As the acrylic or methacrylic monomer having a nucleus-halogen-substituted aromatic ring and a hydroxyl group in the molecule (hereinafter referred to as monomer (a) for brevity), compounds represented by the following formulae (I), (II) and (III) are preferably used in the present invention: ##STR1## wherein X is chlorine, bromine or iodine, each of R1 and R2 is a methyl group or hydrogen, n is