The arrangement of asymmetric molecules along the length of a polymer chain.This is an extremely important concept in polymer stereochemistry.
There are three tacticities. Each tacticity is determined by the arrangement of the
functional groups of each
monomer with respect to one another.
- atactic --------------- random
- isotactic ------------- all on the same side
- syndiotactic --------- alternating
Due to steric effects, the tacticity of a polymer can dramatically affect its ability to form crystals, and thus have an immense impact on its properties. Only isotactic and atactic polypropylene are useful. Most polystyrene is of the atactic variety.
Example
Atactic
R R R R R R R R R R R R R R
-----------------------------------------------------
R R R R R R R R R R R R R
Isotactic
R R R R R R R R R R R R R R R R R R R R R R R R R R R
-----------------------------------------------------
Syndiotactic
R R R R R R R R R R R R R R
-----------------------------------------------------
R R R R R R R R R R R R R