Abstract: A novel positive photoresist formulation is provided based on a 1:1 copolymer of maleimide and an aliphatic vinyl ether or ester in combination with a photoactive sensitizer capable of undergoing a change in aqueous alkaline solubility upon exposure to actinic radiation. The copolymers disclosed have structures of the following type: ##STR1## where R is an alkyl substituent of from 1 to 20 carbon atoms, benzyl, C.sub.1 to C.sub.10 aralkyl, C.sub.3 to C.sub.12 cycloalkyl or ##STR2## where R" has the structures assigned to R, and where R' is independently H, C.sub.1 to C.sub.10 alkyl, phenyl, benzyl or C.sub.1 to C.sub.10 aralkyl. The polymers are compounded with a photoactive sensitizer capable of undergoing a change in aqueous alkaline solubility upon exposure to actinic radiation such as with diazonaphthoquinone sulfonic acid esters and amides. The polymer and sensitizer compositions are dissolved together in a solvent useful for spin casting of thin films on substrates.