This thesis focused on comparing various levels of a coagent (bismaleimide, BMI) within an unfilled fluoroelastomer (FKM) in both the cured and uncured states, and determining whether high levels of coagent could still produce an elastomer with acceptable mechanical properties. Further, to determine any links between morphology, cure chemistry/kinetics, and the mechanical properties of the material.Adding BMI as a coagent, even at higher than normal loadings, was shown to produce a material with acceptable mechanical properties (as per ASTM D2000). This conclusion is different to that drawn from literature, where it is suggested that materials with high levels of coagent are brittle and cannot form 'useful' products.In the uncured state, the BMI powder acts as a filler of low structure. In the cured state, the BMI coagent also acts as a filler, with SEM and EDX analysis demonstrating that any domains of coagent acting as a filler were below the resolution of the microscope, even though DSC analyses indicated that the two materials were immiscible. The effectiveness of the reinforcement using BMI as a coagent at high loadings has shown to be very high; potentially greater than that of some carbon blacks in other elastomers. With increasing levels of BMI coagent, it was also shown that the molecular weight between cross-links decreased. This occurs even though the elastomer chains can only be cross-linked at the chain ends. Therefore, it is proposed that the BMI is forming filler-like domains. However, these interact with the elastomer molecules, restricting chain mobility. Following progression of the cure process was possible using infrared analyses and by rheometer studies, with infra-red analysis shown not to be as reliable as utilising the rheometer. The cure reactions associated with increasing BMI content were non-linear with regards to Arrhenius plots. This demonstrates different competing reactions when curing the material.