Influence of crosslinking conditions on the phase behavior of a polyacrylate-based liquid-crystalline elastomer

The influence of crosslinking conditions (γ-radiation-induced and chemical crosslinking above and below the clearing point) on the phase behavior of a liquid-crystalline polyacrylate-based elastomer is shown and discussed. The network formation in samples γ-irradiated in the nematic phase results in an increase of the clearing point T_n-i which does not depend on the crosslinking density expressed as the ratio of weight-average molecular weight over number-average molecular weight between crosslinks M _w/M _c within a wide M _w/M _c range. The distorting action of the crosslinking agent at the same temperature leads to the opposite tendency in the change of T_n-i. Crosslinking in the isotropic phase shows a strong decrease in T_n-i.     

Copolymerization of N,N‐Dimethylacrylamide with Styrene and Butadiene: The First Example of Polar Growing Chain End/Nonpolar Monomer Cross‐Initiation

Living potassium poly(N,N‐dimethylacrylamide) initiates the polymerization of styrene and butadiene, and adds 1,1‐diphenylethylene in THF solution. The model compound α‐potassio‐N,N‐dimethylpropionamide also polymerizes styrene and butadiene in contrast to esterenolates, which are known to be incapable of such reactions. The IR spectra and SEC traces of the polymers obtained unequivocally prove that styrene and butadiene initiation proceeds directly via the amidoenolate anion. Apparently, this is the first case observed where the polymerization of a nonpolar monomer can be initiated by the growing chain end of a polar polymer.     

Polymer-colloid complexes in three-component system: poly(styrene-alt-maleic acid)-poly(ethylene oxide)-silica sol in aqueous medium

Complex formation in the model three-component system, including polymer-polymer complex of poly(styrene-alt-maleic acid) (PSMA) and poly(ethylene oxide) (PEO), and also silica sol (SiO₂) in aqueous solution as a function of molecular weight of PEO and the order of component mixing, were investigated. The degree of binding of PSMA links with PEO and SiO₂ as well as the Gibbs energy of formation of the polymer-polymer complex and polymer-colloid complexes were defined. It was shown that the main factor of stabilization of the structure is hydrogen bonds. The conditions of three-component polymer-colloid system are practically independent of the order of component mixing. The spontaneous formation of polymer-colloid complexes between chemically complementary polymers and small dispersed particles is considered as the main reason for the abnormally high binding ability of colloid particles to the polymer-polymer complex.     

Conformational changes in poly(vinyl alcohol)-graft-polyacrylamide in aqueous solutions vs graft content

Conformational changes have been studied in intramolecular polymer-polymer complexes (intraPC) of graft copolymers of poly(acrylamide) and poly(vinyl alcohol) (PVA-g-PAA) with various numbers of grafts (4-42) per molecule as a function of temperature and copolymer concentration. It is shown that the magnitude of conformational change depends on the grafts content while the temperature range over which the conformation changes occur is essentially determined by copolymer concentration. The conformational changes are reversible on heating and cooling.     

Effect of titanium,antimony, and ruthenium doping on tin dioxide adsorption properties. Quantum-chemical modeling

The influence of the composition of oxides supports on the specific electroactive surface area of Pt in the catalysts, the platinum nanoparticles dispersion, and Pt contents in the catalysts was studied. The Sb-doped SnO₂ oxides with various Sb-doping levels were prepared as a supports of platinum catalysts in polymer electrolyte membrane fuel cells. Density functional theory simulation of Ti, Sb, and Ru doping of tin dioxide and interaction of the doped surfaces with platinum cluster Pt₁₉ have been carried out. All calculations were performed in PBE exchange–correlation functional, with periodic boundary conditions and projector-augmented waves (PAW) basis set. The calculation results were compared with the experimental data X-ray diffraction and transmission electron microscopy (TEM). It was shown that Sb doping of tin dioxide (in quantity of less than 10%, that is, the quantity which cannot provoke significant defects of crystal structure of the supports) leads to a significant increase in a number of platinum clusters adsorbed from the colloidal solution onto the supports surface which results to an increase of the platinum cluster interaction with the supports. The calculated and experimental results are in close fit.     

Liquid-crystalline ordering in two-dimensional systems with discrete symmetry

The mean-field theories of liquid-crystalline (nematic) ordering developed for three-dimensional systems are applied to describe two-dimensional systems of both geometrically anisotropic and anisotropically interacting particles. Systems with discrete symmetry (lattice models) for which long-range order is possible are considered on the base of the Landau free-energy expansion. It is shown that the Hamiltonian describing the energy of intermolecular interactions may be written in a common form for lyotropic and thermotropic systems. The mean-field theory gives a continuous phase transition (second-order phase transition) for a square lattice, whereas for a triangular lattice it gives a phase transition with latent heat (first-order phase transition) like for three-dimensional systems. These results are compared with results of the exact theories (two-dimensional Ising and Potts models). It is concluded that for realistic two-dimensional models the orientational in-plane ordering is not sharper than a second-order phase transition.     

About the compatibility of polymer components in polymer complexes based on poly(acrylamide) and poly(vinyl alcohol)

The issue of applying the usual concepts of polymer compatibility to nonstoichiometric PVA/PAA mixtures of chemically complementary poly(vinyl alcohol) and poly(acrylamide), which form in water solution InterPC (intermolecular polymer complex) stabilyzed by H‐bonds, and PAA to PVA graft copolymers (PVA‐PAA_N) with different grafted chains number N, that are IntraPC (intramolecular polymer complexes) is discussed. PVA and PAA are compatible on molecular level. At the same time PVA/PAA mixture (50/50 W/W) is characterized by heterogeneous structure consists of InterPC with ϕ_char=9g_PVA/g_PAA and the excess of unconnected PAA. In the case of IntraPC, yet, only PVA‐PAA_N, where N=25, is characterized by a single glass transition temperature (Tg). At larger values of N separate PAA domains form giving rise to the corresponding Tg. These results are discussed in view of IntraPC structure peculiarities as a function of N investigated by IR spectroscopy.