287  US 9,411,230 B2  288  -continued  n represents an integer of 1 to 5. n is preferably an integer  of2 to 4.  Specific examples of the repeating unit containing a fluo› rine atom or a silicon atom are illustrated below. In specific  examples, X, represents a hydrogen atom, -CH$_{3}$ ,  -F or  -CF$_{3}$ ,  andX$_{2 }$ represents -F or----CF$_{3}$ .  X1  I  --+CH2-Cr  OAO  ’Yy’  F~F  F  X1  I  --+CH2-Cr  OAO  F3C+CF3  ~~'  F  X2  I  --+CH2-Cr  OAO  ~ 