Influence of Macrodiol on Phase Separation and Crystallization Processes in Hard-Phase Reinforced Polyurethane Elastomers Based on Isocyanates of Variable Conformational Mobility

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Abstract
An investigation was performed to determine how aspects of microstructural changes in polyurethane elastomers vary with composition: the hard segment and soft segment were varied in a family of six segmented copolyurethane elastomers. Two hard segments were compared, based on the rigid model diisocyanate 4,4′-methylene bis(phenyl isocyanate) (MDI) or a novel flexible 4,4′-dibenzyl diisocyanate (DBDI). The hard segment fraction was held constant at approximately 40%. The soft segment macrodiols were polyesteric poly(butylene adipate) (PBA) and poly(caprolactone) glycol (PCD), or polyetheric polytetrahydrofuran (PTHF). The molar masses were 2000 ± 50 g mol−1 for PBA and PTHF and 1250 ± 50 g mol−1 for PCD. For all materials, the chain extender used in the synthesis was butylene glycol (BG). Materials were studied using wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS). There was no indication of crystallinity arising from the soft segments in these materials. The broad WAXS peaks measured for the elastomers found no crystalline domains for the hard segments with MDI, while for the materials achieved with DBDI, high crystallinity is observed. All materials with PTHF showed much higher intensity in SAXS. Due to less hydrogen bonding, irrespective of the type of diisocyanate, all the materials with PTHF displayed higher phase segregation (quantified in terms of the SAXS peak areas).

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