Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Patent
1996-11-26
2000-03-28
Wu, David W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
5261245, 5261246, 5261247, 5261248, C08F 444
Patent
active
060433264
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for copolymerizing ethene and .alpha.-olefins comprising reacting at least the following components with each other: of groups 4 to 8 of the periodic table of elements, 2 or 3 of the periodic table of elements,
The invention also relates to a catalyst composition for polymerizing olefinic compounds consisting of at least the following components: of groups 4 to 8 of the periodic table of elements, 2 or 3 in the periodic table of elements.
The Ziegler-Natta catalyst system, comprising a "procatalyst" and a "cocatalyst", is generally used for olefin polymerization. A procatalyst is a component based on a transition metal compound in any of groups 4 to 8 of the periodic table of elements (Hubbard, IUPAC 1970). A cocatalyst is a component based on an organometallic compound in any of groups 1 to 3 of the periodic table of elements. Conventional catalytic systems usually also comprise carriers, electron donor compounds and other adjuvants enhancing and modifying catalytic properties.
Currently hundreds of different polyethene qualities are available, most of them having qualitative or other mutual differences. Qualitative differences may be due to the following facts: partly due to long-chained branches, of them risking to be associated with the polymer.
Branching in high-pressure, i.e. low-density polyethene appeared for the first time as polymers were found to contain 20 to 30 methyl groups per 1,000 carbon atoms by means of an IR spectrometer. It ultimately transpired that methyl groups are due to ethyl and butyl secondary groups, formed as the point of growth shifts somewhat backwards in the chain being generated (Back-biting).
However, such short-chained branches do not appear to any notable degree in homopolymers prepared with co-ordinating catalysts.
The appearance of branching in ethene polymers has a significant impact on the crystallisation of polymers, being subsequently reflected in the properties of the polymer. Branched low-density polyethenes (LDPE) have low density (due to high atom crystallisation packing density reduced by branches), low opacity (given that large reflective crystal agglomerations are hampered) and a low melting point yield limit, surface hardness and Young index (all these properties depending on the crystallisation degree). Moreover, with higher branching and lower crystallisation, gas and vapour permeability of the polyethene will be higher. For technical purposes, polyethene density has been chosen as a measure of short branching appearing in polymers.
Alongside short branches, a number of long branches appear in LDPE polymer per polymer molecule. These side chains may be of the same length as the original main chain, resulting in a broad chain length distribution in the same manner as the main chain. Long side chains affect the viscosity of LDPE polymers. Unbranched polymers have higher melt viscosities than long-chained polymers with the same average molecular weight. This is in fact to be expected, because long-chained molecules are more solid, and are not as easily twisted around other molecules as linear polymers.
Lately linear low-density polyethene qualities, called LLDPE qualities, have been developed, being practically totally without long-chained branches, but containing short side chains produced by copolymerization of ethene and a minor amount of .alpha.-olefins (.alpha.-olefin, e.g. 1-hexene, 1-octene and similar). This type of branching hampers polymer crystallisation in the same way as in former LDPE qualities, yielding a low-density product in the way they did. In this conjunction "linear" implies absence of long chains, not short chains.
In the copolymerization of ethene with longer .alpha.-olefins, the comonomers mentioned above tend to be irregularly distributed over the molecule chains. The concrete result of polymerization is a mixture containing polyethene qualities with various densities. In heat-fractioning by means of a TREF analyser, high-density (HDPE), linear low-density (LLDPE) and very low-density (VLDPE) poly
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Iiskola Eero
Koivujarvi Susanna
Palmqvist Ulf
Sillantaka Leona
Borealis Polymers OY
Choi Ling-Siu
Wu David W.
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