Biocompatible polymeric systems: Copolymerization of 4-methacryloyloxy-acetanilide with 2-hydroxyethyl-methacrylate

Soluble copolymers of 4-methacryloyloxy-acetanilide (M), an acrylic derivative of paracetamol, with 2-hydroxyethyl-methacrylate (H) were prepared by free radical polymerization in DMF solution at 50°C, using 2,2′-azobisisobutyronitrile (AIBN) as initiator. The reactivity ratios of both monomers were determined by the application of conventional linearization methods suggested by Fineman-Ross and Kelen-Tudos. The results obtained make clear that this system copolymerizes at random with the reactivity ratios r_m = 2.15 ± 0.05 and r_H = 0.90 ± 0.10. The microstructure of copolymer chains is described on the basis of the first order Markov statistics. The copolymer glass transition temperatures were determined calorimetrically and the variation of T_g with the copolymer composition is discussed according to modern methods, considering the sequence distribution of monomeric units along the copolymer chains. Also the T_g of the corresponding homopolymers were determined giving the values of T_g(M) = 471 K and T_g(H) = 358 K.     

On the interaction of palladium with olefinic systems

We have performed all electron Hartree–Fock gradient calculations and geometry optimizations on systems composed of one to three palladium atoms and: CH₃ cation and anion, C₂H₄, C₂H₃NH₂, C₄H₄, NH₃, and (NH₃) + (C₂H₄). Several basis set considerations are discussed and the binding energies of Pd to these small molecules are reported. We find the counterpoise correction to the binding energies of these systems to be large. We also present MP2 calculations of the palladium binding energy with a large uncontracted palladium spd basis set in the PdC₂H₄ and PdNH₃ systems. The binding interaction between ethylene and palladium results in a mixing of the 4d–π* and 5s–π orbitals, and, is dissociative to the ethylene. The palladium-butadiene and palladium-cyclobutene relative stabilites and structures are interesting since these molecules could form from acetylene on a palladium surface. We find the Pd-butadiene cyclic structure to be 43 kcal/mol more stable than the Pd-cyclobutene product.     

硫化聚并苯导电材料结构的理论化学研究

采用量子化学从头算方法和AM1半经验方法,探讨了聚并苯导电聚合物硫掺杂前后结构和电子性质的变化,提出了硫化聚并苯导电材料的“双层夹心”分子结构模型.研究表明,硫化后的聚并苯材料,S原子位于两层聚并苯分子平面中间,并与两个聚并苯分子平面中相应的两个C原子相键合,形成C—S—C“桥式”共价单键;并解释了硫化聚并苯导电材料比本征态聚并苯材料作电极时可逆容量增大的原因.     

Copolymerization of new pyrazolone-containing monomers with certain vinyl comonomers

The polymerization ability of two new pyrazolone-containing monomers—3-methyl-1-phenyl-4-crotonoyl-pyrazolone-5 ( Cr ) and 3-methyl-1-phenyl-4-(3′-phenyl-acryloyl) pyrazolone-5 ( Cy )—was investigated. The monomers were obtained by acylation of 3-methyl-1-phenyl-pyrazolone-5 with crotonyl chloride or cinnamoyl chloride, respectively. It was established that the two monomers do not homopolymerize either under the action of ionic and radical initiators nor with γ-rays (doses between 2 and 10 MRad). In contrast to this, the two monomers copolymerize with other vinyl comonomers. Copolymers of Cr and Cy with methacrylic acid (MAA), methyl methacrylate (MMA), and Styrene (St) were synthesized by radical copolymerization. The molecular weights of the polymer products obtained were in the 10,000–65,000 range. It was established that the molecular weight characteristics of the copolymers were affected by the concentration of the pyrazolone-containing monomer and by the chemical nature of the solvent used. The copolymerization of Cr and Cy with MAA was investigated in detail in order to evaluate the relative activity of the new monomers during copolymerization. The reactivity ratios (r) were calculated by three different methods with good agreement. The values obtained for the monomer pairs are: r_MAA = 0.61 ± 0.01, r_Cr = 0.04 ± 0.01; r_MAA = 0.64 ± 0.05, r_Cy = 0.02 ± 0.02. The Q/e values for Cr and Cy were determined using the reactivity ratios of both monomers.     

Copolymerization of maleic anhydride with certain compounds of the vinyl series

Russian Chemical Bulletin -     

Use of noncovalent interactions to form novel liquid crystalline polymeric materials

A novel concept in polymeric liquid crystalline (LC) materials, via electrostatic grafting or complexation of functionalized mesogens and appropriate polymers, is described. It is applied to three specific systems characterized by side-chain LC architecture, two of which involve hydrogen-bonding interactions, the third ionic interactions. In these systems, complexation tends to create greater order in the mesophases present. In the hydrogen-bonded systems, the transition temperature from the isotropic state tends to decrease compared to that of the functionalized mesogen; in the ionically-bonded system, the reverse is true. At low concentrations, the mesogens act as plasticizers.     

Nonlinear effects in mass transfer of liquid media through polymeric materials

Transport properties of several aromatic polyamides among which there exist fairly subtle structural differences were examined in perva-poration of water-isopropanol solutions. The dependences of the flux density on the membrane area and the oscillatory kinetics of permeability were established, and an unstable steady state arising via predominant permeation of an organic solvent through a highly hydrophilic polymeric membrane was revealed. Conductometric examination of the swelling kinetics showed that chitosan swelling in water gives rise to instabilities in the form of macrofluctuations of local sorbate concentration distribution in the polymer. The wavelet analysis of the time series of the stochastic oscillations was carried out.     

Copolymerization of N,N-diallyl-N′-benzoylhydrazine with acrylonitrile and sulfur dioxide

Radical copolymerization of N,N-diallyl-N′-benzoylhydrazine with acrylonitrile and sulfur dioxide was studied. The kinetic features of the copolymerization of these systems were examined, the relative activities of the monomers were determined, and the structure of the resulting copolymers was elucidated.     

Copolymerization of elemental sulfur with cyclic(arylene disulfide) oligomers

Copolymerization reactions between cyclic(arylene disulfide) oligomers were studied. The cyclic disulfide oligomers derived from 4,4′-isopropylidene bisbenzenethiol gave soluble polysulfanes via copolymerization with S₈. The copolymerization reactions were studied both in solution and melt by GPC and NMR. Solution copolymerization reactions can only form polysulfanes with up to three to four sulfur linkages; however, melt copolymerization reactions gave polysulfanes with up to seven sulfur linkages (average). The melt copolymerization reactions between cyclic disulfide oligomers derived from 4,4′-thiobis(benzenethiol) and S₈ were studied using DSC, TGA, and DMTA. With increasing contents of sulfur in the polysulfanes, T_gs, 5% weight losses by TGA, and tan δ decreased. With seven sulfur linkages in the polymer, it is a rubber with a T_g of 12°C, a 5% weight loss by TGA of 249°C, and tan δ of 44°C, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2961–2968, 1997     

Recent studies on small molecular and polymeric hole-transporting materials for high-performance perovskite solar cells

A decade of significant research has led to the emergence of photovoltaic solar cells based on perovskites that have achieved an exceptionally high-power conversion efficiency of 26.08%. A key breakthrough in perovskite solar cells (PSCs) occurred when solid hole-transporting materials (HTMs) replaced liquid electrolytes in dye-sensitized solar cells (DSSCs), because HTMs play a crucial role in improving photovoltaic performance as well as cell stability. This review is mainly focused on the HTMs that are responsible for hole transport and extraction in PSCs, which is one of the crucial components for efficient devices. Here, we have reviewed small molecular as well as polymeric HTMs that have been reported in the last two years and discussed their performance based on the analysis of their molecular architectures. Finally, we include a perspective on the molecular engineering of new functional HTMs for highly efficient stable PSCs.     

Electrical conductivity studies on discotic liquid crystal-ferrocenium donor-acceptor systems

The dispersion of electron-deficient ferrocenium ions was studied in the electron-rich media of two different triphenylene-based columnar hexagonal liquid-crystalline phases. These composites were characterized using polarizing optical micrography (POM), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), visible absorption spectroscopy, and dc and ac conductivity measurements. It was found that these composites form donor-acceptor systems that enhance the quasi-one-dimensional conductivity of the discotic system without altering the hexagonal columnar mesophase. The absorbance spectra confirm the formation of a charge-transfer complex between the electron-rich discotic molecules and the electron-deficient ferrocenium ions.     

Synthesis, characterization and structure-property relationship studies of cobaloximes with dithienylglyoxime as the equatorial ligand

The synthesis of cobaloximes, X/RCo(dThgH)₂Py (X = Cl, R = Me, Et, n-Pr, n-Bu and Bn) has been described. All the complexes have been characterized by elemental analyses and NMR spectral studies. The molecular structures of ClCo(dThgH)₂Py, MeCo(dThgH)₂Py, EtCo(dThgH)₂Py and BnCo(dThgH)₂Py complexes are determined by X-ray crystallography. The electron withdrawing nature of 2-thienyl ring affects the NMR as well as electrochemical behavior of these complexes. The electrochemical reduction from Co(III) to Co(II) and from Co(II) to Co(I) are much easier in ClCo(dThgH)₂Py as compared to chlorocobaloximes with the other dioximes (gH, dmgH, dpgH, dmestgH). The molecular oxygen insertion in the Co−C bond of benzyl complex (6) has been examined and a comparison of its reaction rate with other similar cobaloximes is discussed. The structural features of a dioxy complex Bn(O₂)Co(dThgH)₂Py (7) have also been reported.     

Molecular modeling studies of polymeric gas separation and barrier materials: structure and transport mechanisms

Molecular modeling studies have been completed on cis-PTBA(poly(tert-butylacetylene)) and Sixef44 polyimide, two glassy polymers that can be used to form gas separation membranes. The modeling studies show that polymer backbone bond rotations in PTBA are not thermally allowed. This leads to a helical structure for the cis-PTBA chains which pack as if the helices were rigid rods. Here, polymer free volume is formed by the interstitial space between adjacent helices, and gas transport occurs via continuous diffusion through the resulting channel-like free volume. On the other hand, Sixef44 exhibits a flexible polymer backbone, which leads to the formation of irregular voids. In this case, gas molecules are free to move within the voids, but transport occurs only by hopping to an adjacent void, or by void diffusion. In either case, gas transport is closely coupled to polymer backbone motion. Thus, these studies suggest two different types of free volume and gas transport mechanisms. The diffusion mechanism in glassy polymer membranes will depend on the nature of the free volume (e.g. the type of chain packing), and the polymer backbone chain flexibility.     

Encapsulation of living cells with polymeric systems

Microencapsulation of cells producing recombinant proteins or hormones leads to immunoprotection and immobilization in culture or in vivo. We are investigating three different strategies for the production of calcium cross-linked alginate beads of a small size with immobilized and immunoprotected mammalian cells: a) the AirJet technology (coaxial gas flow extrusion), b) the vibrating nozzle technology, and c) the JetCutter technology. A alginate/poly-L-lysine/alginate complexation was used as the polymeric system. All three methods may be used for production of homogeneous beads with a diameter of approximately 350 μm. While the vibrating nozzle technique was limited to an alginate viscosity of 0.2 Pa·s or less, the AirJet and JetCutter technology were less sensitive to higher viscosities. High frequency Scanning Acoustic Microscopy is used for mechanical characterization of the microspheres as well as for investigation of surface properties.     

Unfolding the structure-property relationships of Li2S anchoring on two-dimensional materials with high-throughput calculations and machine learning

Lithium-sulfur(Li-S) batteries are notable for their high theoretical energy density, but the ‘shuttle effect’and the limited conversion kinetics of Li-S species can downgrade their actual performance. An essential strategy is to design anchoring materials(AMs) to appropriately adsorb Li-S species. Herein, we propose a new three-procedure protocol, named InfoAd(Informative Adsorption) to evaluate the anchoring of Li2S on two-dimensional(2D) materials and disclose the underlying importance of mat...     

Synthesis of several series of liquid crystalline polyaroyl-bis-oxyarylates and their structure-property relationships

Several series of liquid crystalline polyaroyl-bis-oxyarylates containing 1,4-phenylene, 4,4'-biphenylene and 2,6-naphthylene units have been synthesized with the use of aroyl-bis-oxyaroyl dichlorides. Melting and clearing temperatures of every polymer under investigation were compared with those of corresponding polyterephthaloyl-bis-4-oxybenzoates.     

Generation of redox systems by fiber materials on the reduction of vat and sulfur dyes: Research and practical implementation

An essential part of the processes of refinement of textile materials from natural cellulose fiber is based on redox reactions of the components of process solutions both with admixtures in the fiber and with cellulose. The reducing agents involved in these processes are used in the alkaline treatment of textile materials as antioxidants whose function is to prevent oxidative destruction of cellulose; reducing agents are also introduced into vat or sulfur dye compositions to convert these insoluble dyes into soluble leuco compounds.     

Nanomechanical and optical studies on polymeric membranes

The nanomechanical properties of poly(ethylene terephthalate) (PET) membranes, were examined in light of nanoindentation experiments under conditions of maximum contact load in the range of 0.5-12 m?. Spectroscopic Ellipsometry (SE) from 1.5 to 6.5 ev (Vis-FUV range) was also applied to probe the dielectric function (ϵ(ω) of the industrially supplied membranes, as well as their geometrical structure. Mechanical stretching (uniaxial or biaxial) procedures are usually applied for the elongation of the polymeric membranes, their thickness reduction and enhancement of their mechanical and optical performance, causing a preferable orientation of the macromolecules close to the surface. Nanoindentation and se testing have revealed the existence of a two-layer geometrical structure of the pet membranes, consisting of a thick amorphous pet layer and a thin crystalline-like pet overlayer, with increased hardness (elastic modulus). The analyses of the experimental dataprovides quantitative information on the formed overlayer, which is ascribed to the processing history of the membrane.