The Synthesis Of Poly(Vinyl Acetate) Macro-RAFT Agents And Preparation Of Microgels

In this thesis,RAFT polymerization was employed to achieve precise control on monomeric level which called single unit monomer insert polymerization.The synthesis of low molar mass poly(vinyl acetate)Macro-RAFT agents has been explored using four RAFT agents known to be suitable in controlling vinyl acetate polymerization,namely,the xanthate,S-(cyanomethyl)O-ethyl carbonodithioate(1);and the dithiocarbamates,:cyanomethyl methyl(phenyl)carbamodithioate(2),cyanomethyl methyl(pyridin-4-yl)carbamodithioate(3),and cyanomethyl(3,5-dimethyl-1H-pyrazole)carbodithioate(4)The target degree of polymerization(DP)for experiments were 1 unit(i.e.,single unit monomer insertion,SUMI).The selection of RAFT agent is shown to be of critical importance in achieving selective SUMI.Different RAFT agents give various products.The ideal RAFT agent was chosen based on the SUMI-RAFT mechanism and the property of the Macro-RAFT agent.Those four RAFT agents were chosen to mediate polymerization of Macro-RAFT agent with target degree of polymerization(DP)of single digit units(DP between 2 and 10).In addition,we demonstrated the proportion changes of oligomer(dimer,trimer,etc.)in the experiment of Macro-RAFT agents preparation by 1H NMR,MS and GPC which clearly traced the polymerization process and the component of oligomer mixture in a specific time point.Poly(vinyl acetate)Macro-RAFT agents were used as a precursor of PVA Macro-RAFT agent with low dispersity by methanolysis method.The replacement of initial RAFT agent by poly(vinyl acetate)Macro-RAFT agents in preparation of poly(vinyl acetate)microgels can enhance the controllability of polymerization.In this paper,poly(vinyl acetate)Macro-RAFT agents were used to mediate cross-linked RAFT copolymerization of microgels with three-dimensional structure.Microgels with different size,cross-linking density and morphology were successfully obtained by adjusting solid content and the ratio of RAFT agent and cross-linker.Meanwhile,this work pays attention on the changes of radical concentration of cross-linking copolymerization under RAFT process.