Synthesis and characterization of thioether-containing polyimides with high refractive indices

Abstract

Colorless and transparent polymers with high refractive indices and high temperature resistance have aroused great interest in the industrial community. Here, a series of polyimides (PIs) were prepared from a newly synthesized thioether-containing dianhydride, 1,4-bis(3,4-dicarboxy-phenylenesulfanyl)-benzene dianhydride, and various diamines by a two-step polycondensation reaction. Some flexible and tough films were obtained by casting solutions of them in poly(amic acid) (PAA). The tensile strengths and elongations at break of these PI films were greater than 58 MPa and 10%, respectively. All of them were thermally stable up to 500°C in both air and nitrogen. Their glass transition temperatures were in the range from 204.5 to 265.8°C. PI films with a thickness of 10-20 μm showed good optical transparency in the visible light region. Their cutoff wavelengths were lower than 400 nm and their transmittance was higher than 80% at 460 nm. The thioether linkages in the PIs endowed them with high average refractive indices (n AV ) of 1.68-1.74 and low birefringence values (Δn) of 0.0085-0.0120.

Soluble and transparent polyimides with high Tgs from a new semi-aliphatic diamine with cyclohexyl and ortho-methyl groups

“…[5][6][7][8][9][10] These two drawbacks impede the applications of PIs in microelectronic and optoelectronic engineering. 11,12 Therefore, lots of efforts have been made to overcome above-mentioned problems through the design and modification of PI molecular structures, 13 including introduction of bulky pendent groups (e.g., cyclobutyl and cyclohexyl) to decrease close-packing and intermolecular CT interactions, [14][15][16] flexible linkages (e.g., -O-, -CH 2 -and -S-) to provide kinks in the polymer backbones, [17][18][19] noncoplanar structures to reduce crystallinity and hinder interactions, [20][21][22] and fluorine substituents like trifluoromethyl or perfluoro groups to weaken intermolecular cohesive force and reduce CTC formation. [23][24][25][26][27] However, the approaches to enhance transparency or solubility of PIs are usually contradicted with the demand to keep their good inherent properties, such as excellent mechanical properties, thermal stability and so on.…”

Influence of Chemical Structure on the Refractive Index of Imide‐Type Polymers

“…After an extensive survey of the literature, it could be seen that, among the various substituents incorporated into macromolecular chains, linear thioether linkages, cyclic dibenzothiophene, thianthrene, thiophene, tetrathiaanthracene, pyridine and pyridazine, thiazole, sulfonyl (SO 2 ), selenophene, fluorene, bromine, chlorine, and fluorine units have significant influences on the value of refractive index of polyimides.…”