PREPARATION AND PROPERTIES OF THREAD-THROUGH COPOLYMERS OF POLYETHYLENE WITH POLYISOPRENE

Graft copolymers of polyethylene (PE) with polyisoprene (PI) were synthesized through polymerization of ethylene in toluene solution of PI (cis-1,4-: 95%; 3,4-: 5%) using a homogeneous V(acac)3/Et3Al2Cl3 catalyst. Copolymers are formed when the growing po

ELECTROCHEMICAL PREPARATION OF MICROELECTRODES MODIFIED WITH NONSTOICHIOMETRIC MIXED-VALENT MOLYBDENUM OXIDES

A blue, conductive, compact, mixed-valent Mo(VI, V) oxide film was grown on carbon fiber (CF) microelectrode surface by cycling the potential between +0.20 and -0.70 V vs. SCE in a fresh prepared Na2MoO4 solution (pH = 2, H2SO4). The thickness of the oxid

PREPARATION AND PROPERTIES OF BACUO2.5 AND ITS RELATED OXIDES

The compound BaCuO2.5 Was obtained using BaO2 and CuO as starting materials, and its various properties were investigated. It belongs to the orthorhombic system with a = 8.55 angstrom, b = 10.56 angstrom, and c = 7.62 angstrom. The p-type semiconductor Ba

STRUCTURE AND PROPERTIES OF MALEATED HIGH-DENSITY POLYETHYLENE

Possible changes in the structure and properties of maleated polyethylene (HDPE-MA) at different degrees of grafting (D.G.) were examined. At the level of 1.6 maleic anhydride (MA)/100 ethylene units E, 70-80% of crystallinity of the parent PE was retaine

Study of Methane Oxidative Coupling over Ti-La-Li Mixed Oxides

The composition and structures of Li-Ti-La mixed oxides as well as their catalytic activity for methane oxidative coupling have been studied by means of XRD XPS, IR, SEM and so on. The results indicate that by changing x value in Li-La1-xTixO2 oxides phas

EFFECT OF IRRADIATION ON CRYSTALLINITY AND MECHANICAL-PROPERTIES OF ULTRAHIGH MOLECULAR-WEIGHT POLYETHYLENE

Ultrahigh molecular weight polyethylene (UHMWPE) has been irradiated (0-40 Mrad) with a Co-60 source at room temperature under vacuum. The crystallinity has been investigated by differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS). The mechanical properties have been determined at room temperature. A significant increase of heat of fusion can be seen at low irradiation doses, which is attributed to crystallization, caused by chain scission during the process of irradiation. It is also observed that the thickness of the lamellae changes with irradiation dose. The Young's modulus has been improved significantly after irradiation at low doses. (C) 1993 John Wiley & Sons, Inc.

A STUDY OF CATALYTIC PROPERTIES OF PEROVSKITE-TYPE OXIDES LAMNYCO1-YO3 .1. THE RELATIONSHIP BETWEEN THE TYPE OF OXYGEN SPECIES AND THE CATALYTIC PROPERTY IN AMMONIA OXIDATION

The type of oxygen species in perovskite-type oxides LaMnyCo1-yO3 (y = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, 1.0) has been studied by means of XRD, XPS and TPD. The catalytic activity in ammonia oxidation was also investigated. It was found that there were three desorption peaks in TPD curve corresponding to three types of oxygen species (alpha, beta, beta'). The desorption temperatures were 293 K less-than-or-equal-to T(alpha) less-than-or-equal-to 773 K, 773 K less-than-or-equal-to T(beta) less-than-or-equal-to K and T(beta') greater-than-or-equal-to 1073 K respectively. The relationship among the composition, structure and the catalytic property of.the catalyst was correlated and could be explainned with a model based on solid defect reaction and the interaction between Co and Mn ions. The adsorption strength and quantity of a oxygen are proportional to the catalytic activity. The, result indicates that the synergetic effect between B-site ions seems to the benefit of the ammonis oxidation reaction.

THE THERMAL-STABILITY OF POLYETHYLENE BLENDS DURING HEAT-PROCESSING AND SHORT-TERM PHOTOOXIDATION

The melt flow behaviour of LDPE/HDPE blends with various compositions have been determined by melt flow index (MFI) measurement. The effects of stabilizers, photo-sensitizers, multiple extrusions and short-term photooxidation have been studied. The results show that there is no marked thermal stability difference between homopolymers and blends without multiple extrusions, no matter whether stabilizers or photo-sensitizers are added. Multiple extrusions or photo-sensitizers reduce their thermal stability, shown by the decrease in MFI. The decrease in MFI of photooxidized samples does not imply serious structural change and shows that the active species formed during photooxidation induce a crosslinking reaction in the melt indexer. Multiple extrusions increase the number of active species formed in LDPE or blends and lead to an obvious decrease in MFI. It is suggested that LDPE and LDPE-rich blends after short-term photooxidation can be characterized by MFI measurement. In contrast, HDPE cannot be characterized by this method due to its linear structure.

RADIATION EFFECTS ON CRYSTALLINE POLYMERS .1. GAMMA-RADIATION-INDUCED CROSS-LINKING AND STRUCTURAL CHARACTERIZATION OF POLYETHYLENE OXIDE

By using WAXD, DSC and gel fraction determination techniques, the mechanism of radiation crosslinking of polyethylene oxide (PEO) was explored, and the dependence of aggregated state on the chemical reaction and physical structure was also discussed. It was found that just like other semi-crystalline polymers, the state of aggregation of the specimen has a profound influence on the radiation effects on PEO. On the contrary, the crystalline structure of the specimen is severely affected with the increase in radiation dose and eventually amorphortized when subjected to an extremely high radiation dose.

A HIGH-RESOLUTION SOLID-STATE NMR-STUDY OF THE MISCIBILITY, MORPHOLOGY, AND TOUGHENING MECHANISM OF POLYSTYRENE WITH POLY(2,6-DIMETHYL-1,4-PHENYLENE OXIDE) BLENDS

An extended Goldman-Shen pulse sequence was used to observe indirectly the proton spin diffusion in the blends of polystyrene (PS) with poly(2,6-dimethyl-1,4-phenylene oxides) (PPO). The results indicate that the average distance between PS and PPO is less than 5 angstrom in the intimately mixed phase, but there are heterogeneous domains on a 100-angstrom scale. The data of spin relaxation of carbons, T1(C), for homopolymers and their blends suggest that there is a strong pi-pi electron conjugation interaction between the aromatic rings of PS and those of PPO, while the aromatic rings of PPO drive the aromatic rings of PS to move cooperatively. It is the cooperative motion that markedly improves the impact strength of PS.

EPITAXIAL CRYSTALLIZATION OF SYNDIOTACTIC POLYPROPYLENE ON UNIAXIALLY ORIENTED POLYETHYLENE

The epitaxial crystallization of syndiotactic polypropylene (sPP) on uniaxially oriented polyethylene (PE) has been investigated by electron microscopy and electron diffraction. It is found that the sPP lamellae grow epitaxially on the PE substrate film with the preference in sPP for the b axis as the fast growth direction. Instead of 50-degrees as in the system of isotactic polypropylene with PE, the molecular chains of the sPP crystals are approximately +/- 37-degrees inclined to the chain direction of PE.

STUDIES ON DEFECT STRUCTURE AND CATALYTIC PROPERTIES OF SN-MO OXIDES

The present work is devoted to the studies on relationship of structure and activity of Sn-Mo oxides by using XRD, ESR, IR, XPS, TEM and SEM. Eight samples with Mo/(Mo + Sn) rations: 0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 0.9, 1.0 were prepared. On the basis of structure characterization, Sn-Mo oxides can be divided into three groups: Catalysts I with Mo/(Mo + So) less-than-or-equal-to 0.2, Catalysts II with 0.2 < Mo/(Mo + Sn) < 0.8, and catalysts III with Mo/(Mo + Sn) greater-than-or-equal-to 0.8. The solid solution of Mo5+ in tin oxide was formed and the cation vacancy was formed in catalysts I. The solid solution of Sn4+ in molybdenum oxide was formed in catalysts III. The lattice oxygen in catalysts III has higher mobility and reactivity than that in catalysts I. The catalysts III showed higher activity but lower selectivity than that of catalysts I.

EPITAXIAL CRYSTALLIZATION OF HIGH-DENSITY POLYETHYLENE ON POLYPROPYLENE IN SOLUTION-CAST FILMS

Epitaxial crystallization of high-density polyethylene (HDPE) on isotactic polypropylene (iPP) in solution-cast films has been investigated by electron microscopy. The specimen-tilt technique of electron microscopy has been used to study the structural relationship between HDPE and iPP crystals. HDPE exhibits different crystalline morphologies in the two basic types of iPP spherulite textures, cross-hatched and lathlike regions. In the former, the crystallographic c axis of HDPE lamellae is in the film plane, while in the latter, the c axis of HDPE crystallites is at an angle of about 50-degrees with the normal of the film. In both structural regions of iPP, however, the contact planes of epitaxial growth are (0 1 0) for iPP and (1 0 0) for HDPE.