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Fast pH‐thermo‐responsive copolymer hydrogels with micro‐porous structures
Author(s) -
Kishi R.,
Miura T.,
Kihara H.,
Asano T.,
Shibata M.,
Yosomiya R.
Publication year - 2003
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.11996
Subject(s) - lower critical solution temperature , copolymer , swelling , self healing hydrogels , polymer chemistry , materials science , acrylic acid , volume (thermodynamics) , chemical engineering , transition temperature , composite material , polymer , thermodynamics , physics , superconductivity , quantum mechanics , engineering
Micro‐porous copolymer hydrogels were prepared by γ‐ray irradiation of mixed solutions of N ‐isopropylacrylamide (NIPAAm) and acrylic acid (AAc) above the lower critical solution temperature (LCST). From Cryo‐SEM observations, the gels were found to consist of three‐dimensional fibrous micro‐gels and micro‐pores. The copolymer gels swelled at temperatures below the LCST and shrunk at temperatures above it, and they showed rapid volume transitions on a time scale on the order of a minute when experiencing temperature changes between 10 and 40°C. The transition times for thermal shrinking were almost the same regardless of AAc composition, but the transition times for thermal swelling were increased with increasing AAc contents. The copolymer gels also showed rapid volume transitions with time constants on the order of an hour on experiencing pH changes between 2 and 12. The transition times for pH volume change at 10°C were within one hour, except for the gels containing only small amounts of AAc. On the other hand, the transition times for pH‐dependent volume change at 40°C were increased with increasing AAc content. The lower responsiveness of the transition results from an increase in hydrophobicity arising from the formation of inter‐ and intra‐molecular hydrogen bonds between the non‐ionized carboxylic acid groups and the amide groups. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 75–84, 2003