B. Philipp

13C-N.M.R. spectroscopic study of the homogeneous sulphation of cellulose and xylan in the N2O4-DMF system

Abstract By means of 13 C-n.m.r. spectroscopy the substituent distribution within the anhydroglucose and anhydroxylose units, respectively, in the systems N 2 O 4 -DMF-cellulose, and N 2 O 4 -DMF-SO 3 -xylan has been investigated. In the systems containing cellulose, a derivatization exclusively at C-6 is observed on dissolution in N 2 O 4 -DMF and on subsequent reaction with SO 2 , while with SO 3 as the acylating agent some substitution also takes place on the secondary OH groups at higher d.s. The OH groups of xylan are substituted to a rather low d.s. by nitrite ester groups in the system N 2 O 2 -DMF and by sulphate half-ester groups on subsequent reaction with SO 2 or SO 3 . The results are discussed on the basis of a transesterification from the nitrite to the sulphate ester.

Organic-solvents for cellulose as a biodegradable polymer and their applicability for cellulose spinning and derivatization

Abstract After some introductory remarks on cellulose as a renewable and biodegradable polymer and the relevance of new nonaqueous solvent systems for its processing, a survey is presented on the composition, the method of action and potential applications of these solvent systems, with a distinction between “derivatizing” and “nonderivatizing” solvent systems. The mechanism of dissolution is discussed with regard to interaction on the molecular level and with regard to the influence of cellulose physical structure. Among the systems considered for fiber spinning, the aminoxide-based solvent systems are given special attention. As another potential area of application, the use of nonaqueous solvent systems for performing regioselective derivatization at the cellulose molecule is presented briefly.

Studies on the regioselectivity of cellulose sulfation in an N2O4-N,N-dimethylformamide-cellulose system

Abstract Starting from a cellulose trinitrite solution prepared by dissolving the polymer in a N 2 O 4 -Me 2 NCHO mixture, cellulose sulfation was investigated with different sulfating agents under homogeneous reaction conditions. At room temperature the degree of substitution (ds) increased in the order H 2 SO 4 ⪡ H 2 NSO 3 H ∼ NOSO 4 H 2 3 H 3 2 Cl 2 . Generally, the nitrite group in the 6-position was the preferential reaction site at +20°C. With SO 2 Cl 2 the highest ds values are reached, and considerable sulfation in the 2-, and to some extent in the 3-position, was found by 13 C NMR spectroscopy after decomposition of the residual nitrite groups. At −20°C the secondary nitrite groups in the 2-position were definitely the preferred reaction site for sulfation of the cellulose trinitrite with SO 3 . The results are discussed in relation to stability and availability of the nitrite groups.

Static Light Scattering of Polyelectrolyte Complex Solutions

The study of highly diluted polyelectrolyte complex (PEC) solutions by physico-chemical methods allows the assessment of the influence of the molecular characteristics of the polyelectrolyte components and of the external parameters of the systems investigated. Especially static light scattering (SLS) has been proved to provide instructive quantitative data about the course of PEC formation and the structural parameters of the generated particles. After a brief survey of the characterization of PEC solutions by SLS an improved algorithm of light scattering curve analysis for higher aggregated structures is described. Its efficiency will be demonstrated by the results of SLS studies on the complex formation between anionically and cationically modified poly(acrylamide) of high molecular weight in comparison with the information obtained by other methods.

The formation and stability of partially and completely substituted cellulose nitrite esters in dipolar aprotic solvents containing N₂O₄

Abstract As some contradictions still exist concerning the mechanism of cellulose dissolution in N 2 0 4 N,N ,-dimethylformamide and N 2 O 4 -dimethyl sulfoxide systems, the problem of the existence and stability of cellulose trinitrite in these systems has been investigated using 13 C NMR spectroscopy. Cellulose trinitrite is definitely formed as a rather stable compound provided a very low level of water (0.01–0.02%) is maintained in the system. Upon addition of protic liquids (H 2 0 or McOH), decomposition of the nitrite groups takes place in the order of stability C-2 2 O 4 -Me 2 SO system containing some water, a preferred nitrosation in the order C-6 > C-2 > C-3 was observed. The homogeneous nitrosation of cellulose dissolved in LiCI- N,N -dimethylacetamide indicated a reactivity of OH groups in the order C-6 > C-3 ⩾ C-2.

13C- and 23Na-NMR investigations on alkali cellulose

SummarySolid state 23Na- and 13C-NMR spectra of alkali cellulose are presented as a function of NaOH-concentration of the steeping lye, steeping temperature and amount of adhering lye (press factor). Results are discussed with regard to “chemical binding” of NaOH to the cellulose chain in the system cellulose/ NaOH/H2O.

13C-NMR-spectroscopic investigations on precipitated polyanion-polycation-complexes

SummaryHigh resolution solid state 13C-NMR spectra are reported for polyanion-polycation-eomplexes of poly(dimethyldiallyl)-ammonium chloride with some copolymers of acrylic acid and acrylamide, as well as for some component polyelectrolytes. The Coulombic interaction between the macro-ions definitely leads to changes in position and shape of the NMR signals, and an influence of anionic charge density on signal shape is observed. A stepwise transition from a disturbed ladder structure to a scrambled-egg structure with decreasing charge density of the anionic chain in the polysalt is concluded from the experiments.

13C NMR spectroscopic studies on regioselective derivatization of cellulose

ABSTRACT After some comments on the scope of our 13 C liquid NMR spectroscopic investigations as well as on advantages and problems of 13 C NMR application in cellulose chemistry, recent results on the regioselective sulfation and phosphatation of cellulose under homogeneous conditions of reaction are presented, employing cellulose trinitrite, trimethylsilyl cellulose of varying DS and partially substituted cellulose acetates. The effects of type of intermediate as well as of type and amount of esterifying agent on final substituent distribution are described and probable reaction mechanisms are discussed.

23Na‐NMR‐spektroskopische Untersuchungen zum Bindungszustand von NaOH in Alkalicellulose

Mittels 23Na-NMR wurden die Linienbreite Δv1/2 bzw. die transversale Relaxationszeit T2 der Na-Kerne von Alkalicelluloseproben in Abhangigkeit vom Abpresgrad, der Tauchlaugenkonzentration und der Temperatur bestimmt. Der Verlauf von Δv1/2 in Abhangigkeit von der Tauchlaugenkonzentration wird ganz wesentlich vom Abpresgrad bestimmt. Die Ergebnisse werden im Hinblick auf den Bindungszustand des Na in der Alkalicellulose diskutiert. Es wird angenommen, das sich die Gesamtlinienbreite Δv1/2 additiv aus den Beitragen der lokalisiert gebundenen, der delokalisiert gebundenen und der frei beweglichen Na-Kerne zusammensetzt. By 23Na-NMR the line width Δv1/2, and the transversal relaxation time T2 of the Na atoms of alkali cellulose samples were determined in dependence of press factor, steeping lye concentration and temperature. The relationship between Δv1/2 and steeping lye concentration depends to a large extent on the press ratio. The results are discussed in terms of the state of binding of Na in the alkali cellulose. The total line width Δv1/2 is suggested to be composed additively of the contribution of the localized bound, the delocalized bound and the kinetically free Na nuclei.

Zum Einfluß einer Voraktivierung auf die Carboxymethylierung der Cellulose

Es wurde gepruft, inwieweit die Loslichkeit von Carboxymethylcellulosen bei DS-Werten zwischen 0,3 und 0,4 durch eine Voraktivierung des eingesetzten Buchensulfitzellstoffs mit flussigem Ammoniak beeinflust werden kann. Bei Verwendung rein wasriger Reaktionssysteme wurde kein wesentlicher Einflus der Voraktivierung gefunden. Bei Verwendung eines Ethanol/Wasser-Gemisches als Reaktionsmedium fuhrte eine Voraktivierung zu einer deutlichen Verminderung des unloslichen Ruckstandes beim Reaktionsprodukt. The effect of preactivation of beech sulfite pulp by liquid ammonia on the solubility of carboxymethylcellulose at DS values between 0.3 and 0.4 has been investigated. No essential effect was found with purely aqueous reaction systems. By using an ethanol/water mixture as reaction medium the preactivation resulted in a distinct decrease of the insoluble residue of the reaction product.