ISSN:
0887-624X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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+ to produce PSt-b-PIB—CH2— CH=CH2 prearms, and finally linking by hydrosilation of these prearms with Si—H-containing cyclosiloxanes (e.g., 2,4,6,8,10,12-hexamethylcyclohexasiloxane, DH6). 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 (DH6 to DH12) and a close to exact stoichiometry between the Si—H and allyl groups, [Si—H]/[C=C] ∼ 1, in the essential absence of moisture ([H2O] ∼ 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 Si—H/allyl ratios significantly larger than unity ([Si—H]/[C=C] = 2-3) in the presence of controlled amounts of moisture ([H2O] ∼ 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 1H-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. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2997-3012, 1998
Additional Material:
15 Ill.
Type of Medium:
Electronic Resource
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