Incorporation of nonionic emulsifier inside carboxylated polymer particles during emulsion copolymerization: influence of methacrylic acid content

Synthesis of uniform submicron poly(lactic acid)-based particles/capsules by radical precipitation polymerization

Poly(l-lactic acid) (PLLA) is a well-known biopolymer, usually synthesized via step-growth or ring-opening polymerization from lactic acid or a lactide monomer, respectively. PLLA microspherical particles are produced by dispersion polymerization with a ring-opening lactide monomer using a particular copolymer chain as a stabilizer. This is not easy to achieve when dehydration is needed. Here, a robust and simple synthesis of a nearly monodisperse, submicron PLLA-based particle/capsule was proposed via radical precipitation polymerization without the use of surfactant. A commercial PLLA was first glycolyzed with ethylene glycol to obtain a low molecular weight glycolyzed PLLA (GPLLA). Then, the GPLLA was copolymerized with methacrylic acid and ethylene glycol dimethacrylate monomers using a benzoyl peroxide initiator. Active sites on the GPLLA backbone were generated by hydrogen abstraction of benzoyloxy radicals that further copolymerized before self-assembly to form the polymer particles. Uniform particle size of about 580 nm with a low polydispersity index (PDI) of 0.012 was obtained. This method was also implemented to produce nearly monodisperse capsules containing linalool. The particle size of PLLA-based capsules was about 280 nm with narrow particle size distribution (PDI of 0.120). The PLLA-based capsules effectively inhibited microbial growth of Staphylococcus aureus, Escherichia coli and Candida albicans and were not toxic to human cells.

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.

Role of Osmotic Pressure for the Formation of Sub-micrometer-Sized, Hollow Polystyrene Particles by Heat Treatment in Aqueous Dispersed Systems †

In a previous article, it was reported that a rather amount of sulfate end-groups as initiator fragment were buried in the inside of polystyrene (PS) particles, which were synthesized by emulsion polymerization with potassium persulfate initiator and nonionic emulsifier and operated to absorb water from the aqueous medium, resulting in hollow particles, when the PS emulsion was treated at higher temperature than the glass transition temperature of PS. In this article, it was clarified that the water absorption is based on the osmotic pressure between the outside (aqueous medium) and inside of the PS particles due to the buried sulfate end-groups.

Hollow particles are produced by the burying of sulfate end-groups inside particles prepared by emulsion polymerization of styrene with potassium persulfate as initiator in the absence/presence of a nonionic emulsifier

We resolved the longtime enigma in emulsion polymerization of styrene with K₂S₂O₈ by showing the fact that hollow polystyrene particles were successfully prepared by heat treatment in the emulsion state.

Controllable fabrication of nanocrystal-loaded photonic crystals with a polymerizable macromonomer via the CCTP technique

We report an alternative strategy for fabricating nanocrystal-loaded photonic crystals with a polymerizable macromonomer via catalytic chain-transfer polymerization (CCTP) in which CoBF acted as a chain-transfer agent (CTAs). First, monodisperse, functionalized PS-co-PMAA microspheres with polystyrene (PS) cores and poly(methacrylic acid) (PMAA) shells were controllably prepared using styrene and the as-prepared PMAA macromonomer by surfactant-free emulsion polymerization. Then Cd(0.4)Zn(0.6)S nanocrystals capped with as-prepared PMAA macromonomer were synthesized by an in situ growth method. Finally, Cd(0.4)Zn(0.6)S nanocrystal-loaded PS-co-PMAA microspheres hybrids were obtained through simply mixing an aqueous solution of PS-co-PMAA microspheres with an aqueous solution of Cd(0.4)Zn(0.6)S nanocrystals in the appropriate proportions; the multianchor -COOH groups on the surface of core-shell PS-co-PMAA microspheres favor incorporation with Cd(0.4)Zn(0.6)S nanocrystals. Scanning electron microscopy (SEM) images confirm that PS-co-PMAA microspheres are uniformly surrounded by Cd(0.4)Zn(0.6)S nanocrystals. In addition, discrete electronic and photonic states can be combined both with PS-co-PMAA photonic crystals and fluorescent semiconductor Cd(0.4)Zn(0.6)S nanocrystals.