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Polymers 2016, 8(12), 434; doi:10.3390/polym8120434

Temperature-, pH- and CO2-Sensitive Poly(N-isopropylacryl amide-co-acrylic acid) Copolymers with High Glass Transition Temperatures

1
Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 81148, Taiwan
2
Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
3
Ningbo Institute of Material Technology and Engineering, Key Laboratory of Graphene Technologies and Applications of Zhejiang Province, Chinese Academy of Science, Zhongguan West Road 1219, Ningbo 315201, China
*
Authors to whom correspondence should be addressed.
Academic Editor: Jinlian Hu
Received: 14 November 2016 / Revised: 6 December 2016 / Accepted: 7 December 2016 / Published: 14 December 2016
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
View Full-Text   |   Download PDF [5073 KB, uploaded 14 December 2016]   |  

Abstract

A series of poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAAm-co-PAA) random copolymers were synthesized through free radical copolymerization in MeOH. The incorporation of the acrylic acid units into PNIPAAm tended to enhance the glass transition temperature (Tg), due to strong intermolecular hydrogen bonding between the amide groups of PNIPAAm and the carboxyl groups of PAA, as observed using 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopic analyses. The lower critical solution temperature (LCST) increased upon increasing the pH of the aqueous solution containing PNIPAAm-co-PAA because the COOH groups of the PAA segment dissociated into COO groups, enhancing the solubility of the copolymer. In addition, high-pressure differential scanning calorimetry revealed that the LCSTs of all the aqueous solutions of the copolymers decreased upon increasing the pressure of CO2, suggesting that CO2 molecules had displaced H2O molecules around the polar CONH and COOH groups in PNIPAAm-co-PAA, thereby promoting the hydrophobicity of the copolymers in the aqueous solution. In addition, the values of Tg of a film sample increased upon treatment with supercritical CO2, implying that intermolecular interactions in the copolymer had been enhanced after such treatment. View Full-Text
Keywords: temperature-sensitive; pH-sensitive; CO2-sensitive; hydrogen bonding; copolymers temperature-sensitive; pH-sensitive; CO2-sensitive; hydrogen bonding; copolymers
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Shieh, Y.-T.; Lin, P.-Y.; Chen, T.; Kuo, S.-W. Temperature-, pH- and CO2-Sensitive Poly(N-isopropylacryl amide-co-acrylic acid) Copolymers with High Glass Transition Temperatures. Polymers 2016, 8, 434.

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