Some properties of low molecular weight polybutadiene and polytetrahydrofuran

The proposition, that low molecular weight polymer fractions in good solvents behave as if they were under ? conditions, has been examined experimentally. Series of monodisperse hydroxy-terminated polytetrahydrofuran (PTHF), 82% 1,4-polybutadiene (PBD), and 30% 1,4-PBD were prepared, and values of M?_n obtained by vapor-pressure osmometry and endgroup analysis. The Mark–Houwink viscosity parameters K and ν were determined in a number of solvents. The general conclusion is that the proposition is invalid for these systems notwithstanding the fact that ν = 0.50 for one of them [82% 1,4-PBD in methyl ethyl ketone (MEK) at 25°C]. For this particular case, the following evidence suggests that these are actually ? conditions so that the apparent fulfilment of the proposition is fortuitous. (1) Cloud-point precipitation yields ? = 26 ± 3°C in MEK. (2) The value of K is close to that of K_? found elsewhere for PBD in a different solvent at a similar temperature. (3) Application of the Kurata-Stockmayer iterative procedure for estimating K_? from data in good and bad solvents yields a reasonably small discrepancy (10%) between the K_? values from data in toluene and MEK at 25°C for this polymer and only a 3% difference in the unperturbed dimensions (〈r₀²〉/M)^1/2 derived from them. Measured melting points T_m of PTHF (M?_n = 1000–13000), plotted as a function of chain length Z, viz., 1/T_m = 1/T_m0 + 2R/ZΔH_f, yield 43 ± 3°C and 1.6 kcal/submole, respectively, for the limiting melting point T_m0 and the heat of fusion ΔH_f. The former is in good agreement with the value obtained dilatometrically for high molecular weight polymer, while the latter indicates a degree of crystallinity of ca. 54%.     

Coal liquefaction in nitrogen compounds

Model compound studies have shown that 1,2,3,4-tetrahydroquinoline is an exceptionally good coal solvent. In the pure compound, subbituminous coal conversion to THF-soluble products approaches 100% under relatively mild reaction conditions. The effectiveness of tetrahydroquinoline for coal conversion appears to be related to its concentration relative to coal. The unique behaviour of tetrahydroquinoline is ascribed to its being a highly active H-donor; the fact that it is regenerable under reaction conditions by the reaction of hydrogen and quinoline; and that its polarity allows penetration of the coal structure and aids in dispersion of the dissolved coal. It has been found that, during reaction with coal, tetrahydroquinoline and other nitrogen compounds undergo extensive condensation reactions which result in an increase in the nitrogen content of the high boiling and non-distillable liquefaction products.     

The Assessment Portfolio: A Possible Answer to the Distance Education Assessment Dilemma

ABSTRACT

This “Siteseeing” column provides reviews of Awards sites.     

The development of peat-oil (POM) and peat-alcohol (PAM) slurries as alternative fuels

The preparation and evaluation of peat/No. 2 fuel oil mixtures (POM) and peat/methanol mixtures (PAM) is described. POM and PAM prepared using North Carolina peat and having varied peat loadings, peat moisture contents, and peat particle sizes have been studied by measuring slurry sedimentation ratios and drain times from sedimentation tubes. The peat moisture content was particularly crucial in forming stable slurries. The effect of a variety of additives at 0.5–1.0 wt.% on sedimentation ratios, drain times, and viscosities was studied. Calorimetric studies of several PAM and POM slurries as well as preliminary combustion tests of POM slurries in a salamander burner are also reported.     

Chelates in agriculture

Within the past 20–25 years it has been recognized that many of the micronutrient requirements of plants could be supplied by complexes containing chelated metals. These chelates find uses in a wide variety of agricultural crops such as: corn, bush beans, cucumbers and citrus groves. Applications vary from fertilizer additives and seed dressing to foliar sprays and hydroponics. The chelates themselves have chemical structures that seem to be limited only by the chemists imagination. The critical factors for the use of any of these chelates is the stability constant and the cost to prepare a pound of chelated metal such as iron or zinc. A comparison of costs for a few of the more common chelates indicates a need for agricultural studies on the results of using glucoheptonates for supplying micronutrients.     

Carbon nanofibers with radially oriented channels

An easy templateless method to synthesize porous carbon nanofibers (CNFs) having radially-oriented mesopores is reported, using selective gasification with nano-sized catalyst particles and hydrogen as the gasification reagent. The gasification generated pores whose size corresponds to that of the catalyst particle used for the drilling. The pores were formed along the graphitic layers, reflecting the structural alignment in the CNFs. The pore size and structure can be controlled by selection of catalyst and gasification conditions.     

AN IMPROVED MODEL FOR THE INTERFACIAL BEHAVIOR OF CAUSTIC/CRUDE OIL SYSTEMS

The effects of crude oil acid number and brine concentration on the interfacial behavior of caustic/crude oil systems were investigated. The effect of increased brine concentration was generally to increase the minimum interfacial tension (IFT) while low IFT values were retained for longer periods of time. Varying the crude oil acid number caused the shape of the IFT versus time curve to change, while the minimum IFT remained constant. These combined results imply that Lagmuir and not Henry soption (adsorption/desorption) kinetics were operative

A phenomenological surface phase model for the IFT behavior of caustic/crude oil systems is proposed which incorporates Langmuir kinetics. The model takes into account interfacial activities of the acidic components in the crude and the detailed chemistry of the oil phase, the water phase, and the interface. To allow for realistic comparison of model results with interfacial tensiometer data, drastic interfacial volume changes which accompany the transient interfacial tensions in the system are taken into account.     

The Effect of Film Thickness on Friction Coefficients for Solid Lubricants; CaF2, MoS2 and Graphite

An experimental investigation has been conducted to determine the effect of film thickness on the friction coefficient of solid powdered lubricants, applied as thin films on the mild steel specimens.

Curves representing the coefficient of friction for various film thicknesses, as well as the tabulated data are given. The results are discussed and compared to those theoretically conceivable using the relationship of Bowden and Tabor and that of Rabinowicz.

Solid films of graphite, molybdenum disulphide and calcium fluoride with a thickness range of 0.0002 to 0.0008 in. were used. It has been concluded that, for the solid lubricants tested, the coefficient of friction is dependent upon the film thickness. The Theory of Adhesion by Bowden and Tabor and the mathematical relationship by Rabinowicz do not adequately explain the variation in the coefficient of friction as the film thickness varies.     

In situ comparison of 665 nm and 633 nm wavelength light penetration in the human prostate gland

The depth of treatment in photodynamic therapy (PDT) of tumors varies with the wavelength of light activating the photosensitizer. New generation photosensitizers that are excited at longer wavelengths have the potential for increasing treatment depths. Tin ethyl etiopurpurin (SnET2), a promising second-generation photosensitizer is maximally activated at 665 nm, which may be significantly more penetrating than 633 nm light currently used with porphyrins in PDT. The penetration of 665 nm and 633 nm wavelength red light in the prostate gland was compared in 11 patients undergoing prostatic biopsies for suspected prostatic cancer. Interstitial optical fibers determined the light attenuation within the prostate gland. Of the 11 patients, 7 had dual wavelength and 4 had single wavelength studies. The mean attenuation coefficients, mueff, for 665 nm and 633 nm wavelength light were 0.32 +/- 0.05 mm-1 and 0.39 +/- 0.05 mm-1, respectively, showing a statistically significant difference (P = 0.0003). This represented a 22% increase in the mean penetration depth and at 10 mm from the delivery fiber there was 1.8 times as much 665 nm light fluence than 633 nm. The mean mueff at 665 nm for benign and malignant prostate tissue were similar (P = 0.42), however, there was significant interpatient variation (mueff ranging from 0.24 to 0.42 mm-1) reflecting biological differences of therapeutic importance. The enhanced light fluence and penetration depth with 665 nm light should allow significantly larger volumes of prostatic tissue to be treated with SnET2-mediated PDT.