Microwave-assisted aggregation of CO2-switchable polystyrene latexes prepared through emulsion polymerization using cationic stabilizers

Microwave irradiation (MWI) is introduced as a novel trigger to aggregate CO₂-switchable latexes. The polystyrene (PS) latexes were synthesized through emulsion polymerization in two ways (using polar monomer 2-dimethylaminoethyl methacrylate (DMAEMA) (as in situ copolymerization), and a well-defined block copolymer, poly(dimethylaminoethyl methacrylate-block-methyl methacrylate), PDMAEMA-b-PMMA as positively charged stabilizing moieties in the presence of 4,4'-(diazene-1,2-diyl) bis(N-(3-(dimethylamino) propyl)-4-methylpentanamide) (DABPA) as an “inistab” (initiator + colloidal stabilizer). Since the polymerization was conducted in acidic media using hydrochloric acid (HCl) to protonate stabilizers, PS latexes could be simply destabilized by adding NaOH. The destabilized latexes were redispersed by introducing CO₂ plus sonication to yield CO₂-switchable latexes. The particle size of the resultant latexes after redispersion was very similar to that of primary latexes, as measured by dynamic light scattering. MWI and conventional heating (CH) stimuli were applied to aggregate the CO₂-switchable PS latex particles. The influence of different factors on the time required for aggregation and particle size changes of the synthesized latexes was studied. These two methods of destabilization of PS latexes produce completely different switching behavior. Findings revealed that microwave-assisted aggregation (MAA) relative to CH required less time, but an increase in particle size of the redispersed particles in comparison to the original latexes was observed. Therefore, MAA can be assumed as a promising trigger for the aggregation of CO₂-responsive latexes. This facile aggregation process, which could reduce time and energy input, might be of high interest and importance in various applications.

Graphical Abstract