Tacticity in Vinyl Polymers

AbstractVarious issues of tacticity in vinyl polymers are discussed. First, tacticity is defined and the concepts of tactic forms in polymers as a stereoregular configuration order are introduced, and illustration schemes for common polymer tacticity are shown. Effects of tacticity in polymer structures on crystalline morphology and property are briefly discussed. Several commercially useful tactic polymers are examined, by using examples of vinyl‐type polymers such as tactic polypropylene (PP), polystyrene (PS), and poly(methyl methacrylate) (PMMA). Catalysts and synthesis routes for producing stereoregular tactic polymers are discussed mainly using PMMA as an example. Tacticity in polymers is related to differences in microstructures, morphology, crystalline polymorphism, and physical/mechanical properties. Tactic polymers possess structural order and are to crystallize. Tacticity and crystalline properties of polymers are discussed. Crystal polymorphism in some tactic polymers, such as syndiotactic polystyrene (s‐PS), is discussed in greater detail. Complex formation in mixtures of polymers of opposite tacticities, just like mixtures of polymers of opposite chiral forms, has been reported. Complex formation in mixtures of polymers of opposite (s‐ and i‐tacticity) is discussed using examples of isotactic PMMA (i‐PMMA) and syndiotactic PMMA (s‐PMMA); on the other hand, complex formation of mixtures of other tactic polymers, such as i‐PS/s‐PS or i‐PP/s‐PP, is not known. Effects of tacticity on the miscibility and phase behavior in blends of tactic polymers with other polymers are surveyed and expounded. Blends of polymers of same chemical structure but opposite tacticities are not always miscible, as exemplified in a blend of nonpolar and highly crystalline s‐PP with i‐PP, showing immiscibility with upper critical solution temperature behavior but a‐PP being miscible with s‐PP or i‐PP. In addition, phase behaviors of binary blends of two isomeric polymers are addressed. In blends with weak interactions and borderline phase homogeneity, the tacticity effect on miscibility is usually more pronounced; in contrast, the effect on the phase behavior may be minimal in systems with strong intermolecular interactions.