Metallocene Catalysts and Polymers - November 2011

This month we're looking at the topic of metallocene catalysts and polymers.

In order to successfully and profitably manufacture polymers it is very important to make sure that your final product has the properties you want. Relatively small changes in structure can have big impacts on the properties of the final material, and, considering the variety of polymers which can be made from basic monomers, manufacturing these polymers can seem like quite a challenge. However, this kind of production has developed significantly with the discovery that metallocene catalysts can very accurately control the polymerisation process. This includes the stereospecificity during the reaction, therefore the tacticity of the polymer (e.g. syndiotactic or isotactic) and consequently the polymer's properties.

Large-scale manufacturing of polyolefins has benefitted from the use of metallocene catalysts and interest in this area indicates there is progress yet to be made.

Abstracts

Please see below a selection of abstracts highlighted in the November Newsletter. These are records which relate to metallocene catalysts and polymers that have been recently added to the Polymer Library.

Click on the 7-digit accession numbers to find out about ordering a copyright-cleared full text copy of the items shown.

1093888 - COMPARATIVE STUDY OF COPOLYMERIZATION AND TERPOLYMERIZATION OF ETHYLENE/PROPYLENE/DIENE MONOMERS USING METALLOCENE CATALYST
An indene-zirconium chloride catalyst was synthesised and used for the copolymerisation of ethylene and propylene and terpolymerisation of ethylene-propylene and ethyldiene norbornene. Methylaluminoxane was used as cocatalyst. The effects of aluminium:zirconium molar ratio, polymerisation temperature, pressure ratio of ethylene/propylene and the ethyldiene norbornene concentration on the terpolymerisation behaviour were studied. Dynamic mechanical and rheological properties of the polymers were studied. 36 refs.
Journal of Applied Polymer Science, 122, No.3, 5th Nov.2011, p.1838-1846, ISSN: 0021-8995, DOI: 10.1002/app.34251 Mortazavi M; Arabi H; Ahmadjo S; Nekoomanesh M; Zohuri G H

1092403 - OBSERVATION OF DIFFERENT CATALYTIC ACTIVITY OF VARIOUS 1-OLEFINS DURING ETHYLENE/1-OLEFIN COPOLYMERIZATION WITH HOMOGENEOUS METALLOCENE CATALYSTS (Free Access to Full Text)
This research aimed to investigate the copolymerisation of ethylene and various 1-olefins. The comonomer lengths were varied from 1-hexene (1-C6) up to 1-octadecene (1C18) in order to study the effect of comonomer chain length on the activity and properties of the polymer in the metallocene/MAO catalyst system. The results indicated that two distinct cases can be described for the effect of 1-olefin chain length on the activity. Considering the short chain length comonomers, such as 1-hexene, 1-octene and 1-decene, it is obvious that the polymerisation activity decreased when the length of comonomer was higher, which is probably due to increased steric hindrance at the catalytic centre hindering the insertion of ethylene monomer to the active sites, hence, the polymerisation rate decreased. On the contrary, for the longer chain 1-olefins, namely 1-dodecene, 1tetradecene and 1-octadecene, an increase in the comonomer chain length resulted in better activity due to the opening of the gap aperture between Cp(centroid)-M-Cp-(centroid), which forced the coordination site to open more. This effect facilitated the polymerisation of the ethylene monomer at the catalytic sites, and thus, the activity increased. The copolymers obtained were further characterized using thermal analysis, X-ray diffraction spectroscopy and 13C-NMR techniques. It could be seen that the melting temperature and comonomer distribution were not affected by the 1-olefin chain length. The polymer crystallinity decreased slightly with increasing comonomer chain length. Moreover, all the synthesised polymers were typical LLDPE having random comonomer distribution. 31 Refs.
Molecules, 16, No.1, Jan.2011, p.373-383, ISSN: 1420-3049, DOI: 10.3390/molecules16010373
Mingkwan Wannaborworn; Piyasan Praserthdam; Bunjerd Jongsomjit

1092120 - EFFECTIVENESS OF A MALEATED COMPATIBILIZER ON THE TENSILE AND TEAR PROPERTIES OF PEROXIDE-CURED METALLOCENE POLYETHYLENE/CLAY NANOCOMPOSITES
Peroxide-cured metallocene polyethylene (mPE)/ clay nanocomposites were prepared via melt mixing followed by hot press curing. The maleated compatibiliser, mPE grafted maleic anhydride (mPE-g-MA), was incorporated to improve the dispersion of various amounts of commercial organoclay (denoted as 20A). Experimental samples were analyzed using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated that there was an increase in dispersion with the addition of the compatibiliser. A measurable difference in the crystallisation temperature, up to 9.5 degrees C, can be found for cured mPE reinforced with 5 phr clay in comparison cured mPE, indicating the promotion of crystallisation kinetics through the addition of clay moiety. Taking 5 wt% loss as an index of thermal stability, the degradation temperature increased from 375.2 degrees C in cured mPE to 431.2 degrees C in the maleated 5 phrloaded system, the highest improvement in all investigated cases. The Young's Modulus and tear strength of maleated nanocomposites containing the compatibiliser at 9 phr clay content showed the highest values of up to 2 times increment compared those without clay, reflecting the increased interfacial interaction with the exploit of the compatibiliser. 39 Refs.
Journal of Polymer Research, 18, No.5, Sept.2011, p.1033-1042, ISSN: 1022-9760, DOI: 10.1007/s10965-010-9504-3
Sun-Mou Lai; Wen-Chih Chen; Zi Way Wang

1092065 - EFFECT OF MELT VISCOSITY ON THE CRYSTALLIZATION KINETICS OF PRE-SHEARED METALLOCENE POLYETHYLENE MELTS
This work aims to verify the impossibility mentioned in the literature of saturating the crystallisation kinetics of pre-sheared metallocene polyethylene melts. Similarly to results reported for other materials, and contrary to other published works, an acceleration of crystallisation kinetics with the increase of shear strain and its saturation at large strain values was found. Similar strain values, with the same temperature variation, were evaluated with independent experiments using different devices, which allowed us to identify the steady state as the melt state responsible for the saturation of crystallisation kinetics. Since this is a partially disentangled melt state, with viscosity lower than that of fully entangled (relaxed) melts, we assign the acceleration of crystallisation kinetics by application of shear, and its saturation, mainly to the facilitated diffusion of chain segments to the lamellae growth front. This conclusion is supported additionally with the experimental results of other authors. 30 Refs.
Colloid and Polymer Science, 289, No.12, Aug.2011, p.1347-1359, ISSN: 0303-402X, DOI: 10.1007/s00396-011-2451-7
Krakowiak J; Martins J A; Weidong Zhang

1090682 - POLYETHYLENE NANOCOMPOSITES OBTAINED BY IN SITU POLYMERIZATION VIA A METALLOCENE CATALYST SUPPORTED ON SILICA NANOSPHERES
Nanocomposites were prepared by in-situ polymerisation of ethylene using bis(n-butylcyclopentadienyl)zirconium dichloride supported on sol-gel derived silica nanospheres having diameters of 80 to 100 nm. The metallocene catalyst was supported either directly on the nanospheres or on nanospheres pretreated with methylaluminoxane. The effect of zirconium loading on catalytic behaviour, polymer properties and nanosphere dispersion was investigated and compared with homogeneous polymerisation. Nanocomposite dynamic mechanical properties and polymer particle morphology were also investigated. 42 refs.
Macromolecular Reaction Engineering, 5, No.7-8, 11th Aug.2011, p.294-302, ISSN: 1862-832X, DOI: 10.1002/mren.201100013 Zapata P A; Quijada R; Lieberwirth I; Benavente R

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