Featured Crystallization Polymorphism and Memory Effect in Novel Butene-1/1,5-Hexadiene Copolymers Synthesized by Post-Metallocene Hafnium Catalyst

Abstract

New butene-1/1,5-hexadiene copolymers with 0–2.15 mol % methylene-1,3-cyclopentane (MCP) co-units were synthesized by dimethylpyridylamidohafnium/organoboron catalyst, which for the first time introduces structural unit of five-carbon ring type into the polybutene-1 main chain. The effects of these novel co-units on the crystallization polymorphism, and the featured memory effect that often appears above the equilibrium melting point in copolymers, were investigated with differential scanning calorimetry, wide-angle X-ray diffraction, and polarized optical microscopy. First of all, it was found that the hexagonal form I′ can directly crystallize from the melt in the copolymers possessing the two highest co-unit concentrations of 0.65 and 2.15 mol %. With just 2.15 mol % co-unit, pure form I′ crystallites were obtained by the isothermal crystallization at 65 °C, whereas pure form II appeared at 25 °C and a crystallite mixture of form I′ and form II was generated in the intermediate temperature region. Such...