Методами химической кинетики, ИК-фурье-спектроскопии и термомеханического анализа изучены процессы, происходящие при переработке и вспенивании термореактивных композиций на основе статистического сополимера акриламида с акриловой кислотой: размягчение, собственно вспенивание и отверждение сополимера. Проведено согласование указанных процессов по времени и температуре, предложены прогностические способы расчета их динамики и свойств пеноматериалов в зависимости от состава исходной пенообразующей композиции и условий вспенивания.
The processes that occur during the processing and foaming of thermosetting composites based on a random copolymer of acrylamide and acrylic acid-softening, foaming, and curing of the copolymer-are studied with the use of methods of chemical kinetics, Fourier transform infrared spectroscopy, and thermomechanical analysis. The above processes are coordinated with respect to time and temperature; prognostic methods for calculating the dynamics of these processes and the properties of foam materials as functions of the composition of the original foam-forming composite and the foaming conditions are proposed.
Standard methods were used to investigate the physicomechanical characteristics of the main parts of endotracheal tubes produced by six leading world manufacturers. It was shown that the articles have statistically significant, substantial differences in the physicomechanical properties of their main working units: the main tube and the sleeve. The sleeve is the least strong part on which the functionality of the entire article depends. The best strength characteristics are possessed by the Curity sleeve, but at the same time the Curity main tube possesses practically no thermal plasticity. The Rush main tube possesses high thermal plasticity but has the least strong sleeve. Most balanced from the viewpoint of physicomechanical characteristics is the Portex tube. Having sufficient tube elasticity and strength, among the investigated tubes it has the highest thermal plasticity with minimum hardness at body temperature and a sleeve of high strength.
The effect of the backbone-chain structure of acrylonitrile and methacrylic acid copolymers of various compositions on the maximum degree of intramolecular imidization has been studied. An estimating method for calculating this value on the basis of 13 C NMR spectroscopy data on the sequences of comonomers units in the initial copolymers is proposed. Poly-2-cyanoacrylic acid, in which the carboxylic acid and nitrile groups are located at the same carbon atom, has been used as a reference “ideally regular” polymer. The actual maximum degree of the intramolecular imidization of copolymers after thermolysis was ascertained by means of IR Fourier spectroscopy with the use of Lorentz approximations for deconvolution of absorption peaks in the spectra.
The kinetics of homogeneous hydrolysis of polyacrylonitrile in an aqueous solution of sodium carbonate and the chemical structure of the resulting copolymer are studied by FTIR spectroscopy, 13C NMR analysis, and titration methods. It is found that hydrolysis in the presence of sodium carbonate does not include the stage of amidine formation and does not result in the complete exhaustion of nitrile groups in a polymer. The designed partial-hydrolysis method permits the use of polyacrylonitrile for the synthesis of the copolymer with a predominant unit alternation; this copolymer is identical in terms of chemical structure to the Rohacell copolymer obtained through block copolymerization of acrylonitrile and methacrylic acid.
On the basis of potentiometric investigations of the kinetics, a new mechanism of aniline polymerisation is proposed, including the formation of a charge-transfer complex with the participation of the monomer; also, a kinetic model is constructed and some of its parameters are evaluated.
In the present work an examination is made of the kinetics of the oxidative polymerisation of N-ethylaniline in an aqueous hydrochloric acid solution, with ammonium peroxydisulphate as the oxidant. The key role of protolytic equilibria in this process is shown, a kinetic model is proposed, and its parameters are determined.
