PURPOSE: To obtain the title lightweight resin suitable as optical material, molding material, film, coating compound, especially lens for reforming spectacles, comprising a (co)polymer of a specific (co)monomer.

CONSTITUTION: The aimed resin comprising a homopolymer of a monomer (e.g., 4-vinyl-1,2-1',2,-diphenylenedioxysilane or 4-vinyl-3'-methoxy-1,2-1',2,- diphenylenedioxysilane)shown by the formula [R1 is -CH=CH2, -CH2-CH=CH2, -COOC(CH3)=CH2, -COOCH2-CH=CH2, -OCOO-CH2-CH=CH2, -COO-CH2-C (CH3)=CH2 or -OCOC(CH3)=CH2; R2 is H, OCH3, -SCH3, CH3, C2H5 or -CH=CH2; A is O or S] or a copolymer comprising the monomer and a copolymerizable comonomer.