Temperature rising elution fractionation and characterization of ethylene/octene-1 copolymers synthesized with constrained geometry catalyst

Abstract

We report here the fractionation and characterization of two crystalline ethylene/octene- 1 copolymer samples with octene-1 mole fractions of 0.028 and 0.089, synthesized in a solution continuous stirred-tank reactor (CSTR) using a constrained geometry catalyst (CGC) system. The samples were fractionated by preparative temperature rising elution fractionation (TREF), and the fractions were characterized by 13 C NMR, GPC and DSC. The copolymers were found to have narrow TREF curves, indicating the CGC system produces copolymers with narrow composition distributions. The fractionation was mainly determined by the short chain branching density in the copolymers. The polymer molecular weight also showed an effect on the fractionation for the copolymer with octene-1 mole fraction of 0.028. The first-order Markovian statistical model appeared to be more valid in predicting the comonomer dyad and triad distributions in the copolymer fractions. The combination of TREF and GPC was found to be an effective technique for the analysis of copolymers with low crystallinity.