The Effect Of Branching Agents On The Synthesis Of Branched Polymers

The branching copolymerization of styrene with dimethacrylates as the branching agent was carried out using atom transfer radical polymerization (ATRP) in anisole at 90℃. The ATRP of styrene was taken as the reference for the copolymerization analysis. The resulting copolymers were analyzed using triple detection size exclusion chromatography (TD-SEC) and proton nuclear magnetic resonance (1H-NMR).Analysis of the changes in the molecular weight and polydispersity of the copolymers on the branching procedure throughout the polymerization, several conclusions can been obtained: (1) Branching takes place in the early stages of the reaction, the amount of branched molecules and the degree of branching increase with monomer conversion. (2) The coupling reaction comes mainly from the primary chain in the early stages of the reaction, resulting in the generation of small and slightly branched molecules. In the late stages of the copolymerization, the coupling reaction between branched molecules becomes more and more significant, giving rise to the formation of large and highly branched molecules accompanied with a rapid increase in molecular weight and width in polydispersity. (3) The reaction system consists of three components of marked different molecular weights and degrees of branching; the component 1 is of linear structure, actually the primary chain, the component 2 is the slightly branched molecule bearing two primary chains, and the component 3 is a complex mixture of highly branched molecules containing more than three primary chains. The much broad polydispersity of the branched polymer from ATRP should derive mainly from the coexistence of the primary chain with the highly branched molecules of very high molecular weight. The degree of branching is just a value in average similar to molecular weight of polymer. Analysis of the branched copolymers with different comonomers shows that the lengths of dimethacrylate have little effect on the degree of branching. When DVB was employed, the molecular weight and the degree of branching are the highest.