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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). 

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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 ). 

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Herein RL 41 is as defined above. 

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. 

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. 

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