Synthesis of High Refractive Index Polyamides Containing Thio-ether Units

Two kinds of new aromatic diamine monomer containing thio-amide unit, bis[4-(p-aminothiophenyl)benzoyl]diamine (ATPBA), were synthesized in two steps, which was reacted with 4,4′-(sulphonyl-bis(p-phenylthio)) dibenzoyl chloride (S-DC) to prepare a new polyamide containing high quantity thio-ether unit. The intrinsic viscosity of PASSA was 0.81–0.93dl/g obtained with optimum synthesis conditions. The polymers were found to have excellent thermal performance with glass transition temperature (Tg) of 245.3–265.8°C, initial degradation temperature (Td) of 446.9–441.6°C. They showed improved solubility in polar aprotic solvents. The optical transmittance of the aromatic polyamide (PA-3a and PA-3b) film at 450 nm is higher than 80%. The thio-ether unit provided the PA-3a and PA-3b with a much higher refractive index ranging from 1.699 to 1.701, and low birefringence between 0.006 and 0.007.