SYNTHESIS OF POLYIMIDES OF POLYCHLORINATED CYCLIC DICARBOXYLIC ACIDS ON THE BASIS OF DIENE–DIENOPHILIC BISIMIDES ON THE DIELS–ALDER REACTION

The conditions for the synthesis of N-aminoimides of polychlorinated cyclic dicarboxylic acids has been studied and the possibility to obtain hinge-ladder polyimides by the Diels–Alder reaction has been demonstrated.

There exist many methods of producing of polyimides (PI) synthesis [1], however they are based mainly on a two-stage procedure [2]. Besides the hinged polyimides obtained by the known methods do not possess 100% imidization due to an incomplete conversion of polyamidoacidic links [1][2][3].
Polymerization by the Diels-Alder reaction is one of the promising and developing directions in the preparation of polyimides of various structures that promotes wide modification of their chemical composition and properties.
The obtained bisimides (III a, b, c) and (IV a,b,c) were brought into the reaction with a mixture of pyridine and acetic anhydride in DMF solution aiming at the preparation of diene-dienophile bisimides, N, N'-maleinalkyl(aryl)substituted imides of 1,2,3,4-tetrachlorocyclohexa-1,3diene-5,6-dicarboxylic acid (V a, b, c) and endo, exo -2,3,4,5-tetrachlorobicyclo[4.4.0]deca-2,4-diene-8,9-dicarboxylic acid (VI a, b, c). The reaction proceeded with heat evolution and temperature increase to 50 0 С. Then the mixture was stirred again for 2 h at 110-120 0 C. In the process of polycondensation by the Diels-Alder the choice of the solvent in solution plays a decisive role [5,6]. We have studied seve-ral aprotic solvents (DMF, DMA and DMSO). The reaction was carried out at 150 0 C and a duration of 6-8 hours. It was found that with increasing in the solvent polarity the viscosity and the yield of polyimide is increased. The greatest yield of polymer is reared when using DMA as solvent. It reaches 90-95 %.
To determine the optimal conditions for the synthesis of polyimides, the influence of the concentration of the initial monomer, the temperature, and the duration of the reaction on the course of polycondensation of diene-dienophilic bisimides (V a, b, c) and (VI a, b, c) has been studied.
In the IR spectra of polyimides VII and VIII there are the characteristic absorption bands the field of 1712, 1780 cm -1 for the C=O, 600-750 cm -1 corresponding for the C-Cl bonds vibrations ( Figure 2). Cl  (Figure 3). Therefore, the molecular mass (MM) of the polyimides was judged by the reduced viscosity η re of the reaction solution.
The investigations of the influence of the monomers concentration on η re showed that η re polyimides based on diene-dienophilic bisimides (V a, b, c) and (VI a, b, c) depends on the bi-and tricyclic fragment and is a curve with a maximum of the corresponding initial mono-mers ( Figure 3). The optimum monomer concentration is 20 mas %. Increasing the concentration above the optimum leads to a decrease in the MM polyimide.
The influence of the reaction temperature on the MM polyimide is shown in Figure 3, where η re increases with increasing temperature: at 130 0 C η re 0.10-0.15 dl/g, at 140 0 C 0.22-0.26 dl/g, at 150 0 C 0.36-0.38 dl/g, respectively, temperature increase to 160 0 C leads to a decrease in η re to 0.30-0.25 dl/g.  Optimal duration of the reaction reacher at 150 0 C for 6-8 hours. Increase the duration leads to a decrease in η re .
Thus, the study of the formation of polyimides VII and VIII on the basis of the dienedienophilic bisimides (V b, c) and (VI b, c) in DMA showed that the greatest value of η re is achieved when the concentration of monomers in 20 mass % at 150 0 C for 6-8 hours (Figures 5,  6). The yield of polyimides under these conditions is 90-95%.
The obtained PI are well soluble in polar solvents (DMF, DMA, N-methylpyrrolidone, DMSO and pyridine). They are heat-resistant up to 300-360 0 C. The loss in mass PI of this temperature is 5-6%.
Hence our research demonstrated the possibility to obtain hinge-ladder polyimides with the desired spatial structure.

Experimental part
IR spectra of synthesized compounds were recorded on a spectrophotometer UR-20 from mulls in mineral oil [7]. UV spectrum were obtained on a spectrophotometer Specord UV-Vis from solutions in methanol, concentration 1.5×10 -4 mol l −1 . As internal reference we used CCl 4 . Molecular mass was determined by the method [7] of melting with camphor.
The reduced viscosity η was measured using Ubbelohde viscometer with extrapolation of the values η re/с (at 25 0 С) of the polymer solution in DMF to the zero concentration [9].