The thesis is devoted to the synthesis and research of new pentaza-1,4-dienes and their application as free-radical polymerization initiators. Methods of synthesis of the substituted bis-pentaza-1,4-dienes and the 3-hydroxyethyl-substituted mono-pentaza-1,4-dienes have been optimized. The structure of synthesized compounds has been proved by spectral methods. The main method of synthesis is azo coupling reaction of aryldiazonium salts with monoethanolamine (for mono-3-hydroxyethyl-pentaza-1,4-dienes) and ethylenediamine (for the bis-pentaza-1,4-dienes). The stoichiometry of the azo coupling reaction is very important for product quality and its non-compliance leads to heavy contamination with impurities.
The photochemical properties of the synthesized compounds have been studied. All initial bis-pentaza-1,4-dienes are characterized by two absorption bands ~ 300 nm, which corresponds to the n → π * transition, and ~ 360-380 nm for the π → π * transition. During UV light irradiation of pentaza-1,4-dienes solutions photolytic decomposition occurs, which is accompanied by a rapid decrease in the absorption intensity of band corresponding to the π → π * transition and a slower decrease in the n → π * transition intensity. This is due to the formation and accumulation of primary decomposition products, which has the absorption bands partially overlapping with the original compounds. To check the decomposition process for uniformity AD – diagrams method was used. On such diagrams the dependence of the absorption difference ΔD = Do - Dt on a certain wavelength is plotted against the difference in the maximum of absorption ΔDmax = Do(max) -Dt(max). It was found that at initial stages of a process, the decomposition proceeds uniformly, and, therefore, it can be analyzed by the first-order kinetic equation. Half-life times and decomposition rate constants were calculated. It was found that the decomposition rate depends on a donor-acceptor nature of the substituent in aryl fragment. More electron donor substituents accelerate the decomposition process by increasing the electron density on chromophore azo groups. The quantum yields of photolysis are calculated, which for the most photoactive representatives of pentaza-1,4-dienes exceed 0.5.
The thermolysis process of pentaza-1,4-dienes have been studied and it was shown that decomposition constants has the same order comparing to those for azobisisobutyronitrile, which provides the possibility of their application as radical polymerization initiators.
The kinetic regularities of the reaction of thermally initiated radical polymerization of methyl methacrylate with presence of pentaza-1,4-dienes as initiators have been investigated. It was found that the rate of polymerization increases synchronously with donor properties of the substituent in an aryl fragment of the initiator and it is higher in the case of bis-pentaza-1,4-dienes. If compare bis-pentaza-1,4-dienes with their mono-analogs then at the same concentration of initiator the first ones demonstrate the higher rate of polymerization values.
The matrices for recording media in polarization holography have been created on the basis of obtained polymeric materials. Naphthylazo dye was used as a photoactive dopant. A comparison with samples of polymethylmethacrylate of industrial production has been made. Fundamental differences in the kinetics of the rise and fall of the diffraction efficiency values have been found. Those differences apparently associated with the broad molecular weight distribution of the samples obtained with presence of pentaza-1,4-dienes.
The PMMA thermal destruction obtained with pentaza-1,4-dienes have a peculiarities comparing to PMMA obtained with AIBN. In the first case it has more slow nature. The difference is most explicit in case of BP-Cl initiator, which increase the thermal stabiltity of PMMA up to 40°C. Hence the PMMA synthesis in the presence of pentaza-1,4-dienes as initiators of polymerization is industrially perspective because it leads to more thermally stabilized polymer.
