nched alkyl group having 1 to 22 carbon atoms, an aralkyl group having 7 to 22 carbon atoms, or a substituted or unsubstituted phenylgroup, andan aryl triflate compound of the formula: ##STR18## wherein R is a linear or branched alkyl group having 1 to 22 carbon atoms, an aralkyl group having 7 to 22 carbon atoms, or a substituted or unsubstituted phenyl group.5.