Nonisothermal Crystallization Behavior and Enhanced Heat Resistance and Impact Toughness of Poly(l‑lactic acid) with Bimodal Molecular Weight Distribution

Poor heat resistance and toughness put some limitations on the applications of poly­(lactic acid), one of the most promising eco-friendly polymers. Herein, bimodal poly­(l-lactic acid) (PLLA) was prepared by melt-blending high- and low- molecular-weight PLLAs, and the nonisothermal crystallization behavior, heat resistance, and mechanical properties of bimodal PLLA were investigated. Low-molecular-weight PLLA (L-PLLA) improves the crystallization capability of bimodal PLLA. The double melting behavior is reasonably explained by the melting–recrystallization mechanism. Octamethylenedicarboxylic dibenzoylhydrazide, a typical heterogeneous nucleating agent, significantly enhances the crystallization rate and crystallinity of PLLA. The maximum crystallinity of 100% L-PLLA is as high as 54.4%, and the heat deflection temperature (HDT) of the bimodal PLLA containing 95% L-PLLA is up to 151 °C, while the impact strength drops sharply to 17.2 kJ/m2 due to the large crystallite size. d-Sorbitol (DS) exhibits a completely different mechanism from heterogeneous nucleation, that is, a lower crystallization rate but elevated crystallinity and crystallization temperature. The DS-modified sample realizes an excellent balance between heat resistance (HDT up to 136 °C) and impact strength (47.9 kJ/m2) via a self-toughening effect by increasing the crystallinity and reducing the crystallite size

Pd-Catalyzed Asymmetric Allylation Reaction of 2‑Aryl‑3<i>H</i>‑indol-3-ones with Allyltrimethylsilane

An efficient method for the first ene-reaction of 2-aryl-3H-indol-3-ones with allyltrimethylsilane has been developed for the first time. The reaction proceeded under the catalysis of Pd(OAc)2 and chiral phosphoric ligand L11 in the presence of Cu(CF3COO)2·XH2O, PivOH, and 5 Å molecular sieves in DMSO at 60 °C. The present methodology can avoid the impact of amine products generated by the reaction on the catalyst, and at the same time, the high catalytic activity of classical palladium catalysts still has catalytic ability for low electrophilic keto-imines. The desired products were furnished in excellent yields with good enantioselectivity

Rhodium-Catalyzed Asymmetric Arylative Ring-Opening Reactions of Heterobicyclic Alkenes with Anilines

Asymmetric arylative ring-opening reactions of heterobicyclic alkenes with anilines have been reported for the first time. A wide range of heterobicyclic alkenes, including azabenzonorbornadienes and oxabenzonorbornadienes, were well tolerated in the reaction with various anilines, and they generally delivered the corresponding chiral aryltetralin derivatives in good to excellent enantioselectivities. The reaction is speculated to proceed through the Friedel–Crafts reaction pathway

Copper-Catalyzed Oxidative C–H Amination of Tetrahydrofuran with Indole/Carbazole Derivatives

A simple α-C–H amination of cyclic ether with indole/carbazole derivatives has been accomplished by employing copper­(II) chloride/bipy as the catalyst system. In the presence of the di-<i>tert</i>-butyl peroxide oxidant, cyclic ethers such as tetrahydrofuran, 1,4-dioxane, and tetrahydropyran successfully undergo C–H/N–H cross dehydrogenative coupling (CDC) with various carbazole or indole derivatives in good-to-excellent yields

Iridium-Catalyzed Anti-Stereoselective Asymmetric Ring-Opening Reactions of Azabenzonorbornadienes with Carboxylic Acids

The first anti-stereoselective asymmetric ring-opening reactions of azabenzonorbornadienes with carboxylic acids have been realized with an iridium catalyst assisted by ^<i>n</i>Bu₄NBr. The reaction features broad substrate scope and good functional group tolerance and allows the synthesis of chiral dihydronaphthalene derivatives with high optical purities

Asymmetric Ring-Opening Reactions of Aza- and Oxa-bicyclic Alkenes with Boronic Acids Using a Palladium/Zinc Co-catalytic System

The asymmetric ring opening reactions of bicyclic alkenes with boronic acids were accomplished by using a highly active palladium/zinc co-catalytic system that was suitable for both azabenzonorbornadienes and oxabenzonorbornadienes, which were transformed to the corresponding chiral hydronaphthalene products in high yields (up to 99%) and high optical purities (up to 98% ee). The reaction protocol is general and mild and displays good functional group tolerance

Rhodium-Catalyzed Asymmetric Cyclization/Addition Reactions of 1,6-Enynes and Oxa/Azabenzonorbornadienes

A mild, efficient, and novel rhodium catalyzed asymmetric cyclization–addition domino reaction of oxa/azabenzonorbornadienes and 1,6-enynes is documented. Through the use of a [Rh­(COD)₂]­BF₄-(<i>R</i>)-An-SDP catalytic system, highly enantioenriched cyclization–addition products were obtained in good yields and with excellent enantioselectivities

Palladium/Silver-Cocatalyzed Tandem Reactions of Oxabenzonorbornadienes with Substituted Arylacetylenes: A Simple Method for the Preparation of 1,2-Diarylethanones and 1,2-Diarylacetylenes

The effective synthesis of 1,2-diarylethanones was achieved using palladium­(II) acetate [Pd­(OAc)₂] and silver triflate (AgOTf) as cocatalysts from various oxabenzonorbornadiene derivatives and substituted arylacetylenes via tandem reactions under mild conditions. Exploration of the oxabenzonorbornadiene substrates showed that the 1,2-diarylacetylenes were obtained from adjacent alkoxy substituted oxabenzonorbornadiene derivatives. Preliminary mechanistic studies indicate that the AgOTf served as an indispensable catalyst, and the mechanism of the tandem reaction was proposed

Protective and Flame-Retardant Bifunctional Epoxy-Based Nanocomposite Coating by Intercomponent Synergy between Modified CaAl-LDH and rGO

Extensive utilization in various settings poses extra requirements of coatings beyond just anticorrosion properties. Herein, 8-hydroxyquinoline (8-HQ) intercalated CaAl-based layered double hydroxide (CaAl-8HQ-LDH) was loaded on reduced GO (rGO) through a one-pot hydrothermal reaction, which was employed as the nanofiller endowing the epoxy (EP/CaAl-8HQ LDH@rGO) with excellent flame-retardancy while ensuring efficient protection for mild steel. Results of electrochemical impedance spectroscopy (EIS) demonstrated the durability of the EP/CaAl-8HQ LDH@rGO-coated specimen, with the impedance at the lowest frequency (|Z|0.01Hz) maintained as 1.84 × 1010 Ω cm2 after 120 days of immersion in a 3.5 wt % NaCl solution. Even for the scratched EP/CaAl-8HQ LDH@rGO system, only a slight decline in |Z|0.01Hz was observed during 180 h of exposure to the NaCl solution, indicating a self-healing feature supported by salt spray tests. UL-94 burning tests revealed the V-0 rating for EP/CaAl-8HQ LDH@rGO with improved thermostability. Strong physical barrier from two-dimensional rGO and the release of 8-HQ from LDH interlayers accounted for the anticorrosive and self-healing properties. However, O2-concentration dilution and charring-layer promotion governed the flame-retardant behavior of the nanocomposite coating. The intercomponent synergy of nanofillers achieved in this work may provide a useful reference for designing multifunctional coatings

Rh-Catalyzed Highly Enantioselective Hydroalkynylation Reaction of Norbornadiene Derivatives

The complexes of various Rh precusors with ferrocenyl chiral ligand (<i>R</i>,<i>S</i>)-Cy₂PF-PPh₂ were found effective catalysts for the asymmetric hydroalkynylation reaction of norbornadiene derivatives. When RhCl₃·3H₂O was employed, good yields (up to 98%) and high enantioselectivities (up to >99.9% <i>ee</i>) could be obtained for the reactions of a broad scope of substrates