Polymerizable tertiary ester compound, polymer, resist composition, and patterning process

A polymer comprising any one or more kinds of repeating units represented by the following general formulae (2a) and (2b),

• wherein R1a represents a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group;
• R1b represents a methyl group;
• each of R2 and R3 independently represents a linear, a branched, or a cyclic monovalent hydrocarbon group having 1 to 15 carbon atoms, or R2 and R3 may combine with each other to form a non-aromatic ring having 3 to 8 carbon atoms together with the carbon atoms to which they are bonded;
• Z represents a divalent group forming a substituted or an unsubstituted cyclopropane, cyclobutane, cyclopentane, cyclohexane, or norbornane ring together with the carbon atom to which it is bonded;
• Aa represents a linear, a branched, or a cyclic divalent hydrocarbon group having 1 to 10 carbon atoms;
• Ab represents a linear, a branched, or a cyclic divalent hydrocarbon group having 1 to 6 carbon atoms;
• Ac represents a single bond or a linear, a branched, or a cyclic divalent hydrocarbon group having 1 to 10 carbon atoms;
• R4 represents a hydrogen atom, or a linear, a branched, or a cyclic monovalent hydrocarbon group having 1 to 15 carbon atoms, and when R4 is a monovalent hydrocarbon group, —CH2— may be substituted with —O— or —C(═O)—.