Characterization of molecular properties of propylene impact copolymers

ENGLISH ABSTRACT: This study involves the fractionation and characterization of five propylene impact copolymers as well as the use of preparative temperature rising elution fractionation (prep-TREF) to study batch consistency. The fractionation technique used in the study was prep-TREF. The prep-TREF fractions were subsequently analysed off-line by crystallization analysis fractionation (CRYSTAF), differential scanning calorimetry (DSC), 13C nuclear magnetic resonance {1 3 C NMR) and high-temperature gel-permeation chromatography (HT-GPC). The molecular heterogeneity of these copolymers was illustrated, while optimizing the fractionation technique. Also propylene impact copolymers that seem similar, as well as obviously different in molecular make-up, were compared to illustrate batch consistency. The results for the original polymers show that the ethylene content, as determined by 13C NMR, was significantly different from that claimed by the manufacturers. CRYSTAF analyses indicated differences between two seemingly similar polymers from different batches. The prep-TREF technique was optimized for these materials, particularly with respect to the elution temperatures and temperature intervals of these materials. Up to 15 clearly identifiable fractions, of which 7 comprised about 90 % of the total weight of the polymer fractionated, were obtained. Three major components were isolated from each of the polymers. These were ethylene-propylene-rubber, EPR, (50 - 60 mole %), propylene homopolymer and ethylene-rich copolymers. The EPR was non-crystalline and largely present in the fractions isolated at elution temperatures of 25 and 50 °C. Most of the ethylene in the copolymers is present as EPR. An increase in the ethylene content does correspondingly increase the rubbery, soluble part of the polymer. PrepTREF was shown to be a useful technique to compare very complex materials such as the propylene impact copolymers.