Four fluorene-containing polyimide (PI) resins without per- and polyfluoroalkyl substances (PFAS), including PI-Ia (BPAF-BAOFL), PI-IIa (BPFDA-BAOFL), PI-Ib (BPAF-FDAADA), and PI-IIb (BPFDA-FDAADA) were prepared from two fluo-rene-containing dianhydrides 9,9-bis[(3,4-dicarboxy)benzene]fluorene dianhydride (BPAF, I) and 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPFDA,II) and the fluorene-containing diamines 9,9-bis[(4-aminophenoxy)phenyl]fluorene (BAOFL,a) and 9,9-bis[4-(4-aminobenzamide)phenyl]fluorene (FDAADA,b), respectively via two-step chemical imidization procedure. The corresponding PI films were prepared by the solution processing procedure. The results show that the derived PI resins show good solubility in polar N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc) and cyclopentanone (CPA). The incorporation of fluorene substituents endows the PI films good thermal resistance with the glass transition temperatures (Tg) over 298℃. The BAOFL-based PI films (PI-Ia and PI-IIa) exhibit low dielectric features with the dielectric constants (Dk) and dielectric dissipation factors (Df) in the range of 2.87 to 3.20 and 0.006 6 to 0.012 3, respectively at 10 GHz. While the FDAADA-based PI films (PI-Ib and PI-IIb) shows a bit deteriorated dielectric feature due to the existence of polar amide units (-CONH-). However, the high-temperature dimensional stability of the FDAADA-based PI films is improved with the linear coefficient of thermal expansion (CTE) values as low as 38.9×10-6 K-1.
| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |