High-Performance Poly(ester-Imide)s with Low Dielectric Constant and Low Dissipation Factor at 10 GHz via Cross-Linking of Polymer Backbones

Poly(ester-imide)s (PEIs) are well-known for their ultralow dissipation factor (D f ) of 0.003 at 10 GHz recently. However, the dielectric constant (D k ) and D f seem to be two difficult-to-reconcile indexes in PEIs, a relatively high D k of 3.2 confines the insulating capability of PEIs, owing to the trade-off between the polymer's free volume and rigidity. To address this difficulty, a cross-linking strategy of polymer backbones is proposed to increase the free volume and maintain a rigid structure in PEIs. In this research, the crystallinity of a liquid-crystal-like PEI is gradually diminished, and the molecular chain spacing is slightly enlarged as the degree of cross-linking increases. Besides, the degree of the in-plane orientation of this PEI is obviously reduced, indicating the loose stacking of molecular chains. Consequently, the D k at 10 GHz of this PEI is decreased from 3.26 to 2.85 after cross-linking. Furthermore, the D f of the cross-linked PEI is remained as low as 0.00237. In addition, the tensile strength and elongation at break of this PEI are increased from 219 MPa and 7.4% to 231 MPa and 9.7% after cross-linking, respectively. And the thermal stabilities of the cross-linked PEI are also decent as a candidate for low dielectric materials.