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Tacticity (from Greek: τακτικός, romanized: taktikos, "relating to arrangement or order") is the relative stereochemistry of adjacent chiral centers within a macromolecule. [ 1 ] [ better source needed ] The practical significance of tacticity rests on the effects on the physical properties of the polymer .
In polystyrene, tacticity describes the extent to which the phenyl group is uniformly aligned (arranged at one side) in the polymer chain. Tacticity has a strong effect on the properties of the plastic. Standard polystyrene is atactic.
Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types of tacticity: isotactic (all substituents on the same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents).
A polymer can be described in many ways: its degree of polymerisation, molar mass distribution, tacticity, copolymer distribution, the degree of branching, by its end-groups, crosslinks, crystallinity and thermal properties such as its glass transition temperature and melting temperature.
In some cases, coordination polymerization is also called insertion polymerization or complexing polymerization. Advanced coordination polymerizations can control the tacticity, molecular weight and PDI of the polymer effectively. In addition, the racemic mixture of the chiral metallocene can be separated into its enantiomers.
In addition, by changing the alignment of the monomer within the crystal, the tacticity/stereochemistry of the polymer product could be easily controlled. An intuitive example is shown in the figure. In topochemical polymerization of 1 , 3-diene carboxylic acid derivatives, polymers with four different configurations can be prepared.
Chain shuttling polymerization is a dual-catalyst method for producing block copolymers with alternating or variable tacticity.The desired effect of this method is to generate hybrid polymers that bear the properties of both polymer chains, such as a high melting point accompanied by high elasticity.
For example, the phenyl groups are the pendant groups on a polystyrene chain. Large, bulky pendant groups such as adamantyl usually raise the glass transition temperature (T g) of a polymer by preventing the chains from sliding past each other easily. Short alkyl pendant groups may lower the T g by a lubricant effect.