Sequential Functionalization of a Natural Crosslinker Leads to Designer Silicone Networks.
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Precise silicone networks are difficult to prepare from multiple starting materials because of poor spatial control over crosslink location, competing side reactions, and incompatible catalysts among other reasons. We demonstrate that cure processes catalyzed by B(C6 F5 )3 (the Piers-Rubinsztajn reaction) and platinum-catalyzed hydrosilylation are perfectly compatible, and can be used in either order. It is possible to perform three different, selective, sequential reactions in the same pot using H-terminated silicones as chain extenders in all cases to give explicit networks. Eugenol, a readily available aromatic compound, acts as a trifunctional crosslinker (HO, MeO, HC=CH2 ), each functional group of which can be induced to undergo selective reaction. With platinum catalysis, the reaction of SiH groups with alkenes is fastest, while B(C6 F5 )3 catalyzes reaction at phenols much faster than methoxybenzene. Thus, a variety of H-terminated telechelic siloxanes can be used to form chain extended polymers or elastomers or foams in which the morphology of the material and its constituent parts can be manipulated at will.
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