Stability of flow-induced precursors in poly-1-butene and copolymer of 1-butene and ethylene

Abstract

Intervals of shear flow can induce the formation of crystallization precursors, thereby facilitating crystallization of semicrystalline polymers. This effect can be gradually removed through annealing the presheared samples at high temperature. This study compares the flow-induced crystallization and annealing behavior of a poly-1-butene (PB) sample and a 1-butene/ethylene copolymer (PBE) having a similar molecular weight and polydispersity, with the latter containing 9.88 mol. % ethylene comonomers. For the PB sample, intervals of steady shear flow accelerated the isothermal crystallization that followed, as detected by linear viscoelastic time sweep measurement, and annealing the presheared sample at sufficiently high T effectively removed this acceleration effect. In contrast, for the PBE sample, annealing the presheared sample showed three regimes in which crystallization time, as defined by linear viscoelasticity, first increased, then decreased, and finally increased again with the increase in the annealing temperature. A decrease of crystallization time with increased annealing temperature is quite counterintuitive. In situ X-ray scattering suggested that a cocrystallization of form I′ and form II crystals and a change in their ratio with annealing temperature should account for the three-regime annealing behavior.Intervals of shear flow can induce the formation of crystallization precursors, thereby facilitating crystallization of semicrystalline polymers. This effect can be gradually removed through annealing the presheared samples at high temperature. This study compares the flow-induced crystallization and annealing behavior of a poly-1-butene (PB) sample and a 1-butene/ethylene copolymer (PBE) having a similar molecular weight and polydispersity, with the latter containing 9.88 mol. % ethylene comonomers. For the PB sample, intervals of steady shear flow accelerated the isothermal crystallization that followed, as detected by linear viscoelastic time sweep measurement, and annealing the presheared sample at sufficiently high T effectively removed this acceleration effect. In contrast, for the PBE sample, annealing the presheared sample showed three regimes in which crystallization time, as defined by linear viscoelasticity, first increased, then decreased, and finally increased again with the increase in the a...