PLASMA-INDUCED GRAFTING OF STYRENE ONTO NASCENT POLYETHYLENE POWDER

In this paper, the graft copolymers of styrene to nascent linear polyethylene reactor powders were prepared through plasma graft polymerization. The grafting reaction was initiated by the alkyl radicals formed on the surface of nascent polyethylene with plasma treatment as indicated by electron spin resonance spectra. In graft copolymerization by alkyl radicals, the grafting yield increased with either the plasma power or the plasma treatment lime. Compared with ordinary polyethylene powders, nascent polyethylene reactor powders were found to be more easily plasma-grafted. This has been attributed to the greater sensitivity to irradiation in producing reactive centres under the same conditions. High density polyethylene showed almost the same grafting yield as linear low density polyethylene at 50 degrees C. The surface morphology of nascent polyethylene observed by scanning electron microscope before and after the grafting showed that the silk-like fibrils were not destroyed by plasma treatment.

SYNTHESIS OF A POLYETHYLENE-GRAFT-POLYSTYRENE COPOLYMER AND ITS COMPATIBILIZATION FOR LINEAR LOW-DENSITY POLYETHYLENE/POLY(PHENYLENE OXIDE) BLENDS

Based on unsteady diffusion kinetics, polyethylene(PE)-graft-polystyrene (PS) copolymers were designed and synthesized with a heterogeneous high yield titanium-based catalyst by copolymerization of ethylene with a PS-macromonomer using 1-hexene as a short chain agent to promote the incorporation of the PS-macromonomer. The presence of 1-hexene facilitated the diffusion of the PS-macromonomer, giving rise to the significantly increased incorporation of the PS-macromonomer. Compatibilization of blends of linear low density polyethylene (LLDPE)/poly(phenylene oxide) (PPO) with the PE-g-PS copolymer were investigated using scanning electron microscopy (SEM) and dynamic mechanical analysis (DMA).

A DIFFERENTIAL SCANNING CALORIMETRY STUDY OF PLASMA IRRADIATION GRAFTING OF NASCENT POLYETHYLENE REACTOR POWDER

The melting behavior of poly(methyl methacrylate)-grafted nascent polyethylene reactor powder by plasma irradiation was studied by differential scanning calorimetry (DSC). The grafting yield ranged hom 11 to 190%. Grafting was found to lower both melting point and heat of fusion during the first run of DSC determination. The heat of fusion was used to calculate the apparent grafting yield of the samples. There was little strain induced by plasma-irradiated grafting on the surface of the polyethylene crystals. A method to determine the covalent grafting yield in the graft copolymer systems was developed. (C) 1995 John Wiley & Sons, Inc.

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

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

EFFECT OF HYDROPHOBIC OXIDES ON RADIATION CROSS-LINKING OF LOW-DENSITY POLYETHYLENE

Effect of hydrophobic oxide, containing =Si-CH=CH2 groups, on the radiation crosslinking of low density polyethylene (LDPE) has been studied. It was found that mechanical stability of irradiated LDPE containing improved SiO2 is higher than that of samples containing unimproved SiO2.

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.

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.

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.

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.