IR-Imagable Lithographic Precursor Composition comprising acyclic onium cations

Disclosed is a composition comprising a polymer which contains hydroxyl groups, as herein defined, when used as a coating for an infrared-imageable lithographic precursor, the composition comprising one or more agent(s) which: a) absorbs infra red radiation of wavelength greater than 800 nm and consequently generates heat; b) functions as an insolubiliser which inhibits dissolution of non-imaged regions of the coating in a developer but permits dissolution of imaged regions during development; and c) improves the inhibition to dissolution of the non-imaged regions and/or the dissolution of the imaged regions so as to improve the dissolution contrast ratio (DCR) of the non-imaged/imaged regions; wherein the agent which performs function c) either comprises i) an acyclic onium cation (such as phosphonium and iodonium cations) or carbocation and a hydrophobic anion having at least one of a hydrophobic alkyl group, a hydrophobic silicone containing group, a hydrophobic aryl group, a carboxylate or sulfonate made hydrophobic by the presence of fluorine, silicone, fatty alkyl or aryl moieties, or ii) comprises an acyclic onium cation having at least one of hydrophobic alkyl or fluoralkyl, hydrophobic silicone containing group or hydrophobic aryl, and an alkyl or aryl or sulfonate anion, with the exclusion of anions that have substituents with an alkali dissociative proton.