Double metal cyanide catalyst prepared using H3Co(CN)6 for high carbonate fraction and molecular weight control in carbon dioxide/propylene oxide copolymerization

Simple mixing of H₃Co(CN)₆ and ZnCl₂ in methanol resulted in precipitates of [ZnCl]⁺₂[HCo(CN)₆]^2?, constituting a new type of double metal cyanide (DMC) catalyst exhibiting a high performance in carbon dioxide (CO₂)/propylene oxide (PO) copolymerization. High‐molecular‐weight poly(propylene carbonate‐co‐propylene oxide)s [poly(PC‐co‐PO)s] (M_n～40,000) were consistently obtained with high carbonate fractions (～60 mol %) and a high selectivity (>95%) with the new type of DMC catalyst. Conventional preparation of the DMC catalyst using K₃Co(CN)₆ and ZnCl₂ required removing KCl through thorough washing and resulted in lower carbonate fractions (10–40 mol %), which depended on the washing conditions. Feeding hydrophobic diols such as 1,10‐decanediol as chain transfer agent preserved the high carbonate fraction (～60%) and enabled precise control of the molecular weight, including preparation of a low‐molecular‐weight poly(PC‐co‐PO)‐diol (M_n ～2000), which was a flowing viscous liquid with a low T_g (?30 °C) suitable for polyurethane applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4811–4818     

Role of matrix crystallinity in carbon nanotube dispersion and electrical conductivity of iPP‐based nanocomposites

A homopolymer iPP and a series of propylene‐ethylene random copolymers with a content of ethylene from 7 to 21 mol % were used as matrices to prepare single‐walled carbon nanotube (SWCNT) nanocomposites in a range of SWCNT concentration from 0.15 to 1 wt %. The solution blending and melt‐ compression molding procedures were kept identical for all nanocomposites. The poly(propylenes) have crystallinities ranging from 70 to 10%, and serve to test the role of SWCNTs acting as nucleants to preserve in the nanocomposites the uniform dispersion of SWCNTs after sonication. The major role of polymer crystallinity is to mediate toward a more open and more connected SWCNT network structure. Fast nucleation and growth of high crystalline matrices on multiple sites along the surface of the nanotubes prevents SWCNT clustering, and entraps the SWCNT network between the semicrystalline structure reducing the driving force of nanotubes to curl and twist. Depletion of crystallites in the less crystalline matrices (<35% crystallinity) leads to curled and poorly connected nanotubes. A consequence of the gradual loss of SWCNT connectivity is a decreased electrical conductivity; however, the change with crystallinity is not linear. Conductivity decreases sharply with decreasing crystallinity for SWCNT contents near the percolation region, while for contents approaching the plateau region the electrical conductivity is less sensitive to matrix crystallinity. The percolation threshold decreases rapidly for polymers with <～30% crystallinity and slowly levels off at crystallinities >～40%. At SWCNT concentrations of 0.15 wt %, SEM images of nanocomposites with the highest crystallinity matrix indicate debundled and interconnected nanotubes, whereas more disconnected and curled SWCNTs remain in the lowest crystallinity nanocomposites. Electrical conductivity in the former is relatively high, whereas the latter are insulators. Also discussed is the nucleating effect of nanotubes and restrictions of the filler to polymer chain diffusion in the crystallization of the polymers. SEM images and Raman spectra in the radial breathing modes region (100–400 cm^?1) are complementary tools to extract the quality and details of the SWCNT dispersion in the nanocomposites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2084–2096, 2010     

Acid-functionalized dissymmetric salen ligands and their manganese(III) complexes

Acid-functionalized symmetric and dissymmetric salen-type ligands were synthesized via a novel self-protection step in a quantitative yield. This synthetic method allows one to quickly prepare salen-based dissymmetric chiral compounds with tailorable coordinating properties. Therefore, this approach provides a blueprint for synthesizing and evaluating a new class of acid-functionalized salen ligands that can be used as chiral building blocks for a wide range of catalysts and coordination polymers with chemically tailorable properties.     

Synthesis of linear and hyperbranched poly(etherketone)s containing flexible oxyethylene spacers

As an alternative to strong acid reaction media for the Friedel–Crafts acylation for a polymer‐forming reaction, a mild polyphosphoric acid (PPA) with optimized amount of phosphorous pentoxide (P₂O₅) has been tested for the polymerization of AB monomers 4‐(2‐phenoxyethoxy)benzoic acid and 3‐(2‐phenoxyethoxy)benzoic acid, and an AB₂ monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid. The reaction progress of AB₂ monomer was conveniently traced by FTIR spectroscopy monitoring aromatic ketone (C?O) stretching bands arisen from carboxylic acid groups at the chain ends and carbonyl groups in the backbone as a function of reaction time at 110 °C. The resultant linear and hyperbranched polymers containing flexible oxyethylene spacers, which were prone to be hydrolyzed in strong acids at elevated temperature, displayed high intrinsic viscosities. Thus, the reaction medium PPA/P₂O₅ mixture as an electrophilic substitution reaction was indeed benign not to depolymerize growing polymer molecules but strong enough for the direct generation of carbonium ion from carboxylic acid to promote efficient polymerization. The resultant hyperbranched poly(etherketone) (PEK) displayed the best solubility among samples. All PEKs showed good thermal stability; glass transition temperatures were in the range of 90–117 °C; 5% weight loss generally occurred at greater than 345 °C in air. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5112–5122, 2007     

Microchip-Type InGaN Vertical External-Cavity Surface-Emitting Laser

We fabricated microchip-type InGaN vertical external-cavity surface-emitting lasers (VECSELs) integrated with microlenses and investigated their operational properties using an optical pumping method. We confirmed that the multimode lasing operation is consistent with a given VECSEL structure and that there is an optimized curvature radius in terms of the threshold input energy, slope efficiency, and mode stabilization. A simple theory using the Gaussian beam mode provides an excellent explanation of VECSEL lasing properties and the effect of the microlens on lasing.     

Asymmetric Synthesis of Cα-Substituted Prolines through Curtin–Hammett-Controlled Diastereoselective N-Alkylation

Asymmetric synthesis of α-substituted proline derivatives has been accomplished by an efficient chirality-transfer method. High diastereoselectivity of the N-alkylation of the proline ester (C→N chirality transfer) was achieved when a 2,3-disubstituted benzyl group was used as the N-substituent. DFT calculations provided a mechanistic rationale for the high degree of stereoselectivity. The generated N-chirality of the quaternary ammonium salt was transferred back to the α-carbon through a stereoselective [2,3]-Stevens rearrangement (N→C chirality transfer) to give α-substituted proline ester.     

Mild and direct conversion of esters to morpholine amides using diisobutyl(morpholino)aluminum: application to efficient one-pot synthesis of ketones and aldehydes from esters

Morpholine amide intermediates, which are easily prepared by aminolysis of various esters with diisobutyl(morpholino)aluminum, react with organolithium and reducing agents (DIBALH or LDBMA) without isolation of the aminolysis intermediates to give ketones in 83–95% yields and aldehydes quantitatively.