prov:value
| - (3) ##STR19## wherein R.sup.1, R.sup.2, Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.5, Ar.sup.6, Ar.sup.7, Ar.sup.8, X and Y are the same asthose previously defined in formulas (1) and (2); and n is an integer of 2 to 5000.It is preferable that the repeat unit of formula (3) be represented by the following formula (5): ##STR20## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X, Y and n are the s
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