Polymer Tacticity Many polymers are generated from monomers which, when polymerized, contribute an asymmetric atom to every repeat unit of the chain. Styrene itself is not chiral, but each repeat unit of the chain acquires a pseudo-chiral atom when it is polymerized to form polystyrene. In this case, what becomes important is the sequence of absolute configurations along the backbone of the chain. The shortest distinguishing piece of the sequence is the diad , or two consecutive absolute configurations. Polymer tacticity, then, is classified according the diad sequence.
Syndiotactic polymer consists entirely of racemic diads.
Syndiotactic polymer typically have very different properties from their isotactic analogues. The most usual case is one where the sequence is random. These polymers, and any polymer in which the sequence of absolute configurations is not highly ordered, is called an Atactic polymer . Three 10-repeat unit segments of polystyrene are illustrated here. Examples of meso diads are highlighted in blue, and examples of racemic diads are highlighted in red.