|The ‘Strathclyde Route' to branched vinyl polymers involves the conventional free radical solution polymerization of a monovinyl monomer with a multi-functional monomer in the presence of an appropriate level of a chain transfer agent to suppress crosslinking. For some potential applications of branched polymers solution polymerization would not be cost-effective. We have therefore carried out high conversion aqueous emulsion copolymerizations of methyl methacrylate (MMA) and divinylbenzene (DVB) using sodium dodecyl sulphate as the emulsifier, potassium persulfate as the initiator and benzylthiol as the chain transfer agent. No organic solvent is employed and complete suppression of crosslinking is achieved for MMA/DVB feed mole ratios up to 5/1. 'H NMR spectroscopic and MALS/SEC analyses confirm the highly branched nature of the PMMA products which is far higher than we have been able to achieve under bulk or aqueous suspension polymerization conditions. In addition the molar mass distributions are significantly lower than those of similar materials prepared in solution polymerizations. To date we not been able to rationalise all of these experimental findings. |
Early in our branching studies we realised that use of controlled polymerizations might yield less broad molecular weight distributions. We also speculated that crosslinking might be avoided, even at high conversion and without the use of a chain regulating agent, by employing a mole ratio of difunctional comonomer/initiator of ~ 1/1, to favour statistically one branch per primary polymer chain. This proved to be so experimentally and we have now synthesised densely branched poly(methyl methacrylate)s with high conversions via solution ATR copolymerization of MMA and EGDMA. Also by employing an ATRP initiator with a discrete signature in its 'H NMR spectrum, coupled with MALS/SEC analysis, very detailed evaluation of molecular structure and backbone architecture is possible.
Branched Polymers in Emerging Technologies
1:30 PM-4:25 PM, Monday, April 7, 2008 Hilton New Orleans Riverside -- Grand Salon 13/16, Oral