US Patent 7482405 Cement additive

The present invention concerns a cement additive containing copolymers comprising one or more constitutional units represented by formula A: (A) R1 is hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkenyl group having 1 to 4 carbon atoms or an aryl group having 6 to 9 carbon atoms; 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 (including 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<_m1+m2<_25.