Negative-working radiation-sensitive compositions and imageable materials

An imageable element comprising a substrate having thereon an imageable layer comprising:

• a radically polymerizable component,
• a borate initiator composition capable of generating radicals sufficient to initiate polymerization of said radically polymerizable component upon exposure to imaging radiation,
• a radiation absorbing compound,
• a polymeric binder comprising a polymer backbone to which is directly or indirectly linked a pendant group comprising a reactive vinyl group, and
• a primary additive that is a poly(alkylene glycol) or an ether or ester thereof that has a number average molecular weight of from about 200 and up to 4000 and comprises from about 2 to about 50 weight % based on the total dry weight of said imageable layer.

A method of making a negative-working printing plate comprising:

• A) imagewise exposing an imageable element comprising a substrate having thereon an imageable layer comprising:
• a radically polymerizable component,
• a borate initiator composition capable of generating radicals sufficient to initiate polymerization of said radically polymerizable component upon exposure to imaging radiation,
• a radiation absorbing compound,
• a polymeric binder comprising a polymer backbone to which is directly or indirectly linked a pendant group comprising a reactive vinyl group, and
• a primary additive that is a poly(alkylene glycol) or an ether or ester thereof that has a number average molecular weight of from about 200 and up to 4000 and comprises from about 2 to about 50 weight % based on the total dry weight of said imageable layer, and
• B) without a preheat step, developing said imagewise exposed element to remove only non-exposed regions of said imageable layer.