? or ???OCH2CHR3???, with the proviso that k is 2 or 3, R3 is an alkyl group having 1 to 9 carbon atoms, an aryl group having 6 to 9 carbon atoms; and 6???m 1 +m 2???25. with the proviso that R4 is hydrogen or a methyl group; R5 is hydrogen or a group represented by COOY; Y is hydrogen, an aliphatic hydrocarbon group (including straight-chain, branched, saturated or unsaturated groups) having 1 to