Polyethylene
Ethylene copolymers with unsaturated esters

If unsaturated esters are copolymerized with ethylene, either the alcohol moiety may be in the polymer backbone (as it is the case in ethylene-vinyl acetate copolymer) or of the acid moiety (e. g. in ethylene-ethyl acrylate copolymer). Ethylene-vinyl acetate copolymers are prepared similarly to LD-PE by high pressure polymerization. The proportion of comonomer has a decisive influence on the behaviour of the polymer.

The density decreases up to a comonomer share of 10% because of the disturbed crystal formation. With higher proportions it approaches to the one of polyvinyl acetate (1.17 g/cm). Due to decreasing crystallinity ethylene vinyl acetate copolymers are getting softer with increasing comonomer content. The polar side groups change the chemical properties significantly (compared to polyethylene): weather resistance, adhesiveness and weldability rise with comonomer content, while the chemical resistance decreases. Also mechanical properties are changed: stress cracking resistance and toughness in the cold rise, whereas yield stress and heat resistance decrease. With a very high proportion of comonomers (about 50%) rubbery thermoplastics are produced (thermoplastic elastomers).

Ethylene-ethyl acrylate copolymers behave similarly to ethylene-vinyl acetate copolymers.
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