Thermal,mechanical, and topographical evaluation of nonstoichiometric α-cyclodextrin/poly(ε-caprolactone) pseudorotaxane nucleated poly(ε-caprolactone) composite films

Three pseudorotaxanes (PpR) comprised of poly (ε-caprolactone) (PCL) and α-cyclodextrin (α-CD) with varying stoichiometric ratios were synthesized and characterized. Wide-angle X-ray diffraction (WAXD) and thermogravimetric (TGA) analyses provided conclusive evidence for complexation between the guest PCL and host α-CD. The as-synthesized and characterized PpRs were used at 10 and 20% concentrations as nucleants to promote the bulk PCL crystallization in composite films. Both WAXD and TGA provided evidence for intact PpR structures in the composite films. Isothermal differential scanning calorimetric (I-DSC) analyses, performed at various crystallization temperatures demonstrated significant differences in the crystallization patterns among the composite films. In addition, I-DSC analyses showed higher Avrami constant values (n) in the PpR-nucleated composite PCL films (n ~ 3), indicating 3-dimensional crystal growth. In the case of neat PCL films, however, lower n values indicated crystal growth in 1-dimensions or 2-dimensions. Moreover, atomic force microscopic analyses showed large crests and pits in PpR-nucleated PCL composites, with irregular morphologies leading to higher surface roughness. To the contrary, the crests and pits were much smaller in the neat PCL films, resulting in lower surface roughness values. Finally, mechanical testing revealed higher tensile strength for PpR-nucleated PCL composites films, demonstrating larger load bearing capabilities. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1529–1537     

A Crosslinked Nucleic Acid Nanogel for Effective siRNA Delivery and Antitumor Therapy

Functional siRNAs are employed as cross‐linkers to direct the self‐assembly of DNA‐grafted polycaprolactone (DNA‐g‐PCL) brushes to form spherical and nanosized hydrogels via nucleic acid hybridization in which small interfering RNAs (siRNAs) are fully embedded and protected for systemic delivery. Owing to the existence of multivalent mutual crosslinking events inside, the crosslinked nanogels with tunable size exhibit not only good thermostability, but also remarkable physiological stability that can resist the enzymatic degradation. As a novel siRNA delivery system with spherical nucleic acid (SNA) architecture, the crosslinked nanogels can assist the delivery of siRNAs into different cells without any transfection agents and achieve the gene silencing effectively both in vitro and in vivo, through which a significant inhibition of tumor growth is realized in the anticancer treatment.     

Highly Emissive Fused Heterocyclic Alkynylgold(III) Complexes for Multiple Color Emission Spanning from Green to Red for Solution‐Processable Organic Light‐Emitting Devices

A new class of fused heterocyclic tridentate ligand‐containing alkynylgold(III) complexes with tunable emission color has been successfully designed and synthesized. Structural modification of the σ‐donating fused heterocyclic alkynyl ligands, including substituted fluorene, carbazole, and triphenylamine, enables a large spectral shift of about 110 nm (ca. 3310 cm^?1) that covers the green to red region to be realized with the same tridentate ligand‐containing alkynylgold(III) complexes in solid‐state thin films. Interestingly, the energy of the excimeric emission can be controlled by the rational design of the fused heterocyclic alkynyl ligands. Superior solution‐processable organic light‐emitting devices (OLEDs) with high external quantum efficiencies (EQEs) of 12.2, 13.5, 9.3, and 5.2 % were obtained with green, yellow, orange, and red emission. These high EQE values are comparable to those of the vacuum‐deposited OLEDs based on structurally related alkynylgold(III) complexes.     

Palladium‐Catalyzed Regioselective Aromatic Extension of Internal Alkynes through a Norbornene‐Controlled Reaction Sequence

A regioselective aromatic π‐extension reaction of internal alkynes is reported. The proposed method employs three easily available components, namely aryl halides, 2‐haloarylcarboxylic acids, and disubstituted acetylenes. The transformation is driven by a controlled reaction sequence of C?H activation, decarboxylation, and annulation to give poly(hetero)aromatic compounds in a site‐selective fashion. Unlike in previously reported palladium‐catalyzed three‐component annulations, alkyne carbopalladation is the last step of this tandem reaction.     

Dicobalt octacarbonyl catalyzed carbonylated cycloaddition of triynes to functionalized tetracycles

[reaction: see text]. We have demonstrated that a dicobalt octacarbonyl catalyzed double [2 + 2 + 1] carbonylative cycloaddition reaction of triyne can be carried out to yield a novel 5.5.5.6 tetracyclic di-enone system.     

Rational materials design of sorbent coatings for explosives: applications with chemical sensors

A series of chemoselective polymers had been designed and synthesized to enhance the sorption properties of polymer coated chemical sensors for polynitroaromatic analytes. To evaluate the effectiveness of the chemoselective coatings, a polynitroaromatic vapor test bed was utilized to challenge polymer coated surface acoustic wave (SAW) devices with different explosive vapors. Dinitrotoluene detection limits were determined to be in the <100 parts per trillion ranges. ATR-FTIR studies were used to determine the nature of the polymer-polynitroaromatic analyte interactions, and confirm the presence of hydrogen-bonding between polymer pendant groups and the nitro functional groups of polynitroaromatic explosive materials.     

Structure and thermoelectric properties of the new quaternary bismuth selenides A(1-x)M(4-x)Bi(11+x)Se21 (A = K and Rb and Cs; M = Sn and Pb)--members of the grand homologous series Km(M6Se8)m(M(5+n)Se(9+n))

Several members of the new family A(1-x)M(4-x)Bi(11+x)Se21 (A = K, Rb, Cs; M = Sn, Pb) were prepared by direct combination of A2Se, Bi2Se3, Sn (or Pb), and Se at 800 degrees C. The single-crystal structures of K(0.54)Sn(3.54)Bi(11.46)Se21, K(1.46)Pb(3.08)Bi(11.46)Se21, Rb(0.69)Pb(3.69)Bi(11.31)Se21, and Cs(0.65)Pb(3.65)Bi(11.35)Se21 were determined. The compounds A(1-x)M(4-x)Bi(11+x) Se21 crystallize in a new structure type with the monoclinic space group C2/m, in which building units of the Bi2Te3 and NaCl structure type join to give rise to a novel kind of three-dimensional anionic framework with alkali-ion-filled tunnels. The building units are assembled from distorted, edge-sharing (Bi,Sn)Se6 octahedra. Bi and Sn/Pb atoms are disordered over the metal sites of the chalcogenide network, while the alkali site is not fully occupied. A grand homologous series Km(M6Se8)m(M(5+n)Se(9+n)) has been identified of which the compounds A(1-x)M(4-x)Bi(11+x)Se21 are members. We discuss here the crystal structure, charge-transport properties, and very low thermal conductivity of A(1-x)M(4-x)Bi(11+x)Se21.     

Comparative studies of various run buffers for chiral capillary electrophoresis using chiral crown ether as a chiral selector

In the capillary electrophoretic separation of primary amine enantiomers using (+)-(18-crown-6)-tetracarboxylic acid (18C6H4) as a chiral selector, the presence of run buffer constituents such as tris(hydroxymethyl)aminomethane (Tris) or Na+ competing with analytes for 18C6H4, diminishes the effectiveness of 18C6H4. In order to determine appropriate buffer systems for 18C6H4, various run buffer cationic components including Tris, 1,3-bis[tris(hydroxymethyl)methylamino]propane, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, triethanolamine, tetramethylammonium, and Na+ were compared. Quantitative studies of the effects of the competitive constituents were carried out by measuring the electrophoretic mobilities of histidine as a function of the 18C6H4 concentration. We also derived a simple equation to estimate the optimal chiral selector concentration for a maximum mobility difference in the presence of a competitive inhibitor.     

Analysis of dimensionally stable copolyimide with a low‐level residual stress

Copolyimide thin film, which has low‐level stress and stress relaxation induced by water sorption, was characterized for potential applications as an encapsulant, a stress‐relief buffer, and in interlayer dielectrics. The polyimides examined were poly(p‐phenylene pyromellitimide) (PMDA‐PDA) and poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA) as well as their random copolyimides with various compositions. These copolyimide films exhibited good combinations of physical and mechanical properties with low thermal expansion coefficients, residual stress, and moisture‐induced stress–relaxation behavior by appropriately selecting the ratios of the dianhydride component. For these polyimides, the residual stress increased in the range of −8.1–7.5 MPa, whereas stress relaxation induced by water uptake decreased in the range of 10.3–4.7 MPa with increasing BPDA contents, respectively. The major factor in determining the magnitude of the stress behavior induced by both the thermal mismatch and water uptake in films should be the morphological factors such as chain rigidity, chain orientation, crystallinity, and microvoids. Their morphological structures were examined by wide angle X‐ray diffraction and a prism coupler, and the thermal properties were measured using a dynamic mechanical thermal analyzer as well as thermomechanical analysis. Overall, the candidate for the low level stress buffer application from the PMDA/BPDA‐PDA copolyimide was the 30/70 (= PMDA/BPDA in molar ratio) copolyimide. This copolyimide showed no residual stress after curing at 400 °C and relatively insensitive stress relaxation to ambient humidity. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 796–810, 2001