Waterborne Polyurethane Colloids with Sensitive CO 2 ‐Switchable Hydrophilic/Hydrophobic Properties

A novel conceptual approach to gas‐responsive functionality, with the capability to tune the amphiphilic characteristics of existing waterborne polyurethanes (WPUs), via CO 2 /N 2 bubbling in aqueous solution, is exploited. In this study, a series of functional WPUs are successfully prepared. These colloids exhibit high aqueous stability, excellent capability for emulsification/demulsification as a surfactant, and reversible hydrophilic/hydrophobic phase transition owing to reversible formation of carboxylic acid moieties induced by bubbling CO 2 gas. More interestingly, when carboxylated multiwalled carbon nanotubes (CNTs) are covalently incorporated into these WPUs, the CNT exhibits CO 2 ‐switchable amphiphilic behavior in a two‐phase mixture of n ‐butanol (BuOH)/deionized water, forming a stable hydrophobic CNT dispersion in BuOH upon CO 2 bubbling, and reversibly reverting to the previous hydrophilic CNT dispersion in water upon N 2 bubbling. With simple preparation and switchable amphiphilic properties, these CO 2 ‐responsive WPUs offer a paradigm for the development of multifunctional gas‐responsive polymers.