Synthesis, Microstructure, and Properties of High-Molar-Mass Polyglycolide Copolymers with Isolated Methyl Defects.

An efficient, fast, and reliable method for the synthesis of high-molar-mass polyglycolide (PGA) in bulk using bismuth (III) subsalicylate through ring-opening transesterification polymerization is described. The difference between the crystallization (Tc ≈ 180 °C)/degradation (Td ≈ 245 °C) temperatures and the melting temperature (Tm ≈ 222 °C) significantly affects the ability to melt-process PGA homopolymer. To expand these windows, the effect of copolymer microstructure differences through incorporation of methyl groups in pairs using lactide or isolated using methyl glycolide (≤10% methyl) as comonomers on the thermal, mechanical, and barrier properties were studied. Structures of copolymers were characterized by nuclear magnetic resonance (1H and 13C NMR) spectroscopies. Films of copolymers were obtained, and the microstructural and physical properties were analyzed. PGA homopolymers exhibited an approximately 30 °C difference between Tm and Tc, which increased to 68 °C by incorporating up to 10% methyl groups in the chain while maintaining overall thermal stability. Oxygen and water vapor permeation values of solvent-cast nonoriented films of PGA homopolymers were found to be 4.6 cc·mil·m-2·d-1·atm-1 and 2.6 g·mil·m-2·d-1·atm-1, respectively. Different methyl distributions in the copolymer sequence, provided through either lactide or methyl glycolide, affected the resulting gas barrier properties. At 10% methyl insertion, using lactide as a comonomer significantly increased both O2 (32 cc·mil·m-2·d-1·atm-1) and water vapor (12 g·mil·m-2·d-1·atm-1) permeation. However, when methyl glycolide was utilized for methyl insertion at 10% Me content, excellent barrier properties for both O2 (2.9 cc·mil·m-2·d-1·atm-1) and water vapor (1.0 g·mil·m-2·d-1·atm-1) were achieved.

Effect of concentrated light on morphology and vibrational properties of boron and tantalum mixtures.

Heating a mixture of boron (impurities: carbon ∼ B50C2, boric acid - H3BO3) and tantalum (Ta) powders in nitrogen flow in a xenon high-flux optical furnace was performed. As-received powder composed of h-BN, H3BO3, TaB2, B9H11 and a number of other phases including ß-rhombohedral boron, apparently, heavily doped with Ta. FT-IR examination of any sample of the material reveals the complicated vibration spectrum containing, in particular, an absorption band near 2260 cm-1. The shapes of these bands are different for samples because powders were synthesized at different temperatures. Known, that in ß-rhombohedral boron lattice, there are nano-sized voids of different types, which allow an accommodation of single atoms or small groups of atoms. Theoretical calculations performed by the method of quasi-classical type yields the same value, 2260 cm-1, for the vibrations frequency of Ta atoms in D-type crystallographic voids in ß-rhombohedral boron lattice. Since, Ta atoms are known to prefer accommodation just in D-voids the experimentally detected bands can be identified with localized vibrations of Ta atoms.

Mesoporous Polymer Frameworks from End-Reactive Bottlebrush Copolymers.

Reticulated nanoporous materials generated by versatile molecular framework approaches are limited to pore dimensions on the scale of the utilized rigid molecular building blocks (<5 nm). The inherent flexibility of linear polymers precludes their utilization as long framework connectors for the extension of this strategy to larger length scales. We report a method for the fabrication of mesoporous frameworks by using bottlebrush copolymers with reactive end blocks serving as rigid macromolecular interconnectors with directional reactivity. End-reactive bottlebrush copolymers with pendant alkene functionalities were synthesized by a combination of controlled radical polymerization and polymer modification protocols. Ru-catalyzed cross-metathesis cross-linking of bottlebrush copolymers with two reactive end blocks resulted in the formation of polymer frameworks where isolated cross-linked domains were interconnected with bottlebrush copolymer bridges. The resulting materials were characterized by a continuous network pore structure with average pore sizes of 9-50 nm, conveniently tunable by the length of the utilized bottlebrush copolymer building blocks. The materials fabrication strategy described in this work expands the length scale of molecular framework materials and provides access to mesoporous polymers with a molecularly tunable reticulated pore structure without the need for templating, sacrificial component etching, or supercritical fluid drying.

Influence of alkyl chain length on the surface activity of antibacterial polymers derived from ROMP.

The purpose of this study is to understand the antibacterial properties of cationic polymers on solid surfaces by investigating the structure-activity relationships. The polymer synthesis was carried via ring opening metathesis polymerization (ROMP) of oxanorbornene derivatives. Modulation of molecular weights and alkyl chain lengths of the polymers were studied to investigate the antibacterial properties on the glass surface. Fluorescein (Na salt) staining contact angle measurements were used to characterize the positive charge density and hydrophobicity on the polymer coated surfaces. Positive charge density for the surface coated polymers with molecular weights of 3000 and 10,000 g mol(-1) is observed to be in the range of 2.3-28.5 nmol cm(-2). The ROMP based cationic pyridinium polymer with hexyl unit exhibited the highest bactericidal efficiency against Escherichia coli on solid surface killing 99% of the bacteria in 5 min. However, phenyl and octyl functionalized quaternary pyridinium groups exhibited lower biocidal properties on the solid surfaces compared to their solution phase biocidal properties. Studying the effect of threshold polymer concentrations on the antibacterial properties indicated that changing the concentrations of polymer coatings on the solid surface dramatically influences antibacterial efficiency.