US 9,164,380 B2  23  24  -continued  -continued  (al-3)  k~~l}  I  O=C  ’--o  I  y2  I  O=C  ’--o  I ,  I  2’  R-C-R  I  0  ~  CH2  ~  y  (al-4)  In the formulas, R, R  11 , R  21 , n, Y and Y 2  are each the same as  defined above, and X 1  represents a tertiary alkyl ester-type 35  acid-dissociable group.  In the above formulas, R is the same as defined for R in  formula (al-0-1).  Examples ofX 1  include the same tertiary alkyl ester-type  acid-dissociable groups as those described above.  R 11 , R 21 , n andY are the same as defined above for R 11 , R 21 ,  n and Y respectively in general formula  (p  1) described above  in connection with the "acetal-type acid-dissociable group".  Examples ofY $^{2 }$include the same groups as those described  above for Y $^{2 }$in general formula (al-0-2).  Specific examples of structural units represented by gen› eral formula (al-1) to (al-4) are shown below.  In the formulas shown below, R"’ represents a hydrogen  atom, a methyl group or a trifluoromethyl group.  [Chemical Formula 8]  (al-1-1)  (all-1-7)  (al-1-6)  (al-1-5)  (al-1-4)  (al-1-3)  (al-1-2) 