Mass transfer effects in emulsion polymerization systems. I. Diffusional behavior of chain transfer agents in the emulsion polymerization of styrene

Abstract

SYNOPSISOn the basis of the so-called two-films theory for mass transfer, a mathematical model for transfer of chain transfer agents from monomer droplets to polymer particles, where chain transfer agent molecules are consumed by the chain transfer reaction, is developed for an emulsion polymerization system. It is shown by the model that the concentration of chain transfer agent in the polymer particles during the polymerization is decreased to a value much less than that which would be attained if thermodynamic equilibrium for chain transfer agent were reached between the polymer particles and the monomer droplets, due mainly to the resistance to transfer of chain transfer agent molecules across the diffusion films at the interface between the monomer droplets and the water phase. The validity and utility of the model developed for predicting the diffusion and consumption rates for chain transfer agent are demonstrated experimentally using five normal aliphatic mercaptans from n -C7 to n-Clz as chain transfer agents in the seeded emulsion polymerization of styrene. 0 1994

The Effect of Allylic Sulfide-Mediated IrreversibleAddition-Fragment Chain Transfer on the EmulsionPolymerization Kinetics of Styrene

“…The CTA starts the reaction in monomer droplets, and if it is highly hydrophobic and unable to be efficiently transported via the aqueous phase to growing particles, then the molecular weight regulation efficiency will decrease. Thus, a good balance between water solubility and monomer solubility of the CTA is required [20]. In our previous study [21], a similar conclusion was obtained in which ethyl α-p-toluenesulfonyl-methacrylate with a higher C tr significantly reduced the R p .…”

Emulsion copolymerization of styrene and butyl acrylate in the presence of a chain transfer agent.

“…Glass and gel effects equations used to determine the propagation and termination coefficients are expressed according to the value of the mass fraction of polymer in the particles, W p (Nomura et al (1994)) (see table (2). …”

“…However, in emulsion polymerization both molecular weights and rate of polymerization appeared to be affected by chain transfer agents. The mechanisms of radical desorption and absorption by the particles and, consequently, the particles nucleation and kinetics may be significantly modified (Barudio et al (1998); Nomura et al (1982); Nomura et al (1994); Salazar et al (1998)). It has been reported that the key feature of the CTA effect is the diffusional limitation between the different interfaces mainly droplets and water phase.…”

Emulsion terpolymerization of St/MMA/BuA: Modeling of composition, number of particles and the influence of n -DDM on the molecular weights

“…Nomura considers that the main barrier to the mass transfer is from the surface of the droplets to the water and that the disappearance of the monomer droplets gives a jump in the transfer of the n-DDM to the particles (Nomura et al, 1994). On the other hand, Cunningham determined the concentration in the particle of n-DDM, [n-DDM] p , through the characterization of the instantaneous MWD; nevertheless, this procedure can not be used for online industrial applications as the Nomura's model (Cunningham and Ma, 2000).…”