US 9,052,592 B2  63  64  -continued  -continued  (r-pr-cm4)  (r-pr-cm5)  (r-pr-cm7)  ~  ~  (r-pr-cmS)  (r-pr-csl)  (r-pr-cs2)  [Chemical formula 26]  (al-r-3)  0  Ra’ 7  _LO+Ra’ 8  Ra’ 9  (r-pr-c3)  *  (r-pr-c2)  *  *  (r-pr-cl)  (r-pr-cs5)  (r-pr-cs4)  (r-pr-cs3)  Tertiary Alkyloxycarbonyl Acid Dissociable Group:  Of the above-described polar groups, examples of the acid  dissociable group which protects a hydroxyl group include an  acid dissociable group represented by the following general  formula (al-r-3) (hereinafter, sometimes referred to as "ter- tiary alkyloxycarbonyl acid dissociable group" for the sake of  convenience).  In the formula, each of Ra 0  to Ra’ 9  represents an alkyl  group.  In the formula (al-r-3), eachofRa 0  to Ra’$^{9 }$is preferably an  alkyl group having 1 to 5 carbon atoms, and more preferably  an alkyl group having 1 to 3 carbon atoms.  In addition, the total number of carbon atoms of the respec- tive alkyl groups is preferably 3 to 7, more preferably 3 to 5,  and most preferably 3 to 4.  Examples of the constituent unit (al) include a constituent  unit derived from an acrylic ester in which the hydrogen atom 