The polymer of claim 1, wherein the acid labile group is a C4-20 -tertalkyl group, a tri-C1-10 -alkylsilyl group, a C4-20 -oxoalkyl group, or a group of formula (5) or (6): ##STR51## R7 and R8 each are a hydrogen atom or normal, branched or cyclic alkyl group having 1 to 8 carbon atoms, R9 is a monovalent hydrocarbon group of 1 to 18 carbon atoms, which may have a hetero atom, R7 and R8, R7 and R9