Reversible Addition-Fragmentation Chain Transfer Radical Polymerization Of Vinyl Acetate

As a kind of non-conjugated monomer with wide industrial applications,the RAFT polymerization of vinyl acetate mediated by xanthate proceeds in controlled way.Through feeding strategy,the composite and sequence structure of polymer can be controlled and PVAc homopolymer and copolymer with special structure can be prepared.Because of very high reactivity of the vinyl acetate propagating radical, chain transfer and termination often take place in polymerization of VAc.So,it is a big challenge to realize "living"/controlled free radical polymerization of VAc.During RAFT polymerization of vinyl acetate,tow problems should be solved: dynamic characterizations,i.e.polymerization rate and final conversion of VAc,the other one is chain structure characterizations,i.e.average molecular weight, molecular weight distribution and "living" nature:if Mn of polymer increases linearly with conversion.This paper focuses on the tow problems during RAFT polymerization of VAc. The effects of RAFT agents,ratio of RAFT to initiator,type of initiator, polymerization systems and reactive costabilizer on RAFT polymerization of VAc were carried out.The reversible addition fragmentation chain transfer radical polymerization of vinyl acetate(VAc) was carried out in ethyl acetate.The effects of RAFT agents,ratio of RAFT to initiator and monomer concentration were studied.The draw electricity ability of Z group in RAFT agent has prominent effect on dynamics and controlling characterization of chain.In the presence of MPhSA and CPDB with strong drawing electricity ability of Z groups,RAFT polymerization of VAc showed inhibition and retardation.In the presence of MMSA,MESA and MiPSA with repelling electricity ability of Z groups,the RAFT radical polymerization of VAc could proceed in a "living"/controlled way,the number-average molecular weight of PVAc increased linearly with the conversion,the PDI is 1.2～1.6.The RAFT polymerizations of VAc mediated by MMSA in solution and miniemulsion were carried out.All polymerizations of VAc preceeded in controlled way.Compared with solution polymerizations,the induction period in RAFT miniemulsion polymerization initiated by KPS was the shortest,propagation coefficient was the highest and molecular weight was the highest.At the same time, miniemulsion is an environmentally friendly system to carry out RAFT polymerization of VAc.The PDI of polymer obtained from miniemulsion was higher than that in solution polymerization.Losing activity of RAFT agent and chain transfer to polymer were responsible for losing control of polymerization.The effects of xanthate,the type of initiator,the ratio of xanthate to initiator and the type of emulsifier on RAFT miniemulsion polymerization of VAc were investigated.The polymerization of VAc mediated by MMSA,MESA,MiPSA could proceed in controlled way.The polymerization initiated by water-soluble initiator showed shortest inhibition period,fastest rate and highest conversion than other initiators.With increasing of RAFT agent,inhibition and retardation of polymerization are increasing.Initialed by V44,the polymerizations showed shortest inhibition period,fastest rate and highest conversion.Instead of HD withα-vinyl organosiloxane polymer as costabilizer,the RAFT miniemulsion of VAc was carried out.Multiple peaks were observed in the latex particle size distribution stabilized by SDS/OP10 emulsifier system,the polymerization of VAc preceded in controlled way.Through qualitative analysis by ~1H-NMR,the reason of multiple peaks in latex particle size distribution was coalescent of droplet under polymerization temperature.Dynamic and chain structure characterizations in RAFT polymerization of VAc was studied and conclusions were in favor of realizing application of VAc RAFT polymerization.