专为分子回收而设计：一种褐宁衍生的半芳烃生物基聚合物
Summary
这里介绍了对循环材料经济采取闭环方法的一个例子。整个可持续循环由生物基半芳烃聚酯设计，通过聚合、去聚合，然后重新聚合，其产量或最终特性仅略有变化。
Abstract
化学可回收生物聚合物的发展为追求循环经济提供了机遇。化学可回收生物聚合物在使用阶段后的处置阶段积极努力解决聚合物材料问题。本文对生物基半芳烃聚酯的生产进行了描述和可视化，这种聚酯完全可以从木质素等生物量中提取。本文中描述的聚合物聚氨酯具有与某些常用塑料（如 PET）相似的热性能。我们开发了一种绿色克诺维纳格尔反应，它可以有效地产生芳香醛和马洛尼克酸的单体。这种反应已被证明是可扩展的，并且具有非常低的计算电子因子。这些以利格诺植物化学物质为起点的聚酯显示出高效的分子回收利用，损失最小。聚酯聚（二氢酸）（聚S）是这些半芳香聚酯的示例，并描述了聚合、去聚合和再聚合。
Introduction
与聚合物废物的焚烧相比，化学回收提供了回收单体的可能性。化学回收是聚合物材料技术寿命结束时的一个合乎逻辑的选择，因为这些聚合物材料是化学1生产的。有两种方法可以化学地回收聚合物材料，热解和分子回收2。通过热解，聚合物材料通过极端条件3、4转化为高价值产品。分子回收是利用去聚合回收起始材料的有效方法。去聚合后，单体单元可再聚合成处女聚合材料5。需要有合适的单体来大规模地应用分子回收。目前的塑料问题决定了社会需要坚固耐用的聚合物材料。同时，也更希望同样的聚合物材料易于回收利用，在环境中不耐用。电流聚合物材料具有良好的热和机械性能，不容易去聚合。
利格宁，常见于血管植物，占世界天然碳含量的30%，是仅次于纤维素的第二大生物聚合物。褐金具有复杂的无定形结构，似乎是替代从化石材料中提取的芳香剂的合适替代品。木质素的三维结构为木材提供强度和刚度，以及抗降解。从化学上讲，木质素是一种非常复杂的多酚热集。它由三种不同的甲氧化苯丙烷结构的不同组成组成。西林吉尔、瓜亚基和p-羟基苯基（通常分别缩写为S、G和H）来自单利尼诺西纳皮尔醇、针叶醇和p-库马里尔酒精7。这些单位的分布不同，每个生物质类型，软木，例如，主要包括瓜亚基单位和硬木的瓜亚基和注射器单位8，9。可再生的天然资源，如树木和植物，是生产重新设计的单体创新聚合物材料10的理想。这些单体，从天然来源分离和合成，聚合到所谓的生物基聚合物11。
芳香性碳酸是几个数量级比同等的药化碳酸少12。各种商业聚酯使用芳香的碳酸，而不是药酸。因此，聚酯纺织品中由聚（乙烯四甲酸酯）纤维制成的纤维在洗涤过程中几乎对水解麻木不仁，例如，雨13。当需要聚酯分子回收时，建议在聚合物的积累中使用脂肪酯。
对于上述原因，我们已研究了用4-羟基-3，5-二氧二氢辛酸制造聚酯的可能性。克里切尔多夫15号、迈尔16号和米勒17号、18号先前的研究表明，使用4-羟基-3，5-二氧-二氢辛酸制造聚合物是具有挑战性的。脱卡和交联阻碍了聚合，因此限制了这些合成器的成功。此外，多聚变的机制仍然不清楚。论文描述了聚酯聚（二氢酸）可以定期合成和高产的条件，从而为使用分子可回收的半芳香聚酯铺平了道路。
我们开发了一种绿色和高效的方法，利用注射器醛和恶性酸19，20之间的凝结反应合成西纳皮尼酸。在此绿色克诺维纳格尔之后，氢化产生二氢酸，适用于可逆多聚化。本出版物可视化分子可回收聚合物聚（二氢酸）的合成步骤，指木质素的基础单位，称为聚S。在分析聚合物材料后，聚氨酯在相对有利的条件下去聚聚到单体二氢酸中，并反复再聚。
Protocol
1. 绿色克诺维纳格尔凝结注射器醛对西纳皮尼奇酸与 5 摩尔% 碳酸氢铵 将马洛尼克酸（20.81 克，200.0 mmol）与注射器醛 （36.4 克， 200.0 mmol） 一起加入 250 mL 圆底烧瓶中。溶解两个成分在20.0 mL乙酸乙酸乙酸酯，并添加碳酸氢铵（790毫克，10.0毫米醇）到烧瓶。注：为确保完全完成凝结反应，旋转蒸发器可用于蒸馏乙酸乙酸乙酯并浓缩反应混合物，从而产生无溶剂反应。 将反应混合?…
Representative Results
西纳皮尼酸是使用绿色克诺维纳凝结剂从注射器醛中高纯度和高产量（>95%）合成的。（支持信息：图S1）电子因子表示废物产生，其中较高的数字表示更多的废物。电子因子的计算方法是获取总材料投入，减去所需最终产品的量，并将整个产品除以最终产品的量。这种绿色克诺维纳格尔凝结物的电子因子为1.0， 可以计算： [（29.81 克马洛尼克酸 = 36.4 克注射器醛 = 0.790 克碳酸氢铵 = 18….
Discussion
当二氢酸在反应容器中加热时，启动材料的升华发生，当应用真空时，这种效果得到增强。乙酰化已对二氢酸进行，以避免升华。克里切多夫等人12日、27日承认，不仅乙酰化，而且类似的二寡聚化也发生了。然而，这些酯化单体和寡聚物不再升华，适合作为单体熔化聚合物28。此外，从4-乙氧二氢酸的预聚合物的形成证实了假设反应机…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
作者感谢荷兰科学研究组织（NWO）的财政支持（授予杰克·范·希恩德尔023.007.020）。
Materials
| Reaction 1: Green Knoevenagel condensation | |||
| Ammonium bicarbonate | Sigma Aldrich | >99% | |
| Ethanol | Boom | Technical grade | |
| Ethyl acetate | Macron | 99.8% | |
| Hydrochloric acid | Boom | 37% | |
| Malonic acid | Sigma Aldrich | 99% | used as received |
| Sodium bicarbonate | Sigma Aldrich | >99.7% | |
| Syringaldehyde | Sigma Aldrich | 98% | used as received |
| Reaction 2: Hydrogenation | |||
| Magnesium sulfate | Macron | 99% | dried |
| Raney™ nickel | Sigma Aldrich | >89% | |
| Sodium hydroxide | Boom | Technical grade | dissolved |
| Reaction 3: Acetylation | |||
| Acetic anhydride | Macron | >98% | |
| Acetone | Macron | >99.5% | |
| Sodium acetate | Sigma Aldrich | >99% | |
| Reaction 4A: Polymerisation | |||
| 1,2-xylene | Macron | >98% | |
| Sodium hydroxide | Boom | Technical grade | finely powdered |
| Zinc(II)acetate | Sigma Aldrich | 99.99% | |
| Reaction 4B: Depolymerisation | |||
| Sodium hydroxide | Boom | Technical grade | dissolved |
| Sulfuric acid | Macron | 100% | |
| Analysis | |||
| CDCl3 | Cambride Isotope Laboratories, Inc. | 99.5% | |
| CF3COOD | Cambride Isotope Laboratories, Inc. | 98% | |
| Dimethylformamide | Macron | >99.9% | |
| Hexafluoro-2-propanol | TCI Chemicals | >99% | |
| Methanol | Macron | >99.8% | |
| Tetrahydrofuran | Macron | >99.9% |
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Citazione di questo articolo
Molendijk, D., van Beurden, K., van Schijndel, J. Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer. J. Vis. Exp. (165), e61975, doi:10.3791/61975 (2020).