紫外光引发聚乙二醇二甲基丙烯酸酯的RAFT交联聚合研究

合成了S-1-十二烷基-S′-(α,α′-二甲基-α″-乙酸)三硫代碳酸酯(TTC),以此为链转移剂,采用光差动热分析仪(DPC)和动态力学分析(DMA)方法研究了室温条件下紫外光引发的聚乙二醇二甲基丙烯酸酯(PEGDMA)的可逆加成-断裂链转移(RAFT)自由基聚合行为.发现RAFT光聚合反应的反应速率小于常规自由基聚合,因为体系由扩散控制,反应中自加速趋势减缓.探讨了双键之间聚乙二醇链段长度对于聚合速率和最终转化率的影响.结果发现,随着中间聚乙二醇链段的增加,聚合速率先变小再变大,最终转化率缓慢变大.RAFT光交联产物的交联密度随中间链段长度的增加而下降,交联均匀性提高.

PHOTOINITIATED RAFT CROSSLINKING POLYMERIZATION OF POLYETHYLENE GLYCOL DIMETHACRYLATES

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.