Reactive poly(styrene-co-maleic anhydride) microspheres for simultaneous toughening and strengthening of epoxy resin

High-performance epoxy resins (EPs) are indispensable matrices for advanced load-bearing composites, such as wind turbine blades and automotive lightweight structures. Achieving concurrent improvements in the mechanical and thermal performance of EP remains challenging for conventional toughening approaches. In this study, divinylbenzene (DVB)-crosslinked poly(styrene-co-maleic anhydride) (SMA) microspheres were synthesized via self-stabilized precipitation polymerization (2SP) and subsequently incorporated into the EP matrix. The microspheres combine reactive surface anhydride groups with a rigid aromatic backbone. The anhydride groups can participate in the epoxy–anhydride curing reaction, thereby improving the interfacial compatibility between the microspheres and the EP matrix. Meanwhile, the rigid benzene rings restrict segmental mobility and increase the rigidity of the crosslinked network. Curing kinetic analysis revealed that the incorporation of SMA microspheres reduced the apparent activation energy of the SMA/EP system, suggesting that the curing reaction was facilitated. This reduction may be attributed to the participation of surface anhydride groups in the cross-linking reaction and hydroxyl-mediated autocatalytic effects. Mechanical evaluations showed that, at an SMA loading of 2 wt%, the tensile strength of the SMA/EP composite reached 72.0 MPa, corresponding to a 48.8% increase compared with neat EP. At a loading of 3 wt%, the impact strength reached a maximum value of 19.2 kJ/m 2 , indicating a substantial improvement in toughness. In addition, dynamic mechanical analysis (DMA) indicated that SMA microspheres increased the crosslinking density, while differential scanning calorimetry (DSC) showed that the glass transition temperature (T g ) increased by approximately 9 °C compared with neat EP. These results highlight reactive SMA microspheres as promising modifiers for epoxy composites requiring balanced strength, toughness, and thermal performance.