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Liquid crystals were obtained from poly(4-vinylpyridine) quaternized with 1-bromooctane and 1-bromododecane w-substituted with 4'-methoxy-4-biphenyloxy mesogenic groups. Their thermotropic polymorphism was studied by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Three types of smectic mesophase, namely A, B, and E, were identified and described from a structural point of view. Their structure was found to be very similar to that previously reported for their monomer counterparts. The mesogenic pendant groups are arranged in single layers with the polymer backbones inserted in between. As a function of decreasing degree of quaternization, the smectic period increases slowly, reflecting the expansion of the sublayers containing the polymer backbones along with the free pyridine rings.

Abstract:The isothermal crystallization of poly(ethylene terephthalate) (PET) homopolymers with different molecular weight was studied in a wide temperature range (140-230 °C) using different experimental techniques. Three different morphological regions, labeled r 1 , r 2 and r 3 , were distinguished as a function of crystallization temperature (T c ). In r 1 (low T c ) crystallized samples were characterized by a low crystalline degree with a small spherulite texture containing thin crystals. In r 2 (intermediate T c ) samples showed medium size spherulites composed of two distinct crystalline families (thin and thick crystals). In this temperature range, the crystallization exhibited a maximum value and it was associated with a high content of secondary crystals. In r 3 (high T c ), samples presented considerable amorphous zones and regions consisting of oversized spherulites containing only thick crystals. Time-resolved wide-angle X-ray diffraction measurements, using synchrotron radiation, indicated a rapid evolution of the crystalline degree within the second region, in OPEN ACCESSPolymers 2014, 6 584 contrast with the quite slow evolution observed in the third region. On the other hand, by small-angle X-ray scattering (SAXS) and time-resolved SAXS experiment, it was found that the long period (L) as well as the lamellar thickness (lc) increase as a function of T c , corroborating the formation of the thickest crystals in the third region. From all these observations, a morphological model was proposed for each region.

Morphological and mechanical properties of polypropylene [PP]/poly(ethylene vinyl acetate) [EVA] blends have been studied. Infrared results using thin films first indicated a transition toward compatibility between both components at concentrations above 40% EVA. The transition was verified with different experimental techniques and it was associated to morphological changes and mechanical properties. The PP/EVA blends were mechanically evaluated in terms of impact and tensile strength to determine the influence of blending on the performance properties of these materials. Agreement was found between the transition and the enhancement of both elongation at break and impact strength.