Radical Emulsion Polymerization With Chain Transfer Monomer

Radical polymerization with3-mercapto hexyl methacrylateas thechain transfer monomer (CTM) to prepare branched vinyl polymers hasbeen carired out in aqueous emulsion. Potassium persulfate was used asthe initiator, and sodium dodecyl benzene sulfate or hexadecyl trimethylammonium bromidewas used as the emulsifier. Gas chromatography (GC)and proton nuclear magneti’c resonanceCH-NMR) were used to analyzethe reaction behavior of the chain transfer monomer and vinyl monomer,andthe obtained polymers were characterized using NMR and sizeexclusion chromatography.The emulsion polymerization with chain transfer monomer tosynthesize branched polymers can be prepared at highermonomer/branching monomer feed ratios (100/25) with high monomerconversion (usually>95%) without gelation. The obtained branchedpolymers also showed considerably higher molecular weights andrelatively narrower polydispersities at the same feed ratio of6monomer/branching monomer (Mw4.malls=2.18X10g/mol=, PDI.42).Compared to solution polymeirzation and emulsion polymeirzationwith chain transfer monomer(MHM), the chain transfermonomer(MHM) in emulsion polymerization consumption was similar toin solution polymerization, MHM can enter the pirmary chain througheither the polymerization of the vinyl group or the chaintransferring/initiating reaction via the-SH group.The emulsion polymerization with chain transfer monomer tosynthesize branched polystyrene were also investigated, the result showthat: Macromolecular chain radical is terminated by an entering pirmaryradical instead of another macromolecular chain radical duirng emulsionpolymerization, The unique radical termination mechanism in emulsionreaction determines that soluble branched polymers can be prepared at a wide range of monomer/CTM feed ratios without gelation. At specificfeed ratios of monomer/MHM/initiator and polymerization temperatures,the pirmary chain length and the MHM content per primary chain couldbe adjusted by emulsiifer concentration. The higher is the emulsifierconcentration, the longer is the pirmary chain length and the less is theMHM content per primary chain. The emulsion polymerization withchain transfer monomer obtained branched polymers with high molecularweight-and relatively narrow polydispersity owing to lower molecularweight not residue in the primary chain. But the solution polymeirzationwith chain transfer monomer acquired branched polymers content thepirmary chain residue, and the remaining pirmary chains contained noMHM units, lead to low molecular weight and board polydispersity.