Study of Polyolefin Gel in Organic Solvents IX. Ethylene Sequence Distribution of Ethylene–Propylene Random Copolymer and Crystalline Junction Size in Its Thermoreversible Gel

Abstract

The crystalline junction size ζ, which is the number of consecutive ethylene units per crystalline sequence such as –[–CH2–CH2–]–, in an ethylene–propylene (EP) copolymer gel was determined from gel-melting temperatures using the Takahashi theory. In order to examine the correlation between the size ζ and number-average length of ethylene sequences estimated from NMR measurements, an ethylene sequence distribution curve of the copolymer was established from 13C NMR data assuming 1st-order Markov statistics and number-average length in number of ethylene units (L[EE···E]) was calculated from its distribution curve. The average length L[EE···E] determined from this curve was in good agreement with that calculated directly from E/P triad data of NMR. Moreover, number-average length (L[EE···E≥5]) of ethylene sequences greater than or equal to 5, whose value is the crystallizable minimum number of consecutive ethylene units in an EP copolymer, approximately agreed with the junction size ζ in gel, i.e., ζ≃L[EE···E≥5].