Cheng-Tan Mary Dana Czarinah L, Nguyen Angelyn N, Gordon Collette T, Wood Zachary A, Manjarrez Yvonne, Fieser Megan E
Department of Chemistry, University of Southern California, Los Angeles, California 90089, United States.
Wrigley Institute for Environment and Sustainability, University of Southern California, Los Angeles, California 90089, United States.
ACS Sustain Chem Eng. 2024 Apr 30;12(19):7246-7255. doi: 10.1021/acssuschemeng.3c06766. eCollection 2024 May 13.
Aliphatic polyesters have received considerable attention in recent years due to their biodegradability and biocompatible, mechanical, and thermal properties that can make them a suitable alternative to today's commercialized polymers. The ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides is a route to synthesize a diverse array of polyesters that could be useful in many applications. However, the catalysts used rarely consider biocompatible catalysts in the case that any are left in the polymer. To the best of our knowledge, we report the first example of using deep eutectic solvents (DESs) as biocompatible catalysts for this target ROCOP with polymerization activity for at least six diverse monomer pairs. Choline halide salts are active for this polymerization, with dried salts showing polymerization slower than that of those conducted in air. Hydrogen bonding with water is hypothesized to enhance the rate-determining step of epoxide ring opening. While the presence of water improves the rate of polymerization, it also acts as a chain transfer agent, leading to smaller molar mass polymers than intended. Combining the choline halide salts with urea or ethylene glycol hydrogen bond donors in air led to DES catalysts that reacted similarly to the salts exposed to air. However, when generating these DESs in air-free conditions, they showed similar rates of polymerization without a drop in polymer molar mass. The hydrogen bonding provided by urea and ethylene glycol seems to promote the rate increase without serving as a chain transfer agent. Results reported herein display the promising potential of biocompatible catalyst systems for this ROCOP process as well as introducing the use of hydrogen bonding to enhance polymerization rates.
近年来，脂肪族聚酯因其生物可降解性、生物相容性、机械性能和热性能而备受关注，这些特性使其成为当今商业化聚合物的合适替代品。环氧化物和环状酸酐的开环共聚（ROCOP）是合成多种聚酯的一种途径，这些聚酯可用于许多应用。然而，所使用的催化剂在聚合物中残留任何催化剂的情况下很少考虑生物相容性催化剂。据我们所知，我们报道了首例使用深共熔溶剂（DESs）作为生物相容性催化剂用于该目标ROCOP的例子，该催化剂对至少六种不同的单体对具有聚合活性。卤化胆碱盐对这种聚合反应具有活性，干燥的盐显示出比在空气中进行的聚合反应更慢的聚合速度。据推测，与水形成的氢键会加速环氧化物开环的速率决定步骤。虽然水的存在提高了聚合速率，但它也充当链转移剂，导致聚合物的摩尔质量比预期的小。在空气中将卤化胆碱盐与尿素或乙二醇氢键供体结合，得到的DES催化剂的反应与暴露于空气中的盐相似。然而，在无空气条件下生成这些DES时，它们显示出相似的聚合速率，且聚合物摩尔质量没有下降。尿素和乙二醇提供的氢键似乎促进了速率的增加，而没有充当链转移剂。本文报道的结果展示了生物相容性催化剂体系在该ROCOP过程中的潜在应用前景，并介绍了利用氢键提高聚合速率的方法。
