Radical Photopolymerization in Miniemulsions. Fundamental Investigations and Technical Development

Miniemulsion photopolymerization in a continuous tubular reactor: particle size controlviamembrane emulsification

Synthesis of polymeric nanoparticles of adjustable size in the submicron-range 200–950 nm has been conductedviamembrane emulsification combined with photoinduced miniemulsion polymerization in a continuous tubular flow reactor.

Visible-Light-Regulated Controlled/Living Radical Polymerization in Miniemulsion

The implementation of photopolymerization processes in aqueous dispersed systems has the potential to afford greener approaches to the preparation of polymeric materials and has motivated researchers to perform photopolymerization in emulsion. However, these previous works have employed UV irradiation to induce photodegradation of a photoinitiator in addition to specialized equipment setups, thus limiting widespread use of these approaches. In this work, we aim to remedy these drawbacks via the implementation of photoredox catalysis in the regulation of a controlled/living radical polymerization under visible light. Utilizing the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process, we report the miniemulsion polymerization of styrene mediated by a household grade blue LED (λ_max = 460 nm, 0.73 mW/cm²). The polymerization rate can be easily manipulated by light intensity and catalyst concentration. Finally, temporal control was demonstrated via ON/OFF experiments, which shows that no significant detriment is caused by prolonged interruptions to the light exposure.

The use of chemical actinometry for the evaluation of the light absorption efficiency in scattering photopolymerizable miniemulsions

Oil-in-water miniemulsions containing a mixture of monomers as the dispersed organic phase have been shown recently to be promising media for the development of photoinitiated polymerization processes. Albeit a crucial factor for a successful application, the efficiency of light absorption by the photoinitiator in these highly scattering systems is difficult to evaluate. In this work, a well-characterized water insoluble chemical actinometer (DFIS) replaced the oil-soluble photoinitiator, and was used as a probe and a model for UV light absorption in miniemulsions of variable droplet sizes and organic phase compositions (i.e. at different levels of scattered light). In the first step, the photon flux absorbed by the actinometer was determined in model miniemulsions based on an inert solvent (ethyl acetate), at a low oil phase content (3.0-6.0 wt%). For these low to moderately scattering systems, the photon flux absorbed by the actinometer in the miniemulsions was comparable to that in a homogeneous solution of ethyl acetate. In the second step, the absorbed photon flux was investigated in photopolymerizable miniemulsions (a mixture of acrylate monomers as oil phase). Surprisingly, in spite of much higher scattering coefficients than those found for ethyl acetate based miniemulsions of otherwise the same composition, the photon flux absorbed by the actinometer in photopolymerizable miniemulsions showed only a small decreasing trend. Such a result may be considered favorable for the further development of applications of photopolymerizations in miniemulsions.

Light-Mediated Thiol-Ene Polymerization in Miniemulsion: A Fast Route to Semicrystalline Polysulfide Nanoparticles

Historically, the synthesis of aqueous polymer dispersions has focused on radical chain-growth polymerization of low-cost acrylate or styrene emulsions. Herein, we demonstrate the potential of UV-initiated thiol-ene step-growth radical polymerization, departing from a nontransparent difunctional monomer miniemulsion based on ethylene glycol dithiol and diallyl adipate. Performed without solvent and at ambient conditions, the photopolymerization process is energy-effective, environmentally friendly, and ultrafast, leading to full monomer consumption in 2 s, upon irradiating a miniemulsion contained in a 1 mm thick quartz cell microreactor. The resultant linear poly(thioether ester) particles have an average diameter of 130 nm. After water evaporation, they yield a clear elastomeric film combining chemical resistance and high degree of crystallinity (55%).

Continuous-flow synthesis of polymer nanoparticles in a microreactor via miniemulsion photopolymerization

Water-based photopolymerization in microreactor using compact UV fluorescent lamps can create a breakthrough technology to produce polymer latexes in a safer, more environmental-friendly and energy-efficient way.