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The thermotropic copolyester consisting of 40 mol%p-hydroxybenzoic acid and 30 mol% isophthalic acid/30 mol% hydroquinone (HIQ40), prepared by two different synthetic routes (“acidolysis” or “phenylester”) was studied by differential scanning calorimetry and X-ray diffraction. All these samples show a glass transition temperature in the range of 125–141°C, dependent on the sample thermal history. A crystal to nematic transition is observed between 300 and 375°C. The samples prepared by the acidolysis route, when compared to those producedvia the phenylester reaction, have higher crystallinity which is due to the formation of “IA/HQ” crystals. The crystallinity can be increased significantly (as much as twice) by annealing the polymers at 300°C. The heat of fusion (X → N, crystal to nematic) of the annealed acidolysis samples is also higher than that of the polymers prepared by the phenylester process. The nematic to isotropic (N → I) transitions are broad, exhibiting no definite clearing points. Several mesogenic transitions as suggested by X-ray studies and two crystallization peaks were found for all samples studied. This may be an indication that the samples consist of two, distinct polymeric compositions or that there are two crystal forms. Furthermore, since the intensity ratio of the two crystallization peaks changes as a function of annealing, it is clear that the chemical/physical state of the polymer depends on the thermal history of the samples. Attempts to prepare amorphous HIQ40 and nematic HIQ40 glass by quenching from the isotropic state (480°C and 400°C, respectively) were unsuccessful, however, it can be prepared by precipitation of the acidolysis polymer from solution.

Poly(2-methylpentamethylene terephthalamide) (Nylon M5T) is a new high temperature aromatic polyamide developed by Hoechst Celanese. In this paper thermal properties of Nylon M5T chips, as well as as-spun and drawn fibers were studied by DSC, DMA, hot stage microscopy and WAXS.Tg of the fully amorphous Nylon M5T is 143°C when measured by DSC;Tg increases with crystallinity to 151°C. The temperature dependence of the solid and melt specific heat capacities has also been determined. The heat capacity increase at the glass transition of the amorphous polymer is 103.9 J °C−1 mol−1.Tg by DMA for the as-spun fiber is 155°C, for a drawn fiber is 180°C. Three secondary transitions were observed by DMA in addition to the glass transition. These correspond to a local mode relaxation of the methylene groups at −120°C, onset of rotation of the amide-groups at −65°C and the onset of the rotation of the phenylenegroups (at 63°C). The crystallinity of Nylon M5T strongly depends on the rate of cooling from the melt. The isothermal crystallization data are melt temperature dependent: two-dimensional crystallization takes place when the samples are crystallized from higher melt temperatures, and this phase changes into a spherulitic structure during cooling to room temperature. Spherulitic crystallization occurs when lower melt temperatures are used. This polymer has three crystal forms as indicated by DSC, DMA and WAXS data. The crystal to crystal transitions are clearly visible when amorphous samples are heated in the DSC, or the DMA curves of as-spun fibers are recorded. It is experimentally shown that a considerable melting of the lower temperature crystal forms takes place during the crystal to crystal transitions. The equilibrium melting point as measured by the Hoffman-Weeks method, has been determined to be 339°C.