Multiple endotherm melting behavior in relation to the morphology of poly[3,3‐ bis(ethoxymethyl) oxetane]

Abstract

SynopsisTwo crystalline melting peaks have been observed by differential scanning calorimetry for low molecular weight poly [3,3-bis(ethoxymethyl) oxetane] (polyBEM0) samples, M , < 1 X lo4 g/ mol, whereas only one melting peak has been observed for samples of higher molecular weight, M , 1 X 10' g/mol. Crystallization of low molecular weight samples at large supercoolings produces the lower melting form while low supercooling or annealing favors the higher melting species. Enthalpy of fusion values obtained by DSC for a multiple melting endotherm sample range from 28 to 39 J / g for crystallization temperatures from 58 to 35"C, respectively. Optical microscopy studies indicate that the lower melting peak corresponds to a spherulitic type morphology and the higher melting peak correlates to a fine grained crystal structure. Wide angle X-ray powder diffraction studies do not detect differences in the crystal structures of samples exhibiting either one or two melting peaks, which suggests that the multiple melting phenomenon is due to differences in morphology rather than the presence of different crystal forms.