Variations around the presence and position of sulfur in sugar-derived cyclic monomers: influence on polymerisation thermodynamics, polymer sequence and thermal properties

Introducing sulfur atoms into a polymer backbone is an interesting way to valorise an abundant by-product of the chemical industry and to modulate polymerisation thermodynamics towards polymer recycling to monomer. For bio-derived polymers, which are often highly oxygenated, replacing oxygen for sulfur atoms can also be a way to fine-tune their properties and widen their application scope. Herein, we report a series of 6-membered cyclic carbonate and thiocarbonate (xanthate, thionocarbonate and monothionocarbonate) monomers made from carbohydrate derivative d-glucal, in which the number and position of sulfur atoms in the polymerisable ring have been varied. Their organocatalysed ring-opening polymerisation (ROP) is demonstrated and contrasted in terms of ROP thermodynamics, polymer sequence, regioregularity and thermal properties. While the influence of the thiocarbonyl function varied across the series, a C-S bond in the polymerisable ring reduced ring strain and maximum monomer conversion at equilibrium. Sulfur did not induce crystallinity in the polymers studied, but the onset of thermal degradation and the glass transition temperature decreased with the amount of sulfur in the polymer linkages, regardless of its position. Degradation of the polymers under UV light was also explored. This work provides fundamental insight for the design of future sulfur-containing renewable polymeric materials.