High polymer/surfactant ratio in the seeded semicontinuous heterogeneous polymerization of vinyl acetate

Abstract

Vinyl acetate (VAc) was polymerized by a seeded semicontinuous heterogeneous process. Stable latexes with a polymer/surfactant weight ratio of 65 were obtained, which is comparable with the highest value reported in the literature for emulsion polymerization but with the advantage of obtaining smaller particles (average diameter, D p ¼ 53 nm) which are similar to those obtained by microemulsion polymerization. The surfactant (sodium dodecylsulfate, SDS) concentration used in the recipe (0.32 wt%) is much lower than those typically used in microemulsion polymerization. Although molar masses increased during the continuous monomer addition period, they were small at the end of the reaction (M n ¼ 69 3 10 3 gÁmol -1 ) and this was attributed to bimolecular termination inside the particles. The values of polymerization rate (R p ) and monomer addition rate (F m ) were nearly the same, indicating that polymerization was performed under monomer starved conditions.

Heterophase polymerization of different methacrylates: Effect of alkyl ester group on kinetics and colloidal behavior

“…Common features of these processes are the following: (1) at least two phases are present; (2) the system has spatial density differences; (3) transport of monomer occurs between the phases; and (4) the reaction occurs under nonequilibrium conditions. Advantages of reactions carried out in heterophase systems are the easiness of removal of the heat of reaction, the low viscosity (independent of the polymer molecular weight) of the reaction system at all times and the possibility to feed monomer or an emulsion during the reaction, monomer concentration at the polymerization loci can be maintained stationary at its highest level so that the rate of reaction can be kept high during the whole polymerization, and the particle size distribution (PSD) and average particle diameter ( D p ) can be tailored over wide ranges …”