Characterization and properties of gradient polyacrylate latex particles by gradient emulsion polymerization

In this study, gradient acrylate latex particles were synthesized by gradient copolymerization. n-Butyl acrylate (BA) and methyl methacrylate (MMA) were used as co-monomers, dodecyl diphenyl ether sodium disulfonate as the emulsifier, and potassium persulfate as the initiator. The technique involved the continuous addition of one monomer mixture into a stirred tank containing another monomer mixture. Their microstructure and properties were analyzed by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), atomic force microscopy (AFM), transmission electron microscopy (TEM), and particle size analysis. H-1-NMR spectra show a gradual change in the chemical composition with the growth of molecular chains. The gradient polymer latexes, the instantaneous copolymer composition of which varies as the polymerization proceeds, are obtained. GPC analyses show that the aggregated molecular chain in the BA-centered latex particle experiences a process from dominant BA to MMA with changes in the monomer's feed composition during the polymerization. Particle size and TEM analyses show that the increasing latex size agrees well with the gradient growth pattern. DSC analyses show that the gradient latex particles exhibit only one broadened and ambiguous glass transition region. AFM analyses indicate no obvious microphase segregation occurs in the gradient latex particles, further verifying that the gradient microstructure is obtained.