Synthesis and properties of thermoplastic poly(ester-imide)s with low coefficient of thermal expansion and high transparency

Two series of poly(ester-imide)s (PEsIs) were synthesized by varying the molar ratios of the p -phenylene bis(trimellitate anhydride) (TAHQ) or tert -butylhydroquinone bis(trimellitate anhydride) (TA-BHQ) and 4,4′-biphthalic dianhydride ( s -BPDA) to copolymerize with fixed molar ratios of the rigid diamine 2,2′-bis(trifluoromethyl)benzidine (TFDB) and the flexible diamine 2,2′-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]sulfone (6FBAPS) in a two-step process. All of the PEsIs exhibited moderate glass transition temperatures ( T g s) in the range of 232 − 273 ℃, good thermoplasticity with melt flow index (MFI) values of 0.19 − 2.40 g/10 min, excellent dimensional stability with coefficient of thermal expansion (CTE) values of 32.1 − 37.1 ppm/K, and good optical properties ( T 450 of 85 %−86 %, T 850−1550  ≥ 89 %). PEsI-a4 exhibited the best comprehensive properties among the PEsI-a series, particularly with T g of 247 ℃, MFI of 2.40 g/10 min, CTE of 33.4 ppm/K and excellent light transmittance ( T 450 of 86 %, T 850−1550 of 89 %). PEsI-b2 exhibited the best comprehensive properties among the PEsI-b series, particularly with T g of 256 ℃, MFI of 0.87 g/10 min, CTE of 33.3 ppm/K, T 450 of 86 %, T 850−1550 of 89 %. These thermoplastic PEsIs with low CTE and high transparency had potential applications in the field of optical injection molding materials.