A polymer comprising recurring units of the following general formula (1), ##STR45## wherein R1 is hydrogen or methyl, R2 is a normal, branched or cyclic alkyl group of 1 to 8 carbon atoms, R3 is a divalent hydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom, each of R4 and R5 is hydrogen or a monovalent hydrocarbon group of 1 to 18 carbon atoms which may have a hetero atom, let