Study of copper-chromium oxide catalyst: I. Thermal decomposition of copper(III) chromate,CuCrO4

The kinetics, mechanism, and activation energy of the isothermal decomposition of CuCrO₄ was studied using an isothermal TG method and an X-ray high-temperature diffraction technique in either air or a flowing atmosphere of N₂. The enthalpy change ΔH of the decomposition reaction

$\text{2}\text{CuCrO}{}_4\text{→}\text{CuO}\text{+}\text{CuO}\text{+}\text{CuCr}{}_2\text{O}{}_4\text{+}\text{3}\text{2}\text{O}{}_2$

was determined by DSC analysis. The mechanism of the thermal decomposition of CuCrO₄ is well represented by the standard Avrami-Erofeev kinetic equation $\text{[?}\text{ln}\text{(1 ? α)]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= kt}$. According to this mechanism, the reaction rate is controlled by the formation and growth of nuclei on the surface of the reactant. The activation energy E_A of the process in air is E_A = (248 ± 8) kJ mole^?1, in flowing atmosphere of nitrogen E_A = (229 ± 8) kJ mole^?1. ΔH in air is 110 kJ mole^?1, in flowing nitrogen 67 kJ mole^?1. The lower values of ΔH and E_A in the flowing atmosphere of nitrogen are due to the fast elimination of O₂ from the reaction interface. However, the decay of the crystalline portion of CuCrO₄ during its thermal decomposition, studied by the X-ray diffraction, is controlled by a different reaction mechanism (first-order kinetics). The reaction mechanism is discussed in the relation to the crystal structure of the reactants.     

Studies on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2-́thiazolylazo)-2-methylresorcinol with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid

Spectrophotometric studies have been carried out on the kinetics of the ligand-substitution reaction of the Zinc(II)-4-(4′-methyl-2′-thiazolylazo)-2-methylresorcinol complex with 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, in the pH range 8.4–9.4 at μ = 0.25 and 25 °C. The reaction rate constant was established to be $\text{?}\text{(d[}\text{ZnR}{}_2\text{]}\text{dt)}\text{= K[}\text{ZnR}{}_2\text{][H}{}^{\mathrm{+}}\text{][Y′]/[HR}{}^{\mathrm{?}}\text{], and}\text{K = 6.88 × 10}{}^4\text{liter · mol}{}^{\mathrm{?1}}\text{· sec}{}^{\mathrm{?1}}$ was obtained.     

Verbesserte endpunktsbestimmung in der potentiometrischen analyse

If in a potentiometric titration each addition of reagent equals Δv and if the observed potential steps are, in decreasing order, Δ^E_m, Δ^E₁ and Δ^E₂, the ratio ρ_α = $\text{Δ}{}^{\mathrm{E}}{}_2\text{2Δ}{}^{\mathrm{E}}{}_1$is formed; ρ_αΔv is the difference between the equivalence point and the known volume of reagent next to it. Both an extraordinary increase in the precision and a valuable simplification of the analysis are obtained. For Q = $\text{Δ}{}^{\mathrm{E}}{}_{\mathrm{m}}\text{Δ}{}^{\mathrm{E}}{}_1$ < 2.5 or ρ_α < 0.25 this value is approximated; but in this case a new series with doubled intervals may be formed from the potential steps observed in which ρ_α is very near to 0.5, found hence absolutely accurate.     

Unusual effects of anisotropic bonding in Cu(II) and Ni(II) oxides with K2NiF4 structure

Geometric constraints present in A₂BO₄ compounds with the tetragonal-T structure of K₂NiF₄ impose a strong pressure on the BO_IIB bonds and a stretching of the AO_IA bonds in the basal planes if the tolerance factor is $\text{t ?}\text{R}{}_{\mathrm{<mtext>AO</mtext>}}\text{√2 R}{}_{\mathrm{<mtext>BO</mtext>}}\text{< 1}$, where R_AO and R_BO are the sums of the AO and BO ionic radii. The tetragonal-T phase of La₂NiO₄ becomes monoclinic for Pr₂NiO₄, orthorhombic for La₂CuO₄, and tetragonal-T′ for Pr₂CuO₄. The atomic displacements in these distorted phases are discussed and rationalized in terms of the chemistry of the various compounds. The strong pressure on the BO_IIB bonds produces itinerant bands and a relative stabilization of localized d_z² orbitals. Magnetic susceptibility and transport data reveal an intersection of the Fermi energy with the d²_z² levels for half the copper ions in La₂CuO₄; this intersection is responsible for an intrinsic localized moment associated with a configuration fluctuation; below 200 K the localized moment smoothly vanishes with decreasing temperature as the d²_z² level becomes filled. In La₂NiO₄, the localized moments for half-filled d_z² orbitals induce strong correlations among the electrons above $\text{T}{}_{\mathrm{<mtext>d</mtext>}}\text{? 200}\text{K}$; at lower temperatures the electrons appear to contribute nothing to the magnetic susceptibility, which obeys a Curie-Weiss law giving a μ_eff corresponding to $\text{S =}\text{1}\text{2}$, but shows no magnetic order to lowest temperatures. These surprising results are verified by comparison with the mixed systems La₂Ni_1?xCu_xO₄ and La_2?2xSr_2xNi_1?xTi_xO₄. The onset of a charge-density wave below 200 K is proposed for both La₂CuO₄ and La₂NiO₄, but the atomic displacements would be short-range cooperative in mixed systems. The semiconductor-metallic transitions observed in several systems are found in many cases to obey the relation $\text{E}{}_{\mathrm{<mtext>a</mtext>}}\text{? kT}{}_{\mathrm{<mtext>min</mtext>}}$, where $\text{? = ?}{}_0\text{exp}\text{(}\text{?E}{}_{\mathrm{<mtext>a</mtext>}}\text{kT}\text{)}$ and T_min is the temperature of minimum resistivity ?. This relation is interpreted in terms of a diffusive charge-carrier mobility with $\text{E}{}_{\mathrm{<mtext>a</mtext>}}\text{? ΔH}{}_{\mathrm{<mtext>m</mtext>}}\text{? kT}$ at T = T_min.     

Peroxo salts as initiators of vinyl polymerization—2. Kinetics of polymerization of acrylic acid and sodium-acrylate by peroxodisulphate in aqueous solution—effect of pH and Ag+ catalysis

Results on the rate of polymerization of acrylic acid by S₂O^2?₈ ion in alkaline and acid conditions are presented. R_p depended upon $\text{[S}{}_2\text{O}{}^{\mathrm{2?}}{}_8\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{[monomer]}{}^{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ both in acid and alkaline solutions. The influence of ionic strength, the effect of pH on R_p and the catalytic effect of Ag⁺ and Cu²⁺ on the system have been discussed. Suitable mechanisms are proposed.     

Bifunctional initiators—I. Synthesis and characterization of 4,4′-azobis(4-cyanovaleryl)bisbenzoyl and bisacetyl diperoxides

The paper refers to the synthesis and properties of some bifunctional initiators, viz. 4.4′-azo-bis(4-cyanovaleryl)bisbenzoyl diperoxide (I) and 4,4′-azobis(4-cyanovaleryl)bisacetyl diperoxide (II), obtained from the acid chloride of cyanovaleric acid and condensed with perbenzoic acid or peracetic acid. The structures of the products were established by i.r. and NMR spectroscopy, as well as by elemental analysis. Kinetic studies on the thermolyses of the two initiators led to the following results: for I. $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{azo, 360°K = 129 min}$, $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{peroxy, 360°K = 245 min}\text{, E}{}_{\mathrm{<mtext>azo</mtext>}}\text{=}\text{174.2 kJ/mol}\text{, E}{}_{\mathrm{<mtext>peroxy</mtext>}}\text{=}\text{206.5 kJ/mol}$; for II, $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{azo, 357°K = 152 min}\text{, t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{peroxy, 357°K = 208 min}\text{, E}{}_{\mathrm{<mtext>azo</mtext>}}\text{=}\text{155.4 kJ/mol}\text{, E}{}_{\mathrm{<mtext>peroxy</mtext>}}\text{=}\text{188.5 kJ/mol}$.     

NMR study of hydrogen molybdenum bronzes: H1.71MoO3 and H0.36MoO3

Proton NMR relaxation times (T₂T₁, and T_1?) and absorption spectra are reported for the compounds H_1.71MoO₃ (red monoclinic) and H_0.36MoO₃ (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH₂ groups coordinated to Mo atoms in H_1.71MoO₃ and as pairs of OH groups in H_0.36MoO₃. The room temperature lineshape for H_1.71MoO₃ shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give E_A = 22 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 10}{}^{\mathrm{?13}}\text{sec}$ for H_1.71MoO₃ and E_A = 11 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 3 × 10}{}^{\mathrm{?8}}\text{sec}$ for H_0.36MoO₃.     

Kinetics and mechanism of solid-state reaction between bismuth(III) oxide and molybdenum(VI) oxide

The mechanism of the following solid-state reactions between bismuth(III) oxide and molybdenum(VI) oxide was investigated within the temperature range 400–650°C.

$\text{(i)}\text{Bi}{}_2\text{O}{}_3\text{+ MoO}{}_3\text{→ Bi}{}_2\text{MoO}{}_6\text{, (ii)}\text{Bi}{}_2\text{O}{}_3\text{+ 2MoO}{}_3\text{→ Bi}{}_2\text{MO}{}_2\text{O}{}_9\text{, (iii)}\text{Bi}{}_2\text{O}{}_3\text{+ 3MoO}{}_3\text{→ Bi}{}_2\text{(MOO}{}_4\text{)}{}_3\text{, (iv)}\text{Bi}{}_2\text{MoO}{}_6\text{+ MoO}{}_3\text{→ Bi}{}_2\text{MO}{}_2\text{O}{}_9\text{, (v)}\text{Bi}{}_2\text{Mo}{}_2\text{O}{}_9\text{+ MoO}{}_3\text{→ Bi}{}_2\text{(MoO}{}_{\mathrm{2)3}}\text{.}$

Two types of experiments, capillary and particle size, were performed to ascertain whether MoO₃ diffuses into Bi₂O₃ or vice versa. These show that molybdenum trioxide diffuses into bismuth oxide grains. If α is the fraction of molybdenum trioxide reacted, the kinetics in all five cases are found to be governed by the equation αⁿ = kt throughout the temperature range, where n and k are constants at a given temperature and t is the time. Both n and k are temperature dependent. The characteristic feature of these reactions is that they proceed to completion. Results are also fitted by the relation $\text{α = k}{}_2\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{? k}{}_3\text{t}$, where k₂ and k₃ are constants, which shows that the reactions occur by bulk diffusion through grain boundary contacts. The number of grain boundary contact points decreases with time in the course of reaction.     

Primary radical termination in polymerization: Evaluation of the characteristic constant

Polymerization experiments with styrene in benzene at 60°, initiated by benzoyl peroxide, covering a wide range of concentration of both monomer and initiator are reported; the results cannot be explained in terms of the classical rate relationship with $\text{R}{}_{\mathrm{p}}\text{∝ [}\text{I}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{M}\text{]}$. Deviations were reflected in unexpected orders of monomer up to [M]^1·4 and of initiator down to [I]^0·42 when the initiator concentration is increased and monomer concentration is decreased. Based on the concept of primary radical termination, an equation, viz.

$\text{ln}\text{R}\text{p}\text{2}\text{[I][M]}{}^2\text{=}\text{ln}\text{2f}{}_{\mathrm{k}}\text{k}{}_{\mathrm{d}}\text{k}\text{p}\text{2}\text{k}{}_{\mathrm{t}}\text{?2}\text{k}{}_{\mathrm{prt}}\text{k}{}_{\mathrm{i}}\text{k}{}_{\mathrm{p}}\text{×}\text{R}{}_{\mathrm{p}}\text{[M]}{}^2$

is proposed. Semi-log plots of R_p²/[I] [M]² vs R_p/[M]² show a wide range of linearity; the characteristic constant k_prt/k_ik_p and also f_k can be obtained from the slope and intercept, respectively, k_prt, k_i and k_p are, respectively, the rate constants of primary radical termination, initiation and propagation and f_k is the efficiency of initiation, defined as the fraction of radicals which come out of the solvent cage and take part in initiation, primary radical termination and primary radical recombination. The definition of f_k is thus differentiated from the conventional efficiency of initiation. Finally, we have derived an equation which allows determination of the classical efficiency of initiation as a function of [I]/[M]² and also allows a correction of R_p in handling the above equation by taking into account the small amount of monomer consumed in initiation.     

Transition metalcarbon bonds: LV. Cyclometallation and other reactions of PBut2Bui and PPh2Bui with platinum(II) and palladium(II)

The new phosphine, PBu^t₂Buⁱ (L), was prepared from Bu^t₂PCl and LiBuⁱ. PPh₂Buⁱ (L′) was prepared from Ph₂PCl and LiBuⁱ. Treatment of [PtCl₂(NCBu^t)₂] with L′ gives [PtCl₂L′₂] which does not cyclometallate even on prolonged boiling in 2-methoxyethanol. In contrast, [PtCl₂(NCBu^t)₂] reacts with PBu^t₂Buⁱ in boiling 2-methoxyethanol to give the cyclometallated complex [$\text{Pt}{}_2\text{Cl}{}_2\text{(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{-CHMeCH}$₂)₂] (II, X = Cl). The corresponding bromide, iodide and acetylacetonate were prepared. With PPh₃ II (X = Cl) gives [$\text{PtCl(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{CHMeCH}$₂)(PPh₃)] which with NaBH₄ gives [$\text{PtH(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{CHMeC}$H₂)(PPh₃)]. Na₂PdCl₄ with L (2 mol equivalents) gave trans-[PdCl₂L₂], which was converted into trans-[Pd(NCS)₂-L₂] by metathesis with KSCN. Treatment of Na₂PdCl₄ with L (1 mol equivalent) gave [Pd₂Cl₄L₂], which on heating in 2-methoxyethanol gave [$\text{Pd}{}_2\text{Cl}{}_2\text{(PBu}{}^{\mathrm{t}}{}_2\text{CH}{}_2\text{-CHMeCH}$₂)₂], as a mixture of syn- and anti-isomers. The complexes trans-[PdCl₂-L′₂] and [Pd₂Cl₄L′₂] were also prepared. ¹H- and ³¹P NMR data are given.     

Nonstoichiometry and defect structure of the perovskite-type oxides La1−xSrxFeO3−°

In order to elucidate the defect structure of the perovskite-type oxide solid solution La_1?xSr_xFeO_3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, P_O2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of P_O2 ≥ 0.13 atm, δ in La_1?xSr_xFeO_3?δ was found to be close to 0. With decreasing log P_O2, δ increased and asymptotically reached $\text{x}\text{2}$. The value corresponding to $\text{δ =}\text{x}\text{2}$ was about ?10 at 1000°C. With further decrease in log P_O2, δ slightly increased. For LaFeO_3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log P_O2 is interpreted on the basis of the defect equilibrium among Sr′_La (or V?_La for the case of LaFeO_3?δ), V^··_O, Fe′_Fe, and Fe^·_Fe. Calculations were made for the equilibrium constants K_ox of the reaction

$\text{1}\text{2}\text{O}{}_2\text{(g) + V}{}^{\mathrm{··}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= O}{}^{\mathrm{x}}{}_{\mathrm{o}}\text{+ 2Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe}}$

and K_i for the reaction

$\text{2Fe}{}^{\mathrm{x}}{}_{\mathrm{Fe}}\text{= Fe}{}^{\mathrm{\prime }}{}_{\mathrm{Fe}}\text{+ Fe}{}^{\mathrm{·}}{}_{\mathrm{Fe·}}$

Using these constants, the defect concentrations were calculated as functions of P_O2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements.     

A kinetic study of the permanganate—oxalate reaction and kinetic determination of manganese(II) and oxalic acid by the stopped-flow technique

The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —$\text{d[MnO}{}_4{}^{\mathrm{-}}\text{]}\text{d}\text{t}$ = k [Mn²⁺] [C₂O₄^2-]² [MnO₄^-] [H⁺]^-2 = k' [MnC₂O₄] [MnO₄^-]. The values of k and k' were shown to be 5.4 × 10⁴ M^-1 s^-1 and 8.2 × 10⁴ M^-1 s^-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10^-4 M and 1–10 × 10^-3 M and oxalic acid in the range 0–20 μg ml^-1 can be determined very rapidly with a precision of 1–2%.     

“Normal” and “cine” substitution in the thioalkoxy-dehalogenation of halogenobenzofurazans—III: Investigation on the solvent effect

The reaction of 4-chloro- and 4-chloro-7-deuteriobenzofurazan with MeS^-, isopropyl-S^-, and t-Butyl-S^- in different alcohols as solvents has been investigated. In going from methanol through isopropanol to t-butanol, a progressive decrease of the contribution of the cine-substitution as compared with the normal substitution pathway has been found. By proceeding in the same order, a decrease of the ratio and $\text{k}\text{MeS}{}^{\mathrm{?}}\text{k}{}_{\mathrm{<mtext>t</mtext>}}$-ButylS^? has also been observed.     

Extraction of cobalt(II) and nickel(II) with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one (HPMBP) and tri-n-octylamine (TOA)

The extraction of Co(II) with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazol-5-one ((H)PMBP) and tri-n-octylamine (TOA) is investigated in order to explore the influence of diluents and inorganic anions with synergistic acidic extractant + liquid anion exchanger systems. Although it is proved that the same species [HTOA]⁺ [Co(PMBP)₃]^? is extracted from various inorganic media, with toluene as the diluent, the presence of ClO₄^? SO₄^2? or Cl^? anion modifies the distribution of the anions which are associated to (HTOA)⁺ in the organic phase, leading to different synergistic equilibria; with Cl^? or SO₄^2?: $\text{CO(PMBP)}{}_2$ + $\text{(HTOA}{}^{\mathrm{+}}$,PMBP^?) ?$\text{(HTOA}{}^{\mathrm{+}}$,Co(PMBP)₃^? (log K = 6.10) and with ClO₄^? : $\text{Co(PMBP)}{}_2$ + $\text{HPMBP}$ + $\text{(HTOA}{}^{\mathrm{+}}$,ClO₄^? ? $\text{(HTOA}{}^{\mathrm{+}}$,Co(PMBP)₃^? + H⁺ + ClO₄^? (log K = 2.34) The same synergistic equilibrium is observed for the extraction of Ni(II) from ClO₄^? medium, with a comparable value of the constant (log K = 2.45). The synergistic effect is cancelled in n-octanol.     

Synthèse et caractérisation d'une série de titanates pérowskites isotypes de [CaCu3](Mn4)O12

A series of titanates which have perovskite-like arrangements and are isostructural with [CaCu₃](Mn₄)O₁₂ have been synthesized. The total charge of the A sites can be modified (1) by substituting the Ca²⁺ cations with monovalent ones and the tetravalent manganese cations of the B sites by a mixture of (Ti⁴⁺ + M⁵⁺) in which M = Ta, Nb, Sb, or (2) by substituting the Ca²⁺ cations by a combination of cations plus vacancies. In this case, if the total charge of the A sites is 2, one obtains compounds such as $\text{[}\text{Th}{}^{\mathrm{4+}}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{□}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Cu}{}_3\text{](Ti}{}_4\text{)O}{}_{12}$ and $\text{[T}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{□}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Cu}{}_3\text{](Ti}{}_4\text{O}{}_{12}\text{(T =}\text{rare earth}\text{)}$; on the contrary, if the charge is less than 2, then one has to compensate it by changing that of the B sites. This leads to compounds such as [□Cu₃](Ti₂M₂)O₁₂ (M = Ta, Nb, Sb).     

Vinyl polymerization initiated by the (dimethylaniline-n-oxide)/(phenacyl bromide) system

Binary systems consisting of dimethylaniline-N-oxide (DMOA) and some α-halo-carbonyl compounds, such as phenacyl halide and α-halo-acetic acid ester, were found to induce radical polymerization of vinyl monomers. Bromo-derivatives showed higher initiating activities than chloroderivatives. The polymerization of methyl methacrylate (MMA) with DMAO and phenacyl bromide (PBr) was investigated kinetically. The polymerization rate (R_p) was expressed as follows; $\text{R}{}_{\mathrm{<mtext>p</mtext>}}\text{=}\text{k[DMAO]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{PBr}\text{]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{MMA}\text{]}$.The overall activation energy of the polymerization was calculated to be 42.7 kJ mol^?1. No noticeable chain-transfer from the polymer radical to DMAO or PBr was observed. The benzoyl radical was trapped by 2-nitroso-2-methylpropane, a spin trapping reagent, in the reaction of DMAO and PBr. The u.v. spectrum of poly (MMA) obtained suggests that the polymer contains end-groups similar to acetophenone and DMA. From the results, an initiation mechanism for the polymerization has been proposed and discussed.     

Solution properties of polytrimethylhexamethylenterephthalamide (trogamid TR)

For the polyamide Trogamid T^R, good as well as θ-solvents are available. Determinations of molecular weights by ultracentrifugation, light scattering, osmometry, viscometry and gelchromatography (GPC) are reported. For DMF at 25° the relation

$\text{[η] = 0.02737}\text{M}{}^{0.706}{}_{\mathrm{w}}\text{cm}{}^3\text{g}{}^{\mathrm{?1}}$

was established, [η] = f(T) shows a maximum between ? 70° and + 120°. θ-temperatures are 142° for aniline and 62° for pyrroline, the latter having a negative temperature gradient. The unperturbed dimensions are calculated from the viscosity in θ-solvents and in DMF; for the latter, the Stockmayer-Fixman extrapolation was used. Molecular dimensions proved to be small in comparison with those of similar polymers. This effect is due to the three methyl side-groups for each chain unit sterically preventing a more stretched conformation.