Chris Allen Sumpter

Hydrosilylation catalysts derived from cyclodextrin organometallic platinum inclusion compounds and their use in command-cure applications

Beta-cyclodextrin (β-CD) complexes of CODPtX2 (COD=1.5-cyclooctadiene.X=Cl, Br, and I) have been prepared and employed as hydrosilylation catalysts. When used in cross-linkable, silicone-containing systems, these catalysts provide a long shelf stability at ambient temperature but cure rapidly at elevated temperature. These systems thus have the property of “command-cure”. Extensive analytical investigations were undertaken to develop reproducible synthetic methodology for the preparation of inclusion compounds free of surface contamination of the guest platinum compound. Water plays a key role in the synthesis of such platinum inclusion compounds. Dried β-CD CODPtX2 compounds can be washed with organic solvent to remove residual uncomplexed CODPtX2, while organic solvent washing of wet inclusion compounds results in removal of the guest from the β-CD cavity. Examination of these catalysts in curable silicone systems is described.

Platinum-group metal cyclodextrin complexes and their use as command-cure catalysts in silicones

The Command-Cure concept is defined for a curable formulation as one with long work-like at ambient temperature and rapid cure time at elevated temperature. This concept is explored for a curable silicone system, cured via hydrosilylation. CODMCl2 complexes (COD=1.5-cyclo-octadiene:M=Pt. Pd) are reacted with beta-cyclodextrin (β-CD) to make 1∶1 inclusion compounds,M=Pd.2;M=Pt.4. Compounds2 and4 were analyzed by1H NMR and X-ray powder diffraction. Their catalytic ability was evaluated in a model system as well as a polymeric system that gels upon cure. Surprisingly, the Pd analog2 was a good command-cure catalyst whereas the guest compound CODPdCl2,1, was not active in the hydrosilylation reaction. The Pt analog,4, was an effective command-cure catalyst while the corresponding guest. CODPtCl2,3, was too active at low temperature in the hydrosilylation reaction. Additional Pt compounds and one Rh inclusion compound were evaluated as command cure catalysts. These inclusion compounds were: 1∶1 β-CD:[CODRhCl]2,5: 1∶1 β-CD:CpPtMe3,6 (Cp=cyclopentadienyl): 1∶2 β-CD:MeCpPtMe3,7; 1∶2 β-CO:CODPtMe2,8. The effectiveness of4 8 was evaluated in a number of silicone systems.

Cross-linking of hexenyl silicone polymers via the olefin metathesis reaction

The olefin metathesis reaction was explored as a novel method to produce cross-linked silicone polymers. Although this reaction is well-known for non-silicone-containing monomers, there are no examples of this reaction in the presence of siloxanes. We have discovered a catalyst system for the reaction of silicone substrates comprised of a 1:4 molar ratio of WCl6/Sn(CH3)4. No metathesis is seen with the traditional ratio of catalyst and cocatalyst. In a model system, 1-hexenylmethylbis(trimethylsiloxy)silane underwent self-metathesis in greater than 75% yield. The catalyst system also promoted metathesis of a hexenyl containing silicone polymer.