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.