Novel Strategy for the Synthesis of Polymer/Pigment Hybrid Latex via Sulfur-Free RAFT-Mediated Emulsion Polymerization

Abstract

Reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization is a powerful tool for polymer encapsulation of pigment nanohybrids. Conventional RAFT emulsion polymers, however, contain sulfur residues that contribute to undesired odor and deleterious effects on final materials. Our strategy relies on an amphiphilic macromonomer poly­(methacrylic acid-co-methyl methacrylate) P­(MAA-co-MMA) with an ω-unsaturated end group synthesized in situ via cobalt­(II)-mediated catalytic chain transfer polymerization (CCTP) at the surface of C.I. Pigment Blue 15:3 (PB) particles. Subsequently, these macromonomers are used as the living points to mediate the in situ sulfur-free RAFT (SF-RAFT) emulsion polymerization of monomers (butyl methacrylate (BMA) and butyl acrylate (BA)). It was found that a well-controlled polymerization process was achieved by semibatch SF-RAFT emulsion polymerization on the PB surface, as evidenced by the smooth increase in the molecular weight of polymer chains as the polymerization progressed and by transmission electron microscopy (TEM) results. Due to the sealing effect, these polymer/PB hybrid particles exhibited excellent colloidal stability in the aqueous phase. More importantly, film-forming hybrid particles with a soft P­(BMA-co-BA) shell were successfully prepared in this work, which suggested that SF-RAFT-mediated polymerization may offer a useful alternative approach to traditional RAFT emulsion polymers for the preparation of organic/inorganic nanohybrids.

Sulfur-free and Surfactant-free RAFT-Mediated Hybrid Emulsion Polymerization: A Model System for Understanding the Controlled Synthesis of Hybrid Latex-Encapsulating Pigment

“…Moreover, the particles of the PMMA/P.R-170 hybrid latex in Figure S3c,d were larger and more agglomerated than in Figure b. It was believed that a high feed rate of monomer inhibited the emulsification properties and resulted in the monomer plasticization. , …”

“…The particle size of hybrid latex during storage was particularly important. , The size of the pigment hybrid latex particles acted as the dispersion state of the hybrid particles in the water medium and was also a momentous consideration in determining the efficiency and quality of the actual production process. , To investigate the dispersion stability of polymer/P.R-170 hybrid latex in the water medium, the storage and freeze–thaw stabilities of polymer-coated organic pigment particles were systematically investigated. The average particle size of the polymer/P.R-170 hybrid latex (Table , run 2) increased slightly with the prolongation of storage time, and the average particle size increased after being stored for 6 weeks by about 50 nm (Figure a).…”

“…It was believed that a high feed rate of monomer inhibited the emulsification properties and resulted in the monomer plasticization. 22,40 To verify the adjustable ability of M n on the copolymer/P.R-170 hybrid latex, the SF-RAFT-mediated hybrid emulsion polymerization of MMA was evaluated on the P.R-170 particle surface with a targeted DP n of 100 and M n of 20 Kg/mol and a feeding rate of 0.6 mL/h (Table 2, run 1: 0, 2, 3, 4, 6, and 8 h). According to the SEC analysis (Figure 4c), the unimodal dispersity curves shifted to higher M n with decreasing retention time, indicating that the M n in the PMMA/P.R-170 hybrid latex increased with the addition of the MMA droplet amount.…”

“…These results were attributed to the addition of soft monomer driving the latex to deform, resulting in the easier formation of a copolymer film on the surface of irregular pigment particles and adhesion between the pigment particles was easy to occur. 22,40 As a result, P.R-170 was inclined to migrate to the polymer/water interface to form the agglomeration hybrid particles during the polymerization, which agreed with the literature of RAFT-mediated hybrid emulsion polymerization toward film-formation hybrid latex films by Bourgeat-Lami et al 19,49 On the other hand, the DSC curves (Figure S5) also proved that the T g values of the P(MMA-co-BA) shell gradually decreased with the increasing concentration of soft monomer. The T g values (Table 2, run 1 to run 5) were 28.2, 18.0, 7.5, 6.5, and 2.5 °C for the corresponding copolymer encapsulated P.R-170 hybrid latex films, and these minimum film forming temperatures (Table 2, run 2 to run 5) were 7.35, 6, 4.4, and 2.5 °C, respectively.…”

“…Bon et al − carried out polymerization-induced self-assembly (PISA) in the absence of monomers using macromonomers as seed emulsions. The cross-linked micellar dispersion of macromonomers can be used as nanogel stabilizers in emulsion polymerization to prepare patchy, Janus, and armored polymer particles. − In our previous work, amphiphilic macromonomer poly­(methacrylic acid- co -methyl methacrylate) P­(MAA- co -MMA) was synthetized in situ on the C.I. Pigment Blue 15:3 (PB) particle surface via CCTP.…”