胍基锌/环氧化物催化 ε-己内酯开环聚合及 PCL 的胺解回收

Guanidine-Zinc/Epoxide Catalyzed Ring-Opening Polymerization of ε-Caprolactone and Aminolysis Recycling of PCL

摘要

聚己内酯（PCL）在生物医用与先进制造领域应用前景广阔，但现有催化体系在高温本体聚合反应中难以兼顾高活性、低催化剂用量与高分子量。本文采用胍基锌配合物为催化剂（cat.），引入 4 种环氧化物（甲基丙烯酸缩水甘油酯（GMA）、环氧氯丙烷（ECH）、环氧环己烷（CHO）、环氧丙烷（PO））作为共引发剂高效催化ε-己内酯（ε-CL）本体开环聚合。利用核磁共振氢谱（¹H-NMR）、凝胶渗透色谱（GPC）及差示扫描量热法（DSC）等技术对配合物结构、聚合物相对分子质量及热性能进行了研究。该催化体系可在极低催化剂用量（n（ε-CL）∶n（CHO）∶n（cat.）= 10 000∶2 500∶1）下实现单体高效转化，聚合转化频率（TOF）高达 49.3×10² h⁻¹，并在优化条件（n（ε-CL）∶n（CHO）∶n（cat.）=5 000∶500∶1，反应时间 60 min）下获得数均分子量最高达 81.8×10³ 的 PCL。此外，所合成的 PCL 在无催化剂、温和条件下通过乙醇胺解聚，可完全转化为高附加值的羟基酰胺衍生物。该催化体系为生物可降解聚酯的高效制备提供了一种新的策略，同时所合成的 PCL 在温和条件下可实现化学回收，展现出良好的循环利用潜力。

Abstract

Poly(ε-caprolactone) (PCL), a typical aliphatic biodegradable polyester, holds significant application prospects in biomedical and advanced manufacturing fields due to its excellent biocompatibility and processability. However, existing catalytic systems still face challenges in simultaneously achieving high activity, low catalyst loading, and high molecular weight under high-temperature bulk conditions. In this study, a guanidine-zinc complex was employed as the catalyst, and four epoxides (glycidyl methacrylate (GMA), epichlorohydrin (ECH), cyclohexene oxide (CHO), propylene oxide (PO)) were introduced as co-initiators to efficiently catalyze the bulk ring-opening polymerization ofε-caprolactone (ε-CL). Techniques including proton nuclear magnetic resonance (¹H-NMR), gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) were employed to study the structures of the complexes, along with the molecular weights and thermal properties of the polymers. This catalytic system achieved efficient monomer conversion with an extremely low catalyst loading (n(ε-CL)∶n(CHO)∶n(cat.) = 10 000∶2 500∶1), delivering a turnover frequency (TOF) as high as 49.3×10² h⁻¹. Under optimized conditions (n(ε-CL)∶n(CHO)∶n(cat.) = 5 000∶500∶1, reaction time: 60 min), PCL with a number-average molecular weight (M _n) of 81.8×10³ could be obtained. Furthermore, the obtained PCL could be completely depolymerized into high value-added hydroxyamide derivatives under catalyst-free, mild conditions via ethanolamine aminolysis, demonstrating promising potential for chemical circularity. This catalytic system provides a novel approach that is efficient, cost-effective, and environmentally friendly for the industrial preparation of biodegradable polyesters and the chemical recycling of waste plastics.

关键词

胍基锌配合物 / ε-己内酯 / 开环聚合 / 环氧化物 / 胺解回收

Key words

guanidine-zinc complex / ε-caprolactone / ring-opening polymerization / epoxide / aminolysis recycling

参考文献

[1] 庞烜, 边新超, 陈学思 . 中国可降解、可回收高分子材料化学领域发展现状和未来挑战 [J]. 科学观察， 2023， 18（4）： 1-4.

[2] PANG X, BIAN X C, CHEN X S . Current status and future challenges of chemistry of degradable and recyclable polymer materials in China [J]. Science Focus， 2023， 18（4）： 1-4.

[3] PLACE E S, EVANS N D, STEVENS M M . Complexity in biomaterials for tissue engineering [J]. Nature Materials， 2009， 8（6）： 457-470.

[4] VIEIRA I D S, HERRES—PAWLIS S . Lactide polymerisation with complexes of neutral N—donors：New strategies for robust catalysts [J]. European Journal of Inorganic Chemistry， 2012， 2012（5）： 765-774.

[5] PALIVAN C G, GOERS R, NAJER A, ZHANG X, CAR A, MEIER W . Bioinspired polymer vesicles and membranes for biological and medical applications [J]. Chemical Society Reviews， 2016， 45（2）： 377-411.

[6] POHLMANN A R, PAESE K, DETONI C B, CORADINI K, BECK R C, GUTERRES S S . Poly(ε—caprolactone) microcapsules and nanocapsules in drug delivery [J]. Expert Opinion on Drug Delivery， 2013， 10（5）： 623-638.

[7] JEROME C, LECOMTE P . Recent advances in the synthesis of aliphatic polyesters by ring—opening polymerization [J]. Advanced Drug Delivery Reviews， 2008， 60（9）： 1056-1076.

[8] PARADISO V, CAPACCIO V, LAMPARELLI D H, CAPACCHIONE C . [OSSO]—bisphenolate metal complexes: A powerful and versatile tool in polymerization catalysis [J]. Coordination Chemistry Reviews， 2021， 429： 213644.

[9] ZHANG H, DONG Y, HUANG K, LIU J, DONG B, WANG F . Immortal ring opening polymerization of ε—caprolactone and rac—lactide by magnesium precatalysts bearing sterically congested phenoxide ligands [J]. European Polymer Journal， 2019， 118： 633-641.

[10] LIU H, KHONONOV M, FRIDMAN N, TAMM M, EISEN M S . (Benz)imidazolin—2—iminato aluminum, zinc, and magnesium complexes and their applications in ring opening polymerization of ε—caprolactone [J]. Inorganic Chemistry， 2019， 58（19）： 13426-13439.

[11] OLEJNÍK R, BÍLEK M, RŮŽIČKOVÁ Z, HOŠTÁLEK Z, MERNA J, RŮŽIČKA A . Zinc complexes chelated by bifunctional ketiminate ligands: Structure, reactivity and possible applications in initiation of ROP and copolymerization of epoxides with carbon dioxide [J]. Journal of Organometallic Chemistry， 2015， 794： 237-246.

[12] DARENSBOURG D J, KARROONNIRUN O . Ring—opening polymerization of L—lactide and ε—caprolactone utilizing biocompatible zinc catalysts：Random copolymerization of L—lactide and ε—caprolactone [J]. Macromolecules， 2010， 43（21）： 8880-8886.

[13] HUANG H C, WANG B, ZHANG Y P, LI Y S . Bimetallic aluminum complexes with cyclic β—ketiminato ligands: The cooperative effect improves their capability in polymerization of lactide and ε—caprolactone [J]. Polymer Chemistry， 2016， 7（37）： 5819-5827.

[14] CHAMPOURET Y, HASHMI O H, VISSEAUX M . Discrete iron—based complexes: Applications in homogeneous coordination—insertion polymerization catalysis [J]. Coordination Chemistry Reviews， 2019， 390： 127-170.

[15] ZHONG Z Y, DIJKSTRA P J, FEIJEN J . [(Salen)Al]—mediated, controlled and stereoselective ring—opening polymerization of lactide in solution and without solvent: Synthesis of highly isotactic polylactide stereocopolymers from racemic D, L—lactide [J]. Angewandte Chemie International Edition， 2002， 41（23）： 4510-4513.

[16] DONG S, FENG X, LIU X . Chiral guanidines and their derivatives in asymmetric synthesis [J]. Chemical Society Reviews， 2018， 47（23）： 8525-8540.

[17] MUTHYALA R, BARBOLLA I, SOTOMAYOR N, LETE E . Transition metal—guanidine complexes as catalysts in organic reactions：Recent developments [J]. Arkivoc， 2020， 2020（7）： 158-179.

[18] WITTMANN H, SCHORM A, SUNDERMEYER J . Chelat ligands based on peralkyl bis— and tris—guanidines [J]. Zeitschrift Für Anorganische Und Allgemeine Chemie， 2000， 626（7）： 1583-1590.

[19] WITTMANN H, RAAB V, SCHORM A, PLACKMEYER J, SUNDERMEYER J . Complexes of manganese, iron, zinc, and molybdenum with a superbasic tris(guanidine) derivative of tris(2—ethylamino)amine (tren) as a tripod ligand [J]. European Journal of Inorganic Chemistry， 2001， 2001（8）： 1937-1948.

[20] METZ A, PLOTHE R, GLOWACKI B, KOSZALKOWSKI A, SCHECKENBACH M, BERINGER A, RÖSENER T, MICHAELIS DE VASCONCELLOS J, HAASE R, FLÖRKE U, HOFFMANN A, HERRES—PAWLIS S . Zinc chloride complexes with aliphatic and aromatic guanidine hybrid ligands and their activity in the ring—opening polymerisation of D, L—lactide [J]. European Journal of Inorganic Chemistry， 2016， 2016（31）： 4974-4987.

[21] METZ A, MCKEOWN P, ESSER B, GOHLKE C, KRÖCKERT K, LAURINI L, SCHECKENBACH M, MCCORMICK S N, OSWALD M, HOFFMANN A, JONES M D, HERRES—PAWLIS S . Zn(II) chlorido complexes with aliphatic, chiral bisguanidine ligands as catalysts in the ring—opening polymerisation of rac—lactide using FT—IR spectroscopy in bulk [J]. European Journal of Inorganic Chemistry， 2017， 2017（47）： 5557-5570.

[22] HERMANN A, HILL S, METZ A, HECK J, HOFFMANN A, HARTMANN L, HERRES—PAWLIS S . Next generation of zinc bisguanidine polymerization catalysts towards highly crystalline, biodegradable polyesters [J]. Angewandte Chemie International Edition， 2020， 59（48）： 21778-21784.

[23] D’AURIA I, FERRARA V, TEDESCO C, KRETSCHMER W, KEMPE R, PELLECCHIA C . Guanidinate Zn(II) complexes as efficient catalysts for lactide homo— and copolymerization under industrially relevant conditions [J]. ACS Applied Polymer Materials， 2021， 3（8）： 4035-4043.

[24] CHEN J, WU X, ZHANG L, DUAN Z, LIU B . Ring—opening polymerization of ε—caprolactone mediated by a di—zinc complex bearing a macrocyclic thioether—phenolate —type ligand [J]. Polymer Chemistry， 2022， 13（20）： 2971-2979.

[25] WANG H C, MA H Y . Controlled synthesis of high—molecular—weight and isotactic cyclic polylactides from rac—lactide using aminophenolate zinc chlorides [J]. Macromolecules， 2024， 57（13）： 6156-6165.

[26] SUO H, LIU S, LIU J, ZHANG Z, QU R, GU Y, QIN Y . Novel epoxide—promoted polymerization of lactides mediated by a zinc guanidine complex: A potential strategy for the tin—free PLA industry [J]. Polymer Chemistry， 2023， 14（40）： 4652-4658.

[27] ZHANG Z, ZHOU Y, LIU S, LI B, QU R, GU Y, SUO H, QIN Y . A highly active zinc—based catalyst system for lactide homo— and copolymerization under industrially relevant conditions [J]. Polymer Chemistry， 2024， 15（46）： 4732-4740.

[28] 马钰琨, 沈勇, 李志波 . 高热稳定 Lewis 酸碱对催化 L—丙交酯均聚及与乙交酯共聚的本体开环聚合研究 [J]. 高分子学报， 2022， 53（8）： 923-932.

[29] MA Y K, SHEN Y, LI Z B . Bulk ring—opening polymerization of L—lactide and its copolymerization with glycolide catalyzed by highly thermal stable Lewis pairs [J]. Acta Polymerica Sinica， 2022， 53（8）： 923-932.

[30] LIU S, HU L, LIU J Y, ZHANG Z S, SUO H Y, QIN Y S . Zinc catalyst for chemical upcycling of PLA wastes: Novel industrial monomer resource toward poly(ester—amide) [J]. Macromolecules， 2024， 57（10）： 4662-4669.

[31] ZHOU X, CHAI M, XU G, YANG R, SUN H, WANG Q . Catalyst—free amino—alcoholysis depolymerization strategy: A facile and powerful tool for chemical recycling of poly(bisphenol A carbonate) [J]. Green Chemistry， 2023， 25（3）： 952-959.

基金资助

国家自然科学基金(52073244)

国家自然科学基金(52103011)

国家自然科学基金(52473010)

山东省自然科学基金(ZR2021QE211)