A polymerizable monomer represented by the general formula (1) ##STR63## wherein R.sup.1 is a hydrogen atom, methyl, chlorine or cyano, R.sup.2 is alkylene having 1 to 4 carbon atoms, R.sup.3 is alkylene having 3 to 10 carbon atoms, R.sup.4 is alkyl having 6 to 18 carbon atoms, R.sup.5 to R.sup.8 are the same or different and are each alkyl or substituted alkyl having 1 to 3 carbon atoms, A is methylene, phenylene, substituted phenylene, --CH.sub.2 O--, --CH.sub.2 CH.sub.2 O--, --CO--, --CO--N(R.sup.9)-- (wherein R.sup.9 is a hydrogen atom or methyl) or vinylene, m is 0 or 1, and X and Y are the same or different, and are each a monovalent anion or form a bivalent anion when taken together.