Editing Polyethylene (section)

=== Polar ethylene copolymers ===
The basic compounds used as polar comonomers are vinyl alcohol ([[Vinyl alcohol|Ethenol]], an unsaturated alcohol), acrylic acid ([[propenoic acid]], an unsaturated acid) and [[ester]]s containing one of the two compounds.

==== Ethylene copolymers with unsaturated alcohols ====
Ethylene/vinyl alcohol copolymer (EVOH) is (formally) a copolymer of PE and vinyl alcohol (ethenol), which is prepared by (partial) hydrolysis of ethylene-vinyl acetate copolymer (as vinyl alcohol itself is not stable). However, typically EVOH has a higher comonomer content than the VAC commonly used.<ref name="Domininghaus">{{cite book|last1=Elsner |first1=Peter|last2=Eyerer |first2=Peter|last3=Hirth|first3=Thomas|title=Domininghaus - Kunststoffe|date=2012 |publisher=Springer-Verlag|location=Berlin Heidelberg |isbn=978-3-642-16173-5|edition=8. |page=224}}</ref>{{rp|239}}

EVOH is used in multilayer films for packaging as a barrier layer (barrier plastic). As EVOH is hygroscopic (water-attracting), it absorbs water from the environment, whereby it loses its barrier effect. Therefore, it must be used as a core layer surrounded by other plastics (like LDPE, PP, PA or PET). EVOH is also used as a coating agent against corrosion at street lights, traffic light poles and noise protection walls.<ref name="Domininghaus" />{{rp|239}}

==== Ethylene/acrylic acid copolymers (EAA)  ====
Copolymer of ethylene and unsaturated carboxylic acids (such as acrylic acid) are characterized by good adhesion to diverse materials, by resistance to stress cracking and high flexibility.<ref>{{cite book|author1=Elsner, Peter |author2=Eyerer, Peter |author3=Hirth, Thomas |title=Kunststoffe Eigenschaften und Anwendungen |date=2012|publisher=Springer Berlin Heidelberg |location=Berlin, Heidelberg|isbn=978-3-642-16173-5 |edition=8.}}</ref> However, they are more sensitive to heat and oxidation than ethylene homopolymers. Ethylene/acrylic acid copolymers are used as [[adhesion promoter]]s.<ref name="Kaiser" />

If salts of an unsaturated carboxylic acid are present in the polymer, thermo-reversible ion networks are formed, they are called [[ionomer]]s. Ionomers are highly transparent thermoplastics which are characterized by high adhesion to metals, high abrasion resistance and high water absorption.<ref name="Kaiser" />