Polymer-supported zirconocene catalyst for ethylene polymerization

The use of crosslinked poly(styrene-co-4-vinylpyridine) having functional groups as the support for zirconocene catalysts in ethylene polymerization was studied. Several factors affecting the activity of the catalysts were examined. Conditions like time, temperature, Al/N (molar ratio), Al/Zr (molar ratio), and the mode of feeding were found having no significant influence on the activity of the catalysts, while the state of the supports had a great effect on the catalytic behavior. The activity of the catalysts sharply increased with either the degree of crosslinking or the content of 4-vinylpyridine in the support. Via aluminum compounds, AlR3 or methylaluminoxane (MAO), zirconocene was attached on the surface of the support. IR spectra showed an intensified and shifted absorption bands of C-N in the pyridine ring, and a new absorption band appeared at about 730 cm(-1) indicating a stable bond Al-N formed in the polymer-supported catalysts. The formation of cationic active centers was hypothesized and the performance of the polymer-supported zirconocene was discussed as well. (C) 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 37-46, 1999.

Poly(ethylene glycol)-block-poly(butyl acrylate). II. Characterization and properties

Poly(ethylene glycol)-block-poly(butyl acrylate) synthesized by radical polymerization in a one-step procedure were characterized by gel permeation chromatography, infrared, IH-NMR spectroscopy, and differential scanning calorimetry (DSC). The crystalline property, emulsifying property, and phase transfer catalytic effect in the Williamson reaction were studied. It was found that the crystallinity of the copolymer increased with an increase in both the content and molecular weight of poly( ethylene oxide) (PEO) sequences. DSC curves showed two distinct crystallization temperature due to the heterogeneous nucleation and homogeneous nucleation crystallization. The casting solvent significantly affected the morphology and crystallinity of the solvent cast films. Both the emulsifying volume and the phase transfer catalytic efficiency in the Williamson reaction increased with the amount and PEO content of the block copolymers used, but decreased with an increase in the molecular weight of PEO sequences. (C) 1998 John Wiley & Sons, Inc.

Thermodynamics of blends of poly(ethylene oxide) with poly(methyl methacrylate) and poly(vinyl acetate): prediction of miscibility based on Flory solution theory modified by Hamada

Flory solution theory modified by Hamada et al. (Macromolecules, 1980, 13, 729) was used to predict the miscibility of blends of poly(ethylene oxide) with poly(methyl methacrylate) (PEO-aPMMA) and with poly(vinyl acetate) (PEO-PVAc). Interaction parameters of a PEO-aPMMA blend with the weight ratio of PEO/aPMMA = 50/50 at the temperature range of 393-433 K and PEO-PVAc blends with different compositions and temperatures were calculated from the determined equation-of-state parameters based on Flory solution theory modified by Hamada ed al. Results show that interaction parameters of the PEO-aPMMA blend are negative and can be comparable with values obtained from neutron-scattering measurements by Ito et al. (Macromolecules, 1987, 20, 2213). Also, interaction parameters and excess volumes of PEO-PVAc blends are negative and increase with enhancing the content of PEO and the temperature. (C) 1998 Elsevier Science Ltd. All rights reserved.

Study on a comb-like polymer electrolyte based on the backbone of ethylene-maleic anhydride copolymer

A comb-like polymer host(CBPE) as polymer electrolyte was synthesized by reacting poly(ethylene glycol) monomethyl ether (PEGME) with ethylene-maleic anhydride copolymer(EMAC) and endcapping the residual carboxylic acid with methanol. The synthetic process was followed by IR and the amorphous product characterized by IR and elemental analysis. There were two peaks in the plot of the ionic conductivity against Li salt concentration. The plot of log sigma vs. 1/(T - T-0) may exhibit dual VTF behavior when using the glass transition temperature of PEO of side chain as T-0. The comb-like polymer is a white rubbery solid which dissolves in acetone. (C) 1998 Elsevier Science B.V. All rights reserved.

Toughening of nylon with epoxidised ethylene propylene diene rubber

Blends of nylon-6 and epoxidised ethylene propylene diene (eEPDM) rubber were prepared through reactive mixing. It is found that the toughness of nylon-6 can be much improved by this method, and that the particle size of eEPDM is much smaller than that of unexpoxidised EPDM (uEPDM) rubber in a nylon-6 matrix. This indicates that the epoxy group in eEPDM could react with a nylon-6 end group to form a graft copolymer which could act as an interfacial compatibiliser between the nylon-6 and the eEPDM rubber dispersed phase. (C) 1998 Elsevier Science Ltd. All rights reserved.

The crystallization behavior of the metastable melts of poly(ethylene terephthalate) from the multiple melting process

During heating of semicrystalline PET, a metastable melt forms far below the equilibrium melting temperature. Crystallization kinetics of this metastable melt is discussed on the basis of DSC results. From the metastable melt almost one-dimensional growth of the crystal occurs through heterogeneous nucleation.

High resolution solid-state NMR and DSC study of poly(ethylene glycol) silicate hybrid materials via sol-gel process

Hybrid materials incorporating poly(ethylene glycol) (PEG) with tetraethoxysilane (TEOS) via a sol-gel process were studied for a wide range of compositions of PEG by DSC and high resolution solid-state C-13- and Si-29-NMR spectroscopy. The results indicate that the microstructure of the hybrid materials and the crystallization behavior of PEG in hybrids strongly depend on the relative content of PEG. With an increasing content of PEG, the microstructure of hybrid materials changes a lot, from intimate mixing to macrophase separation. It is found that the glass transition temperatures (T-g) (around 373 K) of PEG homogeneously embedded in a silica network are much higher than that (about 223 K) of pure PEG and also much higher in melting temperatures T-m (around 323 K) than PEG crystallites in heterogeneous hybrids. Meanwhile, the lower the PEG content, the more perfect the silica network, and the higher the T-g of PEG embedded in hybrids. An extended-chain structure of PEG was supposed to be responsible for the unusually high T-g of PEG. Homogeneous PEG-TEOS hybrids on a molecular level can be obtained provided that the PEG. content in the hybrids is less than 30% by weight. (C) 1998 John Wiley & Sons, Inc.

Preparation and characterization of a new blend of poly(2-hydroxyethyl methacrylate) and poly(ethylene glycol)

A new blend of poly(2-hydroxyethyl methacrylate) (PHEMA) with poly (ethylene glycol) (PEG) was prepared. The results from solid-state NMR indicate that the PHEMA/PEG(88:12, w/w) blend is miscible on a molecular level.

Thermal analysis of ethylene propylene copolymer-grafted-acrylic acid

The thermal properties of ethylene propylene copolymer-grafted-acrylic acid (EP-g-AA) were investigated by using differential scanning calorimetry (DSC). Compared with the ethylene propylene copolymer (EP), the peak values of the melting temperature (T-m) of the propylene sequences in the grafted EP changed a little, the crystallization temperature (T-c) increased about 8-12 degrees C, and the melting enthalpy (Delta H-m) increased about 4-6 J/g. The isothermal crystallization kinetics of grafted and ungrafted samples was carried out by DSC. Within the scope of the researched crystallization temperature, the Avrami exponent (n) of the ungrafted sample was 1.6-1.8, and that of grafted samples were all above 2, which indicated that the grafted monomer could become the crystal nuclei for the crystallization of propylene sequence. With increasing grafted monomer content, the crystallization rate of propylene sequence in grafted EP increased; it might be the result of rapid nucleation rate and crystal growth rate.

Polymerization of ethylene by zirconocene-B(C6F5)(3) catalysts with aluminum compounds

Ethylene polymerization by zirconocene-B(C6F5)(3) catalysts with various aluminum compounds has been investigated. It is found that the catalytic activity depended on zirconocenes used, and especially on the type of aluminum compounds. For Et(H(4)Ind)(2)ZrCl2 (H(4)Ind : tetrahydroindenyl), the activity decreases in the following order: Me3Al > i-Bu3Al > Et3Al much greater than Et2AlCl. While for Cp2ZrCl2(Cp : cyclopentadienyl), it varies as follows: i-Bu3Al > Me3Al much greater than Et3Al. Furthermore, the activity is significantly affected by the addition mode of the catalytic components, which may imply that the formation of active centers is associated with an existing concentration of catalytic components. Results of thermal behavior of polyethylene (PE) studied by differential scanning calorimetry(DSC) show that crystallinity of the polymer prepared with Et3Al is higher than that with Me3Al or i-Bu3Al. It is also found that the number-average molecular weight ((M) over bar) of the polymers prepared with Me3Al or i-Bu3Al is much higher than that with Et3Al. H-1-NMR studies substantiate that i-Bu3Al is a more efficient alkylation agent of Cp2ZrCl2 in comparison with Me3Al. (C) 1997 John Wiley & Sons, Inc.

Toughened blend of polycarbonate and epoxidized ethylene propylene diene rubber

A super-tough polycarbonate (PC) blend was obtained by using epoxidized ethylene propylene diene (eEPDM) rubber as modifier. The notched Izod impact strength of PC/eEPDM (96/4) blend shows a great improvement, with a value about 25 times of that of pure PC. Finely and homogeneously dispersed rubber particles (0.2-0.8 mu m) in the PC matrix indicated good adhesion between the eEPDM rubber phase and the PC matrix. (C) 1997 Elsevier Science Ltd.

In situ epoxidation of ethylene propylene diene rubber by performic acid

In this paper, epoxidation of ethylene propylene diene rubber by in situ generated performic acid is discussed. The samples have been characterized by infra-red and H-1-nuclear magnetic resonance analyses. Quantitative analysis of the reaction products is made possible by using the methyl deformation band at 1377 cm(-1) as internal standard. The conversion of double bonds increases rapidly within the first 1 h, then gradually, over 2 h, has only a slight increase. The maximum conversion ratio of double bonds is about 70%. The relative content of epoxy groups has a top value at about 7 h. The side reactions are also discussed. (C) 1997 Elsevier Science Ltd.

Poly(ethylene glycol) block poly(butyl acrylate) .1. Synthesis

Prepolymers of poly(ethylene oxide) (Pre-PEG) were synthesized by reacting azoisobutyronitrile (AIBN) with poly(ethylene glycol) (PEG), and their structures were characterized by IR and UV. The molecular weight of pre-PEG was related to the feed ratio and reaction time. These prepolymers can be used to prepare block copolymers - poly(ethylene oxide)-block-poly(butyl acrylate) (PEO-b-PBA) by radical polymerization in the presence of butyl acrylate (BA). Solution polymerization was a suitable technique for this step. The yield and the molecular weight of the product were related to the ratio of the prepolymer to BA, the reaction time, and temperature. GPC showed that the molecular weight increased with a higher ratio of BA to pre-PEO. The intrinsic viscosity of the copolymers was only slightly dependent on reaction time, but decreased at higher reaction temperatures, as did the amount of PEA homopolymer. (C) 1997 John Wiley & Sons, Inc.

Studies on water-swellable elastomers .2. Thermal properties and crystalline behavior of amphiphilic graft copolymers with poly(ethylene glycol) side chains

The thermal properties and crystalline structure of the amphiphilic graft copolymers CR-g-PEG600, CR-g-PEG2000, and CR-g-PEG6000 using chloroprene rubber (CR) as the hydrophobic backbone and poly(ethylene glycol) (PEG) with different molecular weights as the hydrophilic side chains were studied by DSC and WAXD. The results showed that a distinct phase-separated structure existed in CR-g-PEGs because of the incompatibility between the backbone segments and the side-chain segments. For all the polymers studied, T-m2, which is the melting point of PEG crystalline domains in CR-g-PEG, decreased compared to that of the corresponding pure PEG and varied little with PEG content. For CR-g-PEG600 and CR-g-PEG2000, T-m1, which is the melting point of the CR crystalline domains, increased with increasing PEG content when the PEG content was not high enough, and at constant PEG content, the longer were the PEG side chains the higher was the T-m1. The crystallite size L-011 of CR in CR-g-PEGs increased compared to that of the pure CR and decreased with increasing PEG content. (C) 1997 John Wiley & Sons, Inc.

Characterization of propylene/ethylene copolymers sequentially polymerized with delta-TiCl3/Et2AlCl catalyst system

Morphological studies of a series of propylene/ethylene sequential polymers have been carried out by permanganic etching and transmission electron microscopy, as an aid to characterization, in conjunction with differential scanning calorimetry. The materials were synthesized using a titanium-based catalyst, with propylene and either ethylene or ethylene/propylene mixture introduced successively, with the aim of examining whether a proportion of block copolymer is obtained. These materials show a complicated phase structure which does not simply reflect polymerization time but varies greatly, especially in regard to the order of introduction of the monomers, and their morphology differs in a number of ways from that of typical commercial materials. Comparison of the materials, as synthesized and after extraction with heptane, suggests that there is a certain amount of material which can compatibilize polypropylene- and ethylene-rich phases, but it was not possible to decide whether it does in fact have block structure.