Thermoviscosifying polymers (TVPs) are a class of promising materials for chemically enhanced oil recovery (EOR) because of their unique viscosity increment with increasing temperature. However, previously reported TVPs have low molecular weight and relatively long dissolution time. To overcome these problems, we synthesized a novel polyether-based TVP (TVP-P) by inverse emulsion polymerization. In this work, the emulsion of TVP-P and the corresponding powder product purified from the emulsion were compared in terms of their solubility, rheological behavior, long-term thermal stability, and core flooding experiments. The results showed that the emulsion could be quickly diluted in water within 10 min by phase inversion, whereas the dissolution time of the powder was as long as 120 min. The thermothickening ability of the emulsion was stronger than that of the aqueous solution of the powder at 0.2 wt % polymer concentration. After aging at 45 degrees C for 2 months, the viscosity retention of the aqueous solution from the powder was 89.7% while that of the emulsion was only 62.4%. Core flooding experiments showed that the aqueous solution of the powder obtained 2.1% higher oil recovery than the diluted emulsion with the same initial viscosity.