Melt processing of binary immiscible polymer systems has been a focus of our group as an economical and scalable route to achieve synergistic or superior mechanical properties at and around the co-continuous region without the need of compatibilization. System of poly(L-lactide) (PLLA) and poly(methyl methacrylate) (PMMA) was selected to target bio-related applications, including bone fillers and scaffolds, where the biodegradability of PLLA will enable the integration of native tissue into the material over time. Tunable properties such as morphology, interconnectivity, resorbability and interfacial bonding control the long-term integrity of the new material and influence the interaction and integration of new tissue. Binary blends of PLLA and PMMA has been prepared and characterized over a large range of compositions in which regions of co-continuity are of special interest. Such regions exhibit a well interconnected structure that ensures controlled release of resorbable PLLA. Modulated differential scanning calorimetry (MDSC) detected a broad and unexpected transition between 70 °C and 100 °C. The magnitude of this transition is greatest within co-continuous regions, suggesting the presence of a complex or other derivative of the two primary phases. This complex appears to provide a degree of compatibilization between the phases, thus inducing mechanical property synergism which has been confirmed by flexural and nano-indentation analyses.