Thermal properties of poly-N-vinylcarbazole derivatives

Thermal studies were carried out on some products of chemical modification of poly-N-vinylcarbazole (PNVC). The effect of a substituent introduced into the carbazole ring on the thermal stability of the polymers was investigated. The kinetic parameters of the thermal degradation process were computed.

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Zusammenfassung An chemisch modifizierten Produkten von Poly-N-Vinylkarbazol (PNVC) wurden thermische Untersuchungen durchgeführt, sowie der Effekt eines in den Karbazolring eingeführten Substituenten auf die thermische Stabilität des Polymers untersucht. Weiterhin wurden die kinetischen Parameter des Zersetzungsprozesses errechnet.

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Charge transfer complexes of N-ethylcarbazole and poly-N-vinylcarbazole

Poly-N-vinylcarbazole and its monomeric analog, i.e., N-ethylcarbazole, act as donors in charge transfer complexes with such electron acceptors as iodine, tetracyanoethylene, and tetracyanoquinodimethane. Poly-N-vinylcarbazole and N-ethylcarbazole are also capable of accepting electrons from an alkali metal such as sodium. A study of the spectral properties of both types of complexes showed that the monomer can both accept and donate electrons to a greater extent than the corresponding unit segment of the polymer chain. Equilibrium constants are presented for both cases, and estimates of the ionization potential of N-ethylcarbazole and related compounds are made from the characteristic charge transfer frequencies. Good agreement between these values and those calculated from molecular orbital theory is outlined.     

Unperturbed dimensions of polypivalolactone

Experimental results concerning the fractionation of polypivalolactone, carried out by gel permeation chromatography (GPC) in m-cresol, are reported. For each fraction, the number average and the weight average molecular weights, obtained by GPC using an osmometric calibration, and the intrinsic viscosities in trifluoroacetic acid at 20° are given. These data have been used to calculate the unperturbed dimensions, following the extrapolation procedures proposed by Stockmayer-Fixman and by Cowie. The characteristic ratio C_x thus obtained has been compared with that computed on the basis of the isomeric rotational model.     

Unperturbed dimensions of cyclochain polymers

The conformational parameters of three polyoxadiazoles were calculated by a direct computer simulation assuming free rotation about virtual bonds. The results obtained proved to be close to those derived from viscosity and sedimentation experiments.     

Unperturbed dimensions of copolymer molecules

Proceeding from the work of Zimm and Stockmayer and of Benoit, a general formula is derived for the calculation of the radius of gyration of block and graft copolymers. It appears that with linear block copolymers the ratio of the mean-square radius of gyration and the mean-square end-to-end distance is usually not far from 1/6. With a great number of blocks the difference from 1/6 can entirely be neglected. Also the influence of the composition of the molecules on the scattered light intensity has been considered.     

Unperturbed dimensions of poly-p-chlorostyrene

Viscosity measurements on poly-p-chlorostyrene (PPCS) in benzene-methanol mixtures have been carried out at their corresponding theta temperatures determined by the phase separation method. Viscosity measurements were also run in benzene at the same temperatures. The Stockmayer-Fixman extrapolation method was applied to the data to obtain the chain unperturbed dimensions. K_θ. It was found that these, for PPCS in benzene, decrease with increasing temperature and that, both in benzene and in binary mixtures, they decrease with increasing values of the parameter a from the relationship [η] = KM^α. PPCS theta temperature in benzene was 8.     

Unperturbed dimensions of some aryloxy polyphosphazenes

Three aryloxyphosphazene copolymers, [P(OR)(OR′)-N-] with R = phenyl, and R′ = p-ethylphenyl, 2,4-dichlorophenyl or 2-naphthyl, were each separated into four fractions using fractional precipitations from tetrahydrofuran (THF) solutions, with n-pentane as non-solvent. Two fractions from each were characterized using osmometry and viscometry, in THF at 25°, thereby providing values of the number-average molecular weight, second virial coefficient, and intrinsic viscosity. This information was used to obtain values of the characteristic ratio <r²>₀/nl² of the unperturbed dimensions relative to the number of skeletal bonds and the square of their length. The values of this ratio show a remarkably large dependence on the nature of side-groups, in agreement with the results of two previous investigations. The observed large variations could be due to experimental difficulties associated with solution properties of this class of polymers. If real, however, the differences could be due to the fact that, when the two bond angles of the repeat unit of these chains are significantly different, then the most likely regular conformations of these chains correspond to extremely different spatial extensions. Markedly different values of the unperturbed dimensions could thus conceivably result from changes in conformational population arising from relatively small changes in intramolecular interactions, stereochemical composition, chemical composition, or chemical sequence distribution.     

Molecular weight distribution of poly-N-vinylcarbazole obtained in catalytic solid-state polymerization

The molecular weight distribution of poly-N-vinylcarbazole (PVCar) obtained in solid-state polymerization with various catalysts or γ-rays was measured by gel-permeation chromatography, in order to determine the mechanism of the solid-state polymerization. In addition, the molecular weight distribution of PVCar obtained in the solution polymerization by the cationic catalyst was also measured. The molecular weight distribution of PVCar obtained in the catalytic solid-state polymerization was broad and had three peaks, independent of the nature of catalysts, radical and cationic. A large amount of low molecular weight oligomer (probably dimer or trimer) was formed in the catalytic solid-state polymerization of VCar. The molecular weight distribution of PVCar obtained in the cationic solution polymerization showed only one sharp peak. On the other hand, the molecular weight of PVCar obtained in the radiation-induced solid-state polymerization was larger than that obtained in the catalytic solid-state polymerization, and dimer or trimer was not formed. The molecular weight distribution of PVCar obtained was composed of one sharp peak in the high molecular weight region, and a broad peak in the low molecular weight region, and was extremely different from that of PVCar obtained in the catalytic solid-state polymerization.     

Viscometric Estimation of Unperturbed Chain Dimensions of Polymers

A new expression is proposed to determine the unperturbed dimensions of coil-like polymers viscometrically by use of the Flory and Kratky expression. The unperturbed dimensions so estimated are compared with the results obtained by using different expressions available in the literature. The results are comparable even for stiff chain polymers. The data obtained under theta conditions also fit this expression very well. The effect of molecular weight, its distribution, and that of the solvent has also been studied. It is concluded that the unperturbed dimensions are independent of molecular weight and solvent but depend on the heterogeneity of the system.     

Unperturbed dimensions of poly(9-vinyladenine)

The effect of base stacking interactions on the conformation of poly(9-vinyladenine) (PVAd) was investigated by osmometry, intrinsic viscosity, and light-scattering measurements. At neutral pH, ideal solution behavior (θ conditions) for this polymer was observed at 26 and 40°C. Intrinsic viscosity measurements revealed a conformational transition on heating from 26 to 40°C, while the ultraviolet absorbance of the solution was insensitive to the change. The transition was accompanied by an inversion in sign of the entropy parameter from negative to positive and an increase in the partial specific volume. At 40°, the variation of intrinsic viscosity with molecular weight corresponded to a random coil conformation, but the characteristic ratio, r?₀²/nl² = 8.6 ± 0.2 indicated that the unperturbed dimensions were smaller than usually observed for comparable vinyl polymers. At 26°, a rare macromolecular phenomenon was found, the intrinsic viscosity–molecular weight relation and the estimated r?₀²/nl² of 6.0–6.8 suggested that the PVAd was in a very highly compacted coil conformation, approaching a semirigid sphere. It is proposed that this effect be named the introversion phenomenon. Unlike polyadenylic acid, whose unperturbed dimensions increase with decreasing temperature due to nearest-neighbor base stacking, the results reported here suggest that both nearest-neighbor and long-range intramolecular base stacking occur in PVAd. The different stereochemical arrangements of bases in PVAd and Poly A are probably responsible for the opposite behavior observed.     

Unperturbed dimensions of poly(ethylene oxide)

The intrinsic viscosities of fractions of poly(ethylene oxide) in the molecular weight range 1.5 × 10³ to 10⁶ have been measured at 25°C in benzene, carbon tetrachloride, and acetone; at 35°C in 0.45M aqueous potassium sulfate; and at 50°C in methyl isobutyl ketone and diethylene glycol diethyl ether. The latter three are practically theta solvents. The value of (r₀² /M)^1/2 for poly(ethylene oxide) is calculated to be 0.84 Å from the molecular weights of the high molecular weight fractions, and their intrinsic viscosities in the theta solvents and acetone. Erroneous values result if the usual methods of determination are applied to the data obtained for the low molecular weight (<10⁴) fractions or to the intrinsic viscosities in the very good solvents, benzene and carbon tetrachloride.     

Unperturbed dimensions of isotactic poly(tert-butylethylene oxide)

The root-mean-square end-to-end distances of isotactic poly(tert-butylethylene oxide) fractions were determined in xylene at 80°C from intrinsic viscosity measurements and in o-dichlorobenzene at 80 and 100°C by light scattering. The characteristic dimension (〈L²〉₀/M)^1/2 was 1.04 × 10^?8 cm in xylene and 0.9 and 0.7 × 10^?8 cm in o-dichlorobenzene at 80 and 100°C, respectively. The value in xylene corresponds to a C_∞ of 15.9. This observation and the large negative temperature coefficient of (〈L²〉₀/M)^1/2 suggest that poly(tert-butylethylene oxide) exists in a helical block conformation under these experimental conditions. This conclusion is in agreement with earlier reported NMR measurements.     

Kinetic analysis of the process of thermal degradation of poly-N-vinylcarbazole and its derivatives

Thermal studies of poly-N-vinylcarbazole and its derivatives containing ?Cl, ?Br, ?I and ?CH₃ as functional groups were carried out by means of thermogravimetry. The kinetics of the processes of thermal degradation of these polymers was examined. Kinetic parameters, i.e. apparent activation energy, reaction order and pre-exponential factor, were evaluated by using an integral method.     

Unperturbed chain dimensions of isotactic polypropylene in theta solvents

The unperturbed mean-square end-to-end distance 〈R₀²〉 and its temperature variation d In 〈R₀²〉/dT for isotactic polypropylene have been estimated from intrinsic viscosity data in three theta solvents, i.e., diphenyl, diphenyl ether, and dibenzyl ether, measured at their θ temperatures as determined by precipitation temperature measurements. The characteristic ratios, 〈R₀²〉/nl², where n is the number of bonds of length l in the main chain, evaluated by assuming Φ = 2.87 × 10²¹, are 5.80 in diphenyl (at θ = 125.1°C.), 5.41 in diphenyl ether (at θ = 142.8°C.), and 4.56 in dibenzyl ether (at θ = 183.2°C.). These values lead to the temperature coefficient d In 〈R₀²〉/dT = ?4.09 × 10^?3 deg.^?1 Results are compared with the data previously reported on polyethylene.