Silvia Ioan

Effect of segmented poly(ester-siloxane)urethanes compositional parameters on differential scanning calorimetry and dynamic-mechanical measurements

Segmented poly(ester-siloxane)urethanes containing hard and soft segments were prepared by melt polyaddition using a multistep procedure. The soft segments based on poly(ethylene glycol adipate)diol as ester sequences and α,ω-poly(dimethylsiloxane)diol as silicone sequences were synthesized. The hard segments were based on aromatic or aliphatic diisocyanates and butanediol was used as chain extender. These polyurethane materials were analysed by differential scanning calorimetry and dynamic-mechanical analysis measurements. The shapes of thermal plots are significantly influenced by the soft and hard segment structures and also the compositional parameters.

Dynamic-mechanical and differential scanning calorimetry measurements on crosslinked poly(ester-siloxane)-urethanes

Abstract Various crosslinked poly(ester-siloxane)-urethanes containing hard and soft segments, were prepared by a one-step melting/polyaddition. Thus, soft sequences based on poly(ethylene glycol adipate)diol (PEGA) or poly(diethylene glycol adipate)diol (PDEGA) as ester components, α,ω-poly(dimethylsiloxane)diol (PDMS) and/or polybutadienediol (PBD), were built. The hard segments were composed from diglycerin maleate tetrol (DGMA) and two aromatic diisocyanates, 4,4′-diphenylmethane diisocyanate (MDI) and 2,4-tolylene diisocyanate (TDI). Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) were employed to characterise crosslinked polyurethane materials. The obtained data revealed that the thermal curves are influenced significantly by the soft and hard segment structures in the temperature range studied.

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.

Influence of mixed solvents and temperature on the solution properties of quaternized polysulfones

Modification of intrinsic viscosity and the preferential adsorption coefficients of quaternized polysulfones with various contents of ionic chlorine in N,N‐dimethylformamide/water and methanol/water mixed solvents was investigated at different compositions and temperatures. The polyelectrolyte effect induced by an enhanced dissociation of the ionizable groups determines both the modification of the swelling degree of the polymer coil and the difference in composition of the mixed solvent inside and outside the coil. The results obtained were correlated with the interaction parameters of the above‐mentioned polymer/solvent/solvent systems.

Effect of Alkyl Side Chain on the Conformational Properties of Polysulfones with Quaternary Groups

Modification of intrinsic viscosity, temperature coefficient, and preferential adsorption coefficient of polysulfones with different alkyl side groups in N,N-dimethylformamide/methanol and N,N-dimethylformamide/water was investigated at different compositions and temperatures. The specific interactions, such as hydrogen bonding and polyelectrolyte effect induced by an enhanced dissociation of the ionizable groups, determine both the modification of the solvation power of the polymer coil and the difference in the composition of the mixed solvent inside and outside the coil.

Ultrahigh molecular weight polymers in dilute solutions

Abstract The article reviews the thermodynamic aspects of ultrahigh molecular weight polymers in dilute solutions. The investigation of these compounds is much more complicated as compared to the study of usual length polymer–solvent systems. The restrictions applying to the establishment of concentration regimes, short range interactions (theta condition, unperturbed dimensions, chain flexibility, the transition from theta to collapsed regime), and long range interactions (excluded volume effect by intermolecular and intramolecular interactions, conformational characteristics and conformational transitions phenomena) are discussed. Systematic studies, based on the coupling of different experimental techniques, are described for the elucidation of diverse theoretical and experimental contributions.

High molecular weight polystyrene in solvent mixtures. Preferential and total adsorption

Abstract The behaviour of high molecular weight polystyrene in three binary solvent systems, i.e. cyclohexane/benzene (theta solvent/solvent), cyclohexane/acetone (theta solvent/nonsolvent) and benzene/methanol (solvent/nonsolvent) is studied by viscometry and refractometry. The experimental results on the preferential and total adsorption coefficients are discussed and compared to those predicted by different theoretical treatments.

Conformational characteristics of oligo- and polyacrylonitrile in dilute solution

Abstract The paper is concerned with the conformational characteristics of oligo- and polyacrylonitrile in dilute solution as evidenced by gel permeation chromatography (GPC) and viscometric data. The effects of chain ends and chain stiffness on the Mark–Houwink dependencies are discussed for a large domain of molecular weights.

Morphological Properties and Antibacterial Activity of Nano-Silver-Containing Cellulose Acetate Phthalate Films

Modification of the rheological properties of cellulose acetate phthalate in 2-methoxyethanol/acetone/water, at different compositions of solvent mixtures, allowed the identification of optimal composition of solvent mixtures for obtaining fibers with controlled diameters. Changing the solvent content in the casting solutions favors modification of the morphological aspects of cellulose acetate phthalate (CAP) films, as observed from atomic force microscopy images. Silver nitrate was incorporated into CAP, as a dispersion medium, and the silver-containing polymer (Ag-CAP) films thus obtained were studied for obtaining information on antimicrobial activity, using Escherichia coli ATCC 10536 and Staphylococcus aureus ATCCC 6538 microorganisms. The results were compared with the antibacterial activity of nano-silver-containing cellulose acetate (Ag-CA) films. The different inhibiting effects of CA or Ag-CA and of CAP or Ag-CAP on the tested Escherichia coli and Staphylococcus aureus bacteria are due to a different antimicrobial activity of the polymers and to the antiseptic character of nano-silver.

Phase-Transfer-Agent-Aided Free Radical Polymerization of Methyl Methacrylate-A Kinetic Study

Abstract The kinetics of phase-transfer-agent-aided free radical polymerization of methyl methacrylate was investigated by using K2S2O8 as the initiator and cetyltrimethyl ammonium chloride (Arquad) as the phase transfer agent. The rate of polymerization was found to be proportional to [M]1.23[K2S2O8]0.8 [Arquad]0.25 and almost independent of the volume of water (V w)/volume of organic solvent (V o) (benzene) ratio for V w/V o < 0.33. A reaction mechanism is proposed.