USRE45666EExpiredUtilityPatentIndex 50
Preparation of hydrophilic pressure sensitive adhesives having optimized adhesive properties
Est. expiryJul 7, 2020(expired)· nominal 20-yr term from priority
A61K 9/7053A61L 15/58A61K 9/7069A61K 9/0014A61L 15/585A61L 15/44
50
PatentIndex Score
0
Cited by
470
References
122
Claims
Abstract
A method for preparing hydrophilic pressure sensitive adhesive (PSA) compositions is provided, wherein the method enables preparation of adhesives having a particular, optimized degree of adhesion. That is, the hydrophilic PSA is comprised of a hydrophilic polymer and a complementary short-chain plasticizing agent, wherein the hydrophilic polymer and plasticizing agent are capable of hydrogen bonding or electrostatic bonding to each other and are present in a ratio that optimizes key characteristics of the adhesive composition, such as adhesive strength, cohesive strength and hydrophilicity. The adhesive is useful in a wide variety of contexts, e.g., as a biomedical adhesive for application to the skin or other body surface, and as such finds utility in the areas of drug delivery systems (e.g., topical, transdermal, transmucosal, iontophoretic), medical skin coverings and wound healing products and biomedical electrodes.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1. A method of preparing an adhesive composition having an optimized degree of adhesion, comprising:
(a) preparing a plurality of compositions each comprised of a hydrophilic polymer having a glass transition temperature T g pol admixed with a plasticizer miscible therewith and having a glass transition temperature T g pl and capable of covalently or noncovalently crosslinking the hydrophilic polymer, wherein the weight fraction of the hydrophilic polymer in each composition is w pol , and the weight fraction of the plasticizer in each composition is w pl ; (b) calculating predicted glass temperatures T g predicted for each composition using the Fox equation (1)
1
T
g
predicted
=
w
pol
T
g
pol
+
w
pl
T
g
pl
(
1
)
and plotting T g predicted versus w pl for each composition;
(c) determining the glass transition temperature T g actual for each composition, and plotting T g actual versus w pl for each composition;
(d) identifying the region of the plots of (b) and (c) wherein T g actual is less than T g predicted ; such that there is a negative deviation from T g predicted ;
(e) within the region identified in (d), identifying the optimum weight fraction of plasticizer w pl optimum at which the negative deviation from T g predicted is at a maximum; and
(f) admixing a monomeric precursor to the hydrophilic polymer and the plasticizer under polymerizing conditions to provide an adhesive composition having an optimized degree of adhesion, wherein the weight fraction of plasticizer in the composition is w pl optimum , and the weight fraction of the hydrophilic polymer in the composition is 1-w pl optimum .
2. The method of claim 1 , wherein the plasticizer is capable of covalently crosslinking the hydrophilic polymer.
3. The method of claim 1 , wherein the plasticizer is capable of noncovalently crosslinking the hydrophilic polymer.
4. The method of claim 1 , wherein the plasticizer is capable of crosslinking the hydrophilic polymer by hydrogen bonding thereto.
5. A method of preparing an adhesive composition having an optimized degree of adhesion, comprising:
(a) preparing a plurality of compositions each comprised of a hydrophilic polymer having a glass transition temperature T g pol admixed with a plasticizer miscible therewith and having a glass transition temperature T g pl and capable of covalently or noncovalently crosslinking the hydrophilic polymer, wherein the weight fraction of the hydrophilic polymer in each composition is w pol , and the weight fraction of the plasticizer in each composition is w pl , such that w pol is equal to 1-w pl ; (b) calculating predicted glass temperatures T g predicted for each composition using the Fox equation (1)
1
T
g
predicted
=
w
pol
T
g
pol
+
w
pl
T
g
pl
(
1
)
and plotting T g predicted versus w pl for each composition;
(c) determining the glass transition temperature T g actual for each composition, and plotting T g actual versus w pl for each composition;
(d) identifying the region of the plots of (b) and (c) wherein T g actual has a predetermined deviation from T g predicted ; and
(e) admixing a monomeric precursor to the hydrophilic polymer and the plasticizer under polymerizing conditions to provide an adhesive composition having a desired degree of adhesion, wherein the weight percent of plasticizer in the composition corresponds to a value within the region identified in section (d).
6. The method of claim 5 , wherein the plasticizer is capable of covalently crosslinking the hydrophilic polymer.
7. The method of claim 5 , wherein the plasticizer is capable of noncovalently crosslinking the hydrophilic polymer.
8. The method of claim 5 , wherein the plasticizer is capable of crosslinking the hydrophilic polymer by hydrogen bonding thereto.
9. The method of claim 1 , wherein the difference between T g pol and T g pl is at least about 50° C., such that T g actual for each composition is determined solely by T g pl .
10. The method of claim 2 , wherein the difference between T g pol and T g pl is at least about 50° C., such that T g actual for each composition is determined solely by T g pl .
11. The method of claim 1 , wherein the hydrophilic polymer is selected from the group consisting of poly(N-vinyl lactams), poly(N-vinyl amides), poly(N-alkylacrylamides), polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, polyvinylamine, and copolymers and blends thereof.
12. The method of claim 11 , wherein the hydrophilic polymer is selected from the group consisting of poly(N-vinyl lactams), poly(N-vinyl amides), poly(N-alkylacrylamides), and copolymers and blends thereof.
13. The method of claim 12 , wherein the hydrophilic polymer is a poly(N-vinyl lactam).
14. The method of claim 13 , wherein the hydrophilic polymer is a poly(N-vinyl lactam) homopolymer.
15. The method of claim 14 , wherein the poly(N-vinyl lactam) is selected from the group consisting of polyvinyl pyrrolidone, polyvinyl caprolactam, and blends thereof.
16. The method of claim 15 , wherein the poly(N-vinyl lactam) is polyvinyl pyrrolidone.
17. The method of claim 15 , wherein the poly(N-vinyl lactam) is polyvinyl caprolactam.
18. The method of claim 12 , wherein the hydrophilic polymer is a poly(N-vinyl amide).
19. The method of claim 18 , wherein the poly(N-vinyl amide) is polyacetamide.
20. The method of claim 12 , wherein the hydrophilic polymer is a poly(N-alkylacrylamide).
21. The method of claim 20 , wherein the poly(N-alkylacrylamide) is polymethacrylamide or poly(N-isopropyl acrylamide).
22. The method of claim 1 , wherein the hydrophilic polymer has a weight average molecular weight in the range of approximately 100,000 to 2,000,000.
23. The method of claim 22 , wherein the hydrophilic polymer has a weight average molecular weight in the range of approximately 500,000 to 1,500,000.
24. The method of claim 1 , wherein T g pl is in the range of approximately −100° to −30° C.
25. The method of claim 24 , wherein the melting temperature of the plasticizer is lower than about 50° C.
26. The method of claim 1 , wherein the plasticizing agent has a molecular weight in the range of about 45 to 800.
27. The method of claim 26 , wherein the plasticizing agent has a molecular weight in the range of about 45 to 600.
28. The method of claim 24 , wherein the plasticizing agent has a molecular weight in the range of about 300 to 600.
29. The method of claim 26 , wherein the plasticizing agent is selected from the group consisting of of polyalcohols, monomeric and oligomeric alkylene glycols, polyalkylene glycols, carboxyl-teminated polyalkylene glycols, amino-terminated polyalkylene glycols, ether alcohols, alkane diols and carbonic diacids.
30. The method of claim 29 , wherein the plasticizing agent is selected from the group consisting of polyalkylene glycols and carboxyl-terminated polyalkylene glycols.
31. The method of claim 30 , wherein the plasticizing agent is selected from the group consisting of polyethylene glycol and carboxyl-terminated polyethylene glycol.
32. The method of claim 31 , wherein the plasticizing agent is polyethylene glycol.
33. The method of claim 1 , wherein the adhesive composition further includes a photoinitator, and, following step (e), the adhesive composition is crosslinked using radiation.
34. The method of claim 1 , wherein step (e) further includes admixing the hydrophilic polymer and the plasticizing agent with at least one chemical crosslinking agent that covalently crosslinks the adhesive composition.
35. The method of claim 34 , wherein the at least one chemical crosslinking agent is selected from the group consisting of dipentaerythritol pentaacrylate, ethylene glycol dimethacrylate, and triethylene glycol dimethacrylate.
36. The method of claim 35 , wherein the weight ratio of the chemical crosslinking agent to the hydrophilic polymer is below 5%.
37. The method of claim 1 , wherein, following step (e), the adhesive composition is crosslinked using heat.
38. The method of any one of claim 33 , 34 or 36 , wherein the crosslinking density of the crosslinked adhesive composition provides a swell ratio in the range of approximately 20 to approximately 60.
39. A An extruded composition comprising a hydrophilic pressure sensitive adhesive composition comprising (1) a hydrophilic polymer selected from non-crosslinked poly(N-vinyl lactam)s and copolymers and blends thereof having a glass transition temperature, T g pol , and (2) a complementary hydroxyl-terminated or carboxyl-terminated short-chain plasticizing agent selected from the group consisting of monomeric and oligomeric alkylene glycols, polyalkylene glycols, and carboxyl-terminated polyalkylene glycols having a glass transition temperature, T g pl , and capable of hydrogen bonding or electrostatic bonding to the hydrophilic polymer, wherein the weight ratio of hydrophilic polymer to complementary short-chain plasticizing agent is selected so to provide provides a predetermined deviation in (a) the actual glass transition temperature, T g actual , of the composition from (b) the predicted glass transition temperature, T g predicted , calculated for the composition using the Fox equation (1)
1
T
g
predicted
=
w
pol
T
g
pol
+
w
pl
T
g
pl
,
(
1
)
w pol is the weight fraction of the hydrophilic polymer in the composition, w pl is the weight fraction of the plasticizer in the composition, and the ratio of the weight average molecular weight of the hydrophilic polymer to the complementary short-chain plasticizing agent is within a range of about 1,250 and 20,000.
40. The extruded composition of claim 39 , wherein the predetermined deviation is the maximum negative deviation.
41. A hydrophilic, substantially nonaqueous pressure sensitive adhesive composition comprising (a) a hydrophilic polymer, and (b) a complementary hydroxyl-terminated or carboxyl-terminated short-chain plasticizing agent capable of hydrogen bonding or electrostatic bonding to the hydrophilic polymer,
wherein the ratio of hydrogen bonding to covalent crosslinks is selected to optimize adhesive strength, cohesive strength, and hydrophilicity;
wherein the plasticizing agent decreases the glass transition temperature T g of the hydrophilic composition according to Fox equation (1)
1
T
g
predicted
=
w
pol
T
g
pol
+
w
pl
T
g
pl
(
1
)
wherein T g predicted is the predicted glass transition temperature of the hydrophilic polymer/plasticizer composition, w pol is the weight fraction of the hydrophilic polymer in the composition, w pl is the weight fraction of the plasticizer in the composition, T g pol is the glass transition temperature of the hydrophilic polymer, and T g pl is the glass transition temperature of the plasticizer; and The extruded composition of claim 40, wherein maximum adhesiveness is achieved at a point of maximum negative deviation from T g predicted .
42. A The extruded hydrophilic pressure sensitive adhesive composition comprising (a) a hydrophilic polymer and (b) a complementary hydroxyl-terminated or carboxyl-terminated short-chain plasticizing agent capable of hydrogen bonding or electrostatic bonding to the hydrophilic polymer according to claim 39,
wherein the hydrophilic polymer and the plasticizing agent are noncovalently crosslinked to a predetermined an extent effective, and the extent of crosslinking and along with the ratio of the hydrophilic polymer to the plasticizing agent are selected, to optimize the hydrophilicity, adhesive strength and cohesive strength of the composition;
wherein the plasticizing agent decreases the glass transition temperature T g of the hydrophilic composition according to Fox equation (1)
1
T
g
predicted
=
w
pol
T
g
pol
+
w
pl
T
g
pl
(
1
)
wherein T g predicted is the predicted glass transition temperature of the hydrophilic polymer/plasticizer composition, w pol is the weight fraction of the hydrophilic polymer in the composition, w pl is the weight fraction of the plasticizer in the composition, T g pol is the glass transition temperature of the hydrophilic polymer, and T g pl is the glass transition temperature of the plasticizer; and
wherein maximum adhesiveness is achieved at a point of maximum negative deviation from T g predicted .
43. The extruded composition of any one of claims 39 , 41 or 42 , wherein the adhesive composition is substantially non-aqueous.
44. The extruded composition of claim 39 , wherein the difference between T g pol and T g pl is at least about 50° C., such that T g actual for each composition is determined solely by T g pl .
45. The composition of claim 39 , wherein the hydrophilic polymer is selected from the group consisting of poly(N-vinyl lactams), poly(N-vinyl amides), poly(N-alkylacrylamides), polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, polyvinylamine, and copolymers and blends thereof.
46. The composition of claim 45 , wherein the hydrophilic polymer is selected from the group consisting of poly(N-vinyl lactams), poly(N-vinyl amides), poly(N-alkylacrylamides), and copolymers and blends thereof.
47. The extruded composition of claim 46 39, wherein the hydrophilic polymer is a poly(N-vinyl lactam).
48. The extruded composition of claim 47 , wherein the hydrophilic polymer is a poly(N-vinyl lactam) homopolymer.
49. The extruded composition of claim 48 , wherein the poly(N-vinyl lactam) is selected from the group consisting of polyvinyl pyrrolidone, polyvinyl caprolactam, and blends thereof.
50. The extruded composition of claim 49 , wherein the poly(N-vinyl lactam) is polyvinyl pyrrolidone.
51. The composition of claim 49 , wherein the poly(N-vinyl lactam) is polyvinyl caprolactone.
52. The composition of claim 39 , wherein the hydrophilic polymer is a poly(N-vinyl amide).
53. The composition of claim 52 , wherein the poly(N-vinyl amide) is polyacetamide.
54. The composition of claim 39 , wherein the hydrophilic polymer is a poly(N-alkylacrylamide).
55. The composition of claim 54 , wherein the poly(N-alkylacrylamide) is polymethacrylamide or poly(N-isopropyl acrylamide).
56. The composition of claim 39 , wherein the hydrophilic polymer has a weight average molecular weight in the range of approximately 100,000 to 2,000,000.
57. The extruded composition of claim 56 39, wherein the hydrophilic polymer has a weight average molecular weight in the range of approximately 500,000 to 1,500,000.
58. The extruded composition of claim 39 , wherein T g pl is in the range of approximately −100° to −30° C.
59. The extruded composition of claim 58 , wherein the melting temperature of the plasticizer is lower than about 50° C.
60. The extruded composition of claim 39 , wherein the plasticizing agent has a molecular weight in the range of about 45 to 800.
61. The extruded composition of claim 60 , wherein the plasticizing agent has a molecular weight in the range of about 45 to 600.
62. The extruded composition of claim 61 , wherein the plasticizing agent has a molecular weight in the range of about 300 to 600.
63. The composition of claim 60 , wherein the plasticizing agent is selected from the group consisting of of polyalcohols, monomeric and oligomeric alkylene glycols, polyalkylene glycols, carboxyl-teminated polyalkylene glycols, amino-terminated polyalkylene glycols, ether alcohols, alkane diols and carbonic diacids.
64. The extruded composition of claim 63 60, wherein the plasticizing agent is selected from the group consisting of polyalkylene glycols and carboxyl-terminated polyalkylene glycols.
65. The extruded composition of claim 64 , wherein the plasticizing agent is selected from the group consisting of polyethylene glycol and carboxyl-terminated polyethylene glycol.
66. The extruded composition of claim 65 , wherein the plasticizing agent is polyethylene glycol.
67. The composition of claim 39 , wherein the composition is covalently crosslinked.
68. The composition of claim 67 , wherein the crosslinking density of the crosslinked adhesive composition provides a swell ratio in the range of approximately 20 to approximately 60.
69. A therapeutic system for the topical or transdermal administration of a pharmacologically active agent, comprising:
(A) a drug reservoir comprising
(1) a substantially non-aqueous pressure sensitive adhesive matrix of comprising a hydrophilic polymer selected from non-crosslinked poly(N-vinyl lactam)s and copolymers and blends thereof having a glass transition temperature, T g pol , and a complementary hydroxyl-terminated or carboxyl-terminated short-chain plasticizing agent selected from the group consisting of monomeric and oligomeric alkylene glycols, polyalkylene glycols, and carboxyl-terminated polyalkylene glycols having a glass transition temperature T g pl and capable of hydrogen bonding or electrostatic bonding to the hydrophilic polymer, wherein the weight ratio of hydrophilic polymer to complementary short-chain plasticizing agent is selected so to provide provides a predetermined deviation in (a) the actual glass transition temperature, T g actual , of the composition from (b) the predicted glass transition temperature T g predicted for the composition calculated using Fox equation (1)
1
T
g
predicted
=
w
pol
T
g
pol
+
w
pl
T
g
pl
(
1
)
and the ratio of the weight average molecular weight of the hydrophilic polymer to the complementary short-chain plasticizing agent is within a range of about 1,250 to 20,000, and
(2) a therapeutically effective amount of the active agent; and
(B) a backing layer laminated to the drug reservoir that serves as the outer surface of the device system during use,
wherein the drug reservoir comprising the pressure sensitive adhesive matrix and the active agent is in extruded form.
70. The system of claim 69 , wherein the predetermined deviation is the maximum negative deviation.
71. The system of claim 69 , wherein the hydrophilic polymer is comprised of repeating units resulting from polymerization of an N-vinyl lactam monomer, a carboxy vinyl monomer, a vinyl ester monomer, an ester of a carboxy vinyl monomer, a vinyl amide monomer, a hydroxy vinyl monomer, or a combination thereof.
72. The system of claim 71 , wherein the hydrophilic polymer is selected from the group consisting of poly(N-vinyl lactams), poly(N-vinyl amides), poly(N-alkylacrylamides), polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, polyvinylamine, and copolymers and blends thereof.
73. The system of claim 72 , wherein the hydrophilic polymer is selected from the group consisting of poly(N-vinyl lactams), poly(N-vinyl amides), poly(N-alkylacrylamides), and copolymers and blends thereof.
74. The system of claim 73 69, wherein the hydrophilic polymer is a poly(N-vinyl lactam).
75. The system of claim 74 , wherein the hydrophilic polymer is a poly(N-vinyl lactam) homopolymer.
76. The system of claim 75 , wherein the poly(N-vinyl lactam) is selected from the group consisting of polyvinyl pyrrolidone, polyvinyl caprolactam, and blends thereof.
77. The system of claim 76 , wherein the poly(N-vinyl lactam) is polyvinyl pyrrolidone.
78. The system of claim 76 , wherein the poly(N-vinyl lactam) is polyvinyl caprolactone.
79. The system of claim 73 , wherein the hydrophilic polymer is a poly(N-vinyl amide).
80. The system of claim 79 , wherein the poly(N-vinyl amide) is polyacetamide.
81. The system of claim 73 , wherein the hydrophilic polymer is a poly(N-alkylacrylamide).
82. The system of claim 81 , wherein the poly(N-alkylacrylamide) is polymethacrylamide or poly(N-isopropyl acrylamide).
83. The system of claim 69 , wherein the hydrophilic polymer has a weight average molecular weight in the range of approximately 100,000 to 2,000,000.
84. The system of claim 83 69, wherein the hydrophilic polymer has a weight average molecular weight in the range of approximately 500,000 to 1,500,000.
85. The system of claim 69 , wherein T g pl is at least 50° C. below T g pol .
86. The system of claim 85 , wherein T g pl is in the range of approximately −100° to −30° C.
87. The system of claim 69 , wherein the melting temperature of the plasticizer is lower than about 50° C.
88. The system of claim 87 , wherein the plasticizing agent has a molecular weight in the range of about 45 to 800.
89. The system of claim 88 , wherein the plasticizing agent has a molecular weight in the range of about 45 to 600.
90. The system of claim 89 , wherein the plasticizing agent has a molecular weight in the range of about 300 to 600.
91. The system of claim 88 , wherein the plasticizing agent is selected from the group consisting of of polyalcohols, monomeric and oligomeric alkylene glycols, polyalkylene glycols, carboxyl-teminated polyalkylene glycols, amino-terminated polyalkylene glycols, ether alcohols, alkane diols and carbonic diacids.
92. The system of claim 91 69, wherein the plasticizing agent is selected from the group consisting of polyalkylene glycols and carboxyl-terminated polyalkylene glycols.
93. The system of claim 92 , wherein the plasticizing agent is selected from the group consisting of polyethylene glycol and carboxyl-terminated polyethylene glycol.
94. The system of claim 93 , wherein the plasticizing agent is polyethylene glycol.
95. The system of claim 69 , wherein the composition is covalently crosslinked.
96. The system of claim 95 , wherein the crosslinking density of the crosslinked adhesive composition provides a swell ratio in the range of approximately 20 to approximately 60.
97. The system of claim 69 , wherein the backing layer is non-occlusive.
98. The system of claim 69 , wherein the backing layer is occlusive.
99. An extruded hydrophilic adhesive composition, comprising:
(a) a non-crosslinked hydrophilic polymer selected from polyvinylcaprolactone, polyvinylpyrrolidone, copolymers thereof, and blends of any of the foregoing; (b) a plasticizing agent selected from the group consisting of monomeric and oligomeric alkylene glycols, polyalkylene glycols, and carboxyl-terminated polyalkylene glycols capable of hydrogen bonding to the hydrophilic polymer, having a glass transition temperature T g in the range of about −100° C. to about −30° C., and a melting temperature T m lower than about 20° C., wherein the weight ratio of the hydrophilic polymer to the plasticizing agent is in the range of approximately 1:1 to 4:1 and the ratio of the weight average molecular weight of the hydrophilic polymer to the complementary short-chain plasticizing agent is within a range of about 1,250 and 20,000, and (c) an active agent, wherein the composition is substantially nonaqueous, absorbs water upon application to a hydrated surface, and adheres thereto.
100. The extruded composition of claim 99, wherein the hydrophilic polymer is a blend of polymers selected from polyvinylcaprolactone, polyvinylpyrrolidone, and copolymers thereof.
101. The extruded composition of claim 99, wherein the plasticizing agent is selected from the group consisting of oligomeric alkylene glycols, polyalkylene glycols, and carboxyl-terminated alkylene glycols.
102. The extruded composition of claim 101, wherein the plasticizing agent is polyethylene glycol.
103. The extruded composition of claim 101, wherein the plasticizing agent is a carboxyl-terminated polyethylene glycol.
104. The extruded composition of claim 99, wherein the plasticizing agent has a molecular weight in the range of about 200 to 800.
105. The extruded composition of claim 104, wherein the plasticizing agent has a molecular weight in the range of about 300 to 600.
106. The extruded composition of claim 99, wherein the active agent is an anti-infective agent.
107. The extruded composition of claim 99, wherein the active agent is an anesthetic agent.
108. The extruded composition of claim 99, further including a non-woven material.
109. The extruded composition of claim 99, further including a woven material.
110. A system comprising (a) a monolithic matrix composed of the composition of claim 99, and (b) a backing layer.
111. The system of claim 110, wherein the backing layer is non-occlusive.
112. The system of claim 111, wherein the backing layer is occlusive.
113. The system of claim 110, wherein the backing layer is comprised of a flexible material.
114. The system of claim 110, wherein the backing layer is comprised of a material selected from the group consisting of polyesters, polyethylenes, polypropylene, polyurethane, and polyether amides.
115. The system of claim 106, wherein the backing layer is about 50 microns to about 250 microns in thickness.
116. A system comprising (a) a monolithic matrix comprised of the composition of claim 99, and (b) a rate-controlling membrane.
117. The system of claim 116, wherein the membrane is comprised of a polyolefinic material.
118. The system of claim 116, wherein the membrane is comprised of a material selected from the group consisting of polyethylene, polypropylene, polyamides, polyesters, ethylene-ethacrylate copolymer, ethylene-vinyl acetate copolymer, ethylene-vinyl methylacetate copolymer, ethylene-vinyl ethylacetate copolymer, ethylene-vinyl propylacetate copolymer, polyisoprene, polyacrylonitrile, and ethylene-propylene copolymer.
119. The system of claim 110, further including a fabric layer.
120. The extruded composition of claim 39 or 99, or the therapeutic system of claim 69, wherein the hydrophilic polymer and the plasticizing agent are miscible.
121. The composition of claim 39 or 99, or the therapeutic system of claim 69, wherein the hydrophilic polymer and the plasticizing agent, when mixed, form a homogeneous blend that exhibits a single Tg intermediate between those of the unblended components.
122. The extruded composition of claim 39 or 99, or the therapeutic system of claim 69, wherein the hydrophilic polymer is polyvinyl pyrrolidone, the plasticizing agent is a polyethylene glycol having a molecular weight in a range from about 300 to 600, and the weight ratio of the hydrophilic polymer to the plasticizing agent is in a range from about 2.3 to 1.2.Cited by (0)
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