Precise silicone networks are difficult to prepare from multiple starting materials because of poor spatial control over crosslinkl ocation, competing side reactions, and incompatible catalysts among other reasons. We demonstrate that cure processes catalyzed by B(C 6 F 5 ) 3 (the Piers-Rubinsztajn reaction) and platinum-catalyzed hydrosilylation are perfectly compatible,a nd can be used in either order.I ti sp ossible to perform three different, selective, sequential reactions in the same potu sing H-terminated silicones as chain extenders in all cases to give explicit networks. Eugenol, ar eadily available aromatic compound, acts as at rifunctional crosslinker (HO,M eO, HC= CH 2 ), each functional group of which can be induced to undergo selectiver eaction. With platinum catalysis, the reaction of SiH groups with alkenes is fastest, while B(C 6 F 5 ) 3 catalyzes reaction at phenolsm uch faster than methoxybenzene. Thus, av ariety of H-terminated telechelic siloxanes can be used to form chain extended polymers or elastomers or foams in whicht he morphology of the material and its constituent parts can be manipulated at will.As with most polymers, the current paradigm for the preparation of silicone polymers, including elastomers, should involve enhanced synthetic control such that desired properties can be attained. Structural control, however,isnot ahallmark of silicone elastomers. The three commercialc ure mechanisms normally utilized are radical, moisture cure (room-temperature vulcanization RTV), and platinum-catalyzed hydrosilylation (PtHSi).[1] Radical cure leads to irreproducible, random networks. In selected cases,m oisture cure allows the controlled incorporation of two different silicone polymers through the use of telechelic crosslinkers;more complex structures are difficult to attain. However, network errors occur when competitive hydrolysisl eads to loss of spatialc ontrolo fc rosslinks at ag iven silicon atom (Scheme 1A).Platinum-catalyzed crosslinking (PtHSi), the most common route to high-quality siliconee lastomers, utilizes the combination of telechelic silicones with pendant functional chains.U nfortunately,t he absolutec oncentration of functional groups on ag iven chain and their relative locations along the chain cannotb er eadily controlled (Scheme 1B). The resulting networks reflect the specific batch of pendant-functional polymers used. It is, therefore, difficult to reproducibly preparep recise networks from commercial materials.It is possible to create networks containing av ariety of silicone precursors in as omewhat controlledm anner by using ac ombinationo fo rthogonal cure technologiess elected from silicone and organic chemistry;d ual cure systemst hat combine any of the cure technologiesn oted above with amine/ epoxy, [2] cationic epoxy polymerization, [3] thiol-ene click, [4] or azide/alkyne click [5] allow complex network materials to be prepared. Most of thesep rocesses, however,s till suffer from random placement of crosslinking groups along as ilicone backbone.T...
