Studies on the First DSC Endotherm of Polyurethane Hard Segment Based on 4,4‘-Diphenylmethane Diisocyanate and 1,4-Butanediol

Abstract

The first high-temperature endotherm (T1) of polyurethane hard segment based on 4,4‘-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) was studied by differential scanning calorimetry (DSC). The materials contain 69% (w/w) of MDI and BD as the hard segment and hydroxyl-terminated cis-polybutadiene with number average molecular weights of 1650 and 2300, respectively, as the soft segment. The hard segment and the soft segment of these polyurethanes appear to be very completely phase-separated, giving rise to very simplified material structures for this study. Samples under melt-quenched condition gave rise to a highly amorphous phase for the hard phase and a distinct hard-segment glass transition behavior, which enabled us to study the T1 behavior in relation to the amorphous hard-segment Tg (Tgh). Upon annealing below the Tgh of the pure amorphous hard phases, both the T1 temperature and magnitude of the T1 endotherm increased linearly with the increase in logarithmic annealing time (log ta). On t...