Improved Processability of High Char Bismaleimide Networks From Acetylene Functional Comonomer Blends

ABSTRACT The present study demonstrates the solventless synthesis of an Acetylene‐Functionalized Bismaleimide (A‐BMI) and systematically incorporates a Meta Comonomer and Para Comonomer isomer to create a Meta and Para Comonomer series of monomer blends, respectively, to evaluate the role of comonomer positional isomerism on the rheological profile and decomposition behavior of A‐BMI. The incorporation of the comonomers was confirmed via Nuclear Magnetic Resonance Spectroscopy. Through Differential Scanning Calorimetry and Near IR, it was shown that both comonomers increased the polymerization temperature (from 176°C to T p > 220°C) and cure enthalpy (from 177.9 J/g to H p > 465 J/g) of A‐BMI. Within the comonomer blends, it was shown that the Para substituted comonomer granted lower polymerization temperatures (~6°C lower than the meta isomers), while the Meta isomer afforded higher consumption of reactive species during polymerization. Through rheological characterization, it was confirmed that the minimum viscosity of the comonomer blends was lower than A‐BMI. Further, this reduced viscosity was a function of comonomer concentration, where higher concentrations led to lower viscosities and higher polymerization temperatures, reflecting tunable processibility and an increased applicability towards resin transfer molding based composite fabrication methodologies. Moreover, the Meta Comonomer created higher reductions in the initial and minimum viscosity. Thermogravimetric analysis indicated that both series of blends exhibited similar char yields (< 3% difference) despite the 12% higher decomposition rate of the Meta Comonomer blends. The net effect of these findings extends the understanding of bismaleimide molecular design and comonomer blending as it relates to processibility and thermal performance.