Resist composition, pattern forming process, polymer, and monomer

A polymer comprising recurring units having the formula (1):

• wherein R1 is hydrogen or methyl,
• R2 is a C1-C20 straight, branched or cyclic divalent hydrocarbon group in which any constituent —CH2— moiety may be replaced by —O— or —C(═O)—,
• R3 and R4 are each independently a C1-C15 straight, branched or cyclic alkyl group, R3 and R4 may bond together to form a ring with the carbon atom to which they are attached, a ring-forming combination of R3 and R4 is a C2-C15 straight, branched or cyclic alkylene group,
• W is —CH2—, —CH2CH2— or —O—, or two separate —H,
• the broken line designates a single bond or divalent organic group bonding the norbornane, bicyclo[2.2.2]octane, 7-oxanorbornane or cyclohexane ring structure to the γ-butyrolactone ring structure, or a structure sharing one or two constituent carbon atoms between these ring structures.