Abstract
This work aims to study the cationic miniemulsion polymerization of styrene catalyzed by iron-containing imidazolium-based ionic liquids. The polystyrenes had very high number-average molar mass around 1300 kg mol-1 at 85 °C, molar-mass dispersity close to 2.0 and glass transition temperature higher than 102 °C with average particle diameter that remained practically unchanged during the reaction, indicating that the monomer droplets correspond to the polymerization locus. First-order kinetics up to a limit conversion, along with the increase in molar mass as the temperature decreases, styrene polymerization at low temperatures and catalyst inability to polymerize monomers that react exclusively via free radical and/or anionic polymerization, indicate the cationic nature of polymerization. 1H-NMR and 13C-NMR spectra suggested the formation of polystyrene, allowing for tacticity distribution quantification: 10% isotactic, 20% atactic and 70% syndiotactic configurations. TEM micrographs confirmed the formation of spherical polymer nanoparticles and the presence of catalysts in the polymer matrix.
Highlights
Polymerizations performed in heterogeneous medium have many advantages, such as high heat removal capacity, low viscosity of the end product, ease of homogenization and manipulation, among others
We recently described the efficient encapsulation of hexadecane in high molar mass polystyrene nanoparticles obtained through cationic miniemulsion polymerization[20], and the synthesis of several ILs catalysts
We extend here the use of different types of iron-containing imidazolium-based ionic liquids: 1-butyl3-methylimidazolium heptachlorodiferrate (BMI⋅Fe2Cl7), 1-methyl-3-carboxymethylimidazolium heptachlorodiferrate (MAI⋅Fe2Cl7) and 1,2-Bis(methylimidazolium)ethane bis(heptachlorodiferrate), which efficiently acted as catalysts for styrene bulk polymerization[25,26], expanding its applications as catalysts in a water-phase dispersed polymerization process
Summary
Polymerizations performed in heterogeneous medium have many advantages, such as high heat removal capacity, low viscosity of the end product, ease of homogenization and manipulation, among others. For these reasons, polymerizations performed in water as a continuous phase are among the most widely used methods for large scale polymer synthesis[1]. In recent decades several efforts have been made in order to develop new catalysts very attractive to the ionic polymerization of different monomers in aqueous dispersed medium[3,4,5,6,7,8,9,10,11,12]. Polymerizations occur slowly and at the monomeric/water droplets interface resulting in low molar mass polymers and narrow molar mass distribution[8,9]
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