High purity cyclic PS (c-PS) samples with number-average molecular weight (MW) of 3.4 and 9.1 kg/ mol were synthesized via atom transfer radical polymerization and "click" chemistry with narrow MW distribution. Bulk glass transition temperature (T g ) measured by differential scanning calorimetry exhibited a much weaker MW dependence for c-PS relative to its linear precursor and anionically polymerized linear PS (A-PS). Using ellipsometry and fluorescence spectroscopy, major differences were observed in the T gconfinement effect in c-PS films supported on silicon substrates compared to A-PS. Whereas a large T g reduction with confinement is commonly observed for A-PS supported on silica, within error, no confinement effect is seen in c-PS/3.4k films on Si/SiO x substrates down to 21 nm thickness. Although the c-PS linking group contains nitrogen and oxygen atoms potentially able to undergo hydrogen bonding, T g is invariant with confinement for c-PS/3.4k or slightly reduced for c-PS/9.1k regardless of the level of substrate-surface hydroxyl groups. Ellipsometry indicates that the near elimination of the T gconfinement effect in c-PS originates mainly from a very weak perturbation to T g near the free surface (in comparison to linear PS) rather than a strong perturbation at the polymer−substrate interface. We hypothesize that unlike linear polymers, the packing efficiency of cyclic PS segments, i.e., cyclic PS fragility, is not significantly perturbed by the free surface, which in turn results in at most a very weak T g perturbation at the free surface and an invariance of average T g across the film with confinement.

We used differential scanning calorimetry and spectroscopic ellipsometry to measure the molecular weight (MW) dependence of bulk fragility (m bulk) and spectroscopic ellipsometry to measure the thickness dependences of the glass transition temperature (T g) and fragility (m) in supported thin films of low MW cyclic or ring polymer. The effects of confinement on T g and m of thin polymer films are important in a range of advanced technology applications, including nanoimprinting. It has previously been shown that nanoconfined films of high MW linear polystyrene (PS) exhibit major T g- and m-confinement effects whereas films of low MW cyclic PS (c-PS) show at most a very weak T g-confinement effect. In the absence of chain ends, c-PS exhibits very weak T g,bulk– and m bulk–MW dependences compared to linear PS. Despite low MW c-PS having m bulk values similar to that of high MW linear PS, we found that low MW c-PS films show a very weak m-confinement effect because of a weak free-surface effect; e.g., m for a 27 nm thick film of 3.4 kg/mol c-PS is the same as m bulk within error. Overall, these results support a strong correlation between the susceptibility of fragility perturbation and the susceptibility of T g perturbation caused by MW reduction, chain topology, and/or confinement.

The purpose of this study is to describe some of the latest advances in using hydrogels for cancer melanoma therapy. Hydrogel formulations of polymeric material from natural or synthetic sources combined with therapeutic agents have gained great attention in the recent years for treating various maladies. These formulations can be categorized according to the strategies that induce cancer cell death in melanoma. First of all, we should note that these formulations can only play a supporting role that releases bioactive agents against cancer cells rather than the main role. This strategy involves delivering the drug via transdermal pathways, resulting in the death of cancerous cells. Another strategy utilizes magnetic gel composites to combat melanoma via hyperthermia therapy. This review discusses both transdermal and hyperthermia therapies and the recent advances that have occurred in the field.

Core‐shell structured barium titanate‐poly(glycidyl methacrylate) (BaTiO3‐PGMA) nanocomposites were prepared by surface‐initiated atom transfer radical polymerization of GMA from the surface of BaTiO3 nanoparticles. Fourier transform infrared spectroscopy confirmed the grafting of the PGMA shell on the surface of the BaTiO3 nanoparticles cores. Transmission Electron Microscopy results revealed that BaTiO3 nanoparticles are covered by thin brushes (∼20 nm) of PGMA forming a core‐shell structure and thermogravimetric analysis results showed that the grafted BaTiO3‐PGMA nanoparticles consist of ∼13.7% PGMA by weight. Upon incorporating these grafted nanoparticles into 20 μm‐thick films, the resultant BaTiO3‐PGMA nanocomposites have shown an improved dielectric constant (ε = 54), a high breakdown field strength (∼3 MV/cm) and high‐energy storage density ∼21.51 J/cm3. AC conductivity measurements were in good agreement with Jonscher's universal power law and low leakage current behavior was observed before the electrical breakdown field of the films. Improved dielectric and electrical properties of core‐shell structured BaTiO3‐PGMA nanocomposite were attributed to good nanoparticle dispersion and enhanced interfacial polarization. Furthermore, only the surface grafted BaTiO3 yielded homogenous films that were mechanically stable. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 719–728

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