INFLUENCE OF THE COMPOSITION ON THE CLASS TRANSITION-TEMPERATURE OF POLYURETHANE AND POLYURETHANE ACRYLATE NETWORKS

Linear polyurethane, linear segmented polyurethane, polyurethane netwo rks, and polyurethane acrylate networks of various composition were sy nthesized. The variation of T-g with the type of macrodiol, its length , and the chemical composition of the polymer were studied in relation with the percentage of soft segments, the molar mass between crosslin ks, and the concentration of urethane bonds. In this work, the network s were considered as composed of chain segments of various composition between point-like crosslinks. The chemical heterogeneities of the ne tworks were not taken into account. For polyurethanes, it was shown th at T-g values are essentially controlled by the amount of urethane bon ds. For polyurethane acrylates, the T-g values are dependent on the am ount of urethane bonds but also on the presence of crosslinks whose nu mber is varying with the excess of diisocyanate of the first step thre e times faster for PUA compared with PU. No clear relation was observe d between T-g and the molar mass between point-like crosslinks. Anothe r approach considering the network heterogeneities is indispensable an d will be used in a following work. (C) 1996 John Wiley & Sons, Inc.