Morphological features and thermal and mechanical response in segmented polyurethane elastomers based on mixtures of isocyanates

Abstract

A family of segmented polyurethane elastomers (SPUs) was synthesized. Hard segments were chosen to be generated from two isocyanates: the rigid 4,4-diphenylmethane diisocyanate (MDI) and the flexible 4,4-dibenzyl diisocyanate (DBDI), alone or as mixtures. A polyester soft segment polyethylene adipate of molar mass 2000 g mol−1 and a small molecule chain-extender diol, ethylene glycol, were used. Hard segment fraction was maintained at ∼40%. The structure–property relationship of SPUs was investigated using several characterization techniques. Morphological features such as interdomains of the soft and hard segments were identified by means of atomic force microscopy. The thermal and mechanical behavior was evaluated by using dynamic mechanical analysis, differential scanning calorimetry and uniaxial tensile tests. Structural changes induced by varying the type and the number of isocyanates and the order of their introduction were also followed by using wide-angle X-ray. Materials with hard segments based on the single diisocyanate DBDI were observed to crystallize. Crystallinity was strongly reduced when DBDI was mixed with MDI. Improvement in elastomeric properties was obtained when both diisocyanates were included and reacted together in a random manner.