Feb.28,2019  16  US 2019/0064665 Al  [0122]  It is noted that in the above formulae (L4-1) to  (L4-4), (L4-3-l) and (L4-3-2), and (L4-4-1) to (L4-4-4), the  bond direction is on the exo side relative to the bicyclo[2.  2.l]heptane ring, which ensures high reactivity for acid  catalyzed elimination reaction (see JP-A 2000-336121). In  preparing these monomers having a tertiary exo-alkyl group  of bicyclo[2.2.l]heptane skeleton as a substituent group,  there may be contained monomers substituted with an  endo-alkyl group as represented by the following formulae  (L4-1-endo) to (L4-4-endo ). For good reactivity, an exo  proportion of at least 50 mo! % is preferred, with an exo  proportion of at least 80 mo! % being more preferred.  [0123]  Illustrative, non-limiting examples of the acid  labile group of formula (L4) are given below.  Herein  RL 41  is as defined above.  [0125]  Illustrative examples of the recurring units of for› mula (a) are given below, but not limited thereto. Herein  RA  is as defined above.  [0124]  Examples of the C$_{4}$ -C$_{20 }$ tertiary alkyl groups, tri› alkylsilyl 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 above for  RL 04 .  -continued  (IA-1-endo)  RM~  (IA-2-endo)  RMA  (IA-3-endo)  RM~  (IA-4-endo) 