Bismaleimide and Biobased Limonene Copolymer Microspheres as Reactive Fillers to Fabricate Low-k, High-Toughness Cyanate Ester Resin Composites

Bismaleimide and biobased copolymer microspheres (BMPL) of bis[4-(4-maleimidoyloxy)phenyl]propane (BMIP) and limonene (LIM) with different compositions are synthesized via self-stabilizing precipitation copolymerization and applied as reactive modifiers of 2,2-bis(4-cyanatophenyl) propane (BADCy) resin. Due to the different reactivities of exo- and endocyclic vinyl groups in the LIM monomer, the content of the vinyl groups in the BMPL can be simply tuned by copolymerization temperature. There are some endocyclic double bonds of LIM in BMPL prepared at 75 °C but no observable endocyclic double bonds in BMPL prepared at 130 °C. The presence of LIM endocyclic double bonds in BMPL microspheres can effectively reduce the curing temperature of BADCy resin via the formation of chemical bonds between the BADCy matrix and BMPL microspheres but without expensing the heat resistance of the composites. The dielectric constant (ε) and dielectric loss (tan δ) of the BMPL/BADCy composite with the addition of 10 wt % of BMPL are 2.67 and 0.0034, respectively, at 106 Hz, which was much lower than those of pure BADCy (2.87, 0.0054). In addition, the maximum impact strength of the BMPL/BADCy composite at 10 wt % BMPL loading is 18.21 kJ/m2, which is 88.3% higher than that of pure BADCy. The BMPL/BADCy composite demonstrates low-k dielectric properties, high toughness, and thermal stability and has potential in the fields of electronic communication, aerospace, and aviation.