Surface-photopolymerization from hexachlorobutadiene

Abstract

Irradiation of C₄Cl₆ vapour at 0.135 Torr with u.-v. light produces a highly carbonaceous polymeric film on illuminated surfaces. The rate of film formation is linearly dependent on light intensity and exhibits an overall negative temperature coefficient with respect to surface temperature which may be represented as an apparent negative activation energy of approximately –18 kcal/mol. Initial surface products have been identified as predominantly C₈ species. The initial gas phase product C₂Cl₄ is followed by formation of C₂Cl₆ and CCl₄. Formation of HCl in the presence of added ethane identifies intermediate formation of chlorine atoms in the gas phase. A suggested mechanism for film growth involves formation of C₄Cl₅· radicals by photodissociation from C₄Cl₆, combination of these to form C₈ species, followed by chlorine-eliminating photoreactions on surfaces to yield radicals capable of producing low vapour pressure, polymeric material. The formation of more chlorinated gas phase products is initiated by the reaction of chlorine atoms with C₄Cl₅· radicals and with C₄Cl₆.