Herbert Dautzenberg

The degree of acetylation of chitosans and its effect on the chain conformation in aqueous solution

The average degree of acetylation (DA) of chitosans from several sources as well as the distribution of the DA across the molecular weight distribution was measured by titration with poly(styrene sulphonate) as counter polyanion and toluidine blue as metachromatic indicator. The method was shown to be useful within a broad range of DAs. There was no compositional heterogeneity for more than 90% of the population in any sample. Parallel macromolecular characterisation by static light scattering and viscometry standing alone or connected with gel permeation chromatography (GPC) revealed no measurable effect of the DA on the chain conformation where the DA varied between a few percent and ∼60%. Relationships between intrinsic viscosity and radius of gyration with molecular mass were established. The data when considered with previous work suggest no evident differences between chitosans from different sources and no significant effect of the ionic strength between ∼0.1 and 0.3 M on the conformation.

Physico-chemical characterization of chitosans varying in degree of acetylation

Abstract Three commercial chitosans varying in average degree of acetylation (DA) were characterized in terms of average molar massesMn,Mw, the second virial coefficientB and radius of gyrationRgz, and intrinsic viscosities by membrane osmometry, static light scattering, and capillary viscometry in acetate buffer of pH 4.5. To obtain satisfactory light scattering data, the method used for clarification was of great importance. Combined ultracentrifugation and membrane filtration was found to be the method of choice. Using the model for wormlike chains with excluded volume and a logarithmic molar mass distribution, the persistence lengthLp was determined asLp = 6 nm. No concentration-dependent association was observed for the low concentrations studied. Samples were also fractionated on Sepharose CL-2B for subsequent light scattering and viscosity measurements to establish relationships betweenMwand [η] andRg, respectively. These relationships were found to be independent of the DA for the bulk of molecularly dispersed chitosan. Model calculations aimed at checking the consistency of data led, as to be expected, to an increasing excluded volume effect with increasing molar mass and steadily increasing polydispersities of the fractions with increasing elution volume. The levelling off of the [η]-Mw andRg-Mg relations for fractions of increasingly high molar mass was assigned to chemical heterogeneity of samples in terms of DA distributions.

Synthesis and characterization of poly(diallyldimethylammonium chloride) in a broad range of molecular weight

Poly(diallyldimethylammmonium chloride) samples were prepared in a wide range of molecular weight by radical polymerization at low degree of conversion to realize undisturbed molecular weight distributions. Determination of the molecular and thermodynamic parameters by viscometry. osmometry. light scattering. gel permeation chromatography (GPC) and analytical ultracentrifugation (AUC) give acceptable agreement. The high values of the second virial coefficient would result in a corresponding excluded volume. However, the dependencies of the radius of gyration and the second virial coefficient on molecular weight do not reflect the excluded volume effect. The discrepancy can be explained by a dominating Donnan contribution. Taking into account the polydispersities of the samples. a Kuhn segment length of 5 nm was determined for poly(diallyldimethylammonium chloride) in 0.5 M NaCl solutions. [η]-M relations were obtained for 1 M NaNO 3 , 1 M NaCl and 0.5 M NaCl solutions.

Polyelectrolyte complex formation in highly aggregating systems. Effect of salt: response to subsequent addition of NaCl

Polyelectrolyte complex formation between polyanions and polycations with strong ionic groups and high molecular weights in pure water results in highly aggregated compact and nearly spherical particles, consisting of a neutralized core and a stabilizing shell of the excess component. The response of such systems to the addition of sodium chloride was studied by turbidimetry and static light scattering in relation to the ionic group of the polyanion (Na-poly(styrene sulfonate) and Na-poly(methacrylate)) and the charge density of the polycation (poly(diallyldimethylammonium chloride) and its copolymers with acrylamide). While in the systems with Na-PSS the addition of salt causes mainly additional aggregation and macroscopic flocculation, redissolution of the complexes with Na-PMA at a critical salt concentration was found. The use of the copolymers with hydrophilic acrylamide as excess component leads to a stabilization against additional aggregation.

Effect of charge density on the formation and salt stability of polyelectrolyte complexes

Cationic copolymers of diallyldimethylammonium chloride (DADMAC) and N-methyl-N-vinylacetamide (NMVA) were synthesized by radical polymerization in a broad range of composition. Since the cyclocopolymerization of DADMAC and NMVA proceeded as nearly ideal reaction, linear copolymers of different charge densities but approximately equal molecular weights and acceptable polydispersities could be obtained. These polycations were used in combination with a sodium poly(styrene sulfonate) to study the effect of charge density on the course of polyelectrolyte complex (PEC) formation and the response of the PECs to subsequent addition of salt. Static light scattering was employed for the characterization of the complex structures. PEC formation followed in deionized water for all copolymers the same scheme, but yielding higher swollen particles with decreasing charge density of the polycations. In the cases of stronger mismatching of the charge densities of the components the presence of NaCl during complex formation led to highly swollen complexes on a very low level of aggregation. Subsequent addition of NaCl resulted for these polyelectrolyte combinations at first in disintegration into very small subunits before flocculation occurred.

New and effective entrapment of polyelectrolyte-enzyme-complexes in LentiKats.

Amyloglucosidase EC 3.2.1.3 was used as model for the immobilisation of enzymes in poly(vinylalcohol) hydrogel (LentiKats) lenses. The entrapment of the enzyme in PVA-hydrogel based on a two-step procedure, firstly its coupling to polyelectrolytes increased the structure level of the enzyme, and subsequently, the resulting complex was entrapped in LentiKats. The immobilised enzyme retained 45% of its original activity and lost no activity over five repeated batch runs.

Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper

Polyelectrolyte complexes (PEC) were formed between a cationic polyamideamine epichlorohydrine condensate (PAE) and an anionic carboxymethylcellulose (CMC) at different ratios between the polymers, ...

Light scattering studies on polyelectrolyte complexes.

The Coulomb interaction between oppositely charged polyelectrolytes leads to spontaneous formation of interpolymer complexes. Such complexes are of high practical relevance, but also interesting objects of fundamental research. The level of aggregation depends on the nature of the components as well as on the medium and external conditions of the polyelectrolyte complex formation. An appropriate combination of methods provides detailed information on the stoichiometry and structure of such systems. Especially, light scattering techniques proved to be a powerful tool in studying the structure and behavior of the complexes in solution. Selected examples will demonstrate the efficiency of such investigations.

Amphiphilic cationic block copolymers via controlled free radical polymerization.

N-oxyl terminated vinylbenzyl chloride macromonomers, available via controlled free radical polymerization, were used to synthesize AB-block copolymers of vinylbenzyl chloride and styrene with low polydispersity and different block lengths and block length ratios. The vinylbenzyl chloride blocks were quantitatively converted into cationic polyelectrolytes by reactions with tertiary amines. The micellization of the synthesized amphiphilic cationic block copolymers was investigated using different techniques such as static light scattering, ultracentrifugation and size exclusion chromatography.

The determination of the molecular weight distribution of pectins by calibrated GPC Part I. Calibration by light scattering and membrane osmometry

Abstract Commercial high methoxyl citrus pectin was fractionated on Sepharose 2 B/Sepharose 4 B. Fractions were used to calibrate GPC by light scattering and membrane osmometry. The angular dependence of light scattering of the fractions was interpreted in terms of a two-component system giving reliable M w / M n ratios for the major molecularly dispersed component which forms coils of considerable stiffness in solution. A minor particulate spherical component was identified which was rich in neutral sugars. Structural parameters of this component were determined by comparison of the experimental scattering behavior with master curves. β-Elimination of the fully esterified pectin was carried out to reveal the chemical nature of the particulate component.