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This work focuses on two meaningful points in green chemistry, one is providing a practical solution for CO2 transformation into a CO2 copolymer, and the other is disclosing the potential application of a CO2 copolymer as a water dispersible binder to overcome the bottleneck in heavy metal free anti-corrosion coatings. For the first point, a CO2-copolymer like CO2-polyol is synthesized from the telomerization of CO2 and propylene oxide using a zinc–cobalt double metal cyanide complex as a catalyst and terephthalic acid as a chain transfer agent. For the second point, for the past 30 years conducting polyaniline, with its unique anti-corrosion behaviour, has been regarded as a heavy metal free anti-corrosion material, but the development of a waterborne polyaniline anti-corrosion coating has encountered an impasse owing to the lack of a compatible binder. Therefore, a water borne cationic polyurethane dispersion (CPUD) was developed for this purpose, in which CO2-polyol was used as a soft segment, and 1,4-butanediol di(3-diethylamino-2-hydroxypropyl alcohol) ether was synthesized as a side-chain cationic extender. Unlike earlier acidic water borne dispersions, this water borne CPUD was near neutral, ensuring good compatibility with an aqueous conducting polyaniline dispersion, and is expected to create significant possibilities for the development of a novel generation of sustainable and eco-friendly metal anti-corrosion materials. [ABSTRACT FROM AUTHOR]

An elevated-temperature dispersing (ETD) strategy was developed to disperse prepolymers at 80 °C for producing waterborne CO2-based polyurethane (CO2-WPU) in a whole-procedure organic solvent-free route. The obstacle of high viscosity challenging the traditional prepolymer-dispersing process was overcome, and the concern of significant NCO loss at high temperature was eliminated because prepolymer dispersion ensured ＞90% NCO retention. The particle size of the typical CO2-WPU emulsion lay between 45 nm and 70 nm, and it showed excellent stability even after centrifugation for 30 min at 3000 rpm. The dried CO2-WPU film showed not only good mechanical performance with a tensile strength of 54.3 MPa and elongation at break of 641%, but also excellent hydrolysis resistance owing to the unique structure of the CO2-polyol. This ETD strategy showed clear feasibility for commercial polyether or polyester oligomerols. It avoids the cooling step and solvent-removal procedure required in a traditional prepolymer-dispersing process, thereby greatly shortening the preparation period and reducing energy consumption. [ABSTRACT FROM AUTHOR]

Carbon dioxide based oligo(carbonate–ether) diols (CO2-polyols) with both carbonate units and ether units in one polymer chain were prepared by copolymerization of CO2 and propylene oxide (PO) using a zinc–cobalt double metal complex as the catalyst, and used to prepare CO2 based waterborne polyurethanes (CO2-WPUs). The carbonate units in CO2-polyols improved the mechanical and oxidation resistance properties of CO2-WPUs, while the ether units in CO2-polyols enhanced the hydrolysis resistance of CO2-WPUs. The tensile strength of CO2-WPUs didn't show any obvious drop during immersion in a 0.25% sodium hydroxide solution, whereas that of oligoesterol based WPUs dropped over 50% after 300 min, and lost their mechanical properties after 520 min of immersion. Meanwhile, the retention of the tensile strength of the CO2-WPUs was ca. 72% even after 46 h of immersion in a 6 wt% H2O2 solution, while it was only ca. 32% for the oligoetherol based WPUs. Moreover, the thermal–mechanical performance of CO2-WPU films can be conveniently improved by adjusting the carbonate unit content (CU%) in CO2-polyols, i.e. when CU% in CO2-polyol increased from 30% to 66%, the glass transition temperature (Tg) increased from −7.8 °C to 18.8 °C, accompanied by an increase of tensile strength from 35.6 MPa to 52.2 MPa, and a decrease of elongation at break from 630% to 410%. This work suggests that the CO2-WPU may be a promising alternative to conventional WPU whose oligoetherol and oligoesterol were from fossil resources, and its comprehensive hydrolysis/oxidation resistance may be a bonus unavailable from common oligomerol based WPUs. [ABSTRACT FROM AUTHOR]