Synthesis, characterization, and crosslinking of novel stars comprising eight poly(isobutylene-azeotropic-styrene) copolymer arms with allyl or hydroxyl termini. II. Stars of eight isobutylene/styrene azeotropic copolymer arms emanating from a calix[8]arene core

Abstract

Our objective was the precision synthesis of novel stars consisting of a well-defined calix[8]arene core out of which radiate eight poly(isobutylene-aze-styrene) [P(IB-aze-St)] arms fitted with crosslinkable end groups. We reached our objective by preparing the octafunctional calixarene derivative C[8]OCH3, inducing the living azeotropic copolymerization of IB/St charges with the C[8]OCH3/BCl3·TiCl4 initiating system, and end-quenching living IB/St copolymerizations with allyltrimethylsilane. With this strategy, we obtained stars C[8][P(IB-aze-St)CH2CHCH2]8 of various molecular weights. The number of CH2CHCH2 termini of the arms was 8.0 ± 0.2 by quantitative 1H NMR analysis. The eight allyl termini were quantitatively converted to CH2CH2CH2OH termini by hydroboration/oxidation. To confirm that the latter second-generation stars possessed eight primary alcohol end groups, we quantitatively converted the CH2OH termini to OSi(CH3)3 termini, the concentration of which was quantitated by 1H NMR spectroscopy. According to this analysis, the stars contained 8.0 ± 0.3 hydroxyl termini. The glass-transition temperatures of the P(IB-aze-St) arms increased from 59 to 65 °C as the weight-average molecular weights of the arms increased from about 2500 to about 4300 g/mol, respectively. The α and K constants of the Mark–Houwink–Sakurada relationship and the intrinsic viscosity of a representative allyl-telechelic star were determined and compared with a linear azeotropic IB/St copolymer of similar molecular weight. The crosslinking of C[8][P(IB-aze-St)CH2CH2CH2OH]8 stars with 4,4′-methylene bis(phenyl) diisocyanate and 2,4-tolylene diisocyanate in various solvents afforded tightly crosslinked films of potential interest for scratch-resistant coatings, mar-resistant coatings, or both. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1525–1532, 2001