Synthesis, characterization, and crosslinking of novel stars comprising eight poly(isobutylene-azeotropic-styrene) copolymer arms with allyl or hydroxyl termini. I. Living azeotropic copolymerization of isobutylene and styrene

Abstract

The overall objective of this research is the creation of novel star polymers consisting of well-defined stable cores out of which radiate multiple poly(isobutylene-co-styrene) [P(IB-co-St)] arms whose glass-transition temperature (Tg) can be controlled over a wide range (-73 to +100°C) and whose arm termini are fitted with multipurpose (e.g., crosslinkable) functionalities. The first article of this series relates the synthesis and characterization of azeotropic IB/St copolymers [P(IB-aze-St)], which are to be subsequently used as end-functional arms of the target stars. The P(IB-aze-St)s are models for statistical IB/St copolymers. The azeotropic composition is 21/79 (mol/mol) IB/St, and NMR, Fourier transform infrared, and gel permeation chromatography techniques demonstrate copolymer compositional homogeneity over the 12-96% conversion range. Conditions were developed for living azeotropic IB/St copolymerization. The livingness of the azeotropic copolymerization was proven by kinetic investigations. P(IB-aze-St)s with number-average molecular weights of up to 24,000 g/mol and polydispersity indices (weight-average molecular weight/number-average molecular weight) less than 1.5 were prepared. The copolymerization reactivity ratios were determined: rIB = 3.41 ± 0.23 and rSt = 1.40 ± 0.26. The effect of the P(IB-aze-St) molecular weight on Tg was studied by DSC. Tg increases linearly with the number-average molecular weight and reaches a plateau at 62°C at 24,000 g/mol. The heat stability of P(IB-aze-St) was investigated by thermogravimetric analysis, and a 5% weight loss was found at 250°C in air.