A.V. Sidorovich

Structure of rigid chain polyimides based on the dianhydride of pyromellitic acid

X-ray structure analysis and the calculation of intermolecular interaction energies with an atom-atom approximation have been used as methods to study the crystal structure of three polyimides based on the dianhydride of pyromellitic acid and differing with respect to the number of phenylene rings in the monomeric link. The mutual packing of the molecules in the ordered regions is put forward, corresponding to the minimum lattice free energy and to the principle of dense packing of the pyromellitimide fragments. The principal intermolecular forces determining this packing are the forces of van der Waals interaction in the densely packed layers of pyromellitimide fragments.

Structural properties of a polyesterimide film prepared from p-phenylene-bis-trimellitate dianhydride and 4,4′-diaminodiphenylsulphide☆

Abstract IR spectroscopic, X-ray, thermo-mechanical and dielectric studies were made of the structure and relaxation behaviour of polyesterimide prepared from p -phenylene-bis-trimellitate and 4,4′-diaminodiphenylsulphide(PEIS-P). It was shown that during heat treatment of chemically and thermally imidized PEIS-P films an ordered structure is formed with axially plane orientation of crystallites. During elongation and heat treatment of PEIS-P films a highly oriented crystalline structure is formed. Elementary cell parameters of PEIS-P were determined and a macromolecular conformation structure proposed.

Special features of the thermomechanical behaviour of polyaminodoimides as related to molecular structure

Abstract Three regions of the state of matter with temperatures of transition at 110 and 280–290° were detected in polyamidoimide (PAI) films. Heating PAI samples to 350° increases rigidity (flexibility decreases by 1·5 order of magnitude) and results only in one region of transition at 280–290°. From spectroscopic variations in the region of 3320 and 1670 cm −1 it was established that transition at 280–290° is due to the variation of the type of hydrogen bonds and structural ordering of amide groups. Using X-ray and IR spectroscopic investigations of the crystallization of oriented PAI films a conformation structure of macromolecules was proposed.

Structure of comb-like polyfluoroalkyl acrylates and methacrylates☆

Abstract It is shown by X-ray analysis and calorimetry that polyfluoroalkyl acrylates and methacrylates have a mesomorphic structure. The degree of ordering is directly related to the number of CF 2 groups in the side chains of the polymer. The formation of a liquid crystal state in one of the polymers studied is proved by an optical method.

The mesomorphous state of polyamic acids

Calorimetric, optical and X-ray studies have been used to establish the existence of a meso-phase in polyamic acid (PAA) films; it forms in concentrated solutions and consists of the aggregates of straightened parts of macrochains with an azimuthal dis-arrangement of the fragments relative to the macromolecular axis. The existence of such structural parts produces an orientation increase in the direction of the polymer chains and explains the features of the observed diffraction picture, the optical properties of the films, and the fact that there are no energetical effects present during the polyimides crystallization.

The phase state and structure of polyamidoimides and polyester-amidoimides☆

Imidization, crystallization and the thermal transitions in unorientated films of polyamidoimides and polyester-amidoimides, have been studied by the thermomechanical, IR-spectroscopic and K-radiographic methods. It was found that the chemical structure of the diamine and dianhydride fragments exert a substantial effect on the thermomechanical properties of the polymers and on the structural changes that they undergo in the course of heat treatment at 400°C. A benzene ring in the para-position in the diamine component of the chain promotes formation of a partially ordered, mesomorphic structure in untreated samples, and of the maximal number of intermolecular hydrogen bonds during heat treatment. All the crystallizable polyamidoimides and polyester-amidoimides exhibit X-ray texture, with pre-dominant arrangement of the axes of the macromolecules in the plane of the film. A spontaneous elongation effect was found in the case of the polyester-amidoimides, which have ester groupings in the dianhydride fragment.

Study of the phase aggregate state and of the structure of some polyimides

Abstract IR spectroscopy, dilatometry and X-ray structural analysis have been used to study the orientation and crystallization processes of two polyimides (PI) produced from p -phenylene-bis-trimellitic acid anhydride and aromatic diamines, namely 4,4-diaminotetra- p -oxyphenylene (PI-IV) and 4,4-diaminopenta- p -oxyphenylene (PI-V) [1]. The spontaneous orientation found on heating the respective films has been found not to be associated with the presence of a solvent in the samples, but with changes in macromolecular conformation. The formation of an axial texture during the crystallization of the non-orientated PI films results in an intensity drop of the imide absorption lines; this must be taken into account when making a qualitative evaluation of the imidization efficiency.

The Structure of oriented films of polyamidoimides and polyester amidoimides

Methods of X-ray analysis, IR spectroscopy and thermomechanical analysis have been used to investigate the structure of oriented polyamidoimides (PAI) and polyester amidoimides (PEAI) differing as to the structure of the diamine fragments. It is shown that heat treatment of polyamidoacid films with 150–250% elongation is accompanied by a marked change in the dichroism of absorption bands in the temperature interval 270–300° for polymers having phenylene in the meta-position. In this case it appears from the X-ray data that a highly oriented crystalline or mesomorphic structure is formed. Crystallographic parameters were determined for the ordered structures and conformational structures for the PAI and PEAI are proposed. For PAI containing the p-phenylene unit in the diamine the energetically most favourable packing of chains in the crystal lattice was calculated on the basis of atom-atom potentials.

Effect of molecular orientation and crystallization on mechanical properties of oriented polypyromellitimides

Abstract By the action of a temperature field of force a highly oriented crystalline structure could be obtained for four polymers prepared from pyromellitic acid dianhydride and unable to crystallize during imidization by heat. Results are given of a study of the structure and mechanical properties of fibres of this group of polymers. It was shown that, in contrast to pyromellitimide (PM), diamine fragments and not dianhydride fragments are responsible for intermolecular packing of chains. It was assumed that increasing the cross section of the diamine fragment of the recurrent unit, compared with the dianhydride one, weakens intermolecular contacts in the dianhydride layer and is the main cause of noticeably poorer mechanical properties of polymers, compared with similar properties of PM.

The structure of oriented crystalline polyester imides

Abstract X-ray structural analysis and infrared spectroscopy were the basis of investigation of the crystalline structure of two oriented polyester imides (PEI-II and PEI-III) prepared by chemical and thermal imidization of poly(acid)amido esters (PAAE) based on paraphenylene-bis-trimellitatedianhydride and aromatic diamines, namely the 4,4′-diaminodiphenyl and bis-4-aminophenyl esters of hydroquinone. It is shown that, as a result of stretching (150–250% extensions) and further heat treatment (370–390°), highly oriented crystalline structures appear in the samples. the space cell of PEI-II is monoclinic ( a = 5·56; b=7·94; c=58 A ; γ=86° ). The parameters of the rhombic cell proposed for PEI-III are: a=5·64; b=8·05; c=34·5 A . The dichroism of the absorption bands in the IR polarized spectra of PEI-II and PEI-III provided a basis for calculating the direction of the transition moments of a number of vibrations relative to the molecular axis. The conformational structure of the macromolecules is proposed for the polyester imides in the light of experimental results.