Unperturbed dimensions of isotactic and atactic polypropylene at various temperatures

The dimensions of both atactic and isotactic polypropylene were determined at various temperatures in θ solvents with the following results:$\text{—(}\text{d ln}\text{r}{}_{\mathrm{o}}{}^2\text{/d}$T) = 1 · 8 (atactic polymer), and 3 (isotactic polymer). These results, compared with those obtained in our laboratory for polybutene-1 and poly-pentene-1, allow us to construct a general picture of the variation of the unperturbed dimensions of poly-α-olefins with temperature.     

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.     

Unperturbed dimensions of polystyrene in mixed solvents at high temperature

At 371.5 K, which is the θ-temperature for polystyrene (PS) in 3-methyl cyclohexanol (MC), intrinsic viscosities [η] have been measured for PS samples of different relative molar mass M in mixtures of MC with a thermodynamically good solvent 1,2,3,4-tetrahydronaphthalene over the whole range of solvent composition. Eleven graphical procedures have been utilised and assessed in deriving the unperturbed polymer dimensions expressed as K_θ (in the relation $\text{[η] = K}{}_{\mathrm{\theta }}\text{M}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{α}{}^3$ where α is the expansion factor). For those procedures concluded to be the most reliable, there was no influence of binary solvent composition: the value of K_θ = 78 (±1) × 10^?3 dm³ kg^?1 was the same as that obtained directly under θ-conditions.     

Unperturbed dimensions of amylose tributyrate from viscosity data in non-ideal solvents

The unperturbed dimensions of amylose tributyrate have been estimated from viscosity measurements in non-ideal solvents. The validity of several methods of extrapolation has been assessed for this polymer. A small solvent dependence of the unperturbed dimensions has been observed and the characteristic ratio C_∞ has been found to vary between 5·6 and 6·8. One can conclude from this that the ester chain is only slightly more extended than the native amylose, assuming that the ring conformation in the backbone remains unaltered when the ester is formed.     

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.     

Morphologies of long chain branched isotactic polypropylene crystallized from melt

The crystallization behavior and resulting crystalline morphologies of long chain branched isotactic polypropylene (LCBPP) under different conditions were studied by means of differential scanning calorimetry and transmission electron microscopy combined with electron diffraction. The results indicate that the crystallization of LCBPP during fast cooling process, or at lower crystallization temperature, leads to the formation of mainly edge-on lamellar structures. The LCBPP exhibits also the wide angle lamellar branching frequently observed for linear isotactic polypropylene. Crystallizing LCBPP in temperature range of 110∼140 °C results in the formation of both edge-on and flat-on crystals, which coexist side by side with the content of flat-on crystals increases with increasing crystallization temperature. At high crystallization temperature, e.g. 145 °C, flat-on crystals with chain axis aligned perpendicular to the film plane are the only observed morphology. Moreover, the crystals of LCBPP grow slower than its linear counterpart and the crystal growth rates of both linear and long branched PPs are temperature dependent.     

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.     

Variation of polymer chain dimensions with temperature below the theta point

The temperature dependence of the intrinsic viscosity [η] for the system polystyrene-cyclohexane in the interval ?20 < (T ? ψ) ≤ 0 near the ideal temperature ψ has been investigated. The observed diminution in size of the molecular coil with decreasing temperature is attributable to attractive net polymer-solvent interactions, denoted by negative values for the excluded volume parameter z. The data thus comprise an interesting selection for comparison with the predictions of various excluded volume theories. Among the approximate, closed-form expressions the functional relationship of Flory (x⁵ ? α³ ～ z) appears to describe best the variation of [η] with temperature in the region examined. The behavior of the Huggins constant k′ derived from the intrinsic viscosity plots is also examined, in accordance with the Peterson-Fixman model, suitably extended to the temperature region below ψ.     

Production and properties of polyacenaphthylene VII. Unperturbed dimensions and chain conformational studies of polyacenaphthylene

The unperturbed dimensions of polyacenaphthylene in solution were determined from light scattering, osmotic and viscometric data in thermodynamically good solvents and in the theta solvent, 1,2-dichloroethane, using direct and indirect evaluation methods. The estimated value of the steric factor, α, shows polyacenaphthylene to be a relatively rigid polymer in contrast to the results obtained from hydrodynamic investigations. An attempt was made to explain this discrepancy in terms of a tightly coiled conformation is solution due to weak links in the polymer chain.     

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.     

Crystallization of oxidized isotactic polypropylene

The effect of processes accompanying thermal oxidation of the polymer on the characteristics of its isothermal crystallization has been revealed. It has been shown that crystallization decelerates with a rise in the degree of PP oxidation. The higher the concentration of functional groups, the stronger the deceleration. The energy of nucleation increases when passing from virgin to oxidized PP samples. The higher the concentration of carbonyl groups accumulated in polymer chains, the more pronounced this effect, although the degradation of the chains must lead to a reduction in this parameter. It has been concluded that the kinetic and thermodynamic parameters of the isothermal crystallization are applicable to investigation of processes accompanying thermal oxidation of the crystallizable polymer.     

Unidirectional solidification of isotactic polypropylene

Thin films of isotactic polypropylene have been solidified unidirectionally by pulling specimens through a fixed temperature gradient of 5.5°/mm at rates ranging from 0.07 to 7 mm/hr. At pulling rates lower than 1.7 mm/hr, polypropylene spherulites grew preferentially in the direction of solidification with a tendency to the generation of more asymmetric spherulites at lower rates of solidification.     

Low and high-yield isotactic polypropylene

The crystallization and melting behaviour of isotactic polypropylene (iPP) samples synthetized with different catalyst systems (low and high-yield) have been studied by differential scanning calorimetry and optical microscopy. The isothermal crystallization rates from the melt have been found to depend on the catalyst system employed and on the isotacticity index of the sample. Moreover, for low-yield iPP, Avrami analysis of the overall kinetics has provided evidence of the presence of secondary crystallization phenomena. The values of the equilibrium melting point, energy of nucleation and surface energy of folding of iPP lamellar crystals have been calculated according to the ‘Kinetic theories’ of polymer crystallization. The observed variation of such thermodynamic parameters for the various iPP samples has been accounted for by the amount and type of configurational irregularities present along the chains and by the differences in the molecular weight distribution.