A High Functionality Crosslinked Resin from 3,5-Diacryloyloxybenzoic Acid and Studies of Its De-Crosslinking

Abstract

The diacrylate of 3,5‐dihydroxybenzoic acid was readily prepared under standard interfacial Schotten‐Baumann conditions. This novel crosslinker is rather unique as it contains a carboxylic acid functionality in addition to the two polymerizable acrylate groups. The free‐radical polymerization of this monomer resulted in a highly crosslinked polymer, possessing a very high density of carboxylic acid groups. These acid groups impart a high level of hydrophilicity to the matrix, especially in alkaline medium. An interesting feature of this crosslinked matrix is the facile hydrolytic de‐crosslinking that occurs when it is subjected to aqueous alkali, although it is very stable under neutral and acidic conditions. The kinetics of this de‐crosslinking was readily studied by following the concentration of the degradation products using UV‐Visible spectroscopy. NMR investigations confirm that the de‐crosslinking process is indeed hydrolytic, and that it leads to the formation of poly(acrylic acid) and 3,5‐dihydroxybenzoic acid. In an effort to understand the role of the carboxylic acid groups in the degradation process, other structurally similar crosslinkers that are devoid of the acid groups, namely methyl 3,5‐diacryloyloxybenzoate, 3,5‐diacryloyloxyacetophenone, and 1,3‐diacryloyloxybenzene, were synthesized, and the degradation of the corresponding crosslinked polymers was investigated. It is apparent from these studies that the acid‐containing polymer matrix degraded at significantly faster rates when compared to the other crosslinked systems suggesting the occurrence of a reactive diffusion controlled rate enhancement.