Surface,thermal and mechanical characteristics of polymeric solids

Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of lateral force microscopic (LFM) and scanning viscoelasticity microscopic (SVM) measurements. SVM measurement revealed that the molecular motion at the surface of the monodisperse polystyrene (PS) film with Mn less than ca.30k was fairly activated compared with that in a bulk region, mainly due to the surface segregation of chain end groups. Temperature dependent LFM and SVM measurement revealed that the surface glass transition temperature, Tg of the monodisperse PS film was lower than the bulk one, even though Mn was fairly large as 140k and also, that the time-temperature superposition was applicable to the surface relaxation process. The chain end group segregation at the air/PS interface was verified from the dynamic secondary ion mass spectroscopic (DSIMS) depth profiling of the proton and deuterium ion for the end-labeled deutrated-PS (dPS) film. These results suggest that the surface Tg is depressed due to an increase in free volume near surface region, being induced by the preferential surface localization of chain end groups.     

Surface aggregation structure and surface mechanical properties of binary polymer blend thin films

During preparation of very thin polymer belnd films from a solution of polymers, the phase‐separated structures which are quite different from that observed for the bulk blend film was observed. From atomic force microscopic(AFM) observation, it is concluded that the surface undulation, which reflects the phase separated morphology of the blend system, is present. In the case of (polystyrene(PS)/poly(methyl methacrylate)(PMMA)) blend system, a large influence of end‐group chemistry on the surface morphology was observed. The phase identification of the (rubbery polymer/glassy polymer) binary blend thin films was successfully achieved by scanning vioscoelasticity microsopy(SVM).     

Effect of glass fiber-matrix polymer interaction on fatigue characteristics of short glass fiber-reinforced poly(butylene terephthalate) based on dynamic viscoelastic measurement during the fatigue process

Fatigue behaviors of glass fiber-reinforced poly(butylene terephthalate) (PBT) were studied based on dynamic viscoelastic measurements during the fatigue process. The fatigue strength of glass fiber-reinforced PBT was greatly improved by strengthening the interfacial adhesion between glass fiber and matrix PBT. The heat generation rate under cyclic fatigue for PBT reinforced with surface-unmodified short glass fiber was always larger than that reinforced with surface-modified short glass fiber because of the large net imposed strain amplitude of PBT matrix which occurred due to the interfacial debonding under cyclic fatigue. A fatigue fracture criterion based on the magnitude of hysteresis energy loss being consumed for a structural change was established for the PBT/short glass fiber composites in consideration of glass fiber-matrix polymer interfacial interaction. © 1994 John Wiley & Sons, Inc.     

Extended RPA with ground-state correlations

We propose a time-independent method for finding a correlated ground state of an extended time-dependent Hartree-Fock theory, known as the time-dependent density matrix theory (TDDM). The correlated ground state is used to formulate the small amplitude limit of TDDM (STDDM) which is a version of extended RPA theories with ground-state correlations. To demonstrate the feasibility of the method, we calculate the ground state of ²² O and study the first 2 ⁺ state and its two-phonon states using STDDM.Received: 7 November 2003, Published online: 10 August 2004PACS: 21.10.Re Collective levels - 21.60.Jz Hartree-Fock and random-phase approximations - 27.30. + t      

Synthetic Strategies for Artificial Lipidation of Functional Proteins

Biosynthesis of natural lipidated proteins is linked to important signal pathways, and therefore analyzing protein lipidation is crucial for understanding cellular functions. Artificial lipidation of proteins has attracted attention in recent decades as it allows modulation of the amphiphilic nature of the protein of interest, and is used in the design of drug-delivery systems containing antibodies anchored on a lipid bilayer carrier. However, the intrinsic hydrophobicity of lipids makes the synthesis of lipid–protein conjugates challenging with respect to the yield and selectivity of the lipidation. In this Minireview, the development of chemical and enzymatic synthetic strategies for the preparation of a range of lipid–protein conjugates that do not compromise the functions of the proteins are discussed as well as applications of the conjugates.     

Diffusion-weighted MRI for the detection of colorectal polyps: feasibility study

The purpose of this study was to determine the feasibility of diffusion-weighted magnetic resonance imaging (DWI) for detecting colorectal polyps. DWI (high b-value of 1000 s/mm²) was prospectively performed in 26 symptomatic patients who were scheduled to undergo colonoscopy. DWI and colonoscopic findings were interpreted in a blinded manner. The sensitivity and positive predictive value (PPV) of DWI for the detection of clinically relevant polyps (≥ 6 mm) and colorectal cancer (CRC) were calculated on a per-lesion basis, using colonoscopy results as the standard of reference. Sensitivity, specificity, PPV and negative predictive value (NPV) on a per-patient basis were also calculated. Sensitivity and PPV on a per-lesion basis were 80.0% [95% confidence interval (CI): 49.0%–94.3%] and 72.7% (95% CI: 43.4%–90.3%) for polyps ≥ 6 mm and CRC. Sensitivity, specificity, PPV and NPV on a per-patient basis were 85.7% (95% CI: 48.7%–97.4%), 84.2% (95% CI: 62.4%–94.5%), 66.7% (95% CI: 35.4%–87.9%) and 94.1% (95% CI: 73.0%–99.0%) for polyps ≥ 6mm and CRC. In conclusion, DWI cannot yet be recommended in a clinical setting in which DWI is performed first and subsequent colonoscopy is only performed in patients with positive findings at DWI. Further (technical) developments are required to increase its diagnostic yield.     

Characterization of catechol‐containing natural thermosetting polymer “urushiol” thin film

Urushi (oriental lacquer) is made from the sap of Rhus vernicifera and consists mainly of the catechol derivative urushiol. Thermal curing of urushiol, unlike other catechol derivatives, is possible because of the unsaturated double bonds in the long hydrocarbon side chain. We described here a simple, efficient method to produce a thermally cross‐linked urushi thin film using iron(II) acetate as the additive. The cured thin films showed robust, flexible feature as confirmed by strain‐induced elastic buckling instability for mechanical measurements (SIEBIMM) and bulging experiments. In contrast, a thin film of poly(dopamine) that is a typical catechol derivative without long hydrocarbon side chain showed brittleness. The long hydrocarbon side chain of urushiol plays an important role for both thermal processability and superior mechanical properties of the material. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3688–3692     

Laboratory and practical synthesis of Suvorexant,a selective dual orexin receptor antagonist

The development of a laboratory and practical synthesis of Suvorexant 1, using intramolecular Mitsunobu cyclization reaction of intermediate 5 as the key reaction, has been reported. Compound 5 was obtained from known chiral ester 2 in three steps, and the key cyclization proceeded smoothly to provide the core seven-membered ring compound 6, which was transformed into 1 by an additional four-step sequence. The procedure described here needs no chiral-HPLC separation, no classical resolution, and no unique enzyme reactions, and offers an alternative practical synthesis of 1.     

Long‐Range Hydrophilic Attraction between Water and Polyelectrolyte Surfaces in Oil

The outstanding water wettability and the capability of polyelectrolyte surfaces to spontaneously clean oil fouling are determined by their wetting mechanism in the surrounding medium. Here, we have quantified the nanomechanics between three types of polyelectrolyte surfaces (i.e. zwitterionic, cationic, and anionic) and water or oil drops using an atomic force microscope (AFM) drop probe technique, and elucidated the intrinsic wetting mechanisms of the polyelectrolyte surfaces in oil and water media. The measured forces between oil drops and polyelectrolyte surfaces in water can be described by the Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) theory. Surprisingly, strong long‐range attraction was discovered between polyelectrolyte surfaces and water drops in oil, and the strongest interaction was measured for the polyzwitterion. This unexpected long‐range “hydrophilic” attraction in oil could be attributed to a strong dipolar interaction because of the large dipole moment of the polyelectrolytes. Our results provide new nanomechanical insights into the development of novel polyelectrolyte‐based materials and coatings for a wide range of engineering, bioengineering, and environmental applications.