Thermodynamic stabilities of the three crystalline forms of isotactic poly-1-butene as a function of temperature

Thermodynamic stabilities of the 3 crystalline forms of isotactic poly-1-butene as a function of the temperature has been evaluated by packing energy calculations using the values of the axes of the unit cells obtained by X-ray measurements. The lengths of the axes of the unit cells have been determined from X-ray powder spectra at different temperatures in a range between 170 K and temperatures near the melting point for each form. The packing energy has been calculated by minimizations performed using the experimental values of the axes of the unit cells at the various temperatures. The results show that form 1 is the stablest form in all the range of temperature and that form 3 is lower in energy with respect to form 2, but the 2 forms become almost isoenergetic at high temperatures.     

Heat resistant allylic resin matrix for composite

Three structurally different imido group containing diallyl monomers were synthesized. They were polymerized using initiators dicumyl peroxide and/or benzoyl peroxide in polar aprotic solvent. The pre-polymers were characterized by i.r., NMR, elemental analysis, TGA/DTA, viscometry and VPO techniques. Laminates were fabricated by impregnating carbon fibre with these resins and cured by a hot press mould at 180–190° in the presence of the named initiators. Laminates were evaluated by measuring flexural strength and interlaminar shear strength.     

Morphological characteristics of products of styrene-butadiene-1,3-polybutadiene copolymerization in the presence of ZnCl2 and a network reagent

The morphological characteristics of the copolymerization system “styrene-butadiene-1,3-polybutadiene” are investigated in the presence of ZnCl₂, network reagent (ZnO, 2-mercaptobenzothiazole), tert-dodecylmercaptan, azobisisobutyronitrile and benzoyl peroxide by phase-contrast and electron microscopy. The investigations concern the pre-copolymerization of the system as well as the end product, i.e. impact polystyrene (IPS). It is established that, for definite concentrations and proportions of the components in the copolymerization system, a specific morphology of the copolymer as well as of the dispersed elastomeric particles is formed. The found morphological states “quasi-net-like inversion” and “small elliptical particles” supplement the types of morphological states in IPS, systematized by Echte and Kruse.     

Structural defects in poly(vinyl chloride)—V. Thermal and photodegradation of copolymers of vinyl chloride with various acetylene derivatives

Vinyl chloride has been copolymerized with various acetylene derivatives in bulk at 50. It has been shown by ozonolysis that these copolymers contain a significantly increased amount of internal double bonds. A comparison of the thermal and photodegradation behaviours of the copolymers has been made. The built-in double bonds show an effect on the reactivity of the adjacent allylic chlorine depending on the electron-withdrawing or repelling nature of the substituent. Among the comonomers investigated, copolymers containing 3-chloropropine have the least reactive defect sites, because of the electron-withdrawing chloromethyl substituent. On the contrary, the electron-repelling n-butyl group, built-in by using hexine-1 as comonomer, results in enhanced reactivity of the allylic chlorines.     

Structural defects in poly(vinyl chloride)—IV. Thermal degradation of vinyl chloride/acetylene copolymers

Vinyl chloride/acetylene copolymers have been prepared under subsaturation conditions. Copolymerization rates and molecular weights of the copolymers decrease with increasing concentration of acetylene in the monomer feed, indicating that acetylene is a retarder in vinyl chloride polymerization. The concentration of internal double bonds in the copolymers determined by ozonolysis increases with increasing amount of acetylene in the feed. Thermal degradation has been performed at 110 with solid samples and at 170° in solution under inert atmosphere. The extent of HCl loss as a function of time shows a rapid initial phase followed by a slower steady rate The initial dehydrochlorination rates are higher for copolymer samples containing higher concentrations of internal double bonds. Quantitative analysis of the u.v. and visible spectra of degraded copolymers shows that the sum of the concentration of polyenes with 4–12 conjugated double bonds increases rapidly in the first phase of degradation, but then decreases slowly, due to secondary reactions of polyene sequences.     

Excitons in direct band gap cubic semiconductors

Perturbation is applied to study of the Wannier-Mott excitons in direct band gap cubic semiconductors with a fourfold degenerate highest valence band. The fine structure of exciton energy levels is investigated. General formulae are derived for the matrix elements of the perturbation. From these expressions it is straightforward to obtain values of the fine structure splittings of the energy levels and the wave functions of corresponding staes in any order of perturbation theory. A comparison with results of previous works is made.     

The inelastic neutron scattering spectrum of chloroform in solution

The incoherent inelastic neutron scattering (INS) spectrum of CHCl₃ in liquid SO₂ (ambient temperature) in the region 0–3600 cm⁻¹ is presented. For the first time it has been demonstrated that good quality INS data on solutes can be obtained over this energy transfer range. A discussion of suitable solvents for further work is included.     

Comparison of a very high frequency 148 MHz inductively coupled plasma to a 27 MHz ICP

Physical parameters and analytical performance are determined for an analytical ICP operated at 148 MHz, a frequency nearly three times higher than any previously reported. The iron(I) excitation temperatures are approximately 1.5 times lower and the electron densities are five times lower than at 27 MHz. The consequences of these changes are lower analyte and background continuum emission intensities, such that the signal to background ratios are decreased at the higher frequency. Freedom from interferences and working curve linearity are unaffected while ease of sample introduction is improved. A shift towards atomic emission indicates a deviation farther from LTE at 148 MHz. These effects are attributed to the decrease in skin depth with increasing frequency.     

Raman and infrared studies of NaLa(MoO4)2:Nd3+

The polarized Raman and i.r. (powder) spectra of 0.5 mole % neodymium doped NaLa(MoO₄)₂ have been analysed on the basis of C_4h crystal symmetry. Group theoretically predicted fundamentals have been observed. The frequencies and intensities are not altered due to doping.     

Amorphous magnetic state established by Mössbauer spectroscopy on powders obtained by borohydride reduction

The Mössbauer spectra of a series of iron-cobalt-boron powders with different boron contents are discussed in association with the conditions of borohydride reduction. The most important structural peculiarities due to the composition and the amorphous-crystalline state of the powders are established on the basis of the hyperfine field distribution.