A new type of polymer-supported metallocene catalyst for ethylene polymerization

A new polymer-supported metallocene catalyst has been prepared, The polymer-supported metallocene displayed considerably high activity in ethylene polymerization, the highest being 3.62x10(7) gPE/molZr.h, the molecular weight of the polyethylene produced was Mn = 1.29x10(5). about 3-4 times those of corresponding homogeneous zirconocenes. The polymer-supported metallocene keeps the characteristics of homogeneous metallocene catalysts, and offers some features, such as adaptable to gas phase and slurry processes: easy to prepare in low cost: relatively high activity and lower MAO/Zr ratio; lower inorganic residues in the polyolefins as compared to cases of SiO2, Al2O3 or MgCl2; unitary active structure, no complex surface as with SiO2; good control of morphology of the resulting polymer.

Helical single-lamellar crystals thermotropically formed in a synthetic nonracemic chiral main-chain polyester

Phase structures and transformation mechanisms of nonracemic chiral biological and synthetic polymers are fundamentally important topics in understanding their macroscopic responses in different environments. It has been known for many years that helical structures and morphologies can exist in low-ordered chiral liquid crystalline (LC) phases. However, when the chiral liquid crystals form highly ordered smectic liquid crystal phases, the helical morphology is suppressed due to the crystallization process. A double-twisted morphology has been observed in many liquid crystalline biopolymers such as dinoflaggellate chromosomes (in Prorocentrum micans) in an in vivo arrangement. Helical crystals grown from solution have been reported in the case of Bombyx mori silk fibroin crystals having the beta modification. This study describes a synthetic nonracemic chiral main-chain LC polyester that is able to thermotropically form helical single lamellar crystals. Flat single lamellar crystals can also be observed under the same crystallization condition. Moreover, flat and helical lamellae can coexist in one single lamellar crystal, within which one form can smoothly transform to the other. Both of these crystals possess the same structure, although translational symmetry is broken in the helical crystals. The polymer chain folding direction in both flat and helical lamellar crystals is determined to be identical, and it is always along the long axis of the lamellae. This finding provides an opportunity to study the chirality effect on phase structure, morphology, and transformation in condensed states of chiral materials. [S0163-1829(99)01042-5].

Ring-banded spherulite surface structure of poly(epsilon-caprolactone) in its miscible mixtures with poly(styrene-co-acrylonitrile)

The surface structure of the ring-banded spherulites in polymer blends PCL/SAN (90/10) was studied by optical microscopy, SEM, and TEM, respectively. It is interesting to find that the surface structure of the ring-banded spherulites in polymer blends PCL/SAN (90/10) is made up of the convex bands. The landscape of the convex bands on the surface has been little emphasized before. Radial fibrils are arranged on the bands. Details of the radial fibrils on the bands can be observed by TEM. The landscape of the convex bands on the surface and twisting of lamellae in the convex bands for PCL/SAN blends may be useful to explain the formation mechanism of the ring banded spherulites in polymer blends or even in homopolymers. (C) 1999 John Wiley & Sons, Inc.

Blends of polyamide1010 with unmodified and maleic-anhydride-grafted high-impact polystyrene

The crystallization behaviors, dynamic mechanical properties, tensile, and morphology features of polyamide1010 (PA1010) blends with the high-impact polystyrene (HIPS) were examined at a wide composition range. Both unmodified and maleicanhydride-(MA)-grafted HIPS (HIPS-g-MA) were used. It was found that the domain size of HIPS-g-MA was much smaller than that of HIPS at the same compositions in the blends. The mechanical performances of PA1010-HIPS-g-MA blends were enhanced much more than that of PA1010-HIPS blends. The crystallization temperature of PA1010 shifted towards higher temperature as HIPS-g-MA increased from 20 to 50% in the blends. For the blends with a dispersed PA phase (less than or equal to 35 wt %), the T-c of PA1010 shifted towards lower temperature, from 178 to 83 degrees C. An additional transition was detected at a temperature located between the T-g's of PA1010 and PS. It was associated with the interphase relaxation peak. Its intensity increased with increasing content of PA1010, and the maximum occurred at the composition of PA1010-HIPS-g-MA 80/20. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 857-865, 1999.

Monte Carlo simulation of phase separation of A/B/A-B ternary mixtures

Monte Carlo simulations were used to model A/B/A-B ternary mixtures with different AB diblock copolymer volume fractions for which both the dispersed and continuous phase volume fractions were kept constant. For concentrations of the diblock copolymer below a critical value, the domain size increment of the dispersed phase decreases linearly with the copolymer concentration. This is in agreement with the predictions of Noolandi and Hong. The dependence of the domain size as a function of the copolymer volume fraction can also be fitted by the equation of Tang and Huang. Our simulations indicate, for the first time, that the micelles form before saturation of the interface occurs. This means that the formation of the micelles is not a result of the saturation of the interface.

In-situ microscopic Fourier transform infrared spectroelectrochemistry of redox mechanism for electroactive species in polyelectrolyte

Studies for the development of the in-situ microscopic FTIR spectroelectrochemistry (MFTIRS) have been carried out in polyethylene glycol(PEG) polyelectrolyte, Redox reaction mechanisms of various electroactive substances involving inorganic salt, organic compound and inorganic polymeric particles have been studied.

Preparation of the HIPS/MA graft copolymer and its compatibilization in HIPS/PA1010 blends

The graft copolymer of high-impact polystyrene (HIPS) grafted with maleic anhydride (MA) (HIPS-g-MA) was prepared with melt mixing in the presence of a free-radical initiator. The grafting reaction was confirmed by infrared analyses, and the amount of MA grafted on HIPS was evaluated by a titration method. 1-5% of MA can be grafted on HIPS. HIPS-g-MA is miscible with HIPS. Its anhydride group can react with polyamide 1010 (PA1010) during melt mixing of the two components. The compatibility of HIPS-g-MA. in the HIPS/PA1010 blends was evident. Evidence of reactions in the blends was confirmed in the morphology and mechanical behavior of the blends. A significant reduction in domain size was observed because of the compatibilization of HIPS-g-MA in the blends of HIPS and PA1010. The tensile mechanical properties of the prepared blends were investigated, and the fracture surfaces of the blends were examined by means of the scanning electron microscope. The improved adhesion in a 15% HIPS/75% PA1010 blend with 10% HIPS-g-MA copolymer was detected. The morphology of fibrillar ligaments formed by PA1010 connecting HIPS particles was observed. (C) 1999 John Wiley & Sons, Inc.

Studies on blends of LLDPE and ethylene-methacrylic acid random copolymer

Blends of linear low-density polyethylene (LLDPE) and poly(ethylene-co-methacrylic acid) (EMA) random copolymer were studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and excimer fluorescence. In binary blends, crystallization of EMA was studied, and no modification of crystal structure was detected. In excimer fluorescence measurements, emission intensities of blends of EMA and naphthalene-labeled LLDPE were measured. The ratio of the excimer emission intensity (I-D) to the emission intensity of the isolated "monomer" (I-M) decreases upon addition of EMA, indicating that PE segments of EMA interpenetrate into the amorphous phase of LLDPE. (C) 1998 Published by Elsevier Science Ltd,. All rights reserved.

Studies on blends of LLDPE and polar polymers compatibilized by a random copolymer

Compatibilization of blends of Linear low-density polyethylene (LLDPE)-poly(methyl methacrylate) (PMMA) and LLDPE-copolymer of methyl methacrylate (MMA) and 4-vinylpyridine (poly(MMA-co-4VP) with poly(ethylene-co-methacrylic acid) (EMAA) have been studied. Mechanical properties of the LLDPE-PMMA blends increase upon addition of EMAA. In order to further improve interfacial adhesion of LLDPE and PMMA, 4-vinyl pyridine units are introduced into PMMA chains, or poly(MMA-co-4VP) is used as the polar polymer. In LLDPE-poly(MMA-co-4VP)-EMAA blends, interaction of MAA in EMAA with 4VP of poly(MMA-co-4VP) causes a band shift in the infrared (IR) spectra. Chemical shifts of N-1s binding energy in X-ray photoelectronic spectroscopy (XPS) experiments indicate a transfer of proton from MAA to 4VP. Scanning electron microscopy (SEM) pictures show that the morphology of the blends were improved upon addition of EMAA. Nonradiative energy transfer (NRET) fluorescence results attest that there exists interdiffusion of chromophore-labeled LLDPE chains and chromophore-labeled poly(MMA-co-4VP) chains in the interface. Based on experimental results, the mechanism of compatibilization is studied in detail. Compatibilization is realized through the interaction between MAA in EMAA with 4VP in poly(MMA-co-4VP). (C) 1999 John Wiley & Sons, Inc.

Phase transition temperature of HPT(2,3,6,7,10,11-hexa-n-pentyloxytriphenylene) from molecule dynamic simulation

Molecule dynamics simulation was used on HPT(2,3,6,7,10,11-hexa-n-pentyloxytriphenylene), which is a discotic Liquid crystal. From analyzing the energy and displacement varying with the temperature, the phase transition temperature of PM6MPP can be predicted. The deviations of T-g, T-m and T-i due to the MD time scale are small enough that it should be possibly used to predict the material properties especially when more powerful computers are available.

In-situ microscopic FTIR spectroelectrochemical study of the reduction of K3Fe(CN)(6) in polymer electrolyte

Cyclic voltammetry and in-situ microscopic FTIR spectroelectrochemistry were used for the electrochemical and vibrational characterizations of the reduction process of K3Fe (CN)(6) in polyethylene glycol(PEG) with LiClO4 as supporting electrolyte at a Pt microelectrode. The rate of electron transfer is a function of the concentration of the supporting electrolyte. The redox potentials and cyclic voltammetric currents vary with Li/O molar ratio. The bl-situ spectroelectrochemistry shows that the infrared spectra are influenced by the concentration of LiClO4. The bridging cyanide groups with a structure Fe-I-C drop N ... Fe-I-C drop N are formed during the reduction process of K3Fe (CN)(6). There may be an activated complex between the Lif cation and the complex anion.

The rheological and extrusion behaviour of blends based on phenolphthalein poly(ether-ether-sulfone) and thermotropic liquid crystalline polymer

A novel engineering thermoplastic, phenolphthalein poly (ether-ether-sulfone) (PES-C) was blended with a commercial thermotropic liquid crystalline polymer(TLCP), Vectra A950, up to 30 weight percent of TLCP. A rheometrics dynamic spectrometer (RDS-I) and a CEAST capillary rheometer, a rheoscope 1000 were employed to investigate the melt rheology and extrusion behaviour at both the low and high shearing rates. The morphologies of the blends under different shearing were observed with a scanning electron microscope(SEM) and correlated to the observed rheology. The principal normal stress differences measured with cone-and-plate geometry give a temperature-independent correlation for both blend and PES-C when they are plotted against shear stress. But the extrudate swell of the blends showed a strong temperature dependence at each shear stress. The concentration dependence of extrudate swell shows a contrary behaviour to that of the inorganic filled system. A reasonable hypothesis based on the relaxation and disorientation of TLCP during flowing in the capillary and exiting was given to explain it. The melt fracture was checked after extrusion from capillary and was discussed.

Epitaxial crystallization of sPP on the (100) lattice plane of HDPE crystals

Crystallization behavior of syndiotactic polypropylene(sPP) on the (100) lattice plane of high-density polyethylene(HDPE) crystals was studied by means of transmission electron microscopy and electron diffraction. The results indicate that sPP crystals can grow epitaxially on the (100) PE lattice plane with their chain directions +/-37 degrees apart from the chain direction of the HDPE substrate. The contact planes are (100) lattice planes for both polymers. This kind of epitaxy is explained in terms of parallel alignment of HDPE chains along the rows formed by the {CH3, CH2,CH3} groups in the (100) lattice plane of the sPP crystals. This implies that in the epitaxial crystallization of sPP with fiber oriented HDPE substrate, not only the (110) but also the (100) HDPE lattice planes can act as the oriented nucleation sites. Furthermore, according to the poor matching between HDPE chains in the (100) lattice plane and the {CH3, CH2, CH3} group rows in the (100) lattice plane of the sPP crystals, it is concluded that the geometric matching is not the only controlling factor for the occurrence of polymer epitaxy.

Tremolite-reinforced nylon 66 composites: Mechanical and rheological properties

The reinforcement effect of an acicular inorganic filler, tremolite, on nylon 66 was studied. The mechanical properties of tremolite-filled nylon 66 composites and the effect of the filler particle size on them were obtained. The dynamic mechanical properties and rheological properties of the composites were measured. Two treatments, silane and unsaturated polyester, were used to improve the interface between tremolite and the nylon matrix. The morphologies of the composites were investigated using SEM. (C) 1998 John Wiley & Sons, Inc.