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 or arylene having 6 to 9 carbon atoms; n is 0 or 1; S1 and S2 are, independently of one another, ???OCkH2k??? 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