Boiko V. The role of solvent in the initiation of the radical polymerization of dienes under the action of hydrogen peroxide

The dissertation is devoted to the study of the role of solvent in the radical polymerization of dienes under the influence of hydrogen peroxide (HP). A systematic study of the polymerization kinetics in various types of solvents and the processing of its results on the basis of the principle of linearity of free energies by multiple correlation analysis established the dependence of the initial polymerization rate on the characteristics of the solvents. This dependence is described by a four-parameter equation that characterizes the influence of solvent parameters, the most important of which was the electrophilic solvation of ET according to Reichardt. This parameter characterizes the ability of a solvent molecule to interact with a hydrogen peroxide molecule, in which the oxygen atom of the peroxide bond is the electron donor. The determination of the polymerization orders by the monomer and the initiator showed that the orders of magnitudes exceed the values for ideal radical polymerization. This indicates the formation of complexes between the components of the polymerization system. The use of alcohols labeled with carbon 14C as solvents shows that their fragments are included into oligomers. The label functionality was 0.5, regardless of the alcohol used, monomer conversion and molecular weight of the oligomers. This indicates that alcohols are included at the initiation stage. In the range of molecular weights of about 2000, the total functionality in the oligomers obtained in solutions of primary alcohols was close to 2, and in a solution of isopropyl alcohol (IPA) – to 1.5. If we take into account that tertiary hydroxyl groups are not determined by the acetylation method, then these results are consistent with the idea that the total functionality, taking into account the label, is 2 in the oligomer obtained in IPA solution. The nonequivalence of hydroxyl groups in oligodienes was demonstrated by spectral methods, as well as the reactivity of hydroxyl groups in acetylation and urethane formation reactions. The decomposition of the HP-IPA complexes proposed by different researchers is not realized under polymerization conditions. The only way to generate radicals proceeding with negative enthalpy is the decomposition of the ternary monomer-initiator-solvent complex [butadiene٠٠٠HP٠٠٠IPA]. The coordinated decomposition of this complex in two bonds gives two hydroxyl-containing radicals and water: НОСН2СН=СНСН2• + (СН3)2С•ОН + Н2О. When using IPA, one of the radicals contains a tertiary hydroxyl group. The formation of such a complex is confirmed by quantum chemical calculations, which showed that the formation of the complex proceeds with positive energy relative to the sum of the energies of the individual components of the system. Kinetic calculations performed using published data for reaction rate constants of individual polymerization stages taking into account chain transfer reactions were performed. They showed that chain termination is carried out through chain transfer by a macroradical to the HP initiator. In this case, a terminal hydroxyl group and a hydroxyl radical in the oligomer are formed. It is this radical that transfers the chain to the polymer with the formation of tri- and polyfunctional molecules. The use of all the results presented allowed us to propose a new scheme for the radical polymerization of dienes in alcohol solutions under the action of HP. Its fundamental difference from the previously proposed schemes lies in the method of generating primary radicals through the decomposition of the ternary complex [monomer٠٠٠initiator٠٠٠solvent], which involves the inclusion of alcohol hydroxyl-containing fragments into the oligomers. Another difference is the way of chain termination, which is carried out by transferring the chain by a macroradical to the HP. The inclusion of solvent fragments into the oligomer at the initiation stage was also established when using labeled 14C acetone as a solvent. In this case, the label functionality was 0.18-0.20 what is explained by decomposition of primary acetonyl radicals.