U. Heinze

Effective Approaches for Estimating the Functionalization Pattern of Carboxymethyl Starch of Different Origin

Three types of differently prepared carboxymethyl starches were analyzed by HPLC and 1H-NMR spectroscopy after chain degradation. In derivatives obtained in the conventional manner with values of the degree of substitution (DS) up to 0.85; glucose, mono- and di-O-carboxymethyl glucose were detected as building units. Comparison with statistic calculations revealed an even distribution of functional groups along the chain. 1H-NMR studies confirmed a preferred substitution at the 2 position of the repeating unit. Comparable results were obtained for the carboxymethyl ether of amylose, amylopectin and β-cyclodextrin. The analysis of carboxymethylated starch samples prepared using a new synthesis concept via a reactive microstructure revealed a high DS achieved in a one-step synthesis as well as a non-statistic distribution of carboxymethyl groups along the chain. A significant amount of 2,3,4,6-tetra-O-functionalization, caused by the branched structure of starch, was found. Moreover, carboxymethylation of 6-O-triphenylmethyl starch and subsequent detritylation yields a regioselectively functionalized polymer consisting not only of the expected mono- and di-O-carboxymethylated repeating units but also containing a significant amount of 2,3,4-tri-O-functionalized anhydro-glucose units.

Development and evaluation of methods for determining the pattern of functionalization in sodium carboxymethylcelluloses

SUMMARY: Sodium carboxymethylcellulose (NaCMC) with varying degrees of substitution (DS) was investigated with different analytical methods in order to characterize the functional group distribution. The following methods were tested and adapted: high-resolution 13 C NMR spectroscopy in the solid state ( 13 C CP/ MAS NMR) and 13 C NMR spectroscopy on solutions of NaCMC samples with a reduced molar mass. Partial degradation was accomplished by ultrasonic means and with the enzyme endoglucanase. Combining the two techniques resulted in the greatest reduction in molar mass and hence in the best spectral resolution. Analysis of the NaCMC fragments following ultrasonic and/or endoglucanase degradation also reveals another interesting experimental finding. It appears that ultrasonic degradation is favored at unsubstituted areas near the center of the chain. These methods were compared with the following already familiar techniques of analysis: titrimetric techniques; 13 C and 1 H NMR spectroscopy as well as HPLC on completely hydrolysed solutions (hydrolysis with perchloric acid, trifluoroacetic acid and sulfuric acid). All of the methods characterize the samples as a series with increasing DS, the values of which range from 0.9 to 2.4. Methods that permit analysis of the partial degree of substitution produced the distribution x 2 A x6 A x3. Therefore, they are in principle suited for determining the functionalization pattern of the NaCMC samples relative to one another. The most suitable method can therefore be selected according to the objectives and the apparatus available. However, the measured values do exhibit considerable spread, variances of approx. 20%, thus, place restrictions on using the values of DS or xi in absolute comparisons beyond these methods.

Characterisation of regioselectively functionalized 2,3-O-carboxymethyl cellulose by enzymatic and chemical methods

The determination of the molecular structure of 2,3-O-carboxymethyl cellulose (2,3-O-CMC), prepared via 6-O-(4-monomethoxy)triphenylmethyl cellulose, was carried out in detail by means of enzymatic and chemical methods. The 2,3-O-CMCs had degrees of substitution (DS) in the range of 0.5–1.2 showing a narrow molar mass distribution as revealed by SEC. As a result of an endoglucanase treatment, an intensive depolymerization of the samples occurred which was more pronounced for 2,3-O-CMC with comparatively low DS. All degraded samples could be separated into 18 fractions by preparative SEC and the proportion of each individual repeat unit was analysed by anion exchange chromatography (AEC) following complete hydrolytic chain degradation. The results indicated a homogeneous distribution of the functional groups within the polymer chain. Moreover, it became obvious that a preferred carboxymethylation of O-2 compared with O-3 occurred and that a preferred functionalization of already carboxymethylated units occurred as the reaction progressed. AEC with pulsed amperometric detection, which was used to separate and analyse the differently functionalized repeating units as well as glucose, had to be calibrated. Therefore, a method to determine the response factors of the individual carboxymethylated glucose units was developed using 13C NMR spectroscopic measurements (inverse gated decoupling) of depolymerised 2,3-O-CMC.

Starch Derivatives of High Degree of Functionalization. 4. Homogeneous Tritylation of Starch and Subsequent Carboxymethylation

The synthesis of monomethoxytriphenylmethyl (MMtrityl) starch and the subsequent carboxymethylation of the 6-O-functionalized products were investigated. The trityIation both in N,N-dimethylacetamide (DMA)/LiCl and in dimethyl sulfoxide (DMSO) occurred homogeneously. The highest degree of substitution of trityl groups (DSTrityI) obtained after a single conversion step was 0.77 in both solvents. A complete functionalization of primary OH-groups was achieved only with unsubstituted triphenylmethyl chloride in these reaction media. In case of monomethoxytriphenylmethyl chloride (MMTMC) as reagent an additional conversion step is necessary to synthesize products with a DSTrityI = 1. The structure of the products was analyzed by FTIR- and 13C-NMR spectroscopy. Subsequent carboxymethylation of the MMtrityl starch samples leads to products with a preferred functionalization of the unprotected secondary OH-groups. After removal of the trityl moieties, the DSCM and the distribution of carboxymethyl groups within the anhydroglucose unit was investigated by means of HPLC and 1H-NMR spectroscopy. The carboxymethylation was more effective at O-2 than at O-3. In case of ether products with DSTrityl < 1 a partial substitution of the primary OH group took place as well.

New Highly Functionalised Starch Derivatives

Pure, well soluble p-toluenesulfonyl (tosyl) starch samples with a DSTos range from 0.4 to 2.0 were prepared by reacting starch with tosyl chloride in the presence of triethylamine dissolved in the solvent N,N-dimethyl acetamide in combination with LiCl. The thermal degradation starts at a temperature of 166 °C for a sample with DSTos of 0.61 which is sufficiently high for subsequent modifications of the remaining OH groups, for instance by acylation reactions. The total DSTos can be determined using the signal of the methyl protons of the tosyl, acetyl or propionyl moieties of peracylated samples. Moreover, the NMR characterisation reveals that a predominant functionalisation at position 2 occurs. On the other hand, 6-O-tosyl starch products can be synthesised via 2-O-acetyl starch which is accessible by a new acylation procedure. The functionalisation patterns of new synthesised polymers with an unusual distribution of functional groups and high DS values were unambiguously characterised by various NMR techniques.