isotactic

Isotactic refers to a class of polymers with a uniform stereochemistry along the backbone. In isotactic polymers, substituent groups attached to every repeat unit lie on the same side of the chain. The term is most commonly applied to polypropylene, where all methyl groups are aligned on the same side, in contrast to atactic polymers (random configuration) and syndiotactic polymers (alternating sides).

This regular arrangement promotes crystallization, which increases density, rigidity, and resistance to heat and chemicals. Isotactic polymers tend to have higher melting points and higher degrees of crystallinity than their non-isotactic counterparts. These properties enable higher mechanical strength and dimensional stability, but can reduce processability in some applications compared with amorphous forms.

Isotacticity is achieved with stereoselective polymerization, using catalysts that control the orientation of each added monomer. Ziegler-Natta catalysts and modern metallocene catalysts are capable of yielding isotactic polypropylene from propylene monomers. In contrast, many conventional catalysts produce atactic polymers, and other catalyst systems may favor syndiotactic sequences.

Isotactic polypropylene is the most widely produced isotactic polymer and is used in packaging, automotive parts, textiles, and consumer goods due to its strength, chemical resistance, and recyclability. The term isotactic can also describe other stereoregular polymers, but polypropylene remains the archetype and most commercially important example of an isotactic polymer.