Nonisotactic

Nonisotactic refers to a type of polymer chain arrangement that is neither isotactic nor syndiotactic. In stereoregular polymers, the stereocenters (chiral carbon atoms) along the polymer backbone can be arranged in specific patterns. Isotactic polymers have all stereocenters with the same configuration (e.g., all R or all S), leading to a highly ordered, crystalline structure. Syndiotactic polymers have stereocenters alternating in configuration (e.g., R-S-R-S), also resulting in a regular, often crystalline, structure.

Nonisotactic polymers, also known as atactic polymers, lack a regular arrangement of stereocenters. The configurations of these chiral centers are essentially random along the polymer chain. This randomness prevents the polymer chains from packing closely and regularly. Consequently, atactic polymers are typically amorphous, meaning they do not exhibit long-range molecular order and do not readily crystallize. Their properties, such as mechanical strength and melting point, are generally different from their isotactic or syndiotactic counterparts, often being softer, more flexible, and having lower melting points or no sharp melting point at all. Many common polymers, such as atactic polypropylene and polystyrene, are produced in their atactic form.