基于熔环环辛烯单体的可解聚烯烃聚合物
Summary
在这里，我们描述了制备 反式环丁烷熔融环辛烯（tCBCO）的方案，它们的聚合以制备可解聚的烯属聚合物，以及这些聚合物在温和条件下的解聚。此外，还描述了基于该系统制备可解聚网络和刚性线性塑料压缩成型的协议。
Abstract
合成聚合物消费量的增加和聚合物废物的积累导致迫切需要可持续材料的新途径。通过化学回收到单体（CRM） 来实现 闭环聚合物经济就是这样一条有前途的途径。我们小组最近报道了一种基于 反式环丁烷熔融环辛烯（tCBCO）单体的开环复分解聚合（ROMP）制备的聚合物的新型CRM系统。该系统具有几个关键优势，包括在环境温度下易于聚合，在温和条件下定量解聚为单体，以及广泛的功能和热机械性能。在这里，我们概述了制备 TCBCO基单体及其相应聚合物的详细方案，包括弹性聚合物网络的制备和线性热塑性聚合物的压缩成型。我们还概述了高环应变 E-烯烃 tCBCO单体的制备及其活性聚合。最后，还演示了线性聚合物和聚合物网络的解聚程序。
Introduction
合成聚合物的多功能性和坚固性使其成为现代人类生活中无处不在的固定装置。另一方面，同样坚固和环保的特性使聚合物废料具有极强的持久性。这一点，再加上有史以来制造的所有合成聚合物中有很大一部分最终进入垃圾填埋场的事实1，引起了对其环境影响的合理担忧2。此外，传统聚合物经济的开环性质导致石化资源的稳定消耗和碳足迹的增加3。因此，通往闭环聚合物经济的有前途的途径备受追捧。
化学回收单体（CRM）就是这样一种途径。与传统回收相比，CRM的优势在于它导致可用于制造原始聚合物的单体的再生，而不是在多个加工周期中机械回收性能恶化的材料。基于开环聚合的聚合物已成为CRM材料特别有吸引力的途径4.聚合的热力学通常是两个相反因素之间的相互作用：聚合焓（ΔH p，通常为负值，有利于聚合）和聚合熵（ΔSp，通常也是负的，但不利于聚合），其中上限温度（Tc）是这两个因素相互平衡的温度5.为了使聚合物能够在实际和经济上有利的条件下进行CRM，必须实现ΔH p和ΔSp的正确平衡。环状单体允许通过选择合适的环尺寸和几何形状来调节这些因素的便捷方法，因为在这里，ΔHp主要由环状单体4，5的环应变决定。因此，具有多种单体的CRM聚合物已被报道为6，7，8，9，10，11。在这些体系中，由环戊烯制备的ROMP聚合物特别有前途，因为所需的起始材料相当便宜，并且聚合物具有水解和热稳定性。此外，在没有复分解催化剂的情况下，解聚在动力学上是不可行的，尽管Tc12较低，但仍能提供高热稳定性。然而，环戊烯（和其他基于小环状结构的单体）提出了一个关键的挑战 – 它们不容易官能化，因为主链上官能团的存在会以剧烈的，有时是不可预测的方式影响聚合的热力学13，14。
最近，我们报告了一个克服其中一些挑战的系统15.受文献16，17中低应变熔融环环辛烯示例的启发，基于反式环丁烷熔融环辛烯（tCBCO）的ROMP聚合物设计了一种新的CRM系统（图1A）。tCBCO单体可以从马来酸酐和1，5-环辛二烯的[2+2]光环加合物中以克级制备，其可以很容易地官能化以获得多样化的取代基（图1B）。所得单体的环形菌株与环戊烯相当（~5 kcal·mol−1，使用DFT计算）。热力学研究显示低ΔH p（−1.7 kcal·mol−1至-2.8 kcal·mol−1），被低ΔSp（−3.6 kcal·mol −1·K−1 至 −4.9 大卡·摩尔−1·K−1），允许在Grubbs II催化剂（G2）存在下，在环境温度下制备高分子量聚合物（在高单体浓度下）和近乎定量的解聚（>90%，在稀条件下）。还证明，在保持聚合/解聚的便利性的同时，可以获得具有不同热机械性能的材料。这种能力被进一步用于制备软弹性网络（也可以很容易地解聚）以及刚性热塑性塑料（具有与聚苯乙烯相当的拉伸性能）。
该系统的一个缺点是需要高单体浓度来获取高分子量聚合物。同时，由于广泛的链转移和环化反应，聚合本质上不受控制。在随后的工作中，通过对tCBCO单体中的Z-烯烃进行光化学异构化以制备高度应变的E-烯烃tCBCO单体18，解决了这一问题。这些单体可以在Grubbs I催化剂（G1）和过量的三苯基膦（PPh 3）存在下，以低初始单体浓度（≥25mM）以活的方式快速聚合。然后聚合物可以解聚以产生单体的Z-烯烃形式。这为获得新的可解聚聚合物架构创造了机会，包括嵌段共聚物和接枝/瓶刷共聚物。
在这项工作中，概述了具有不同官能团的 tCBCO 单体的合成及其聚合以及所得聚合物的解聚的详细方案。此外，还描述了用于制备软弹性网络狗骨样品及其解聚的方案，以及N-苯基酰亚胺取代的刚性热塑性聚合物的压缩成型。最后，还讨论了吨CBCO单体光异构化为其应变的E-烯烃tCBCO形式的方案及其随后的活ROMP。
Protocol
Representative Results
Discussion
所述tCBCO单体可由一种常见的前体制备：马来酸酐和1，5-环辛二烯的[2+2]光环加合物，酸酐1。由于粗酸酐1难以纯化，但易于水解，因此粗光反应混合物经受甲醇分解条件以产生易于分离的甲酯酸2。柱层析后2的重结晶是获得2纯反式环丁烷异构体的关键。如图2所示，可以容易地衍生化以制备几种不同的T</em…
Disclosures
The authors have nothing to disclose.
Acknowledgements
我们感谢阿克伦大学和国家科学基金会在DMR-2042494赠款下的资助。
Materials
| 1 and 3 dram vials | VWR | 66011-041, 66011-100 | |
| 1,4-butanediol | Sigma-Aldrich | 240559-100G | |
| 1,5-cyclooctadiene | ACROS | AC297120010 | |
| 1-butanol | Fisher | A399-1 | |
| 20 mL scintillation vials | VWR | 66022-081 | |
| Acetic Anhydride | Alfa-Aesar | AAL042950B | |
| Acetone | Fisher | A18-20 | |
| Aluminum backed TLC plates | Silicycle | TLA-R10011B-323 | |
| Ammonium hydroxide | Fisher | A669-212 | |
| Aniline | TCI | A0463500G | |
| BD precisionglide (18 G) | Fisher | ||
| Chloroform | Fisher | C298-4 | |
| Column for circulation (to be packed with silver nitrate treated silica gel) | Approximately 1 cm radius and 25 cm long, with inner thread on either end | ||
| d-Chloroform | Cambridge Isotopes | DLM-7-100 | |
| Dichloromethane | VWR | BDH1113-19L | |
| EDC.HCl; 3-(3-dimethylaminopropyl)-1-ethyl-carbodiimide hydrochloride | Chemimpex | 00050 | |
| Ethyl Acetate | Fisher | E145-20 | |
| Ethyl Vinyl Ether | Sigma-Aldrich | 422177-250ML | |
| Glass chromatography columns | Fabricated in-house | D = 20 mm, L= 450 mm and D = 40 mm, L = 450 mm | The columns are fitted with a teflon stopcock at one end and a 24/40 ground glass joint to accommodate a solvent reservoir if needed. |
| Grubbs Catalyst 1st Generation (M102) | Sigma-Aldrich | 579726-1G | |
| Grubbs Catalyst 2nd Generation (M204) | Sigma-Aldrich | 569747-100MG | |
| Hexanes | Fisher | H292-20 | |
| Hydraulic press | Carver Instruments | #3912 | Coupled with temperature control modules (see below) |
| Hydrochloric acid | Fisher | AA87617K4 | |
| Maleic Anhydride | ACROS | AC125240010 | |
| Methanol | Fisher | A412-20 | |
| Micro essential Hydrion pH paper (1-13 pH) | Fisher | 14-850-120 | |
| Normject Luer Lock syringes (1, 3 and 10 mL) | VWR | 89174-491, 53547-014 and 53547-010 | |
| Photoreactor chamber | Rayonet | RPR-100 | |
| QuadraPure TU (catalyst scavenger) | Sigma-Aldrich | 655422-5G | |
| Quartz tubes | Favricated in-house | D=2", L=12.5" and D=1.5", L=10.5" | |
| Rotavap | Buchi | ||
| SciLog Accu Digital Metering Pump MP- 40 | Parker | 500 mL capacity | |
| Siliaflash Irregular Silica, F60 | Silicycle | R10030B-25KG | |
| Silver Nitrate | ACROS | AC197680050 | |
| Sodium hydroxide | VWR | BDH9292-2.5KG | |
| Steel Mold | Fabricated in-house | Overall dimensions of mold cavity: length 20 mm, width 7 mm and depth 1 mm; gauge dimensions: length 10 mm, width 3 mm) | |
| Steel Plates | Fabricated in-house | 100 mm x 150 mm x 1 mm | |
| Teflon Mold (6-cavities) | Fabricated in-house | Overall cavity dimensions: length 25 mm, width 8.35 mm and depth 0.8 mm; gauge dimensions: length 5 mm, width 2 mm) | |
| Teflon Sheets (0.005" thick) | McMaster-Carr | 8569K61 | |
| Temperature Control Modules | Omega | C9000A and C9000 | °C units (two modules, one for top and one for bottom) |
| Triphenyl Phosphine | TCI | T0519500G | |
| UV lamps | Rayonet | RPR2537A and RPR3000A | |
| Vacuum pump | Welch Duoseal | ||
| Whatman Filter Paper (grade 2) | VWR | 09-810F | filter paper |
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