Using a quartz crystal microbalance, the sorption of several different solvents, benzene, 1,2-dichloroethane, dichloromethane, and chloroform in three triblocks of the homopolymers polycaprolactone (PCL) and polyethylene glycol (PEG) were observed at 298.15 K. The solvent-polymer interaction was modeled using a modified Flory-Huggins equation and weight-based activity coefficients at infinite dilution were obtained from it to study the trend as the PCL/PEG ratio increases in the triblock copolymer system.