T g,α . We explain our experimental results using the concepts of free volume and discuss the interactions of the polypeptide and copolymer matrix and steric effects. We define T g,β as the point at which the material has sufficient amount of activation energy and free volume to allow for local motions to occur, and T g,α as the point at which large-scale movement can take place, and relate the onset of the transition temperatures to the interaction strength between the polymer and the peptide. Our work provides a physical explanation for the behaviour of these microspheres leading to T g , and is in agreement with the PES concept outlined by Goldstein. This work provides a framework for understanding the dynamics of complex systems, such as lyophilised microspheres, and considers the parameter of T g,β as a valuable criterion for preparing stable formulations. Finally, this work demonstrates that THz-TDS is an effective method to measure the molecular dynamics and temperaturedependant behaviour of a polymer-polypeptide microsphere system.