In-reactor blends based on ultrahigh molecular weight polyethylene: Effect of microstructure of modifying fraction on the morphology and viscoelastic behavior of blends

A morphology and viscoelastic behavior of a wide range of in-reactor blends (RBs) on the base of ultrahigh molecular weight polyethylene (UHMWPE) with Mw = 1000 kg mol⁻¹ and polymer fractions of different microstructure were investigated to develop the understanding of relationships between the structure and properties of polyolefin materials. Linear low-molecular weight polyethylene of high density (LMWPE) with Mw = 160 kg mol⁻¹ as well as ethylene/1-hexene copolymers (CEH-n) containing from 3 to 19 mol% of 1-hexene were used as the components of RBs. In-reactor blends UHMWPE/CEH-n and UHMWPE/LMWPE with a varied content of CEH-n or LMWPE fractions were prepared in the two-step polymerization processes of ethylene homo- and copolymerization over metallocene catalyst. It was found by the methods of differential scanning calorimetry (DSC) and Wide Angle X ray Scattering (WAXS) methods, that the percentages of crystalline and amorphous phases and the lamella sizes in the materials depend on the nature and amount of modifying polymer fractions. Linear dependences of α-relaxation temperature on the lamella sizes in crystalline phase and β-relaxation temperature on the density of butyl branches in copolymer fractions of in-reactor blends UHMWPE/CEH-n were found by the method of dynamic mechanical analysis (DMA) method. The mechanisms of the processes of α- and β-relaxations in the in-reactor blends including polymer fractions with different microstructure are discussed.