N. A. Plate

High transport parameters and free volume of perfluorodioxole copolymers

Abstract Permeability (P) and diffusion (D) coefficients of perfluoro-2,2-dimethyl-1,3-dioxole-tetrafluoroethylene copolymers were determined with respect to different gases (He, H2, O2, N2, CO2, hydrocarbons C1C3). The copolymers with large content of perfluorodioxole comonomer exhibit high permeability with respect to lighter gases comparable to that of poly(trimethylsilyl propyne). However, the copolymers studied are much more permselective than the latter polymer. Free volume as estimated via Bondis method and free volume size distribution parameters which were determined by means of positron annihilation lifetimes (PAL) method are also unusually high if compared with other glassy polymers. A novel correlation of the P and D values, as well as of the solubility coefficients S with the PAL parameter t 4 I 4 are reported.

Gas and vapor permeation and sorption in poly (trimetylsilylpropyne)

Abstract Permeability coefficients were determined and sorption properties were studied for poly (1-trimethylsilyl-1-propyne) (PTMSP), the most permeable of the known (rubbery or glassy) polymers. The values measured for PTMSP are compared with those for poly (vinyltrimethylsilane) (PVTMS), another glassy polymer with similar structure, which has high permeability, although lower than that of PTMSP and high diffusion coefficients. It was shown that permeability coefficients differ by 1-3 orders in favor of the former, depending on the nature of the diffusant molecules. This is due to the increase in diffusivity and sorption parameters or solubility coefficients. One can conclude that non-equilibrium free volume in a polymer with bulky Si (CH 3 ) 3 substituents is larger when the backbone chain is stiff (PTMSP) than when it is more flexible (PVTMS).

Novel poly(silicon olefins) for gas separations

Methods are discussed for the synthesis of poly(triorganovinylsilanes), viz. poly(vinyltrimethylsilane) and poly(vinylallyldimethylsilane), silane-siloxane and silane-butadiene blockcopolymers. Mass-transfer properties (permeability, diffusion and solubility coefficients;P, D and σ respectively) are presented for poly(vinyltrimethylsilane), vinylsilane copolymers and poly(trimethylsilylpropyne). The detailed studies on mass-transfer parameters of these and some other polymers revealed that those with pendent organosilicon groups are characterized by higher P, D, and a values compared with the values for other glassy and many rubbery polymers. Spin probe and positron annihilation studies on poly(vinyltrimethylsilane) point to high free volume in the polymer, due apparently to the presence of bulky trimethylsilyl substituents.

Liquid crystal acrylate-based networks : polymer backbone-LC order interaction

Abstract New synthetic pathways to poly- and monodomain acrylate-based networks via gamma-irradiation and chemical crosslinking are described. Strain-induced orientation transitions and phase behavior are studied by X-ray scattering, differential scanning calorimetry and optical microscopy. Analysis of the observed phenomena is given in terms of crosslinking conditions, network topology, structure and spatial distribution of crosslinks. The pretransitional behavior and the observed shifts in clearing point Tn–i are in good agreement with theoretical predictions. The reorientation process in monodomain networks is regulated via strain gradients generated by external mechanical field. The variation in geometrical shape of the samples gives an opportunity to control and realize two different reorientation mechanisms: uniform director rotation and reorientation via stripe domains. Gamma-irradiation is found to be a powerful tool for fixation of any current distribution of poly- and monodomain regions within the LC film. ‘Macroscopic memory’ of the information recorded on the films is observed and discussed.

The regulation of liposome permeability by polyelectrolyte

Abstract The effect of the synthetic polycation polydimethylaminoethylmethacrylate on liposome permeability was studied. Liposomes were prepared from pure dipalmitoylphosphatidyl-choline with the addition of dipalmitoylphosphatidic acid. Poly electrolyte can form electrostatic complexes with liposomes, thereby changing their permeability for liposome-entrapped 6-carboxyfluorescein. The presence of charged lipids in the liposomal membrane facilitates complex formation and increases permeability changes in pH-dependent fashion. The maximal permeability increase was observed during the first 15–30 min of poly electrolyte-liposome interaction. The mechanism of liposome permeability changes was suggested assuming charged phospholipid cluster formation on the liposome surface under the action of poly electrolyte.

Polysilicon hydrocarbons: Synthesis, structure and gas separating properties: review☆

The link between the structure of silicon-containing polymers and their transferring properties is considered. Methods are described for synthesizing polyvinyltrimethyssilane and copolymers of vinyl trimethylsilane with dienes and siloxanes. Information is presented on a commercial gas-separating membrane based on polyvinyltrimethylsilane—technology of production, characteristics and areas of application. The properties of new silicon-containing polymers of the acetylenic and allyl types are briefly discussed.

Ecologically benign motor fuels and petrochemicals from alternative raw materials

Physicochemical foundations of various processes which comprise the single stages of natural gas processing into motor fuels are considered. Among them are: novel process of syngas production by methane reforming using rocket technology, direct dimethyl ether synthesis from syngas and its conversion into the ecologically benign gasoline, an advanced technology of methanol synthesis, as well as methanol transformation into pure hydrogen, Fischer–Tropsch synthesis with increased selectivity. New developments made by the Topchiev Institute of Petrochemical Synthesis Russian Academy of Sciences (TIPS RAS) in this field are discussed. In this light, the achievement of a global goal, to make synthetic motor fuels cheaper than their oil counterparts, appears to be a solvable task for the nearest future.

A mesophasic state in poly(vinyltrimethylsilane)

Structure of poly(vinyltrimethylsilane) was investigated over a broad temperature interval by X-ray diffractometry, calorimetry, and mechanical spectroscopy. The polymer glass-transition temperature was found to lie at ≅390 K. Below this temperature poly(vinyltrimethylsilane) crystallized from solution is in an imperfect mesophasic state. The transition runs to completion after devitrification and annealing at temperatures close to the melting point: a part of the material is then in a mesophasic state characterized by long-range two-dimensional order with regard to arrangement of macromolecular centres of mass, and by near order along the chain axes. The polymer melts at 513 K to a highly viscous isotropic melt.

Theoretical Considerations on the Reactions in Polymer Blends

Advances in theory of reactions in polymer blends are reviewed. For polymeranalogous reaction, the evolution of the blend structure under concerted action of the reaction and interdiffusion is described for the first time. For endcoupling reaction, the reaction kinetics both in a homogeneous melt and at the interface is considered. An influence of the diblock copolymer formed both on the reaction kinetics and on the thermodynamic equilibrium is analyzed. Theoretical models account for interchain interactions between the block copolymer and homopolymers and analyze such phenomena as segregation of the copolymer to the interface leading to the significant change in the interface properties and the blend stability. For interchain exchange reaction proceeding in a homogeneous melt, an analytical description of the molecular weight and block length transient distributions of the reaction product has been developed. The competition between the reaction and spinodal decomposition has been described. Some unsolved important problems are formulated. The role of experimental studies of the reactions in relatively simple model systems, which stimulate formulating appropriate theoretical problems, is emphasized.

Aspects of flow and structural transitions in alkylene aromatic polyesters

Thermomechanical, rheological and X-ray methods have been used to study a series of poly(decamethyleneterephthaloyl-bis-4-hydroxybenzoates) in the interval M = (0.8−4.2) × 104. The LC melts of the polymers constitute quasiviscoplastic liquids. The flow limit is probably connected with the formation of a network of dislocations. The existence of breaks in the dependences of viscosity on MM (on logarithmic scales) and on temperature (in Arrhenius coordinates) has been demonstrated. The characteristic MW and temperature ranges are linked with the presence in the region of the LC state of structures with a different level of orderliness. Depending on the specific LC structure and the intensity of deformation extrudates may be obtained not only oriented in different ways but also with a different structure of the elementary cell.