Aromatic polyamides. I. Synthesis and characterization of some aromatic polyamides and their model diamides

The synthesis of some wholly aromatic polyamides based on unsubstituted and chloro- and nitro-substituted diamines by low temperature solution polymerization is described. Poly(1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylene isophthalamide) were selected for further investigation. To study the two polyamides on a systematic basis their model diamides were synthesized. These materials were characterized with respect to chemical structure and purity by elemental analysis, infrared (IR), and nuclear magnetic resonance (NMR) spectroscopic techniques. The usefulness of the model compounds in the interpretation of the polymer spectra is also demonstrated.     

Synthesis and characterization of aromatic polymers containing pendant silyl groups. II. Aromatic polyamides

In order to improve the solubility of aromatic polyamides without significant loss of thermal stability, synthesis of aromatic polyamides containing pendant silyl groups was carried out by direct polycondensation of silylated aromatic diacids such as 2-trimethylsilylterephthalic acid (TSTA), 2,5-bis (trimethylsilyl) terephthalic acid (BTSTA), 5-trimethylsilylisophthalic acid (TSIA), 5-dimethylphenylsilylisophthalic acid (DMSIA), and 5-triphenylsilylisophthalic acid (TPSIA) with various aromatic diamines. The resulting polyamides had inherent viscosities in the range of 0.18–1.10 dL/g and showed improved solubilities toward aprotic polar solvents such as NMP, DMF, DMSO, etc. The prepared aromatic polyamides exhibited fairly good thermal stabilities, which were almost comparable to those of corresponding nonsubstituted aromatic polyamides. That is, thermogravimetric analysis (TGA) data revealed 10% weight losses at 358–500°C and residual weights at 700°C were 46–67% under nitrogen atmosphere. © 1992 John Wiley & Sons, Inc.     

Aromatic polyamides. V. A general synthesis of polyamides from aromatic diacids and aromatic diamines in sulfur trioxide

The reaction of terephthalic acid (TA) and para-phenylenediamine sulfate (PPD-S) in sulfur trioxide to form anisotropic, sulfonated poly(p-phenyleneterephthalamide) (SPT) dopes was reported in Part IV of this series. We have found now that the TA/PPD-S polymerization is only one example of a more general polyamide condensation reaction of aromatic diamines and aromatic diacids. Sulfonation of the aromatic diamine ring during TA/PPD-S polymerization in SO₃ was a major side reaction. Sulfonation was reduced or eliminated by aromatic diamine ring substitution with unreactive substituents, particularly chlorine and fluorine. Polymerization of 2,3,5,6-tetrafluoro-phenylenediamine with TA in SO₃ at 80°C (18% concentration) produced unsulfonated poly(tetrafluoro-para-phenyleneterephthalamide) (F-PPT) with an inherent viscosity of 2.2. The halogenated, all-para aromatic polymers formed highly anisotropic (liquid crystalline) dopes. Monomers that formed polymers in which the chain bond angle deviated from 180° (e.g., meta-oriented monomers) yielded only isotropic polymer solutions. The mechanism and rate of diamine–diacid reactivity in SO₃ was related to diamine basicity. Whereas the less basic aromatic diamines (as sulfates) polymerized with aromatic diacids in SO₃, the more basic aliphatic diamines (as sulfates) would not. Aliphatic, cycloaliphatic, and aryl-aliphatic diacids were degraded by or reacted with the solvent (SO₃). Thermogravimetric analyses of F-PPT and monosulfonated poly(chloro-para-phenyleneterephthalamide) at 20°C/min showed weight loss only above 380 and 370°C, respectively.     

Thermal degradation of polymers with phenylene units in the chain. IV. Aromatic polyamides and polyimides

The breakdown mechanism of an aromatic polyamide and four polyimides has been studied under vacuum in the temperature range of 375–620°C, by using techniques described earlier, involving collection and analysis of volatile products as well as analyses of residues at different temperatures. The decomposition of the polyamide up to 375°C yielded predominantly carbon dioxide, while between 375 and 450°C about equal amounts of carbon dioxide and carbon monoxide formed. Hydrogen is the major product between 450 and 550°C, along with hydrogen cyanide, methane, and carbon monoxide. The major reaction at the lower temperatures seems to be the cleavage of the linkage between the carbonyl group and the ring, with subsequent formation of a carbodiimide linkage via isocyanate intermediates, and liberation of carbon dioxide. Alternatively, cleavage between the carboxyl and the NH-group leads to the formation of carbon monoxide. Carbon dioxide and carbon monoxide are also the major volatile decomposition products of the polyimides at the lower temperatures. The primary cleavage reaction is believed to be the rupture of the imide ring between a carbonyl and nitrogen, with subsequent formation of isocyanate groups. The latter react with each other to form carbodiimide linkages and carbon dioxide, while the remaining benzoyl radical is the source for carbon monoxide.     

Thermal properties of wholly aromatic polyamides

Various wholly aromatic polyamides based on m-and p-phenylene diamines and isophthaloyl and terephthaloyl chloride have been synthesized and their thermal properties and oxygen index values have been studied. The effect of different substituents on the aromatic ring of the diamine have been explored by comparing their differential thermal analysis (DTA) and thermogravimetric analysis (TGA) behavior, their relative char yields at 700°C, and their oxygen indices. The ? Cl, ? NO₂, and ? OH substituted polyamides have been found to produce the highest char yields. The high char yields are probably associated with crosslinking occurring at high temperatures. Attempts at correlating char yield with oxygen index indicated enhancement for the chlorosubstituted aramids.     

Aromatic polyamides. III. Mechanistic studies on the role of substituent chlorine in flame retarding aromatic polyamides

The flammability of poly(1,3-phenylene isophthalamide) and poly(chloro-2,4-phenylene isophthalamide) was measured by the oxygen index method. The chloro polyamide had reduced flammability shown by a 10–15 higher oxygen index. Analysis of the chars of the two polymers at 700°C by thermogravimetry (TGA) and elemental analysis showed that the chlorine caused a significant increase in the retention of C, H, N, and O in the pyrolysis residue. Most of the chlorine in the chloro polyamide, however, was lost by 700°C. Based on these results, we have suggested that the chlorine imparts flame retardancy by a combination of vapor- and condensed-phase mechanisms. The origin of condensed-phase activity is discussed.     

Heat-resistant polymers with thianthrene analog units. II . Aromatic polyamides

A series of polyamides which contained thianthrene, phenoxatiin, and dibenzo-p-dioxin units was synthesized from tricyclic fused-ring diamines and aromatic diacid chlorides by solution polycondensations at a low temperature. The amorphous polyisophthalamides were highly soluble in polar organic solvents, whereas some of the polyterephthalamides with a fair degree of crystallinity were insoluble. The solubility of the series of polyamides increased in the order of the dibenzo-p-dioxin-containing polymers < phenoxatiin-containing polymers < thianthrene-containing polymers. The thermal stability increased in the reverse order and the dibenzo-p-dioxinpolyamides were more thermostable than the corresponding open-chain polymers with diphenyl ether linkages. The polyamides derived from 2,8-oriented tricyclic diamines showed somewhat lower glass transition temperatures than those from 2,7-oriented diamines.     

Conformational properties of structurally rigid polyamides. I. Conformation of polyamides and model diamides derived from optically active cyclic 1,2-dicarboxylic acids

The conformational equilibria of piperidine diamides derived from five cyclic 1,2-dicarboxylic acids (I–V) have been investigated by dipole moment measurements and a priori conformational energy estimates. Since these diamides represent the building blocks of the polyamides derived from the above cyclic diacids and piperazine or trans-2,5-dimethylpiperazine, the results obtained in the study of the models have been used to investigate the conformation of the polymers. The overall evidence suggests that cyclopentane, cyclohexane, and bicyclooctane piperazine polymers behave as rigid rods in which the structural units possess approximately the same conformational preference exhibited by the respective model diamides.     

Synthesis and characterization of some novel organometallic aromatic polyamides

Some novel ferrocene containing aromatic polyamides were prepared by low‐temperature solution phase polycondensation of 1,1′‐ferrocenedicarboxylic acid chloride with some newly synthesized aromatic diamines in tetrahydrofuran, in the presence of triethylamine. The amorphous polymers were derived in good yields, and did not melt at >350 °C. The monomers and the resulting polymers were characterized by their physical properties, elemental analysis, ¹H‐NMR, FTIR spectroscopy, differential scanning calorimetry and thermogravimetric analyses. The polymeric products were insoluble in common solvents tested. However, all were miscible in concentrated H₂SO₄, forming reddish brown solutions at ambient conditions. The glass transition temperatures (T_g) of these polymers were quite high, which is characteristic of aramids. They are stable up to 500 °C, with 10% mass loss observed in the range 400–650 °C. The activation energies of pyrolysis for each of the products were calculated by Horowitz and Metzger's method. Solution viscosities of the polymers were reduced in concentrated sulfuric acid, which is due to their non‐Newtonian behavior. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis and characterization of some aromatic polyamides containing double bonds

Ten polyfumaramides based on fumaric acid and aromatic diamines and six polystilbenediamides based on 4,4′-stilbenedicarboxylic acid and aromatic diamines were synthesized and characterized by solubility, viscosity, density, infrared and UV-visible spectroscopy, and thermal analyses. Variation in properties with structure is discussed here.     

Aromatic polyamides. VI. Synthesis of aromatic copolyamides and copolyamide–oxadiazoles in sulfur trioxide

Copolymerization of para-phenylenediamine sulfate (PPD-S), hydrazine sulfate (Hy-S), and terephthalic acid (TA) in SO₃ yielded solutions of poly[p-(disulfonatophenylene)terephthalamide]–co-poly(p-phenylene-1,3,4-oxadiazole) (SPT-co-POx). Reaction of PPD-S, TA, and 4,4′-sulfonyldibenzoic acid (SDBA) in SO₃ gave sulfonated copolyamide (SPT-co-SPSDB) solutions. Solutions of both SPT-co-POx (mole % ratios of 70:30 to 90:10) and SPT-co-SPSDB (75:25 to 90:10) were anisotropic, illustrating liquid crystalline behavior for polymeric structures containing significant amounts of noncoaxial backbone components.     

Aromatic polyamides. XII. Effect of the polymeric unit linkage position on the thermal decomposition and flammability of the unsubstituted and halogen-substituted aromatic polyamides

The synthesis, thermal characterization, and oxygen index of aromatic polyamides varying with polymeric unit linkage positions (meta and/or para units) and halogen substitution have been reported. It has been found that polyamides containing para units are more thermal stable than those containing meta units. There is no significant effect of the main chain structure studied here on either the pyrolysis pathways or flammability of similarly halogen substituted polyamides.     

Some thermodynamic aspects of the thermal degradation of wholly aromatic polyamides

The mechanism of thermal degradation of wholly aromatic polyamides has been investigated in the light of several thermodynamic parameters, such as resonance stabilization of the free radicals formed, bond enthalpy changes and entropy changes. It has been shown that the scission of the NH bond in the beginning is both thermodynamically and kinetically favoured over the scission of the aromatic ring-carbonyl carbon bond. CN bond and the aromatic ringNH bond in the polymer chain backbone. Formation of the major products and some minor products has been explained with the help of the proposed mechanism.     

Dynamic-mechanical properties and melting points of some aliphatic and partially aromatic polyamides

Some aliphatic and partially aromatic polyamides have been prepared from hexamethylene diamine and the following dicarboxylic acids: deca-, octa-, hexa-methylenedicarboxylic, p-carboxymethylphenoxyacetic, p-carboxyethylphenoxyacetic, p-phenylenedipropionic, p-phenylenediacetic, p-carboxymethoxyphenoxyacetic, β(p-carboxymethyl)phenylpropionic.The dynamic-mechanical properties at 110 Hz have been measured between ?140° and about 200. Three relaxation processes α β and γ have been found: only the main transition α appreciably depends on chemical structure.The influences of the length of repeating unit and of in-chain substitution on melting points, crystallinity and the dynamic-mechanical α transition have been investigated. The results have been discussed in terms of chain flexibility, chain packing and intermolecular forces.     

Thermal properties and solubility of ordered aromatic polyamides containing a methyl-substituted phenylene linkage

Ordered aromatic polyamides and copolyamides were prepared by the polycondensation of terephthaloyl and isophthaloyl dichlorides with symmetrical diamines containing preformed amide linkages derived from unsymmetrical methyl—substituted aromatic diamines at low temperature. Thermal properties and solubilities of the ordered polyamides were compared with those of the corresponding random polyamides. There was little difference between thermal stabilities of the ordered polyamide and the corresponding random one, while the former was less soluble in organic solvents than the latter, depending on the extent of hydrogen bonding of the amide groups. The thermal stability of the alternating copolyamides containing both terephthaloyl and isophthaloyl groups as acid components was less than that of the corresponding homopolymers having either a terephthaloyl or an isophthaloyl group, and the solubility of the former resembled that of the corresponding ordered homopolysiophthalamides in accord with the extent of hydrogen bonding of the amide groups in both polymers.     

Dendritic aromatic polyamides and polyimides

The syntheses and properties of dendritic and hyperbranched aromatic polyamides and polyimides are reviewed. In addition to conventional stepwise reactions for dendrimer synthesis, an orthogonal/double‐stage convergent approach and dendrimer syntheses with unprotected building blocks are described as new synthetic strategies for dendritic polyamides. Hyperbranched polyamides and polyimides composed of various repeating units are presented. Besides the self‐polycondensation of AB₂‐type monomers, new polymerization systems with AB₄, AB₈, A₂ + B₃, and A₂ + BB′₂ monomers have been developed for hyperbranched polyamides and polyimides. The copolymerization of AB₂ and AB monomers is discussed separately with respect to the effects of branching units on the properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1293–1309, 2004     

Mass spectrometric investigation of polymers: Thermal degradation of truxillic and truxinic polyamides

The thermal degradation mechanism of four isomeric truxillic and truxinic polyamides were investigated by direct pyrolysis in the ion source of a mass spectrometer. Thermal degradation reactions were followed directly by this method by detecting the thermal and electron impact-induced fragments. The results obtained have shown that the thermal degradation products are sensibly different for the head-to-head (hh) and head-to-tail (ht) polymers and that the predominant pyrolytic process is the cyclobutane ring cleavage. In the hh isomers, both symmetrical and asymmetrical cyclobutane ring cleavage was detected, while in the ht isomers only symmetrical cleavage occurs; this explains the noticeable difference found in the thermal stability of the two polymer types.