NEW MATERIAL:A trialkyl or triphenyltin ester of an α-methyleneδ-methyladipic acid expressed by formulaI[X is SnR (R is alkyl or phenyl)].

USE: Useful as a raw material for copolymers used in coating materials for antistaining or antimicrobial use, characterized by the high copolymerizability and low homopolymerizability of the group of the double bond in the molecule and further the sterilizability unique to the tin-containing compound.

PROCESS: An alkali metallic salt of an α-methylene-δ-methyladipic acid expressed by formula II (Z is Na or K) is reacted with a trialkyltin halide or triphenyltin halide in the presence of a quaternary ammonium salt, etc. at 30W100°C to give the compound expressed by formulaI. A small amount of a polymerization inhibitor, e.g. hydroquinone, is preferably added to the reaction mixture.