Editing Polyethylene (section)

=== Non-polar ethylene copolymers ===

==== α-olefins ====
In the low pressure process [[Alpha-olefin|α-olefins]] (e.g. [[1-Butene|1-butene]] or [[1-Hexene|1-hexene]]) may be added, which are incorporated in the polymer chain during polymerization. These copolymers introduce short side chains, thus [[crystallinity]] and [[density]] are reduced. As explained above, mechanical and thermal properties are changed thereby. In particular, PE-LLD is produced this way.

==== Metallocene polyethylene (PE-MC) ====
Metallocene polyethylene (PE-M) is prepared by means of [[metallocene catalysts]], usually including copolymers (z. B. ethene / hexene). Metallocene polyethylene has a relatively narrow [[molecular weight distribution]], exceptionally high toughness, excellent optical properties and a uniform comonomer content. Because of the narrow molecular weight distribution it behaves less pseudoplastic (especially under larger shear rates). Metallocene polyethylene has a low proportion of low molecular weight (extractable) components and a low welding and sealing temperature. Thus, it is particularly suitable for the food industry.<ref name="Kaiser" />{{rp|238}}<ref name="Vasile">{{cite book|last1=Pascu|first1=Cornelia Vasile: Mihaela|title=Practical guide to polyethylene|date=2005|publisher=Rapra Technology Ltd.|location=Shawbury|isbn=978-1859574935|edition=[Online-Ausg.].}}</ref>{{rp|19}}

====Polyethylene with multimodal molecular weight distribution====
Polyethylene with multimodal molecular weight distribution consists of several polymer fractions, which are homogeneously mixed. Such polyethylene types offer extremely high stiffness, toughness, strength, stress crack resistance and an increased crack propagation resistance. They consist of equal proportions higher and lower molecular polymer fractions. The lower molecular weight units crystallize easier and relax faster. The higher molecular weight fractions form linking molecules between crystallites, thereby increasing toughness and stress crack resistance. Polyethylene with multimodal molecular weight distribution can be prepared either in two-stage reactors, by catalysts with two active centers on a carrier or by blending in extruders.<ref name="Kaiser" />{{rp|238}}

==== Cyclic olefin copolymers (COC) ====
[[Cyclic olefin copolymer]]s are prepared by copolymerization of ethene and [[cycloolefin]]s (usually [[norbornene]]) produced by using metallocene catalysts. The resulting polymers are amorphous polymers and particularly transparent and heat resistant.<ref name="Kaiser" />{{rp|239}}<ref name="Vasile" />{{rp|27}}