We report here the carbon dioxide sorption properties for a series of conjugated microporous polymer (CMP) networks. These CMP materials incorporate a range of chemical functionalities including carboxylic acids, amines, hydroxyl groups, and methyl groups. The carboxylic acid functionalised network, rather than its amine analogue, shows the highest isosteric heat of sorption for CO2. This supports recent computational predictions for metal-organic frameworks and suggests that acid-functionalised frameworks could outperform more widely studied amine sorbents in CO2 capture and separation application.