toms; R2 is hydrogen or an alkyl group having 1 to 9 carbon atoms, an alkenyl group having 1 to 9 carbon atoms or an aryl group having 6 to 9 carbon atoms; T is alkylene (straight-chain and branched alkylene) having 1 to 4 carbon atoms such as methylene, ethylene, propylene, butylene, etc., or arylene having 6 to 9 carbon atoms; n is 0 or 1; S1 and S2 are, independently of one another, ???OCkH2k??