U.S. patent application number 09/778081 was filed with the patent office on 2002-10-31 for biodegradable triblock copolymers and process for their preparation.
This patent application is currently assigned to Korea Institute of Science and Technology. Invention is credited to Kim, Soo Hyun, Kim, Young Ha, Lee, Soo-Hong, Park, Ki Dong.
Application Number | 20020161134 09/778081 |
Document ID | / |
Family ID | 19646093 |
Filed Date | 2002-10-31 |
United States Patent
Application |
20020161134 |
Kind Code |
A1 |
Kim, Young Ha ; et
al. |
October 31, 2002 |
BIODEGRADABLE TRIBLOCK COPOLYMERS AND PROCESS FOR THEIR
PREPARATION
Abstract
The present invention relates to polyethyleneglycol/polylactide
(or polyglycolide or polycaprolactone)/polyethyleneglycol triblock
copolymers with an enhanced reactivity, and process for their
preparation. More specifically, the present invention is directed
to triblock copolymers that are obtained by the process comprising
the step of synthesizing a polylactide (or polyglycolide or
polycaprolactone) having hydroxy groups at both ends and the step
of coupling said polylactide with polyethyleneglycol having an
acylhalide group of a high reactivity at one of its ends, and the
process for preparing the same. Since the triblock copolymer
according to the present invention has an ester structure with good
biocompatibility, it can be applied extensively for biomaterials
used in tissue engineering, in a matrix that slowly releases drugs,
etc.
Inventors: |
Kim, Young Ha; (Seoul,
KR) ; Kim, Soo Hyun; (Seoul, KR) ; Park, Ki
Dong; (Seoul, KR) ; Lee, Soo-Hong; (Seoul,
KR) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
Korea Institute of Science and
Technology
Seoul
KR
|
Family ID: |
19646093 |
Appl. No.: |
09/778081 |
Filed: |
February 7, 2001 |
Current U.S.
Class: |
525/408 ;
525/403; 525/411; 525/413; 525/415; 525/417; 525/418; 525/437;
525/439; 525/444; 525/450; 525/523; 525/533; 528/354; 528/403;
528/405; 528/421 |
Current CPC
Class: |
C08L 71/02 20130101;
C08G 65/3324 20130101; C08G 63/664 20130101; C08L 71/02 20130101;
C08L 2666/18 20130101 |
Class at
Publication: |
525/408 ;
525/403; 525/411; 525/413; 525/415; 525/417; 525/450; 525/418;
525/437; 525/439; 525/444; 525/523; 525/533; 528/354; 528/403;
528/421; 528/405 |
International
Class: |
C08G 065/32; C08F
283/06; C08G 063/91; C08G 063/66; C08G 063/664; C08L 067/00; C08L
067/04; C08L 071/00; C08L 071/02; C08G 063/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2000 |
KR |
2000-6745 |
Claims
What is claimed is:
1. A biodegradable triblock copolymer selected from the group
consisting of copolymers of formula (1) to (4). <formula
1>PEG-COO-PL-OCO-PEG <formula 2>PEG-COO-PG-OCO-PEG
<formula 3>PEG-COO-(PLPG)-OCO-P- EG <formula
4>PEG-COO-PCL-OCO-PEG In the formula, PEG is polyethyleneglycol,
PL is polylactide, PG is polyglycolide, PCL is
polycaprolactone.
2. The biodegradable triblock copolymer according to claim 1,
wherein a molecular weight of PEG is 750 to 10,000.
3. The biodegradable triblock copolymer according to claim 1,
wherein a molecular weight of polylactide, polyglycolide,
polylactide/polyglycolide or polycaprolactone is 500 to 30,000.
4. A method for preparing a triblock copolymer which comprises
coupling polyethyleneglycol having an acylhalide group of a high
reactivity at one of its ends with polylactide, polyglycolide,
polylactide/polyglycolide or polycaprolactone having a hydroxy
group at both ends in the presence of pyridine.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to
polyethyleneglycol/polylactide (or polyglycolide or
polycaprolactone)/polyethyleneglycol triblock copolymers with an
enhanced reactivity, and a process for their preparation.
[0003] Specifically, the present invention is directed to a
triblock copolymers that are obtained by the process comprising the
step to synthesize a polylactide (or polyglycolide or
polycaprolactone) having hydroxy groups at both ends, and the step
of coupling said polylactide with polyethyleneglycol having
acylalide group of a high reactivity at one of its ends, and the
process for preparing the same.
[0004] 2. Description of the Prior Art
[0005] Among the different applications of degradable polymer
materials, it is most actively investigated in the field of
medicine. A general medical polymer is used as a permanent material
with replacement of parts for a living body, whereas a
biodegradable polymer is used as a transient material to help
healing of the body and disappears through the body's metabolism
after completing its function. Due to these properties of the
biodegradable polymer, an additional surgical operation to remove
the polymer is not necessary after the body has healed. Also, as
the body gradually heals, the polymer gradually degrades so that it
can help newly developed tissue to function sufficiently.
[0006] Since the biodegradable polymer essentially has to have
biocompatibility, only limited materials as polylactide,
polyglycolide, polycaprolactone and polyethyleneglycol have been
used to form the polymer. Many biodegradable polymers comprising
polylactide and polyethyleneglycol have been studied in the form of
block copolymers. Such polymers are comprised of hydrophobic
polylactide and hydrophilic polyethyleneglycol and take the form of
micelle in a solution. Also, since said polymers can make the
hydrophobic polylactide hydrophilic, they can be applied widely as
a bio-materials to be used as a matrix for the slow release of
drugs, in tissue engineering, etc.
[0007] It was reported that block copolymer consisting of
polylactide and polyethyleneglycol forms hydrogel in water and can
be in a form of gel or sol by parameters of a temperature, pH, etc.
so that it shows a behavior that can be used as slow releasing
matrix of drug (Macromol. Chem. Phys. 198, 3385-3395 (1997)).
[0008] Most of such block copolymers, however, are in the form of a
double block or triblock that is produced by a ring-open
polymerization of lactide by polyethyleneglycol. Most triblocks are
copolymers with a structural configuration of
polylactide/polyethyleneglycol/polylactide, wherein hydrophilic
polyethyleneglycol is present in the center and the hydrophobic
polylactide is located at both ends.
[0009] In comparison to a block copolymer having the aforesaid
configuration, a copolymer having a structural configuration of
polyethyleneglycol/polylactide/polyethyleneglycol has the advantage
to form harder micelle in a physical configuration when it is used
as hydrogel. Furthermore, since hydrophilic polyethyleneglycol is
present at both ends, its hydrophilizing effect is very great and
it is expected to show a superior effect in the compatibility
between hydrophobic material and hydrophilic material, and surface
hydrophilization of hydrophobic material.
[0010] Because of these advantages, many efforts have been made to
synthesize triblock copolymers to have a structural configuration
of polyethyleneglycol/polylactide/polyethyleneglycol.
[0011] To synthesize the triblock copolymer, a method is used to
couple the end groups of the synthesized polymer. In this case, the
functional groups which are present at the ends of the polymer
should have a very high reactivity so as to make the coupling
reaction proceed quantitatively and, thus, to prepare block
copolymers of the desired structure.
[0012] A generally used method is to couple the hydroxy group and
the carboxyl group that are present at both ends of the polymer by
use of a coupling agent such as diethyl azodicarboxylate (DEAD),
triphenylphosphine (TPP), 1,3-dicyclohexylcarbodiimide (DCC) or
4-dimethylaminopyridine (DMAP). This method is generally used in
coupling an organic compound. However, if it is used in the
coupling reaction of the end groups in polymers, the reactivity is
not high and, thus, the yield of block copolymer is very low and
the catalysts used in the reaction are not easily removed.
[0013] Recently, a method is prevalently used to obtain a high
reaction rate by use of a diisocyanate functional group having a
high reactivity (J. Polym. Sci., Part A: Polym. Chem. 37, 751-760
(1999)). However, the block copolymer prepared by this method has
the disadvantage that diisocyanate functional group with a strong
toxicity remains in it.
[0014] Therefore, in preparing the block copolymer, it is very
important to maintain the high reactivity of the functional groups
and to connect the resulting copolymer only by non-toxic ester
binding.
SUMMARY OF THE INVENTION
[0015] The present invention relates to
polyethyleneglycol/polylactide (or polyglycolide or
polycaprolactone)/polyethyleneglycol triblock copolymers with an
enhanced reactivity, and the process for their preparation.
[0016] The present invention is specifically directed to triblock
copolymers that are obtained by a process comprising the step of
synthesizing a polylactide (or polyglycolide or polycaprolactone)
having hydroxy groups at both ends and the step of coupling it with
a polyethyleneglycol having an acylhalide group of a high
reactivity at one of its ends, and a process for preparing the
same.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The present invention provides a non-toxic biodegradable
triblock copolymer having an ester structure and a method for
preparing the same with a high yield by using a starting material
having functional groups of high reactivity.
[0018] The inventors have carried out a study to achieve the object
and found that triblock copolymers having an ester structure can be
prepared with high yield by coupling polyethyleneglycol, having an
acylhalide group of a high reactivity at one of its ends, with
polylactide (or polyglycolide or polycaprolactone), having a
hydroxy group at both ends.
[0019] Therefore, the invention relates to a
polyethyleneglycol/polylacitd- e (or polyglycolide or
polycaprolactone)/polyethyleneglycol copolymer with a structural
configuration of hydrophilicity/hydrophobicity/hydrophilicit- y,
and a method for preparing the same.
[0020] The copolymer according to the present invention can be
prepared by coupling polyethyleneglycol having acylhalide of a high
reactivity at one of its ends with polylactide (or polyglycolide or
polycaprolactone) having a hydroxy group at both ends in the
presence of pyridine.
[0021] Specifically, the present invention provides a biodegradable
triblock copolymer selected from the group consisting of copolymer
of formula (I) to (4) as follows:
[0022] <formula 1>
PEG-COO-PL-OCO-PEG
[0023] <formula 2>
PEG-COO-PG'OCO-PEG
[0024] <formula 3>
PEG-COO-(PL/PG)-OCO-PEG
[0025] <formula 4>
PEG-COO-PCL-OCO-PEG
[0026] In the formulas,
[0027] PEG is polyethyleneglycol,
[0028] PL is polylactide,
[0029] PG is polyglycolide,
[0030] PCL is polycaprolactone.
[0031] According to the present invention, polylactide having a
hydroxy group at both ends is first synthesized by ring-open
polymerization of lactide monomer in the presence of secondary
alcohol. The ring-open polymerization is carried out under reduced
pressure with heating by using a conventional catalyst such as
stannous octotate. If .alpha.,.omega.-alkanediol such as ethylene
glycol, 1,3-propanediol, 1,4-butanediol, and 1,6-hexanediol, which
is a secondary alcohol, is used as a polymerization initiator, the
resulting polylactide has hydroxyl groups at both ends (see scheme
1). At this time, the molecular weight of the polymer can be
variously controlled depending on the added amount of the initiator
and monomer. Polyglycolide and polycaprolactone can be prepared in
the same manner as in the preparation of polylactide. 1
[0032] Polyethyleneglycol having acylhalide group at one of its
ends can be synthesized in a two-step reaction. The first step is
to substitute the carboxyl group for the hydroxyl group at one of
its ends, and the second step is to replace the carboxyl group with
the acylhalide group. First, the hydroxy group which is present at
one of its ends of monomethoxypolyethyleneglycol (m-PEG) is reacted
with succinic anhydride under 4-dirnethyarninopyridine (DMAP) and
triethylamine (TEA) as catalysts so that the carboxyl group is
introduced at the end of m-PEG (see scheme 2). If a solvent used in
the reaction is nonpolar one, such as methylene chloride and
chloroform, there is almost no reaction; but if a high polar
solvent such as 1,4-dioxane is used, the reaction takes place very
well.
[0033] Monomethoxypolyethyleneglycol (mPEG-COOH) having a carboxyl
group at one of its ends is reacted with thionyl chloride to
convert the carboxyl group into an acylhalide group having a high
reactivity. This reaction is carried out for 3 to 4 hours at
60.degree. C. in methylene chloride solvent. Since the synthesized
monomethoxypoly-ethyleneglycol (mPEG-COCI) having the acylhalide
group at one of its ends has a high reactivity, it is very
unstable. Thus, because it reacts with moisture in the air while in
storage over a long period of time and is thus reconverted into
mPEG-COOH, it should be used in the coupling reaction immediately
after its preparation. 2
[0034] Polyethyleneglycol/polylactide/polyethyleneglycol copolymer
is prepared by coupling monomethoxypolyethyleneglycol (mPEG-COCl)
having the acylhalide group at one of its ends with polylactide
(OH-PL-OH) having hydroxyl group at both ends as synthesized above
(see scheme 3). Basic pyridine which functions as both a solvent
and catalyst is used in the reaction. It removes HCI, which is
produced in the reaction and plays a role in inducing the reaction
toward the forward reaction. Furthermore, since addition of
pyridine causes the exothermic reaction, it is gradually added with
a small amount at 0.degree. C. 3
[0035] Thus prepared
polyethyleneglycol/polylactide/polyethyleneglycol copolymer was
obtained with a quantitative yield of more than 90%, and
introduction of each functional group and coupling reaction of the
end groups could be identified by means of FT-IR and .sup.1H-NMR.
Also, a high reaction rate of more than 90% was identified through
an integral ratio of lactide monomer and ethyleneglycol monomer
that are analyzed by .sup.1H-NMR. In GPC (Gel Permeation
Chromatography) molecular weight determination, the prepared
triblock copolymer showed unimodal molecular weight distribution
and had a higher molecular weight than each polylactide and
polyethyleneglycol. From the results, it was found that the
triblock copolymer of the complete structure was obtained.
[0036] As a result of Thermal Gravimetric Analysis (TGA), the
prepared triblock copolymer showed a higher pyrolysis temperature
than polylactide. Pyrolysis of polylactide has been reported to
generally take place by means of an unzipping mechanism due to a
hydroxy end group (Polymer, 2229-2234, 29, 1988), and pyrolysis of
the triblock copolymer is presumably inhibited by replacement of
hydroxy groups, which are present at both ends of polylactide, with
polyethyleneglycol.
[0037] As a result of the analysis by a Differential Scanning
Calorimeter (DSC), the prepared triblock copolymer had a lower
crystallization temperature, a lower melting temperature and a
smaller melting enthalphy than polylactide. This lowering
phenomenon was enhanced proportionally to increase the molecular
weight of the monomethoxypolyethyleneglycol that was added.
[0038] In determining the static contact angle which indicates
hydrophilicity of the copolymer, introduction of polylactide
sharply decreased the hydrophiticity of the copolymer, and as
molecular weight of the polylactide become larger, the
hydrophobicity of the copolymer increased.
[0039] Even in instances where polyglycolide or polycaprolactone is
used in place of polylactide as a hydrophobic polymer, the triblock
copolymer of a complete structure was obtained and it showed the
similar thermal properties and hydrophilicity to the copolymer that
was prepared by using polylactide.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] The present invention is further described by the following
examples but should not be construed as being limited by them.
EXAMPLE 1
[0041] L-lactide monomer 17.280 g (0.120 mol) was put in a 100 ml
dried glass ampule, and stannous octotate 0.269 g (0.00066 mol) as
a catalyst and 1,6-hexanediol 0.598 g (0.005 mol) as an initiator
were added therein. A teflon-coated magnetic bar was introduced in
the ampule. The ampule was maintained in a vacuum state at 0.01
mmHg for 20 min. to remove water, and then dry nitrogen was
introduced. This procedure was repeated three times and the ampule
was heat sealed under vacuum with a torch.
[0042] The sealed ampule was put in an oil bath of 130.degree. C.
and polymerization was carried out with stirring for 5 hours. As
the polymerization proceeded, the viscosity of the polymerizaton
system increased and stirring of the reactions could no longer be
made. The polymerization system was initially in a clear gel state,
but as the reaction proceeded, it became a white solid. After
completing the reaction, the ampule was fully cooled by liquid
nitrogen and then destroyed to collect the copolymer. The collected
sample was dissolved in chloroform. Thereafter, it was precipitated
in methanol to remove the catalyst, unreacted monomer and a low
molecular weight of oligomer and dried under vacuum at ambient
temperature for at least 12 hrs.
[0043] The obtained polymer had white color and the yield was in a
quantitative value of above 99%. From .sup.1H-NMR analysis, it was
identified that the nng of lactide was opened by the initiator and
the hydroxy groups were introduced at both ends. From the integral
ratio of end groups and the monomer, the molecular weight of the
polymer was identified to be about 4,700. Determined through the
use of a Differential Scanning Calorimeter, the glass transition
temperature and melting point of the polymer were 49.5 C and 147.0
C, respectively.
[0044] By controlling the molar ratio of the initiator
1,6-hexanediol and the monomer lactide, polylactides (HO-PL-OH)
having 500 to 30,000 of the molecular weight were prepared. Also,
polylactides (HO-PL-OH) were prepared in the same manner by using 1
,4-butanediol and 1,3-propanediol in place of 1,6-hexanediol.
EXAMPLE 2
[0045] 150 ml of 1,4-dioxane was put in a 25 ml flask, and
monomethoxy-polyethyleneglycol (mPEG-OH, molecular weight 750)
having a hydroxy group at one of its ends 10.07 g (0.0134 mol) and
succinic anhydride 2.0160 g (0.0201 mol) were added therein.
Thereafter, DMAP 1.643 g (0.0134 mol) and TEA 1.356 g (0.0134 mol)
were added as catalysts. The reaction was carried out at ambient
temperature for 24 hours, and the reaction solution was then
distilled under vacuum to remove the solvent. The resulting product
was dissolved in CCl.sub.4 and then filtered to remove unreacted
succinic anhydride. The filtered solution was precipitated in cold
ethylether solvent and then dried under vacuum at ambient
temperature for more than 12 hours. From .sup.1H-NMR analysis, it
was identified that the ring of succinic anhydride was opened by
the hydroxy group. Thus, the carboxyl group was introduced at the
end of mPEG.
[0046] Using monomethoxypolyethyleneglycols with a molecular weight
of 750 to 10,000, each product (mPEG-COOH) was synthesized in the
same manner as above and purified.
EXAMPLE 3
[0047] mPEG-COOH 2.785 g (0.0037 mol), which was synthesized in
Example 2, was put in 50 ml flask and completely dissolved in 50 ml
of a purified methylene chloride. Thionyl chloride 0.88 g (0.0074
mol) and two drops of dimethylformamide as a catalyst were added to
the solution. The reaction was carried out at 60.degree. C. for
about 3 hours, and the reaction solution was then distilled under
vacuum to remove the solvent and unreacted thionyl chloride. From
.sup.1H-NNR analysis, it was identified that the acylhalide group
was introduced at the end of mPEG and the product was used
immediately in the coupling reaction.
[0048] Using monomethoxypolyethyleneglycols (mPEG-COOH) prepared in
Example 2 with a molecular weight of 750 to 10,000, wherein
carboxyl group was introduced at its end, each product (mPEG-COCl)
was synthesized in the same manner as described above.
Example 4
[0049] The MPEG-COCl having the molecular weight of 750, which was
synthesized in Example 3, 2.70 g (0.0032 mol), and the polylactide
(HO-PL-OH) having the molecular weight of 4,700, which was
synthesized in Example 1, 3.67 g (0.00078 mol), were put in a 50 ml
flask and the reaction was placed completely under nitrogen
atmosphere. By using an ice bath of 0.degree. C., the reaction
system was maintained at a sufficiently low temperature and the
purified pyridine 20 ml was then slowly added. Thereafter, the
reaction system was maintained at ambient temperature, and the
reaction was carried out for 24 hours. After the reaction solution
was subject to precipitation in methanol, the solution was
centrifuged. By repeating the procedure of the precipitation in
methanol and centrifugation two or three times, an excess of
monomethoxypolyethyleneglycol was completely removed. The
thus-obtained sample was dried under vacuum at ambient temperature
for at least 12 hours.
[0050] From .sup.1H-NMR analysis, it was identified that the
hydroxyl group and acylhalide group at the ends were quantitatively
coupled. Furthermore, through GPC analysis, the prepared triblock
copolymer had a larger molecular weight than each polylactide and
polyethyleneglycol and showed uimodal molecular weight
distribution, from which it was identified that the triblock
copolymer of the complete structure was obtained.
[0051] Also, by using the materials obtained from Examples 1 and 3,
respectively, each product was synthesized and purified in the same
manner as described above. The formation of the triblock was then
identified through the same analysis.
EXAMPLE 5
[0052] Polyglycolide (PG) was prepared by the same method as
described in Example 1 except that the glycolide 13.920 g (0.120
mol) was used as the monomer and 1,4-butanediol was used as an
initiator under the reaction temperature of 170 C. By controlling
the molar ratio of the initiator 1,4-butanediol and the monomer
glycolide, PGs having a molecular weight of 500 to 30,000 were
prepared.
[0053] The prepared sample was coupled with the MPEG-COCl prepared
in Example 3 in the same manner as described in Example 4, and a
polyethyleneglycol/polyglycolide/polyethylene-glycol triblock
copolymer was prepared.
EXAMPLE 6
[0054] A polylactidelpolyglycolide (PL/PG) copolymer was prepared
by the same method as described in Example 1 except that the
lactide 12.096 g (0.084 mol) and glycolide 4.176 g (0.360 mol) were
used as the monomers and the reaction temperature was 140.degree.
C. By controlling the molar ratio of the initiator 1,3-propanediol
and the monomers lactide and glycolide, PL/PG copolymers were
prepared with a molecular weight of 500 to 30,000.
[0055] The prepared sample was coupled with the mPEG-COCl prepared
in Example 3 in the same manner as described in Example 4, and a
polyethyleneglycol/polyglycolide-polylactide/polyethyleneglycol
triblock copolymer was prepared.
EXAMPLE 7
[0056] Polycaprolactone (PCL) was prepared by the same method as
Example 1 except that caprolactone 13.680 g (0.120 mol) was used as
the monomer and the reaction temperature was 140.degree. C. By
controlling the molar ratio of the initiator 1,6-hexanediol and the
monomer caprolactone, PCLs were prepared with a molecular weight of
500 to 30,000.
[0057] The prepared sample was coupled with the MPEG-COCl prepared
in Example 3 in the same manner as described in Example 4 and
polyethyleneglycol/polycaprolactone/polyethyleneglycol triblock
copolymer was prepared.
[0058] According to the present invention,
polyethyleneglycol/polylactide (or polyglycolide or
polycaprolactone)/polyethyleneglycol triblock copolymer can be
obtained with a higher yield compared to the conventional coupling
methods. Furthermore, the triblock copolymer according to the
present invention is connected by ester coupling in its molecular
chain so that it can disappear in a form nontoxic to the human body
through the metabolism in vivo.
[0059] Since the present copolymer has hydrophilic groups at both
ends, it can easily hydrophilize a biomaterial. Also, since the
physical property and hydrophilicity of the copolymer can be
controlled by controlling the molecular weight of polylactide (or
polyglycolide or polycaprolactone) and polyethyleneglycol, it can
be widely used as a biomaterial. In view of its structure, it can
be utilized as a material capable of forming a hydrogel, especially
as a drug-releasing material. Also, the copolymer is thermally
stable so that the deterioration of its physical property that can
be caused in heat treatment can be prohibited.
[0060] Such material of the invention can be applied extensively as
a bio-absorbable material, a material for tissue engineering,
agricultural chemicals or medicine, a matrix that slowly releases
drugs, etc.
* * * * *