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Shape memory polymers (SMP) are prepared, via dual thiol‐epoxy/thiol‐ene reactions, from diglycidyl ether of bisphenol A (DGEBA), a trithiol (TMP), a tetraallyl amine (TAA), and small amounts (0.1–0.5 wt.%) of graphene oxide either pristine (GO) or functionalized with methacrylate groups (GOM). The incorporation of GOM to the epoxy resin network permits a good load transfer, which is reflected in improved properties such as Young modulus (from 220 to 519 MPa), tensile strength (from 46.3 to 69.2 MPa), Izod impact strength (from 0.051 to 0.42 J/mm), torque (from 0.008 to 0.031 Nm), and glass transition temperature (from 75 to 105°C). Such improvement in properties is attributed to the incorporation of GOM via covalent linking, which is a good strategy for improving polymer‐particle interaction and particle dispersion. The epoxy‐based SMP also show high storage modulus (up to 2.36 GPa) and high deformation capacity, which are reflected in good shape fixity (between 97% and 100%) and thermo‐induced shape recovery (between 97% to 99.7%) behaviors in flexion mode tests. [ABSTRACT FROM AUTHOR]

ABSTRACT Poly(4-vinylpyridine) was partially (20% and 50%) and fully (100%) quaternized with a bromo-terminated 4,4′-dialkyloxy-substituted cyanophenyleneazobenzene group (Azo-Br). The resulting liquid crystal azopolymers were studied by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) to determine their thermotropic behavior. They showed only a smectic phase that extends over a broad temperature range. The smectic period was found to correspond to a double layer stacking where the pendant groups (mesogens) are partially interpenetrated. On the other hand, the azopolymers were irradiated (UV-vis wavelengths) to induce trans-to- cis conversion (photoisomerization), molecular alignment (birefringence), and mass migration (surface relief gratings). Results showed the lowest trans-to- cis photo conversion for the polymer with the highest content (100%) of chromophore units, and it was simply attributed to constrains arising from their close packing. On the contrary, this polymer showed the highest birefringence value suggesting a coordinated motion of the tightly held chromophore units at the smectic domains, as it was indeed reported for other photo-active liquid crystal azopolymers. Finally, surface relief gratings, having a sinusoidal profile with regular periodicity, were registered. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44819. [ABSTRACT FROM AUTHOR]

A series of side-chain liquid-crystalline methacrylic copolymers, having various amounts of 4′-(4-decyloxyphenyl)-4-(hexyloxy)-azobenzene as the mesogenic group, were synthesized and characterized by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction to determine their mesomorphic properties, and by UV−visible spectrometry to elucidate their optical absorption characteristics. Also, birefringence and surface relief gratings were photoinduced in the films using a laser beam of 413 nm. Copolymers with high mesogen contents display a polymorphic behavior of the smectic type. The smectic order tends to disappear as the content of mesogens in the copolymer decreases, going from extended lamellar domains of chromophores packed in a parallel position, typical for smectic liquid crystals, to small aggregates of chromophores dispersed in an amorphous matrix. Important hypsochromic shifts (Δ λmax ≈ 20 nm), associated with π interactions between neighboring aromatic groups, confirm the aggregation of chromophores in lamellar structures. The light-induced birefringence (0.005 − 0.06) is not as high as expected but it corroborates that there exists a tight interplay between photoinduced orientation and intrinsic molecular order. Surface relief gratings were recorded in copolymers with low mesogen content (15 − 30 mol%), showing by atomic force microscopy sinusoidal profiles with an average depth of around 150 nm. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Poly(4-vinylpyridine)s (P4VPs) fully and partially quaternized with dialkyloxyterphenyl groups were synthesized and characterized. These new polymers developed both liquid-crystalline (LC) properties and a light emission (luminescence) in the blue region. The mesomorphic behavior of the polymers was initially characterized by differential scanning calorimetry and polarizing optical microscopy and was further corroborated by X-ray diffraction analyses. The X-ray diffraction patterns showed in the low-angles region several equidistant diffraction peaks ( d, d, d, ...) and in the wide-angles region a broad peak typical of nonordered mesophases. From d and the length of the monomers, we deduced that the molecular arrangement in the mesophase corresponded to a double-layered stacking of molecules with mesogens tilted with respect to the smectic plane and the backbones sandwiched between. In this arrangement, the different parts of mesogens are segregated from one another in layered domains. The longer smectic periods observed for copolymers indicated that the nonsubstituted pyridine cycles were sandwiched between two smectic layers. The emission spectra of these polymers were characterized by a broad signal centered at 365 nm. The combination of LC properties with luminescence in the polymers is interesting for the preparation of thin films with aligned emitters, particularly for linearly polarized light emission. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

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A series of penta(p-phenylene)s modified with short and long alkoxy groups was synthesized via palladium complex-catalysed cross-coupling reactions. Molecules substituted with butoxy groups in the central ring showed a nematic phase characterized by a schlieren optical texture, whereas those molecules lacking lateral groups, or substituted with shorter than butoxy groups, did not exhibit liquid crystallinity. Also, it was determined that both the mesophase stability and the clearing point were strongly dependent on the length of the terminal chains. Finally, optical studies of these compounds indicated that the observed light absorption/ emission characteristics are independent of the chain lengths. [ABSTRACT FROM AUTHOR]