Positive resist compositions and patterning process

A positive resist composition comprising a polymer comprising units A having an exo-form ester group represented by the general formula (1a) and units B having an ester group having two hexafluoroisopropanol groups represented by the general formula (1b) in a molar proportion satisfying:

• 0.1≦A/(A+B)≦0.8 and
• 0.01≦B/(A+B)≦0.9,
• wherein R1 is hydrogen, methyl or CH2CO2R14, R2 is hydrogen, methyl or CO2R14, R3 is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms or a substituted or unsubstituted aryl group of 6 to 20 carbon atoms, R4 to R9, R12 and R13 are each independently hydrogen or a monovalent hydrocarbon group of 1 to 15 carbon atoms which may contain a heteroatom, R10 and R11 are hydrogen, or a pair of R4 and R5, R6 and R8, R6 and R9, R7 and R9, R7 and R13, R8 and R12, R10 and R11, or R11 and R12, taken together, may form a ring, each R being a divalent hydrocarbon group of 1 to 15 carbon atoms which may contain a heteroatom when they form a ring, or a pair of R4 and R13, R10 and R13, or R6 and R8 which are attached to adjoining carbon atoms may bond together directly to form a double bond, R14 is hydrogen or a straight, branched or cyclic alkyl group of 1 to 15 carbon atoms, the formula also represents an enantiomer,
• wherein R15 is hydrogen or methyl, R16 and R17 each are hydrogen or an acid labile group.