We report on the tail-tail cyclization and unfolding kinetics of a poly(dimethylsiloxane) oligomer that is end-labeled with pyrene (Py-PDMS-Py) when it is dissolved at low concentration in liquid ethyl acetate (a Theta solvent for PDMS) or methanol (a poor PDMS solvent) at 308 K as a function of added CO2 (0-1 mole fraction). In all liquids, the tail-to-tail cyclization rate increases as the CO2 mole fraction increases. The tail-to-tail unfolding rate is CO2 independent, and generally slower in comparison to the cyclization rates. As CO2 is added, toluene (a good solvent for PDMS) and ethyl acetate move toward becoming poorer PDMS solvents. At a given CO2 mole fraction in the liquid phase, the Theta solvent (ethyl acetate) quality for PDMS decreases ahead of and in greater magnitude than the good solvent (toluene). In methanol, the Py-PDMS-Py molecules appear to aggregate below similar to0.2 CO2 mole fraction. Above similar to0.2 CO2 mole fraction, the Py-PDMS-Py dynamics appear to obey a Birks-like model. As we increase the CO2 mole fraction in the Py-PDMS-Py/methanol system above similar to0.2, there is not a significant change in the Py-PDMS-Py tail-to-tail distance; the internal polymer dynamics increase. The overall effects of solvent and CO2 mole fraction on the Py-PDMS-Py dynamics in CO2-expanded liquids are captured by a simple model.