Analysis of the macroscopic thermal and mechanical behavior, and microscopic chain packing and dynamics, of two hyperbranched polycarbonates and their compositionally exact linear analogues leads to the conclusion that nearest-neighbor chains (or chain segments) pack and move similarly in linear and hyperbranched systems. However, the distance scale for cooperative motion is much smaller in the hyperbranched polycarbonates, and this leads to mechanical embrittlement.