Creating Silicones: Exerting Control at Interfaces

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In spite of their higher cost than organic alternatives, silicone polymers are found in almost every technological area of developed economies because of their unique interfacial behavior. Lacking efficient syntheses, most commercial silicone polymers are ill-defined mixtures with respect to molecular weight, frequency and type of branching, distribution of functional groups and network structures. The hypothesis driving the research program is that silicone polymers of precise structure will improve our ability to reinforce interfaces, leading to higher value materials with enhanced properties. In addition to pure silicones, new polymers with new hydrophilic functionalities will be prepared that can enhance our ability to control heterogeneous interfaces. The outcomes of the proposed research will be new synthetic strategies leading to novel silicone polymers with applications ranging from self-lubricating contact lens surfaces to thermally stable LED domes.***New strategies to use the Piers-Rubinsztajn reaction (PR, R3SiH + R'OSilicone -> R3SiOSilicone (or R'OAr -> R3SiOAr) in the presence of B(C6F5)3) to create novel materials was an important outcome of the last 5 years. Structure matters! Small structural differences in the head group of branched silicone surfactants led to large changes in surface activity. This concept will be extended to yield a library of complex 3D silicone structures, including bottlebrush polymers, that will be assembled from precise dendrons in a ‘mix and match' manner. ***Tuning behavior at interfaces requires new routes to hydrophilically modified silicones. New metal free strategies to link silicone to small and polymeric hydrophiles, particularly those based on natural materials, using xanthates, hydrazones and additionalmetal free click chemistry will be developed with hydrophiles. Hydrophiles will include lignin and saccharides such as guar and hyaluronic acid because they are associated with biocompatible surfaces. Green composites will be formed using these principles, by diluting of silicones with natural, renewable, biodegradable materials.***Achieving these outcomes requires thorough characterization of the polymers and composites prepared in this program. This will include physical testing (modulus and extension at break), surface analysis (adhesion (peel tests), XPS), in addition to molecular characterization (NMR, MS).***An important aspect of reaching the proposed scientific objectives is continued training of HQP (last 6 years: 32 undergrad, 8 MSc, 13 PhD students, 8 PDFs) in technical areas, such as polymer/materials synthesis and characterization. This will enhance the HQP's ability to attain employment in academia and industry, particularly the 3 silicone and the many polymer companies located in Southern Ontario. Training in polymer processing is required for Canada's continued economic growth.**