Effect of crystallization on the lamellar orientation in thin films of symmetric poly(styrene)-b-poly(L-lactide) diblock copolymer

The effect of crystallization on the lamellar orientation of poly( styrene)-b-poly(L-lactide) (PS-PLLA) semicrystalline diblock copolymer in thin films has been investigated by atomic force microscopy (AFM), transmission electronic microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). In the melt state, microphase separation leads to a symmetric wetting structure with PLLA blocks located at both polymer/substrate and polymer/air interfaces. The lamellar period is equal to the long period L in bulk determined by small-angle X-ray scattering (SAXS). Symmetric wetting structure formed in the melt state provides a model structure to study the crystallization of PLLA monolayer tethered on glassy (T-c < T-g,T-PS) or rubber (T-c > T-g,T-PS) PS substrate. In both cases, it is found that the crystallization of PLLA results in a "sandwich" structure with amorphous PS layer located at both folding surfaces. For T-c <= T-g,T- PS, the crystallization induces a transition of the lamellar orientation from parallel to perpendicular to substrate in between and front of the crystals. In addition, the depletion of materials around the crystals leads to the formation of holes of 1/2 L, leaving the adsorbed monolayer exposure at the bottom of the holes.

Synthesis of fluorene-based oligomeric organoboron reagents via Kumada, Heck, and stille cross-coupling reactions

Boronic pinacol ester group is not reactive in Kumada, Heck and Stille coupling reaction conditions. Fluorene-based sophisticated organoboron compounds were synthesized by means of Palladium catalyzed Kumada, Heck and Stille cross-coupling reactions from halofluorenyl boronic esters.

Formation of a unique crystal morphology for the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer

The crystallization behaviors of the poly(ethylene glycol)-poly(epsilon-caprolactone) diblock copolymer with the PEG weight fraction of 0.50 (PEG(50)-PCL50) was studied by DSC, WAXD, SAXS, and FTIR. A superposed melting point at 58.5 degrees C and a superposed crystallization temperature at 35.4 degrees C were obtained from the DSC profiles running at 10 degrees C/min, whereas the temperature-dependent FTIR measurements during cooling from the melt at 0.2 degrees C/min showed that the PCL crystals formed starting at 48 degrees C while the PEG crystals started at 45 degrees C. The PEG and PCL blocks of the copolymer crystallized separately and formed alternating lamella regions according to the WAXD and SAXS results. The crystal growth of the diblock copolymer was observed by polarized optical microscope (POM). An interesting morphology of the concentric spherulites developed through a unique crystallization behavior. The concentric spherulites were analyzed by in situ microbeam FTIR, and it was determined that the morphologies of the inner and outer portions were mainly determined by the PCL and PEG spherulites, respectively. However, the compositions of the inner and outer portions were equal in the analysis by microbeam FTIR.

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.

Surface morphology evolution of a thin polymeric supramolecular film by tuning interactions

A polymeric supramolecule consisting of symmetric polystyrene-block-poly(4-vinylpytidine) (PS-b-P4VP), dodecylbenzenesulfonic acid (DBSA), and 3-pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology,of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)(1.0)(PDP)(1.0) matrix are observed for the as-cast film because the weight fraction, f(comb), of the P4VP(DBSA) (1.0)(PDP)(1.0) blocks is much higher than that of PS as a result of the non-covalent interactions of P4VP and DBSA and DBSA and PDR Upon annealing the PS-b-P4VP(1:1)(DBSA)(1.0)(PDP)(1.0) film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.

A Monte Carlo simulation for the micellization of ABC 3-miktoarm star terpolymers in a selective solvent

We have used Monte Carlo simulation to study the micellization of ABC 3-miktoarm star terpolymers in a selective solvent (good to A segment, bad to B and C segments). The simulation results reveal that the self-assembled morphology is determined by the block length, molecular architecture, terpolymer concentration and insolubility of insoluble block in the solvent. In dilute solution, symmetric terpolymers (N-B = N-C = 30) tend to aggregate into a novel wormlike pearl-necklace structure linked by an alternating arrangement of B and C spheres, whereas the asymmetric terpolymers (NB = 10, NC = 50) are likely to aggregate into spherical or cylindrical micelles (formed by C blocks) connected with some small B spheres, when the concentration of terpolymer is relatively low (chain number is 100). However, when the concentration of terpolymer is relatively high (chain number is 250), the symmetric terpolymers tend to aggregate into a netlike structure linked by an alternation of B and C spheres, whereas the asymmetric terpolymers are likely to aggregate into wormlike micelles (formed by C blocks) connected with some of small spheres (formed by B blocks). Moreover, when the insolubility of insoluble block in the solvent is weak, the insoluble blocks aggregate into some incompact micelles.

Melt rheological properties of polypropylene-polyarnide6 blends compatibilized with maleic anhydride-grafted polypropylene

The melt rheological properties of binary uncompatibilized polypropylene -polyamide6 (PP-PA6) blends and ternary blends compatibilized with maleic anhydride-grafted PP (PP-PP-g-MAH-PA6) were studied using a capillary rheometer. The experimental shear viscosities of blends were compared with those calculated from Utracki's relation. The deviation value delta between these two series of data was obtained. In binary PP-PA6 blends, when the compatibility between PP and PA6 was poor, the deformation recovery of dispersed PA6 particles played the dominant role during the capillary flow, the experimental values were smaller than those calculated, and delta was negative. The higher the dispersed phase content, the more deformed the droplets were and the lower the apparent shear viscosity. Also, the absolute value of delta increased with the dispersed phase composition. In ternary PP-PP-g-MAH-PA6 systems, when the compatibility between PP and PA6 was enhanced by PP-g-MAH, the elongation and break-up of the dispersed particles played the dominant role, and the experimental values were higher than calculated. It was observed that the higher the dispersion of the PA6 phase, the higher the delta values of the ternary blends and the larger the positive deviation.

Reactive blending of modified polypropylene and polyamide 12: Effects of compatibilizer content on crystallization and blend morphology

The crystallization behavior and morphology of nonreactive and reactive melt-mixed blends of polypropylene (PP) and polyamide (PA12; as the dispersed phase) were investigated. It Was found that the crystallization behavior and the size of the PA12 particles were dependent on the content of the compatibilizer (maleic anhydride-modified polypropylene) because an in situ reaction occurred between the maleic anhydride groups of the compatibilizer and the amide end groups of PA12. When the amount of compatibilizer was more than 4%, the PA12 did not crystallize at temperatures typical for bulk crystallization. These finely dispersed PA12 particles crystallized co-incidently with the 1313 phase. The changes in domain size with compatibilizer content were consistent with Wu's theory. These investigations showed that crystallization of the dispersed phase Could not be explained solely by the size of the dispersion. The interfacial tension between the polymeric components in the blends may yield information on the fractionation of crystallization.

One-pot synthesis of polyetherimides from bis(chlorophthalimide) and dichlorodiphenylsulfone in diphenylsulfone

Polyetherimides and copolymers have been synthesized in one pot from bis(chlorophthalimide), dichlorodiphenylsulfone, and bisphenolate using diphenylsulfone as the solvent. The inherent viscosities of the obtained polyimides are in the range of 0.32-0.72 dL/g, and the structures of polyimides were confirmed by IR and elemental analyses. All of the polyimides have good solubility in common organic solvents. The 5% weight-loss temperatures of the polyimides were 429-507 C in air. The glass transition temperatures (T3) of 4,4'-(9-fluorenylidene) diphenol-based polyimides are in the range of 253-268 degrees C. The Tg of bisphenol A-based polyimides is in the range of 198204 degrees C, while the T-g change inconspicuously when the ratios of diphenylsulfone increase. The wide-angle X-ray diffraction showed that all polyimides prepared are amorphous.

Compatibilization of PP/EPDM blends by grafting acrylic acid to polypropylene and epoxidizing the diene in EPDM

In this article, ethylene-propylene-diene-rubber (EPDM) was epoxidized with an in situ formed performic acid to prepare epoxided EPDM (eEPDM). The eEPDM together with the introduction of PP-g-AA was used to compatibilize PP/EPDM blends in a Haake mixer. FTIR results showed that the EPDM had been epoxidized. The reaction between epoxy groups in the eEPDM and carboxylic acid groups in PP-g-AA had taken place, and PP-g-EPDM copolymers were formed in situ. Torque test results showed that the actual temperature and torque values for the compatibilized blends were higher than that of the uncompatibilized blends. Scanning electron microscopy (SEM) observation showed that the dispersed phase domain size of compatibilized blends and the uncompatibilized blends were 0.5 and 1.5 mu m, respectively. The eEPDM together with the introduction of PP-g-AA could compatibilize PP/EPDM blends effectively. Notched Izod impact tests showed that the formation of PP-g-EPDM copolymer improved the impact strength and yielded a tougher PP blend.

Synthesis of eight-arm polystyrene by atom transfer radical polymerization

A new initiator for atom transfer radical polymerization (ATRP), (Cl2HCCOOCH2)(4)C(TDCAP) was designed and successfully synthesized. The initiator was,used to initiate,the polymerization of styrene via ATRP to method yield an eight-arm polystyrene with functional end-group chlorides. The different polymers could be prepared via ATRP of different monomers at 130 degrees C using TDCAP/CuCl/bPy as the initiating system. The initiator and eight-armed polymer were characterized by means of H-1 NMR, FTIR and GPC.

Polylactide-based polyurethane and its shape-memory behavior

A series of polylactide polyurethanes (PLAUs) were synthesized from poly(L-lactide) diols, hexamethylene diisocyanate (HDI), and 1,4-butanediol (BDO). Their thermal and mechanical properties and shape-memory behavior were studied by infrared spectroscopy (IR), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXID), tensile testing, and thermal mechanical analysis (TMA). The T(g)s of these polymers were in the range of 33-53 degrees C, and influenced by the Mn of the PLA diol and the ratio of the soft-segment to the hard-segment. These materials can restore their shapes almost completely after 150% elongation or twofold compression. By changing the M-n of the PLA diol and the ratio of the hard-to-soft-segment, their Ts and shape-recovery temperatures can be adjusted to the neighborhood of the body temperature. Therefore, these PLAUs are expected to find practical medical applications.

Boundary effect of relief structure on crystallization of diblock copolymer in thin films

In this Letter, crystal growth of a symmetric crystalline-amorphous diblock copolymer, poly(styrene-b-epsilon-caprolactone) (PS-b-PCL), in thin films was investigated by atomic force microscopy (AFM), Relief structures of holes and islands were formed during annealing the film at the molten state, and the in situ observation of subsequent crystal growth at room temperature indicated that the crystals were preferred to occur at the edge of holes or islands and grew into the interior area. It was concluded that the stretched PCL blocks at the edge of relief structures, caused by material transportation or deformation of the interface, could act as nucleation agents during polymer crystallization. The crystal growth rate of individual lamellae varied both from lamellae to lamellae and in time, but the area occupied by crystals increased constantly with time. At 22 degreesC, the growth rate was 1.2 x 10(-2) mum(2)/min with the scan size 2 x 2 mum(2).

Crystallization of weakly segregated poly(styrene-b-epsilon-caprolactone) diblock copolymer in thin films

The surface morphology and crystallization behavior of a weakly segregated symmetric diblock copolymer, poly(styrene-b-6-caprolactone) (PS-b-PCL), in thin films were investigated by optical microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). When the samples were annealed in the molten state, surface-induced ordering, that is, relief structures with uniform thickness or droplets in the adsorbed monolayer, were observed depending on the annealing temperature. The polar PCL block preferred to wet the surface of a silicon wafer, while the PS block wet the air interface. This asymmetric wetting behavior led to the adsorbed monolayer with a PCL block layer having a thickness of around 4.0 nm. The crystallization of PCL blocks could overwhelm the microphase-separated structure because of the weak segregation. In situ observation of crystal growth indicated that the nucleation process preferred to occur at the edge of the thick parts of the film, that is, the relief structures or droplets. The crystal growth rate was presented by the time dependence of the distance between the tip of crystal clusters and the edge. At 22 and 17 degreesC, the average crystal growth rates were 55 +/- 10 and 18 +/- 4 nm/min, respectively.

Simple preparation method of Pd nanoparticles on an Au electrode and its catalysis for dioxygen reduction

A simple method for the fabrication of Pd nanoparticles is described. The three-dimensional Pd nanoparticle films are directly formed on a gold electrode surface by simple electrodeposition at -200 mV from a solution of 1 M H2SO4+0.01 mM K2PdCl4. X-Ray photoelectron spectroscopy verifies the constant composition of the Pd nanoparticle films. Atomic force microscopy proves that the as-prepared Pd nanoparticles are uniformly distributed with an average particle diameter of 45-60 nm. It is confirmed that the morphology of the Pd nanoparticle films are correlated with the electrodeposition time and the state of the Au substrate. The resulting Pd-nanoparticle-film-modified electrode possesses high catalytic activity for the reduction of dissolved oxygen in 0.1 M KCl solution. Freshly prepared Pd nanoparticles can catalyze the reduction of O-2 by a 4-electron process at -200 mV in 0.1 M KCl, but this system is not very stable. The cathodic peaks corresponding to the reduction of O-2 gradually decrease with potential cycling and at last reach a steady state. Then two well-defined reduction peaks are observed at -390 and -600 mV vs. Ag/AgCl/KCl (sat.). Those two peaks correspond to a 2-step process for the 4-electron reduction pathway of O-2 in this neutral medium.