US 9,703,193 B2  43  44  -continued  -continued  Herein  RL 41  is as defined above.  Illustrative examples of the acid labile group of formula  (L4) are given below.  Examples of the tertiary C$_{4}$ -C$_{20 }$alkyl groups, trialkylsilyl  groups in which each alkyl moiety has 1 to 6 carbon atoms,  and C$_{4}$ -C$_{2}$ ,  oxoalkyl groups, represented by  XA,  are as  exemplified for  RL 04 .  Illustrative examples of the recurring units of formula (2)  are given below, but not limited thereto. Herein  RA  is as  defined above.  (IA-4-endo)  i  ;=a  0  i  ;=a  0  (++)  i  ;=a  0 