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

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. (C) 2001 John Wiley & Sons, Inc.