Relative activity of hexafluorobutadiene‐1,3 in polymerization and copolymerization reactions with other dienes

Abstract The effect of conjugation on the reactivity of perfluorinated diolefins has been little investigated. A characteristic representative of this class of compounds is hexafluorobutadiene, the activity of which in polymerization reactions is much less than that of tetrafluoroethylene. There is an inadequacy of published data on the polymerization of hexafluorobutadiene. We have investigated the conditions for the polymerization of this compound and have found that it takes place only in emulsions in the presence of a cationactive emulsifier in acid medium (pH 1–3) in the presence of a radical type of initiator. The effect of the basic parameters on the emulsion polymerization was investigated. The hexafluorobutadiene polymer obtained in emulsion, in contrast to the polytetrafluoroethylene, is characterized by a low melting point and little stability. It is insoluble in most organic solvents. To ascertain the relative activity of hexafluorobutadiene as compared with other dienic compounds a study was made of copolymerization with chloroprene, fluoroprene, and isoprene, both in emulsion and in solution, and the reactivity constants were determined. The monomer reactivity ratios of the systems are as follows. Chloroprene‐hexaflurobutadiene: r 1 = r 2 = 0.1; fluoroprene‐hexafluorobutadiene: r 1 = 2.93, r 2 = 0.24; isoprene‐hexafluorobutadiene: r 1 = 1.19, r 2 = 0.78. On the basis of the monomer reactivity ratios in the monomer‐hexafluorobutadiene systems and of reported data on the ratios for chloroprene‐fluoroprene and isoprene‐fluoroprene copolymerization, the relative reactivity of the monomers was calculated with respect to a common radical, the relative reactivity constant of the radical and its monomer being taken as unity. Chloroprene is 10 times more active than hexafluorobutadiene with respect to the radical of the latter; it is 8 times as reactive as isoprene and 2.4 times as reactive as fluoroprene. The results are in conformity with data on the separate polymerization of the monomers in emulsion. The considerable fall in activity of hexafluorobutadiene in polymerization and copolymerization reactions can probably be interpreted by localization of π‐electrons at the double‐bonded carbon atoms and weakening of the conjugation effect owing to a shift in electron density to the highly polar fluorine atom. Similar effects were observed for hexafluorobutadiene in diene synthesis.