Self-Adapting Peripherally Heterofunctionalized Hyperbranched Polymers: Formation of Janus and Tripodal Structures

A peripherally clickable hyperbranched polyester carrying numerous propargyl terminal groups was prepared by a simple melt transesterification polycondensation of a suitably designed AB(2) monomer; this clickable hyperscaffold was then transformed into a variety of different derivatives by using the Cu-catalyzed azide-yne click reaction. Functionalization of the periphery with equimolar quantities of mutually immiscible segments, such as hydrocarbon, fluorocarbon, and PEG, yielded frustrated molecular systems that readapt and form structures wherein the immiscible segments appear to self-segregate to generate either Janus structures (when two immiscible segments are present) or tripodal structures (when three immiscible segments are present). Evidence for such self-segregation was obtained from a variety of studies, such as differential scanning calorimetry, Langmuir isotherms, AFM imaging, and small-angle X-ray scattering measurements. Crystallization of one or more of the peripheral segments reinforced this self-segregation; the weight-fraction-normalized enthalpies of melting associated with the different domains revealed a competition between the segments to optimize their crystalline organization. When one or more of the segments are amorphous, the remaining segments crystallize more effectively and consequently exhibit a higher melting enthalpy. AFM images of monolayers, transferred from the Langmuir trough, revealed that the thickness matches the expected values; furthermore, contact angle measurements clearly demonstrated that the monolayer films are fairly hydrophobic, and in the case of the tripodal hybramers, the presence of domains of hydrocarbon and fluorocarbon appears to impart nanoscale chemical heterogeneity that is reflected in the strong hysteresis in the advancing and receding contact angles.

Dispersion of polymer grafted nanoparticles in polymer nanocomposite films: Insights from surface x-ray scattering and microscopy

Dispersion of nanoparticles in polymer nanocomposite films determines the application potential of these systems as novel materials with unique physical properties. Grafting polymers to, mostly inorganic, nanoparticles has been suggested as an effective strategy to enhance dispersion and hence the efficacy of materials. In this review, we discuss the various parameters which control dispersion of polymer grafted nanoparticles in polymer nanocomposite films. We discuss how surface x-ray scattering and microscopy can provide complementary and unique information in thin polymer nanocomposite films to unravel the subtle interplay of entropic and surface interactions, mediated by confinement, that leads to enhanced dispersion of the nanoparticles in these films. (C) 2014 AIP Publishing LLC.

New (1R,4R)-2-arylidene-p-menthan-3-ones with a bridging ester group in the arylidene fragment. Synthesis and behavior in liquid-crystalline systems

(1R,4R)-2-(4-Hydroxybenzylidene)- and (1R,4R)-2-(4′-hydroxybiphenyl- 4-yl)methylene-p-menthan-3-ones were synthesized by condensation of (-)-menthone with O-tetrahydropyran-2-yl derivatives of 4-hydroxybenzaldehyde and 4′-hydroxy-4-formylbiphenyl, respectively, in a DMSO - base medium followed by the removal of the protective group. The reactions of these hydroxy derivatives with 4-alkylbenzoic, 4-alkyloxybenzoic, trans-4-alkylcyclohexane-4- carboxylic, and 4′-alkylbiphenyl-4-carboxylic acids afforded three series of new chiral esters. Compounds containing the arylidene moiety with three benzene rings were found to exhibit liquid-crystalline properties. The characteristic features of these compounds are discussed based on the results of studies by polarizing microscopy, differential scanning calorimetry, and small-angle X-ray scattering. It was found that the mesomorphic compounds under study can form a smectic A mesophase, twist grain boundary mesophases (TGBA), and blue phases in a wide temperature range. Upon dissolution of certain of chiral compounds in 4′-cyano-4-pentylbiphenyl, a rather high twisting power and the thermal stabilizing effect on mesophases were observed.

DETERMINATION OF SURFACE-ROUGHNESS OF INP (001) WAFERS BY X-RAY-SCATTERING

The surface roughness of polished InP (001) wafers were examined by x-ray reflectivity and crystal truncation rod (CTR) measurements. The root-mean-square roughness and the lateral correlation scale were obtained by both methods. The scattering intensities in the scans transverse to the specular reflection rod were found to contain two components. A simple surface model of surface faceting is proposed to explain the experimental data. The sensitivities of the two methods to the surface structure and the role of the resolution functions in the CTR measurements are discussed.

X-RAY-SCATTERING FROM A ROUGH-SURFACE AND DAMAGED LAYER OF POLISHED WAFERS

Theoretical and experimental investigations were performed to show the application of x-ray crystal truncation rod scattering combined with x-ray reflectivity in the measurements of surface roughness and near-surface damage of mechanochemically polished wafers. By fitting the measured crystal truncation rod curves it has been shown that polished wafers are divided into three parts -irregular steps on the surface, a damaged thin layer beneath the surface and a perfect bulk. The results show that the root mean square of the surface roughness of mechanochemically polished Fe-doped and/or S-doped InP wafers is one to two atom layers, and that the lateral correlation length of the surface roughness is about 3000-7500 Angstrom. The thickness of the damaged region is found to be about 1000 atom layers.

INPLANE X-RAY-SCATTERING OF EPITAXIAL STRUCTURES

A new approach for in-plane X-ray scattering from the cleavages of epitaxial films or superlattices, where the scattering vectors are parallel to the interfaces, is proposed. This method can be employed to determine directly the in-plane X-ray strains and other atomic registry along the interfaces of the epitaxial structures.

Influence of Annealing on Microstructure and Mechanical Properties of Isotactic Polypropylene with beta-Phase Nucleating Agent

The microstructure and mechanical properties of beta-nucleated iPP before and after being annealed at different temperatures (90-160 degrees C) have been analyzed, Annealing induced different degrees of variation in fracture toughness of beta-nucleated iPP samples. namely, slight enhancement at relatively low annealing temperatures (< 110 degrees C) and great improvement at moderate temperatures (120-130 degrees C), whereas dramatic deterioration at relatively high temperatures ( > 140 degrees C) has been observed. The variation of fracture toughness of beta-nucleated iPP is observed to be dependent on the content of beta-NA. Experiments, including scanning electronic microscope (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamic mechanical analysis (DMA), are performed to study the variations of microstructures as well as the toughening mechanism of the beta-nucleated iPP after being annealed.

Thermal and crystallization behaviors of polyethylene blends synthesized by binary late transition metal catalysts combinations

A series of reactor blends of linear and branched polyethylenes have been prepared, in the presence of modified methylaluminoxane, using a combination of 2,6-bis[1(2,6-dimethyphenylimino) pyridyl]-cobalt(II) dichloride (1), known as an active catalyst for producing linear polyethylene, and [1,4-bis(2,6-diidopropylphenyl)] acenaphthene diimine nickel(II) dibromide (2), which is active for the production of branched polyethylene. The polymerizations were performed at various levels of catalyst feed ratio at 10 bar. The linear correlation between catalyst activity and concentration of catalyst 2 suggested that the catalysts performed independently from each other. The weight-average molecular weights ((M) over bar (w)), crystalline structures, and phase structures of the blends were investigated, using a combination of gel permeation chromatography, differential scanning calorimetry, wide-angle X-ray diffraction, and small angle X-ray scattering techniques. It was found that the polymerization activities and MWs and crystallization rate of the polymers took decreasing tendency with the increase of the catalyst 2 ratios, while melting temperatures (T-m), crystalline temperatures (T,), and crystalline degrees took decreasing tendency. Long period was distinctly influenced by the amorphous component concentration.

The influence of hard-segments on two-phase structure and shape memory properties of PCL-based segmented polyurethanes

Poly(epsilon-caprolactone)-based segmented polyurethanes (PCLUs) were prepared from poly(epsilon-caprolactone) diol, diisocyanates (DI), and 1,4-butanediol. The DIs used were 4,4'-diphenylmethane diisocyanate (MDI), 2,4-toluenediisocyanate (TDI), iso-phorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI). Differential scanning calorimetry, small-angle X-ray scattering, and dynamic mechanical analysis were employed to characterize the two-phase structures of all PCLUs. It was found that HDI- and MDI-based PCLUs had higher degree of microphase separation than did IPDI- and TDI-based PCLUs, which was primarily due to the crystallization of HDI- and MDI-based hard-segments. As a result, the HDI-based PCLU exhibited the highest recovery force up to 6 MPa and slowest stress relaxation with increasing temperature. Besides, it was found that the partial damage in hard-segment domains during the sample deformation was responsible for the incomplete shape-recovery of PCLUs after the first deformation, but the damage did not develop during the subsequent deformation.

Composition dependence of the crystallization behavior and morphology of the poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (M-n = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae.

Investigation on isothermal and non-isothermal crystallization kinetics of poly (epsilon-caprolactone)

The crystallization kinetics and the development of lamellar structure during the isothermal crystallization of poly (epsilon-caprolactone) (PCL) were investigated by means of differential scanning calorimetry (DSC) and real-time synchrotron small angle X-ray scattering (SR-SAXS) techniques, respectively. The Avrami analysis was performed to obtain the kinetics parameters. The value of Avrami index, n, is about 3, demonstrating a three-dimensional spherulitic growth on heterogeneous nuclei in the process of isothermal crystallization. The activation energy and the surface free energy of chain folding for isothermal crystallization were determined according to the Arrhenius equation and Hoffman-Lauritzen theory, respectively. In the process of nonisothermal crystallization of PCL, the value of Avrami index, n, is about 4, which demonstrates a three-dimensional spherulitic growth on homogeneous nuclei. In addition, lamellar parameters were obtained from the analysis of SR-SAXS data.

Influence of annealing on structure of Nylon 11

Differential scanning calorimeter (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and density techniques have been used to investigate the structural parameters of the solid state of Nylon 11 annealed at different temperatures. The equilibrium heat of fusion Delta H-m(0) and equilibrium melting temperature T-m(0) were estimated to be 189.05 J g(-1) and 202.85 degrees C respectively by using the Hoffman-Weeks approach. The degree of crystallinity (W-c,W-x) ranged approximately 24-42% was calculated by WAXD and compared with those by calorimetry (W-c,W-h) and density (W-c,W-d) measurements. The radius of gyration R-g, crystalline thickness L-c, noncrystalline thickness L-a, long period L, semiaxes of the particles (a, b), electron-density difference between the crystalline and noncrystalline regions eta(c) - eta(a), and the invariant Q increased with increasing annealing temperature. The analysis of the SAXS data was based upon the particle characteristic function and the one-dimensional electron-density correlation function. An interphase region existed between the crystalline and noncrystalline region with a clear dimension of about 2 nm for semicrystalline Nylon 11. Instead of the traditional two-phase model, a three-phase model has been proposed to explain these results by means of SAXS.

Miscibility, crystallization kinetics, and morphology of poly(beta-hydroxybutyrate) and poly(methyl acrylate) blends

The miscibility, spherulite growth kinetics, and morphology of binary blends of poly(beta-hydroxybutyrate) (PHB) and poly(methyl acrylate) (PMA) were studied with differential scanning calorimetry, optical microscopy, and small-angle X-ray scattering (SAXS). As the PMA content increases in the blends, the glass-transition temperature and cold-crystallization temperature increase, but the melting point decreases. The interaction parameter between PHB and PMA, obtained from an analysis of the equilibrium-melting-point depression, is -0.074. The presence of an amorphous PMA component results in a reduction in the rate of spherulite growth of PRE. The radial growth rates of spherulites were analyzed with the Lauritzen-Hoffman model. The spherulites of PHB were volume-filled, indicating the inclusion of PMA within the spherulites. The long period obtained from SAXS increases with increased PMA content, implying that the amorphous PMA is entrapped in the interlamellar region of PHB during the crystallization process of PHB. All the results presented show that PHB and PMA are miscible in the melt. (C) 2000 John Wiley & Sons, Inc.