stereoregular

Streoregularity, in polymer science, refers to the regularity of the three‑dimensional arrangement of pendant groups along a polymer backbone. When the orientation of substituents along the chain follows a repeating pattern, the polymer is said to be stereoregular. The term is most often applied to polymers with chiral centers or directional substituents whose relative positions can be described as isotactic, syndiotactic, or atactic.

Isotactic polymers have all substituents on the same side of the polymer chain, creating a highly regular structure that often promotes crystallinity. Syndiotactic polymers feature alternating substituent positions along the chain, also favoring regular packing in many cases. Atactic polymers lack a regular pattern of substituent placement, leading to more amorphous materials with typically lower crystallinity and different mechanical properties.

The degree of stereoregularity influences key physical properties such as melting temperature, glass transition temperature, stiffness, transparency, and barrier performance. Isotactic and syndiotactic polymers frequently exhibit higher melting points and better crystallinity than atactic analogs, while atactic forms tend to be more flexible and processable but less crystalline.

Production and analysis: the tacticity of polymers can be controlled by polymerization catalysts and conditions. Ziegler–Natta and metallocene catalysts are commonly used to tailor isotactic or syndiotactic sequences in polyolefins; specific living or coordination polymerization methods can enhance stereoregularity. Techniques such as 13C NMR and differential scanning calorimetry are used to quantify tacticity and assess crystallinity.

Stereoregularity is distinct from regioregularity, which concerns the order of attachment points along the chain, whereas stereoregularity concerns the spatial orientation of substituents.