Polyaramids

Polyaramids are a family of high-performance polymers known for their rigid, aromatic backbone and amide linkages. They are typically divided into para-aramids and meta-aramids, reflecting the position of the amide linkages on the aromatic rings. Notable examples include para-aramids such as Kevlar, Twaron, and Technora, and meta-aramids such as Nomex and TeijinConex.

Para-aramids are distinguished by very high tensile strength and modulus, combined with relatively low density. They offer excellent abrasion resistance and thermal stability, making them well suited for ballistic protection, body armor, and reinforcement in high-strength composites. Meta-aramids, while generally not as strong or stiff as para-aramids, provide superior flame resistance and heat tolerance and are widely used in fire-protective clothing, heat shields, and electrical insulation.

Synthesis typically involves condensation polymerization between diamines and diacid chlorides to form aramide linkages. For para-aramids, terephthaloyl chloride is reacted with para-diaminobenzene, whereas meta-aramids use meta-diaminobenzene with isophthaloyl chloride or related monomers. This chemistry yields fibers and films that resist melting and maintain strength at elevated temperatures, though exposed to extreme UV light they can degrade without stabilization.

Applications span protective gear, aerospace and automotive composites, ropes and cables, and industrial insulation. Key advantages include high strength-to-weight ratio, high stiffness, and flame resistance; limitations include UV sensitivity, processing costs, and sometimes lower impact performance compared with other fiber systems.