Photosensitive polymeric printing medium and water developable printing plates

A water-developable photosensitive printing medium, comprising,

• a latex copolymer comprising an aliphatic conjugated diene monomer, an .alpha.,.beta.-ethylenically unsaturated carboxylic acid, and a polyfunctional .alpha.,.beta.-ethylenically unsaturated compound;
• a linear thermoplastic, elastomeric block copolymer having at least one unit of a general formula selected from the block copolymer group consisting of (A-B-A), (A-B).sub.n, and (A-B), wherein A is a non-elastomeric polymer block having a number average molecular weight of 2,000 to 100,000 and a glass transition temperature of above about 25.degree. C., and B is an elastomeric polymer block having a number average molecular weight of 25,000 to 1,000,000 and a glass transition temperature below about 10.degree. C.;
• a basic nitrogen atom-containing compound having a tertiary basic nitrogen atom;
• an ethylenically unsaturated compound containing at least one terminal ethylenically unsaturated group, said compound being capable of forming a polymer by free-radical chain polymerization;
• and
• a polymerization initiator which, upon exposure to actinic, light, initiates free-radical chain polymerization of the ethylenically unsaturated compound.

A water-developable photosensitive printing medium, comprising,

• from about 25 to about 75 percent by weight of a latex copolymer comprising from about 5 to about 95 mol percent of an aliphatic conjugated diene monomer, from about 1 to about 30 mol percent of an .alpha.,.beta.-ethylenically unsaturated carboxylic acid, from about 1 to about 30 mol percent of a polyfunctional .alpha.,.beta.-ethylenically unsaturated vinyl monomer, and from about 0 to about 70 mol percent of a monofunctional vinyl monomer;
• from about 15 to about 50 percent by weight of a linear thermoplastic, elastomeric block copolymer having at least one unit of a general formula selected from the block copolymer group consisting of (A-B-A), (A-B).sup.n, and (A-B), wherein A is a nonelastomeric polymer block having a number average molecular weight of 2,000 to 100,000 and a glass transition temperature of above about 20.degree. C., and B is an elastomeric polymer block having a number average molecular weight of 25,000 to 1,000,000 and a glass transition temperature below about 10.degree. C.;
• a basic nitrogen atom-containing compound having a tertiary basic nitrogen atom present in an amount of from about 0.02 to about 2.5 mole per mole of acid groups in the latex copolymer;
• from about 10 to about 60 percent by weight of an ethylenically unsaturated compound containing at least one ethylenically unsaturated group, the compound being capable of forming a polymer by free-radical chain polymerization;
• and
• from about 0.001 to about 10 percent by weight of a polymerization initiator which, upon exposure to actinic light, initiates free-radical chain polymerization of the ethylenically unsaturated compound.