Molecular factors affecting solubility in rigid-rod polyamides

Highly Transparent Aromatic Polyamides from Unsymmetrical Diamine with Trifluoromethyl Groups

Soluble and transparent wholly aromatic polyamides (PAs) were synthesized from an unsymmetrical diamine monomer having trifluoromethyl (CF₃) groups, 4-(4′-aminophenoxy)-3,5-bis(trifluoromethyl)aniline. The monomer was polymerized with several dicarboxylic acid monomers via the Yamazaki–Higashi polycondensation method. All of the synthesized polyamides have an amorphous morphology, and they are soluble in many polar organic solvents at room temperature. Flexible and transparent films of the polyamides were prepared by solution casting and these polymer films show good optical transparencies with cut-off wavelengths of 337–367 nm and transparencies of 88%–90% at 550 nm. In addition, all the polymers were thermally stable over 400 °C and exhibited glass transition temperatures (T_g) higher than 300 °C. Unsymmetrically inserted trifluoromethyl groups on polyamides improves the solubility as well as the transparency of the polymers while maintaining good thermal properties. They also showed low refractive indices around 1.5333~1.5833 at 633 nm owing to the existence of low polarizable trifluoromethyl groups.

Organo-Soluble Polyimides: Synthesis and Characterization of Polyimides Containing Phenylated p-Biphenyl and p-Terphenyl Units

4, 4′-diamino-2, 2′-diphenylbiphenyl (1), 4,4″-diamino-2′, 3′, 5′-triphenyl- p-terphenyl (2a) and 4,4″-diamino-2′, 3′, 5′, 6′-tetraphenyl- p-terphenyl (2b) have been polymerized with several aromatic dianhydrides in refluxing m-cresol containing isoquinoline to afford a series of phenylated polyimides. The polymerization mixtures of 1 and 3, 3′, 4, 4′-biphenyltetracarboxylic dianhydride (BPDA) and 3, 3′4, 4′-benzophenonetetracarboxylic dianhydride (BTDA) and of 2a and pyromellitic dianhydride (PMDA) set to gel-like structures upon cooling. The gels, which displayed optical anisotropy typical of a liquid crystalline-like phase, could be dissolved by heating and re-formed by cooling. Although the p-catenated, rigid-rod polymers obtained from the diamines and PMDA were only soluble in concentrated sulphuric acid, the polymers that were prepared from 1 and 2a and 3, 3′, 4, 4′-diphenylethertetracarboxylic dianhydride (ODPA), 3, 3′, 4, 4′-diphenylsulphonetetracarboxylic dianhydride (DSDA) and 2, 2-bis[4-(1, 2-dicarboxyphenyl)]-1, 1, 1, 3, 3, 3-hexafluoropropane dianhydride (6FDA) were soluble in N-methyl-2-pyrrolidinone (NMP), m-cresol and chlorinated solvents. In general, polymers prepared from 2a were the most soluble, while polymers prepared from 2b were the least soluble. The intrinsic viscosities of the polymers ranged from ′.61 to 5.1 dl g−1 in concentrated sulphuric acid or NMP at 3′°C. The glass transition temperatures of most of the polymers could not be detected with differential scanning calorimetry. The temperatures at which the polymers underwent 5% weight losses when subjected to thermal gravimetric analysis ranged from 5″ to 6′°C in both air and nitrogen. Several of the polymers could be solution cast into thin, water-white flexible films.

Rigid-rod Benzobisazole Polymers Containing Benzothiazole Pendent Groups

Novel polybenzobisazoles containing benzothiazole pendent groups were prepared by the reaction of 2-benzothiazole or 2,5-dibenzothiazole terephthalic acids with the appropriate aminomercapto, aminohydroxy or tetraamino -nonomers in poly phosphoric acid at elevated temperatures. The polymerizations were carried out at concentrations (10-18%) which would promote anisotropic reaction mixtures. Intrinsic viscosities in the range of 4-19 dl/g were measured in methanesulfonic acid at 30°C. Thermogravimetric-mass spectral analysis in vacuo showed that the pendent benzothia zole group was the initial product of thermal degradation, maximizing at 590°C. Anisotropic polymerization mixtures could be wet-spun into fibres with modulus values between 25-30 Msi and tenacity values up to 350 Ksi.

Synthesis and Characterization of Polyimides Based on 3,6-Diphenylpyromellitic Dianhydride

3,6-Diphenylpyromellitic dianhydride (DPPMDA) has been synthesized from 2,5-diphenyl-3,4-bis(4-methoxyphenyl)cyclopentadiene-1-one and dimethyl acetylenedicarboxylate. The monomer was polymerized with 11 aromatic diamines in refluxing m-cresol containing isoquinoline to afford two new series of phenylated polyimides. The polymers containing flexible ether or methylene linkages, meta-catenation, or cardo linkages were soluble in m-cresol, N-methylpyrrolidinone, and symtetrachloroethane. Their intrinsic viscosities ranged from 0.81 to 2.40 dl/g. The polymers prepared from 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylmethane, and 1,3-diaminobenzene underwent extensive crystallization in concentrated m-cresol solutions. These polymers displayed weak glass-transition temperatures between 310°C and 320°C and melting points near 430°C. Three para-catenated, rigid-rod polymers were also prepared from DPPMDA and substituted 4,4′-diaminobiphenyls that displayed limited solubility in m-cresol. Solutions containing 8.5 to 15% (w/v) of the polymer prepared from 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl underwent reversible gellation near 85°C. Liquid-crystalline spherulites formed in the gels upon standing at ambient temperatures.