Strong Memory Effect of Metastable β Form Trans‐1,4‐Polyisoprene above Equilibrium Melting Temperature

Abstract

AbstractThe memory effect of metastable β form crystals of trans‐1,4‐polyisoprene (TPI) is investigated with its thermodynamically stable α‐TPI as reference. Unexpectedly, β‐TPI exhibits a stronger memory effect over α‐TPI. The memory temperature of β‐TPI can be 20 °C higher than its equilibrium melting point (78 °C), while α‐TPI has lost memory below the equilibrium melting point (87 °C). Moreover, the ordered structures in β‐TPI memorized melt accelerate spherulite growth, and the growth rate depends on melting time, similar to previous mesomorphic isotactic polypropylene studies, implying metastable phase may have universal memory effects: wide memory temperature range, crystal nucleation and growth accelerating. The higher memory temperature of metastable phase may be from weak entropic difference with isotropic melt, which cannot overcome the barrier from entanglements as thermodynamically stable phase, leading to slow relaxation. This discovery can regulate crystalline morphologies of polymers by controlling the locations of different form crystals.