Abstract: A binder is formed by polymerizing or hardening a binding material or composition, an unsaturated polymer or unsaturated monomer or mixtures thereof (polymer solution), wherein at least part of the unsaturation is ethylenic, preferably of vinyl or acrylic type, by free radical polymerization. The free radical polymerization is caused by contacting the unsaturated binding material with a free radical initiator comprising a peroxide and catalytic agent. In the preferred embodiment the binding material is a solution of an ethylenically unsaturated polymer in a solvent of unsaturated monomeric compound or compounds, in which vinyl or acrylic unsaturation is present. The binder is formed upon polymerization which occurs when the unsaturated monomer, polymer or polymer solution is exposed to the free radical initiator. Subjection of the unsaturated monomer, polymer or polymer solution to the initiator begins the formation of free radicals and subsequently the binding composition is polymerized to form the binder.