Conventional emulsion and miniemulsion homopolymerization and copolymerization of vinyl acetate and vinyl 2-ethylhexanoate monomers

For monomers possessing significantly low water solubility (V2EH), miniemulsion polymerization can substantially enhance the reaction kinetics compared to conventional emulsion systems. While the monomer droplets in a conventional emulsion only serve as reservoirs supplying monomer, diffusional restrictions of the monomer to get to the site of nucleation and the growing particles effectively slows the reaction. For miniemulsions, the monomer is already at the site of nucleation and growth; and therefore, is not as severely afflicted.;When using reactive TREM LF-40 versus its nonreactive, hydrogenated derivative, trends comparing VAc and V2EH conventional emulsion homopolymerization kinetics display that the chain transfer to the surfactant retards the reaction. This effect was not as prevalent in the miniemulsion systems, which was attributed to larger particles being generated. The miniemulsion particles' surface-to-volume is less compared to conventional emulsions; therefore, the role TREM LF-40 plays in slowing the reaction is diminished.;The polymeric version of TREM is also a reasonably good surfactant in both conventional and miniemulsion homopolymerization. Although a nonreactive form without allylic functionality, increasing poly(TREM) concentration lead to slower kinetics. This result is attributed to the polymeric surfactant sitting on the outside of the particle and effectively behaving as a barrier to radical entry.;Copolymerization showed V2EH incorporates well with VAc. Kinetics studies indicated that varying the monomer ratio did not affect the miniemulsion system as significantly compared to conventional emulsion copolymerization, which was attributed to V2EH monomer's low water solubility. VAc's higher water solubility is suspected to facilitate V2EH's transport through the aqueous phase; therefore, enhancing the kinetics as the VAc component is increased. Additionally, miniemulsion copolymerization has each monomer already present at the site of nucleation and growth; therefore, little is gained as the comonomer ratio is altered.;Miniemulsion copolymerization also resulted in better incorporation of the two monomers. Increased alkaline stability of the miniemulsion copolymers stems from having the two monomers forced to copolymerize at the same location. VAc has the potential to more readily homopolymerize in the aqueous phase than does V2EH; therefore, in conventional copolymerization a significant component of the final latex product richer in VAc content exists.