PHOTOINITIATED RAFT CROSSLINKING POLYMERIZATION OF POLYETHYLENE GLYCOL DIMETHACRYLATES

Abstract

A reversible addition-fragmentation chain transfer (RAFT) agent,S-1-dodecyl-S'-(α,α'-dimethyl-α″-aceticacid) trithioncarbonate was synthesized. The UV-initiated RAFT polymerization of polyethylene glycol dimethacrylates ( PEGDMA ) at room temperature was investigated by using differential scanning photocalorimetry (DPC) and dynamic mechanical analysis (DMA). The photopolymerization rate of the RAFT system was much lower than that in conventional free radical polymerization,a mild autoacceleration occurred as the addition reaction became diffusion controlled. In addition the influence of different spacer lengths between the methacrylate groups on RAFT polymerization rate and final conversion was also explored. The results show that the final conversion increases slowly and the polymerization rate decreases at first and then increases as the number of ethylene glycol units between the methacrylate groups increaseing. Comparison with three different PEGDMAs,PEGDMA with longer middle segments yields more homogeneous networks and lower crosslinking density.