Challenges in the Emulsion Co- and Terpolymerization of Vinylidene Fluoride.

The feasibility of co- and terpolymerizing vinylidene fluoride (VDF) with ethylene (C2) and/or vinyl acetate in an emulsion polymerization process was studied for different C2 pressures, initiator concentration, surfactant concentration, pH, C2 injection protocols, and the influence of vinyl acetate (VAc) in the reaction medium. Pressure drop and temperature profiles as well as gravimetry were used to follow the rate of polymerization. The microstructure of the synthesized products was assessed by fluorine and hydrogen nuclear magnetic resonance spectroscopy (19F and 1H NMR). C2 was found to cause an inhibition/retardation effect on the copolymerization with VDF (and with VDF/VAc). However, statistical copolymers containing VAc and VDF were synthesized by reducing as much as possible the homogeneous nucleation of the VAc in the water phase. This was done by adding VAc into the reaction after the homogeneous-coagulative nucleation of VDF takes place (around 5 min after initiator injection).

Investigation of the Adsorption of Amphipathic macroRAFT Agents onto Montmorillonite Clay.

Recently, there has been significant interest in the use of the reversible addition-fragmentation chain-transfer (RAFT) technique to generate a variety of organic/inorganic colloidal composite particles in aqueous dispersed media using the so-called macroRAFT-assisted encapsulating emulsion polymerization (REEP) strategy. In this process, special attention should be paid to the adsorption of the macromolecular RAFT (macroRAFT) agent onto the inorganic particles, as it determines the final particle morphology and can also influence latex stability. In this work, different amphipathic macroRAFT agents were synthesized by RAFT, and their adsorption onto commercial Montmorillonite clay Cloisite Na+ (MMT) was studied by means of adsorption isotherms. Three types of macroRAFT agents were considered: a nonionic one based on poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA), anionic ones, including a block copolymer and random copolymers, based on acrylic acid (AA), BA and PEGA, and cationic ones based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), BA and PEGA. Six adsorption isotherm models (Langmuir, Freundlich, Tempkin, Redlich-Peterson, Sips, and Brunauer-Emmett-Teller) were adjusted to the experimental isotherms. The nonionic macroRAFT agent formed a monolayer on the clay surface with a maximum adsorption capacity of 400 mg g-1 at pH 8, as determined from the Sips adsorption model. Adsorption of the AA-based macroRAFT agents onto MMT was moderate at alkaline pH due to electrostatic repulsions, but increased with decreasing pH. The DMAEMA-based macroRAFT agents displayed a much stronger interaction with the oppositely charged MMT surface at acidic pH due to electrostatic interactions, and the concentration of adsorbed macroRAFT agent reached values as high as 800 mg g-1. The BET model fitted the experimental data relatively well indicating multilayer adsorption promoted by the presence of the hydrophobic BA units. In addition, the cationic macroRAFT agents afforded stable MMT/macroRAFT agent complexes as evaluated by dynamic light scattering and zeta potential analyses.