Transparent Aromatic Polyimides Derived from Thiophenyl-Substituted Benzidines with High Refractive Index and Small Birefringence

Abstract

2,2′-Bis­(thiophenyl)­benzidine (BTPB) and 2,2′-bis­(4-chlorothiophenyl)­benzidine (BCTPB) were synthesized via a benzidine rearrangement reaction of the corresponding hydrazobenzene derivatives obtained after the reduction of (3-nitrophenyl)­(phenyl)­sulfane and (4-chlorophenyl)­(3-nitrophenyl)­sulfane, respectively. Transparent polyimides (PIs) with high refractive indices and small birefringences as well as good thermomechanical stabilities were synthesized by the conventional two-step thermal polycondensation of BTPB and BCTPB with five different dianhydrides in N-methyl-2-pyrrolidone. 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA)/BCTPB PI, a fully aromatic and non-fluorinated PI, with a highly distorted noncoplanar conformation of the main chain was transparent and colorless with a transmittance of ∼83% and >88% at 450 nm and in the visible region, respectively. In addition, all six non-fluorinated sulfur-containing aromatic PIs exhibited high average refractive indices (1.7112–1.7339), and small birefringences (0.0007–0.0022) at 633 nm, because of the high atomic polarizability of sulfur and the rigid bulky molecular structure of BTPB and BCTPB. The more effective steric effect caused by bulky 4-chlorothiophenyl in BCTPB improved the optical transparency but decreased the average refractive indices of BCTPB-based PIs compared to BTPB-based PIs.

Synthesis of novel biobased polyimides derived from isomannide with good optical transparency, solubility and thermal stability

“…1 It is also known that conventional aromatic PIs generally exhibit deep color and low optical transparency, as well as poor solution processability, caused by the intra-or intermolecular charge transfer complexes (CTC) formation in their conjugated molecular structures. Considerable progresses have been achieved to synthesize new optically transparent PIs by introducing alicyclic units, [4][5][6] fluorinated, 7-9 chlorinated 10 or sulfurated 11,12 groups, and bulky or twisted rigid moieties 13,14 into PIs, so as to inhibit or reduce the CTC formation. 2,3 The common transparent polymers, such as polyethylene naphthalate (PEN) and polyethylene terephthalate (PET) cannot support the high-temperature processing of those devices, e.g., barrier coating, electrode deposition, and patterning., due to their low T g values (80-150 °C).…”

Effects of alicyclic moiety incorporation on the properties of polyimide/silica hybrid films

“…The silica particles in the polymer matrix would increase the disorder of the polymer chains. In addition, the alicyclic moiety existing on the silica particle surface can weaken the inter‐chain interactions and reduce the chain packaging efficiency to hinder polymer crystallization …”

Recent Trends on Transparent Colorless Polyimides with Balanced Thermal and Optical Properties: Design and Synthesis

“…Synthetic scheme of benzidine monomers BTPB and BCTPB. Reproduced with permission . Copyright 2015, American Chemical Society.…”

“…Ha et al synthesized 2,2′-bis (thiophenyl)benzidine (BTPB) and 2,2′-bis(4-chlorothiophenyl)benzidine (BCTPB) via a benzidine rearrangement reaction of the corresponding hydrazobenzene derivatives obtained after the reduction of (3-nitrophenyl) (phenyl)sulfane and (4-chlorophenyl) (3-nitrophenyl)sulfane, respectively (Scheme 14). [43] T g s of the PIs derived from BCTPB/BTPB were in the range 207−282 °C. In addition, all the six nonfluorinated sulfur-containing aromatic PIs exhibited high average refractive indices (1.7112−1.7339), and small birefringences (0.0007−0.0022) at 633 nm.…”