Polyisobutylene model elastomers prepared using demonstrably complete end-linking reactions

Summary Cationic polymerizations with a trifunctional initiator-chain transfer agent were used to prepare three-arm polyisobutylene C(CH₃)₂CH₂] (PIB) molecules with hydroxyl groups at all three chain ends. Extensive spectroscopic analyses confirmed the essentially perfect trifunctionality of the polymers, which were then end-linked using an aromatic diisocyanate to give trifunctional model networks. The PIB elastomers were found to have negligible sol fractions, which demonstrates that the end-linking reactions used to prepare them were essentially complete. They were studied, swollen, with regard to their equilibrium stressstrain isotherms in uniaxial extension at 25°C. As was found to be the case for trifunctional and tetrafunctional PIB networks prepared from the linear chains, the results were in satisfactory agreement with theory and yielded no evidence that inter-chain entanglements contribute to the modulus at elastic equilibriums.