Experiments on the small-strain behaviour of crosslinked natural rubber: 1. Torsion

The torsional behaviour of 1, 3 and 5 phr peroxide crosslinked natural rubber has been characterized over a range of strains from near the undistorted state (γ ≈ 0.017) to γ ≈ 1.0. Isochronal measurements of both torque and normal force were used to calculate values of the derivatives of the strain energy function W with respect to the first and second stretch invariants I₁ and I₂. In the course of our work we found that, contrary to many reports in the literature, $\text{?W}\text{?I}{}_1$ was affected significantly by the amount of crosslinking. Finally for the 1 phr peroxide crosslinked rubber it was found that, while ageing for 14 months at ambient conditions did not significantly affect the small-strain torsional modulus, $\text{G = 2(}\text{?W}\text{?I}{}_1\text{+}\text{?W}\text{?I}{}_2\text{)}$, it did significantly affect the individual derivatives $\text{?W}\text{?I}{}_1$ and $\text{?W}\text{?I}{}_2$.     

Thermal expansion and Grüneisen parameter of polyethylene between 5 and 320 K

The linear thermal expansion coefficient, α, of polyethylene with crystallinity X=0.44, 0.62, 0.77 and 0.98 has been measured between 5 and 320 K with an experimental accuracy of about 5% above 15 K and 10% below 15 K using an interferometric dilatometer system. In the temperature range 40 to 100 K the thermal expansion is found to be independent of crystallinity, whereas at lower as well as higher temperatures, α increases with increasing noncrystallinity. By linear extrapolation the thermal expansion coefficient of the noncrystalline phase can be estimated. The influence of the phonon spectrum on the thermal expansion is discussed in terms of the Grüneisen parameter. For completely crystalline polyethylene, a bulk-Grüneisen parameter of $\text{γ}{}_{\mathrm{<mtext>b</mtext>}}\text{?2}$ is found below 20 K. This value is smaller than expected from theories for polymer crystals. For noncrystalline polyethylene, γ_b is constant ($\text{γ}{}_{\mathrm{<mtext>b</mtext>}}\text{?1.6}$) between 30 and 100 K, showing a rapid increase at lower temperatures with $\text{γ}{}_{\mathrm{<mtext>b</mtext>}}\text{?12.5}$ at 5 K. This high value for γ_b can be related to excess modes in the vibration spectrum of the noncrystalline phase, which have previously been found to contribute also to the heat capacity at these temperatures.     

Raman spectra,effective Debye parameter and magnetoresistance of graphitized cokes

The Raman intensity ratio R ($\text{I}{}_{1360}\text{I}{}_{1580}$), the effective Debye parameter B_eff and the maximum transverse magnetoresistance ($\text{Δρ}\text{ρ}\text{)}{}_{\mathrm{mx}}$ at liquid nitrogen temperature and 10 kG were measured on various cokes heat-treated at high temperatures. The observed values of R, B_eff and ($\text{Δρ}\text{ρ}\text{)}{}_{\mathrm{mx}}$ are closely related with each other and are discussed in relation to the lattice defects in the graphite layer planes. The plot of R against B_eff shows a linear relation, suggesting that both parameters are related to projections along a- and c-axes respectively of the same carbon atom displacement due to lattice defects. With decreasing B_eff, ($\text{Δρ}\text{ρ}\text{)}{}_{\mathrm{mx}}$ increases gradually but almost linearly with B_eff and then rapidly. This behavior has been interpreted by an analysis based on a simple two band model.     

Non-classical free-radical polymerization: 3. Diffusion-control in degradative addition

The different kinetic features associated with polymerizations in which retardation arises through degradative transfer and degradative addition processes are considered. Reasons are given for believing that in reactions retarded by degradative transfer neglect of the interaction between ‘inactive’ radicals is justifiable, while with degradative addition this is not so. A kinetic treatment of the latter is developed in which all three termination reactions between propagating and inactive radicals are assumed to be diffusion-controlled with a single rate coefficient and equations are derived which permit from experimental data on rates of polymerization estimation of the definitive kinetic parameters $\text{k}{}_{\mathrm{p}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$, $\text{k}{}_{\mathrm{pm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ and $\text{k}{}_{\mathrm{fm}}\text{k′}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}{}_{\mathrm{t}}$ (k_p, k′_t, k_pm, k_fm are the rate coefficients of propagation, termination, reinitiation and degradative additions, respectively). The kinetic equations are satisfactorily consistent with ew experimental data on the polymerization of 1-vinylimidazole in ethanol solution at 70°C, for which there is strong evidence for the occurrence of degradative addition. A modified procedure for processing data for polymerizations with degradative transfer is put forward which is convenient for estimating the kinetic parameters and reveals in a simple manner the importance of re-initiation. It is suggested that this treatment could be generally useful in the early stages of the study of a retarded polymerization.     

Branched poly(ethylene terephthalate) correlations between viscosimetric properties and polymerization parameters

Samples of poly(ethylene terephthalate) (PET) modified with small amounts of trimesic acid groups and hence containing long chain branching have been prepared. From the content of trifunctional modifier and from the experimental value of the extent of reaction, the weight-average molecular weight $\text{M}\text{?}{}_{\mathrm{w}}$ and branching density $\text{B}\text{?}{}_{\mathrm{w}}$ have been calculated, assuming that all the end-groups are equally reactive and intramolecular reactions are absent. The values of $\text{M}\text{?}{}_{\mathrm{w}}$ and $\text{B}\text{?}{}_{\mathrm{w}}$ have been correlated with the experimental values of intrinsic viscosity [η] and the Newtonian melt viscosity η₀. General relations of the following type have been obtained:

$\text{f}{}_1\text{([η],}\text{M}{}_{\mathrm{w}}\text{,}\text{B}{}_{\mathrm{w}}\text{) = 0; f}{}_2\text{(η}{}_0\text{,}\text{M}{}_{\mathrm{w}}\text{,}\text{B}{}_{\mathrm{w}}\text{) =0; f}{}_3\text{(η}{}_0\text{, [η],}\text{B}{}_{\mathrm{w}}\text{) = 0; f}{}_4\text{(η}{}_0\text{, [η],}\text{M}{}_{\mathrm{w}}\text{) = 0;}$

In particular, [η] and η₀ increase on increasing $\text{M}\text{?}{}_{\mathrm{w}}$ and decrease on increasing $\text{B}\text{?}{}_{\mathrm{w}}$, but, at equal [η] values, η₀ increases with $\text{B}\text{?}{}_{\mathrm{w}}$. Through the last relation, the reliability limits of which should be experimentally checked, and from measurements of [η] and η₀, it is possible to calculate $\text{M}\text{?}{}_{\mathrm{w}}$ of a branched PET.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Polymerization of poly(dimethylsiloxane) macromers: 1. Copolymerization with styrene

The synthesis and characterization of methacrylate-ended macromers ($\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}$ 500 to 10 000) and their copolymerization with styrene (M₂) is described. The experimental errors in the values of the reactivity ratios r₁ render them meaningless. Values of r₂ can be determined with more precision and increase from 1.06 to 1.55 as the molecular weight of the macromer increases. This behaviour is due to steric effects, not diffusion-controlled propagation. It is shown that the assumptions that $\text{1 > r}{}_1\text{[}\text{M}{}_1\text{]}\text{[}\text{M}{}_2\text{]}$ and $\text{r}{}_2\text{>}\text{[}\text{M}{}_1\text{]}\text{[}\text{M}{}_2\text{]}$ are only valid for macromers of $\text{M}\text{?}{}_{\mathrm{<mtext>n</mtext>}}\text{> ca. 10 000}$.     

Interaction parameters in the n-undecane/butanone/poly(dimethyl siloxane) system

Intrinsic viscosities, [η], second virial coefficients, A₂, preferential solvation coefficients, λ, and binary interaction potential as measured by light scattering, g₁₂, for the system n-undecane(1)/butanone(2)/poly(dimethylsiloxane) (3) have been determined at 20.0°C. The system shows cosolvent character, as the inversion in λ and the maxima in A₂ and in [η], at $\text{ø}{}_{10}\text{?0.65}$, seem to indicate. (g₁₃ – sg₂₃) and the ternary interaction potential, g_T, and its derivatives on system composition, and , have been evaluated. Global interaction parameters, χ_m3, have also been evaluated and a critical analysis on the approximations usually followed for χ_m3 calculations is undertaken.     

Cyclization dynamics of polymers: 9. The effect of polymer concentration on the slowest internal relaxation mode of a labelled polystyrene chain

A combination of steady-state and fluorescence decay techniques permits one to measure the dynamics of end-to-end cyclization of a polymer chain substituted at both ends with pyrene groups. In the limit of low concentration, the rate constant for cyclization, k_cy, can be identified with the slowest relaxation rate $\text{τ}{}_1{}^{\mathrm{?1}}$ of a Rouse—Zimm chain. Experiments are reported which allow k_cy to be examined for two chain lengths of polystyrene substituted on both ends with pyrene groups. These chains have $\text{M}\text{?}{}_{\mathrm{n}}\text{= 9200}$ and 25 000 ($\text{M}\text{?}{}_{\mathrm{w}}\text{M}\text{?}{}_{\mathrm{n}}\text{? 1.15}$). Added unlabelled polystyrene polymer [PS] causes $\text{k}\text{?}{}_{\mathrm{<mtext>cy</mtext>}}$ to decrease in cyclohexane just above the θ-temperature, whereas in toluene, a good solvent, k_cy is largely unaffected, even at [PS] concentrations of 50 wt%. These results are explained in terms of frictional effects—hydrodynamic screening—dominating in the poor solvent, whereas other factors tend to have offsetting effects in the good solvent.     

Redispersion of supported platinum catalysts

The redispersion of platinum on γ-Al₂O₃, SiO₂, and TiO₂ is experimentally studied by means of hydrogen chemisorption, X-ray diffraction, transmission electron microscopy, temperature-programmed reduction, and cyclohexene hydrogenation reaction. The increase in dispersion following treatment in oxygen below 600 °C occurs only for $\text{Pt}\text{γ-Al}{}_2\text{O}{}_3$. For $\text{Pt}\text{TiO}{}_2$, only the presence of chlorine during oxidation brings about a significant redispersion. For $\text{Pt}\text{SiO}{}_2$, redispersion does not occur under any condition. Redispersion can occur only in the presence of platinum oxide which could be stabilized by forming a complex with the support. The method for determining whether or not redispersion will occur for any systems and the conditions needed for redispersion are discussed.     

The θ-behaviour of heterogeneous macromolecules

A polymer chain consisting of N_r segments with a repulsive interaction (binary cluster integral β_r) and N_a ? N_r segments with a stronger, attractive and pairwise saturable interaction (β_a), which is at the averaged θ-point N²_rβ_r + N²_aβ_a = 0 deviations from the predictions of the two parameter theory: $\text{α}{}^2{}_{\mathrm{<mtext>R</mtext>}}\text{? 1 ～ δz}{}_{\mathrm{<mtext>r</mtext>}}\text{< 0}$ and A₂ ～ δz_r > 0 with $\text{δz}{}_{\mathrm{<mtext>r</mtext>}}\text{～ β}{}_{\mathrm{<mtext>r</mtext>}}\text{(}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. It is shown that the deviations from the universal behaviour are due to the existence of an intermediate length scale $\text{～}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}$.     

The energetic contribution to rubber elasticity in the range of small uniaxial compression and moderate elongation

The relative energetic contribution to the retractive force of a deformed rubber sample, $\text{f}{}_{\mathrm{e}}\text{f}$, has been evaluated from thermoelastic measurements at constant pressure. Extension ratios λ have been studied in the range 0.88 ? λ ? 1.70 at 20° and 40°C. The results are given for a reference temperature, 30°C. Since data in the transition region from uniaxial elongation to compression were to be evaluated, a new set of equations was derived on the basis of the Gaussian force law, because the usual equation for measurements at constant pressure tends towards infinity when approaching the undeformed state λ = 1.Considerable difference between the results obtained by different, though apparently equivalent, equations have their origins in the deviation of the experimental data from ideal Gaussian behaviour. The influence of this inaccuracy on the terms of the equations is discussed and the most reliable functions for small deformations 0.88 ? λ ? 1.15 and for moderate elongation λ > 1.10 have been identified. With these precautions the Gaussian force law is a satisfactory approximation for the determination of reliable values of $\text{f}{}_{\mathrm{e}}\text{f}$.The evaluation of data at small deformations is extremely sensitive to experimental error. Even smoothed polynomials L (f) were not sufficient to eliminate an apparent maximum in the $\text{f}{}_{\mathrm{e}}\text{f}\text{vs}\text{. λ}$ curve. Therefore the linear thermal expansion coefficient β_lin(λ), which is a major term in all the $\text{f}{}_{\mathrm{e}}\text{f}$ equations at small deformations, had to be scrutinized critically. Although experimental data in this range showed that β_lin(λ) is a slightly S-shaped function, a linear approximation is adequate at moderate elongations.Using one of the new equations together with the linear approximation for β_lin(λ) in the region of small deformations, and two equivalent equations at moderate elongation, the energetic contribution to the total stress was found to be $\text{f}{}_{\mathrm{e}}\text{f}\text{= 0.18 ± 0.02}$ for lightly crosslinked natural rubber. Little variation in $\text{f}{}_{\mathrm{e}}\text{f}$ was observed over the full range of measurements: 0.88 ? λ ? 1.70.     

Distribution of straight-chain lengths in unannealed and annealed solution-crystallized polyethylene by Raman spectroscopy

The effect of annealing on the morphology of solution-crystallized polyethylene has been studied by analysing the shape of the low-frequency Raman LAM-1 band. The distributions of lengths of straight-chain segments have been determined for samples annealed at different temperatures. Unannealed samples, which have distribution peaks L_max near 100 Å, have halfwidths $\text{ΔL}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ less than 20 Å. However, this narrow distribution is drastically broadened when the sample is annealed. The broadening is less if the breadth of the distribution of the unannealed sample is initially less. For equilibrium crystallized samples, the observed halfwidth and peak position of LAM-1 are found to be related. This relation can be understood quantitatively if it is assumed that $\text{ΔL}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and L^?1_max are linearly related as is indeed found to be the case for solution-crystallized samples. As L^?1_max becomes very large, $\text{ΔL}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ approaches a limiting value near 300 Å.     

Synthesis of electroreactive polymers from poly (m,p-chloromethylstyrene) and copoly (m,p-chloromethylstyrene-styrene)

Polymerization, and copolymerization with styrene, of m,p-chloromethylstyrene have been carried out at 75°C, in chlorobenzene and in the presence of AIBN ($\text{[}\text{AIBN}\text{] ? 6 × 10}{}^{\mathrm{?2}}$, and $\text{12 × 10}{}^{\mathrm{?2}}\text{m}$, respectively). The polymer molecular weights, determined by g.p.c., are: $\text{M}\text{?}{}_{\mathrm{w}}\text{= 8670}$, $\text{M}\text{?}{}_{\mathrm{n}}\text{= 5860}$, and $\text{M}\text{?}{}_{\mathrm{w}}\text{/-M}{}_{\mathrm{n}}\text{= 1.48}$ for the homopolymer, poly(m,p-chloromethylstyrene), (1a); and $\text{M}\text{?}{}_{\mathrm{w}}\text{= 8805}$, $\text{M}\text{?}{}_{\mathrm{n}}\text{= 5144}$, and $\text{M}\text{?}{}_{\mathrm{w}}\text{/-M}{}_{\mathrm{n}}\text{= 1.71}$ for the copolymer, copoly(m,p-chloromethylstyrene-styrene), (2a). A series of phosphine derivatives of both 1a and 2a are prepared by the reaction of the polymers with either chlorodiphenylphosphine/lithium, or diphenylphosphine/potassium tert. butoxide. A number of other potentially electroreactive derivatives of 2a are obtained by reacting the polymer with 2-aminoanthraquinone, 3-N-methylamino-propionitrile, or 2-(2-aminoethyl) pyridine. The phosphinated polymers are reacted with bis-benzonitrilepalladium-(II) chloride to obtain a series of polymer-palladium(II) complexes containing 8.5–12.9% palladium. Similarly, reaction of the last-named bidentate polymeric ligand with cupric acetylacetonate, or cupric sulphate pentahydrate, produces polymer-copper(II) complexes having 5.8, or 3.3% copper, respectively. The inter/intra-chain nature of some of the side reactions during the derivatization of the chloromethylated polymers, and that of the complex formation between transition metal centres and macromolecular ligands, are briefly discussed in view of the experimental results.     

Analysis of the temperature-time sequences for deactivating isothermal catalyst beds

A procedure is shown to determine the temperature-time sequences to keep the conversion at outlet of a fixed bed reactor subject to catalyst deactivati constant.The calculated sequences for different reaction systems follow the equation: t=$\text{k}{}_0$/k_0d$\text{E}\text{E}{}_{\mathrm{d}}$ exp($\text{E}{}_{\mathrm{d}}\text{RT}{}_0$/1.258×10⁵p_A^0.79{1-exp[$\text{E}{}_{\mathrm{d}}\text{R}$($\text{1}\text{T}$- $\text{1}\text{T}{}_0$)]}.From the analysis of the calculated sequences we have determined the values of the parameters of operation (space time, conversion and initial temperature) that give maximum values to the two functions which we sought to maximize, namely the time of operation and production.     

Electrochemical determination of the standard Gibbs free energy change of the graphite-Oxygen reactions

A calcia doped zirconia solid oxide electrolyte galvanic cell was investigated in the temperature range of 700–950°C to directly and more accurately measure the standard Gibbs free energy change of the following reactions: $\text{CO(g) +}\text{1}\text{2}\text{O}{}_2\text{(g) = CO}{}_2\text{(g)}$C_(graphite) + CO₂(g) = 2 CO(g). The results obtained in the present investigation are well within the scatter band of the calorimetric and spectroscopic data.     

Mixtures of potassium sulphate and iron sulphate as catalysts for water vapour gasification of carbon: 3. Chemsitry of the in situ activation of the catalyst

Previously it was shown that certain mixtures of K₂SO₄ and FeSO₄ were excellent raw materials for catalytic water vapour gasification of carbon. It was suggested from the results that the iron salt catalyses the reduction of K₂SO₄ to K as the main catalyticly active species of gasification. This paper is concentrated on this activation process. Using TGA, DTA, ESCA, EPMA and visual observations of the melting behaviour after or during treatment of varying $\text{K}{}_2\text{SO}{}_4\text{FeSO}{}_4$ mixtures in H₂ and $\text{H}{}_2\text{H}{}_2\text{O}$ atmospheres it is found that elemental iron is formed in an early stage during heating up. This then catalyses the reduction of K₂SO₄ to K₂S, which is readily hydrolysed by water vapour to liquid KOH. K₂SO₄ and K₂S form an intermediate eutectic (m.p. = 610 °C), which favours wettability of the carbon surface and hydrolysis of K₂S. As well as FeSO₄ any iron salts can be used that are easily reduced to elemental iron in the gasification atmosphere. A general reaction scheme, including activation and catalytic gasification, is proposed. The activation of K₂SO₄ to catalytically active KOH can be described as follows: Fe-saltγFe3K₂SO₄ + 8Feγ3K₂S + 4Fe₂O₃Fe₂O₃ + 3H₂γ 2Fe + 3H₂OK₂S + H₂OγKHS+KOHKHS + H₂OγKOH + H₂S     

Studies of cyclic and linear poly(dimethyl siloxanes): 1. Limiting viscosity number-molecular weight relationships

The limiting viscosity numbers of ten cyclic and ten linear poly(dimethyl siloxane) fractions have been measured in a π-solvent (butanone at 293K) and in two ‘good’ solvents (toluene and cyclohexane at 298K). The dimethyl siloxane fractions studied were in the molecular weight range $\text{800 <}\text{M}\text{?}{}_{\mathrm{w}}\text{< 17 000}$. The data obtained are compared with related studies published in the literature. The ratio of the limiting viscosity numbers [η]_r and [η]_l of the cyclic and linear poly(dimethyl siloxanes) with $\text{M}\text{?}{}_{\mathrm{w}}\text{> 2500}$ was found to be 0.67 in butanone at 293K. This value is identical (within experimental error) to the theoretical ratio $\text{[η]}{}_{\mathrm{r}}\text{[η]}{}_{\mathrm{l}}\text{= 0.66}$ predicted by Bloomfield and Zimm and others for ring and chain polymers in π-solvents. The ratio $\text{[η]}{}_{\mathrm{r}}\text{[η]}{}_{\mathrm{l}}$ was found to be somewhat smaller for the higher molecular weight polymers in the ‘good’ solvents.