Two-Stage Dispersion Polymerization toward Monodisperse, Controlled Micrometer-Sized Copolymer Particles

Abstract

We describe a two-stage dispersion polymerization process to prepare monodisperse micrometer-sized polymer particles in which problematic reagents, such as functional monomers and cross-linkers that commonly disrupt the particle-forming process, were added to the reaction after the nucleation stage was complete. Comonomers added after this point became incorporated into the particles without disturbing the final particle size and size distribution. In this way dye-labeled or functional group-containing micrometer-sized particles with a very narrow size distribution were prepared. By varying the amount of monomer added in the second stage, the final particle diameter could be controlled precisely. Most important of all, this synthetic strategy allowed us to prepare cross-linked particles containing up to 3 mol % cross-linking agent.

Porous polymer particles—A comprehensive guide to synthesis, characterization, functionalization and applications

“…7(D)), resulting in porous particles. The reason that the crosslinker should be introduced later is well explained by Winnik et al [64] They reported that crosslinkers and polar monomers significantly influence the particle growth and the monodispersity may be lost in such cases. The most important stage for the monodispersity of final particles was found to be the nucleation step.…”

“…The crosslinker should be added only after the nucleation stage ( Fig. 7(C)), which corresponds to less than 1% monomer conversion [64]. By the addition of crosslinker, porogen swollen particles continue to grow and crosslink ( Fig.…”

Controlled/living heterogeneous radical polymerization in supercritical carbon dioxide

“…28,29 Choe and coworkers 113 have reported that RAFT dispersion polymerization of S in ethanol at 70 C results in phase separation (a pink coagulant at the bottom of the reactor) when the RAFT agent is charged at the beginning of the polymerization. However, use of the two-stage method, [114][115][116] whereby the RAFT agent is added after the particle nucleation has been completed, results in good control/livingness without phase separation as well as a narrow particle size distribution. It cannot be stated with certainty whether the scCO 2 /MMA RAFT dispersion polymerization 28,29 proceeds satisfactorily without application of the two-stage method due to the characteristic features of scCO 2 (e.g., low viscosity, high diffusivity, etc.).…”

“…68 However, the addition of CLRP reagents (e.g., RAFT agent) leads to a marked broadening of the distribution. [114][115][116]138 In the dispersion polymerization of MMA in scCO 2 at 65 C using a PDMS stabilizer, the addition of a RAFT agent led to a slight reduction in particle diameter from $4.0 lm to 1.4 lm, and a broadening in the particle size distribution. The conversion range over which nucleation (particle formation) occurs is the most important factor-a short nucleation stage is required for a narrow particle size distribution.…”

“…The nucleation stage is prolonged in dispersion CLRP because high MW polymer is not formed instantaneously, unlike in a nonliving system. This problem has been overcome by using the ''twostage'' approach [114][115][116] developed by Song and Winnik, whereby, e.g., the RAFT agent is added after the nucleation stage has been completed (\a few percent conversion 139 ). The problem with broad particle size distributions in dispersion CLRP remains when using scCO 2 as the continuous phase, as expected based on the above rationale.…”