AbstractThis paper concerns the synthesis, characterization, and physical properties of novel polyisobutylene (PIB)‐based urethane model networks prepared from diphenylmethane diisocyanate (MDI) and three‐arm star PIBs capped with CH2OH end groups (PIB(CH2OH)3). The PIB(CH2OH)3starting materials were produced by the inifer method in theM̄n= 13,550–27,000 range. The best networks were obtained with NCO : OH = 1. Solvent extractions showed uncatalyzed network formation to be essentially complete and swelling studies indicated the expected architecture, i.e.,M̄c= 2M̄n/3 and virtual absence of dangling chains. Stannous octoate was found to increase the rate of network formation in the absence of side reactions (i.e., allophanate formation), while other catalysts also accelerated undesirable reactions. The effect of molecular weight between crosslinks (M̄c) on network physical properties has been studied in theM̄c= 900–18,500 range. The tensile strength increases with decreasingM̄cup to a limiting value after which it sharply declines. Elongations at break decrease monotonously with decreasingM̄c. Low temperature tensile studies show higher tensile data at −20°C, and, surprisingly, a retention of elongations at break. TheTg's decrease with increasingM̄c's until a plateau is reached at −73°C. Hysteresis is fairly constant and permanent set is constant and low. The PIB‐based urethane networks exhibit excellent hydrolytic stability, negligible moisture absorption, and outstanding heat‐aging stability, far beyond what is expected for a polyurethane. Conceivably the thermal deblocking of the urethane group may be reversible (NHCOOCH2⇌ NCO + HOCH2) because the isocyanate that arises in the highly hydrophobic PIB matrix recombines with the alcohol, and cannot react with mois
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