Effect of 2,2,6,6-tetramethyl-1-piperidinyloxy nitroxide substituent on kinetic parameters of pseudoliving polymerization

The main kinetic and thermodynamic parameters of the pseudoliving radical polymerization of styrene mediated by 4-linoleamido-2,2,6,6-tetramethyl-1-piperidinyloxy have been studied. It has been shown that the introduction of the said substituent into nitroxide leads to a marked reduction in the rate constant of reinitiation that is compensated for by the simultaneous reduction in the rate constant of reversible termination. As a result, the rate of pseudoliving polymerization, the rate of molecular mass growth, and the polydispersity of the polymer appear to be practically the same for processes mediated by both unsubstituted and substituted nitroxides.     

Atomic-force microscopy of submicron films of electroactive polymer

Atomic-force microscopy is used to study the supramolecular structure of submicron films of electroactive thermally stable polymer (polydiphenylenephthalide (PDP)). It has been demonstrated that PDP films produced using centrifuging are solid homogeneous films with thicknesses down to several nanometers, which correspond to two or three monomolecular layers. The film volume is structurized at thicknesses greater than 100 nm. The study of the rheological properties of solutions used for film production yields a crossover point that separates the domains of strongly diluted and semidiluted solutions. A transition from the globular structure to the associate structure is observed in films that are produced using solutions with a boundary concentration. A model of the formation of polymer film that involves the presence of associates in the original solution is discussed.     

Supramolecular structure of electroactive polymer thin films

This paper presents the results of an experimental investigation of the supramolecular structure of polydiphenylenephthalide thin films that exhibit effects of resistive switching. The supramolecular structure of the polymer has been investigated using small-angle neutron scattering in conjunction with atomic force microscopy. It has been found that the internal structure of polymer films consists of structural elements in the form of spheroids. The sizes of the structural elements, which were obtained from the neutron scattering data and analysis of the atomic force microscopy images, correlate well with each other. A model of the formation of polymer layers has been proposed. The observed structural elements in polymer films are formed due to the association of macromolecules in the initial polymer solution.     

Emission properties of a silicon-polymer-vacuum planar structure

Self-sustained electron emission from a silicon-polymer planar structure is studied experimentally. It is found that emission can be initiated by a short-term action (e.g., a vacuum microdischarge). The I–V characteristics and time dependence of the emission current are recorded. It is shown that the value and stability of the emission current depend on the thickness of the polymer film. A model explaining the origin of and conditions for self-sustained electron emission is proposed. It is based on today’s concepts of electron emission from insulating layers (Malter effect) with regard to the structure and properties of polymer films.     

Effect of interface in bilayer polydiphenylenephthalide film on electron transport

The results of studies of multilayer film structures based on a wide-gap polymer using the time of flight technique are shown. Experimental data showed that transport of charge carriers depends strongly on the presence of a polymer/polymer interface. The possibility is shown of increasing the threshold thickness of the experimental structure, in which effects of switching to a highly conducting state induced by uniaxial mechanical pressure are also found. Preliminary interpretation of the obtained data is performed.     

Effect of excessive pressure on the drift mobility of charge carriers in poly(diphenylene phthalide) films

The electron-hole transport in poly(diphenylene phthalide) films has been investigated. The dependence of the drift mobility of charge carriers on the excessive mechanical pressure has been studied using the time-of-flight method. It has been revealed that, with an increase in the thickness of the polymer film, the dispersive transport of charge carries gives way to the quasi-dispersive transport. In thin films in the prethreshold range (i.e., before switching of the samples to the highly conductive state under excessive pressure), the electron mobility increases and exceeds the hole mobility. The experimental results have been discussed in the framework of the model describing the transport through the channels formed by metastable electron-hole pairs.     

Radical polymerization of N-vinylcaprolactam in benzene solutions in a wide conversion range

The kinetics of radical polymerization of N-vinylcaprolactam initiated by the thermal decomposition of AIBN at 60°C in monomer solutions in benzene has been studied in a wide range of conversions. The heat of polymerization of N-vinylcaprolactam is 76.0 ± 0.9 kJ/mol; at initial conversions, the polymerization of N-vinylcaprolactam is of the first order with respect to the monomer and of the 0.5th order with respect to the initiator. The ratio of chain propagation and chain termination rate constants k _p/k _ter ^0.5 is 0.578 l^0.5/(mol s)^0.5, thus suggesting a high propagation rate constant k _p > 10³ l/(mol s). At a high initial concentration of the monomer, the kinetic curves demonstrate a weakly pronounced gel effect, and, in the gel permeation chromatography curves of the polymers, the second high-molecular-mass mode emerges, whose intensity grows with conversion. The observed kinetic features are interpreted in terms of the diffusion control of the gel effect.     

Synthesis of polyarylenephthalides prospective as smart polymers

The data on the synthesis of polyarylenephthalides, their analogs, and derivatives are surveyed. The main attention is given to the synthesis of polyarylenes through the polycondensation of pseudoacid chlorides according to several variants, predominantly via the self-condensation of pseudoacid chlorides, which may be depicted by the general scheme

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(?RH is the radical of aromatic or heterocyclic polynuclear hydrocarbon.). The reaction affords polyarylenephthalides (I) (X = CO, Y = O), polyarylenephthalimidines (II) (X = CO, Y = NR₁, where R₁ is an aromatic hydrocarbon), and polyarylenesulfophthalides (III) (X = SO₂, Y = O). Polymers I and II hold promise for designing thermostable, heat-(T _g ≥ 420–470°C) and chemoresistant, and functional materials. One should distinguish the valuable functional properties of polymers I and III that make them prospective as smart polymers, namely, the switching effect induced by temperature, pressure, and electric and magnetic fields along with changes in color, electro-and photoluminescence. Owing to the presence of sulfophthalide groups, polymers III are candidates for use as latent polyelectrolytes. With consideration for the foregoing reasoning, phthalide-containing polyarylenes of several other classes, namely, polyaryleneketones, poly(arylene ether ketones), polyarylates, oligomer resols, and crosslinked systems on their basis, which are prospective as smart polymers, have been synthesized.

     

New possibilities for the effective influence on the charge transport in poly(arylene ether ketones) without using phthalide-containing fragments in the polymer chains

A number of copoly(arylene ether ketones) containing the phenolfluorene and bisphenol A fragments were synthesized. By the example of these compounds, it was shown for the first time that the effect of reversible electronic switching can exhibit in the copolymer films even if this effect is absent in the corresponding homopolymer films.     

Giant magnetoresistance of strong magnet–polymer heterostructures with a wide band gap

We present the results of studying the effect of a weak external magnetic field on the conductivity of heterostructures containing a wide-gap polymer layer. A set of experiments is singled out for switching the metal–dielectric conductivity, controlled by a weak magnetic field. Evidence of the reliability and repeatability of key experiments are reviewed, and the effect of possible artifacts on switching of the conductivity in the heterostructures under study is discussed.