syndiotaktisen

Syndiotaktinen (syndiotactic) is a term used in polymer chemistry to describe a specific type of tacticity in which the substituent groups on successive repeat units alternate orientation along the polymer backbone. Tacticity refers to the stereoregularity of the chain: isotactic polymers have all substituents on the same side, atactic polymers have a random arrangement, and syndiotactic polymers exhibit a regular alternating pattern.

The arrangement influences how polymer chains pack and crystallize. Syndiotactic polymers often show improved crystallinity and distinct thermal and mechanical properties compared with their atactic counterparts. The degree of crystallinity and the resulting properties depend on the monomer and backbone structure. In many cases, specifically engineered syndiotactic polymers exhibit higher melting temperatures and rigidity, while maintaining processability that differs from isotactic versions.

Common examples and synthesis are centered on syndiotactic polystyrene (SPS), a well-studied crystalline polymer, with reports of syndiotactic forms for polypropylene and other vinyl polymers. Synthesis of syndiotactic materials is achieved with catalysts that prefer syndioselective enchainment, including certain rare-earth and metallocene-based systems, as well as specific polymerization conditions. The choice of catalyst and conditions determines the probability of alternating configurations along the chain.

Characterization of tacticity typically uses 13C nuclear magnetic resonance spectroscopy to identify and quantify alternating sequences. Differential scanning calorimetry and X-ray diffraction provide information about crystallinity and phase structure, aiding the correlation between tacticity and material performance.

See also isotactic, atactic, tacticity, polystyrene, polypropylene.