Polyurethane triblock copolymers with mono‐disperse hard segments. Influence of the hard segment length on thermal and thermomechanical properties

Polyurethane triblock copolymers were synthesized by reacting 4,4′‐methylenebis(phenyl isocyanate) (MDI)‐endcapped poly(tetramethylene oxide) (PTMO) with mono‐amine‐amide (MMA) units. Four different MMA units were used, i.e. no‐amide (6m), mono‐amide (6B), di‐amide (6T6m) and tri‐amide (6T6B), based on hexylamine (6m), 1,6‐hexamethylenediamine (6), terephthalic acid (T), and benzoic acid (B). The PTMO had a molecular weight of 2000 g/mol. Thermal and thermo‐mechanical properties were studied by means of differential scanning calorimetry and dynamic mechanical analysis, respectively. The structure of the carbonyl bond was explored by infra‐red analysis and the elastic behavior of the materials by compression set experiments. The triblock polyurethanes with mono‐disperse, hard end‐segments displayed low molecular weights (3200–3800 g/mol). The crystallinity of the MDI urethane‐urea group was found to depend on the structure of the amide. Increasing the number of amide bonds in the mono‐disperse hard segment increased the modulus and the hard segment melting temperature, and decreased the compression set values. The low temperature properties were hardly affected by the amide length. POLYM. ENG. SCI., 2008.