The Impact of Highly Functional Microspheres on Diels–Alder Network Formation

The Diels–Alder reaction is a representative example of a dynamic covalent network capable of being constructed and deconstructed at moderate temperatures. Particles are commonly employed in polymer networks to strengthen mechanical properties, but they also impact network formation. In particular, reactive particles interact with molecular precursors; thus, they decrease aggregation and increase reactivity for the curing reaction. For small molecular precursors, theories such as that of Flory-Stockmayer are well-established to predict the extent of reaction at the gel point. However, the same assumptions may not be applied to a particle with numerous functionalities and orders of magnitude bigger than molecular precursors. In this work, maleimide-functionalized microspheres were synthesized by copolymerization of bismaleimide and styrene in marginal solvents. Gelation behavior of Diels–Alder networks using furan and maleimide functional groups was investigated via rheometry with varying maleimide-functionalized microsphere loading. A 5 wt.% loading of the maleimide microsphere decreased the gelation time by 23%. The impact of the maleimide microspheres was validated by comparison with gelation behavior using non-reactive polystyrene microspheres. The maleimide microspheres were able to accelerate the gel time and facilitate network formation in off-stoichiometric conditions.