US 10,054,853 B2  46  45  -continued  -continued  Examples of the C$_{4}$ -C$_{20 }$tertiary alkyl groups, trialkylsilyl  groups in which each alkyl moiety has 1 to 6 carbon atoms,  and C$_{4}$ -C$_{20 }$ oxoalkyl groups, represented by  XA,  are as  exemplified for  RL 04 .  Illustrative examples of the recurring units of formula (6)  are given below, but not limited thereto. Herein R 1  1s as  defined above.  Herein  RL 41  is as defined above.  Illustrative examples of the acid labile group of formula  (L4) are given below, but not limited thereto.  (IA-4-endo)  H  ’j==o  H  ’j==o  ~  (++)  H  ’j==o  0  (++)  H  ’j==o  0  (++)  H  ’j==o  0  (++)  H  ’j==o  0 