“Continuous” Emulsifier-Free Emulsion Polymerization Brian Edwards McMaster University, Department of Chemistry

Contents Introduction Equipment/Polymerization Particle Growth Mechanism CEFEP Vs. Multistage Seeding Conclusions

Introduction Simple alternative for the production of mono-disperse polymeric particles in a wider range of sizes Larger size mono-disperse particles have been produced by a multistage seeding process, however this is: Tedious Difficult to control

Polymerization - Equipment Monomer tank Water tank Reactor Condenser N2 continuously bubbled through system

PS/2% DVB - CEFEP A. 284 nm at 1.5 h B. 442 nm at 6 h

PS/2% DVB – Batch/CEFEP 630 nm at 5 h B. 1.9 m at 14 h

PMMA/3 mol % EGDMA – Batch/CEFEP A.758 nm at 4.5 h B.1.3 m at 5.5 h

CEFEP Amount and timing of initiator is significant Rate of polymerization & particle size determined by monomer feed rate Low initiator concentrations function well

CEFEP – Contributions To Polydispersity Later addition of initiator Excessive initiator Increase in polymerization temperature

CEFEP Therefore: Polymerization rate and initiator concentration should be monitored Add initiator only when a significant decrease in these variables

Mechanism of Particle Growth Oligomeric free radicals: May terminate - in situ surfactants May grow – particle precursors & decrease in situ surfactant concentration

Mechanism of Particle Growth CEFEP continues with a core-shell growth mechanism Monomer feed rate is slow Polymerization occurs in outer shell

Multistage Seeding Process First stage B. Second stage

Multistage Seeding Process Third Stage B. Fourth Stage

Multistage Vs. CEFEP Smaller particle size (Direct CEFEP) Larger particle size, however Preparation of seed lattice – multistage Consideration of seed particle concentration – hard to control later in reaction Phase separation Secondary nucleation Smaller particle size (Direct CEFEP) After particle nucleation, just add monomer Need to consider monomer and initiator feed rates/amounts

Conclusions Simple Preliminary batch polymerization can produce quite large particles Spherical particles with uniform cross-linking Monodispersity is achieved – simply maintain temperature and monomer/initiator amounts/feed rate

References Li, J.Q. and Salovey, R. J Polym Sci Part A: Polym Chem 2000, 38, 318. Zou, D., Ma, S., Guan, R., Park, M., Sun, L., Aklonis, J.J. and Salovey, R. J Polym Sci Part A: Polym Chem 1992, 30, 137. Zou, D., Sun, L. and Aklonis, J.J. J Polym Sci Part A: Polym Chem 1992, 30, 1463.

References 4. O’Callaghan, K.J., Paine, A.J. and Rudin, A. J Appl Polym Sci 1995, 58, 2047. 5. Kim, J.H., Chainey, M., El-Aasser, M.S. and Vanderhoff, J.W. J Polym Sci Part A: Polym Chem 1992, 30, 171. 6. O’Callaghan, K.J., Paine, A.J. and Rudin, A. J Polym Sci Part A: Polym Chem 1995, 33, 1849.