Synthesis and polymerization of polyacrylic esters

Abstract

The method of telomerization has been employed in the synthesis of the telomer homologs of polyacrylate esters with successively increasing degrees of polymerization (n) and of telomers differing in the nature of the polyester chain. Compounds have been synthesized of the general formula where R and R1are alkyl or aryl radicals and n = 2, 4, 8, and 20. With changes in (n) from 2 to 20 the structural viscosity of the polyacrylate esters increased from 150 to 8000 centistokes (at 20°), the specific gravity from 1.213 to 1.308, and nD20 from 1.515 to 1.5479. The presence of double bonds in the molecules of the polyacrylate esters synthesixed made it possible to carry out their polymerization (hardening) in the presence of radical chain initiators with the formation of glassy or elastic, insoluble, nonmelting polymers of sufficient thermal stability and endowed with a number of valuable properties so as to be of considerable practical potentiality. The changes in physical properties of the reaction system (gelation, gradual increase in density and finally the formation of a glass structure) in the course of the polymerization beginning from the very early stages (the gelation point is reached at 5–10% conversion) are responsible for a number of specificities in the kinetics of the hardening of polyacrylate esters. Owing to this we undertook a detailed investigation of the polymerization kinetics under widely varying conditions. Polymerization in bulk takes place autocatalytically, since with increasing degree of structuration in the course of polymerization the rate of diffusion of free radical diminished, leading to a decrease in rate of chain termination. The rate of reaction begins to diminish markedly only at large extents of polymerization. A study has been made of the effect of diluting the reaction mixture with an inert solvent, of the initiation rate, nature of the initiating agent, temperature, chemical structure of the initial polyacrylate ester, as well as of the addition of inhibiting agents on the polymerization kinetics. The results obtained have been discussed from the standpoint of the capacity of the system for structuration under the various conditions of reaction. The heats of hardening of the polyacrylate esters with successively increasing distance between their values have been discussed with respect to the reaction mechanism.

Current trends in investigations into the microheterogeneous mechanism of three-dimensional radical polymerisation

“…The higher is the viscosity, the larger is W 0 . 11,13,45,87,88 As in the case of the reactivity at a high conversion, the physical properties (those, which control the level of intermolecular interactions in the reaction system) of the starting oligomers rather than their conformational properties have a dominant role, i.e., the presence of centres of strong intermolecular interactions, which can form hydrogen dipole ± dipole and other labile bonds, is of importance. Cooperative hydrocarbon groups characterised by very weak dispersion interactions can also serve as such centres [for example, the methylene groups 7(CH 2 ) n 7 at n > 4 are involved in intermolecular interactions with the energy E > 17 kJ mol 71 comparable to the energy of hydrogen bonds and the phenyl groups are involved in intermolecular interactions with E = 29 ± 33.5 kJ mol 71 ].…”