Effect of partitioning of monomer and emulsifier in aqueous media on particle formation in emulsion homopolymerization of hydrophobic and hydrophilic monomers with a nonionic emulsifier

Polymerization and Applications of Poly(methyl methacrylate)-Graphene Oxide Nanocomposites: A Review

Graphene oxide (GO)-incorporated poly(methyl methacrylate) (PMMA) nanocomposites (PMMA-GO) have demonstrated a wide range of outstanding mechanical, electrical, and physical characteristics. It is of interest to review the synthesis of PMMA-GO nanocomposites and their applications as multifunctional structural materials. The attention of this review is to focus on the radical polymerization techniques, mainly bulk and emulsion polymerization, to prepare PMMA-GO polymeric nanocomposite materials. This review also discusses the effect of solvent polarity on the polymerization process and the types of surfactants (anionic, cationic, nonionic) and initiator used in the polymerization. PMMA-GO nanocomposite synthesis using radical polymerization-based techniques is an active topic of study with several prospects for considerable future improvement and a variety of possible emerging applications. The concentration and dispersity of GO used in the polymerization play critical roles to ensure the functionality and performance of the PMMA-GO nanocomposites.

Incorporation Behavior of Nonionic Emulsifiers inside Particles and Secondary Particle Nucleation during Emulsion Polymerization of Styrene

In previous studies, it was found that a large amount of the polyoxyethylene nonylphenyl ether nonionic emulsifier, Emulgen 911 (E911), was incorporated inside polymer particles obtained at the completion of a conventional emulsion polymerization with potassium persulfate as a typical water-soluble initiator. In this study, to understand the incorporation phenomenon in more detail, the incorporation behavior during a batch emulsion polymerization of styrene was investigated. The percentage of E911 incorporated inside polystyrene (PS) particles relative to the total weight of E911 used in the polymerization increased to 18% until 50% conversion and then decreased and levelled off to 13% at 70-80% conversion. A similar incorporation behavior was observed in a seeded emulsion polymerization of styrene, in which E911 was added to an emulsifier-free PS seed emulsion to set the same E911 concentration as the batch emulsion polymerization before swelling of the PS seed particles with styrene at 70 °C for 24 h. These indicate that E911 molecules absorbed once into styrene-swollen PS particles partially exited therefrom into the aqueous medium during the polymerizations. When the E911 concentration in the aqueous medium is kept above the critical micelle concentration for a long period by the repartitioning process of E911 from styrene droplets into styrene-swollen particles via aqueous medium and/or exiting from the styrene-swollen particles into the aqueous medium, secondary particle nucleation continues during the polymerization, resulting in PS particles having a broad size distribution.

Amphoteric Ion Exchange Membranes Prepared by Preirradiation-Induced Emulsion Graft Copolymerization for Vanadium Redox Flow Battery

A series of poly(vinylidene difluoride)-based amphoteric ion exchange membranes (AIEMs) were prepared by preirradiation-induced graft copolymerization of styrene and dimethylaminoethyl methacrylate in an aqueous emulsion media followed by solution casting, sulfonation, and protonation. The effects of absorbed dose and comonomer concentration on grafting yield (GY) were investigated. The highest GY of 44.5% at a low comonomer concentration of 0.9 M could be achieved. FTIR, TGA, and X-ray photoelectron spectroscopy (XPS) confirmed the successful grafting and sulfonation of the as-prepared AIEMs. Properties of the AIEMs such as water uptake, ion exchange capacity (IEC), ionic conductivity, and crossover behavior of VO²⁺ ions prepared by this novel technique were systematically investigated and compared with those of the commercial Nafion 115 membrane. It was found that at a GY of 28.4%, the AIEMs showed higher IEC and conductivity, lower permeability of VO²⁺ ions, and a longer time to maintain open circuit voltage than Nafion 115, which was attributed to their high GY and elaborate amphoteric structure. Consequently, this work has paved the way for the development of green and low-cost AIEMs with good performance for vanadium redox flow battery applications.

Hollow polymer nanocapsules: synthesis, properties, and applications

Hollow polymer nanocapsules (HPNs) have gained tremendous interest in recent years due to their numerous desirable properties compared to their solid counterparts.

Emulsion Polymerization with a Biosurfactant

Emulsion polymerization of styrene was conducted using a biosurfactant (i.e., sodium surfactin, hereinafter called just "surfactin") having very low critical micelle concentration (CMC, 2.9 × 10^-3 mmol/L) and biodegradability characteristics. The nucleation mechanism was investigated by comparing with a conventional surfactant (i.e., sodium dodecyl sulfate) system. Unlike the emulsion polymerization systems using conventional surfactants, nucleation mechanisms changed above CMC in the presence of a biosurfactant. At low concentrations of surfactin (above CMC), the polystyrene (PS) particles are likely generated via a soap-free emulsion polymerization mechanism. In contrast, at high surfactin concentrations, the PS particles would be synthesized by following a micellar nucleation mechanism. However, the slope (0.23) of the log N_p versus log C_s plot (N_p: number of particles; C_s: concentration of surfactin) did not obey the Smith-Ewart theory (0.6), this probably being produced by the high adsorbability of surfactin.

Water Absorption Behavior of Polystyrene Particles Prepared by Emulsion Polymerization with Nonionic Emulsifiers and Innovative Easy Synthesis of Hollow Particles

Submicrometer-sized raspberry-like polystyrene (PS) particles, which were prepared by emulsion polymerization with polyoxyethylene nonylphenyl ether nonionic emulsifier (Emulgen 910, HLB 12.2) and potassium persulfate initiator, contained 8.5 vol % (relative to the particle) of water and 5.5 wt % (relative to PS) of Emulgen 910 in the inside. The water absorption decreased the glass transition temperature of the PS particles dispersed in an aqueous medium. The wt % (relative to PS) of the incorporated Emulgen 910 increased with increasing initial Emulgen 910 concentration in the emulsion polymerization, but the wt % (relative to the total Emulgen 910 used) of the incorporated Emulgen 910 was constant at approximately 50% independent of the initial concentration. The vol % (relative to particle) of water increased to 46% by heat treatment at 90 °C for 24 h, which was based on further water absorption, and resulted in spherical hollow particles, where the amount of the incorporated Emulgen 910 remarkably decreased in a short treatment and then remained almost constant during the heat treatment. After another 24 h treatment, the percentage of nonhollow particles increased gradually, which was based on the escape of the water domain together with Emulgen 910 from the inside of the particles. On the other hand, spherical PS particles prepared by emulsifier-free emulsion polymerization did not contain water in the inside and were not changed to hollow ones by a similar heat treatment. From these results, an innovative easy method to synthesize hydrophobic hollow PS particles is proposed.