The Effect of Heat Treatment on the Higher‐Order Structure and Fracture Behavior of Simultaneously Polymerized Polymethacrylate/Polyurethane Blends

Simultaneous polymerization of methacrylate monomers and urethane prepolymers allows for the formation of higher‐order structures within the polymer blend that do not exist in poly(methyl methacrylate). In this study, polymethacrylate/polyurethane blends, containing a 100‐nm soft phase and structures with dimensions of several micrometers containing quasi‐spherulites, were investigated to examine the effect of heat treatment on their higher‐order structure and fracture behavior. The micrometer‐scale structures containing grew larger with increasing heat‐treatment temperature because the mobility of the matrix chains improved. The fracture toughness ( G Ic ) of the polymer blends increased as the size of the structures containing quasi‐spherulites increased, owing to increased stress concentration in the matrix polymer around these structures, leading to an increased number of crazes. However, the G Ic for the sample heat‐treated at 150°C was low despite the wide region of craze occurrence. The G Ic for the sample heat‐treated at 150°C was underestimated because it deviated from the linear region at low stress. These outcomes suggest that the difference in higher‐order structure of the polymer blends influences their deformation and fracture mechanisms, despite identical constituent components.