Carboxymethylation of cellulose in unconventional media

Abstract

Carboxymethylation of cellulose in the new and highly efficient aqueous solvent Ni(tren)(OH)2 (trenDtris(2-aminoethyl)amine) and in melts of LiClO4 3H2 Oo rN-methyl- morpholine-N -oxide (NMMNO), which is now widely applied for cellulose fibre production, was investigated. In case of Ni(tren)(OH)2, a totally homogeneous carboxymethylation of cellulose with sodium monochloroacetate, in the presence of an aqueous NaOH solution is possible for the first time. Structure analysis by means of HPLC and 1 H-NMR after chain degradation showed results comparable with findings for CMC obtained by the heterogeneous slurry process, that is, a statistic distribution of substituents along the polymer chain and functionalisation of the hydroxyl groups in the order C-6 C-2> C-3. The etherification of cellulose in a melt of LiClO43H2O, a new type of cellulose solvent, was shown to be possible and gave products of a statistic functionalisation pattern as well. In contrast, carboxymethyla- tion starting from solutions of cellulose in NMMNO initiated with solid NaOH particles yields polymers with a nonstatistic distribution of functional groups along the chain, as observed for cellulose ethers prepared in reactive microstrctures starting from solutions of cellulose inter- mediates in dimethyl sulfoxide as well as of unmodified cellulose dissolved in N,N-dimethyl acetamide/LiCl.