Polyisobutylene-based segmented polyureas. I. synthesis of hydrolytically and oxidatively stable polyureas

Abstract

Novel segmented polyurea elastomers containing soft polyisobutylene (PIB) segments were synthesized and characterized. The key ingredient, primary amine-telechelic PIB oligomers (NH2-PIB-NH2) with number average molecular weights of 2500 and 6200 g/mol were synthesized. PIB-based polyureas were prepared by using various aliphatic diisocyanates and diamine chain extenders with hard segment contents between 9.5 and 46.5% by weight. All copolymers displayed microphase morphologies as determined by dynamic mechanical analysis. Tensile strengths of nonchain-extended and chain-extended polyureas showed a linear dependence on the urea hard segment content. PIB-based polyureas prepared with NH2-PIB-NH2 of M-n = 2500 g/mol, 4,4'-methylendbis(cyclohexylisocyantate), and 1,6-diaminohexane containing 45% hard segment exhibited 19.5 MPa tensile strength which rose to 23 MPa upon annealing at 150 degrees C for 12 h. With increasing hard segment content, elongation at break decreased from similar to 450% to a plateau of 110%. The hydrolytic and oxidative stability of PIB-based polyureas were unprecedented. Although commercial "oxidatively resistant" thermoplastic polyurethanes degraded severely upon exposure to boiling water or concentrated nitric acid, the experimental polyureas survived without much degradation in properties.