Novel thermoplastic elastomers. I. Synthesis and characterization of star-block copolymers of PSt-b-PIB arms emanating from cyclosiloxane cores

✍ Scribed by Jung S. Shim; Siddhartha Asthana; Naoki Omura; Joseph P. Kennedy

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 398 KB
• Volume: 36
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(199812)36:17<2997::aid-pola1>3.0.co;2-1

✦ Synopsis

The synthesis and characterization of novel thermoplastic elastomers consisting of multiple polystyrene-b-polyisobutylene (PSt-b-PIB) arms emanating from cyclosiloxane cores is described. The synthesis involved the sequential living cationic block copolymerization of styrene (St) and isobutylene (IB), followed by quantitative allylic end-functionalization of the living PSt-b-PIB ϩ to produce PSt-b-PIBOCH 2 O CHACH 2 prearms, and finally linking by hydrosilation of these prearms with SiOHcontaining cyclosiloxanes (e.g., 2,4,6,8,10,12-hexamethylcyclohexasiloxane, D 6 H ). Two types of star-blocks, namely primary and higher-order star-blocks, were prepared: Primary star-blocks containing 3-9 PSt-b-PIB arms were obtained by using various cyclosiloxanes (D 6 H to D 12 H ) and a close to exact stoichiometry between the SiOH and allyl groups, [SiOH]/[CAC] ϳ 1, in the essential absence of moisture ([H 2 O] ϳ 100 ppm). Higher-order star-blocks consisting of 13-24 PSt-b-PIB arms radiating from complex coupled cyclosiloxanes were prepared by the use of SiOH/allyl ratios significantly larger than unity ([SiOH]/[CAC] ϭ 2-3) in the presence of controlled amounts of moisture ([H 2 O] ϳ 600 ppm). Reaction conditions (temperature, concentration, stoichiometry, solvent nature, catalyst concentration, etc.) for efficient syntheses have been developed. The products were characterized by 200 and 600 MHz 1 H-NMR spectroscopy and triple-detector (RI, UV, LLS) GPC. The microstructure of the condensed cores in the higher-order star-blocks was studied by 2D-NMR (HMQC) spectroscopy, and the number of cyclosiloxane rings in the cores (i.e., the content (wt %) of cores in the star-blocks) was determined.