Most preferably, R1 and R2 are both methyl.Preferably R3 is an alkyl group having from 1 to 7 carbon atoms, more preferably from 1 to 3 carbon atoms, most preferably methyl, or an alkyl group having from 8 to 22 carbon atoms, more preferably from 10 to 18 carbon atoms, most preferably dodecyl, or a mixture thereof.Suitable cationically modified celluloses have a weight average molecular weight (Mw