US 9,703,193 B2  41  42  -continued  -continued  (L4-2)  (L4-3)  (L4-4)  In formulas (L4-1) to (L4-4), the broken line denotes a  bonding site and direction. RL 41  is each independently a  monovalent  hydrocarbon  group,  typically  a  straight,  branched or cyclic C$_{1 }$-C$_{10 }$alkyl group, such as methyl, ethyl,  propyl, isopropyl, n-butyl, s-butyl, t-butyl, t-pentyl, n-pen› tyl, n-hexyl, cyclopentyl and cyclohexyl.  For formulas (L4-1) to (L4-4), there can exist enantiomers  and diastereomers. Each of formulae (L4-1) to (L4-4) col› lectively represents all such stereoisomers. When  XA  is an  acid labile group of formula (L4), a plurality of stereoiso› mers may be contained.  For example, the formula (L4-3) represents one or a  mixture of two selected from groups having the following  formulas (L4-3-l) and (L4-3-2).  Similarly, the formula (L4-4) represents one or a mixture  of two or more selected from groups having the following  formulas (L4-4-1) to (L4-4-4 ).  It is noted that in the above formulas (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 bioyclo[2.2.1]  heptane ring, which ensures high reactivity for acid cata› lyzed elimination reaction (see JP-A 2000-336121). In pre› paring 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 formulas (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.  Each of formulas (L4-1) to (L4-4), (L4-3-l) and (L4-3-2),  and  (L4-4-1)  to  (L4-4-4)  collectively  represents  an  enantiomer thereof and a mixture of enantiomers.  Herein  RL 41  is as defined above.  (L4-3-1)  (L4-3-2)  (L4-4-1)  (L4-3-endo)  (L4-2-endo)  (L4-1-endo)  (L4-4-4)  (L4-4-3)  (L4-4-2) 