Synthesis of highly thermoplastic polyamide-imides with high transparency and low coefficient of thermal expansion

With the applications of injection molding optical components, higher requirements are put forward for thermoplastic polyimides (TPIs) in terms of transparency and coefficient of thermal expansion (CTE). Two series of thermoplastic polyamide-imides (PAIs) derived from 2,2'-(2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diyl)bis(1,3-dioxoisoindoline-5-carbonyl chloride) (CT-TFDB) and rigid/flexible aromatic diamines with specific groups were prepared at room temperature, which both exhibited moderate glass transition temperatures (Tgs) in the range of 251–274 °C, excellent dimensional stability with CTE values of 17–34 ppm/K, high transmittance (T450nm ≥ 59%) and good thermoplasticity with -d logE'/dT values of 0.08–0.34. Among them, PAI-2a exhibited the best comprehensive performances, especially for the high thermoplasticity (-d logE'/dT = 0.34), low CTE (28 ppm/K), and high transmittance (T450nm = 84%), which provides a new strategy for the research on thermoplastic PAI materials in optical field. [Display omitted] •Highly thermoplastic PAIs were prepared using CT-TFDB and diamines on the basis of Torlon resin.•The properties of PAIs were adjusted using monomers with -CF3, -SO2- and distorted structure.•The low CTE (28 ppm/K), high transmittance (T450nm = 84%) and thermoplasticity (MFI = 7.5 g/10min) were achieved.•PAIs showed good thermodynamic properties and excellent solubility.