Preparation of Oxidized Poly (2-hydroxyethyl acrylate) with Multiple Aldehyde Groups by TEMPO-mediated Oxidation for Gelatin Crosslinking

Abstract

Oxidized poly (2-hydroxyethyl acrylate) (OPHEA) with multiplealdehyde groups was prepared as a gelatin crosslinker bypolymerization of 2-hydroxyethyl acrylate and then2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) -mediatedoxidation of poly (2-hydroxyethyl acrylate) (PHEA). Theoxidation conditions were optimized so as to form aldehydegroups in OPHEA as many as possible. The maximum aldehydecontent reached 3.66 mmol/g (accounts for 42.5% of the totalhydroxyl groups in PHEA) when the oxidation was conducted at5oC and pH 9.4 for 90 min, by using 30% NaClO as oxidant and0.1% TEMPO as catalyst. FT-IR and 13C-NMR analysesdemonstrated the formation of aldehyde and carboxyl groups inOPHEA. The crosslinking reactivity of OPHEA was confirmedby the enhancement of thermal stability of modified gelatin byDSC and TG analyses. Furthermore, the viscosity of themodified gelatin was significantly increased when thecrosslinking reaction was performed at 40oC and pH 8.0. Theseresults could provide support for developing novel aldehydetanning agents without free formaldehyde.