PBI
Polybenzimidazole
Glass Transition (Tg)
425–435 °C
Melting Point (Tm)
— (decomposes)
Density
1.30 g/cm³
CAS Number
25928-81-8
Recycling Code
♺ 7
Category
High-Performance
Repeat Unit
–[C₆H₃(NH)₂C–C₆H₄–C(NH)₂C₆H₃]ₙ–
The repeating unit is the smallest structural fragment whose repetition builds the whole chain. Subscripts show the relative share of each unit in copolymers.
Key Properties
Highest Tg of any commercial polymer; does not burn in air; retains useful strength above 400 °C; extremely expensive and hard to process.
Applications
Firefighter turnout gear, aerospace bushings, fuel-cell membranes.