Characterization Of Acrylate Polymer Latex With Gradient Structure

Gradient copolymers represent a relative new type of copolymers with unique structureand properties where the monomer composition changes continuously along the backbonefrom predominantly one monomer to another monomer. There are two kinds of gradientcopolymers, one is intramolecular gradient copolymer, the other is intermolecular gradientcopolymer. Due to each of the copolymer chain being formed instantaneously, thecomposition of gradient latex particle prepared by radical emulsion polymerization changesirregularly but uniform in statistics for a single molecular chain. However, for the differentmolecular chains in the particle, there is a huge difference between the first formed copolymermolecular chains and the subsequent formed molecular chains, as the feeding composition ofco-monomers varies instantaneously. Thus a gradient structure of the particle is obtained.Batch emulsion polymerization technique was used to determine reactivity ratio of MMAand BA. The results show that the reactivity ratio of MMA is1.84, and the reactivity ratio ofBA is0.23.Gradient latex particles with n-BA-centered and MMA-centered arrangements weresynthesized by gradient emulsion copolymerization, where the sodium dodecyl diphenyloxidedisulfonate （DSB） used as emulsifier and potassium persulfate （KPS） used as initiator. Duringthe polymerization, one monomer mixture was continuously added into a stirred tankcontaining another monomer mixture, so the monomers fed into the reactor changedinstantaneously.¹H NMR,¹³C NMR and two dimensional NMR spectrum were used tocharacterize the gradient structure. The1H NMR results show that FMdecreases from86.01%to55.45%with the reaction progress for the MMA-centered gradient latex particles, while FMincreases from14.19%to69.26%with the reaction progress for the n-BA-centered gradientlatex particles. The¹H NMR results also shows that when FMis lower than50%, the–OCH3proton signal of MMA is sensitive to triad composition, for soft core hard shell gradient latexparticles obtained at different conversion show that the dominant triad structure changes fromBMB to MMM triad. The¹³C NMR results indicate that the dominant triad structure changesfrom MMM to BBB triad for MMA-centered latex particles. Combing¹H NMR and twodimensional NMR spectrum for BA-centered gradient latex particles, it indicates that the dominant unit in molecular chain changes from BA unit to MMA unit.