The tensile mechanical properties and fracture toughness of a Bisphenol‐A type difunctional epoxy resin, cured with different amounts of metaphenylene diamine, using two cure cycles, were determined over a range of temperature. The tensile modulus in the glassy state was seen to be predominantly related to intermolecular packing, while in the rubbery state crosslink density was the important factor. Yielding appeared to be due to an increase in free volume as a result of dilatation during the tensile test and was related to a critical shear stress. The large strain properties like tensile strength, elongation‐to‐break, and toughness showed a more complex dependence on chemical structure, molecular architecture, intermolecular packing, and crosslink density. The roles played by the relaxation processes in determining mechanical properties are highlighted.

Benzobisthiazole polymers containing mono‐, bi‐, and terthiophene moieties were synthesized through polycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzenedithiol dihydrochloride with thiophene‐2,5‐dicarboxylic acid, 2,2′‐bithiophene‐5,5′‐dicarboxylic acid, and 2,2′:5′,2″‐terthlophene‐5,5″‐dicarboxylic acid, or their corresponding diacid chlorides, respectively. Intrinsic viscosities of up to 8.1 dL/g (methanesulfonic acid, 30°C) were recorded. Polymer structures were verified by elemental analysis and spectroscopic comparison of the polymers with appropriate model compounds. Onset of breakdown under thermogravimetric analysis in air occurred in the 460–590°C range with the benzobisthiazole polymers containing a monothiophene linkage being the most stable. Films suitable for third‐order optical susceptibility measurements could be prepared by extrusion techniques from the benzobisthiazole polymer containing a monothiophene linkage. Degenerate four wave mixing measurements on this film yielded a third order optical susceptibility χ(3) of approximately 4.5 × 10−10 esu. © 1993 John Wiley & Sons, Inc.

The high degree of electron delocalization in heterocyclic aromatic molecules makes this class of chemistry ideal for hyperpolarizability and NLO (nonlinear optics) polymer developments. This type of polymer is usually insoluble in common solvents and is not amenable to common optical film processing techniques like spin coating. A study of the approach in using an acidic solution extrusion followed by coagulation for optical quality film forming is reported in this paper. The polymers studied are: PBZT (poly (p-phenylene benzobisthiazole)); 6F-PBO (polybenzobisoxazole containing hexaflorinated moities); and Zytel 330 (an amorphous nylon). Some of the resulting films showed an improved optical quality while others showed an extremely poor optical quality over the films used in a previous study. The optically clear films, however, were not of wave-guiding quality. The defects in the films that would cause light scattering were characterized and the probable causes of these defects were discussed. The defects were: (a) optically inferior morphology, (b) micro-voids, (c) macro-voids, (d) solid particles, (e) lines in the transverse direction, and (0 lines in the machine direction.Identification and classification of these defects will help additional efforts in the future for improving the optical quality of heterocyclic aromatic polymer films.

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SynopsisTorsional impregnated cloth analysis (TICA) temperature scan results of an acetylene-terminated quinoxaliie system indicated the presence of two different reactions with different activation energies. Two additional effects are delineated when cure is carried out in the presence of air. Curing at low temperature in the presence of air will lower the final Tg, but at high temperature it will have the opposing effect. The two reactions that can occur under nitrogen are affected differently by air curing. It appears that one is prohibited by the lower temperature curing in air while the other is not.