Hemisilicone Elastomers That Are Recyclable to the Monomer

Methyl-, vinyl-, and hydride-terminated polymers of the heterocyclic monomer, 2,2,5,5-tetramethyl-2,5-disila-1-oxacyclopentane (c-M₂E) were prepared by sulfuric acid-catalyzed, ring-opening equilibration with the end-capping agents hexamethyldisiloxane (MM), divinyltetramethyldisiloxane (M^VM^V), and tetramethyldisiloxane (M^HM^H), respectively. The molecular weights of the polymers were controlled by adjusting the ratio of monomer to end-capping agent. All of these polymers are oils and exhibit molecular weight-dependent viscosities that are qualitatively similar to those of polydimethylsiloxane (PDMS)-based analogs prepared by the same reaction using octamethylcyclotetrasiloxane (D₄) instead of c-M₂E. Vinyl end-capped polymers with a range of molecular weights were cross-linked by platinum-catalyzed hydrosilylation with tetramethylcyclotetrasiloxane (D^H₄) to prepare a series of transparent solid elastomers with moduli that increase with decreasing molecular weight. These studies suggest that reactive polymers prepared from c-M₂E may be useful resins in two-part curable elastomer formulations. Several experiments, as well as the over 60-year-old initial synthesis of this polymer, suggest that the recyclability of these resins and elastomers may be practical.