US 10,054,853 B2  57  58  -continued  While the foregoing examples correspond to those units  wherein  zA  is a single bond,  zA  which is other than a single  bond may be combined with similar acid labile groups.  Examples of units wherein  zA  is other than a single bond are  substantially the same as illustrated above.  In formula (7), R $^{1 }$is as defined above, and  yA  is hydrogen,  or a polar group having one or more structures selected from  among hydroxyl, cyano, carbonyl, carboxyl, ether bond,  ester bond, sulfonic acid ester bond, carbonate bond, lactone  ring, sultone ring, and carboxylic anhydride.  Illustrative, non-limiting examples of the recurring units  having formula (7) are shown below. Herein R $^{1 }$is as defined  above.  H  ’j==o  (++)  H  ’j==o  (++)  H  ’j==o  HO~OH  OH 