T- and Q-rich Linear Silicones from the Piers-Rubinsztajn Reaction

Most silicone polymers are linear compounds derived from dimethylsiloxane (D) monomers; the incorporation of tri- (T) and tetra-functional (Q) monomers usually leads to elastomers. MQ or MT resins, high value materials used as reinforcing agents, are exceptions in that they are very highly branched, and highly reticulated but remain mobile and fluid. We report the formation of analogous linear T- and Q-rich polymers. The Piers-Rubinsztajn (PR) reaction between Si(OEt)4 and HSiMe(OSiMe3)2 led to mixtures of highly branched monomers that were separated by distillation to provide mono- and dialkoxy-Q monomers. Chain extension, also using the PR reaction with telechelic HSi-modified silanes, led to small to medium size linear polymers that were rich in T and Q groups. The polymers were mobile fluids, typically with only slightly higher viscosities than their unbranched counterparts. Alternating silphenylene Q(TM2)2 copolymers were also fluids as a consequence of steric inhibition of aromatic group association. The PR reaction provides a simple and viable strategy to introduce spatially controlled branching in pure, linear silicone polymers.