Crystallinity in Polymers

Polymers are generally amorphous in nature. However, some of the linear and branched thermoplastics shown in the last lecture could show a partial crystalline form. The presence of crystalline regions analogous to precipitation hardening in metals cause improvement in the mechanical properties. It also affects the optical property of the polymers converting them from transparent to translucent polymers.

The crystallinity of the branched polymers often depend on another interesting characteristics of the polymer called ‘Tacticity’. Tacticity is the way pendant groups are arranged along the backbone chain of a polymer. The figure below shows different types of tacticity in polymers. Atactic polymers are poorly crystalline, while syndiotatctic and isotactic polymers are more crystalline in nature.

Some Highly Crystalline Polymers:

Polypropylene (PP)
Syndiotactic Polystyrene
Nylon
Polyaramids like Kevlar and Nomex

Some Highly Amorphous Polymers

Polymethyl-methacrylate (PMMA)
Atactic Polystyrene
Polycarbonate (PC)
Polyisoprene