Dmitri Likhatchev

Soluble aromatic polyimides based on 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane: Synthesis and properties

Aromatic polyimides were synthesized from 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6F-OH diamine) and different aromatic dianhydrides by a one-step hightemperature polycondensation, or by a two-step procedure using either thermal or chemical imidization of poly(amic acids), PAA. The obtained polyimides were compared in terms of their chemical structure, molecular weight, mechanical and thermal properties. The reaction of 6F-OH diamine with different aromatic dianhydrides in amide solvents at room temperature resulted in the formation of PAA with moderate molecular weight (ηinh ⩽ 0.7 g/dL). The thermal imidization of these PAAs led to brittle hydroxy polyimides (PI-6F-OH). In contrast, chemical imidization of similar PAAs in acetic anhydride and pyridine brought about flexible self-supporting polyimide films. The FTIR analysis indicated that the latter process was accompanied by an esterification of the OH groups in the diamine moieties, resulting in the formation of the polymers with side acetate groups (PI-6F-Ac). The high molecular weight hydroxy polyimides, suitable for preparation of films with good tensile properties, were synthesized by a one-step high-temperature polycondensation in phenolic solvents. All obtained polyimides were well soluble in common organic solvents. The highest solubility was observed for PI-6F-Ac. It was found by means of FTIR and TGA that the polyimides with the R group (R = OH or acetate) in orto position to the nitrogen atom in the diamine moiety underwent a rearrangement to benzoxazoles above 300°C. The starting temperature and conversion of this rearrangement reaction were controlled by the type of R group. The imide-to-benzoxazole rearrangement shifted to lower temperatures, and higher conversion was encountered for the polyimides with side acetate group, PI-6F-Ac, obtained by chemical imidization.

Preparation and Characterization of Sulfonated Polyphenylquinoxalines

Poly(phenylquinoxaline)s.(PPQs) are a family of aromatic condensation polymers known for their outstanding thermal and chemical stability. The pendant phenyl groups and chains isomerism improve the solubility and processing characteristics of these polymers. PPQs have also been shown to possess excellent thermo-oxidative stability and thermohydrolytic stability. This stability makes these polymers candidates for development as proton exchange membranes (PEMs) to be used in fuel cells. In addition to thermohydrolytic stability, PEMs require high protonic conductivity and, in order to achieve this they also require high water uptake. Aromatic condensation polymers do not possess these properties, but ionomers derived from them may. The usual method to derivatiziting these polymers is through sulfonation. In the frames of the present investigation we have carried out sulfonation of two PPQs using an H2SO 4—oleum mixture (4 : 1) as sulfonating agent at 125 3C. As a quinoxaline ring is readily formed in acidic medium synthesis of sulfonated PPQs (SPPQs) was also carried out directly from monomers using an H 2SO4—oleum mixture as solvent, catalyst and as sulfonating agent. Depending on the conditions of the reaction (temperature, duration, and the ratio of components in a sulfonating mixture) the polymers containing 0.2—6.7% S were prepared. SPPQs are soluble in polar organic solvents1 from the solutions of SPPQs high strength films (3 = 80—100 MPa) were cast. On the basis of sulfonated PPQs new cation-exchange membranes were prepared and investigated. Among the cation-exchange membranes developed those of the greatest interest are proton-exchanging membranes for fuel cells. Proton conductivity of the membranes prepared strongly depends on relative humidity and comparable with the conductivity of Nafion 117.

Topochemical polymerization of butadiynylene dibenzamides

SummarySeries of meta- and para-substituted butadiynylene dibenzamides were synthesized, and their solid state polymerization was studied. The meta-isomers were light sensitive but not heat sensitive. The polymerizability of para-isomers depended on the type of N-substitutents. The polydiacetylenes from the para-isomers were blue, while those of the meta-isomers were light purple. Studies with molecular models and computer imaging suggested that hydrogen bonding between the topochemically polymerizable dibenzamides in the polymerization array is rather unlikely.

Bulk polymerization of 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane induced by gamma radiation

Abstract Gamma ray-induced bulk polymerization of 1,3,5,7-tetravinyltetramethylcyclotetrasiloxane at ambient temperature has been investigated. It was found that the polymerization proceeds via a free radical mechanism through the reaction of vinyl groups, and the resulting polymer had a three-dimensional network structure. Kinetic features of the reaction were also studied, strong postpolymerization effects were observed at doses between 8 and 80 kGy. The composition of the sol fractions was determined by high pressure liquid chromatography, and the chemical structure of both the sol and gel fractions was analyzed by FTIR spectroscopy. Thermal stability of the gel fractions, determined by thermogravimetric analysis, and the thermomechanical behavior of unextracted samples were found to depend on the irradiation dose.

Theoretical simulation of the topochemical polymerization of some diacetylene molecules

The solid-state reaction of crystalline diacetylenes to yield polydiacetylenes is studied from a theoretical point of view to understand the possible reaction pathway and the nature of the resultant crystal in the case of a meta-substituted isomer. The lack of crystallization of the para isomer of the same molecule is also analysed, and it is shown that the large change required of the crystal cell parameters can explain this feature.

One-step synthesis of aromatic polyimides based on 4,4′-diaminotriphenylmethane

The feasibility of using a one-step high-temperature polycondensation for the synthesis of aromatic polyimides, based on 4,4′-diaminotriphenylmethane (DA-TPM), was studied. It was found that the reaction of DA-TPM with various aromatic dianhydrides in nitrobenzene at 180–200°C resulted in the formation of the high molecular weight soluble polyimides, PI-TPM. The reaction solutions cooled to ambient temperature were used for casting films. These PI-TPM films significantly exceeded their prototypes obtained by the thermal imidization of poly(amic acids) in terms of solubility and tensile properties. All studied polyimides demonstrated well-distinguished glass transition at 260–320°C.

Low-Temperature Route to 1, 2-Benzoylenebenzimidazole Ladder Structure

Low-temperature catalytic conversion of N-(o-aminophenyl)phthalamic acid (I) was studied as a model reaction for the synthesis of ladder poly(aroylenebenzimidazole)s. The treatment of I with acetic anhydride/pyridine or trifluoroacetic anhydride resulted in the selective and quantitative cyclodehydration to yield either imide or isoimide structures respectively. The imidization was accompanied by acylation of the ortho amino group to form lateral acetamide or trifluoroacetamide substitutes. Thermodynamically unstable N-(o-trifluoroacetamidophenyl)phthalisoimide (III) underwent secondary cyclization to yield ladder 1, 2-benzoylenebenzimidazole (V) between 130 and 150 °C. The conversion of this reaction did not exceed 35% because it competed with the thermal isomerization of III to the stable N-(o-trifluoroacetamido-phenyl)phthalimide (IV). The cyclization of N-(o-trifluoroacetamidophenyl)phthalisoimide (III) was found to be possible even at room temperature. The formation of 30–35% of the ladder 1, 2-benzoylene-benzimidazole (V) was observed after III was dissolved in DMF and stored at room temperature for 4–10 h. This also was accompanied by the catalytic isoimide-to-imide isomerization. The obtained data may be useful for the further development of novel low-temperature approaches to the synthesis of ladder poly(aroylenebenzimidazole)s. Synthesis of aromatic polyimides and polyisoimides with lateral alkylamide or trifluoroalkylamide from available aromatic dianhydrides and tetraamines may also be of practical interest.

Theoretical study of N-(o-aminophenyl amic) acid cyclodehydration to 1,2-benzoilenebenzimidazole as a model reaction of ladder polypyrrones synthesis: thermodynamic and thermochemical data

Abstract The mechanism of polyimidazopyrrolones formation was studied via thermodynamic simulation of N-(o-aminophenyl)amic acid cyclodehydration to 1,2-benzoylenebezimidazole. It was found that 2-(o-carboxyphenyl)benzimidazole and N-(o-aminophenyl)phthalimide were the most thermodynamically favorable intermediates of this process. The thermodynamic possibility of 1,2-benzoylenebezimidazole formation from N-(o-acetamidophenyl)phthalimide and N-(o-trifluoroacetamidophenyl)isophthalimide was also evaluated using the same method. All thermodynamic values were obtained from semiempirical quantum mechanics calculations.