Syntheses and characterizations of high refractive index and low birefringence polyimides containing spirobifluorene in the side chain

• Published in: Polymer (Guilford) Vol. 117; pp. 76 - 83
• Main Authors: Wen, Pushan, He, Rui, Li, Xiang-Dan, Lee, Myong-Hoon
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 19.05.2017; Elsevier BV
• Subjects: Addition polymerization; Birefringence; Chemical synthesis; Dianhydrides; Glass transition temperature; Monomers; Optical materials; Optical properties; Organic solvents; Polyimide resins; Polymerization; Polymers; Refractive index; Refractivity; Spirobifluorene; Substrates; Thermal properties; Thermal stability; Thermodynamic properties; Transparency; Birefringence; Transparency; Spirobifluorene; Refractive index; Thermal stability
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2017.04.020

Two new diamine monomers having a spirobifluorene structure were synthesized through four steps, and polymerized with three different dianhydrides (PMDA, CBDA and 6FDA) to obtain six polyimides with spirobifluorene structure in the side chain. All the resulting polyimides displayed excellent thermal stability and high glass transition temperature. These polyimides synthesized from CBDA and 6FDA showed good solubility in typical organic solvents such as NMP, DMF and DMSO. Transparent and flexible cast films can be obtained from soluble polyimides or poly(amic acid) solution. The transmittance of polyimide films was higher than 90% in the visible wavelength range (higher than 80% in case of polyimide containing PMDA). The refractive indices of the result polyimides were found to be in the range from 1.6343 to 1.7007, which is higher than that of normal polymers. In addition, the optical birefringences of these polyimides were extremely low (0.0005–0.0014). The high refractive index and low birefringence of these polyimides as well as other descent physical and thermal properties would offer them possible applications in high performance optical materials such as flexible substrates. Novel polyimides containing 9,9′-spirobifluorene unit in the side chain, which exhibit high transparency, high refractive index and low birefringence, have been developed as promising candidates for advanced optical applications. [Display omitted] •Novel polyimides containing 9,9’-spirobifluorene unit in the side chain were synthesized.•The polyimides exhibit high thermal stability (T5 > 420 °C) with excellent optical properties such as high transparency (>90% at 400 nm), high refractive index (1.6342–1.7007) and low birefringence (0.0005–0.0014).•The resulting polymer materials could be promising candidates for advanced optical applications.