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

The overall objective of this research is the creation of novel star polyme rs consisting of well-defined stable cores out of which radiate multiple po ly(isobutylene-co-styrene) [P(IB-co-St)] arms whose glass-transition temper ature (T-g) can be controlled over a wide range (-73 to +100 degreesC) and whose arm termini are fitted with multipurpose (e.g., crosslinkable) functi onalities. The first article of this series relates the synthesis and chara cterization 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 compositio n is 21/79 (mol/mol) IB/St, and NMR, Fourier transform infrared, and gel pe rmeation chromatography techniques demonstrate copolymer compositional homo geneity over the 12-96% conversion range. Conditions were developed for liv ing azeotropic IB/St copolymerization. The livingness of the azeotropic cop olymerization was proven by kinetic investigations. P(IB-aze-St)s with numb er-average molecular weights of up to 24,000 g/mol and polydispersity indic es (weight-average molecular weight/number-average molecular weight) less t han 1.5 were prepared. The copolymerization reactivity ratios were determin ed: r(IB) = 3.41 +/- 0.23 and r(St) = 1.40 +/- 0.26. The effect of the P(IB -aze-St) molecular weight on T,was studied by DSC. T,increases linearly wit h the number-average molecular weight and reaches a plateau at 62 degreesC at 24,000 g/mol. The heat stability of P(IB-aze-St) was investigated by the rmogravimetric analysis, and a 5% weight loss was found at 250 degreesC in air. (C) 2001 John Wiley & Sons, Inc.