Samples of GR-S—the familiar copolymer of butadiene and styrene—were taken from a continuous emulsion-polymerization system at conversions 32.0, 45.1, 61.2, and 73.4% respectively, and each, after careful drying, was carefully fractionated to give five or six "top" fractions. For each of these fractions values of intrinsic viscosity [η] and of the viscosity slope "constants" β and k′ were determined. As with normal and cross-linked polystyrene, β and k′ appear to be constant for all linear species, but to have higher values for branched species, the increase being a measure of the extent or degree of branching. From the data obtained it is concluded that in GR-S there is little or no branching at low conversions, that the degree of branching increases markedly with increasing conversion, and that branching occurs to the greatest degree in the species of highest molecular weight.There seemed to be, for this polymer at least, a molecular weight below which branching could not be detected, regardless of conversion, but above which branching increased with increasing molecular weight.
Calculations of the Average Number of Radicals per Particle in Emulsion Polymerization
