G. N. Bondarenko

Oxidative Polymerization of Diphenylamine: Synthesis and Structure of Polymers

Three procedures for the chemical oxidative polymerization of diphenylamine, namely, in solutions of sulfuric acid, in an H2SO4-tert-butanol mixture, and via the interfacial process, are considered. It was shown that the highest molecular mass products are formed by the interfacial process. Oxidative hydrolysis and chain termination reactions predominate in a homogeneous medium. The effects of polymerization conditions, such as the concentration of reagents, their ratio, and the reaction temperature, on the yield and molecular-mass characteristics of polydiphenylamine were studied. The structure of reaction products was investigated by UV spectroscopy. It was demonstrated that, even when ammonium persulfate is in excess, the degree of oxidation of polydiphenylamine is rather small and chain propagation proceeds as a C-C rather than N-C addition as in the case of aniline.

Nanofiltration and sorption of organic solvents in poly(1-trimethylsilyl-1-propyne) samples of different microstructures

For two PTMSP samples synthesized on various catalytic systems (TaCl5/TIBA and NbCl5) and having different chain configurations (the ratio of cis/trans units is equal to 50/50 or 63/37 for PTMSP/Ta and PTMSP/Nb, respectively), sorption and organic solvent nanofiltration (OSN) behavior is studied. Equilibrium sorption (a homological series of linear alcohols C1-C10, diols and ketones for PTMSP/Ta and a homological series of linear alcohols C1-C10 for PTMSP/Nb) and equilibrium swelling of polymers in the above solvents are estimated. Nanofiltration of dilute ethanol solutions of three dyes (Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R) is studied for the PTMSP/Ta sample, and the resultant nanofiltration characteristics of this sample are compared with the earlier data on PTMSP/Nb. Analysis of the experimental results on sorption and swelling of the PTMSP/Ta samples makes it possible to conclude that PTMSP contains sorption sites which are able to coordinate two hydroxyl groups. Structure of the PTMSP/Ta and PTMSP/Nb samples is studied by the methods of vibrational IR spectroscopy and quantum chemistry. The nature of sorption sites in PTMSP is likely to be related to an exceptionally high polarity of the C=C and Si-C bonds in the repeat polymer units. Computational simulation for the model composed of five PTMSP units in the presence of ethanol monomer shows that, in this system, a complex with ΔE = 18 kJ/mol is formed. Nanofiltration studies indicate that, for the PTMSP/Ta sample, the permeability coefficient of ethanol and overall flux of dye-containing ethanol solutions are nearly two times lower than those for PTMSP/Nb. For both PTMSP samples, dye retention increases in the following order: Solvent Blue 35, Safranine O, and Remazol Brilliant Blue R, and this tendency agrees with the increase in the partition coefficients of the above dyes. For the PTMSP/Ta sample, dye retention of Solvent Blue 35 and Safranine O dyes with molecular masses of 350 g/mol appears to be lower than that of the PTMSP/Nb samples. Sorption and nanofiltration behavior of PTMSP/Ta and PTMSP/Nb can be reasonably explained in line with the existing approaches which treat glassy amorphous polymers as microheterogeneous systems containing structural regions with different ordering of polymer chains, and the observed difference in their sorption behaviour and membrane characteristics can be explained by the fact that packing of polymer chains in the PTMSP/Ta is more loosened as compared with that of the PTMSP/Nb sample.

PIM-1/MIL-101 hybrid composite membrane material: Transport properties and free volume

A hybrid composite membrane material based on the PIM-1 polymer of intrinsic microporosity and MIL-101 nanoparticles of mesoporous chromium terephthalate has been prepared and tested. Fourier-transform IR spectroscopy has revealed the presence of interaction between the polymer matrix and the nanoparticles introduced into it. The addition of MIL-101 nanoparticles leads to an increase in the permeability and diffusion coefficients for gases (He, O2, N2, CO2) compared to the original polymer. Using positron annihilation lifetime spectroscopy (PALS), it has been shown that these changes result from an increase in the free volume in the polymer composite material.

Chain Structure and Stiffness of Teflon AF Glassy Amorphous Fluoropolymers

The structure of the amorphous perfluorinated polymer Teflon AF 2400 and other structurally close perfluoropolymers was studied by means of a quantum chemistry method. The electronic and structural characteristics of the repeating unit and polymer models with ten and nine monomer units were obtained. It was found that two nonplanar isomers can exist for different models of the perfluorinated dioxole ring with a difference of their energy minimums of 10.8 kJ/mol. The orthogonal-block structure of the polymer chain of the perfluorodioxole homopolymer and its copolymer with tetrafluoroethylene was proposed, the block size was found, and a possible diameter of the void formed by two neighboring polymer chains was evaluated. Potential energy curves for the rotation of certain chain fragments about different bonds of the polymer main chain were constructed, and the polymer stiffness was shown to substantially depend on the molar ratio between perfluorodioxole and tetrafluoroethylene units in the copolymer and on the geometry of the perfluorodioxole ring.

Sorption and catalytic effects upon the dehydration of methanol on perfluorinated copolymer-containing sulfo groups

The peculiarities of methanol transformation on the surface of perfluorinated copolymer, fluoroplastic, containing sulfo groups were studied. At temperatures of 70–120°C, the polymer was established to have high initial activity during the conversion of methanol into dimethyl ether; this reaction was, however, accompanied by strong water sorption that leads to a rapid drop in the activity. The sorption/desorption processes were characterized by temperature effects such as heating during sorption and cooling during desorption. The structure of the polymer in the salt (sodium cations) and acid (hydrolyzed polymer) forms was studied by IR spectroscopy. H3O+SO3− ionic pairs were found to be present in the acid form.

Effect of chloroform on the structure and gas-separation properties of poly(ether imides)

The FTIR spectra of poly(ether imide) films prepared from their chloroform solutions were recorded in a wide temperature interval. The cast films were shown to contain residual solvent. This residual solvent existed in films as unbound chloroform that may be removed by heating to 60–70°C and as bound chloroform that is involved in complex formation with polymers and may be removed by heating at temperatures close to their glass transition temperatures (180°C). Quantum-chemical calculations were performed for structures that model fragments and monomer units of poly(ether imides), as well as their complexes with chloroform. Chloroform was shown to be capable of preferential binding with an oxygen atom in a Ph-O-Ph′ fragment via hydrogen bonds. In this case, the conformational set of poly(ether imide) chains is changed. The above evidence is invoked to explain changes in transport characteristics with time for poly(ether imide) films cast from chloroform solutions.

Evidence of hydrogen bonding during sorption of chloromethanes in copolymers of chloroprene with methyl methacrylate and methacrylic acid

Sorption of chloromethanes (CH 2 Cl 2 , CHCl 3 , and CCl 4 ) in copolymers of chloroprene with methyl methacrylate and methacrylic acid was studied using inverse gas chromatography and infra-red (i.r.) spectroscopy. The chromatographic study showed that introduction of ester and carboxylic side groups into main chains resulted in a selective increase of the solubility coefficient of chloroform and methylene dichloride, the solutes capable to form hydrogen bonds with proton acceptors in polymer. Heats of formation of hydrogen bonds were determined by comparison of the partial molar heats of mixing in these systems and in reference systems where hydrogen bonding is excluded. The shifts of maxima of i.r. bands belonging to CH 2 Cl 2 and CHCl 3 and to C-O bonds of the copolymers confirmed the formation of hydrogen bonds. The variation of the solubility coefficients and the shifts of absorption bands indicated that hydrogen bonds formed by methylene dichloride are somewhat stronger than those formed by chloroform.

Effect of structure and conformational composition on the transport behavior of poly(ether imides)

With the example of two isostructural poly(ether imides), the effects of isopropylidene and hexafluoroisopropylidene groups and hydrogen bonding with chloroform on changes in geometry and energy parameters of polymer chains have been analyzed. The relationship between changes in the geometry characteristics of polymer chains and the gas-separation behavior of films cast from these poly(ether imides) has been established. It has been shown that an increase in permeability is related to a rise in rotation barriers and, consequently, to enhancement of chain rigidity, while the improvement of gas-separation selectivity is associated with a reduction in the amount of isoenergy conformers and an increase in the conformational uniformity of polymer chains. As was detected by FTIR spectroscopy and confirmed by quantum-chemical calculations, the conformational nonuniformity and the small-scale mobility of poly(ether imide) chains are possible only in the Ph-O-Ph′ fragment. The data obtained are applicable for estimation of the role of molecular mobility of polymer chains in the mechanism of gas or penetrant transfer through the polymer film and for predicting the transport behavior of polymers from this family. With the example of two other poly(ether imides), the prediction is confirmed by the experimental data on gas separation.

Oxidative polymerization of diphenylamine-2-carboxylic acid: Synthesis, structure, and properties of polymers

Polymers of diphenylamine-2-carboxylic acid are synthesized for the first time via chemical oxidative polymerization. The effects of the concentration of reagents, their ratio, and the temperature and time of reaction on the yield and chemical structure of poly(diphenylamine-2-carboxylic acid) are studied by IR and UV spectroscopy. It is shown that the growth of polymer chains proceeds through the C-C addition in the para position of phenyl rings relative to nitrogen. During the thermal oxidation of poly(diphenylamine-2-carboxylic acid), COOH groups and dopant molecules are successively eliminated; with a further increase in temperature, the polymer behaves as polydiphenylamine. The main processes of thermooxidative degradation of poly(diphenylamine-2-carboxylic acid) begin at 570°C. This value is 120°C higher than the corresponding parameter in the case of polydiphenylamine.

Interfacial oxidative polymerization of phenothiazine

Phenothiazine polymers have been prepared for the first time by interfacial oxidative polymerization. Effects of the concentration and ratio of reagents, temperature, and time of reaction on the yield and molecular mass characteristics of polyphenothiazine are investigated. The study of phenothiazine oxidation indicates that high-molecular-mass products can be prepared if this reaction is carried out in the absence of acids, in contrast to the classical oxidative polymerization of aniline. It is shown that phenothiazine polymers are characterized by a low oxidation state. IR spectroscopy is employed to investigate the chemical structure of the polymers as depending on the synthesis conditions. The propagation of polyphenothiazine chains occurs via the C-C addition in para positions of phenyl rings relative to nitrogen.