Dec. 3, 2020  79  US 2020/0379345 Al  [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.  -continued 