PHOTOPOLYMERISABLE COMPOSITIONS

A photopolymerisable composition comprising at least one polymerisable ethylenically unsaturated material and a photo-sensitive catalyst comprising (a) at least one photosensitiser having the structure (I) where R and R1 may be the same or different and each is a hydrocarbyl or a substituted hydrocarbyl group and A is a hydrocarbyl or a substituted hydrocarbyl group or a group of formula (II) or (III) where X and Y may be the same or different and each is hydrogen, a hydrocarbyl group or a substituted hydrocarbyl group (preferably X is R and Y is R1), and (b) at least one reducing agent capable of reducing the photosensitiser when the photosensitiser is in an excited state. In addition, there is described a process for the preparation of a polymeric material which comprises irradiating a photopolymerisable composition as described previously with radiation having a wavelength which is capable of being absorbed by the photosensitiser so as to convert the photosensitiser to an excited state. The compositions are stable in the dark over long periods of time. The combination of photosensitiser and reducing agent produces a composition which is polymerisable at a considerably greater rate than are those compositions which do not contain a reducing agent, but only a photosensitiser.