Crosslinking Polymerization Of RAFT Living Radical

The application of crosslinked polymers in high performance fields, such as information storage materials, optical fiber coatings, microelectronics, and biomedical materials demands structural homogeneity of the networks. However, the extremely fast chain grow rate of primary chains in the free radical crosslinking polymerizations (FRP) induces the intramolecular cyclizations between the pendant vinyl groups and the growing radicals and quickly generates microgels, giving rise to crosslinking polymers with very heterogeneous networks. Living/controlled radical polymerizations could be used to control the process of radical crosslinking polymerization and improve the structural heterogeneity of the network. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a novel"living"and controlled radical polymerization technique and has potential applications in industries. The thesis was aimed to investigate the RAFT radical crosslinking polymerization of dimethacrylates. By comparing with FRP of dimethacrylates, the effectiveness of the RAFT in suppressing the formation of microgels and improving the structural heterogeneity of the network were examined, and the mechanistic explanation regarding the formation and the development of the networks in the RAFT system was proposed. Meanwhile, the polymerization behavior and the reaction kinetics of the RAFT of dimethacrylates were studied with different crosslinking systems, monomer structures and the reaction conditions. It was found that the RAFT polymerization of PEGDMA proceeded with"living"/controlled character, and the structural heterogeneity of the resulting networks was greatly improved. RAFT polymerization rate of dimethacrylate depended on the structures of the leaving group and the stabilizing group, as well as the dosage of initiator, CTA/initiator ratio, and the reaction temperature. The RAFT polymerization rate increased as the number of ethylene glycol units between the methacrylate groups in the PEGDMA increased from 4 to 9, and then dropped as the ethylene glycol units further increased to 14, while the network structures become more homogeneous. Dimethacrylates with more flexible spacer produced more homogenous networks with higher polymerization rate and vinyl conversion. The kinetics of RAFT of PEGDMA was also influenced by the type of vinyl group and the functionality of the monomers.