Gabriel Jaramillo-Soto

A Comparison of Reaction Mechanisms for Reversible Addition‐Fragmentation Chain Transfer Polymerization Using Modeling Tools

A kinetic model based on a detailed reaction mechanism of the reversible addition‐fragmentation transfer (RAFT) polymerization was developed. By neglecting some reactions, or using simplifying assumptions, three different reaction mechanisms proposed in the literature can be described with this model. The resulting equations were solved using a self‐developed Fortran code. The cases were also modeled using the Predici® commercial software. Parameter sensitivity analyses and a comparison of performance of the models for the different reaction mechanisms are presented. It was found that the simplest reaction mechanisms considered in this paper cannot adequately describe the behavior of the RAFT polymerization process. It is demonstrated that the controversy in the literature regarding the “six orders of magnitude difference” in the fragmentation rate coefficient, and the “concern” about the “validity” of the commercial software package Predici® to represent the RAFT mechanism have nothing to do with model inadequacy or the alluded “empirical nature” of Predici®. Rather, these issues are merely a matter of not having precise parameter estimates in a very complex, multi‐parameter model, where similar model profiles can be generated with different combinations of model parameters.

RAFT Copolymerization of Styrene/Divinylbenzene in Supercritical Carbon Dioxide

An experimental study on the kinetics of the reversible addition–fragmentation chain transfer (RAFT) dispersion copolymerization with crosslinking of styrene and divinylbenzene in supercritical carbon dioxide (scCO2) is presented. This is the first time that such a controlled polymer network synthesis is carried out in scCO2. S-Thiobenzoyl thioglycolic acid (TBTGA) and dibenzoyl peroxide were used as RAFT agent and initiator, respectively. The polymerizations were carried out in a high pressure cell with lateral sapphire windows at 80°C. The effect of RAFT agent concentration, including the case without RAFT controller, on polymerization rate, molecular weight development, gel fraction, swelling index, and particle morphology was analysed.

RAFT Copolymerization with Crosslinking of Methyl Methacrylate and Ethylene Glycol Dimethacrylate in Supercritical Carbon Dioxide

An experimental study on the kinetics of the reversible addition-fragmentation chain transfer (RAFT) copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDMA) in supercritical carbon dioxide (scCO2) at 65°C and 172 bar is presented. Azobisisobutyronitrile (AIBN) was used as initiator, S-Thiobenzoyl thioglycolic acid as RAFT agent, and Krytox 257 FSL (Dupont) as stabilizer. A 38 mL, high pressure view cell, equipped with one frontal and two lateral sapphire windows, was used as the reacting vessel. The effect of RAFT agent concentration on polymerization rate, molecular weight development, gel fraction, swelling index and particle morphology was analyzed.