Modeling of precipitation polymerization II: calculation of macroradicals concentrations in the continuous and dispersed phases

Abstract

According to Hunkeler model, precipitation polymerization of acrylic acid in organic media takes place simultaneously in the both dispersed and continuous phases. In this research, a model is presented based on mass balances of individual species. Hence, concentrations of macroradicals and polymer chains, in different chain lengths, were calculated in the both phases. Number-and weightaverage degrees of polymerization and their distributions were concluded in the both dispersed and continuous phases. Calculation of macroradicals concentration was conducted with quasi-steady state approximation (QSSA) as well as without QSSA (based on the governing differential equations). Macroradical precipitate as soon as reaching to critical chain length. Moreover, precipitation is the main termination reaction in the continuous phase. Polymer with critical chain length is the most populated species in the dispersed phase. Comparison of theoretical and experimental results is in good agreement. QSSA theory gives better results than without QSSA theory because occlusion of macroradicals in the dispersed phase does not occur in the precipitation polymerization of water-soluble monomers in the organic media. This article has proved that the polydispersity index (PDI) of polymer product in the precipitation polymerization of acrylic acid in toluene that follows simultaneous polymerization model is less than that of PDI in the other free radical polymerization methods. Centrifugation method was used to sediment fine polymer particles. The yield of reaction was increased by sedimentation process.

Modeling RAFT Gelation and Grafting of Polymer Brushes for the Production of Molecularly Imprinted Functional Particles

“…Modeling of precipitation/dispersion polymerization is a complex subject even with a vinyl monomer homopolymerization. Different modeling approaches are reported in the literature to deal with such kinds of reaction systems . In the solution polymerization model, it is considered that polymerization takes place only in the continuous phase .…”

“…The interior polymerization model accounts for initiation in the continuous phase and propagation/termination in the polymer particles . Finally, with the simultaneous polymerization model, the polymerization reactions are considered to occur both in the continuous and dispersed phases . As far as it is of our knowledge, the modeling of RAFT or FRP precipitation crosslinking polymerization has not been previously addressed in the framework of any of these four theoretical alternatives.…”