Chapter 15
Multiarm Star Polyisobutylenes
Downloaded by STANFORD UNIV GREEN LIBR on August 27, 2012 | http://pubs.acs.org Publication Date: May 1, 1997 | doi: 10.1021/bk-1997-0665.ch015
Polyisobutylene Arms Connected to a Cyclosiloxane Core 1,3
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Naoki Omura , Alexander V. Lubnin , and Joseph P. Kennedy 1
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Maurice Morton Institute of Polymer Science, University of Akron, Akron, OH 44325-3909 BFGoodrich Company, 9921 Brecksville Road, Brecksville, O H 44141-3289 The synthesis and characterization of novel multi-arm stars comprising polyisobutylene (PIB) arms connected to various cyclo-siloxane cores are described. The syntheses have been achieved by hydrosilating allyl- or isopropenyl-capped PIB with cyclosiloxanes carrying 6 or 8 Si-Η groups. The products were characterized by H and C-NMR spectroscopy and GPC equipped with refractive index and laser light scattering detectors. The stars with close to the expected structures can be obtained under carefully controlled polymerization conditions. Traces of water in the charge may give higher-order stars by star 1
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-star coupling, however, this byproduct can be eliminated by the use of allyl-capped PIB and/or high [C=C]/[Si-H] ratios. Key words: Star polymers, star-shaped polymers, secondary stars, octopus molecules, polyisobutylene, allyl endgroups, isopropenyl endgroups, hydrogensiloxanes, hydrogencyclosiloxanes, silicones, hydrosilation, hexachloroplatinic acid, NMR spectroscopy, G P C , light scattering. Permanent address: Shin-Etsu Chemical Company, Limited, Silicone-Electronics Materials Research Center, 1-10 Hitomi Matsuida Usui Gunma 379-02, Japan
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Corresponding author
NOTE: This article is part four of a series. For part three of this series of publications, see T. Marsalko, I. Majoros, and J. P. Kennedy, in Macromol. Symp., 107, 319 (1996).
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© 1997 American Chemical Society In Cationic Polymerization; Faust, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
Downloaded by STANFORD UNIV GREEN LIBR on August 27, 2012 | http://pubs.acs.org Publication Date: May 1, 1997 | doi: 10.1021/bk-1997-0665.ch015
15.
OMURA ET AL.
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Multiarm Star Polyisobutylenes
In the course of our fundamental studies concerning novel multi-arm stars [1, 2], we became interested in the possibility of assembling architectures consisting of multiple PIB arms connected to a well-defined cyclosiloxane core. Recently, we have gained considerable experience in working with PIB stars having a crosslinked and therefore difficult-to-characterize aromatic (i.e., polydivinylbenzene) core [1], however, have not yet explored the potentialities offered by readily characterizable siloxane cores. The PIB-based stars with polydivinylbenzene cores [1,2] are still being evaluated and tested, particularly in regard to their potential application as motor oil additives. In the latter field shear stability is of critical importance. In view of the demonstrated superior shear stability of silicone oils over hydrocarbon oils [3], siloxane cores appeared to be of particular interest; for example, in an aircraft gear pump, the viscosity of a silicone oil decreased less than 2 % after 105000 cycles, whereas, that of a petroleum oil dropped more than 50% after only 18000 cycles [3]. We theorized that the synthesis of the target PIB-arm cyclosiloxane-core stars could be accomplished in two steps: 1) Preparation of olefin (allyl or isopropenyl)-terminated PIBprearms of desired molecular weights, followed by 2) Linking these PIB prearms by hydrosilation to well-defined cyclic siloxanes containing a desirable number of Si-Η functions. According to recent literature, both steps are efficient: Allylor isopropenyl-ended PIBs have been prepared by living polymerization of isobutylene to practically any lengths [4] followed by quantitative end-functionalization to the CH CH=CH [5] or -CH C(CH )=CH [6] terminus; hydrosilation was also demonstrated to be a quantitative reaction [7, 8]. Fig. 1 shows the structure of the siloxane fragments and molecules employed in these studies together with their abbreviations, and Scheme 1 helps to visualize the synthetic strategy to the target stars. One of the great advantages of the D and T cores over those of polydivinylbenzene cores is that the formers are individual well-defined cyclic compounds and thus should yield relatively simple core architectures. In contrast, polydivinylbenzene cores are complex networks whose detailed structural characterization is well-nigh impossible. 2
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In Cationic Polymerization; Faust, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1997.
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CATIONIC P O L Y M E R I Z A T I O N
H
Ç 3 , I ι C H — S i — φ — I C 3
, ι
CH I
i
l i CH
3
Η I
1
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