Synthesis Of Branched Polystyrene Via Radical Polymerization In The Presence Of Chain Transfer Monomer

An approach to branched polystyrene through radical polymerizationin the presence of3-mercapto hexyl methacrylate (MHM) as the chaintransfer monomer is reported in this paper. Gas chromatography (GC),triple detection size exclusion chromatography (TD-SEC) and protonnuclear magnetic resonance (1H-NMR) were used to analyze the reactionbehavior of the chain transfer monomer and the formation anddevelopment of branched chains.In the case of polymerization at styrene100MHM5AIBN2, themolecular weight increased with conversion and reached a value of7.3×105g/mol at99%conversion; in addition, the Zimm branching factor,g′, decreased with conversion and was0.46finally, which implied theformation of the branched chain and development of branching.MHM can enter the primary chain through either the polymerizationof the vinyl group or the chain transferring/initiating reaction via the SHgroup. Higher reaction temperature would stimulate the chaintransferring/initiating reaction of-SH much more than the polymerizationof the vinyl group. Excess polymerization of MHM would introducemore-SH moieties into a particular primary chain, increasing the risk ofgelation. A higher initiator concentration could shorten the primary chainlength and effectively inhibit the gelation. In conclusion, a high initiatorconcentration and elevated temperature are propitious for the preparationof soluble-branched polymers.Analysis of the formation of branched chains and branchingprocedure throughout the polymerization showed several conclusions:(1)Branching takes place in the early stages of the reaction, the weightfraction and branching degree of the branched chains increase withstyrene conversion.(2) The reaction system consists of three componentsof different molecular weights and degrees of branching; the component1 is linear primary chains with or without reaction group, the component2is slightly branched chains bearing at least two primary chains, and thecomponent3is highly branched molecules with relatively highermolecular weight and branching degrees.(3) Branched polystyrene withdifferent degrees of branching can be obtained by changing the initialconcentration of chain transfer monomer MHM and initiator AIBN.