Photopolymerizable composition comprising α,αdiketone catalyst

Claim 1

A polymeric composition capable of being shaped and which is formed by partially reacting a mixture comprising: (a) 5% to 95% by weight of the precursors of a polyurethane comprising at least one polyisocyanate and at least one polyol free of ethylenic unsaturation and having isocyanate-reactive groups; (b) 95% to 5% by weight of the precursors of a cured polyester resin comprising at least one ethylenically unsaturated polyester reactive with said polyisocyanate and at least one ethylenically unsaturated monomer copolymerisable therewith, wherein the mixture is reacted to an extent such as to produce a handleable composition which is capable of being shaped; and (c) at least one photosensitive catalyst capable of initiating copolymerisation of the ethylenically unsaturated polyester and the ethylenically unsaturated monomer upon exposure of the composition to visible radiation said photosensitive catalyst comprising at least one photosensitiser and at least one compound having the structure ##STR9## where the units R, which may be the same or different, are hydrogen atoms, hydrocarbyl groups, substituted hydrocarbyl groups or groups in which two units R together with N form a cyclic ring system, no more than two of the units R being hydrogen atoms, and where N is attached directly to a hydrocarbyl group R, at least one of the groups R has a ##STR10## group attached to N, said photosensitiser having the structure ##STR11## wherein the groups A, which may be the same or different, are hydrocarbyl or substituted hydrocarbyl groups, and wherein the groups A may be further linked together by a direct link or by a divalent hydrocarbyl group or wherein the groups A together form a fused aromatic ring.