Melting of low molecular weight poly(ethylene oxide)

Abstract The melting behaviour of fractions of poly(ethylene oxide) of narrow molecular weight distribution and of molecular weight of 20 000 or less has been studied. Fractions of molecular weight 4000 or less have one melting transition; those with molecular weight of 6000 or greater may have two melting transitions. Consideration of the influence of molecular weight and crystallization temperature on the melting transitions, of the low-angle scattering of X-rays, and of calculations based upon Flory's theory of melting enables us to ascribe the transitions to the melting of extended-chain or of variously folded-chain lamellar crystals. The end interfacial free energy ( σ e ) of extended-chain crystals of poly(ethylene oxide) is found to increase within the range 1 to 4 kcal/mol as the molecular weight increases. It is suggested that this increase in σ e is related to an increase in polydispersity of molecular weights in the fractions.