Synthesis of highly branched poly(methyl methacrylate)s using the "strathclyde methodology" in aqueous emulsion

High-conversion copolymerizations of methyl methacrylate (MMA) and divinylbenzene (DVB) in aqueous emulsion have been carried out using sodium dodecyl sulfate as the emulsifier and potassium persulfate as the conventional free radical initiator. Various thiols have been investigated in order to inhibit cross-linking and hence favor the formation of branched products. Hexanethiol (HT) and benzylthiol (BT) have been found to be particularly effective. Use of appropriate levels of BT allow mole feed ratios of MMA/DVB up to 100/20 to be employed in producing highly branched products without cross-linking. Typically DVB/BT mole ratios of <= 1 ensure that cross-linking is avoided. Perhaps most remarkably of all no organic solvent is required in producing these branched products, whereas analogous polymerization feed compositions under bulk or aqueous suspension polymerization conditions lead inevitably to cross-linked products irrespective of the level of chain transfer agent used. The molar mass and branching architecture of the products have been characterized by H-1 NMR and MALS/SEC analyses, and the complete incorporation of DVB residues as branching units has been confirmed.