A series of fully aromatic copolyesters based on p-acetoxybenzoic acid (p-ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m-acetoxybenzoic acid (m-ABA) were prepared by a modified melt-polycondensation reaction. The copolyesters were characterized by DSC, thermogravimetric analysis, 1 H NMR, polarized optical microscopy, X-ray diffraction, and intrinsic viscosity measurements. The copolyesters exhibited nematic liquid-crystalline phases in a broad temperature range of about 150°C, when the content of linear (p-ABA, HQDA, and TPA) units was over 67 mol %. DSC analysis of the anisotropic copolyesters revealed broad endotherms associated with the nematic phases, and the melting or flow temperatures were found to be in the processable region. The flow temperatures and crystal-to-nematic and nematicto-isotropic transitions depend on the type of linear monomer units, and these transitions increased as the content of the p-ABA units increased, as compared to the HQDA/TPA units. When the content of the p-ABA units increased, as compared to other linear units (HQDA and TPA), the intrinsic viscosity and degree of crystallinity of the copolyesters also increased, implying a higher reactivity for p-ABA in the p-ABA/ HQDA/TPA/m-ABA polymer system. The aromatic region in the 1 H NMR spectra of the copolyesters containing equal molar compositions of p-ABA, HQDA, and TPA units were sensitive to the sequence distribution of aromatic rings.
Pure poly(N-vinyl-2-pyrrolidone) (PVP) and P(VP-crotonic acid) [P(VP/CrA)] copolymers with different CrA contents were prepared by the ␥-ray-induced polymerization technique. The change in the surface free energy of the copolymers was investigated using the Van Oss-Good contact angle evaluation methodology in order to estimate their wettability properties. The apolar Lifshitz-van der Waals component (␥ S LW ) and the electron donor component (␥ S Ϫ ) of the PVP network were calculated as 27.6 and 56.5 mN m
Ϫ1, respectively. In this case, the surface of the PVP network had a basic character (electron donor). By contrast, the ␥ S LW component of P(VP/CrA) copolymers increased and then remained almost constant with increasing CrA content. In addition, the surface of these copolymers changed from a basic character (␥ S Ϫ ϭ 56.5 mN m
Ϫ1) to an acidic character (␥ S ϩ ϭ 0.07 mN m
Ϫ1) with increasing CrA contents in the copolymer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.