Studies On RAFT Reagents Based On Carbazole And Synthesis Of Thermo-responsive Block Copolymer

One of the effective methods of living radical polymerization was reversible addition-fragmentation chain transfer (RAFT) polymerization, which was the extremely versatile member of the class of controlled radical polymerization processes.In our work,a kind of solid RAFT agent--cumyl N-carbazolylcarbodithioate(CCBD) was synthesized, which was one of the dithiobenzoate derivatives with R=cumyl and Z=carbazolyl. The crude product was purified by recrystallizing in petroleum ether or chromatographing on silica eluting with 10% THF in petroleum spirits. It's structure was identified by methods of ¹H-NMR,MS and UV. With CCBD as a chain transfer agent, reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene (St), methyl methacrylate (MMA) and ethyl acrylate (EA) was conducted. These polymerizations showed the character of living polymerization, the molecular weight of polymerization products increasing with conversion and molecular weight distribution (Mw/Mn) below 1.2. These results indicated that CCBD possessed good control ability to radical polymerization.At present, retardation was the focus research in RAFT process. In this paper we compared the ability of retardation in four RAFT agents(CYCBD,BCBD,PCBD and CCBD), which had the same Z group(Z= carbazolyl), to the polymerization. We studied the retardation by dilatometry polymerizing through changing the quantity of RAFT agent, verifying the polymerization temperature or using different monomers and concluded that the retardation ability depended strongly on R substitution. The result indicated that the ability of retardation of above four RAFT agents decreased in the order: CCBD> PCBD>BCBD>CYCBD.In the RAFT polymerization of styrene (St) at 60℃, we determined the chain transfer constant of four RAFT agents through"two-point method"and the result was: C_tr(CYCBD)= 20.25>C_tr(CCBD)= 16.65>C_tr(PCBD)= 12.95>C_tr(BCBD)= 10.25.At last, we chose the CYCBD as the RAFT agent which hade the smallest retardation and the best controlling ability in the four RAFT agents to prepare thermo-responsive block copolymer: PNIPAm-b-PDMAM. The cloud point temperature was investigated by dynamic light scattering (DLS). The study showed that di-block copolymer——PNIPAm-b-PDMAM possessed the quality of thermo-responsive still and the cloud point increased for the PDMAM.