Cationic polymers are promising flocculants for highly efficient solid-liquid separation, because of their tailorable molecular structures, they can realize remarkable ability of adsorbing contaminant. Herein, a novel copolymerization strategy is reported to obtain a well-designed CO2-responsive cationic copolymer for effective solid-liquid separation. To be specific, a series of novel CO2-responsive hyamine-based cationic copolymers (CHOPs) with different molecular structures were synthesized via copolymeization reactions between acryloyl oxygen ethyl trimethyl ammonium chloride (DAC), methyl acryloyl oxygen ethyl trimethyl ammonium chloride (DMC), methyl acryl-amide propyl trimethyl ammonium chloride (MAPTAC) and CO₂-responsive monomer dimethyl amino ethyl methacrylate (DMAEMA). The molar ratios of the monomers were optimized and the copolymerization kinetics followed to obtain the best relative molecular weight of CHOPs with good CO₂-responsiveness and flocculation ability. Of note, the tertiary amine groups of CHOPs could be protonated by the reaction with CO₂, leading to positively charged chains on the copolymers for enhanced flocculation ability. Furthermore, the network structure derived from CO₂ bridging between the two tertiary amine groups were conducive to the viscosity improvement and flocculation enhancement. Moreover, DMAEMA and DMC had the best polymerization kinetics, and the obtained P(DMC₁-DMAEMA₃) copolymer was found to be the optimized monomer molar ratio and gave the highest relative molecular mass which showed prominent flocculation ability under selected CO₂ import mode (only import in the flocculation system). The unique CO₂ import method facilitated homogenous reaction between the polymer and CO₂ while combing with solid particles to form ionic hydrophilic quaternary ammonium salts, leading to enhanced electrostatic repulsion between the copolymer chains and weakened interaction. As a result, the copolymer chains were more easily extended to improve bridge-effect. Combined with multiple fine particles, they resulted in increased flocculation volume and accelerated sedimentation rate for highly efficient solid-liquid separation.

Junyan Zhang, Anqi Ming, Wencong Li Yan Zhong, Wei Qi, Yuhan Ma, Yuxiang Cao, Yanyan Liu, Haibao Zhang, Xiaoxiao Li. The Co-polymerization Kinetics and Flocculation Effects of CO2-Responsive Cationic Polymers. Academic Journal of Materials & Chemistry (2025), Vol. 6, Issue 2: 82-91. https://doi.org/10.25236/AJMC.2025.060211.

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