Abstract
cis- and trans-Isomers of the platinum(II) nitrile complexes [PtCl2(NCR)2] (R = NMe2, N(C5H10), Ph, CH2Ph) were examined as catalysts for hydrosilylation cross-linking of vinyl-terminated polydimethylsiloxane and trimethylsilyl-terminated poly(dimethylsiloxane-co-ethylhydrosiloxane) producing high quality silicone rubbers. Among the tested platinum species the cis-complexes are much more active catalysts than their trans-congeners and for all studied platinum complexes cis-[PtCl2(NCCH2Ph)2] exhibits the best catalytic activity (room temperature, c = 1.0 × 10−4 mol/L, τpot-life 60 min, τcuring 6 h). Although cis-[PtCl2(NCCH2Ph)2] is less active than the widely used Karstedt’s catalyst, its application for the cross-linking can be performed not only at room temperature (c = 1.0 × 10−4 mol/L), but also, more efficiently, at 80 °C (c = 1.0 × 10−4–1.0 × 10−5 mol/L) and it prevents adherence of the formed silicone rubbers to equipment. The usage of the cis- and trans-[PtCl2(NCR)2] complexes as the hydrosilylation catalysts do not require any inhibitors and, moreover, the complexes and their mixtures with vinyl- and trimethylsilyl terminated polysiloxanes are shelf-stable in air. Tested catalysts do not form colloid platinum particles after the cross-linking.
Highlights
In the framework of our projects aimed, on the one hand, toward verification of catalytic properties of metal species in organic transformations On the other hand, on reactivity of platinum nitrile complexes, we focused our attention on the possibility of applying platinum(II) nitrile species in hydrosilylation cross-linking of vinyl polysiloxanes
Platinum-catalyzed hydrosilylation cross-linking was studied for siloxane polymers PDMS and EHDMS (Scheme 1) at room temperature (RT) and at 80 ̋ C and catalyst concentration range of 10 ́3 ́10 ́5 mol/L
In the field of catalysis, we observed that isomeric platinum(II) complexes featuring benzyl- and phenylcyanides and dialkylcyanamides, cis- and trans-(1–4), behave as efficient catalysts for the cross-linking of vinyl terminated polydimethylsiloxane and trimethylsilyl terminated poly(dimethylsiloxane-co-ethylhydrosiloxane)
Summary
Viz. catalytic addition of silicon hydrides to multiple bonds, is among the most important reactions in the silicone industry, in particular, for hydrosilylation cross-linking of multifunctional silicone hydride polymers with multi-vinyl functional silicon polymers giving broad spectrum of the silicone compositions of superior practical importance [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28]. It is noteworthy that reported data on metal-catalyzed hydrosilylation cross-linking of vinyl polysiloxanes is substantially less abundant than those for monomeric dienes. Taking the analogy between two reactions into account, Pt- and Rh-based systems applied for various hydrogenations are usually considered as the most promising for hydrosilylation. A number of new catalysts for hydrosilylation of vinyl polysiloxanes have emerged in the past two decades [7,16,19,21,25], Karstedt’s complex (or its modified analogs) still remains the most widely used catalyst for cross-linking [7,21]. Its main disadvantage is hyperactivity that makes the cross-linking unselective even at room temperature (RT) and requires application of an inhibitor that, in many
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