Mariana Cristea

Influence of low-molecular-weight salts on the formation of polyelectrolyte complexes based on polycations with quaternary ammonium salt groups in the main chain and poly(sodium acrylate)

Abstract The effects of NaCl, NaI and Na2SO4 on the formation of polyelectrolyte complex (PEC) between a polycation with N,N-dimethyl-2-hydroxypropyleneammonium chloride units in the main chain (PCA5) and poly(sodium acrylate) (NaPA) were studied. The NaCl concentration in the polyelectrolyte solutions ranged from 0 to 2 M. Viscometric and turbidimetric measurements were used to follow the effect of the salt concentration and of the counterion nature on the PEC formation. The influence of counterions was different depending on both the radius of the hydrated ion and its valence. At the same concentration of the low-molecular-weight salt, the following order of the PEC separation in dependence on the counterion was evidenced: Rsep(SO42−)

Polyelectrolyte complexes. I. Synthesis and characterization of some insoluble polyanion-polycation complexes

The synthesis of some water-insoluble synthetic polyelectrolyte complexes formed between a weak polyanion and a strong polycation was followed. Sodium salts of poly(acrylic acid) and of some copolymers of acrylic acid with itaconic acid or maleic acid were used as anionic polymers. Cationic polyelectrolytes with quaternary ammonium salt groups in the main chain were used as strong polycations. The cationic polymers were different as concerns both the content of quaternary nitrogen atoms and the degree of branching. The complex formation was followed by the variation of the conductivity and of the specific viscosity of the reaction medium as well as by the turbidimetric titration versus the unit molar ratio polyanion/polycation. The deviation of the endpoint from stoichiometry was influenced mainly by the structure of the complementary polymers and by their molecular weights. The greater the structural differences, the higher the endpoint deviation from stoichiometry. Only insoluble polyelectrolyte complexes (PEC) were obtained in all the polyanion/polycation systems taken into account. The PECs were separated and characterized by elemental and spectral analyses as compared with the complementary polymers.

Imino-chitosan biopolymeric films. Obtaining, self-assembling, surface and antimicrobial properties

The paper reports the preparation of twelve imino-chitosan biopolymer films by acid condensation of the amino groups of chitosan with various aldehydes, in aqueous medium, followed by slow water removal. FTIR spectroscopy has shown drastic conformation changes of chitosan macromolecular chains—from a stiff coil to a straight one, while wide angle X-ray diffraction evidenced a layered morphology of the biopolymer films. Contact angle and surface free energy determination indicated a higher biocompatibility of the new biopolymers as compared to the chitosan parent, while the microbiological screening demonstrated their self-defense properties against common and virulent pathogen agents. It was concluded that the reversibility of imine forming promotes the self-assembling of imino-chitosan biopolymer films into a lamellar morphology and, on the other hand, the slow release of the antimicrobial aldehyde in the microbiological culture. The obtained results demonstrate that chitosan polyamine is a challenging workbench to functional biodynamic materials.

Polyelectrolyte complexes. II. Specific aspects of the formation of polycation/dye/polyanion complexes

We report on the formation of the polycation/dye/polyanion (PC/D/PA) complexes by the interaction between nonstoichiometric polycation/dye (PC/D) complexes with polyanions. Polycations differed in their content of the (N,N-dimethyl-2-hydroxypropylene ammonium chloride) units in the main chain. Poly(sodium acrylate) (NaPA), poly(sodium 2-acrylamido-2-methylpropane sulfonate) (NaPAMPS) and poly(sodium styrenesulfonate) (NaPSS) were used as polyanions. Crystal Ponceau 6R (CP6R) and Ponceau 4R (P4R) with two or three sulfonic groups were used as anionic dyes. The interaction between nonstoichiometric PC/D complexes and polyanions was followed by UV-VIS spectroscopy, viscometry, and conductometry measurements. Formation of PC/D/PA complexes takes place mainly by the electrostatic interaction between the polyanion and the free positive charges of the nonstoichiometric PC/D complex. The stoichiometry and the stability of the tricomponent complexes depended on the polycation structure, the structure and molecular weight of polyanion, the dye structure, and the P/D molar ratio. A high amount of the dye was excluded from the complex before the end point when a branched polycation was used. The higher the solubility of the dye the lower the stability of the PC/D/PA complexes.

Formation of polyelectrolyte complexes with diethylaminoethyl dextran: Charge ratio and molar mass effect

The formation of polyelectrolyte complexes (PECs) between carboxymethyl pullulan and DEAE Dextran, was investigated, in dilute solution, with emphasis on the effect of charge density (molar ratio or pH) and molar masses. Electrophoretic mobility measurements have evidenced that insoluble PECs (neutral electrophoretic mobility) occurs for charge ratio between 0.6 (excess of polycation) and 1 (stoichiometry usual value) according to the pH. This atypical result is explained by the inaccessibility of some permanent cationic charge when screened by pH dependant cationic ones (due to the Hoffman alkylation). Isothermal titration calorimetry (ITC) indicates an endothermic formation of PEC with a binding constant around 10(5) L mol(-1). Finally asymmetrical flow field flow fractionation coupled on line with static multi angle light scattering (AF4/MALS) evidences soluble PECs with very large average molar masses and size around 100 nm, in agreement with scrambled eggs multi-association between various polyelectrolyte chains.

Thermal behaviour of some cationic polyelectrolytes and polyelectrolyte complexes

Thermogravimetric and differential thermal analysis were developed on some cationic polymers, different both by the content of the quaternary ammonium salt groups in the main chain and by the content and type of polyfunctional amines, as well as on some polyelectrolyte complexes (PECs), when the cationic component was one of the above cationic polymers and the anionic component was poly(acrylic acid) sodium salt (PANa). The polycation with the lowest content in the quaternary ammonium salt groups had the highest thermal stability. The electrostatic interactions between the oppositely charged polyions in PECs induced a greater thermal stability of their structure compared with the starting polycations. The thermal behaviour of the PECs was compared with that of the physical mixtures of the corresponding complementary polymers taken in the same mass ratio as in PECs.

Nanocomposites Based on Aromatic Polyamide-Imide and Magnesium Hydrosilicate Nanotubes

Structure, morphology, and thermal properties of nanocomposites based on thermally stable poly(diphenyloxydamide-N-phenylphtalimide) (PAI) and layered magnesium hydrosilicate nanotubes (NTs) were studied using thermogravimetric analysis, dynamic mechanical analysis, atomic force microscopy, and differential scanning calorimetry. Thermal stability and glass transition temperature of the composites were shown to exceed those of the PAI matrix. Introduction of NT into the polymer matrix appreciably increased the elasticity and deformability of the composite material. The content of NT was also shown to greatly influence the surface morphology of the PAI-NT composites.

Morphology and mechanical properties of polymer-inorganic nanocomposite containing triple chain fibrous Na-Mg hydrosilicate

A polymer-inorganic nanocomposite of fibrous Na-Mg triple chain hydrosilicate and polyamidoimide based on 4-chloroformyl-(N-p-chloroformylphenyl)phthalimide and 4,4′-diaminodiphenyl ether has been developed. Morphology and dynamic mechanical properties of the nanocomposite films have been studied. Anisotropy of mechanical properties of the nanocomposite and the pristine polyamidoimide films has been revealed. Introduction of the fibrous filler disrupts the ordered mesomorphic structure of the polymer matrix; its recovery upon heating above the glass transition temperature is possible.