Film shrinkage inducing strong chain entanglement in fluorinated polyimide. (26th June 2015)

• Record Type: Journal Article
• Authors: Kim, Gahee; Byun, Sunjung; Yang, Yooseong; Kim, Sangmo; Kwon, Soonchul; Jung, Youngsuk
• Is Part Of: Polymer. Volume 68(2015)
• Page Start: 293
• Page End: 301
• Publication Date: 2015-06-26
• Subjects: Fluorinated polyimide -- Entanglement -- Film shrinkage; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; 547.7
• DOI: 10.1016/j.polymer.2015.05.038
• Languages: English
• ISSNs: 0032-3861

Abstract

Abstract: Toughness and high elastic elongation are important requirements for polyimide films used as substrates in flexible displays. However, these properties can be altered by imidization during the thermal treatment. In the present study, we investigated a probable mechanism to enhance the toughness by shrinking fluorinated polyimide films containing benzidine moieties. A higher degree of fluorination leads to weaker intermolecular charge transfer and optically clearer films, but it also degrades the mechanical properties. Moreover, β -transition originating from the molecular rotation around benzidines makes the film dependent on the elongation conditions during solvent drying. According to frequency-sweeping measurements and simulations based on density functional theory and molecular dynamics, the β -transition temperature increases and the phase lag in elastic energy loss decreases with increasing shrinkage. Both experimental and theoretical findings suggest that the change in frequency dependence can be attributed to the variation in elasticity retardation, which possibly originates from the chain-entanglement density. Graphical abstract: Highlights: Polyimides with fluorine side groups and benzidine moieties exhibit marked decrease in modulus during thermal treatment. Film shrinkage can induce an increment in chain entanglement density and improve mechanical properties. Change of β -transition temperature and elasticity retardation provide the information of chain entanglement. Enhancement of chain entanglement by film shrinkage should be applied to develop an optimized process condition.