where, to simplify, other Pt ligands and other Si substituents are omitted. There are no by-products with this reaction. Molded pieces made with silicone using this addition-cure mechanism are very accurate (no shrinkage). However, handling these twopart products (i.e., polymer and Pt catalyst in one component, SiH oligomer in the other) requires some precautions. The Pt in the complex is easily bonded to electron-donating substances such as amine or organosulfur compounds to form stable complexes with these “poisons,” rendering the catalyst inactive and inhibiting the cure.