Preparation of aromatic copolyamides containing regularly placed 1,6-hexamethylenediamine units

Copolyamides based on poly(m-phenylene isophthalamide) and poly-(p-phenylene terephthalamide), to which 1,6-diaminohexane units were regularly inserted every 3 or 5 phenylene monomer units, were synthesized. The copolymers were obtained by condensation of individually prepared diamino- and dicarboxylic-building blocks via the Yamazaki–;Higashi reaction. Solubility of the copolyamides are discussed in relation with the structure. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2379–2386, 1997     

Thermal flexibility of aromatic polymide chains in solution from viscometric analysis

Intrinsic viscosities of poly(p-phenylene terephthalamide) (PPTA) and poly(m-phenylene isophthalamide) (PMIA) samples of the same molecular weight are determined in 90%, 96% and 100% sulfuric acid at temperatures from 0 to 130°C. Conditions are established under which the degree of coiling of PPTA molecule is close to that for PMIA. Experimental data are compared with the results of theoretical calculations of the Kuhn segment length. In the light of this comparison, some quantitative characteristics of the deformational flexibility mechanism for aromatic polyamide chains and the hindrance to intramolecular rotation are discussed. © 1993 John Wiley & Sons, Inc.     

Preparation and physical properties of poly(4,4′‐diamino‐3′‐carbamoylbenzanilide terephthalamide) and poly(4,4′‐diamino‐3′‐carbamoylbenzanilide isophthalamide) films

To prepare thermally stable and high‐performance polymeric films, new solvent‐soluble aromatic polyamides with a carbamoyl pendant group, namely poly(4,4′‐diamino‐3′‐carbamoylbenzanilide terephthalamide) (p‐PDCBTA) and poly(4,4′‐diamino‐3′‐carbamoylbenzanilide isophthalamide) (m‐PDCBTA), were synthesized. The polymers were cyclized at around 200 to 350 °C to form quinazolone and benzoxazinone units along the polymer backbone. The decomposition onset temperatures of the cyclized m‐ and p‐PDCBTAs were 457 and 524 °C, respectively, lower than that of poly(p‐phenylene terephthalamide) (566 °C). For the p‐PDCBTA film drawn by 40% and heat‐treated, the tensile strength and Young's modulus were 421 MPa and 16.4 GPa, respectively. The film cyclized at 350 °C showed a storage modulus (E′) of 1 × 10¹¹ dyne/cm² (10 GPa) over the temperature range of room temperature to 400 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 775–780, 2000     

Thermal degradation of aramids: Part I—Pyrolysis/gas chromatography/mass spectrometry of poly(1,3-phenylene isophthalamide) and poly(1,4-phenylene terephthalamide)

The thermal degradation reactions of poly(1,3-phenylene isophthalamide) or Nomex (I) and poly(1,4-phenylene terephthalamide) or Kevlar (II) aramids have been investigated in the temperature range 300–700°C by pyrolysis/gas chromatography/mass spectrometry. The initial degradation products below 400°C of (I) are carbon dioxide and water. At 400°C benzoic acid and 1,3-phenylenediamine are detected. Benzonitrile, aniline, benzanilide, N-(3-aminophenyl)benzamide as well as carbon monoxide and benzene are evolved in the range 430–450°C. The yields of these products increase rapidly in the range 450–550°C. Isophthalonitrile is observed at 475°C and hydrogen cyanide is detected above 550°C, as are other secondary products such as toluene, tolunitrile, biphenyl, 3-cyanobiphenyl and 3-aminobiphenyl. Pyrolysis of (II) below 500°C evolves only water and trace amounts of carbon dioxide. At 520–540°C the following degradation products have been detected: 1,4-phenylenediamine, benzonitrile, aniline, benzanilide and N-(4-aminophenyl)benzamide. These products as well as carbon dioxide and water increase appreciably between 550°C and 580°C; benzoic acid, terephthalonitrile, benzene and 4-cyanoaniline are also detected in this temperature range. Above 590°C, hydrogen, carbon monoxide, hydrogen cyanide, toluene, tolunitrile, biphenyl, 4-aminobiphenyl and 4-cyanobiphenyl are evolved. Degradation reactions consistent with the formation of these products, which involve initial heterolytic cleavage of the amide linkage for (I) and initial homolytic cleavage of the aromatic NH and amide bonds for (II), are described.     

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.     

Broad-line NMR and dynamic mechanical behavior of some aromatic polyesters

The dynamic mechanical properties of four aromatic polyesters were measured at temperatures in the 78–540°K region at 10³–10⁴ cps. The polymers studied were: poly(1,3 phenylene isophthalate), poly(1,4 phenylene terephthalate), poly(4,4′ diphenylene isophthalate), and poly(4,4′ diphenylene terephthalate). All four polymers had β loss peaks at about 280°K. Distinct β^* mechanical processes were found for the two terephthalate esters. Broad-line nuclear magnetic resonance measurements were carried out in the 150–440°K temperature range on the four polyesters mentioned above in addition to poly(4,4′ diphenylene 4,4′ biphenyl dicarboxylate). A change in NMR second moment takes place in the 190–330°K region, the magnitude of which is dependent on the polymer structure. The results are compared with those found for a series of aromatic polyamides and are discussed in terms of possible motional processes.     

Influence of aryl substituents on the thermal and solubility behavior of poly(p-phenylene terephthalate) and poly(p-phenylene terephthalamide)

The substitution of poly(p-phenylene terephthalate) and poly(p-phenylene terephthalamide) with phenyl and biphenylyl substituents (4-biphenylyl and 2-biphenylyl) in the terephthalic acid unit lowers the melting temperatures and crystallization tendency and increases the solubility. The melting temperatures of the polyesters are in the range of 285–350°C. Melting of the polyamides occurs between 440–490°C. The polyamides begin to decompose in the same temperature range. In polyesters as well as in polyamides the 2-biphenylyl substituent was found to be more effective in decreasing the crystallinity, lowering the melt transition temperatures and increasing the solubility.     

Crystal structure of poly(m-phenylene isophthalamide)

The crystal structure of poly(m-phenyulene isophthalamide) was determined by x-ray analysis. The triclinic cell, with a = 5.27 Å, b = 5.25 Å, c (fiber axis) = 11.3 Å, α = 111.5°, β = 111.4° and γ = 88.0° and space group P1, contains one monomeric unit. The crystal density is 1.47 g/cc. The molecules in the crystal are contracted by 1 Å per monomeric unit from the fully extended conformation, and the planes of the benzene rings and adjacent amide groups make angles of about 30°. The crystal is composed of molecular chains connected by N? H···O hydrogen bonds along the a and b axes forming a “jungle gym” network structure. The low tensile modulus of this polymer as compared with that of poly(p-phenylene terephthalamide) is attributed to the contracted molecular conformation.     

The synthesis of a precursor of polybenzimidazole (PBI) and blends with polyamic acid (PAA)

The precursor of polybenzimidazole (PBI), poly(3,3′-diamino-4,4′-benzidine isophthalamide) (PDABI), was synthesized from poly(3,3′-dinitro-4,4′-benzidine isophthalamide) (PDNBI) by reduction. With increasing temperature, the NH₂ moiety which was protected by SnCl₅^?1 could cyclize and form PBI. Blends with polyamic acid (LaRC-TPI) were prepared. Clear blend films were prepared at up to 400°C. The IR spectra displayed shifts in the NH stretching band, thereby providing evidence for specific interactions related to the miscibility of their cured blends. © 1993 John Wiley & Sons, Inc.     

Photosensitive thiol–ene composition for DLP 3D printing of thermally stable polymer materials

N-allylated derivatives with a modification degree of 80% were obtained by reacting poly[N,N′-(1,3-phenylene)isophthalamide] with allyl bromide in the presence of a strong base. Using the obtained functionalized polyamide and pentaerythritol tetrakis(3-mercaptopropionate), we formulated new photo- sensitive compositions capable of forming crosslinked structures due to UV-initiated thiol–ene polymerization. High-resolution 3D objects that are heat resistant up to 380 °C were formed using digital light processing (DLP) 3D printing     

Nematogenic block copolymers of rigid and flexible aromatic units. I. Synthesis and characterization

Three types of wholly aromatic block copolymers were synthesized using the phosphorylation reactions of Yamazaki and Higashi. Each copolymer contained blocks of rigid and flexible units. The first copolymer, PBA/PABH-T, contains blocks of poly(p-benzamide) and the polyterephthalamide of p-aminobenzhydrazide. The second copolymer, PBA/MPD-I, contains blocks of poly(p-benzamide) and poly(p-phenylene isophthalamide), whereas the third, PPD T/MPD-I, contains blocks of poly(p-phenylene terephthalamide) and poly(m-phenylene isophthalamide). Three synthetic routes were used for the preparation of the block copolymers. In the two-step polycondensation (A), monomers of the flexible block are added to the rigid prepolymer. The multistep method (B) differs in that the rigid prepolymer is carboxy-terminated prior to addition of the monomers of the flexible block. Carboxy-terminated prepolymer of the rigid block is reacted with amine-terminated prepolymer of the flexible block in the two-pot condensation (C). The presence of a considerable amount of the flexible homopolymer is indicated by viscosity, extraction, and NMR studies, particularly when methods A and C were used. The flexible homopolymer can be extracted by using a nonsolvent for the rigid blocks. Extraction of the rigid homopolymer (which may also be presumed to be produced) entails a more elaborate procedure. In principle, one can use these methods to obtain pure block copolymer for study of mixtures with the rigid and flexible homopolymers. Phase studies of some of these systems will be reported in a following paper.     

Synthesis and characterization of aromatic poly(ether sulfone imide)s derived from sulfonyl bis(ether anhydride)s and aromatic diamines

Two sulfonyl group-containing bis(ether anhydride)s, 4,4′-[sulfonylbis(1,4-phenylene)dioxy]diphthalic anhydride ( IV ) and 4,4′-[sulfonylbis(2,6-dimethyl-1,4-phenylene)dioxy]diphthalic anhydride (Me- IV ), were prepared in three steps starting from the nucleophilic nitrodisplacement reaction of the bisphenolate ions of 4,4′-sulfonyldiphenol and 4,4′-sulfonylbis(2,6-dimethylphenol) with 4-nitrophthalonitrile in N,N-dimethylformamide (DMF). High-molar-mass aromatic poly(ether sulfone imide)s were synthesized via a conventional two-stage procedure from the bis(ether anhydride)s and various aromatic diamines. The inherent viscosities of the intermediate poly(ether sulfone amic acid)s were in the ranges of 0.30–0.47 dL/g for those from IV and 0.64–1.34 dL/g for those from Me- IV. After thermal imidization, the resulting two series of poly(ether sulfone imide)s had inherent viscosities of 0.25–0.49 and 0.39–1.19 dL/g, respectively. Most of the polyimides showed distinct glass transitions on their differential scanning calorimetry (DSC) curves, and their glass transition temperatures (T_g) were recorded between 223–253 and 252–288°C, respectively. The results of thermogravimetry (TG) revealed that all the poly(ether sulfone imide)s showed no significant weight loss before 400°C. The methyl-substituted polymers showed higher T_g's but lower initial decomposition temperatures and less solubility compared to the corresponding unsubstituted polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1649–1656, 1998     

Thermal degradation of aramids—Part II: Pyrolysis/gas chromatography/mass spectrometry of some model compounds of poly(1,3-phenylene isophthalamide) and poly(1,4-phenylene terephthalamide)

The thermal degradation reactions of seven aromatic amides which are structurally related to the commercial aramids Kevlar (poly(1,4-phenylene terephthalamide)) and Nomex (poly(1,3-phenylene isophthalamide) have been investigated in the temperature range 450 to 700°C by pyrolysis/gas chromatography/mass spectrometry. Benzanilide, N,N′-dibenzoyl-1,4-phenylenediamine, N,N′-dibenzoyl-1,3-phenylenediamine, N,N′-diphenylterephthalamide, N,N′-diphenylisophthalamide, N-(4-aminophenyl)-benzamide and N-(3-aminophenyl)benzamide all gave very low yields of carbon oxides and water. The structures of the higher molecular weight products were related to those of the parent compounds and their yields are presented quantitatively. The principal mechanism for thermal cleavage of the amide bonds in the N,N′-dibenzoylphenylenediamines is mainly heterolytic, while for the other compounds thermal cleavage of the amide bonds is homolytic. The relationship between the pyrolysis products of the model compounds and those of the corresponding aramids is discussed.     

Studies on dilute solutions of rodlike macroions. II. Electrostatic effects

A group of rodlike polymers soluble only in strong protic acids was studied using light scattering and viscosity techniques. These include poly(1,4-phenylene benzobisoxazole), poly(1,4-phenylene benzobisthiazole) and poly(1,4-phenylene terephthalamide). The solution properties were dependent on the ionic strength of the acid used as solvent. In a low ionic strength acid such as chlorosulfonic acid, the polymer solutions exhibited decreased unpolarized scattering, an extremely small translational diffusion coefficient, and high viscosity. All of these effects could be eliminated by the addition of a salt such as lithium chlorosulfonate, which increased the ionic strength of the solvent. The effects were attributed to a pseudo ordering of the polymer solvent system caused by electrostatic repulsions between protonated polymer chains effective over large distances (ca. 100 Å) in the low ionic strength solvent. This type of ordering is distinct from actual anisotropic phase formation, which occurs at higher concentrations in these systems. Analysis of data at infinite dilution gave a persistence length of at least 45 nm for poly(1,4-phenylene terephthalamide), larger than previous experimental results, but in accord with recent rotational isomeric state calculations and similar to experimental data for poly(p-benzamide).     

Preparation and properties of a new aromatic polyamide with an ethoxycarbonyl pendant group: Poly(4,4′‐diamino‐2′‐ethoxycarbonyl‐benzanilide terephthalamide)

A new aromatic polyamide containing a pendant ethoxycarbonyl group was successfully synthesized from the reaction between 4,4′‐diamino‐2′‐ethoxycarbonylbenzanilide and terephthaloyl chloride. The new polymer was soluble in organic solvents such as N‐methyl‐2‐pyrrolidone and dimethylacetamide, and a tough and transparent film was cast from the polymer solution with viscosities ranging from 2.6 to 5.6 dL/g. When the polymer film was heat‐treated at a temperature greater than 300 °C, a cyclization reaction occurred between the ethoxycarbonyl group and the adjacent amide bond to form a benzoxazinone unit in the polymer backbone. The thermal decomposition onset temperature of the cyclized film was about 523 °C, which was somewhat lower than that of poly(p‐phenylene terephthalamide) (PPTA; 566 °C); however, the decomposition rate was slower than that of PPTA to yield a higher char residue. The dispersion temperature of the uncyclized poly(4,4′‐diamino‐2′‐ethoxycarbonylbenzanilide terephthalamide) (PDEBTA) was about 340 °C, whereas that of the cyclized PDEBTA was not clear. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 936–942, 2000     

Novel aromatic polyhydrazides and poly(amide-hydrazide)s based on “multiring” flexible dicarboxylic acids

Two flexible dicarboxylic acid monomers, 4,4′-[isopropylidenebis(1,4-phenylene)dioxy]dibenzoic acid ( 1 ) and 4,4′-[hexafluoroisopropylidenebis(1,4-phenylene)-dioxy]dibenzoic acid ( 3 ), were synthesized from readily available compounds in two steps in high yields. High molecular-weight polyhydrazides and poly(amide-hydra-zide)s were directly prepared from dicarboxylic acids 1 and 3 with terephthalic dihydrazide ( 5 ), isophthalic dihydrazide ( 6 ), and p-aminobenzhydrazide ( 7 ) by the phosphorylation reaction by means of diphenyl phosphite (DPP) and pyridine in N-methyl-2-pyrrolidone (NMP)/LiCl, or prepared from the diacyl chlorides of 1 and 3 with the hydrazide monomers 5–7 by the low-temperature solution polycondensation in NMP/LiCl. Less favorable results were obtained when using triphenyl phosphite (TPP) instead of DPP in the direct polycondensation reactions. Except for those derived from terephthalic dihydrazide, the resulting polyhydrazides and poly(amide-hydrazide)s could be cast into colorless, flexible, and tough films with good tensile strengths. All the hydrazide polymers and copolymers are amorphous in nature and are readily soluble in various polar solvents such as NMP and dimethyl sulfoxide (DMSO). Their T_gs were recorded in the range of 162–198°C and could be thermally cyclodehydrated into the corresponding polyoxadiazoles and poly(amide-oxadiazole)s approximately in the region of 300–380°C, as evidenced by the DSC thermograms. The oxadiazole polymers and copolymers showed a dramatically decreased solubility and higher T_g when compared to their respective hydrazide prepolymers. They exhibited T_gs of 190–216°C and were stable up to 450°C in air or nitrogen. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1847–1854, 1998     

Synthesis and thermal properties of a new class of high-temperature polyamides from hexahydrobenzodipyrrole

A series of polyamides was synthesized by the interfacial polycondensation of 1,2,3,5,6,7-hexahydrobenzo [1,2-c:4,5-c′] dipyrrole with isophthalic, terephthalic, oxydibenzoic, sebacic and adipic acid chlorides. High molecular weight polymers with inherent viscosities ranging from 0.4 to 2.3 dl/g were obtained. Polymerization with isophthaloyl chloride gave the highest molecular weight polymer in this series. These polyamides melt between 350°C and 475°C, depending on structural differences as determined by differential scanning calorimetry (DSC). Rapid weight loss in these polymers was observed in the range of 350–400°C under thermogravimetric analysis in a nitrogen atmosphere. All these polyamides are susceptible to photooxidative degradation. The results were compared with Nomex polymer poly(1,3-phenylene isophthalamide).     

Densimetric study of solutions and fibers based on aromatic poly(amides)

The densimetric characteristics of solutions and fibers are obtained and analyzed for two aromatic poly(amides) poly(p-phenylene terephthalamide) and a copolymer composed of poly(p-phenylene terephthalamide) and poly(amide benzimidazole) units. For poly(p-phenylene terephthalamide) solutions in sulfuric acid in the concentration interval ranging from 3 to 19 wt %, the linear concentration dependences of density show the points of discontinuity, which correspond to the concentration boundaries of phase states: liquid crystalline and crystal solvate states. Under all of the processing conditions under study, Armos fibers are characterized by a low level of overall maximum porosity. This factor seems to be advantageous from the viewpoint of strength characteristics and other unique properties of fibers.     

Preparation of dibenzofuran-type amorphous polyetherketone by novel etherification reaction

4-Fluorobenzophenone reacted with potassium carbonate in the presence of silica catalyst in diphenyl sulfone solvent to yield 4,4′-dibenzoyldiphenyl ether. This new etherification reaction was extended to three difluoro aromatic ketones. 4,4′-Bis(4-fluorobenzoyl)diphenyl ether ( I ) reacted with potassium carbonate to yield a crystalline poly(oxy-1,4-phenylene-carbonyl-1,4-phenylene) (PEK) and 4,4′-bis{4-[4-(4-fluorobenzoyl)phenoxy]benzoyl}benzene ( II ) gave a crystalline poly(oxy-1,4-phenylene-carbonyl-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene-carbonyl-1,4-phenylene)(PEKEKEKK). 2,8-Bis(4-fluorobenzoyl)dibenzofuran ( III ) or 2,8-bis(4-chlorobenzoyl)dibenzofuran ( IV ) reacted with potassium carbonate to yield a poly(oxy-1,4-phenylene-carbonyl-2,8-dibenzofuran-carbonyl-1,4-phenylene) (PEKBK). The PEKBK was a noval amorphous polymer with the glass transition temperature of 222°C and it showed excellent thermal stability [T. Tanabe and I. Fukawa, Jpn. Pat., Kokai 64–74223 (1989)]. Several amorphous dibenzofuran type polyetherketone copolymers were prepared by coplycondensation of III with 4,4′-difluorobenzophenone ( V ) or 1,4-bis(4-fluorobenzoyl)benzene ( VI ) [T. Tanabe and I. Fukawa, Jpn. Pat., Kokai 1153722 (1989)]. © 1992 John Wiley & Sons, Inc.     

Polyaromatic pyrazines: Synthesis and thermogravimetric analysis

The syntheses of five polyaromatic pyrazine polymers are described. These polymers were synthesized by the condensation of bis-α-haloaromatic ketones with ammonia in N,N-dimethylacetamide (DMAc) solvent in the presence of air or peroxides. The condensation of bis-p-(α-bromoacetyl)benzene (IIIa), bis-p,p′-(α-chloroacetyl)biphenyl (IIIb) bis-p,p′-(α-chloroacetyl)diphenyl ether (IIIc), bis-p,p′-(α-chloroacetyl)diphenylmethane (IIId), and α,α′-dibenzoyl-α,α′-dibromo-p-xylene (V) under these reaction conditions gave poly[2,5-(1,4-phenylene)pyrazine] (IVa), poly[2,5-(4,4′-biphenylene)-pyrazine] (IVb), poly[2,5-(4,4′-oxydiphenylene)pyrazine] (IVc), poly[2,5-(4,4′-methylenediphenylene)pyrazine] (IVd), and poly[2,5-(1,4-phenylene)-3,6-diphenylpyrazine] (VI), respectively. Thermogravimetric analysis (TGA) of these polymers showed them to be thermally stable up to the temperature range of 450–550°C in air for short periods of time. The inherent viscosities of these polymers ranged from 0.18 to 1.30.