Lithium Perchlorate-Doped Poly(styrene-<i>b</i>-ethylene oxide-<i>b</i>-styrene) Lamellae-Forming Triblock Copolymer as High Capacitance, Smooth, Thin Film Dielectric

A symmetric poly(styrene-b-ethylene oxide-b-styrene) (SOS) triblock copolymer with block molecular weights (Mn) of 7k−14k−7k was synthesized by anionic polymerization. Various amounts of lithium perchlorate salt ([O/Li] = 3, 6, 12, 24, and 48) were incorporated into the SOS block copolymer to achieve an elevated charge carrier density, which also led to lamellae formation and reduced crystallinity of the poly(ethylene oxide) block according to small-angle X-ray scattering and differential scanning calorimetry. Spin-coated SOS/LiClO4 capacitors of 30 nm thickness exhibit very high capacitances (up to 4.5 μF/cm2 at 10 Hz and 1.5 μF/cm2 at 1000 Hz with an amplitude of 0.1 V) and rather smooth surfaces (root-mean-square roughness of 0.5−2 nm). We expect to optimize these thin-film capacitors for high-performance organic thin film transistor applications

Well-Defined Polyisoprene-<i>b</i>-Poly(acrylic acid)/Polystyrene-<i>b</i>-Polyisoprene-<i>b</i>-Poly(acrylic acid) Block Copolymers: Synthesis and Their Self-Assembled Hierarchical Structures in Aqueous Media

The synthesis and characterization of well-defined polyacid based block copolymers containing polyisoprene (PI) are reported. The challenge of maintaining the integrity of the polydiene while producing polyacid from the tert-butyl ester precursor is addressed in this communication. A general purification method was also developed, taking advantage of the different polarities of each block. The polystyrene-b-polyisoprene-b-poly­(acrylic acid) (PS-b-PI-b-PAA) triblock terpolymers form multicompartmental micelles via aqueous self-assembly. Our work reveals the morphological consequences of unique balances among global and local interactions

Relationships between dental plaque and staining scores and study parameters (<i>n</i> = 222).

<p>Relationships between dental plaque and staining scores and study parameters (<i>n</i> = 222).</p

Poly(ethylene oxide)-Assisted Macromolecular Self-Assembly of Lignin in ABS Matrix for Sustainable Composite Applications

In this effort, we report the compatibilization of biomass-derived lignin polymer in acrylonitrile butadiene styrene (ABS) thermoplastic matrix without loss of mechanical properties via poly­(ethylene oxide) (PEO)-mediated macromolecular self-assembly. ABS was blended with lignin in different concentrations, and blends with 10 wt % PEO (relative to lignin) were prepared. The relative tensile strength improved slightly at low lignin content but diminished rapidly as the lignin content was increased. However, the inclusion of PEO as an interfacial adhesion promoter helped avoid deleterious effects. Dynamic mechanical analysis showed that PEO plasticized the hard phase and thus lowered the activation energy (<i>E</i>_a) for its relaxation but caused stiffening of the soft phase and increased its <i>E</i>_a. Microscopy revealed that incorporating lignin in ABS led to the statistical dispersion of discrete lignin domains (300–1000 nm) which, after PEO addition, were reduced to smaller interconnected particles (200–500 nm). The lignin-extended partially renewable ABS resins showed shear-thinning behavior and reduced viscosity compared to neat ABS. The preferred lignin-loaded compositions reinforced with 20 vol % chopped carbon fibers exhibited mechanical performances (77–80 MPa) equivalent to those of reinforced ABS materials reportedly used in 3D printing applications. This approach could lower the cost of ABS while reducing its carbon footprint

Demographic characteristics, basic denture information, and daily maintenance habits of denture wearers in Xi’an, China (<i>n</i> = 222).

<p>Demographic characteristics, basic denture information, and daily maintenance habits of denture wearers in Xi’an, China (<i>n</i> = 222).</p

Results of stepwise MLRA with denture plaque as the dependent variable (<i>n</i> = 222).

<p>Denture plaque scores were dichotomized using the median (1.67) as a cutoff value (≤1.67, >1.67). Independent variables included duration of denture use, denture wear status, and cleaning and overnight storage methods. Omnibus tests of model coefficients indicated that the χ² value of the logistic regression model was 40.129 and the <i>P</i> value was <0.001.</p

Results of stepwise MLRA with denture staining as the dependent variable (<i>n</i> = 222).

<p>Denture staining scores were dichotomized using the median (0.83) as a cutoff value (≤0.83, >0.83). Independent variables included patients’ gender, smoking status, tea consumption, duration of denture use, denture wear status, and cleaning and overnight storage methods. Omnibus tests of model coefficients indicated that the χ² value of the logistic regression model was 115.239 and the <i>P</i> value was <0.001.</p

Crystallization-Driven Thermoreversible Gelation of Coil-Crystalline Cyclic and Linear Diblock Copolypeptoids

Methanol solutions of cyclic and linear coil-crystalline diblock copolypeptoids [i.e., poly­(N-methyl-glycine)-<i>b</i>-poly­(N-decyl-glycine)] (5–10 wt %) have been shown to form free-standing gels consisting of entangled fibrils at the room temperature. The gelation is thermally reversible and mechanically nonreversible. The gel-to-sol transition at the elevated temperature is induced by the melting of the PNDG crystalline domains which results in the morphological change of the fibrillar network into an isotropic solution. Variable-temperature NMR studies reveal that the cyclic polymer gels have higher gel-to-sol transition temperatures than the linear analogs. The hydrophobic segment is substantially less solvated in the cyclic polymers than the linear analogs both in gel and sol states. Rheological measurements reveal that the cyclic gels are stiffer than the linear counterparts, presumably due to the enhanced crystallinity in the fibrillar network in the formers relative to the latters. This study is the first example of thermoreversible gelation of coil-crystalline block copolymers, where the crystallization of the solvophobic segment has been shown to drive the gelation through the formation of crystalline fibrils

SEM photographs of the etched polished surface of lithium disilicate glass ceramics.

<p>(a) before heat-pressing, (b) heat-pressed at 950°C, (c) heat-pressed at 960°C, (d) heat-pressed at 970°C, (e) heat-pressed at 980°C. Crystal size of ELDC showed a small extent of growth as heat-pressing temperature increased and crystal alignment along the direction of pressing was observed in the heat-pressed specimens.</p

In Situ Formation of Pyridyl-Functionalized Poly(3-hexylthiophene)s via Quenching of the Grignard Metathesis Polymerization: Toward Ligands for Semiconductor Quantum Dots

The synthesis of well-defined, end-functional poly­(3-hexylthiophene)­s (P3HTs) by in situ quenching of the Grignard metathesis (GRIM) polymerization is complicated by the extreme tendency to favor difunctional products in all but a few cases. A facile one-pot method for preparing 2-pyridyl and 3-pyridyl P3HTs with high abundance of monofunctional products is established via an examination of the kinetics of the end-functionalization quenching reaction with lithium chloride complexes of 2- and 3-pyridyl Grignard reagents. Density functional theory calculations guide the selection of pyridine as the end group, which provides the capacity to ligate cadmium selenide (CdSe) nanocrystals and arrests aggregation upon thermal annealing when dispersed in a P3HT matrix. The relative abundances of various end-functional products, as ascertained by high-resolution matrix assisted laser desorption ionization time-of-flight mass spectrometry, can be altered through the use of 1-pentene as an additive: GRIM polymerizations quenched with 3-pyridyl and 2-pyridyl Grignard reagents show 5% and 18% abundances of difunctional, pyridyl-capped P3HTs, respectively, when 1-pentene is present at 1000:1 relative to the nickel catalyst. This represents a significant improvement compared to quenching with aryl Grignard reagents, where difunctional products predominate. The ability to manipulate end group compositions coupled with the propensity of pyridyl-functionalized P3HTs to ligate semiconductor quantum dots (SQDs) opens new possibilities for tuning the morphology of conjugated polymer/SQD blends