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[0130] Examples of the tertiary C$_{4}$ -C$_{20 }$ 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 R 53 , are as exemplified for RL 04 . 

[0131] The (u+l)-valent hydrocarbon or fluorinated hydrocarbon group represented by R5 4 may be straight, branched or cyclic and examples thereof include the fore› going monovalent hydrocarbon or fluorinated hydrocarbon groups from which the number (u) of hydrogen atoms are eliminated. 

[0132] The fluorinated hydrocarbon group represented by Rsa may be straight, branched or cyclic and examples thereof include the foregoing monovalent hydrocarbon groups in which some or all hydrogen atoms are substituted by fluo› rine atoms. Illustrative examples include trifluoromethyl, 2,2,2-trifluoroethyl, 3,3,3-trifluoro-l-propyl, 3,3,3-trifluoro- 2-propyl, 2,2,3,3-tetrafluoropropyl, 1, 1,1,3,3,3-hexafluor› oisopropyl, 2,2,3,3,4,4,4-heptafluorobutyl, 2,2,3,3,4,4,5,5- octafluoropentyl, 2,2,3,3,4,4,5,5,6,6, 7, 7- dodecafluorohepty 1, 2-(perfluoro butyl )ethy 1, 2-(perfluorohexyl)ethyl, 2-(perfluorooctyl)ethyl, and 2-(per› fluorodecy 1 )ethyl. 

[0133] Examples of the recurring units having formulae (IA) to (IE) are shown below, but not limited thereto. Herein RA is as defined above. 

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