Nonionic hydrogels by copolymerization of vinylene carbonate and oligo(ethylene glycol) vinyl ethers

Abstract

Bulk polymerization of vinylene carbonate (VCA) with ethylene glycol monovinyl ether (EMVE), diethylene glycol monovinyl ether (DMVE) and methyl triethylene glycol vinyl ether (MTVE), respectively, was carried out. Compared with DMVE and MTVE, the yield of the VCA copolymer with EMVE was low due to a side reaction of acetalization. The copolymerization of MTVE with VCA has been shown to produce linear copolymers and alternating copolymers have been found to form at a 1:1 molar monomer ratio. The copolymerization of EMVE and DMVE with VCA, on the other hand, generally yielded crosslinked copolymers. The reason may be a radical transfer reaction that occurred at methylene groups adjacent to hydroxyl groups of pendent oxyethylene moieties, as inferred from studying the swelling behavior of hydrolyzed copolymers in acidic aqueous solution. The copolymers and their hydrolysis products, especially copoly(MTVE/VCA) and copoly(DMVE/VCA), exhibited low glass transition temperatures, which is apparently due to flexible pendent groups on polymer chains. The copolymerization in the presence of oligo(ethylene glycol) divinyl ethers as crosslinking agents followed by hydrolysis with a 5wt.% NaOH solution gave rise to the formation of three different nonionic hydrogels. The swelling behavior of all the gels was found to be independent of the presence of some electrolyte salts at various concentrations in an aqueous solution. However, the hydrogels based on copoly(EMVE/VCA) and copoly(DMVE/VCA) were shown to be unstable under acidic conditions, whereas those based on copoly(MTVE/VCA) were found to be only slightly influenced by the pH value of an aqueous medium.