Chemically induced dynamic electron polarization (CIDEP) in an acetone/2-propanol system is investigated in the L band microwave frequency region at various temperatures. The polarization due to the ST- mechanism is analyzed in terms of the mixing of hyperfine-independent (ST-M-i) and hyperfine-dependent (ST-M-d) mechanisms. At higher temperature, ST-M-d dominates over ST-M-i in the ST-M polarization, while the relative contribution of ST-M-i increases with decreasing temperature. A mechanism of ST-M-d is discussed based on the radical diffusion in solution and a possible contribution of the ST+M polarization in the CIDEP spectrum is discussed.