Two commercial ethylene-propylene random copolymers(A and B) for hot water piping of which A has better long term heat stability and slow crack growth resistance performance than B were fractionated with respect to the isotactity distribution by preparative temperature-rising elution fractionation(TREF).The molecular weight and distribution of fractions and the original resins were investigated by gel permeation chromatography.The results indicated that both A and B had broad isotacticity distribution and A had fewer portions of high isotacticity than B.At the same time A had broader and more typical double-peak molecular weight distribution.The fractions of A had higher molecular weight and broader molecular weight distribution than those of B’s.All of these results implied the differences between the catalysts or the polymerization processes for the two copolymers.
