PHASE-STRUCTURE OF RANDOM ETHYLENE COPOLYMERS - A STUDY OF COUNIT CONTENT AND MOLECULAR-WEIGHT AS INDEPENDENT VARIABLES

The phase structure of a series of random ethylene copolymers with 1-b utene, 1-hexene, or 1-octene as comonomers, which have narrow molecula r weight and composition distributions, has been studied by treating b oth the counit content and molecular weight as independent variables. Essentially no difference in behavior has been found between the three types of branches in most of the properties analyzed. However, the in terfacial content of the ethylene-octene copolymers showed consistentl y higher values than the others. The interphase is shown to be a relat ively important component of the copolymeric lamellae, with thicknesse s varying from 10 to almost-equal-to 45 angstrom. The melting temperat ures and the levels of crystallinity of these copolymers adhere to the reference curves established for the model hydrogenated polybutadiene s and random copolymers. It is found to be very important to separate and distinguish the influence of molecular weight and of copolymer com position on the phase structure.