Carbon Dioxide Switchable Polymers – Recent Developments and Emerging Applications

Abstract

Dedicated to Professor Timothy McKenna on the occasion of his 60th birthdayCarbon dioxide has emerged as an alternative trigger for stimuli-responsive or "switchable" materials that has unique advantages compared to conventional triggers. The principles of CO 2 switching have been applied to a wide range of materials and processes, including polymeric materials and polymerization processes. This Perspective briefly reviews the types of polymer materials that have been made CO 2 -switchable, and the types of processes where CO 2 switching has been utilized to address process-related challenges such as catalyst recovery. Recent research is then highlighted conducted in the groups on a range of new switchable polymers and processes, emphasizing emerging applications where CO 2 switching may offer novel solutions and opportunities for commercial development.

CO2-responsive gels

“…A diverse range of CO 2 -responsive materials has been formed. These include polymers and polymer colloids; 50,53,[58][59][60][61] solvents, 54,62,63 catalysts, [64][65][66] and surfactants; 54,67,68 surfaces and coatings; 69,70 emulsions; [71][72][73][74][75] foams; [76][77][78] membranes; 63,79,80 particles and latexes; [81][82][83] cotton fibres, [84][85][86] and ionic liquids. [87][88][89] Similarly, CO 2 -induced self-assembled structures with complex morphologies have been realised including vesicles, 90,91 worm-like micelles, [92][93][94] and nano-objects.…”

CO2-Switchable colloids

“…The principles of CO 2 switching have been demonstrated for numerous potential applications including purifications, catalysis, forward osmosis, drying agents, nanoparticle aggregation/redispersion, reversible selfassembly, responsive surfaces and sensor design. [4][5][6][7] Although CO 2 responsiveness is fundamentally a subset of pH responsiveness, using addition and removal of gaseous CO 2 as triggers, as opposed to most other pH-switchable materials that use acids and bases as triggers, provides unique advantages in both performance and reduced environmental impact. For (2019).…”

“…The past decade has witnessed a surge in research activity focussed on CO 2 -switchable materials, including polymers, surfactants, solvents (both switchable polarity solvents (SPS) and switchable hydrophilicity solvents (SHS)), solutes, and surfaces. 1–8 When CO 2 is added or removed, CO 2 -switchable materials undergo a reversible change in properties of interest ( e.g. hydrophilicity, polarity, solubility in various solvents, morphology, particle size, colloidal stability, surface activity, etc. )…”

“…The principles of CO 2 switching have been demonstrated for numerous potential applications including purifications, catalysis, forward osmosis, drying agents, nanoparticle aggregation/redispersion, reversible self-assembly, responsive surfaces and sensor design. 4–7…”

CO2-switchable thermoresponsiveness of poly(N,N-(diethylamino)ethyl acrylamide)-based homo- and copolymers in water

“…Carbon dioxide (CO2) has emerged as an innovative and green trigger for switching the properties (such as solubility, dimension, chain conformation, morphology, shape...) of responsive polymer materials in aqueous media. [1][2][3][4][5] As a key metabolite in living organisms, CO2 displays excellent biocompatibility and membrane permeability; as an industrial production waste, it is abundant, inexpensive, available and nontoxic. Moreover, in aqueous solution, CO2 combines with water to form carbonic acid, which lowers the solution pH.…”