Segmental dynamics in poly(oxymethylene) as studied via combined differential scanning calorimetry/creep rate spectroscopy approach

Abstract

The peculiarities and kinetics of segmental dynamics in semi-crystalline poly(oxymethylene) (POM) were studied over the temperature range from 130 to 430 K, covering three broad relaxation regions, using DSC and laser-interferometric creep rate spectroscopy (CRS). A number of dynamic anomalies are observed. These included a suppressed glass transition ( T g) with its transformation into a number of segmental relaxations below and above T g, and the pronounced dynamic heterogeneity, with the dispersion of activation energies of segmental motion at elevated temperatures from 80 to 500 kJ mol −1. The formation of double or triple folds was found indicating a predominant contribution of “straightened out” tie chains to the structure of disordered regions in isotropic POM. Discrete high-resolution CRS analysis showed that up to 10 creep rate peaks (kinds of segmental motion) constituted dynamics in POM interlamellar layers. All the anomalies observed could be treated in terms of the concept of 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 different constraining influence of crystallites on dynamics in the intercrystalline layers.