Endothermic and exothermic components of an inverse temperature transition for hydrophobic association by TMDSC

Temperature modulated differential scanning calorimetry (TMDSC) has been used to study the phase separation process of three elastin-like model polymers; chemically synthesized poly(GVGVP) and genetically engineered (GVGVP)251 and (GVGIP)320. By these means, the characteristic endothermic peak found for these polymers in conventional calorimetry is revealed as being composed of two components, one endothermic due to loss of hydrophobic hydration and an oppositely signed exothermic component due to the physical association of chains (Vander Waals cohesive interactions) with the magnitude of the exothermic component being less than one-third that of the endothermic component. The magnitude of both components seems to depend mainly on the mean hydrophobicity of the monomer and not on the polymer molecular weight or dispersity.