Research Interests

There is compelling evidence that chemistry is an important contributor the non-sustainable direction in which the planet is heading. Chemistry MUST be part of the solution. Our hypothesis is that silicones can be a part of a sustainable future.
Silicones undergo degradation in the environment through hydrolysis, oxidation and microbiological processing to give CO2, water and sand. To improve sustainability, we need to reduce the energy content of silicones for a given application, use more natural feedstocks, and better design for (bio)degradability; this would align silicone polymers with the 12 rules of Green Chemistry. Our approaches are summarized below.

A. Sustainable Silicones Using Natural Materials (Green Chemistry Rule 7)

Nature provides many different products that can serve as starting materials for silicones: lipids (255, 302), proteins (145),antioxidants, including vitamins, and saccharides. Some of these can simply act as diluents that should improve degradation in the environment. More interesting is the ability to deliver new function to silicones, including antioxidant properties (300), artificial enzymes (294) and more force responsive, thermoplastic elastomers based on sugar (268).
Bouncing ball on sugar silicones

B. Catalysts are Great (Green Chemistry Rule 9); Would Avoidance Be Better?
Catalysts can dramatically reduce both inputs and waste produced. However, they can also be problematic do to cost or toxicity; silicone elastomers are frequently formed using tin and platinum catalysts. Less problematic catalysts include bleach (282), peroxide, or photogenerated radicals to generate (in some cases, recyclable thermosets (252, 271). Alternatively, simple organic chemistry leads to thermosets from click reactions based on the Huisgen cyclization (244), dynamic, thermoplastic  elastomers using  imine bonds (267, 289),  or even simple ionic bonds (275). We continue to explore simple organic processes that use more benign, or no catalysts at all.

C. Silicone Elastomer Can Benefit from Unusual Fillers
Silicones elastomers are normally reinforced with expensive fumed silica or really expensive MQ resins, without which their properties are relatively poor (e.g., poor tear resistance). We are exploring the use of other materials that could reduce cost while improving the performance of the silicone in use, and facilitate degradation at the end of life. We have published on the use of alpaca wool (hence the picture of the alpaca above, 293). We are expanding the work to other fillers based on saccharides (268), and waste materials that would otherwise go to landfill. 

D. Silicones Degrade Used Tire Rubber - an Egregious, Single Use Elastomer
We reported the ability to completely dissolve used automobile rubber under mild conditions using silicones (265). The process is mild and efficient, but the catalyst makes the process non-competitive on price. We are adapting the process to use less chemistry for new applications, including  silicone elastomers reinforced with automobile rubber.

          Rubber Tires

E. New Routes to Explicit, Functional Silicones
Most silicone polymers are complex mixtures. The Piers-Rubinsztajn reaction
(248) allows exquisite control over synthesis of highly branched structures, as shown in this MDTQ dendron (264). These silicones will be more sustainable, because less material will be needed for a given application; the properties of the compounds are explicit, rather than a composite of the contents of the mixture. We continue to exploit structural control over silicone to optimize existing and target new properties.
MDTQ Silicone
                          dendron from the Piers-Rubinsztajn Reaction

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