The melt rheology of highly-purified ring polystyrenes in a wide range of molecular weights (10K ≤ M w ≤ 240K g/mol) was investigated. All the rings revealed no obvious rubbery plateau and faster terminal relaxation compared to the linear counterparts. The rheological data obtained were compared with some theoretical models such as the Rouse ring model and the lattice-animal model. Moreover, two rheological parameters, zero-shear viscosities η0 and the steady-state recoverable compliances J e, were estimated, and their M w dependence was discussed. From these data analysis, it was found that relaxation mechanisms of ring chains can be divided into three categories depending on their M w as follows: (i) Smaller rings (M w ≤ 20K) exhibit faster terminal relaxation than the predicted Rouse rings. This behavior is related to the difference of the local chain conformation from linear chains. (ii) Rings with the moderate molecular weight (40K ≤ M w ≤ 90K) exhibit dynamic moduli similar to the Rouse ring prediction. (iii) A larger ring (M w > 90K) also shows deviant behavior from the Rouse chain because its relaxation time is much longer than the Rouse ring prediction and also the lattice-animal model, where some intermolecular interactions are considered to occur.

Ring polystyrenes (PSs) were synthesized by anionic polymerization technique and purified with preparative size-exclusion chromatography (SEC). Seven ring PSs with their weight-average molecular weight (M w ) ranging from 17k to 570k were prepared and they were confirmed to have high purities all over 96% by liquid chromatography at the chromatographic critical condition (LCCC) analyses. Their radii of gyration (R g s) were determined in benzene-d 6 as a good solvent and in cyclohexane-d 12 or cyclohexane-h 12 as Θ solvents by small-angle neutron scattering (SANS) or light scattering (LS). It has been found that R g s of ring polymers are scaled with M w as R g ∝M w 0.60 in a good solvent and as R g ∝M w 0.53 in Θ solvents. Moreover it was confirmed that g factors, R g 2 (Ring) /R g 2 (Linear) , obtained in Θ solvents are meaningfully larger than theoretically predicted values owing to the topological effect stored in ring molecules.

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Liquid crystal “Blue Phases” (BP) have evolved, in the last years, from a scientific curiosity to emerging materials for new photonic and display applications. They possess attractive features over standard nematic liquid crystals, like submillisecond switching times and polarization- independent optical response. However, BPs still present a number of technical issues that prevent their use in practical applications: their phases are only found in limited temperature ranges, thus requiring stabilization of the layers; stabilized BP layers are inhomogeneous and not uniformly oriented, which worsen the optical performance of the devices. It would be essential for practical uses to obtain perfectly aligned and oriented monodomain BP layers, where the alignment and orientation of the cubic lattice are organized in a single 3D structure. In this work we have obtained virtually perfect monodomain BP layers and used them in devices for polarization independent phase modulation. We demonstrate that, under applied voltage, well aligned and oriented layers generate smoother and higher values of the phase shift than inhomogeneous layers, while preserving polarization independency. All BP devices were successfully stabilized in BPI phase, maintaining the layer monodomain homogeneity at room temperature, covering the entire area of the devices with a unique BP phase.

Clear cell ependymoma has been included in the WHO classification of the central nervous system in 1993, after the first report by Kawano et al. Since then, only a few cases have been reported. Most clear cell ependymoma cases reported in the literature so far were located in the supra-tentorial compartment and/or cerebellum, and one case was in the cervical spinal cord. We report a case of clear cell ependymoma whose histological features were sufficient for the diagnosis and was unusually located in the fourth ventricle originating from the medulla oblongata. The tumor showed uniform tumor cells with perinuclear halo, nuclei being centrally located. Most of the tumor cells were arranged as perivascular pseudorosettes, and no ependymal canals or rosettes were evident. Mitotic figures were not frequent. Immunohistochemically, the tumor cells were strongly reactive for glial fibrillary acidic protein and vimentin, and weak and dot-like positive for epithelial membrane antigen. Clear cell change of the tumor cells appeared to be fixation artifact because this feature was not evident in the frozen section.