone fresh feed stream versus 2.sup.nd AC
zone feed stream is 1
TABLE-US-00012 Pressure level: 2137 bar AC zone control
temperature: 1.sup.st AC zone: 210.degree. C. 2.sup.nd AC zone:
233.degree. C. Simulated product: Melt-index: 10 gr/10 min AA
content: 9.7 wt %
[0175] The temperature, conversion levels, and distribution of
ethylene and AA, as shown in Table 11, results in a polymer with a
final acid content of 11 wt % in the autoclave top zone, and an
acid content of 9.7 wt % in the final polymer product. Based on
ethylene and AA flows and temperature conditions, the conversion
and polymer composition can be calculated in each zone.
TABLE-US-00013 TABLE 11 Acid Compositions for EAA 40 Reactor
conditions Polymer composition AA Ethy kg kg wt % Tfeed Tcontrol
conv conv* AA Eth AA AC-zone 1 35 210 0.94 0.135 245 1984 11.0%
AC-zone 2 28 233 0.94 0.155 245 2585 8.7% Final product 491 4569
9.7% Note*: Ethylene conversion is calculated by 13.degree. C.
temperature increase per 1 wt % ethylene conversion
[0176] The fresh ethylene and fresh AA are equally distributed over
both zones. The simulated polymerizations, additional conditions,
are also shown in Table 13. Simulation results are with Goto model
and Mortimer chain transfer activity of application of invention
with different CTA's. Simulations were performed at EAA 40
conditions. "2.4 vol % isobutene" was replaced by other type of
CTA's. Cloud point reduction was derived from CTA concentration in
top zone and cloud point reduction data measured (bar/wt %).
Isobutane shows a negative effect due to its lower density.
[0177] As shown in Table 12, the additional lowering of cloud point
pressure is achieved by using an inventive process (CTA split).
Furthermore the inventive process shows a lowering of the molecular
weight of the polymer formed in AC-zone 1. This lower molecular
weight in AC-zone-1 improves polymer solubility as well as improved
mixing efficiency, by which the colder subzone phase separation
will be reduced. The reduced or eliminated phase separation will
results in a polymer product with reduced gel levels, and which can
be used to form films with improved optical properties.
Simulation Procedure
[0178] The process conditions and the dimensions of the reactor
were entered into the model. Xn in Table 12 stands for number
average degree of polymerization and reflects the number of monomer
and comonomer units built in per average final polymer molecule.
The melt index is calculated from Xn.
[0179] The observed isobutane concentration was taken for the
reference isobutane case.
[0180] The chain transfer activity from process impurities and the
acrylic acid comonomer were simulated by matching the product
melt-index by assigning chain transfer activity to acrylic acid and
simulating the remainder effect by process impurities by
incorporating a low level of n-butane (used as model component) to
the system. In the remainder of the simulations the chain transfer
activity provided by the acrylic acid and process impurities was
kept constant.
[0181] Only the observed level of 2.4 vol % isobutane was replaced
by alternative CTA's.
[0182] All CTA's were simulated by Cs values and temperature
dependences as derived by Mortimer (see Ref 1-4).
TABLE-US-00014 TABLE 12 Simulation Results with Different CTAs
Reactor pressure, bar 2137 Temperature, AC-zone 1 210.degree. C.
Temperature, AC-zone 2 233.degree. C. AA wt % in EAA 9.7
Melt-index, 10 g/min 10 CTA- CTA- conc. conc. Additional CP top-
bottom- Xn* in Estimated .DELTA.P in CP CP reduction (by zone zone
top zone MI in per wt % reduction CTA) by CTA conc [mol- [mol-
Monomer AC-zone Xn final cosolvent** by CTA invention ratio Z1/Z2
ppm] ppm] units 1 (10 MI) bar bar bar iso-butane reference 1.000
24000 24000 587 7.0 564 -6 -30 (comparative) iso-butane
(comparative) 1.150 28400 21000 565 9.9 564 -6 -35 -5 Ethanol
reference 1.000 24000 24000 585 7.4 564 44 219 (comparative)
Ethanol inventive 1.150 28400 21000 563 10.1 564 44 259 40 Acetone
reference 1.000 25400 12700 582 7.7 564 41 216 (comparative)
Acetone inventive 1.150 30000 22200 559 10.8 564 41 255 39 MEK
reference 1.000 4950 4950 577 8.3 564 33 42 (comparative) MEK
inventive 1.150 5800 4290 555 11.4 564 33 49 7 *Definition of Xn:
(co) monomer units incorporated into polymer. **Cloud point
reduction of MEK is derived from acetone on a molar basis of ketone
functional group. For example, the CP reduction for MEK = CP
reduction acetone .times. Mw acetone/Mw MEK = 41 .times. 58/72 = 33
bar/wt % MEK
[0183] The direct consequence of the CTA arrangement of the
invention leads to a narrower MWD, and the inventive polymers
should have lower melt elasticity which translates to better optics
in the films formed from such polymers.
[0184] Although the invention has been described with certain
detail through the preceding description of the preferred
embodiments, this detail is for the primary purpose of
illustration. Many variations and modifications can be made by one
skilled in the art without departing from the spirit and scope of
the invention as described in the following claims.
* * * * *