"A polymer according to claim 1, wherein the ethylenically unsaturated monomer is at least one monomer selected from the group consisting of an ethylenically unsaturated compound of the formula: ##STR28## wherein R2 is a hydrogen atom, a halogen atom or a substituted or unsubstituted C1-C 10 monovalent hydrocarbon group, and R3 is a hydrogen atom, a halogen atom, a substituted or unsubstituted C1-C" . . . . .