Sustainable polymers from native silicon

Wide-ranging research efforts over the last several decades have pursued the conversion of organic, biobased feedstocks to sustainable polymers with the goal of replacing commodity plastics derived from fossil fuels. In their produced proportions, the six major commodity plastics are 77% carbon, 11% hydrogen, 8% chlorine, and 4% oxygen. This is incongruent with the elemental composition of the earth’s crust, which is mostly oxygen (47%) and silicon (28%), but only 0.02% carbon. Thus silica (SiO₂), which comprises 59% of our terrestrial environment, is an ideal, but mostly ignored inorganic building block for the preparation of large-scale polymers. The conversion of silica to a chemically useful form has heretofore proceeded through carbothermal reduction of Si(IV) to Si(0) followed by oxidation back to Si(IV), an expensive and energy-squandering process. We have demonstrated the direct conversion of native silica (non-redox silica) and biobased diols to discrete alkylorthosilicates, which can immediately function as monomers for polymerization, yielding polyalkylorthosilicates, a.k.a. organoglasses. An acid-catalyzed alkylorthosilicate metathesis reaction has been confirmed and presents a novel pathway for polymerization. The incorporated alkylorthosilicate functionality in this novel family of polymers yields new polymeric properties and provides an opportunity for tuning these polymers toward facile environmental degradation.

Paradigm for the direct conversion of native silicon (silica) to alkylorthosilicate monomers. Their polymerization yields novel thermoplastic polyalkylorthosilicates with desirable properties and pathways for benign degradation in the environment.