Light-Color Soluble Polyimides Based on α,α′-Bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]-1,3-diisopropylbenzene and Aromatic Dianhydrides

Abstract

A fluorine-containing crystalline diamine, α,α′-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]-1,3-diisopropylbenzene (II), was prepared through nucleophilic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and α,α′-bis(4-hydroxyphenyl)-1,3-diisopropyl in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C. A series of polyimides (PIs) Va–f were then synthesized from this diamine (II) by polymerizing with various commercially available aromatic dianhydrides (pyromellitic dianhydride (PMDA, IIIa), 3,3′,4,4′-benzopheno tetracarboxylic dianhydride (BTDA, IIIb), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA, IIIc), diphenylsulfone-3,3′,4,4′-tetracarboxylic dianhydride (DSDA, IIId), 4,4′-oxydiphthalic anhydride (ODPA, IIIe) and 4,4′-hexafluoro isopropylidenediphthalic anhydride (6FDA, IIIf)) via thermal (H) or chemical (C) imidization methods. The polyimides had inherent viscosities ranging from 0.60 to 0.95 dL/g. Except for the thermal imidization of Vb(H), the V-series polyimides were readily soluble in amide-type solvents, such as N-Methyl-2-pyrrolidone (NMP), N,N-dimethyl acetamide (DMAc), N,N-dimethyl formamide (DMF), and dimethyl sulfoxide (DMSO), and also soluble even in less polar solvents such as m-cresol or pyridine. Most polyimides (film samples) had good tensile strengths of 70 to 110 MPa, elongations at break of 8 to 13% (except for Vc, 37%), and initial moduli of 1.7 to 2.0 GPa. The glass-transition temperatures of V-series polyimides were in 182–202 °C, and had good thermal stability of 10% weight loss temperatures (491–541 °C in nitrogen or 495–537 °C in air), and char yields at 800 °C in nitrogen ranging 46–61 wt %. Except for Va,b series, the V(H) series had cutoff wavelengths between 364.5 to 399.5 nm and the b* (yellowness index) values ranging from 12.7 to 39.5. The polyimides were found to possess low moisture absorption in the range of 0.19–0.91 wt %.