57  US 9,360,753 B2  58  -continued  and Rc1 2 , Rc1o and Rc1 1 , or Rc1 $^{1 }$and Rc1 2 , taken together, may  form a ring, and in that event, each ring-forming R is a  divalent C$_{1 }$-C$_{15 }$hydrocarbon group which may contain a het› eroatom. Also, a pair ofRc 4  and Rc 13 , Rc1o and Rc 13 , or Rc 6  and Rc $^{8 }$which are attached to vicinal carbon atoms may bond together directly to form a double bond. The formula also  represents an enantiomer.  The ester form monomers from which recurring units hav› ing an exo-form structure represented by formula (A-3)-21  are derived are described in U.S. Pat. No. 6,448,420 (JP-A  2000-327633). Illustrative non-limiting examples of suitable  monomers are given below.  Also included in the acid labile groups of formula (A-3) in  recurring units (al) are acid labile groups of(meth)acrylate  having furandiyl, tetrahydrofurandiyl or oxanorbomanediyl  as represented by the following formula (A-3)-22.  Herein, R"’ is as defined above; Rc1 4  and Rc1 5  are each inde- pendently a monovalent, straight, branched or cyclic C$_{1 }$-C$_{10 }$ hydrocarbon group, or Rc1 4  and Rc1 5 , taken together, may  form an aliphatic hydrocarbon ring with the carbon atom to  which they are attached. R c1  $^{6 }$is a divalent group selected from  furandiyl, tetrahydrofurandiyl and oxanorbomanediyl. Rc1  7  is hydrogen or a monovalent, straight, branched or cyclic  C$_{1 }$-C$_{10 }$hydrocarbon group which may contain a heteroatom.  Examples of the monomers from which the recurring units  substituted with acid labile groups having furandiyl, tetrahy› drofurandiyl and oxanorbomanediyl are derived are shown  below. Note that Me is methyl and Ac is acetyl.  (A-3)-22 