Double Cross‐Linked Polyisobutylene‐Based Polyurethane (xPIB‐PU) I: Synthesis, Processing, and Properties

Abstract

This publication concerns the synthesis of a novel class of hybrid thermoset/thermoplastic elastomers, i.e., double cross‐linked polyisobutylene‐based polyurethanes (xPIB‐PUs), together with their processing and some key properties. These materials are designed to exhibit a combination of properties for indwelling medical applications, specifically for heart valve prostheses. The chemical cross‐links are introduced by well‐defined 3‐arm PIB stars fitted with HO‐end groups of molecular weights (MWs) of Mn = 3081 and 9000 g mole−1 and narrow MW dispersities (<1.3). Processibility of xPIB‐PU containing 70 wt% PIB (for biocompatibility and calcification resistance) is achieved by driving the syntheses to high conversions (>97%) close to but still below the gel point and completing the cross‐linking in heated molds. The processibility period (minutes) is controlled by controlling the MW of the cross‐linking agent in the 3081 to 9000 g mole−1 range. Blends of 3‐arm stars and linear bifunctional PIBs can also control the processibility period. The creep resistance of xPIB‐PU is significantly improved (from 13.2% to 5.5%) relative to physically cross‐linked PIB‐PU. xPIB‐PUs exhibit negligible permanent set (1–2%), and high Young's modulus (41 MPa). The stress/strain properties of xPIB‐PUs are also investigated. The data clearly show the contribution of two modes of cross‐linking.