Melting of poly(oxyethylene) analyzed by temperature-modulated calorimetry

Recently a small amount of locally reversible melting was observed in semicrystalline poly(ethylene terephthalate) during temperature-modulated differential scanning calorimetry (TMDSC). To further study the reversibility of melting, poly(oxyethylene) (POE) is analyzed. Low molar mass POE is known to be able to form extended-chain, equilibrium crystals, while at higher molar mass and less favorable crystallization conditions, nonequilibrium, folded-chain crystals grow. The TMDSC of POE reveals variable amounts of reversible melting depending on crystallization conditions and molar mass. The crystals closest to equilibrium show no reversible melting, proving the inherently irreversible nature of polymer melting. Crystals of high molar mass show a small amount of the prior discovered locally reversible melting. Poorly crystallized POE of low molar mass have, because of their lower zero-entropy-production melting temperature, a sufficiently smaller gap between crystallization and melting temperature to show some reversing melting.