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Preparation and Characterizations of Intrinsically Black Polyesterimide Films with Good Thermal Endurance at Elevated
Shujun Han1, Xi Ren1, Duanyi Li1
1Engineering Research Center of Ministry of Education for Geological Carbon Storage and Low Carbon Utilization of Resources, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China.
Abstract:
Polymer films with combined properties of good thermoplasticity, good electrical properties, and good thermal endurance are highly required for two-layer flexible copper clad laminate (FCCL) applications. Meanwhile, the black appearance is also required for specific FCCL applications. Therefore, in the present work, a series of ester-linked polyimide (PEsI) films were designed and developed via the copolymerization chemistry of an ester-containing dianhydride of biphenyl dibenzoate-3,3',4,4'-tetracarboxylic acid dianhydride (BPTME), a rigid-rod dianhydride of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), an ester-bridged diamine of 2-(4-aminobenzoate)-5-aminobiphenyl (ABABP), and a functional diamine of 4,4'-iminodianiline (NDA). The molar proportion of the BPTME/BPDA was fixed to be 20:80 and that of ABABP/NDA increased from 50:50 for PEsI-1 to 0:100 for PEsI-VI. The afforded PEsI films showed obviously enhanced blackness with the increasing molar ratio of NDA in the polymers. The PEsI-VI film exhibited the optical transmittance values of 0 and 27.4% at the wavelength of 500 nm (T500) and 760 nm (T760), respectively. The values were apparently lower than those of the standard PI-ref produced from common pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) (T500 = 63.2%; T760 = 86.3%). Meanwhile, the PEsI-V film showed good blackness with the CIE Lab optical parameters of 1.83 for L*, 11.46 for a*, 3.13 for b*, and 0 for haze. The PEsI samples exhibited good thermoplasticity and the storage and loss modulus of the films rapidly decreased around the glass transition temperatures (Tg) in the dynamic mechanical analysis (DMA) tests. The PEsI samples revealed the Tg values from 247.2 °C to 286.1 °C in the differential scanning calorimetry (DSC) measurements. The PEsI samples exhibited the linear coefficients of thermal expansion (CTE) of (27.1~33.4) × 10-6/K from 50 to 250 °C, which was comparable to that of the PI-ref sample (CTE = 29.5 × 10-6/K), however, a bit higher than that of the copper foil (CTE = 17.0 × 10-6/K).
