The development of a new generation of carbon dioxide (CO₂) thickeners is significant for improving carbon dioxide flooding technology. Here, co-polymers based on epoxide heptamethyltrisiloxane and glycidyl phenyl ether are prepared, and their solubility and thickening ability in CO₂ are evaluated. The solubility of the modified polyethers in CO₂ remarkably increases with the modification of heptamethyltrisiloxane and decreases upon introducing phenyl glycidyl ether. With incorporation of 18.4 mol% phenyl groups into the co-polymer, the co-polymer exhibits a highly increased thickening effect, while maintaining high solubility in CO₂. Implications of the present study for the preparation of a highly efficient CO₂ thickener are discussed.