Jack Preston

Aromatic polyamides with benzothiazole pendent groups: synthesis, nuclear magnetic resonance structural study and evaluation of properties☆

Abstract A new family of aromatic polyamides were prepared from six aromatic diamines and a new monomer derived from isophthalic acid: 5-(2-benzothiazolyl)isophthaloyl chloride. Theoretical calculations of the reactivity of the new monomer were made by semiempirical methods. The polymers were synthesized by the solution polycondensation method at low temperature, in high yields and moderate to high inherent viscosities. The presence of pendent benzothiazole rings brought about remarkable changes in the spectral (nuclear magnetic resonance) characteristics, compared with those of the homologous unmodified polyisophthalamides. Noticeable improvements were observed also for the solubility and for the glass transition temperatures, which rose 20–30°C relative to those of the conventional polysiophthalamides. Thermogravimetric analyses showed that the new polymers have better thermal stability than the unmodified ones.

Aromatic polyamides with pendent heterocycles: 2. Benzoxazole groups

Abstract A series of polyisophthalamides (PIPAs) containing pendent benzoxazole groups was prepared from six aromatic diamines and a new monomer, 5-(2-benzoxazole)isophthaloyl chloride. These polymers, having moderate to high inherent viscosity values, were synthesized by the low temperature polycondensation method in high yields. A striking feature of these polymers is that their solubility and thermal properties were enhanced compared to the corresponding unmodified PIPAs. Thus, all of the polymers were soluble in aprotic polar solvents and glass transition and decomposition temperatures were, respectively, 15–40°C and 25–35°C higher than for the reference PIPAs. The tensile strengths were somewhat lower than those for the unmodified PIPAs.

Processable heat-resistant resins based on novel monomers containing o-phenylene rings: 2. Ordered benzoxazole- and benzthiazole-imide copolymers☆

Abstract Highly processable heat-resistant resins containing o-phenylene rings have been prepared with high molecular weight from the reaction of simple aromatic dianhydrides with aromatic diamines containing preformed bisbenzoheterocyclic groups connected by an o-phenylene ring. Thus, 2,2′-o-phenylene-bis(5-aminobenzoxazole) was polycondensed with 3,3′4,4′-benzophenone dianhydride to yield a polyamic acid precursor, which was converted to an ordered benzoxazole-imide copolymer via cyclodehydration. Polymers can be prepared from diamines that are structural isomers, e.g. the amino groups can be in the 6-position instead of the 5-position. Additionally, polymers have been prepared from diamines, e.g. 2,2′-o-bis(6-aminobenzothiazole), having structurally similar heterocyclic units such as benzothiazole in place of benzoxazole rings. The preparation of the dinitro precursors to the bisbenzoheterocyclic diamines and their reduction is described along with nuclear magnetic resonance data. Polymers were characterized by differential scanning calorimetry, thermogravimetric analysis and inherent viscosity measurements of the polyamic acid precursors.

Polyisopthalamides with pendent heterocyclic groups: 3. Pyridine pendent groups

Abstract A series of polyisophthalamides (PIPAs) containing pendent isonicotinamido groups has been prepared from six aromatic diamines and a novel monomer, 5-(isonicotinoylamino)isophthalic acid. These polymers, which should be considered as modified PIPAs, have high inherent viscosities (about 1.0 dl g −1 ) and are synthesized in high yields by the phosphorylation polycondensation method. They show a better solubility in organic polar solvents than the parent unmodified polyisophthalamides, and their glass transition temperatures are 20–30 C higher. However, the thermal stability, as measured by thermogravimetric analysis, is lower, showing initial thermal decomposition temperatures of about 400°C. These novel PIPAs can take up approximately twice as much water by weight as conventional PIPAs. Equilibrium water absorption of up to 17% can be measured for some samples.

A Thiophene-Based Liquid Crystalline Aromatic Polyamide

We have synthesized a liquid crystalline, aromatic polyamide from p-phenylene diamine (PPD) and 2, 5-thiophene dicarboxylic acid (Th). The new polymer, poly(p-phenylene thiophenylamide), abbreviated PPD-Th, like its terephthalic acid precursor, poly(p-phenylene terepthalamide) (PPD-T), exhibits a lyotropic mesophase in concentrated sulphuric acid solutions. Polarizing optical microscopy and deuterium NMR show that concentrated PPD-Th solutions exhibit nematic-to-isotropic phase transitions at a much lower temperature than comparable PPD-T solutions. More importantly, unlike PPD-T, lyotropic PPD-Th solutions do not form a crystallo-solvate complex gel phase at room temperature, i.e. the fluid PPD-Th mesophase persists below 300 K enabling the spinning of PPD-Th fibres from a lyotropic dope at ambient temperatures. Thermogravimetric analysis shows that the 2, 5-thiophene heterocycle in the PPDTh backbone does not significantly diminish its thermal stability relative to that of PPD-T. Preliminary x-ray diffraction results show that PPD-Th crystallizes in a tentative two-chain, orthorhombic unit cell with dimensions a = 3.73 Å, b = 5.04 Å and c = 25.20 Å (fibre axis). The fibre repeat corresponds to two chemical repeats related by a twofold screw axis. Mechanical properties (tensile strength, modulus and elongation to break) are presented for as-spun and heat-treated PPD-Th fibres.