Poly(vinyl alcohol)/poly(acrylic acid) hydrogels: FT-IR spectroscopic characterization of crosslinking reaction and work at transition point

DSC-FTIR microspectroscopy used to investigate the heat-induced intramolecular cyclic anhydride formation between Eudragit E and PVA copolymer

“…In the range of 1900-800 cm À1 , peaks at 1732 cm À1 (C¼O stretching), 1435 cm À1 (C-H bending), 1261 and 1248 cm À1 (C-O stretching), 1100-1000 cm À1 (C-O stretching in C-O-H groups and COC groups) and 849 cm À1 (C-H rocking mode) were observed. 20,21 Notably, the peak at 1140 cm À1 has been reported to be related to the crystalline C-O stretching vibration of PVA, which depends on the degree of crystallization in the PVA copolymer. 22,23 After heating to 320 1C, four new peaks at 3545, 1799, 1759 and 1012 cm À1 appeared, and the peak at 849 cm À1 vanished.…”

“…A high peak intensity ratio (41.0) implies that the cyclization due to intramolecular ester condensation was predominantly responsible for the cyclic anhydride formation occurring in the film of Eudragit E or PVA copolymer. 20,26 In addition, the magnitude of these peak intensity ratios might be explained by the different numbers of reaction sites in both copolymers. As shown in Scheme 1, the amount of anhydride formed in the film of Eudragit E seemed to be higher than that in PVA copolymer during the heating process.…”

Paradigm change in hydrogel sensor manufacturing: from recipe-driven to specification-driven process optimization

“…The value of G AFM of the less swollen gel at 8 vol% cleaner concentration is peculiar for TSR 1 , because it is smaller than the corresponding value of the highly swollen gel at 1 vol%. This is contrary to the results for TSR 2 and TSR 3 and to the softening with increasing swelling degrees described in the literature (Arndt et al, 1999;Philippova and Khokhlov, 2012 Table A3) were excluded from the further evaluation of the results.…”

“…The thermal crosslinking of PVA and PAA starts at about 120 • C (Arndt et al, 1999). Both polymers are in a liquid-like rubbery state at this temperature and provide a sufficient chain mobility for the cross-linking reaction.…”

“…Thermal cross-linking of the two polymers through the formation of anhydrides and ester bonds using the hydroxyl groups and the carboxylic acid groups (Arndt et al, 1999).…”