US 10,303,056 B2  54  53  -continued  -continued  In the case of a monomer having a hydroxyl group, the  hydroxyl group may be replaced by an acetal group suscep- tible to deprotection with acid, typically ethoxyethoxy, prior  to polymerization, and the polymerization be followed by  deprotection with weak acid and water. Alternatively, the  hydroxyl group may be replaced by an acetyl, formyl,  pivaloyl or similar group prior to polymerization, and the  polymerization be followed by alkaline hydrolysis.  The polymer may further comprise recurring units of at  least one type selected from recurring units having the  formula (dl), recurring units having the formula (d2), and  recurring units having the formula (d3). These recurring  units are referred to as recurring to units (dl), (d2) and (d3),  respectively.  RA  RA  RA  2  CC) ~  ~  0  0  0  0  ~o  ~o  0  0  HN-{  s-{  s-{  0  0  0  XR"  YRA  XR’  (yo  0  0  HN  0  ~  I  (yo  ox:•  RA  RA  )~o  ::to  ~o ~o  HN-{  s-{  0  0  RA  o+  o~o  0  0  ~o  HN-{  0  RA  RA  o~o  0  0  0  0  ~o  HN-{  0  s-{  0  (dl)  ~  RI!  I  R12_ 8 +_R13  M-