Oxygen permeation of blends of copolymers of siloxanes and poly(methylmethacrylate)

A series of low molecular weight (≈40000) copolymers of methylmethacrylate (MMA) and 4-(methacryloyloxy)butylpentamethyldisiloxane (MBPD) have been synthesized by free radical polymerization in dimethylformamide solution. The microstructure, as derived from ¹³C NMR spectra, indicates that the copolymers are about 80% syndiotactic with an overall random distribution of mers. At room temperature, copolymers rich in MMA are clear, rigid glasses but become liquid at high MBPD content. Blends of these copolymers with PMMA are all heterogeneous with visible phase separation over most of the composition range. Differential scanning calorimetry studies show the presence of two T_g's when the relative concentration of PMMA to copolymer is high. Blends of two co-polymers of similar siloxane content produce clear films with no indication of phase separation. The permeability to oxygen at 25°C increases from 0.20 for pure PMMA to 3.0 (fmol/m·s·Pa.) for a copolymer of MMA/MBPD of the mole ratio of 3:1. Evaluation of the permeation behaviors of the blends suggests that blends rich in siloxane exist as a layered structure with the PMMA rich component dominating the observed permeability.     

Service of forsterite refractories in regenerator roofs of open-hearth furnaces

Conclusions The Panteleimonov Refractories Plant produced a large industrial batch of forsterite roof brick for the lower structure of open-hearth furnaces. Tests carried out at the Donetsk Metallurgical Factory showed that it is desirable to use these forsterite refractories: the life of the regenerator roofs was four campaigns in the main roof with an adequately large residual thickness.Investigations established that the changes in the forsterite brick during service in the roof of regenerators are similar to the changes in bricks during service in other structural elements, but the destruction processes occur much more slowly.Translated from Ogneupory, No. 8, pp. 31–38, August, 1968.     

Continuous solvent extraction of sunflower,seed, groundnuts,palmkernels, rapeseed,and copra

In principle, the oil milling process is straightforward. The wide variety of equipment in use reflects, however, a multiparametric process. The main limiting parameters are kind of seed, oil content, particle strength, particle structure, temperature, moisture, particle size, residence time, mechanical forces, etc. Additionally, the seed specific parameters vary not only between kinds of seed but also for the same seed, due to different conditions in climate, soil, and harvesting. Therefore, equipment design must be widely based on statistical averages of the limiting parameters. In other words, exact precalculation of the single technological steps is impossible. As a consequence, for more than 5,000 years, the oil milling process has been in the stage of being optimized. The acutal technical standard is very satisfying, but there is still a strong need for further research and development. Currently, as in the past, the oil milling process seems to be not so much a science as an art.     

Hot-Pressing Behavior of Si3N4

The densification behavior of Si₃N₄ containing MgO was studied in detail. It was concluded that MgO forms a liquid phase (most likely a magnesium silicate). This liquid wets and allows atomic transfer of Si₃N₄. Evidence of a second-phase material between the Si₃N₄ grains was obtained through etching studies. Transformation of α- to β-Si₃N₄ during hot-pressing is not necessary for densification.     

ABA block copolymers without tapering by isokinetic living anionic polymerization in a series of stirred tank reactors

Equations for the molecular weight distribution and the average molecular weights of a living anionic polymerization with very rapid or slow initiation are presented for a series of stirred tank reactors. It is shown that polydispersity of the polymer in the last vessel of a cascade takes for nearly complete conversion of monomer then a minimum, when the reaction is performed isokinetically with concern to monomer conversion, i.e. when monomer conversion in each vessel of a cascade of n tanks is 1/n. Now, polydispersity of the polymer in the mth vessel of the cascade (1 ≤ m ≤ n) is D_m = 1 + 1/m. Values of all systems variables needed for isokinetic control of the polymerization may be precalculated from kinetic models. For vessels of equal size and with equal residence times reaction temperature is suggested as control variable increasing stepwise from vessel to vessel. The proposed procedure was checked for the systems styrene/n-butyllithium/toluene, styrene/s-butyllithium/benzene, and isoprene/s-butyllithium/n-heptane. A satisfying agreement between calculated and measured values of the objectives monomers conversion, number average molecular weight, and polydispersity was found. It is proposed to use the described procedure for the preparation of ABA block copolymers with negligible tapering between the blocks by living anionic polymerization in a series of stirred tank reactors.     

Dielectric relaxation of poly(chlorostyrenes) and their copolymers in the primary transition region

Dielectric relaxation measurements were carried out on a series of bulk poly(chlorostyrene) homopolymers and random copolymers over the frequency range from 50 to 100 kHz and at temperatures in the neighbourhood of the glass transitions of the polymers thus encompassing the α relaxation. Homopolymers examined were polystyrene (PS), poly(2-chlorostyrene) (P2CS), poly(3-chlorostyrene) (P3CS), and poly(4-chlorostyrene) (P4CS). Copolymers were poly(styrene-co-2-chlorostyrene) (PS2CS), poly(styrene-co-4-chlorostyrene) (PS4CS), and poly(2-chlorostyrene-co-4-chlorostyrene) (P2CS4CS). The dielectric data were analysed to yield dipole moments and Kirkwood—Fröhlich correlation parameters. The shapes of the dielectric loss curves were also taken into account. Glass transition temperatures were determined by differential scanning calorimetry (d.s.c.). It was concluded that the phenyl ring rotates freely in the α relaxation regions of PS, P4CS, and P3CS, but not in P2CS. The dipole moments of the copolymers are correlated with dyad distributions calculated from reactivity ratios.     

Heat transfer

Conclusions Numerous new heat transfer developments have been reported in the last few years. These developments are useful for a better understanding of the basic theory and for developing improved equipment. In many cases both heat and mass transfer occur simultaneously in commercial operations.     

Technical new feature

A continuous process for the commercial production of isopropenyl stearate (IPS) from triple pressed stearic acid and a stabilized form of propyne has been developed. Cost estimates, including capital costs, operating costs, and profitability, for commercial scale plant production which show the process to be economically feasible are presented. This potentially profitable process offers the advantages of reliable raw material sources, minimal external thermal requirements, and usable process waste streams. For a plant producing 5 million pounds of IPS per year, the selling price range is 80 to 107 cents/lb IPS, corresponding to a raw material cost range of 27 to 54 cents/lb of IPS. For a 20 million pound per year plant, the selling price range is 58 to 85 cents/lb IPS. The selling prices include a 20% annual return on fixed capital investment. Fixed capital requirement ranges from 2.7 to 10.9 million dollars (3rd quarter, 1975) for plants ranging in size from 5 to 50 million pounds of IPS per year, respectively.     

Stereochemistry and mechanism of the hydrogenation of dialkyl cyclohexenes

In order to investigate the steric effect of the substituents to determine the product distribution, disubstituted cyclohexenes were hydrogenated over several transition metal catalysts. Some cyclohexenes which have two large substituents at the vicinal carbon atoms, at least one of which is trigonal, were not hydrogenated over Raney Ni at all but were hydrogenated over Pt catalyst under our experimental conditions. Presumably, the stereoselectivity depends on the competitive operation of the torsional angle strain and the catalyst hindrance with substituents. In the hydrogenation over Pd catalyst, thermodynamically more stable products were dominant at the standard condition but at high substrate to catalyst ratio the less stable products were slightly preferred. No appreciable stereoselectivity was observed in the hydrogenation of 1,4-disubstituted cyclohexenes.     

Pile electrique a anode d'aluminium—I electrolyte acide

An acid electrolyte (pH ) 3) for an aluminium primary battery has been studied. It contains: Al(CIO₄)₃. 1 M: AlCl₃. $\text{1}\text{30}$ M; (NH₄)₂CrO₄, $\text{1}\text{50}$ M. The performance of three binary aluminium alloys AlZn 2%; AlZn 5%; AlGa 0·3% are compared. Capacity of Al primary battery made with Al 2% is twice that of a conventional Leclanché cell on continuous discharge test. Unfortunately CrO⁼₄ disappears in presence of MnO₂ which is prejudicial to the good conservation of the aluminium cell.