Photosensitive compositions and elements for flexographic printing

In a process for making a printing plate, the process comprising the steps of:

• (a) imagewise exposing to actinic radiation a photosensitive printing element comprising support means having thereon a layer of a photosensitive composition;
• (b) removing the unexposed portions of the imagewise exposed layer with a solvent to form a printing plate;
• and
• (c) post development treating the printing plate;
• wherein the improvement comprises using a photosensitive composition comprising a crosslinking photointiator;
• a thermoplastic, elastomeric, asymmetric, star-shaped block copolymer having an asymmetric, star-shaped structure
• (A-B).sub.m -X-(C).sub.n
• wherein
• A is a polymer block of a monoalkenyl arene,
• B is a polymer block of a conjugated diene,
• C is a polymer block of a conjugated diene,
• X is the residue of a multi-functional coupling agent,
• 3<m+n.ltoreq.40,
• the weight average molecular weight of each block A is between about 3,000 and about 125,000 and the weight average molecular weight of each block B and block C is between about 15,000 and about 250,000;
• and a limited amount of an ethylenically unsaturated, crosslinking agent, the ethylenically unsaturated, crosslinking agent being present in the range from 0 to about 1 part by weight per hundred parts by weight asymmetric, star-shaped block copolymer.