The Piers-Rubinsztajn reaction, involving B(C6F5)(3)-catalyzed siloxane formation from hydrosilanes + alkoxysilanes, is tolerant of a wide variety of functional groups, and provides a generic strategy for the preparation of structurally complex functional silicones.

While silicone elastomers generally have excellent biomaterials properties, their hydrophobicity can elicit undesired local biological responses through adsorption and denaturation of proteins. Surface-bound poly(ethylene glycol) (PEG) can ameliorate the situation by preventing contact between the external biology and the silicone elastomer. It is further possible to manipulate the biocompatibility of the surface by linking peptides, proteins or other biological entities to the PEG. Previous synthetic approaches to PEG-protected surfaces are compromised by issues of reproducibility. We describe two rapid and efficient approaches to silicone surface modification by PEG-linked adhesion peptides that overcome this problem: SiH groups are introduced throughout a silicone elastomer during elastomer synthesis or only at the surface after cure; then, in either case, protein-repellent PEG brushes at the surface are introduced by hydrosilylation to give surfaces that can be stored for extensive periods of time without degradation. Activation of the free alcohol with an NSC group followed by immediate conjugation to relevant biological molecules occurs in high yields, as shown for RGDS and GYRGDS. High surface grafting density of the peptides was demonstrated using radiolabeling techniques. Biological activity was demonstrated by a 5-fold increase in cell adhesion on the peptide-modified surfaces when compared to unmodified PDMS control surfaces.

Tris(pentafluorophenyl)borane is a good catalyst for the preparation of functionalized siloxanes such as (III) and (VI) by Piers—Rubinsztajn reaction of alkoxysilanes with hydrosilanes.

Two strategies were developed for the attachment of sugars to siloxanes using bifunctional silicon linkers: the substrate could be functionalized with a silyl hydride before coupling to a vinyl-terminated siloxane through platinum catalyzed hydrosilylation; alternatively, unprotected glucose could be directly silylated by a silicone terminated with a chlorosilyl group. Optimal steric bulk was found with difunctional diisopropylsilanes, which exhibit excellent reactivity for preparation of sugarsilane derivatives, and also permit efficient grafting to silicones via hydrosilylation. The resulting product alkoxysilane-silicone exhibits greater stability to hydrolysis than the silicone itself.

Hydrophilic silicone polymers offer advantageous properties in a variety of applications. However, it is not always straightforward to control the placement of hydrophilic domains in a hydrophobic silicone elastomer. A facile method for the preparation of poly(ethylene oxide)(PEO)-modified PDMS elastomers is described. Hydrosilane rich elastomers are fabricated by adding poly(hydromethylsiloxane) to a standard addition cure elastomer formula. After curing the elastomer, the silicones can be modified using hydrosilylation with mono- and di-allyl pol(ethylene oxide) of varying molecular weights to give PEO-rich silicone surfaces. The efficiency of the grafting process, as measured by PEO on the surface, depends both on molecular weight and functionality of the PEO. By contrast, when the allyl functional PEO is added directly to the elastomer preparation (co-cure), silicone elastomers with internal PEO domains are formed: SiH rich polymers present preferentially at the external interface.

Few routes to well-defined 3D silicone structures exist because of their susceptibility to depolymerization/metathesis in the presence of acids or bases. The Lewis acid B(C6F5)(3) can be employed to condense hydrosilanes with alkoxysilanes, producing siloxanes and alkanes (R3SiH+R'OSiR ''(3) -> R3SiOSiR ''(3) + R'H). We demonstrate that balancing the steric demands at both the hydrosilane and alkoxysilanes, and the careful control of reaction conditions, permits clean condensation reactions to occur in the absence of competing metathesis processes. The resulting linear or highly branched siloxane compounds can be rapidly and easily assembled into explicit, complex 3D silicone structures in high yield.