N-Heterocyclic Carbene-Carbodiimide (NHC-CDI) Betaines as Organocatalysts for β-Butyrolactone Polymerization: Synthesis of Green PHB Plasticizers with Tailored Molecular Weights,ACS Catalysis

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N-Heterocyclic Carbene-Carbodiimide (NHC-CDI) Betaines as Organocatalysts for β-Butyrolactone Polymerization: Synthesis of Green PHB Plasticizers with Tailored Molecular Weights
ACS Catalysis ( IF 11.3 ) Pub Date : 2024-02-02 , DOI: 10.1021/acscatal.3c05357
David Sánchez-Roa ₁ , Valentina Sessini ₁ , Marta E. G. Mosquera ₁ , Juan Cámpora ₂

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The manufacture of poly(3-hydroxybutyrate) (PHB) stands out as a promising alternative to traditional plastics. This polymer is usually produced by bacteria-based biotechnology or metal-catalyzed ring-opening polymerization (ROP) of β-butyrolactone (β-BL). Nevertheless, commercial PHB suffers from different issues, from poor processability to high production costs. Herein, we report the chemical synthesis of PHB from the ROP of rac-β-butyrolactone promoted by a zwitterionic organocatalyst, an N-heterocyclic carbene-carbodiimide (NHC-CDI) betaine adduct. This reaction has been investigated by a combination of experimental and computational methods. The catalyst cleaves the β-BL via nucleophilic displacement of the C–O(carboxyl) bond followed by intramolecular elimination to give protonated betaine–crotonate ion pairs, the active polymerization initiators. Polymer growth is propagated and controlled by these betaine ion pairs, which render amorphous low-molecular-weight PHBs by an unusual mechanism with rapid chain transfer to the monomer regime, analogous to the well-known mechanism of ethylene oligomerization with late transition-metal catalysts. The resulting material is suitable as a biodegradable and biocompatible plasticizer for commercial bacterial or synthetic PHB. Perfect compatibility between the matrix and the additive and a significant reduction of the crystallinity resulted in a more flexible and resilient material.

中文翻译：

N-杂环卡宾碳二亚胺 (NHC-CDI) 甜菜碱作为 β-丁内酯聚合有机催化剂：合成具有定制分子量的绿色 PHB 增塑剂

聚（3-羟基丁酸酯）（PHB）的制造是传统塑料的一种有前景的替代品。这种聚合物通常通过基于细菌的生物技术或金属催化的 β-丁内酯 (β-BL) 开环聚合 (ROP) 生产。然而，商业 PHB 存在不同的问题，从加工性能差到生产成本高。在此，我们报道了在两性离子有机催化剂、N-杂环碳烯-碳二亚胺（NHC-CDI）甜菜碱加合物的促进下，从外消旋-β-丁内酯的ROP化学合成PHB 。该反应已通过实验和计算方法相结合进行了研究。该催化剂通过 C-O（羧基）键的亲核置换来裂解 β-BL，然后进行分子内消除，得到质子化的甜菜碱-巴豆酸根离子对，即活性聚合引发剂。聚合物的生长是由这些甜菜碱离子对传播和控制的，它们通过一种不寻常的机制提供无定形低分子量 PHB，快速链转移到单体体系，类似于众所周知的使用后过渡金属催化剂的乙烯低聚机制。所得材料适合作为商业细菌或合成 PHB 的可生物降解和生物相容性增塑剂。基体和添加剂之间的完美相容性以及结晶度的显着降低导致材料更加柔韧和有弹性。

更新日期：2024-02-02

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