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Abstract

A photopolymer useful in preparing water-developable, solid printing plates is prepared by (A) preparing a urethane prepolymer by reacting a polyoxyalkylene diol (optionally carboxylic acid grafted) with an excess of diisocyanate, followed by chain extending the resulting prepolymer mixture with a dialkylolpropionic acid and preferably with additional diols(s) such as alkane diol(s) and (meth)acrylate-containing diol(s). Use of a new (meth)acrylate-containing diol in such chain extension completes the formation of photopolymer. However, in a third operation (B) hydroxyalkylmethacrylate may be reacted with the result of (A) whether or not (meth)acrylate-containing diol is used in (A). The carboxylic acid groups of the photopolymer may also be partially neutralized with a base. The photopolymer is suitably formulated with additional photoactive (meth)acrylate monomers or oligomers and photoinitiator for casting on a substrate or extruding to form a flexographic printing plate. Following UV exposure of the plate through a negative, unexposed areas can be removed by washing with an aqueous alkaline solution to give a plate with a desirable relief image. The use of the aqueous alkaline washout solution as opposed to organic solvents minimizes pollution problems.

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