In order to prepare polyimide resins with excellent melt processing properties and high transmittance, a series of thermoplastic fluorinated polyimide resins was prepared by copolycondensation of the flexible dianhydride monomer 4,4′-(4,4′-isopropyldiphenoxy)bis(phthalic anhydride) (BPADA) and the fluorinated diamine monomer 2,2′-bis(trifluoromethyl)benzidine (TFMB) with different contents of fluorinated dianhydride 4,4′-(hexafluoroisopropyl)diphthalic anhydride (6FDA) or cyclobutanetetracarboxylic dianhydride (CBDA) via chemical imidization. The effects of the third monomer content on the melt processing properties, optical properties, heat resistance, and mechanical properties of the polyimide resins were systematically investigated. The minimum melt viscosity of the PI resins reached 630 Pa·s below 400 °C. The transmittance at 450 nm of PI sheets prepared by compression molding reached 77%, and the color was significantly lighter than the commercial thermoplastic resin ULTEM, indicative of excellent processability and optical properties. Besides, the PI resins displayed outstanding thermal performance with glass transition temperatures ranging from 224 °C to 242 °C, 5% weight loss temperatures higher than 520 °C in a nitrogen atmosphere, and coefficients of thermal expansion of 51.45–68.97 ppm/K. Moreover, the PI sheets possessed tensile strengths of 88.4–104.7 MPa.
Qi Li,Sung S Park,Chang-Sik Ha,Shuai Yuan,Liyi Shi
In this work, a copolyimide (Co-PI) film with high transparency was prepared by the copolymerization of hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 2,2′-Bis(trifluoromethyl)benzidine (TFMB) and adamantane-1,3-diamine (DAA). The effects of DAA monomers on the optical, thermal, and mechanical properties of the co-PIs were discussed in detail. We found that the preparation of polyimide (PI) based on the combination of two dianhydrides and two diamines could obtain the co-PI film with excellent comprehensive performance due to the synergy between the -CF3 group, the aliphatic ring and the aromatic structure. Through the structure and composition optimization, the co-PI film with 1.30% DAA (Q3) has a Tg of 374oC, T5 higher than 530oC, T430 of 82% and the tensile strength higher than 145 MPa. These results indicate that the Co-PI films can be successfully utilized in the development of novel heat-resistant plastic substrates for the optoelectronic engineering applications.
Hong Chen,Jindong Huang,Chao Zhang,Peng Gao,Hongchang Huang,Junlan Li,Juncheng Liu
A foldable polyimide (PI) protective layer with high transmittance and high ultraviolet (UV) resistance is crucial for the practical application of flexible solar cells. Herein, the commercially 2,2′-Bis(trifluoromethyl) benzidine (TFMB) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) as the monomers, and five ionic liquids (ILs) as the regulators were used to synthesize PI/IL films (PI/IL1, PI/IL2, PI/IL3, and PI/IL4). The outcomes reveal that the average transmittance ( AT ) of PI/IL1 (50 μm thickness) outperforms others, which can be attributed to the expanded π-π stacking distance between PI molecules and the intermolecular multipoint interaction between IL1 and PI. The AT and the elongation at break ( ε ) of PI/IL1 increase sequentially with the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C 2 mim][NTf 2 ])/TFMB mole ratio, and those of PI/IL1-3 reach the maximum values of 94.23 % and 49.42 % at a 3:1 ratio, respectively. However, the tensile strength ( σ ) of the PI/IL1 film is inferior to that of the pure PI film, and consistently decreases with the increase of [C 2 mim][NTf 2 ]/TFMB mole ratio. Nevertheless, the UV-induced degradation of PI can be delayed through the [C 2 mim][NTf 2 ] regulation. The attenuations of AT , σ and ε of PI/IL1-3 films after 1000 equivalent solar hours (ESHs) UV irradiation are 0.85 %, 14.63 % and 2.99 %, respectively, which are significantly lower than those of pure PI films (2.23 %, 32 % and 23 %). This is attributed to the interaction between the positive and negative charges from [C 2 mim][NTf 2 ] and those from the PI chain breaking. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of PI/IL1-3 are calculated with the density functional theory to reveal the charge transfer between [C 2 mim][NTf 2 ] and PI.
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