Vinyl polymers are a group of polymers derived from vinyl monomers. Their backbone is an extended alkane chain, made by polymerizing an alkene group (C=C) into a chain (..-C-C-C-C-..). In popular usage, "vinyl" refers only to polyvinyl chloride (PVC). A very thin film of monomer was prepared in a vacuum chamber on a tantalum substrate at -173°C and then photopolymerized. Due to the poor penetration depth of the radiation, thin polymer films with thickness several micrometres were obtained nevertheless with degree of polymerization in the 10,000 range.