Tran David K, Braaksma Ashley N, Andras Autumn M, Boopathi Senthil K, Darensbourg Donald J, Wooley Karen L
Departments of Chemistry, Texas A&M University, College Station, Texas 77842, United States.
Materials Science & Engineering, Texas A&M University, College Station, Texas 77842, United States.
J Am Chem Soc. 2023 Aug 23;145(33):18560-18567. doi: 10.1021/jacs.3c05529. Epub 2023 Aug 14.
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 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--isopropylidene-α-d-xylofuranose monothiocarbonate)s were investigated by ring-opening copolymerizations of 3,5-anhydro-1,2--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 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 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.
由碳水化合物与C1原料共聚构建的聚合物是很有前景的目标，它能将可持续来源的结构单元转化为下一代环境可降解的塑料材料。在这项工作中，最初的意图是超越通过将源自d-木糖的氧杂环丁烷与CO共聚制备的聚碳酸酯，并通过建立单硫代碳酸酯引入硫原子，这将能够调节主链组成，并对化学、物理和机械性能产生独特影响。因此，通过（salen）CrCl/助催化剂体系促进3,5-脱水-1,2-异丙叉基-α-d-木糖呋喃糖与羰基硫（COS）的开环共聚，研究了聚（1,2-异丙叉基-α-d-木糖呋喃糖单硫代碳酸酯）的合成。出乎意料的是，当共聚温度超过40℃时，发生了氧/硫交换反应，通过一系列相互关联且复杂的机理途径导致主链动态重组，将单硫代碳酸酯单体重复单元转化为碳酸酯和硫醚二聚体重复单元。通过傅里叶变换红外光谱和核磁共振光谱技术相结合的方法研究了这些主链结构组成的转变，并证明其易于通过温度和催化剂/助催化剂化学计量比进行调节。此外，这些基于d-木糖的含硫聚合物的区域化学表明，单硫代碳酸酯单体重复单元具有头对尾连接，而碳酸酯和硫醚二聚体重复单元具有双头对双尾连接。与它们的含氧聚碳酸酯类似物相比，这些含硫聚合物表现出更高的热稳定性，并揭示了对玻璃化转变温度影响的变化，证明了在聚合物主链中引入硫的效果。这些发现有助于通过使用天然来源的原料与COS来推进可持续聚合物的生产。
