V. N. Artem'eva

THE ROLE OF THE PYRIMIDINE RING IN THE MAIN CHAIN OF POLYANIC ACIDS AND POLYIMIDES. IV: INFLUENCE OF PYRIMIDINE RING BASICITY ON THERMOIMIDIZATION OF POLYAMIDOACIDS

Thermoimidization kinetics of polypyromellitamic acids prepared from 2,5-bis(p-aminophenyl)pyrimidine and 4,4″-diaminoterphenyl have been investigated by IR spectroscopy. It has been shown that the activation energy for the pyrimidine-containing polymer is nearly twice as low as that for the aromatic analog. This is explained by base catalysis of cyclization of the amidoacid fragments by pyrimidine rings in polymer chains. Base catalysis facilitates the process of imidization and favors the formation of polyimidic macromolecules with a lower incidence of defects. Also, the pyrimidine rings obviously catalyze the resynthesis of amidoacid fragments from the anhydride rings and amino groups formed on the destruction of the polymer chain during thermoimidization, and ensure almost complete recovery of the macromolecules with the previous bonds.

The role of the pyrimidine ring in the main chain of polyamic acids and polyimides

A comparative study of the behavior of polypyromellitamic acids based on 2,5-bis(p-aminophenyl)pyrimidine and 4,4″-diaminoterphenyl in concentrated dimethylacetamide solutions was carried out by the light-scattering method. It was shown that mutual ordering of the scattering elements is much higher for the pyrimidine-containing polyamic acids than for benzenoid polyamic acids. The Flory-Huggins parameters of the polymer-solvent interaction thus determined indicate that the polymer-polymer interactions increase when a pyrimidine ring is introduced into the polyamic acid or polyimide. Hence, the hypothesis postulating that the amide solvent is displaced by the pyrimidine ring during the shear packing of pyrimidine-containing polymers is confirmed.

Investigation of polyimide formation from the complexes of the diester of benzophenonetetracarboxylic acid with diamines 7. Role of theo-carboxylic group of acid diester in the formation and imidization of H-complexes

The kinetics of thermal imidization of various H-complexes of semiesters of bis(o-phthalic) acids with diamines was studied. The activation energy of the imidization was shown to increase with increasing pKa value of the diamine andEa value of the dianhydride and with decreasing nucleophilicity of the alcohol used for the synthesis of H-complexes. The experimental kinetic data and the results of quantum chemical calculations of the heats of formation of the initial H-complexes and transition states made it possible to propose a mechanism for the imidization reaction. This mechanism takes into account the catalytic effect of the carboxylic group of the semiester in theo-position with respect to the ester group.

The study of the structure of solutions of the H-complexes of diesters of tetracarboxylic acids with diammes by the light scattering method

The parameters of the hypermolecular orientation order in H-complexes of the dimethyl ester of 3,3′,4,4′-benzophenonetetracarboxylic acid with 1,6-hexamethylenediamine (BPE · HMDA) and 4,4′-diaminodiphenylmethane (BPE · DADPM) in methanol and aqueous methanol have been investigated using the angular dependences of the isotropic and anisotropic components of scattered light. The radii of the inertias of the fluctuation domains and the factors of the orientation order of their scattering elements were determined. A model for the structure of the solutions of the complexes considered is presented. The experimental values of optical anisotropy have been compared with those calculated by the valence-optical scheme. The inversion of the calculated and experimental values of optical anisotropy is explained by the nature of the bonds fixing the ester and diamines in both complexes.

Investigation of the process of polyimide formation from complexes of the diester of benzophenonetetracarboxylic acid with diamines

The kinetics of thermal imidization of the H-complexes derived from the diethyl ester of 3,3′,4,4′-benzophenonetetracarboxylic acid (EBZP) and various diamines have been studied. A comparison of kinetic parameters obtained for the imidization of H-complexes based on ethyl or methyl esters of this acid has disclosed the differences in the behavior of each of the two H-bonds and the contribution of each bond to the mechanism of polyimide formation from the respective H-complexes.

Formation of polyimide from benzophenonetetracarboxylic acid diester complexes with different diamines. 4. Gas-chromatographic study of thermal cyclization of complexes

Thermal cyclization of H complexes is characterized by one rate constant which significantly distinguishes it from thermal cyclization of polyamido acids. The degree of completion of thermal cyclization of the H complex and its rate are determined by diffusion processes related to the structure of the H complex and mobility (softening) of the system during thermal cyclization.

Study of the structure of solutions of the H-complexes of diesters of tetracarboxylic acids with diamines by the light scattering method 1. H-complex of the dimethyl ester of benzophenonetetracarboxylic acid with hexamethylenediamine

Conclusions about structure formation in solutions of the H-complexes of benzo-phenonetetracarboxylic acid with hexamethylenediamine have been drawn from the angular dependence of the intensity of scattered polarized light. The calculated statistical structural parameters show that the H-complexes form dipentameric associations. At high concentrations of the complexes in aqueous-methanolic solution the supermolecular structure is disrupted, while in the pure alcohol the reverse process is observed.