Peculiarities of supermolecular structure of polyimides and polyester imides

Abstract

SYNOPSISSupermolecular structures of fourteen heterocyclic thermally stable polymers of the polyimide (PI) and polyesterimide (PEI) class have been investigated by X-ray scattering, optical, dilatometric and thermomechanical methods. Quasi-crystalline structure of these polymers in the initial amorphous state of poly(amic acid) and poly(ester amic acid) and also after chemical imidization has been revealed. The quasi-crystalline structure is characterized by a biaxial polarizability ellipsoid with a negative sign. This is indicated by distinct conoscopic figures recorded with a polarizing microscope. The effect of the number of oxyphenylene groups on the crystallizability of PI and PEI was investigated. For PEI the effect of self-orientation of macromolecules induced by conformational transition was observed. Discrete small-angle x-ray scattering pattern (a long period) was also revealed for PEL The appearance of long periods is caused by polymorphism of PEI uniquely determined for one of its types (PEI-11). X-ray scattering data confirmed by calculations of the lattice energy show that dianhydride pyromellitimide chain portion is the element determining the crystalline structure of PI. The structure is determined by van der Waals' forces and obeys the principle of dense packing. This leads to the appearance of layer structure with alternating layers of diamine and dianhydride portions. It was found that, depending on the rigidity of the diamine portion, PI and PEI exhibit different abilities of forming axial-planar or axial textures in nonoriented films.Preparation of polymers in an oriented state is of great practical and scientific interest. Self-oriented systems receive increasing attention in this respect [ 11. Flory [2] has shown that when the rigidity of the polymer chain changes, the requirement of the minimum free energy on attaining a critical concentration leads to the appearance of the nematic phase, i.e., of self-ordering. Effects of self-ordering appear in conformational transition for polypeptides [3] and in spontaneous elongation for cellulose diacetate [4]; they are responsible for specific properties of solutions of aromatic polyamides [5]. Self-ordering of the polymer chain can appear only if it contains both flexible and rigid portions [ 11. From this standpoint, heterochain polymers of the polyimide (PI) and polyester imide (PEI) classes are of great interest.PIS investigated by us (Table I) were prepared from pyromellitic dianhydride and different diamines representing both rigid portions: para-phenylene, benzidine, meta-phenylene (group I, 1-4) and more flexible oxyphenylene units (group II,5-9). In PEI (group 111, 10-14) the dianhydride component is more complex owing to the introduction of an oxyphenylene ring with a planar rigid

Pressure-Induced Changes in Crystalline Structures of Polyimides Analyzed by Wide-Angle X-ray Diffraction at High Pressures

“…As stated in the Introduction, the insight into the PVT behaviors of crystalline PIs is valuable to predict the responses to pressures and temperatures of PIs and to investigate the limiting values of compressibility and thermal expansion coefficients of PIs. Because all the PIs prepared in this study were reported to form crystalline structures based on the orthorhombic unit cell, 6 the volumetric variations at elevated pressures in the ordered region were calculated as a summation of the variations in the lattice parameters along the a-, b-, and c-axes. Figure 9 shows the volumetric variations in the ordered region of the PMDA/ PPD, PMDA/DATP, and PMDA/ODA powders.…”

Near Surface Structure of Solvent-free Processed Polyimide Thin Film

“…The crystal structure of PMDA-ODA has been reported in the literature by several groups. [8][9][10][11][12] All studies indicate that the chain forms a planar zigzag (2/1 helix) conformation and that the c-axis is perpendicular to the a-b plane (Figure 1). However there are significant variations in the dimensions of a and b and in the number of chains per unit cell (1 or 2 chains/cell), and the angle between the aand b-axes is determined to be either 90°or 100°.…”

“…However there are significant variations in the dimensions of a and b and in the number of chains per unit cell (1 or 2 chains/cell), and the angle between the aand b-axes is determined to be either 90°or 100°. 11 Since the periodicity of the PMDA-ODA chain is dependent on the curing process, as apparent in the literature, [8][9][10][11][12] it is also reasonable to expect variations in the lateral dimensions. Furthermore, the limited number and large breadth of overlapping reflections (at least in the bulk samples) can partially explain the discrepancies in the unit cell structure determination.…”

Tailoring the surface morphology of polyimide for improved adhesion

“…The indexing of the WAXS pattern reported for PMDA-ODA indicates either an orthorhombic [15,16] or monoclinic [17] structure with one chain per unit cell. However, a crystal structure calculation which allows for perturbations in the chain conformation and interchain differences indicates that two chains per lattice cell is more suitable [18], and our indexing is based on the latter structure.…”