Radical ring-opening polymerization of sustainably-derived thionoisochromanone

Abstract

We present the synthesis, characterization and radical ring-opening polymerization (rROP) capabilities of thionoisochromanone (TIC), a fungi-derivable thionolactone. TIC is the first reported thionolactone to readily homopolymerize under free radical conditions without the presence of a dormant comonomer or repeated initiation. Even more, the resulting polymer is fully degradable under mild, basic conditions. Computations providing molecular-level insights into the mechanistic and energetic details of polymerization identified a unique S,S,O-orthoester intermediate that leads to a sustained chain-end. This sustained chain-end allowed for the synthesis of a block copolymer of TIC and styrene under entirely free radical conditions without explicit radical control methods such as reversible addition-fragmentation chain transfer polymerization (RAFT). We also report the statistical copolymerization of ring-retained TIC and styrene, confirmed by elemental analysis and energy-dispersive X-ray spectroscopy (EDX). Computations into the energetic details of copolymerization indicate kinetic drivers for ring-retaining behavior. This work provides the first example of a sustainable feedstock for rROP and provides the field with the first six-membered monomer susceptible to rROP, expanding the monomer scope to aid our fundamental understanding of thionolactone rROP behavior.

An orthogonal O,S-CKA monomer for the introduction of thioester and/or thionoester functionalities by radical polymerization

“…Therefore, if a radical species were to add onto an inchain thionoester, unless there is a driving force that could facilitate further reactivity, the radical species should be released and the thionoester group regenerated. Ring-strain is one of the possible driving forces, this force being harnessed by thionolactone rROP monomers to introduce thioester groups during radical polymerization, [17][18][19][20][21][22][23][24] but this phenomenon can be excluded in this case. If analogous processes are indeed occurring, they do not occur to a significant extent that could explain the formation of substantial levels of thioester moieties.…”

“…2, DOT, compound 2 ). 17–24 These additional susceptibilities have been envisioned to be able to assist in their environmental degradation as nitrogen and sulfur containing molecules ( i.e. , amino acids) are ubiquitous throughout the natural environment, as are natural oxidation processes.…”

Ring size-reactivity relationship in radical ring-opening copolymerisation of thionolactones with vinyl pivalate

“…Recently, the Roth group 16 reported the homopolymerisation of 7-membered DBT (Scheme 1b) and the degradation of the obtained polymers with N -ethylamine or sodium methoxide. Earlier this year, the Reineke group 17 reported TARO homopolymerisation of the 6-membered 3-thionoisochromanone (TIC, Scheme 1b) and its copolymerisation with styrene. Our team 18 reported successful copolymerisation of 3,6-dimethyl-5-thioxo-1,4-dioxan-2-one and 3,6-dimethyl-1,4-dioxane-2,5-dithione (respectively TLD and DTLD, Scheme 1b) with tert -butyl acrylate, styrene and methyl methacrylate with a fraction of thionolactone incorporated in the ring closed form.…”