Semi-renewable latex via step-photopolymerization of dithiol and dienic terpenes

Abstract

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.

β-Carotene/Limonene Derivatives/Eugenol: Green Synthesis of Antibacterial Coatings under Visible-Light Exposure

“…Among the bio-sourced monomers, terpenes were widely investigated in photochemical processes because of their structural versatility. For instance, limonene, extracted from citruses, shows two allyl functions, which were used in the thiol-ene “click reaction” process. − These allyl groups can also be epoxidized for the cationic polymerization. It is possible to modify only the allyl groups on the cycle selectively, which gives limonene 1,2-epoxide (Lim), while dipentene dioxide (DPDO) is obtained when the two allyl groups are epoxidized.…”

Thiol–Ene (Click) Reactions as Efficient Tools for Terpene Modification

“…As an alternative method, a step‐growth linear photopolymerization reaction of terpenes has also been reported . Thus, four non‐modified diolefin monoterpenes, that is, limonene, geranyl acetate, geraniol, and linalool, were treated with ethylene glycol dithiol ( 26 ) under UV irradiation under either bulk and solution or mini‐emulsion conditions to afford polythioethers 27 – 30 (Scheme ).…”