镍/锌配合物介导的O-Carboxyanhydrides 的控制 Photoredox 环开聚合
Summary
介绍了由 Ni/锌配合物介导的受控 photoredox 环开放聚合的O-carboxyanhydrides 的协议。
Abstract
在这里, 我们描述一个有效的协议, 结合 photoredox 镍/Ir 催化与使用锌醇的有效开环聚合, 允许合成的规聚 (α-羟基酸) 与预期的分子量 (> 140kDa) 和窄分子量分布 (Mw/mn < 1.1)。这种环开聚合由 Ni 和锌配合物在乙醇引发剂和 photoredox 红外催化剂的存在下进行介导, 由蓝色 LED (400-500 nm) 照射。在低温 (-15 ° c) 下进行聚合以避免不受欢迎的副反应。完整的单体消耗可以在 4-8 小时内完成, 为聚合物提供接近分子量的分子量分布。结果数字平均分子量显示一个线性相关与聚合程度1000。homodecoupling 的1H 核磁共振研究证实, 所获得的聚合物是规没有异构化。本文所报告的聚合提供了一种实现快速、受控的O-carboxyanhydrides 聚合的策略, 以制备 stereoregular 聚 (α-羟基酸) 及其承载各种功能侧链基团的共聚物。
Introduction
聚 (α-羟基酸) (PAHA) 是一类重要的生物降解和生物相容性高分子材料, 其应用范围广泛, 从医用设备到包装原料。1,2虽然 PAHAs 可以通过α-羟基酸的缩聚直接制备, 但产生的 PAHAs 的分子量 (MWs) 普遍较低。3酯 (如丙交酯和乙) 的开环聚合 (ROP) 是一种替代合成方法, 可以更好地控制 MWs 和分子量分布 (Đ), 而不是缩聚。然而, PAHAs 和酯的侧链功能的缺乏限制了物理和化学性质及其应用的多样性。4,5自2006年以来, 13–1,3–24-diones, so-called O-carboxyanhydrides (oca), 可以用丰富多样的侧链功能编写,6,7,8,9,10,11,12,13已成为聚酯聚合中一种高活性单体的替代类。14,15
oca 的催化系统可分为有机、8、12、16、17有机金属催化剂12、18、19 ,20,21和催化剂。22一般情况下, 由有机促进的 oca 的 ROP 以或多或少不受控制的方式进行, 例如异构化 (即缺少 stereoregularity), 用于 oca 轴承电子提取组,8,17不可预知的 MWs, 或慢聚合动力学。13为了解决这些问题, 研制了一种活性锌-醇络合物, 用于 oca 的 ROP。12井控保护在低聚合 (DP) 的情况下, 没有异构化。然而, 这种锌-醇催化剂不能有效地产生高聚合度的聚合物 (DP ≥ 300)。13
我们最近报告了一种有希望的方法, 大大提高了 PAHA 合成的可和效率 (图 1)。13将 photoredox 镍/Ir 催化剂与锌醇脱, 以调节环开聚合 oca。低温 (-15 ° c) 和 photoredox 镍/Ir 催化的使用, 协同加速了脱链的传播, 同时避免了不受欢迎的副反应, 如镍羰基的形成。23,24在转移与 Ni 复合体的活性锌-醇位于链终点链传播。13
在本协议中, 我们添加新鲜准备 (bpy) Ni (COD) (bpy = 22 ‘-吡啶, COD = 15-1,5-), Zn (HMDS)2 (HMDS = 烷),25苄醇 (BnOH) 和 Ir [dF (CF3) 吡]2(dtbbpy) PF6 (Ir-1, dF (CF3) 吡 = 2-(24-氟)-5-三氟甲基吡啶, dtbbpy = 44 “-di-叔-butyl-2,2′-bipyridine) 到单体 l-1解决方案26在一个带有冷陷阱的手套箱中, 在一个蓝色 LED 灯 (400-500 nm) 和风扇以保持温度 (图 1)。在聚合过程中, 温度保持在-15 ° c ±5° c。采用傅里叶变换红外光谱法对亚奥氏转化率进行了监测。由此产生的聚合物 MWs 和Đs 的特点是凝胶渗透色谱 (GPC)。homodecoupling 的1H 核磁共振研究确定所得到的聚合物是否是规的。由于大多数化学品对湿气高度敏感, 详细的视频协议旨在帮助新的从业者避免与 oca photoredox ROP 相关的陷阱。
Protocol
Representative Results
Discussion
协议中的关键步骤是保持反应温度在-15 ±5° c。在聚合之前, 所有的催化剂溶液和亚奥基单体都必须在-35 ° c 的手套箱冷冻库中储存。在寒冷的陷阱中, 反应瓶必须预。在反应过程中, 由于 LED 灯散热, 必须每 15-20 分钟监测反应。一旦温度上升到-10 ° c, 液态氮应加入到杜瓦瓶冷却陷阱。低温的原因是室温下镍 (CO) 络合物的形成, 这对受控的 photoredox 聚合是不利的, 并影响到兆瓦和Đ。<sup class="xr…
Disclosures
The authors have nothing to disclose.
Acknowledgements
这项工作得到了弗吉尼亚理工学院和州立大学开办资金的支持。Q.F. 承认中国国家自然科学基金 (21504047)、江苏省自然科学基金 (BK20150834)、南京邮电大学科学基金 NUPTSF (NY214179) 的支持。
Materials
| Ni(COD)2 | Strem | 28-0010 | Stored in the glove box freezer. |
| 2,2′-bipyridine | Strem | 07-0290 | Stored in the glove box freezer. |
| Zn(HMDS)2 | N/A | N/A | Synthesized following reported procedures.25 Stored in the glove box freezer. |
| Benzyl alcohol | Sigma-Aldrich | 402834 | Stored with 4Å molecular sieve |
| Ir[dF(CF3)ppy]2(dtbbpy)PF6 | Strem | 77-0425 | Stored in the glove box freezer. |
| THF | Sigma-Aldrich | 34865 | Dried by alumina columns and stored with 4Å molecular sieve in the dark bottle in the glove box. |
| Ethanol | Sigma-Aldrich | 793175 | |
| GPC with an isocratic pump | Agilent | Agilent 1260 series | |
| Dawn Heleos II Light Scatterer | Wyatt | ||
| Optilab rEX differential refractive index detector | Wyatt | ||
| Size exclusion columns | Phenomenex | ||
| Glass Scintillation Vials – 7 ml | VWR | ||
| FTIR spectrometer | Agilent | ||
| Stir bars | VWR | 58948-091 | |
| Balance | |||
| Glove box | Mbraun | Labstar Pro |
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