Crystal structures of some common polymers

In the following section examples of the actual crystal structures of some common polymers are given. 

Polyethylene is orthorhombic, with two chains per unit cell. The cell dimensions are a = 0.742, b = 0.495 and c = 0.255 nm. The angle between the plane of the zigzag backbone and the )-axis is approximately 45° and the planes of the two chains passing through the unit cell are at right angles to each other. The chains are almost close-packed, as discussed in section 4.2.3. The structure is shown in fig. 4.17. 

Commercial PVC is very nearly atactic and therefore crystallises only to a very small extent. Syndiotactic PVC, which can be made only by a rather special polymerisation technique, crystallises with an orthorhombic unit cell. Like the unit cell of polyethylene, there are two chains passing through it, but this time they are oriented at 180° to each other, with the planes of both backbones parallel to the -axis. The cell dimensions are a = 1.026, b = 0.524 and c = 0.507 nm. The structure is shown in fig. 4.18. 

PET is a polyester indeed, the word polyester is often used in the textile trade to mean PET. The crystal structure is triclinic, i.e. none of the cell angles is a right angle, and there is only one chain per unit cell. The cell 

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