RAFT Polymerization In Inverse Emulsions

A conventional emulsion is an aqueous dispersion of oil droplets. While an inverse emulsion is an emulsion in which the continuous phase and dispersed phase are inverted. Inverse miniemulsion is similar to inverse emulsion, the main differences between them are that inverse miniemulsion have smaller particles and more uniform particle size distribution. Inverse emulsion polymerization and inverse miniemulsion polymerization are the main methods for obtaining water-soluble polymers based on poly (acrylamide) (PAM) and poly (acrylic acid) (PAA) with high molecular weight and low viscosity.Living free radical polymerization (LRP) can be used to synthesize polymers with predetermined molecular weight, narrow molecular weight distribution and controllable end groups. Till now, three major LRP processes, nitroxide radical mediated polymerization (NRMP), Aton transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) polymerization have been studied extensively. RAFT polymerization is especially suitable for miniemulsion since RAFT polymerization can be performed under mild reaction conditions and has a faster polymerization rate than SFRP and ATRP from a mechanism perspective. In this current research, RAFT polymerization was utilized in inverse miniemulsion polymerization and well controlled PAA was synthesized. Premium reaction parameters were also determined. According to published reports, the dominant nucleation mechanism in inverse miniemulsion of acrylamide (AM) is droplet nucleation. Acrylic acid (AA) is water-soluble, but also has significant solubility in cyclohexane (continuous phase). The kinetics of AA polymerization could be different from AM. Therefore, DLS and GPC were used to investigate the polymerization process and nucleation mechanism of AA. In addition, well-defined statistical and diblock copolymers with AM and AA were synthesized by inverse miniemulsion RAFT polymerization. Compositional drift was observed and discussed. GPC, NMR and SEM were used to analyze and characterize poly (AA-co-AM) and PAA-b-PAM.For inverse emulsion polymerization, the kinetic mechanism can be affected by many factors such as initiators, surfactants, and continuous phase. Until now, a fully comprehensive description of the nucleation mechanism of inverse emulsion polymerization has not been made. Based on the fact that GPC RI trace accounts for the polymer species and UV trace at 311 nm reflects the presence of the C=S double bond in the RAFT agent, the fraction of controlled polymer and uncontrolled polymer can be determined respectively by comparing and calculating the areas of RI and UV curves. Thus, well-defined PAM was synthesized by RAFT inverse emulsion polymerization and the nucleation mechanism is proposed and studied by GPC, the polymerization process was fully described and verified by SEM. RAFT polymerization can be used as a universal technique in investigating the kinetic mechanism of inverse emulsion polymerizations of various monomers.