Melting temperatures and enthalpies of polyethers: Poly(hexamethylene oxide)

Abstract

An experimental study is reported of the dependence of the melting temperature T, on the crystallization temperature T, for molecular weight fractions of poly(hexamethy1ene oxide) in the range from M , = 2260 to M. = 35 500, with attention to the level of crystallinity.It has been found that for the highest molecular weight fraction, at low levels of crystallinity, the extrapolated linear relation T, vs. T, yields an equilibrium melting temperature of 346,5K in very good accord with theoretical expectations. Moreover, the behaviour and theory for low-molecular-weight fractions is analyzed.The enthalpy of fusion for poly(hexamethy1ene oxide) has been determined from two kinds of experiments: by measuring calorimetrically the apparent heat of fusion at different levels of crystallinity, and by using the polymer-diluent method in decahydronaphthalene and 1,2,3,4-tetrahydronaphthalene. The enthalpy of fusion was found to be 54-57 cal/g (=22&238 J/g).