New Chain-Extended Bismaleimides with Aryl-Ether-Imide and Phthalide Cardo Skeleton (II): Creep, Stress Relaxation, Shape Memory and Self-Repairing Properties

Abstract

In Part I of the paper, we have focused on the synthesis, characterization and solubility of three chain-extended bismaleimides containing aryl-ether-imide and phthalide cardo skeleton with different molecular weight (MPEIBMI-2.0, MPEIBMI-1.5 and MPEIBMI-1.25) and the thermal stability and thermal mechanical properties of their cured resins. In Part II of the paper, their high-temperature static viscoelasticity, shape memory (SM) performance and self-repairing behavior for micro-damages were investigated by dynamic mechanical analyzer and optical microscope. The creep test results exhibit the MPEIBMI-2.0 cured film has the strongest creep resistance at the same testing temperature due to the highest stiffness of its network structure, and the maximum allowable load of MPEIBMI-1.25 film at 200 °C reaches 15 MPa for 60 min creep experiment. The rate of stress relaxation for MPEIBMI-1.25 film is slower in spite of having relatively lower stress level. The MPEIBMI-1.25 film has the largest ultimate elongation at high temperature and this deformability confers it excellent shape memory (SM) ability. The shape fixity ratio reaches above 98% and the recovery rate is increased to above 96% from 94.5% after one SM cycle. The micro-damages on the surface of cured films could be repaired when heated to the temperature above their glass transition temperature, and the repairing temperature is increased with their crosslinking density to obtain perfect repairing efficiency.