No abstract

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%).

Organic−inorganic UV-curing of organosilanes containing epoxy and trialkoxysilyl functional groups in the same monomer was implemented using a diaryl iodonium salt as cationic photoinitiator. UV-generated Brönsted acids through photolytic degradation were found to be effective in catalyzing both epoxy ring-opening polymerization and alkoxysilane sol−gel polycondensation reactions. Competition between the formation of inorganic and organic phases was kinetically studied using real-time Fourier transform infrared spectroscopy (RT-FTIR). The nature of the hybrid monomer, the effect of changing the film thickness, the type of substrate and the influence of laminated conditions on the polymerization kinetics were assessed. 29Si and 13C solid state NMR measurements were also performed to investigate the structure of the UV-cured hybrid materials.

Radical step-growth photopolymerization of dithiol−diene monomer miniemulsion is shown to be a highly efficient, robust, and versatile route to generate film-forming linear poly(thioether) latexes. At extremely fast rates, the process results in high-molecular-weight polysulfide products, exhibiting both semicrystalline and oxidation-responsive properties. Four key issues are addressed as regards the practical implementation of this novel UV-driven waterborne technology: the preparation of a photolatent and colloidally stable thiol−ene monomer miniemulsion, the identification of key experimental parameters controlling reaction kinetics and polymer microstructure, the characterization of film semicrystallinity, and the application of poly(thioether ester) latexes as dual-stimuli-responsive nanocarriers sensitive to both oxidation and hydrolysis.