Library

Notes: Soluble oligoarylenes based on naphthalene and anthracene, and fractions of different molecular weights have been studied by electron microscopy. For the examined samples, a definite interrelation is ascertained between microstructure and physicochemical properties, such as density, x-ray parameters, heat of solution, electron paramagnetic resonance (EPR) spectra, and dark conductivity. The molecular-weight distribution of oligoarylenes is shown to decisively influence the degree of packing of macromolecules and their physicochemical properties. This allows interpretation of some anomalous properties of oligoarylenes in comparison with the first members of the corresponding homologous series.

Notes: The kinetics of copolymerization of styrene with p-benzoquinone in the presence of BF3OEt2 is investigated. The rate constants and activation energy of the copolymerization process are determined. The reaction orders for monomer and catalyst are estimated. It is found that the rate of styrene and quinone copolymerization increase and the induction period decreases owing to addition of the latter. It is shown that the copolymerization rate achieves its maximum at an equimolal ratio of monomers. This phenomenon is explained by formation of active molecular complex between styrene and p-benzoquinone. On the basis of obtained data the course of copolymerization is interpreted and the cationic mechanism of copolymerization process is proposed.

Notes: During the freezing (cryolysis) of aqueous solutions or suspensions of high molecular compounds degradation of the macromolecules is observed due to the pressures obtaining in the phase transition and in the growth of ice crystals. As a result of the cryolysis active degradation products are formed which are susceptible to further chemical conversion. Products of the cryolytic degradation of starch formed during single and repeated freezing of its solutions (from t = -4° to -195°C.) with subsequent thawing (to -3 to -4°C.) are characterized by enhanced reducing properties, increased iodine numbers, decreased ηsp values, the appearance of a water-soluble fraction, a shift in maximum absorption of the iodine complex to shorter wave lengths (from 580-600 mμ to 540-560 mμ) and a twofold increase in hydrolysis rate under the action of mineral acids. This is explained by degradation of the macromolecules and decrease in degree of polydispersity during the repeated freezing and thawing of the solutions or of the moist starch. Prolonged storage of the thawed starch specimens in argon and in air at +20°C., as well as short heat treatment at +37-75°C. (5-30 min., respectively) leads to decrease in the reducing capacity, increase in ηsp and to a shift in the absorption maximum of the starch-iodine complex in the longer wave length direction. On adding free radical acceptors to the starch solution no changes in the characteristics are observed. This gives grounds to the assumption that the relations are due to the chemical conversions of macroradicals. Heating the cryolytic degradation products for longer periods in air causes intensification of the hydrolysis. Such hydrolysis does not take place in an atmosphere of the inert gas. Heating under these conditions solutions of starch that had not been subjected to freezing does not cause any changes in the product. The increased reactivity of starch cryolysis products in air is evidently the result of the formation of labile peroxide bonds in the starch macromolecule. The degradation of the initial soluble starch by dilute (0.15-0.25%) solutions of its cryolyzate has been experimentally established. In order to elucidate the effect of mechanical rupture of the chains on enzymatic activity experiments were carried out on determination of the activity of the cryolytic degradation products of amylase and pepsin. It has been found that under suitable conditions of freezing and thawing sharp changes in the enzymatic activity during storage are brought about. In contrast with the enzymes not subjected to this action the activity of the cryolyzed enzymes increases and in a number of cases exceeds that of the original preparations. The radical concept of degradation of starch and other polymers gave grounds for carrying out the block copolymerization of mixtures of polymers in solutions or in the presence of moisture by the method of repeated freezing and thawing in an inert gas atmosphere. The formation of block copolymers has been demonstrated on the example of the freezing of finely dispersed polystyrene emulsions as well as styrene monomer in starch solution with varying ratios of the components. A study of the resultant products showed that under the chosen conditions block copolymers of nonpolar polystyrene blocks and polar starch blocks are formed.

Notes: Multinuclear aromatic compounds are distinguished by considerable thermostability. In a number of cases they have been shown to be endowed with semiconductor properties. In view of this the development of a method of synthesis and investigation of aromatic polymers with a common system of conjugated bonds has both theoretical and practical interest. Such substances have been synthesized by the authors on decomposing bisdiazo compounds by an ammoniacal solution of univalent copper, and also on decomposition of bisnitroso acetates. In particular, 4,4′-bisdiazobiphenyl, 4,4′-bisdiazobitoyl, 4,4′-bisdiazobiphenyl-3,3-dicarboxylic acid, and benzidine N,N′-bis-nitroso acetate were employed. On decomposition of the bisdiazo compounds a powder of orange to brown color was formed, soluble in concentrated sulfuric acid and isoluble in most organic solvents. Analysis showed it probably to possess the composition: where R may be H, COOH, or CH3. On the average one azo group is present for each 4-10 benzene rings and two chlorine atoms for each 10-20 rings. The mean molecular weight determined for one of the carboxylated polymer specimens was found to be 3000. On heating to 400° the polymer decarboxylates. At 450° decomposition sets in. Viscosity curves of the solutions (plots of ηsp/C vs. C) exhibit an anomalous rise within the limits C = 0.1-1%. The concentration of unpaired electrons in the polymers was shown by the electron resonance method to be ∼1019/g. Heating the substances leads to an increase in concentration of unpaired electrons by 1-2 magnitudes. The spectra and x-ray diagrams of the substance were obtained. Evidently the formation of polymers from bisdiazo compounds is of a radical nature, leading to the formation of stable radicals of low activity. Low molecular fractions isolated from the polymers are fusible and soluble in benzene. They are capable of reacting with diethynylbenzene with the formation of nonmelting and insoluble thermostable products. Carboxylated polymers form salts with transition elements that evidently are of the nature of intracomplex compounds with intermolecular crosslinkage. Products of the decomposition of benzidine bisnitroso acetate are in general similar to those resulting from bisdiazodiphenyl, but contain less unpaired electrons.