65  US 9,360,753 B2  66  -continued  -continued  The acid labile group R $^{2 }$in recurring units (al) may be a  group having the general formula (A-3)-24.  X  (2)  ~  o!)  \  ~  X  (2)  (2)  0  0  I  X  (2) (2)  CN  F  X  X  (2)  0  ~  0  Cl  0  ~o  0  0~  0  0  0  0  0  0 