The influence of molecular weight on the degradation of poly(N-vinylcarbazole)

The methods of isothermal and dynamic thermogravimetry have been used to study the degradation of poly(_{N-vinylcarbazole}) (PNVC). The multiple heating rate method has been used, as a dynamic method, to obtain kinetic parameters. A linear relationship between the activation energy. E, and $\text{M}{}_{\mathrm{w}}{}^{\mathrm{?1}}$ ($\text{M}{}_{\mathrm{w}}$ being weight average molecular weight) was found. From isothermal experiments, a temperature was found for which E was independent of molecular weight. We could then refer to a degradation characteristic- temperature of the polymer. On the other hand, altering the heating rate leads to changes in the values of E for each molecular weight indicating two kinds of scission: one occurs in the backbone, producing mainly monomer; in the other, both side-group and backbone scissions occur producing different products.     

Effect of some additives on the photoxidation of rigid PVC

The photoxidative degradation of PVC was studied by i.r. and u.v. spectroscopy and gel permeation chromatography. It was found that the photoxidative degradation of unprocessed PVC is an auto-accelerating chain scission process. Carboxylic groups were found to be the main product formed during degradation. The molecular weights $\text{M}{}_{\mathrm{n}}$ and $\text{M}{}_{\mathrm{w}}$ both decreased, but the molecular weight distribution widened with increasing length of exposure. Single additives, such as calcium stearate. Wax E and a solid organotin stabilizer, altered the rate but not the mode of the degradation. Combination of the three additives changed the mode of the photoxidation from auto-accelerating to constant rate of degradation. Processing at 170° with the combined additives increased the rate constants.     

The thermal polymerization of styrene at temperatures up to 250°

The kinetics of the thermal polymerization of styrene have been studied over the range 60–250°. The overall energy of activation was 86 ± 2 kJ/mole, a value identical to that obtained for the thermal polymerization of styrene in diethyl adipate. As expected, the molecular weight of the polymer decreases with increase in the temperature of the polymerization, and the ratio $\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{M}{}_{\mathrm{<mtext>n</mtext>}}$ becomes greater than 2 for polymer formed at above 140°. The plot of log ($\text{1}\text{M}{}_{\mathrm{<mtext>n</mtext>}}$) against (absolute temperature)^?1 can be represented by two straight lines yielding 24.5 and 32,0 kJ/mole for the activation energies at temperatures below 120° and above 140°, respectively. The former value is in keeping with the molecular weight being controlled by chain transfer with monomer; the latter value would be that expected if the termination process controls the molecular weight of the polymer. Mark Houwink relationships between intrinsic viscosity and $\text{M}$_n and $\text{M}$_w have been found to apply to polymer samples when the molecular weight averages were determined by osmometry and by light scattering. However, deviations were found for low molecular weight material when measured using gel permeation chromatography. The K values were considerably lower, and the α values higher than reported in the literature.     

Proprietes dielectriques d'une serie de polyoxyethylene (POE) presentant des masses moleculaires lentement variables (200 ≤ Mw ≤ 4 × 106)

In this paper, we present dielectric results for samples of POE (polyethyleneoxyde) divided into three classes. Compounds of low molecular weight ($\text{M}{}_{\mathrm{w}}\text{< 1000}$) show very weak absorption at lower temperatures. At higher temperatures (below the melting point), there appears a very important peak (stronger for lower $\text{M}{}_{\mathrm{w}}$) which corresponds to the supercooled phase. Compounds of intermediate molecular weight ($\text{1000 ≤}\text{M}{}_{\mathrm{w}}\text{≤ 10}{}^5$) show a β relaxation near 250 K (bis$\text{M}{}_{\mathrm{w}}\text{? 3000}$) which is due to the movement of chain-ends in the amorphous phase. This process increases with the importance of that part of the structure formed of shorter lamellae, thus explaining the marked diminution of this absorption for higher molecular weight compounds (the shorter lamellae cannot be obtained for $\text{M}{}_{\mathrm{w}}\text{> 4000}$). The α relaxation (obtained for T > 300 K) is perturbed by an important conduction; however, we have found a peak and a shoulder at lower frequencies, due to shorter and longer lamellae respectively. The shoulder is also present for high molecular weight compounds ($\text{M}{}_{\mathrm{w}}\text{≥ 0.1–10}{}^6$). At lower temperatures, they display a very broad γ absorption, superposed at higher frequencies with a β relaxation. The nature of this β relaxation is different from that observed for the intermediate molecular weight compounds.     

Pyrolyse eclair de polyacrylonitriles entre 400 et 800°

Flash pyrolysis of radical and anionic polyacrylonitriles between 400 and 800° and in the absence of oxygen leads to various degradation products, the most characteristic being cyanhydric acid,. cyanogen, acrylonitrile and two dimers α-methyleneglutaronitrile and a cyanopicoline. Two important parameters have been studied: molecular weight ($\text{4 × 10}{}^3\text{<}\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{< 1·6 × 10}{}^6$) and branching density (0 < N/X < 0·6). At 400°, the yields in acrylonitrile and α-methylene glutaronitrile increase with branching density. All the experimental results may be interpreted on the basis of random chain scission, hydrogen transfer reactions and cyclization of the nitrile groups.     

Dependence of polymer specific volume on molecular characteristics

Linear and branched bisphenol A polycarbonate (PC) samples were characterized by their average molecular weights, $\text{M}{}_{\mathrm{<mtext>n</mtext>}}$ and $\text{M}{}_{\mathrm{<mtext>w</mtext>}}$, polydispersity degree $\text{q =}\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{/}\text{M}{}_{\mathrm{<mtext>n</mtext>}}$, and branching degree g_v. The weight fraction of microgel was also determined for branched samples. The samples were amorphized and densities were measured at 23°C to obtain the values of specific volume, v_sp. The dependence of v_sp on molecular characteristics is described by the multivariable power function $\text{Δv}{}_{\mathrm{<mtext>sp</mtext>}}\text{=}\text{A}{}_{\mathrm{sp}}\text{M}{}_{\mathrm{<mtext>x</mtext>}}{}^{\mathrm{<mtext>a</mtext>}}\text{q}{}^{\mathrm{<mtext>apx</mtext>}}\text{g}{}_{\mathrm{<mtext>v</mtext>}}{}^{\mathrm{<mtext>ab</mtext>}}$, where Δv_sp = v_sp ? v_sp,∞, and A_sp, a, a_px and a_b are constants. It has been confirmed that a = ?1, a_pn = 0 and a_pw = 1. It has also been found that the branching exponent a_b significantly depends on microgel content. The relationships found for PC should, in principle, be valid for other polymers. Examples based on literature data are given for linear polyethylene and polydimethylsiloxane.     

Intramolecular relaxation of polystyrene in a theta solvent by photon-correlation spectroscopy

Photon-correlation spectroscopy has been used to measure the diffusion coefficient D and first-mode intramolecular relaxation time τ₁ of polystyrene in a theta solvent, cyclohexane at 34.5°C. Measurements were made on five narrow fractions ($\text{M}$_w = 2.88 × 10⁶ to 9.35 × 10⁶) as a function of concentration c, in the dilute regime. D varied linearly with c, D = D_o (I + k_Dc), with D_o = (1.4 ± 0.2) × 10^?4$\text{M}{}_{\mathrm{w}}{}^{\mathrm{?(0.508\pm 0.007)}}$ cm² s^?1. Although the values obtained for τ₁ were reproducible to within 5%, no systematic variation with c was detected. The results are fitted by the relation τ₁ = (7.7 ? 0.3) × 10^?8$\text{M}{}_{\mathrm{w}}{}^{\mathrm{(1.42\pm 0.05)}}$ μs, which agrees well with the theoretical expression of Zimm for the non-draining bead-and-spring model, modified for the light-scattering case.     

Absolute bestimmung der molekulargewichtsverteilung von anionisch und radikalisch polymerisierten polystyrolen durch lichtstreuung

The scattering function P₀ for classical elastic light scattering is specified for several molecular weight distribution functions (Schulz-, Square root-, Maxwell-, Normal-, Poisson-, Logarithmic-normal-distribution function). Precision measurements on anionic polymerized polystyrene from Pressure Chemical Co. $\text{(}\text{M}{}_{\mathrm{w}}\text{= 2 · 10}{}^6\text{and}\text{M}{}_{\mathrm{w}}\text{= 6,7 · 10}{}^6\text{)}$ and radical initiated polystyrene were performed in transdecalin with the light scattering photometer Fica 50. Comparison of experimental results with theoretical curves indicate that the anionic polystyrenes exhibit a broader distribution than given by Pressure Chemical Co. The distribution of the radical polystyrene conforms with distributions found by other methods.     

The oxygen defect perovskite Ca3Mn1.35Fe1.65O8.02: A highly frustrated antiferromagnet

A new oxygen defect perovskite Ca₃Mn_1.35Fe_1.65O_8.02 has been isolated. It crystallizes in the orthorhombic system with the following parameters: $\text{a ? a}{}_{\mathrm{<mtext>p</mtext>}}\text{√2; b ? 3a}{}_{\mathrm{<mtext>p</mtext>}}$, and $\text{c ? a}{}_{\mathrm{<mtext>p</mtext>}}\text{√2}$. X-Ray diffraction shows that it corresponds to the second member of the structural series (AMO₃)_m(AMO₂□) and thus consists of double perovskite layers separated by tetrahedral layers. This phase, related to the brownmillerite structure, differs from the latter, in that it exhibits oxygen defects in the perovskite layer and an excess of oxygen in the tetrahedral layer. These results are explained by the ability of Mn^III to adopt pyramidal coordination. Its magnetic properties have been investigated by susceptibility and magnetization measurements and Mössbauer spectroscopy in the temperature range 4–300 K. The dependence of the freezing temperature on the measuring technique (125 K with Mössbauer spectroscopy and 100 K from magnetization), the wide range of temperature where the freezing of the spins occurs, the sensitivity of χ on the cooling magnetic field and the drastic lowering of C_M characterize a highly frustrated behavior due to cationic disorder in the structure.     

Isotope effects in electron-donor-acceptor complexes involving aromatic hydrocarbons and fluoranil from NMR shift measurements

Equilibrium constants and NMR shift parameters have been determined for complexes of benzene, toluene and p-xylene and their perdeutero-analogues with fluoranil in cyclohexane solution from NMR shift measurements. Isotope effects are observed in the 1:1 equilibrium constants for the complexes of p-xylene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$= 1.1₀) and toluene $\text{(}\text{K}{}_1\text{(D)}\text{K}{}_1\text{(H)}$ = 1.0₉). A much smaller effect was observed for the benzene complex which could not be quantified. These results may be interpreted through either the larger electronegativity of H over D, or the greater steric requirements of H over D.     

Transfer to monomer in the polymerization of N-(3-dimethylaminophenyl) maleimide and N-(3-dimethylamino-6-methylphenyl) maleimide

The kinetics of the homopolymerizations of styrene, N-(3-dimethylaminophenyl) maleimide (I) and N-(3-dimethylamino-6-methylphenyl) maleimide (II) in benzene and dimethylformamide, and the molecular weights of the polymers were studied. N-(3-Dimethylaminophenyl) succinimide, regarded as a model for polymer I, did not affect the polymerization of styrene. The data indicate degradative transfer of polymer radicals to dimethylformamide and pronounced transfer to monomers I and II (C_M ≈ 0.06–0.07). The value of $\text{k}{}_{\mathrm{p}}\text{/k}{}_{\mathrm{t}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for II is 0.09 $\text{dm}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$$\text{mole}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$$\text{s}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$.     

Détermination des constantes de la relation de Mark-Houwink et des caractéristiques d'un polymère à partir d'un échantillon polymoléculaire—I.: Méthode expérimentale, étalonnage et exploitation des résultats application au polystyrène

We report here a method which affords the magnitude of the characteristic parameters of a macromolecular chain starting from a polydisperse sample. A statistical treatment of viscosity measurements made on the small fractions of a GPC elution wave enables us to assign to each of them its $\text{M}{}_{\mathrm{n}}$ value. By numerical calculations it is then possible on the one hand to evaluate the Mark-Houwink constants, $\text{M}{}_{\mathrm{n}}\text{and}\text{M}{}_{\mathrm{w}}$, the f(M) function and on the other hand to estimate according to a hydrodynamic model, the unperturbed geometrical dimensions. The method is tested for polystyrene samples under conditions which allow the dissolution of many polymers, viz in tetrachloroethane (TCE) at 50° and N-methylpyrrolidone at 85°.     

Dilute solution properties of polylaurolactam

For a number of fractions and unfractionated samples of polylaurolactam, molecular weights ($\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{= 1 × 10}{}^4\text{?12·5 × 10}{}^4$) were measured by the light-scattering method in a mixed solvent of m-cresol with 60 vol. % 2,2,3,3-tetrafluoropropanol; intrinsic viscosities were determined in m-cresol and 96% H₂SO₄, and the constants of the Mark-Houwink equation were calculated. The calculated values of the characteristic ratio of unperturbed dimensions (virtually identical for m-cresol and 96% H₂SO₄) were compared with the respective values for polypyrrolidone and polycaprolactam. It was found that the higher frequency of the CONH-groups reduces the rigidity of the polyamide chain.     

On rheological properties of polydisperse polymers

An investigation has been carried out into the effect of the fractional composition on the rheological (flow and elastic) properties of a system, using mixtures of polybutadienes with narrow molecularweight distribution (MWD). For mixtures of high-molecular-weight components, the initial Newtonian viscosity is determined by the weight-average molecular weight: $\text{η}{}_0\text{～}\text{M}{}^{\mathrm{\alpha }}{}_{\mathrm{<mtext>w</mtext>}}$; when low-molecular weight components are introduced, it is also determined by the MWD moment ratio. The characteristic relaxation time of a system is determined by the z-average molecular weight: , and in the general case α₁ ≠ α. A new model has been proposed to explain the non-Newtonian phenomenon as a consequence of the existence of a molecular-weight distribution. According to this model, as the shear rate increases the high-molecular-weight components gradually (at their critical rates) pass over to the high-elastic state. Therefore, at high shear rates, their contribution to viscous losses of a polydisperse polymer is associated with their behaviour as a viscoelastic filler in a viscous liquid.     

Application of a calorimetric method in radiation-induced polymerization—IV: Determination of propagation and termination rate constants for cyclohexyl-methacrylate

A calorimetric method has been used to study the gamma-induced polymerization of cyclohexyl-methacrylate (CHMA) under non-stationary conditions. As for other methacrylates already studied in this laboratory, the polymerization rate of CHMA is proportional to (dose-rate)${}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for all temperatures and dose rates examined. The rate constants for propagation and termination have been determined and the results compared with those for methyl, ethyl and n-butyl methacrylates. The $\text{M}$_w values of CHMA, formed in tetrahydrofuran at different dose rates, agree with the kinetic behaviour.     

Evaluation of the type of polymer property average

A method for evaluation of the type of average, which is experimentally obtained for a given property of polydisperse polymer, is described. A multivariable power function

where P is the polymer property, $\text{M}{}_{\mathrm{x}}$ is the x-average molecular weight, q is the polydispersity degree, A_p, a and a_px are constants, and the a_px = 0 criterion (a_px being the polydispersity exponent) is used for this purpose.     

Dilute solution properties of poly(N-vinyl-3,6-dibromo carbazole)—III. Phase equilibrium studies

The phase relationships of poly(N-vinyl-3,6-dibromo carbazole) (PVK-3, 6-Br₂) were examined for four solvents, viz, o-chlorophenol, p-chloro-m-cresol, o-dichlorobenzene and bromobenzene. Upper critical solution temperatures (UCST) have been determined for solutions of PVK-3,6-Br, fractions in o-chlorophenol and p-chloro-m-cresol over the molecular weight range $\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{× 10}{}^{\mathrm{?4}}\text{= 125.0}\text{to}\text{4.8}$. The Flory temperature, θ, obtained from UCST for the PVK-3,6-Br₂/o-chlorophenol and PVK-3,6-Br₂/p-chloro-m-cresol systems are 66.0 and 112.9°C, respectively. The θ-temperatures were checked against molecular weight and viscosity data to determine the Mark-Houwink equations for these two theta solvents, with satisfactory agreement. The relations are

$\text{[ν] = 27.5}{}_4\text{× 10}{}^{\mathrm{?10}}\text{×}\text{M}{}^{0.50}{}_{\mathrm{<mtext>w</mtext>}}\text{(o-}\text{chlorophenol}\text{, 60.0°}\text{C}$

$\text{[ν] = 30.2}{}_4\text{× 10}{}^{\mathrm{?10}}\text{×}\text{M}{}^{0.50}{}_{\mathrm{<mtext>w</mtext>}}\text{(p-}\text{chloro}\text{-m}\text{cresol}\text{, 112.9°}\text{C}$

The characteristic ratio C_∞ = 〈R²〉₀/nl² was found to be 16.6 in o-chlorophenol at 60.0°C and 17.6 in p-chloro-m-cresol at 112.9°C. The value of the characteristic ratio C_∞ of PVK-3,6-Br₂ is of the same order of that for poly(N-vinyl carbazole). This indicates that the bromine atoms at the 3 and 6 (meta) positions have only an inappreciable effect on the hindering potential for rotation about the CC bond. This agreement of C_∞ for both polymers may also be taken as indicating that the effect of interaction between polar groups at the m-position on the hindering potential for rotation is small. The phase diagrams of PVK-3,6-Br₂ obtained in o-dichlorobenzene and bromobenzene seem to be characteristic of organized phase structures such as those found in systems exhibiting thermoreversible gelation. Light scattering measurement on PVK-3,6-Br₂ dissolved in o-dichlorobenzene, a gelation promoting solvent, and tetrahydrofuran, a very good solvent, strongly indicate that the macromolecular species in o-dichlorobenzene contain some extent supermolecular structures (aggregates, association of chain segments, etc.). These characteristic structures of PVK-3,6-Br₂ in o-dichlorobenzene and bromobenzene at 25°C are also characterized by high values of the Huggins' constant k′; for tetrahydrofuran solutions, the k′ values were in the range normally found for many good solvent-polymer systems.