Rigid Photosensitive Polyimide Significantly Improves the Comprehensive Performance of UV-Curing Epoxy Acrylic Resins

Epoxy acrylate (EA) resins have excellent light-curing properties and play a crucial role in UV-curable resins, but poor mechanical properties, lower thermal stability, and stronger hydrophilicity hinder their applications in high technic areas such as circuit board printing and electronic packaging. In this study, to enhance UV-curing EA resins, a photosensitive polyimide (PSPI) with a highly rigid and twisted skeleton was developed as a macromolecular cross-linker. This PSPI is featured with a unique diamine monomer that possesses a spirocyclic fluorene-xanthene core double-grafted with methacryloylamino groups. Commercial EA resins (EB600) were blended with varying levels of PSPI to modify the density and structure of the cross-linked network of the EB resins. The methylacrylamide groups branching on xanthene rings in the PSPI participate in radical UV-curing by crossing over with the main-chain helixes, resulting in three-dimensional cross-cured networks and unique structural rigidity of the resins. EB resins with different PSPI contents demonstrate apparently improved overall properties, compared with the nonmodified EB600. Among these cured resins, the overall performance of EB10PSPI1 (weight ratio of EB/PSPI 10/1) was superior. The initial thermal decomposition temperature (Td5%) of EB10PSPI1 resin is 353 °C, 78 °C higher than that of EB1PSPI0 (without PSPI), and the residual carbon rate is increased by 12.36% at 600 °C. The Tg of EB10PSPI1 resin was 122 °C, while that of EB1PSPI0 resin is only 87 °C. The tensile strength and modulus of elasticity of EB10PSPI1 resin increased by 162 and 246%, respectively, and the hardness increased by 291 MPa compared with EB1PSPI0 resin. In addition, the surface of EB10PSPI1 resin exhibited good hydrophobicity with significantly lower water absorption and swelling rate than that of EB1PSPI0. Also, EB10PSPI1 exhibits good adhesion capability. Finally, the curing performance of the EB10PSPI1 resin is better, almost doubling the curing speed at weak UV-light irradiation intensities, demonstrating the excellent sensitivity of the PSPI in radical polymerization reactions and the enhancement of the UV-curing network of the EB resin. This study opens a way to comprehensively enhance the thermodynamic and mechanical properties of EB1PSPI0 resins, which is promising in circuit board printing and electronic packaging.