Effect of mastication on molecular weight and molecular weight distribution of EPDM polymer and SBR

EPDM and SBR were masticated on an open mill. The temperature range of mastication for EPDM was 68–480°F. SBR was milled at 170–200°F. The gel‐permeation chromatography analyses were made on the masticated samples. For EPDM at 68°F, molecular weight decreases and molecular weight distribution narrows with mastication time; the degradation process is nonrandom. At constant mastication time between 182 and 315°F, there is little change in molecular weight. Mastication for 18 min at 480°F broadens the molecular weight distribution; the degradation is random. For SBR at 170–200°F, molecular weight decreases and molecular weight distribution narrows with mastication time; the degradation process is also nonrandom. Nonrandom degradation for both EPDM and SBR results in a narrowing of the molecular weight distribution, without build‐up of low molecular weight molecules, and without a shift in the peak molecular weight. This is contrary to nonrandom degradation of natural rubber where a shift in the peak molecular weight occurs with mastication time.