Molecular mobility and crystallinity in polytetramethylene ether glycol in the bulk and as soft component in polyurethanes

We revisit molecular mobility and crystallinity in a series of Polyurethanes prepared with polytetramethylene ether glycol (PTMEG) with varying molecular weights as soft component, methylene diisocyanate (MDI) as diisocyanate component and butanediol as chain extender in close comparison to the properties of the respective macrodiols used as soft segments. Modulated differential scanning calorimetry (MDSC) was utilized to study the glass transition and in detail crystallization and melting. Thermally stimulated depolarization currents (TSDC), and dielectric relaxation spectroscopy (DRS) were used to investigate local dynamics, dynamic glass transition and indirectly, crystallinity and morphology. The dielectric data were evaluated through representation by contour plots in the Arrhenius plane. Glass transition temperature of the diols is practically unaffected by molecular weight due to H-bonding effect, while for the PUs it showed a decreasing dependence due to higher microphase separation. Results are also discussed in terms of fragility. Crystallization of PTMEG becomes more intense and stable with increasing molecular weight, while the reflection of its melting process on its dielectric response was also observed. A weak crystallization process in the Polyurethane with long soft segments was well resolved using MDSC. Evidence for the occurrence of spinodal decomposition before this crystallization was observed by means of DRS.