Studies on the synthesis and characterization of carboxymethylcellulose

Carboxymethylcellulose (CMC) was prepared in a completely heterogeneous pro cedure in an isopropanol/water slurry and the influence of the reaction con ditions on the pattern of functionalization within the anhydroglucose repea ting unit as well as due to the formation of the four main repeating units (i.e. unfunctionalized, mono-, di-, and tricarboxymethylated) was checked. The concentration of aqueous sodium hydroxide solution, which is used to ac tivate the cellulose, was varied in the range from 8 to 30% at reaction tim es from 2 to 6 h at 55 degrees C. The reaction with sodium monochloroacetat e leads to the highest degree of substitution (DSCMC) of 1.24 at a NaOH con centration of 15% and 5 h reaction time. Using a lye concentration of 30%, no influence of the reaction time between 2 h and 6 h was found. From H-1 NMR spectroscopical studies it was concluded that both the concent ration of the alkali hydroxide solution and the reaction time influence the partial DSCMC at positions O-2 and O-6, while position O-3 shows the lowes t reactivity in any case, independent of the reaction conditions used. With increasing lye concentration, carboxymethylation occurs preferably at O-6. Information about the content of the differently functionalized repeating units can be obtained by chromatographic analysis after complete depolymeri zation of the polymer chains. Surprisingly, in any product synthesized a st atistic content of the building units of the polymer was found even at low activation of cellulose.