The Development of Novel Bio-Based CO2-Responsive Polymers for Binder Applications
CO2-switchable materials use CO2 as the trigger to induce a change in one or more of the material’s physiochemical properties. The mechanism of switching, in most cases, is the reversible protonation of tertiary amines in aqueous solution in the presence of CO2 but not in its absence. This type of stimuli-responsive materials is attractive since the trigger CO2 is a benign and non-toxic gas. The application of CO2-switchable materials could be well suited to binder polymers in various coating formulations, such as the preparation of polymer latexes. In addition, the environmental impact of these polymers could be reduced and the sustainability improved as fatty acids from renewable sources are used as the precursors for polymer synthesis. To convert natural fatty acids to polymers, two steps were followed: 1) functionalization of fatty acid with 2-hydroxyethylmethacrylate (HEMA); 2) free radical polymerization of the bio-based monomers using azoisobutyronitrile (AIBN) or benzoyl peroxide (BPO). A series of homopolymers and copolymers were synthesized by varying two main factors: the content of the bio-based material present in the polymer and the ratio of alkyl to tertiary amine containing monomers. CO2-switchable monomers, derived from lauric and oleic acid, were synthesized and polymerized individually or jointly with 2-(dimethylamino)ethyl methacrylate (DMAEMA) to prepare CO2-responsive polymers. To incorporate tertiary amines to fatty acids, two synthetic strategies were used: 1) halogenation, followed by substitution with an amine; 2) epoxidation of unsaturated C=C, followed by ring opening with an amine. 1H NMR, 13C NMR, FTIR, GPC and mass spectroscopy were used to characterize the novel monomers and polymers. The CO2-responsiveness of the various polymers was tested by electrical conductivity and 1H NMR spectroscopy. The thermal behavior of the synthesized polymers was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The newly synthesized copolymer poly(N,N-dimethylaminoethyl methacrylate-co-2-(methacryloloxy)ethyl dodecanoate) (p(DMAEMA-co-MAED)) exhibited a change in its physical and chemical properties when exposed to CO2 in aqueous solution.