Extraction of Admixed Polymers from Natural Rubber Vulcanizates

Extraction by solvent of admixed poly(methyl methacrylate) or polystyrene from natural rubber vulcanizates is dependent on the crosslink density, the solvent, the molecular weight of the polymer, and the size of sample extracted. High molecular weight polymer is extracted very slowly, and in some cases several weeks of continuous extraction have been found necessary. The rate of extraction is increased, as would be expected, by solvents which swell the rubber strongly, and by increase in temperature of extraction. In some cases the vulcanization procedure degrades the polymer, while in others there is a possibility of cocrosslinking the rubber and polymer. Graft copolymers from rubber and methyl methacrylate or styrene possess similar characteristics when vulcanized. In consequence, analysis of the content of free homopolymer is subject to considerable uncertainty. In the analysis of these rubber and polystyrene mixtures by ozonolysis, polystyrene was found to be very susceptible to attack by ozone.