Positive resist material and patterning process

A positive resist material comprising:

• an acid generator;
• and
• a base polymer comprising a repeating unit comprising two carboxyl groups whose hydrogen atoms are substituted with two tertiary carbon atoms each bonded to a double bond or triple bond, wherein
• the repeating unit comprising two carboxyl groups whose hydrogen atoms are substituted with two tertiary carbon atoms each bonded to a double bond or triple bond is a repeating unit-a in the following formula (1),
• wherein RA's are identical to or different from each other and each represent a hydrogen atom or a methyl group;
• X1 and X3 each represent a single bond, a phenylene group, or a linking group having 1 to 12 carbon atoms containing at least one selected from the group consisting of an ester bond, an ether bond, and a lactone ring, provided that the linking group excludes the following formula (1′);
• R1 to R4 each represent a linear, branched, or cyclic alkyl group having 1 to 8 carbon atoms;
• and X2 represents a vinylene group or an ethynylene group,
• wherein an oxygen atom in the formula (1′) is bonded to a carbon atom of a carboxyl group in the formula (1);
• and each broken line represents a bonding arm.