Structural Metamorphoses of d-Xylose Oxetane- and Carbonyl Sulfide-Based Polymers In Situ during Ring-Opening Copolymerizations

Abstract

Polymers constructed from copolymerizations of carbohydrates with C1 feedstocks are promising targets that provide transformation of sustainably sourced building blocks into next-generation, environmentally degradable plastic materials. In this work, the initial intention was to expand beyond polycarbonates prepared by the copolymerization of oxetanes derived from D-xylose with CO 2 and incorporate sulfur atoms through the establishment of monothiocarbonates that would provide the ability to modulate the backbone compositions and result in unique effects upon the chemical, physical, and mechanical properties. Therefore, the syntheses of poly(1,2-O-isopropylidene-α-D-xylofuranose monothiocarbonate)s were investigated by ring-opening copolymerizations of 3,5-anhydro-1,2-O-isopropylidene-α-D-xylofuranose with carbonyl sulfide (COS) facilitated by (salen)CrCl/cocatalyst systems. Unexpectedly, when copolymerization temperatures exceeded 40 °C, oxygen/sulfur exchange reactions occurred, causing in situ dynamic backbone restructuring through a series of inter-related and complex mechanistic pathways that transformed monothiocarbonate monomeric repeating units into carbonate and thioether dimeric repeating units. These backbone structural compositional transformations were investigated through a combination of Fourier transform infrared and nuclear magnetic resonance spectroscopic techniques and were demonstrated to be easily tuned via temperature and catalyst/cocatalyst stoichiometries. Furthermore, the regiochemistries of these D-xylose-based sulfur-containing polymers revealed that monothiocarbonate monomeric repeating units had a head-to-tail connectivity, while the carbonate and thioether dimeric repeating units had dual head-to-head and tail-to-tail connectivities. These sulfur-containing polymers exhibited enhanced thermal stabilities compared to their oxygen-containing polycarbonate analogues and revealed variations in the effects upon glass transition temperatures, demonstrating the effect of sulfur incorporation in the polymer backbone. These findings contribute to the advancement of sustainable polymer production by using feedstocks of natural origin coupled with COS.

Ring-opening terpolymerisation of phthalic thioanhydride with carbon dioxide and epoxides

“…9 However, sulfur-containing variants also exist, such as cyclic thioanhydride/epoxide ROCOP forming poly(ester- alt -thioesters) or CS 2 /epoxide ROCOP yielding poly(thiocarbonates) with improved photochemical and oxidative degradability compared to their related all-oxygen analogues. 10–22 Thermal properties can also be improved by formal sulfuration as recently reported for CS 2 /oxetane copolymers, which are semi-crystalline, whereas the CO 2 /oxetane analogues are amorphous. 23–25 Moving to more complex monomer mixtures comprising three monomers A , B and C ( e.g.…”

Organocatalytic Synthesis of Poly(thiocarbonate) from Xylose and Carbonyl Sulfide

“…The organocatalytic copolymerization of XO and COS yields the copolymer incorporating two major repeating units of monothiocarbonate and carbonate-co-thioether (Table 1), which is similar to the results demonstrated by Darensbourg and co-workers. 45 XO was synthesized from D-xylose according to the literature 46 via three steps with 51% yield, an E factor of 2.31, and an atom economy of 30% (Supporting Information, Scheme S1 and Figures S1−S4). The relatively low E factor means little waste and, consequently, a small negative environmental impact.…”

“…By contrast, when the polymerization temperature was set as 60 °C, the metal catalyst system of (salen)CrCl/PPNCl resulted in oxygen/sulfur exchange reactions and afforded the copolymer with more than 30% carbonate-co-thioether units, as reported by Darensbourg and co-workers. 45 Further increasing the polymerization temperature to 80 °C, the binary organocatalysts of TEB/PPNCl yielded the copolymer with 48% monothiocarbonate and 52% carbonate-co-thioether units (Figures S13 and S14). Our polymers show a much broader Đ values (1.4−2.1) than that (1.1−1.3) obtained from the (Salen)CrCl/PPNCl system by Darensbourg and Wooley, 45 which is mainly related to the S2).…”

“…45 Further increasing the polymerization temperature to 80 °C, the binary organocatalysts of TEB/PPNCl yielded the copolymer with 48% monothiocarbonate and 52% carbonate-co-thioether units (Figures S13 and S14). Our polymers show a much broader Đ values (1.4−2.1) than that (1.1−1.3) obtained from the (Salen)CrCl/PPNCl system by Darensbourg and Wooley, 45 which is mainly related to the S2). trace amount of water in the reaction mixture and the occurrence of transesterification in our polymerization system.…”

“…44 Recently, Darensbourg and co-workers reported the copolymerization of COS and a biorenewable cyclic ether of D-xylose oxetane (XO), which was facilitated by the (salen)-CrCl/cocatalyst system (Scheme 1). 45 Interestingly, by variation of the temperature, copolymerization was conducted from essentially no to extensive oxygen/sulfur exchange reactions, yielding copolymers with monothiocarbonate or carbonate-co-thioether repeating units. However, the obtained copolymers with complete XO-alt-COS repeating units have low molecular weights (M n ) of 3.8 kDa.…”