Polyethene

Polyethene is a very basic plastic, a simple polymer.

Before polymerization, it is built up of Ethene molecules:

    H   H
    |   | 
    C = C
    |   |
    H   H

The angles are somewhat different than shown in ASCII.

(CH2 = CH2) (Two CH2 connected by a double bond?)

In the polymerization process, the [double bonding]? is split up and a macromolecule? is thus created.

    H   H   H
    |   |   |
R - C - C - C - R
    |   |   |
    H   H   H

(R-CH2-CH2-CH2-R)

R indicates that the chain consisting of the same Compound CH2 continues.

Types of polyethene

Their are two main types of polyethene: High Density Poly(ethene) (HDPE) and Low Density Poly(ethene) (LDPE). The main difference between these is the extent of branching? in the polymer chains. LDPE has many branches which means that the chains do not fit well together. It has therefore less strong intermolecular forces as the Instantaneous-dipole induced-dipole attraction is less. This results in a lower density and tensile strength. LDPE is created by free radical polymerization.

HDPE has virtually no branching and thus stronger intermolecular forces and tensile strength. The lack of branching is ensured by the the aid of a Zieglar-Natta catalyst, where the polymer chain actually grows out from the catalyst.