Ring-Opening Copolymerization of Maleic Anhydride with Epoxides: A Chain-Growth Approach to Unsaturated Polyesters

We report the ring-opening copolymerization of maleic anhydride with a variety of epoxides catalyzed by a chromium(III) salen complex. Quantitative isomerization of the cis-maleate form of all polymers affords the trans-fumarate analogues. Addition of chain transfer reagents yields low Mn, narrow PDI polymer samples. This method provides access to a range of new unsaturated polyesters with versatile functionality, as well as the first synthesis of high molecular weight poly(propylene fumarate)

Alternating Copolymerization of Epoxides and Cyclic Anhydrides: An Improved Route to Aliphatic Polyesters

Beta-diiminate zinc catalysts are reported for the synthesis of aliphatic polyesters via the highly alternating copolymerization of epoxides and cyclic anhydrides under mild reaction conditions. The polymers formed have high Mn values and narrow molecular weight distributions

Poly(propylene succinate): A New Polymer Stereocomplex

Herein we show the formation of a polymer stereocomplex by mixing isotactic, regioregular chains of poly­(propylene succinate) synthesized via the copolymerization of cyclic anhydrides and epoxides. The stereocomplex exhibits significantly improved thermal properties in comparison to the enantiopure parent polymers. We demonstrate that stereocomplexation is a route to a new class of semicrystalline polyesters with improved properties, produced from readily accessible starting materials

Alternating Copolymerization of Epoxides and Cyclic Anhydrides: An Improved Route to Aliphatic Polyesters

Beta-diiminate zinc catalysts are reported for the synthesis of aliphatic polyesters via the highly alternating copolymerization of epoxides and cyclic anhydrides under mild reaction conditions. The polymers formed have high Mn values and narrow molecular weight distributions

Alternating Copolymerization of Epoxides and Cyclic Anhydrides: An Improved Route to Aliphatic Polyesters

Beta-diiminate zinc catalysts are reported for the synthesis of aliphatic polyesters via the highly alternating copolymerization of epoxides and cyclic anhydrides under mild reaction conditions. The polymers formed have high Mn values and narrow molecular weight distributions

Hierarchical Pattern Formation in the Diffusion-Controlled Reduction of HAuCl₄ in Poly(vinyl alcohol) Hydrogels

Gold nanoparticles (AuNPs) were incorporated in poly(vinyl alcohol) (PVOH) hydrogel cylinders via diffusion-controlled reductions of tetrachloroauric acid dissolved in the gels using sodium borohydride or ascorbic acid. At certain reagent concentrations, the two reducing agents formed very different hierarchical structured patterns due to their different chemical nature. Sodium borohydride reduction, which likely follows the classical “supersaturation” mechanism, results in the formation of spherical and monodisperse AuNPs of ∼4 nm in diameter located in micrometer-scale stripes in the outer region of the gels. The mobility of the small colloids in the gels allows the formation of alternating particle-rich and particle-depleted stripes. The reaction of sodium borohydride with water and the −OH groups of the gel matrix diminishes its reducing ability over time and limits the AuNP formation to the outer region of the gels. AuNPs of >20 nm in diameter are formed throughout the gel matrices by ascorbic acid reduction, which is consistent with an “organizer” mechanism. Concentric bands of different colors from the outer to the inner regions of the gelsalong the direction of ascorbic acid diffusionare formed as the result of increased particle size and percentage of nonspherical shapes. The lack of stripes on the micrometer scale in the ascorbic acid system is likely due to the impeded mobility of the larger AuNPs. The structural features observed in this study are attributed primarily to the nature of the reaction matrix: reduction is controlled by the diffusion of reducing agents in the hydrogel matrix and the PVOH matrix polymer facilitates the dispersion and stabilization of the AuNPs formed

Comparison of virus recovery from unirradiated mask sites after virus desiccation to control virus added directly into recovery media.

(TIFF)</p

Custom N95 respirator with calibrated sensors used for the measurement and according irradiance measurement at each site.

(TIFF)</p

Minimal data set.

(XLSX)</p

Photo of a N95 respirator in the UVGI device.

Front panel was removed for visibility. (TIF)</p