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Low volume shrinkage of polymers by photoring-opening polymerization of 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane (VCP) and its methyl substituted derivate 1,1-bis(ethoxycarbonyl)-2-(prop-1-en-2-yl)-cyclopropane (Me-VCP) is presented. The aim of this study was to evaluate the photopolymerization behavior and structure of the corresponding polymers from VCP and its methyl substituted derivates 1,1-bis(ethoxycarbonyl)-2-(prop-1-en-2-yl)-cyclopropane (Me-VCP) and 1,1-bis(ethoxycarbonyl)-2-methyl-2-(prop-1-en-2-yl)-cyclopropane (DiMeVCP). VCP monomers were polymerized using camphorquinone (CQ) as a photo-initiator either in a binary or ternary photo-initiator system. The binary systems were formulated with ethyl 4-dimethylaminobenzoate (EDMAB) in relation to the monomer and 1 mol% of CQ. The ternary system was a mixture of 1 mol% of CQ, 2 mol% of EDMAB and 2 mol% of DPIHFP. Ternary photo-initiator systems showed high polymerization rates leading to high conversion in a short photo-activation time. One of the important findings is the formation of higher amounts of 1,5-type ring-opened units and lower amounts of cyclobutane-containing units in photopolymerization, which can make VCP an attractive component of dental composites, as the volume shrinkage is proportional to the 1,5-ring opening. Earlier it was observed that thermal free radical polymerization of VCPs gives higher amounts of cyclobutane structures compared to 1,5-type ring-opened units in the corresponding polymers, causing VCP to be excluded from the list of promising dental composites, as the volume shrinkage was higher than expected.

Low volume shrinkage of polymers by photopolymerization of 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropanes