Network formation and compositional drift during photo-initiated copolymerization of dimethacrylate monomers

The copolymerization of viscous monomers with a nonviscous diluent comonome r was investigated. Overall, photopolymerization kinetics was compared for equimolar mixtures of triethylene glycol dimethacrylate (TEGDMA), a low vis cosity monomer, with either a rigid aromatic dimethacrylate (Bis-GMA) or a flexible aliphatic urethane dimethacrylate (UDMA), as examples of viscous c omonomers. Sal fraction analysis from partial curl polymerizations provided individual monomer reactivities as a function of conversion. The resin con taining UDMA reached greater maximum polymerization rate and final conversi on compared with the resin based on Bis-GMA. The viscous monomers (Bis-GMA or UDMA were found to be less reactive than the diluent comonomer (TEGDMA) at nearly all stages of the photopolymerization process. The reactivity dif ferential was especially dramatic at the latter stages of the polymerizatio n. (C) 2001 Elsevier Science Ltd. All rights reserved.