rein R.sup.1 denotesa hydrogen atom, a halogen atom, a cyano group or a monovalent organic group, R.sup.2 denotes a bivalent organic group being cleaved by an acid catalyst to dissociate R.sup.3, R.sup.3 denotes a monovalent organic group having at least one polymerizablesubstituent group, and m is an integer of 2 or more.2.