Thermal Analysis to Probe the Complex Bivariate Distribution (Molecular and Branching Distribution) of Ethylene-1-Alkene Copolymers

摘要

It is well reported in the literature that the ethylene copolymers properties are driven by its molecular weight and comonomer content [1]. For the case of narrow molecular weight and random copolymer distribution this relation is well understood. However, when there is a complex bivariate distribution, i.e, when the comonomer is broadly distributed across the molar mass; understanding between structure and properties is lacking. For any two similar overall molecular weight and comonomer content resins, its properties change drastically with the differences in its bivariate distribution. To understand and shed some light on the complex bivariate distribution and its impact on performance, in this study we selected ethylene copolymers with similar average molecular weight and comonomer contents, but having different end use properties. Melting and crystallization of whole resins are insufficient to correlate with differences in its properties. Hence these resins were cross fractionated based on molecular weight and comonomer content using laborious fractionation techniques. Molar mass fractions were obtained by a solvent-non-solvent fractionation technique and compositional fractions were obtained by Temperature Rising Elution Fractionation (TREF) technique. The elution and the molecular weight profiles were combined to obtain the 3D overall distribution to understand the bivariate distribution. This provided us some understanding of the inter chain distribution of the resins across the molecular weight.