DYNAMICS IN POLY(OXYMETHYLENE) AND POLY(OXYMETHYLENE-CO-OXYETHYLENE) AS STUDIED VIA A COMBINED CREEP RATE SPECTROSCOPY/DIFFERENTIAL SCANNING CALORIMETRY APPROACH

Abstract

The peculiarities and kinetics of segmental dynamics in a few semi-crystalline poly(oxymethylene) (POM) samples and in poly(oxymethylene-co-oxyethylene) with 1.5% ethylene oxide units were studied over the temperature range from 110 to 430K. Differential scanning calorimetry (DSC) and laser-interferometric creep rate spectroscopy (CRS) were used. The latter was operated under uniaxial tension or compression. A number of dynamic anomalies were observed. These included a suppressed glass transition (T g) with its transformation into segmental relaxations below and above T g, and a pronounced dynamic heterogeneity, with the dispersion of activation energies of segmental motion ranging from 60 to 500 kJ mol−1. Formation of anomalous long folds in POM and the copolymer structure is assumed from DSC data, indicating a predominant contribution of “straightened out” tie chains to the structure of disordered regions in these isotropic polymers. Discrete high-resolution CRS analysis showed that numerous peaks (separate types of segmental motion) constituted dynamics in the interlamellar layers of the polymers under study. Considerable influence of comonomer or small additives, or preliminary treatments (quenching, small pre-straining) on discrete CR spectra was observed and are discussed in the text. All the anomalies observed could be treated in terms of the concept of the common segmental nature of α and β relaxations in flexible-chain polymers; as the breakdown of intermolecular motional cooperativity due to nanoscale confinement effect, and as a different constraining influence of crystallites on dynamics in the intercrystalline layers.