High Performance Polymers

Quantum-chemical calculations and calculations by the Monte Carlo method were used for conformational analysis of heterocyclic polymers. The steric effect of various substituents on the equilibrium geometry and conformational dynamics of 1, 4, 5, 8-naphthalenetetracarboxydiimide was studied using the AM1 semiempirical quantum-chemical method. It was shown that addition of bulky groups to the naphthalene moiety of 1, 4, 5, 8-naphthalenetetracarboxydiimide increases conformational rigidity of the imide rings. Using the example of rigid-chain polymers containing the naphthoileneimide ring, it was demonstrated that the introduction of four bulky substituents into the structure of 1, 4, 5, 8-naphthalenetetracarboxydiimide results in a considerable increase in the equilibrium rigidity of the polymer.

Semiaromatic polyimides with a polyalicyclic structure were prepared by the polycondensation of bis(aminomethyl)bicyclo[2.2.1]heptane (BBH) with aromatic dianhydrides. The corresponding poly(amic acid)s possessed an inherent viscosity range of 0.60–1.00 dl g⁻¹. The polyimides were soluble in organic polar solvents and most of them formed flexible, free-standing films. The polyimides had good thermal stability with no significant weight loss up to approximately 400 °C and possessed a 5% weight loss temperature range of 428–465 °C. These polyimide films showed a tensile modulus range of 1.4–3.0 GPa, a tensile strength range of 62–115 MPa, and an elongation at break range of 5.4–6.1%. The semiaromatic polyimide films exhibit a cut-off wavelength around 322–362 nm and are entirely colourless, while the cut-off wavelengths of PI(PMDA-DDE) and PI(BPDA-DDE) films were 426 and 376 nm respectively. The origin of coloration in the aromatic polyimides and the lack of colour in the semiaromatic polyimides were elucidated from the standpoint of molecular orbital (MO) calculations of the model compounds using semiempirical AM1 and INDO/S methods. The calculated λ_max of the M(PMDA-BBH) was 371 nm, and the first excited state is mainly characterized by an n−π* transition. Based on both the MOs and the difference in electron density between the ground and the first excited states, the first excited state is attributable to light-induced polarization in the five-membered imide ring. The λ_max of the M(PMDA-DDE) model for a representative aromatic polyimide was calculated to be 392 nm. From the charge difference map, it is theoretically evident that the coloration in the aromatic polyimides caused intramolecular charge transfer between the diamine and dianhydride moieties.

Radical chain (co)polymerization of a set of acrylates containing dissolved high performance polymers, namely fluoropolyimide, is performed. Based on the study of the structure and properties of the polymers (elemental composition, solubility, molecular weight parameters, etc) it is proposed that the copolymer formation reaction takes place due to a transfer chain reaction on the polyimide. The influence of acrylate (ethyl-, n-butyl-, methyl-α- fluoro-, ethyl-α-fluoro-, methyl-glycidyl-, butyl-, hexafluoro-iso-propylmethacrylate) and polyimide content on the properties of the copolymers obtained is studied. Clear and opaque, hard and elastic materials are obtained. These polymers differ in their characteristics from the relevant polyacrylates and their blends with polyimide prepared by the usual method of mixing. One-step catalytic polycondensation of diamines and tetracarboxylic acid dianhydrides in a solution of preformed polyimide is studied. It is shown that such a procedure influences the structure and properties of polyimides formed in situ.

A series of aliphatic 1, 4-diaminobutane based polyamides 4.y with y = 8, 9, 10 and 12 was synthesized and characterized. For comparison, some 1, 6-diaminohexane based counterparts were also studied. PA 4.12, and in particular PA 4.10, proved to have a very beneficial combination of T_m , crystallization rate and physical properties. First indications were obtained, that for a series of aliphatic polyamide isomers, containing 16 carbon atoms in the repeating unit, the melting points are related to the number of ways to make an energetically favourable chain fold upon crystallization: isomers having two possible ways of chain folding have T_m s which are 13–15 °C lower than isomers having only one possible way of chain folding upon crystallization.

The interaction of the demethylation product of 1, 3, 5-trinitrobenzene—2, 4, 6-trinitrotoluene—with fluorinated alcohols followed by reduction of the perfluoroalkoxy-substituted m-dinitrobenzenes thus formed led to the formation of new fluorinated diamines. The reaction of these diamines with aromatic tetracarboxylic acid dianhydrides led to the formation of new fluorinated polyimides combining solubility in organic solvents with large ‘windows’ between glass transition and degradation temperatures.

Low-temperature catalytic conversion of N-(o-aminophenyl)phthalamic acid (I) was studied as a model reaction for the synthesis of ladder poly(aroylenebenzimidazole)s. The treatment of I with acetic anhydride/pyridine or trifluoroacetic anhydride resulted in the selective and quantitative cyclodehydration to yield either imide or isoimide structures respectively. The imidization was accompanied by acylation of the ortho amino group to form lateral acetamide or trifluoroacetamide substitutes. Thermodynamically unstable N-(o-trifluoroacetamidophenyl)phthalisoimide (III) underwent secondary cyclization to yield ladder 1, 2-benzoylenebenzimidazole (V) between 130 and 150 °C. The conversion of this reaction did not exceed 35% because it competed with the thermal isomerization of III to the stable N-(o-trifluoroacetamido-phenyl)phthalimide (IV). The cyclization of N-(o-trifluoroacetamidophenyl)phthalisoimide (III) was found to be possible even at room temperature. The formation of 30–35% of the ladder 1, 2-benzoylene-benzimidazole (V) was observed after III was dissolved in DMF and stored at room temperature for 4–10 h. This also was accompanied by the catalytic isoimide-to-imide isomerization. The obtained data may be useful for the further development of novel low-temperature approaches to the synthesis of ladder poly(aroylenebenzimidazole)s. Synthesis of aromatic polyimides and polyisoimides with lateral alkylamide or trifluoroalkylamide from available aromatic dianhydrides and tetraamines may also be of practical interest.

This paper discusses the evolution observed in the field of high performance polymers and tries to forecast the future in different domains. The paper is divided into four sections: 1. From the 1960s to the 21st century. 2. What’s new in chemistry and why? 3. What could be the future for high performance polymers in structural applications, electrical industries, electronic and electro-optical industries, membrane technologies, fuel cell membranes and other fields such as conductive polymers. 4. Concluding remarks.

A novel series of poly(arylidene-ether)s containing cyclopentanone was synthesized by polycondensation of 4, 4′-diformyl-α, ω-diphenoxyalkane and 4, 4′-diformyl-2, 2′-dimethoxy-α, ω-diphenoxyalkane with cyclopentanone. The polymers were characterized by elemental and spectral analyses, inherent viscosity, solubility and thermal analyses. Their thermotropic liquid crystalline properties were examined by DSC, optical polarizing microscopy using a heated stage and thermogravimetric analyses. Almost all the polymers exhibited thermotropic liquid crystalline properties. In most cases the mesophase extends up to 358°C, where thermal decomposition prevents further observations. In addition, the crystallinity of some polymers was examined by x-ray analysis; all showed some degree of crystallinity. The morphology of one polymer was examined by scanning electron microscopy (SEM).

The thermal and gamma-irradiation induced curing of two phenylethynyl terminated composite resin systems, DFB/BPF and PETI5A, was investigated. Thermal curing of these matrix resin samples was performed at a temperature of 360 °C, gamma irradiation of the samples was conducted at 300 °C at a dose rate of 2.2 kGy h⁻¹. The reaction and subsequent loss of ethynyl groups in the resins for both cure methods was demonstrated by observing the decrease of the 2215 cm⁻¹ peak in the Raman spectra of the resins. Fully cured resin samples were found to have glass transition temperatures of 244–246 °C and 278–280 °C for DFB/BPF and PETI5A respectively. Similar relationships between T_g and fractional conversion were observed in both resins. The apparent polymerization rate, R_p , for thermal cure at 360 °C, was found to be 4:79 × 10⁻²2%s⁻¹ in PETI5A and 3.22 × 10⁻²%s⁻¹ in DFB/BPF. Catastrophic degradation under nitrogen was observed to commence near 450 °C and 530 °C, with 5% weight losses occurring at 455 °C and 540 °C for DFB/BPF and PETI5A respectively. Gamma radiation induced cure at 300 °C was shown to be feasible, with full cure being reached with doses of 40 kGy for DFB/BPF and 100 kGy for PETI5A.

The bisester 1, 1′-(1-methylethylidene)bis[4-{1-imino-4-ethylbenzoate-2-propanolyloxy}]benzene (DGEBA-4-AEB), synthesized by the reaction of the epoxy resin diglycidyl ether of bisphenol-A (DGEBA) with 4-amino ethyl benzoate (4-AEB), was condensed with different aromatic diamines, namely 4, 4′-diamino diphenyl methane (DDM), 4, 4′-diamino diphenyl sulfone (DDS) and benzidine (Ben) to yield novel epoxy based curing agents. The resultant novel epoxy based polyamides (PAs) were characterized by infrared spectroscopy along with the estimation of number average molecular weight (M_n ) by gel permeation chromatography (GPC). Using differential scanning calorimetry (DSC), the kinetics of the curing reactions of PAs–epoxy resin systems were established by evaluating the usual kinetic parameters. The thermal behaviour of PAs–epoxy cured products was also studied by thermogravimetric analysis (TGA).

New parabanate products containing 1, 3, 5, 7-tetraazabicyclo[3, 3, 0]octane-2, 6-dione are described. The synthesis of αω-diisocyanato-telechelics starting from two diisocyanates having a preformed parabanic unit using a [3+2] dipolar cycloaddition reaction was studied. The obtained products were characterized by IR spectroscopy, elemental and thermogravimetric analyses and solubility tests. The proposed structure was confirmed by analytical data.