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%).
1,3-Bis(mesityl)imidazolium tetraphenylborate (IMesH BPh ) can be synthesized in one step by anion metathesis between the corresponding imidazolium chloride and sodium tetraphenylborate. In the presence of 2-isopropylthioxanthone (sensitizer), an IMes N-heterocyclic carbene (NHC) ligand can be photogenerated under irradiation at 365 nm through coupled electron/proton transfer reactions. By combining this tandem NHC photogenerator system with metathesis inactive [RuCl (p-cymene)] precatalyst, the highly active RuCl (p-cymene)(IMes) complex can be formed in situ, enabling a complete ring-opening metathesis polymerization (ROMP) of norbornene in the matter of minutes at room temperature. To the best of our knowledge, this is the first example of a photogenerated NHC. Its exploitation in photoROMP has resulted in a simplified process compared to current photocatalysts, because only stable commercial or easily synthesized reagents are required.
In this work, maghemite intercalated montmorillonite (γFe2O3-MMT)/polymer nanocomposites loaded with 1 or 2 wt.% of nanofillers were obtained by photopolymerization of difunctional acrylate monomers. The γFe2O3-MMT nanofillers were prepared by a new method based on the in situ formation of maghemite in the interlayer space of Fe-MMT using a three step process. X-ray diffraction (XRD), chemical analysis, TG/DTA and transmission electron microscopy (TEM) characterization of these nanofillers indicated the efficiency of the synthesis. When following the kinetics of the photopolymerization of diacrylate-γFe2O3-MMT nanocomposites using FTIR spectroscopy no significant inhibition effect of the nanofillers was observed at a loading up to 2 wt.%. These innovative nanocomposites exhibit improved mechanical properties compared to the crude polymer.
Abundance, low cost and ene functionality are the key assets of terpenes in view of a large-scale use as renewable monomers in radical polymerisation. However, their sterically hindered ene structure has been mostly ineffective in a chain-growth mechanism, leading to sluggish activity. To address this challenge, the alternative of a step-growth diene-dithiol linear photopolymerisation is investigated here. Four nonmodified dienic terpenes-geranyl acetate, linalool, limonene and geraniol-are reacted with ethylene glycol dithiol in various conditions. In bulk and solution, limited conversions prevent the formation of high-molecular-weight polymers. By contrast, a miniemulsion containing the two difunctional comonomer yields higher conversions (> 98 %) in less than 10 min of UV irradiation, making the formation of polythioether chains possible. Our assumption is that a thiol-ene polymerisation confined in nanodroplets may drive high conversion thanks to a radical compartmentalization effect. The resultant aqueous polymer dispersions show an average diameter ranging from 100 to 140 nm, low glass transition temperature (<-30 °C), but only moderate molecular weights between 4 and 5 kDa for the fraction soluble in THF. These promising results pave the way for a novel semi-synthetic and ecoefficient approach to polymer latexes based on natural terpene monomers.
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