Bogdan C. Simionescu

Oxidized cellulose—Survey of the most recent achievements

The functionalization and particularly the oxidation of cellulose is an intriguing and challenging topic due to the presence of multiple reactive sites, which can undergo specific reactions. The variety of the oxidizing agents used to improve the selectivity and yields of these transformations is illustrated by the steadily growing of the number of publications and patents reported. This paper is focused on the most selective agents for cellulose oxidations, i.e., sodium periodate and stable or non persistent nitroxyl radicals, emphasizing on the most recent developments reported so far.

Synthesis of conducting H-type polysiloxane-polypyrrole block copolymers

Abstract Synthesis of a siloxane polymer with pyrrole end groups has been described. Electrochemical block polymerization of pyrrole through these end groups has been achieved. Characterization of the electrolytic products has been performed by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermal gravimetry analysis (TGA) analyses and FT-IR studies. The effects of different dopant ions, namely, p -toluene sulfonic acid (PTSA) and tetrabutylammonium tetrafluoroborate (TBAFB), in electropolymerization and conductivities of the corresponding block copolymers have been investigated.

Rapid deswelling response of poly(N-isopropylacrylamide)/poly(2-alkyl-2-oxazoline)/poly(2-hydroxyethyl methacrylate) hydrogels.

Ternary poly( N-isopropylacrylamide)/poly(2-alkyl-2-oxazoline)/poly(2-hydroxyethyl methacrylate) (PNIPAAm/PROZO/PHEMA) hydrogels were prepared by the free-radical copolymerization of N-isopropylacrylamide (NIPAAm), 2-hydroxyethyl methacrylate (HEMA), and poly(2-alkyl-2-oxazoline) (PROZO) multifunctional macromonomers. The resulting polymeric materials were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), as well as by equilibrium swelling experiments. All synthesized hydrogels display temperature sensitivity in the 28-38 degrees C range. A high rate of response was registered as compared to that of materials based only on PNIPAAm. The swelling-deswelling peculiar behavior was related to the chemical composition (hydrophile/hydrophobe balance), the length of the inserted PROZO sequence, and inner morphology, an aspect which points on its possible control by synthesis. It was evidenced that the architecture of the resulting porous materials has a high order degree, emerging from the self-assembling of the microgel particles, which provided numerous, nearly uniform, large water release channels.

Mild and Selective Oxidation of Cellulose Fibers in the Presence of N-Hydroxyphthalimide

The oxidation reaction of regenerated cellulose fibers mediated by N-hydroxyphthalimide (NHPI) and various cocatalysts at room temperature for different time intervals and various amounts of low concentration sodium hypochlorite solution has been investigated to produce oxidized cellulose (OC), a biocompatible and bioresorbable polymer. The results revealed that the nonpersistent phthalimide-N-oxyl (PINO) radical generated in situ from NHPI in both, metallic or metal-free systems, is a powerful agent in this kind of transformation. Moreover, the reaction converts highly selectively C(6) primary hydroxyl groups to carboxylic groups under mild reaction conditions and shorter reaction times than previously reported. The amounts of negatively charged groups in OC were determined by means of potentiometric titration. Further characterization of the products were accomplished by using Fourier transform infrared spectroscopy/attenuated total internal reflection spectroscopy (FT-IR/ATR), environmental scanning electron microscopy (ESEM), and X-ray and energy-dispersive X-ray (EDX) spectroscopy. Notably, water retention values of the oxidized fibers increased by 30% in comparison with the original nonoxidized sample, as a result of the introduction of hydrophilic carboxylate groups.

Synthesis and properties of some new polyazomethine-urethanes

Abstract Two new bisazomethine diols were prepared from terephthalaldehyde and aromatic or aliphatic aminoalcohols. The structure of the diols with bisazomethine moieties was confirmed by 1H-NMR, IR, UV spectroscopy and elemental analysis. Bisazomethine aliphatic diol exhibited a smectic phase that has been identified by means of polarizing microscopy and differential scanning calorimetry. By using these diols as partners in polyaddition reaction between poly(tetramethylene oxide)diol of 2000 average molecular weight, tolylene-2,4-diisocyanate (as 2,4- and 2,6-TDI, 80:20 v/v isomers mixture) and bisazomethine diol (1:3:2 molar ratio), two polyazomethine-urethanes were synthesized. Polyazomethine-urethanes with a higher concentration of poly-Schiffs base units were also obtained by reacting the above bisazomethine diols with the same diisocyanate (1:1 molar ratio). All polymers were characterized by viscometry, elemental analysis, IR, UV, 1H-NMR spectroscopy and TGA techniques.

Synthesis and photocrosslinking of benzyl acrylate substituted polydimethylsiloxanes

This article deals with the synthesis of polydimethylsiloxanes (PDMSs) substituted with chain or end benzyl acrylate groups by the hydrosilation of appropriate hydro-siloxanes, followed by phase transfer catalysed reaction of chloromethylated aromatic groups with the sodium salt of acrylic acid. Differential scanning photocalorimetry (DPC) was used to study the crosslinking behaviour of the mentioned functional PDMSs in the presence of different photoinitiators. The reaction rate, the final conversion and the inhibition period characterizing the crosslinking were found to be dependent on reaction atmosphere, light intensity, nature and concentration of photoinitiator and on polymer functional groups content.

Antifungal vanillin–imino-chitosan biodynameric films

Vanillin-chitosan biodynamers have been prepared and structure-morphology correlations revealed the pathway of progressive incorporation of the aldehyde onto chitosan backbones. Such dynamic biopolymers or biodynamers, generated from reversibly interacting components, offer the possibility to address the dynamic covalent behaviour of the reversible imine-bond formation/hydrolysis equilibria between vanillin and chitosan polymeric backbones. The reaction takes place with very low conversion in acidic aqueous solutions (7-12%), but the imine bond formation is amazingly improved (∼80%) when the reaction takes place while solution-solid state transition and solid state phase-organization events occur. The chitosan-vanillin biopolymeric films described here present interesting Candida albicans antifungal activity compared with other common bacterial strands, which suggests the implementation of these biocompatible materials as thin layer protecting systems for medical devices.

Microemulsion photopolymerization of methacrylates stabilized with sodium dodecyl sulfate and poly(N-acetylethylenimine) macromonomers

Abstract Methyl methacrylate and butyl methacrylate were polymerized in oil-in-water microemulsions that were stabilized by sodium dodecyl sulphate (SDS). A poly(N-acetylethylenimine) (PNAEI) macromer was also included in the recipe, as a cosurfactant and a comonomer. Polymerizations were initiated by UV-irradiation. The average diameters of latex particles, obtained by STM, were in the range of 17–200 nm. The experimental data evidenced that the particle size was mainly dependent on the SDS/PNAEI ratio. Polymerization yields were around 75–85%. The synthesized copolymers have viscosity average molecular weights in the range of 2.1–2.4×106 and glass transition temperatures of 38.0–43.5°C, lower than those obtained without using PNAEI. The investigation by means of FTIR and 1 H-NMR techniques revealed that PNAEI was incorporated into the nanoparticles.

Viscometric study of extremely dilute polyacrylonitrile solutions

Abstract The critical overlapping concentration c′ which separates the dilute and extremely dilute regimes for polyacrylonitrile in dimethylformamide was studied by viscometry. A scaling law between the reduced viscosity ηsp/c and the concentration for the extremely dilute regime was found and the deviation from the Huggins dependence was discussed.

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.