Polyvinylidene chloride or Polyvinylidene dichloride (PVDC) is a homopolymer of vinylidene chloride. PVDF resin is produced through polymerization of the vinylidene fluoride monomer. Saran wrap, formed from polymerization of vinyl chloride and vinylidene chloride, is an addition copolymer. PVDF is obtained through the polymerization of the vinylidene fluoride monomer. All FKMs contain vinylidene fluoride as a monomer. The methyl vinylidene content of PIB controls its reactivity toward maleic anhydride. Related compounds include vinylidene chloride and vinylidene fluoride. VDF/HFP is a copolymer system of vinylidene fluoride and (at least 20%) hexafluoropropylene. It and vinylidene fluoride are precursors to commercially useful polymers. Addition of electrophiles to vinylidene ligands also affords carbyne complexes. Many vinylidene and vinylene compounds polymerize in the same manner. Interest then moved to look at whether structures equivalent to vinylidene (Si=SiH) existed.