Amphiphilic cationic polynorbornene derivatives, soluble in water, were prepared from modular norbornene monomers, with a wide range of molecular weights (M(n) = 1600-137 500 g/mol) and narrow polydispersities (PDI = 1.1-1.3). The antibacterial activity determined by growth inhibition assays and the hemolytic activity against human red blood cells were measured and compared to determine the selectivity of the polymers for bacterial over mammalian cells. The effects of monomer repeat unit hydrophobicity and polymer molecular weight on antibacterial and hemolytic activities were determined. The hydrophobicity of the repeat unit was observed to have dramatic effects on antibacterial and hemolytic activities. Lipid membrane disruption activities of the polymers was confirmed by measuring polymer-induced dye leakage from large unilamellar vesicles. By tuning the overall hydrophobicity of the polymer through random copolymerizations of modular norbornene derivatives, highly selective, nonhemolytic antibacterial activities were obtained. For appropriate monomer composition, selectivity against bacteria versus human red blood cells was determined to be over 100.

Polymers featuring photolabile groups are the subject of intense research because they allow the alteration of polymer properties simply by irradiation. In particular, the o-nitrobenzyl group (o-NB) is utilized frequently in polymer and materials science. This Perspective pays particular attention to the increasing utilization of this chemical group in polymer chemistry. It covers the use of (i) o-NB-based cross-linkers for photodegradable hydrogels, (ii) o-NB side chain functionalization in (block) copolymers, (iii) o-NB side chain functionalization for thin film patterning, (iv) o-NB for self-assembled monolayers, (v) photocleavable block copolymers, and (vi) photocleavable bioconjugates. We conclude with an outlook on new research directions in this rapidly expanding area.

This short review is meant to provide the reader with highlights in anion exchange membrane research, describe current needs in the field, and point out promising directions for future work. Anion exchange membranes (AEMs) provide one possible route to low platinum or platinum-free fuel cells with the potential for facile oxidation of complex fuels beyond hydrogen and methanol. AEMs and related stable cationic polymers also have applications in energy storage and other electrochemical technologies such as water electrolyzers and redox flow batteries. While anion exchange membranes have been known for a long time in water treatment applications, materials for electrochemical technology with robust mechanical properties in thin film format have only recently become more widely available. High hydroxide and bicarbonate anion conductivity have been demonstrated in a range of AEM formats, but intrinsic stability of the polymers and demonstration of long device lifetime remain major roadblocks.Novel approaches to stable materials have focused on new types of cations that employ delocalization and steric shielding of the positive center to mitigate nucleophilic attack by hydroxide. A number of promising polymer backbones and membrane architectures have been identified, but limited device testing and a lack of understanding of the degradation mechanisms in operating devices is slowing progress on engineered systems with alkaline fuel cell technology. Our objective is to spur more research in this area to develop fuel cell systems that approach the costs of inexpensive batteries for large-scale applications. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013Phys. , 51, 1727Phys. -1735 KEYWORDS: anion exchange membrane; cationic polymer; conductivity; fuel cell; hydrophilic polymers; membranes; phase separation; stability Anion exchange membrane fuel cell (AMFC) technology has seen a resurgence with new interest in high pH solid polymer membranes to bring alkaline fuel cells into a membrane format similar to now-common proton exchange membrane fuel cells (PEMFC), Figure 1. Major interest in AMFCs was generated by the early reports of Varcoe and Slade 1-4 and commercial advances in materials and devices have been pursued by Tokuyama Corporation, 5 Daihatsu Motor Company, [6][7][8] and CellEra, among others. There are now a number of research groups in China, Europe, Japan, Canada, and the United States that are investigating AMFC technology with the objective of providing a new platform for innovation in fuel cells that can break the cost, fuel flexibility, and materials constraints posed by acidic perfluorinated polymers and precious metal catalysts, Figure 2.The tremendous advances in PEMFC technology over the last couple of decades in the United States, Japan, and Europe have brought fuel cells to the cusp of commercialization in automotive applications. Despite the lack of major consumer market adoption at this time, acid-based fuel cells have seen commercial use in some stationary a...

Novel organic/inorganic hybrid copolymers have been prepared using single site catalysis. Ethylene copolymers incorporating a norbornylene-substituted polyhedral oligomeric silsesquioxane (POSS) macromonomer have been prepared using a metallocene/methylaluminoxane (MAO) cocatalyst system. Isotactic polypropylene-containing POSS nanoparticles were also synthesized for the first time using a similar approach utilizing a C 2 symmetric ansa-metallocene. A wide range of POSS concentrations were obtained in these polyolefin POSS copolymers under mild conditions, up to 56 wt % for PE-POSS copolymers and 73 wt % for PP-POSS copolymers. Initial findings point to improved thermooxidative stability for these nanocomposite polyolefins containing the “molecular silica” side groups relative to their homopolymer analogues. Thermogravimetric analysis of the PE-POSS copolymers under air shows a 90 °C improvement, relative to a polyethylene control sample of similar molecular weight, in the onset of decomposition temperature based upon 5% mass loss. On the basis of dynamic mechanical thermal analysis, the tensile properties of the PE-POSS copolymer were maintained at low POSS loadings. A modulus plateau at temperatures above 175 °C is observed, indicating suppression of melt flow for polyethylene POSS copolymers.

A novel nanocomposite containing polyethylene and polyhedral oligomeric silsesquioxane (POSS) nanoparticles has been characterized using wide-angle X-ray scattering (WAXS). In copolymers formed between ethylene and POSS containing macromonomers, the POSS units, attached as pendant groups off the polyethylene backbones, are found to aggregate and crystallize as nanocrystals. The POSS nanoparticles in such PE-co-POSS copolymers form a lattice separate from the PE lattice with characteristic diffraction signals. From both line broadening of the diffraction maxima and also the oriented diffraction in a drawn material, we conclude that POSS crystallizes as anisotropically shaped crystallites. The presence of POSS disrupts the crystallization of polyethylene and results in less and smaller/disordered polyethylene crystallites. POSS nanocrystals are covalently connected to the PE crystallites via an intermediate disordered interfacial region. The PE crystallites are reinforced by the POSS crystallites, maintaining their crystalline structure under high draw ratio. In total, these contributions help to explain the novel properties of this type of nanocomposite, such as better dimensional stability, extension of high-temperature rubbery plateau, and strong thermal oxidative resistance.