Several different polymer modifications are currently used to produce commercial plastic materials, especially engineering resins, that have significantly improved melt strength. However, these modifications rarely produce materials that can be formed into very large parts. This study shows that the melt strength of engineering resins can be enhanced by rubber particles having grafted shells that are compatible with the resin. The melt strength of the engineering resin can be further improved by the incorporation of compatible high-molecular-weight polymers. The melt strength improvements thus obtained facilitate the formation of very large parts requiring 8-10 ft long parisons. The effects of shear rate on complex viscosity indicate that the extent of interaction between the polycarbonate matrix and the core-shell impact modifier decreases with increasing shear rate. Therefore, the impact strength of the part molded from a matrix modified with a core-shell rubber may depend on the process history. Dynamic mechanical measurements may provide a means to evaluate the interaction between the matrix and a core-shell modifier in an actual blend.