A polymer comprising recurring units having an acid generator bound to the backbone, and recurring units having an optionally acid labile group-substituted carboxyl group and/or recurring units having an optionally acid labile group-substituted hydroxyl group is obtained by polymerizing corresponding monomers under such illumination that the quantity of light of wavelength up to 400 nm is up to 0.05 mW/cm2. The polymer avoids photo-decomposition of the acid generator during polymerization and concomitant deprotection reaction of the acid labile group when used in positive resist compositions. A pattern with high dissolution contrast and rectangularity is formed after development.