Brigitte Heublein

Functional Polymers Based on Dextran

Dextran, comprising a family of neutral polysaccharides consisting of an α-(1 → 6) linked d-glucose main chain with varying proportions of linkages and branches, depending on the bacteria used, is an interesting starting material for chemical modification reactions for the design of new functional polymers with promising properties. The review summarises recent results on structure characterisation of dextran including some comments on biosynthesis of this important class of biopolymers. Applications of dextran are discussed as well. Chemical modification reactions of dextran are increasingly studied for the structure and hence property design. The review highlights recent progress in esterification of dextran, both inorganic and organic polysaccharide esters, etherification reactions towards ionic and non-ionic ethers, and the huge variety of different conversions mainly developed for the binding of drugs. It summarises recent developments in the application of dextran derivatives with a focus on the chemical structures behind these materials such as prodrugs, bioactivity of inorganic dextran esters, heparin sulfate mimics, hydrogels, nanoparticles and self assembly structures for surface modification.

Silylation of Cellulose and Starch – Selectivity, Structure Analysis, and Subsequent Reactions

The silylation of cellulose and starch under different starting conditions is reviewed. The control of the degree of substitution (DS) and regioselectivity in dependence of the reaction pathway are discussed in detail. The synthesis of trimethylsilyl cellulose (TMSC) in the system hexamethyldisilazane (HMDS)/ammonia leads to partially and completely silylated products controlled by the amount of the components. Hydrolytic desilylation of TMSC in tetrahydrofuran (THF)/ammonia gives the partially desilylated products. The desilylation proceeds statistically along the polymer chains. The reaction of cellulose dissolved in N,N-dimethylacetamide (DMA)/LiCl with bulky thexyldimethylchlorosilane (TDSCl) in the presence of imidazole leads to 2,6-di-O-TDS cellulose. The silylation of starch dissolved in dimethylsulfoxide (DMSO) with TDSCl/pyridine results in the formation of regioselectively 2-O and 6-O functionalized silyl ethers with DS values up to 1.8. 6-O Silyl ethers of cellulose and starch were synthesized with TDSCl highly activated in the reaction system N-methylpyrrolidone (NMP)/ammonia. Two- dimensional NMR techniques after subsequent modifications of the remaining OH groups have been established as important methods for the characterization of the substitution pattern of the described silyl ethers. In the case of starch, the distribution of the substituents could be detected not only in the anhydroglucose units (AGU) but also in the non-reducing end groups (NEG).

Hydrogen bond formation in regioselectively functionalized 3-mono-O-methyl cellulose

The hydrogen bond systems of cellulose and its derivatives are one of the most important factors regarding their physical- and chemical properties such as solubility, crystallinity, gel formation, and resistance to enzymatic degradation. In this paper, it was attempted to clarify the intra- and intermolecular hydrogen bond formation in regioselectively functionalized 3-mono-O-methyl cellulose (3MC). First, the 3MC was synthesized and the cast film thereof was characterized in comparison to 2,3-di-O-methyl cellulose, 6-mono-O-methyl cellulose, and 2,3,6-tri-O-methyl cellulose by means of wide angle X-ray diffraction (WAXD) and (13)C cross polarization/magic angle spinning NMR spectroscopy. Second, the hydrogen bonds in the 3MC film were analyzed by means of FTIR spectroscopy in combination with a curve fitting method. After deconvolution, the resulting two main bands (Fig. 3) indicated that instead of intramolecular hydrogen bonds between position OH-3 and O-5 another intramolecular hydrogen bond between OH-2 and OH-6 may exist. The large deconvoluted band at 3340cm(-1) referred to strong interchain hydrogen bonds involving the hydroxyl groups at C-6. The crystallinity of 54% calculated from the WAXD supports also the dependency of the usually observed crystallization in cellulose of the hydroxyl groups at C-6 to engage in interchain hydrogen bonding.

Untersuchungen zur Naßvernetzung von Lyocell‐Fasern

Hintergrund der Arbeiten ist die hohe Nasfibrillierneigung von Lyocell-Fasern. Uber Vernetzungsreaktionen last sich deren Nasscheuerverhalten verbessern. In dieser Arbeit wurden Substanzen mit Sulfatoethylsulfonyl-Ankern, aber unterschiedlichen Bruckengliedern synthetisiert sowie hinsichtlich der Applikation optimiert. Mit den ausgewahlten Substanzen ist die Nasfibrillierung deutlich zu senken. Nimmt man die Faserauflage der Vernetzer als Bezug, so sind zwischen den einzelnen Vernetzer-Strukturen die Effekte auf das Nasscheuerverhalten relativ wenig differenziert. Die Beschaffenheit der gequollenen Lyocell-Faser erlaubt damit bei recht unterschiedlich aufgebauten Vernetzern eine bifunktionelle Reaktion. The high wet fibrillation tendency of Lyocell fibres forms the background to this investigation. The wet abrasion behaviour can be improved by crosslinking reactions. Substances containing sulfato ethyl sulfonyl groups but different bridging groups were synthesised and optimised regarding to their application. The wet fibrillation tendency can be reduced clearly with these selected substances. If the concentration of the crosslinking agent on the fibre is the basis of comparisons the different structures have a similar effect on the fibrillation tendency. So the swollen Lyocell fibre permits a crosslinking reaction with curing agents of different size.

Spectroscopic Investigation of Solid Poly-p-Methoxystyrene-Aerosil Composites Obtained by Triphenylmethylium-Halide-Aerosil Initiation

Abstract The composites of poly-p-methoxystyrene and aerosil obtained by interfacial initiation with triphenylmethylium-halide-aerosil have been investigated by the BET method, UV/Vis spectroscopy, FTIR spectroscopy, thermogravimetry, and elementary analysis. In the case of triphen-ylmethylium-bromide-aerosil initiation, cationically active composites are obtained which have covalent Si-O-C bonds. The structures of the polymer-aerosil bonds are discussed in comparison with results obtained from model compounds.