Synthesis and characterization of high refractive index polyimides derived from 2,5-Bis(4-Aminophenylenesulfanyl)-3,4-Ethylenedithiothiophene and aromatic dianhydrides

J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 944-950 This paper presents the synthesis and characterization of a polyimide (PI) series containing a 2,5-bis(4-aminophenylenesulfanyl)-3,4-ethylenedithiothiophene (APSEDTT) unit in polymer main chain. The APSEDTT monomer with high sulfur content was synthesized and polymerized with several aromatic dianhydrides, such as 4,4′-[p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA). All PIs exhibited high transparency and good thermal properties. In addition, the PIs have excellent optical properties in refractive index and birefringence. In particular, APSEDTT-3SDEA showed a high refractive index (1.7586), and a low birefringence (0.0087).

The authors describe the synthesis and characterization of the polyimide (PI) series containing a 2,5-bis(4-aminophenylenesulfanyl)-3,4-ethylenedithiothiophene (APSEDTT) moiety in their main chain. The APSEDTT monomer with high sulfur content was prepared and polymerized with several aromatic dianhydrides such as 4,4′-[p-thio bis(phenylenesulfanyl)]diphthalic anhydride (3SDEA), 4,4′-biphthalic anhydride (BPDA), and 4,4′-oxydiphthalic anhydride (ODPA) by the traditional two-step polycondensation procedure. All PIs exhibited high transparency, higher than 75% at 550 nm for a thickness of about 20 μm and good thermal properties such as thermal decomposition temperatures (T_10%) in the range of 409-521 C. In addition, the PIs have extraordinarily excellent optical properties in refractive index and birefringence as originally designed. In particular, the PI derived from APSEDTT and 3SDEA showed a high refractive index (1.7586), and a low birefringence (0.0087) because of their very high sulfur content (27.7%).