UV photopolymerization behavior of dimethacrylate oligomers with camphorquinone/amine initiator system

Abstract

Abstract Ultraviolet (UV)‐initiated polymerization of dimethacrylate oligomers with camphorquinone (CQ) and a tertiary amine as a radical photoinitiator system was studied using differential scanning calorimetry. Polymerization behavior of two curing systems, one glass‐forming and the other elastomer‐forming, were compared, based on the rate of polymerization and the double bond conversion. The radical termination in the glass‐forming system (E‐bis‐A DMA‐1) became diffusion controlled immediately upon exposure to UV radiation, with the reaction rate quickly reaching its maximum. The elastomer‐forming system (E‐bis‐A DMA‐2) polymerized at a much lower rate than E‐bis‐A DMA‐1 because of its lower methacrylate group content. The two systems introduced a different temperature dependence on the rate of polymerization. Increasing the temperature reduced the viscosity and enhanced chain segmental mobility. This delayed the autoacceleration in the glass‐forming system. Polymerization rates for both the curing systems increased with initiator concentration, but the dependence on CQ was only characterized by an exponential factor of <0.5. Presumably, this was due to primary radical recombination. The vinyl group conversion and gel fraction of E‐bis‐A DMA‐1 increased with the increase in CQ concentration and/or curing temperature, while the extent of reaction for E‐bis‐A DMA‐2 was relatively insensitive to the latter two factors. A large number of radicals were trapped inside the network of E‐bis‐A DMA‐1 after photocuring and they decayed slowly. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1107–1117, 2001