Melting kinetics of polymer crystals

Abstract

Linear polymers crystallize by the folding of chains on the nanometer scale. Owing to their metastable nature, folded-chain crystals (FCCs) exhibit unique phenomena during crystallization and melting. Understanding the melting kinetics of FCCs is challenging because of the complexity that results from the melting‒recrystallization‒remelting cycle and the reorganization occurring during heating. Fast-scanning calorimetry (FSC) has significantly advanced our understanding of melting kinetics. This review provides an overview of the research conducted on the melting kinetics of melt-grown crystals, focusing particularly on the following aspects: (1) the thermodynamics of folded-chain polymer crystals; (2) Gibbs‒Thomson and Hoffman‒Weeks plots, which are used to determine the equilibrium melting point; (3) the unique kinetic barrier of FCC melting, which is determined from the heating rate dependence of the superheated melting peak examined by calorimetry and from the morphological observation results of the isothermal melting behavior of single crystals in bulk samples; (4) the reconfirmation of results using a recently developed FSC with a chip sensor; (5) the exponential dependence of the melting rate on the degree of superheating, as determined from isothermal melting kinetics conducted using FSC; and (6) thermal Gibbs‒Thomson plots as an application of melting kinetics studies. An overview of the research on the melting kinetics of melt-grown folded-chain crystals (FCC) of polymers are provided, focusing particularly on the following aspects: (1) the thermodynamics; (2) Gibbs‒Thomson and Hoffman‒Weeks plots; (3) the unique kinetic barrier of FCC melting; (4) the results using a recently developed FSC with a chip sensor; (5) the exponential dependence of the melting rate on the degree of superheating, as determined from isothermal melting kinetics conducted using FSC; and (6) thermal Gibbs‒Thomson plots as an application of melting kinetics studies.