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）。

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
<ol><li>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。</li>
	<li>将反应混合物在 90 °C 的开放烧瓶中保持 2 小时，而无需搅拌以完全转化为西纳皮尼酸。 注:在此反应期间，观察到一些形态变化。反应混合物从密集的灰色混合物变为溶解的黄色混合物，原因是水在反应的凝结步骤中形成。冷凝水蒸发后，反应混合物再次凝固，表示完全转换。</li>
	<li>在合成酶酸产品的处理中，将饱和的 NaHCO3溶液的残留物溶解在 100 mL 中。将溶液转移到烧饼上，然后使用 6 M HCl 将其酸化为 2 的 pH 值。 注:在添加饱和的AHCO3溶液时，原油产品溶解缓慢，需要一些时间和手动刮擦才能完全溶解。一旦完全溶解并转移到烧瓶中，6 M HCl 的酸性溶液就会被添加到滴中。西纳皮尼酸会迅速沉淀，CO2 气体的释放会导致产品发泡。</li>
	<li>通过真空过滤分离产生的残留物，然后用非盐化水清洗。 注意:此时，HPLC 可以分析产品的纯度。如果产品出现污染，则必须应用下一个净化步骤（例如再装层）。</li>
	<li>在水乙醇混合物（4:1，v/v）中重新安装后，通过真空过滤分离晶体。在真空烤箱中将残留物在 60 °C 下干燥，产生 42.56 克纯西纳平酸。 注:通过熔点分析和HPPC测量西纳皮尼酸的纯度。</li>
</ol>2. 将西纳平酸氢化为二氢酸与拉尼TM 镍。
<ol><li>用西纳平酸（33.6克，150 mmol）给450mL烧瓶（使用加氢装置）充电。将西纳平酸溶解在 300 mL 的 2 M NaOH 溶液中，在将烧瓶安装到设备之前加入 1.5 克镍浆（参见 材料表）。 注:反应混合物的颜色因添加碱性溶液而改变。新浪酸的晶体形式为黄色，但当基质脱质时，溶液的颜色将变为红色。镍的加入会使颜色变黑。</li>
	<li>用三巴氢气给反应堆加压，在80°C下机械地摇动反应三个小时。</li>
	<li>将反应堆冷却至室温，慢慢减压。用磁铁回收大部分镍催化剂，然后在减压下过滤溶液。 注:反应混合物应从红色变为绿色，过滤后可见。显著的颜色变化是因为结合系统被双键的加氢中断。</li>
	<li>用 4 M HCl 溶液将溶液酸化为 2 pH 值。随后，用乙酸酯（4倍50ml）进行萃取。在MgSO4干燥后，在减压下取出溶剂。在真空烤箱中将固体产品二氢酸干燥至 60 °C。 注:从理论上讲，多聚变反应可以在二氢酸上处理，但也有一些实际的缺点。由于分子结构，二氢酸升华在熔点以上。乙酰化反应可以执行，以防止升华和提高反应性。</li>
</ol>3. 乙酰酸乙酰化对乙酰化单体和寡聚体（聚合物）。
<ol><li>在 250 mL 圆底烧瓶中加入二氢酸（22.6 克，100 mmol），然后是醋酸氢化物（14.2 mL、150 mmol）和醋酸钠（0.82 克、10 mmol）。 注:二氢酸在室温下不会完全溶解在醋酸中。</li>
	<li>将溶液加热至 90 °C，同时搅拌一小时，将二氢酸完全转化为 4-乙氧二氢平酸及其乙酰化寡聚物。 注:所有产品仍溶解在醋酸氢化物中。为了增加4-乙氧二氢酸的总降水量，下一步添加少量水溶性溶剂。</li>
	<li>溶解25mL丙酮的固体，沉淀（溶剂-非溶剂）到250 mL的0.1M HCl，同时大力搅拌，并在真空下过滤。 注:最好的结果显示完全沉淀的白色，粘性固体。如果将产品溶液添加到 HCl 溶液中的速度过快，则产品仍作为棕色液体留在酸性溶液的底部。在这种情况下，用乙酸酯（4 倍 50 mL）提取整个产品溶液。在MgSO4上干燥后，在减压下取出乙酸乙酸乙酯。该产品是4-乙酰氧二氢酸和聚合物。</li>
</ol>4. 乙酰化单体和寡聚物的聚合。
<ol><li>加入单体，4-乙酰氧二氢酸（20.8克，100mmol），和前聚合物到100ml圆底烧瓶，并添加精细粉末NaOH（400毫克，10.0毫米醇）。在开放烧瓶中设定的温度为 140 °C 时加热反应混合物三小时，同时在 100 rpm 时搅拌。 注:在此反应期间，水和醋酸从开放的烧瓶凝结。可以测量蒸汽的pH值，以确认醋酸的凝结。反应产品的形态从熔融状态转变为紧凑的浅棕色产品。设置受氮流，以促进冷凝水的蒸发和防止氧化。由于混合物的粘度很高，这种反应通常用机械搅拌器搅拌。但是，磁搅拌器的使用已经足够了，在这个尺度上，这种差异可以忽略不计的。</li>
	<li>通过在烧瓶中加入锌（II）醋酸（180毫克，1 mmol）和25.0 mL的1，2-xylene，建立溶剂辅助聚合。将设定温度提高到 160 °C。 注:将设定温度提高到 160 °C，以确保 1，2-xylene 的回流和聚合的完全反应性。由于1，2-二甲苯的沸点，反应本身的温度保持在144°C。</li>
	<li>使用 Dean-Stark 头在 144 °C 下倒流混合物三小时，使用恒水和醋酸去除。 注:在加入1，2-xylene并将反应瓶加热到所需的温度后，试剂形成粘度较低的棕色泥浆。这种较低的粘度被认为有利于聚合物末组的移动性，促进反应性。</li>
	<li>冷却反应混合物，通过使用真空（<10mbar）去除1，2-xylene。 注:反应混合物在蒸发溶剂时凝固，变成白色固体。</li>
	<li>在聚合的最后阶段将温度提高到 240 °C，并应用高真空< 1 mbar 30 分钟。 注:在此步骤中，只有少量的冷凝水蒸发，因为在聚合阶段，只需要少量的冷凝剂来大幅提升链条长度。</li>
	<li>将聚合物聚S冷却至室温，并用甲醇清洗，以消除4-乙酰氧-二氢酸酸和前聚合物。获得的产品是浅棕色固体。 注:在此过程之后，GPC 和 DSC 将调查聚酯的链条长度和热性能。</li>
</ol>5. 1 M Naoh 中聚氨酯去聚合的代表程序:
<ol><li>将聚S精细研磨并筛成小于180μm的颗粒，以测量水解降解。 注:要将颗粒研磨到所需的大小，请使用砂浆和液氮冷却多 S，然后采用机械筛分步骤。</li>
	<li>装载多个试管，20毫克多S，并添加1.0 mL的1M NaOH溶液。在三种不同的温度（RT、50 和 80 °C）下孵育管子，使用受控环境孵化器摇床搅拌 500 rpm。 注意:使用具有多个条目的加热块/摇床进行此反应，以确保所有反应均在完全相同的（热）条件下发生。</li>
	<li>以 1.0 mL 的 0.5 M H2SO4 定期中和试管，冷却后加入 2.0 mL 甲醇。 注:少量的多S和只有1.0 mL的1M NaOH被使用，因为这些浓度，在添加甲醇后，可以直接注射到HPPL，不需要任何进一步稀释。</li>
	<li>使用 0.45 μm PTFE 注射器过滤器过滤所有样品，然后使用自动采样器在 HPLC 上注射 （20 μL）。监测 ±254 nm 的吸收量，并计算已知二氢酸标准溶液校准曲线的浓度。 注:校准曲线的标准溶液应与去聚合后的工作用同一溶剂混合物制成。</li>
</ol>

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作者没有什么可透露的。

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制29。
1H NMR 测量用于确定聚合的平均数量程度，GPC 测量用于生成进一步链长数据。GPC 测量总是通过混合聚苯乙烯和用液氮淬火来强制非晶化后执行。
表1中显示的获得结果显示，聚合物样品的GPC Mn值相当于聚合物样品在几代人中平均约670个重复单位的聚S。这些值大大高于图 2中提出的1H NMR 测量获得的相应值，因为这些值大约是 43 个多 S 重复单位。这种变化与合成聚合物中含有化合物的乙酰氧组的微量杂质有关，通过1HNMR测量计算，降低了聚氨酯平均聚合（DPn）的数量。另一种解释与 GPC 测量中使用的聚酯和聚苯乙烯标准的水动力学体积差异有关。多分散性 PDI 低于 2.0。这种相对较低的价值可归因于在GPC分析之前高分子聚合物过滤掉。
热特征是使用 DSC 和 TGA 技术进行的，通过这些技术可以发现与 PET 相当的热特性。DSC分析表明，分子可回收聚合物聚S的熔化温度为281°C。 这种融化温度比PET30高16度。与 PET 相比，多 S 的玻璃橡胶过渡温度也更高，即 PET 的温度为 113 °C，PET 为 67 °C。较高的玻璃橡胶过渡温度通常有利于许多应用。
最后，在冷却周期中，多 S 具有与 PET 相关的较低结晶温度，即 151 °C 与 190 °C。 多 S 的热重力分析表明，多 S 的分解温度为 341 °C。与分解温度为 470 °C 的 PET 相比，多 S 的分解温度较低31（支持信息:图S11）。
在80°C的温度下观察了形成聚合物材料的去聚合两个多小时。 HPLC样本被采集，以分析释放的二氢酸在1M NaOH溶液中的浓度。样品是根据纯二氢酸的校准曲线测量的，以确定HPPC的产量。（支持信息:图S12）
已建立质量平衡，以确定在聚合和去聚合的完整周期中质量损失。在聚合过程中引入了精确量为 5.00 克的二氢酸。经过一个周期的聚合，去聚合到二氢酸，并工作，4.70克二氢酸产生，相当于94%的产量。在第一个周期中，大部分材料被手动处理丢失（支持信息: 图S13-S14）。单体二氢酸的损失是相当有限的，因此，经过三代人，大约85%的单体初始量仍然存在。
本出版物描述了如何设计一种特别适合分子回收的新型聚合物材料。聚合、去聚合化（回收单体）和再聚合相结合，创造了一个完全可持续的循环，损失最小。当绿色化学原理得到进一步应用时，可以优化不同步骤的条件。例如，后续研究可以研究酸性条件下的水解，以防止盐的过度形成。

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。

<table><tbody><tr><td>&lt;strong&gt;Reaction 1: Green Knoevenagel condensation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Ammonium bicarbonate</td><td>Sigma Aldrich</td><td>&gt;99%</td><td></td></tr><tr><td>Ethanol</td><td>Boom</td><td>Technical grade</td><td></td></tr><tr><td>Ethyl acetate</td><td>Macron</td><td>99.8%</td><td></td></tr><tr><td>Hydrochloric acid</td><td>Boom</td><td>37%</td><td></td></tr><tr><td>Malonic acid</td><td>Sigma Aldrich</td><td>99%</td><td>used as received</td></tr><tr><td>Sodium bicarbonate</td><td>Sigma Aldrich</td><td>&gt;99.7%</td><td></td></tr><tr><td>Syringaldehyde</td><td>Sigma Aldrich</td><td>98%</td><td>used as received</td></tr><tr><td>&lt;strong&gt;Reaction 2: Hydrogenation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Magnesium sulfate</td><td>Macron</td><td>99%</td><td>dried</td></tr><tr><td>Raney&amp;trade; nickel</td><td>Sigma Aldrich</td><td>&gt;89%</td><td></td></tr><tr><td>Sodium hydroxide</td><td>Boom</td><td>Technical grade</td><td>dissolved</td></tr><tr><td>&lt;strong&gt;Reaction 3: Acetylation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Acetic anhydride</td><td>Macron</td><td>&gt;98%</td><td></td></tr><tr><td>Acetone</td><td>Macron</td><td>&gt;99.5%</td><td></td></tr><tr><td>Sodium acetate</td><td>Sigma Aldrich</td><td>&gt;99%</td><td></td></tr><tr><td>&lt;strong&gt;Reaction 4A: Polymerisation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>1,2-xylene</td><td>Macron</td><td>&gt;98%</td><td></td></tr><tr><td>Sodium hydroxide</td><td>Boom</td><td>Technical grade</td><td>finely powdered</td></tr><tr><td>Zinc(II)acetate</td><td>Sigma Aldrich</td><td>99.99%</td><td></td></tr><tr><td>&lt;strong&gt;Reaction 4B: Depolymerisation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Sodium hydroxide</td><td>Boom</td><td>Technical grade</td><td>dissolved</td></tr><tr><td>Sulfuric acid</td><td>Macron</td><td>100%</td><td></td></tr><tr><td>&lt;strong&gt;Analysis&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>CDCl&lt;sub&gt;3&lt;/sub&gt;</td><td>Cambride Isotope Laboratories, Inc.</td><td>99.5%</td><td></td></tr><tr><td>CF&lt;sub&gt;3&lt;/sub&gt;COOD</td><td>Cambride Isotope Laboratories, Inc.</td><td>98%</td><td></td></tr><tr><td>Dimethylformamide</td><td>Macron</td><td>&gt;99.9%</td><td></td></tr><tr><td>Hexafluoro-2-propanol</td><td>TCI Chemicals</td><td>&gt;99%</td><td></td></tr><tr><td>Methanol</td><td>Macron</td><td>&gt;99.8%</td><td></td></tr><tr><td>Tetrahydrofuran</td><td>Macron</td><td>&gt;99.9%</td><td></td></tr></tbody></table>

designed for molecular recycling: a lignin-derived semi-aromatic biobased polymer

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。

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 = 18.04 克乙酸酯） = 42.56 克西纳平酸） / 42.56 克西纳平酸] 。西纳平酸被氢化，具有高产（>95%），以获得预期的单体二氢酸。（支持信息:图S2）这种加氢反应的电子因子为0.84。随后，二氢酸被乙酰化，获得4-乙氧-二氢平酸及其聚合物。这种乙酰化反应的电子因子为0.45，假设完全转换为4-乙氧二氢酸（支持信息:图S3）。
通常，药物有机合成反应的电子因子在5到100之间，这些反应经常使用相对有害的化学物质21。与这些数字相比，为绿色克诺维纳格尔和随后的反应计算的电子因子非常低。然而，电子因素表现出一些缺点。例如，电子因素没有反映给定废物成分的环境危害。原则上，这可以通过"环境商"（Q）来补偿，同时考虑到特定废物的"环境不友好"。由于碳酸氢铵的催化剂相对无害，绿克诺维纳格尔的环境不友好商Q也被说成是低。不过，额外的研究对于证实这22点至关重要。通过应用上述有机合成反应，4-乙氧二氢酸及其前聚合物已准备好对多S进行聚聚化。
图1 描绘了4-乙氧二氢酸梯级生长聚合的拟议机制。在第一步中，添加的碱基开始反应，并通过去质化酸组来控制反应速率，从而刺激其反应性23。形成的碳基酸盐攻击乙酰氧体的碳基，并产生三角星。在此状态下，苯氧组通过苯氧转移连接到另一个碳基，而苯甲酸转移最初是脂肪类卡西酸组。当苯甲酸转移发生时，醋酸离子离开中间体，从原始基座中减去质子，然后将反应作为醋酸离开。在实践中，通过在反应容器24中制造真空来促进这一步骤。在每个周期中，链条中都会添加一个新分子。在多聚变量反应的进展过程中，要找到增加分子量和聚合物链降解之间的确切组合是很具有挑战性的。当温度在熔融聚合过程中随着梯度升高时，随着聚合物粘度的增加，降解量会增加。在多聚变的第二步中添加少量溶剂，以降低粘度。在这种溶剂辅助聚凝结中，1，2-xylene被证明是促进聚聚变25的合适剂。
图2 表示聚合过程中的三种不同的 1H NMR 测量。样品溶解良好，在 CF3COOD /CDCl3的混合物中测量。 1HNMR光谱是在西纳平酸乙酰化后拍摄的。中间的 1H NMR 频谱是从相同反应中采集的样本。没有分离特定化合物，因此显示乙酰化的辛辣酸及其聚合物。上面 的1HNMR光谱是在多聚变量完成后从样品中取出的。乙酰末端组的面积在聚合过程中减少，聚合（DPn）的平均程度增加。完成反应后，由 1HNMR测量确定的43个重复单位的聚合度被设定为。
进行了 GPC 测量，以调查多 S 链长度，并测试了各种 GPC 系统进行分析。第一步是溶解几种常见有机溶剂中的聚合物材料，如氯仿 （CHCl3）、二甲基甲酰胺 （DMF）、六氟二丙醇 （HFIP） 和四氢喃 （THF）。然而，在 DSC 热图上可见的多 S 高晶体材料在这些溶剂中似乎很少溶解。此外，当聚合物材料熔化，然后在液氮中快速冷却以增加聚合物的无定形性时，只有短聚合物链溶解在 DMF 中。GPC 上测量的价值只有 1，900 到 2，100 Da，相当于大约 10 个重复单位。
已选择另一种预处理方法进行适当的 GPC 测量。其他研究26 规定，当聚苯乙烯在其实际形式中熔化成聚酯时，可以形成一种更无定形的聚酯材料。两种聚合物（聚酯和聚苯乙烯）被放置在DSC平底锅中，熔化后在液氮中冷却。用丙酮清洗淬火混合物可去除残留的聚苯乙烯，在DMF中成功溶解后，可以观察到高分子量聚合物。
当聚S在1M NaOH中水解时，分子可回收聚酯在不到10分钟内产生起始材料二氢酸。HPLC、熔点分析和 1HNMR证实了这一观察（支持信息: 图S4）。延长反应时间并没有增加产量，如图 3所示。
图4和表1分别显示了聚S 1.0及其历代多S2.0和多S 3.0在强迫性非晶位后与原发性聚苯乙烯的热图和GPC分析。DSC 对多 S 的分析显示玻璃过渡信号 （Tg） 在 113 °C 下，内热熔化信号 （Tm）在 281 °C。 再聚合的西纳平酸3a聚氨酯-S 2.0向上和聚H 3.0的聚合物具有类似的热性能（支持信息:数字S5-S7）。聚S是一种半晶体聚合物材料，因为玻璃过渡温度（Tg）和熔化信号存在于聚S及其后代的温度图中。可以说，GPC分析后，强迫态与战术聚苯乙烯显示一个恒定的聚合物材料长度在整个不同代（支持信息:数字S8-S10）。
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61975/61975fig01.jpg"> 图1:4-乙氧二氢酸梯级生长多聚化的拟议机制。<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig01large.jpg" target="_blank">请单击此处查看此图的较大版本。</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61975/61975fig02.jpg"> 图2:1HNMR光谱（25°C，CF3COOD/CDCl3，Cinapinic酸分离乙酰产物（底部）的剩余溶剂峰值分别为11.49和7.27ppm:聚S（中）的聚合物预聚物:聚S后固态后凝结（240 °C，30分钟，真空）（顶部）。<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig02large.jpg" target="_blank">请单击此处查看此图的较大版本。</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61975/61975fig03.jpg"> 图3:碱性水解（1 M NaOH溶液，80°C）多S随着时间的推移，由二氢酸（DHSA）产量基于HPLC峰区确定。<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig03large.jpg" target="_blank">请单击此处查看此图的较大版本。</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61975/61975fig04.jpg"> 图4:三代多S的DSC热图。<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig04large.jpg" target="_blank">请单击此处查看此图的较大版本。</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always"><tbody>
<tr>
<td>代</td>
			<td>多S （毫克）</td>
			<td>PS （毫克）</td>
			<td>Mn</td>
			<td>Mw</td>
			<td>PDI</td>
			<td>DP</td>
		</tr>
<tr>
<td>1.0</td>
			<td>5.0</td>
			<td>4.8</td>
			<td>120030</td>
			<td>193580</td>
			<td>1.6</td>
			<td>594</td>
		</tr>
<tr>
<td>2.0</td>
			<td>5.0</td>
			<td>5.0</td>
			<td>134740</td>
			<td>194410</td>
			<td>1.4</td>
			<td>667</td>
		</tr>
<tr>
<td>3.0</td>
			<td>4.7</td>
			<td>4.9</td>
			<td>153620</td>
			<td>237210</td>
			<td>1.5</td>
			<td>760</td>
		</tr>
</tbody></table>表1:多S代的GPC测量。

Watch this Scientific Journal Video about Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer at JoVE.com

Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer

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。

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

The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers make ...

designed-for-molecular-recycling-lignin-derived-semi-aromatic

Nanyang Technological University

Research

Education

JoVE Core

JoVE Journal

Organic Chemistry

Chemistry

Unit 1

&alpha;-Carbon Chemistry: Enols, Enolates, and Enamines

SCIENTISTS IN ACTION

3.4K 次观看.  Avans University of Applied Science. 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。

视频: Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer

Methods for Facilitating Microbial Growth on Pulp Mill Waste Streams and Characterization of the Biodegradation Potential of Cultured Microbes

The kraft process is applied to wood chips for separation of lignin from the polysaccharides within lignocellulose for pulp that will produce a high quality paper. Black liquor is a pulping waste generated by the kraft process that has potential for downstream bioconversion. However, the recalcitrant nature of the lignocellulose resources, its chemical derivatives that constitute the majority of available organic carbon within black liquor, and its basic pH present challenges to microbial biodegradation of this waste material. Methods for the collection and modification of black liquor for microbial growth are aimed at utilization of this pulp waste to convert the lignin, organic acids, and polysaccharide degradation byproducts into valuable chemicals. The lignocellulose extraction techniques presented provide a reproducible method for preparation of lignocellulose growth substrates for understanding metabolic capacities of cultured microorganisms. Use of gas chromatography-mass spectrometry enables the identification and quantification of the fermentation products resulting from the growth of microorganisms on pulping waste. These methods when used together can facilitate the determination of the metabolic activity of microorganisms with potential to produce fermentation products that would provide greater value to the pulping system and reduce effluent waste, thereby increasing potential paper milling profits and offering additional uses for black liquor.

Industrial wastes can be collected and modified to analyze microbial growth. Lignocellulose extraction techniques provide components to analyze specific biodegradation ability. Gas chromatography-mass spectrometry identifies fermentation products of microorganisms grown on pulping waste. These methods determine the metabolic capacity of microorganisms to degrade pulping waste.

方法对纸浆厂污水流和培养微生物的生物降解能力的表征促进微生物生长

The kraft process is applied to wood chips for separation of lignin from the polysaccharides within lignocellulose for pulp that will produce a high ...

科研

环境科学

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

朝仿生学木:纳米纤维素，木质素的装配式自由站立电影和合成聚阳离子

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

化学

Pretreatment of Lignocellulosic Biomass with Low-cost Ionic Liquids

A number of ionic liquids (ILs) with economically attractive production costs have recently received growing interest as media for the delignification of a variety of lignocellulosic feedstocks. Here we demonstrate the use of these low-cost protic ILs in the deconstruction of lignocellulosic biomass (Ionosolv pretreatment), yielding cellulose and a purified lignin. In the most generic process, the protic ionic liquid is synthesized by accurate combination of aqueous acid and amine base. The water content is adjusted subsequently. For the delignification, the biomass is placed into a vessel with IL solution at elevated temperatures to dissolve the lignin and hemicellulose, leaving a cellulose-rich pulp ready for saccharification (hydrolysis to fermentable sugars). The lignin is later precipitated from the IL by the addition of water and recovered as a solid. The removal of the added water regenerates the ionic liquid, which can be reused multiple times. This protocol is useful to investigate the significant potential of protic ILs for use in commercial biomass pretreatment/lignin fractionation for producing biofuels or renewable chemicals and materials.

The pretreatment of lignocellulosic biomass with protic low-cost ionic liquids is shown, resulting in a delignified cellulose-rich pulp and a purified lignin. The pulp gives rise to high glucose yields after enzymatic saccharification.

木质纤维素生物质预处理低成本离子液体

A number of ionic liquids (ILs) with economically attractive production costs have recently received growing interest as media for the delignification of ...

Extraction of Lignin with High &#946;-O-4 Content by Mild Ethanol Extraction and Its Effect on the Depolymerization Yield

Lignin valorization strategies are a key factor for achieving more economically competitive biorefineries based on lignocellulosic biomass. Most of the emerging elegant procedures to obtain specific aromatic products rely on the lignin substrate having a high content of the readily cleavable &#946;-O-4 linkage as present in the native lignin structure. This provides a miss-match with typical technical lignins that are highly degraded and therefore are low in &#946;-O-4 linkages. Therefore, the extraction yields, and the quality of the obtained lignin are of utmost importance to access new lignin valorization pathways. In this manuscript, a simple protocol is presented to obtain lignins with high &#946;-O-4 content by relatively mild ethanol extraction that can be applied to different lignocellulose sources. Furthermore, analysis procedures to determine the quality of the lignins are presented together with a depolymerization protocol that yields specific phenolic 2-arylmethyl-1,3-dioxolanes, which can be used to evaluate the obtained lignins. The presented results demonstrate the link between lignin quality and potential for the lignins to be depolymerized into specific monomeric aromatic chemicals. Overall, the extraction and depolymerization demonstrates a trade-off between the lignin extraction yield and the retention of the native aryl-ether structure and thus the potential of the lignin to be used as the substrate for the production of chemicals for higher-value applications.

Here, we present a protocol to perform ethanol extraction of lignin from several biomass sources. The effect of the extraction conditions on the lignin yield and &#946;-O-4 content are presented. Selective depolymerization is performed on the obtained lignins to obtain high aromatic monomer products.

轻度乙醇萃取高β-o-4 的木质素及其对解聚产率的影响

Lignin valorization strategies are a key factor for achieving more economically competitive biorefineries based on lignocellulosic biomass. Most of the ...

Comprehensive Compositional Analysis of Plant Cell Walls (Lignocellulosic biomass) Part I: Lignin

The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st century. This has rekindled interest in the use of plant products as industrial raw materials for the production of liquid fuels for transportation1 and other products such as biocomposite materials7. Plant biomass remains one of the greatest untapped reserves on the planet4. It is mostly comprised of cell walls that are composed of energy rich polymers including cellulose, various hemicelluloses (matrix polysaccharides, and the polyphenol lignin6 and thus sometimes termed lignocellulosics. However, plant cell walls have evolved to be recalcitrant to degradation as walls provide tensile strength to cells and the entire plants, ward off pathogens, and allow water to be transported throughout the plant; in the case of trees up to more the 100 m above ground level. Due to the various functions of walls, there is an immense structural diversity within the walls of different plant species and cell types within a single plant4. Hence, depending of what crop species, crop variety, or plant tissue is used for a biorefinery, the processing steps for depolymerization by chemical/enzymatic processes and subsequent fermentation of the various sugars to liquid biofuels need to be adjusted and optimized. This fact underpins the need for a thorough characterization of plant biomass feedstocks. Here we describe a comprehensive analytical methodology that enables the determination of the composition of lignocellulosics and is amenable to a medium to high-throughput analysis. In this first part we focus on the analysis of the polyphenol lignin (Figure 1). The method starts of with preparing destarched cell wall material. The resulting lignocellulosics are then split up to determine its lignin content by acetylbromide solubilization3, and its lignin composition in terms of its syringyl, guaiacyl- and p-hydroxyphenyl units5. The protocol for analyzing the carbohydrates in lignocellulosic biomass including cellulose content and matrix polysaccharide composition is discussed in Part II2.

Comprehensive Compositional Analysis of Plant Cell Walls Lignocellulosic biomass Part I: Lignin

Plant biomass is a major carbon-neutral renewable resource that could be used for the production of biofuels. Plant biomass consists mainly of cell walls, a structurally complex composite material termed lignocellulosics. Here we describe a protocol for a comprehensive analysis of the content and composition of the polyphenolic lignin.

综合植物细胞壁成分分析（木质纤维素生物质）第一部分：木质素

The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st ...

生物学

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as source of mechanical reinforcement in fully bio-based fiberboards was developed. Various lignocellulosic crop by-products have already been successfully pre-treated through this process, e.g., cereal straws (especially rice), coriander straw, shives from oleaginous flax straw, and bark of both amaranth and sunflower stems.
The extrusion process results in a marked increase in the average fiber aspect ratio, leading to improved mechanical properties of fiberboards. The twin-screw extruder can also be fitted with a filtration module at the end of the barrel. The continuous extraction of various chemicals (e.g., free sugars, hemicelluloses, volatiles from essential oil fractions, etc.) from the lignocellulosic substrate, and the fiber refining can, therefore, be performed simultaneously.
The extruder can also be used for its mixing ability: a natural binder (e.g., Organosolv lignins, protein-based oilcakes, starch, etc.) can be added to the refined fibers at the end of the screw profile. The obtained premix is ready to be molded through hot pressing, with the natural binder contributing to fiberboard cohesion. Such a combined process in a single extruder pass improves the production time, production cost, and may lead to reduction in plant production size. Because all the operations are performed in a single step, fiber morphology is better preserved, thanks to a reduced residence time of the material inside the extruder, resulting in enhanced material performances. Such one-step extrusion operation may be at the origin of a valuable industrial process intensification.
Compared to commercial wood-based materials, these fully bio-based fiberboards do not emit any formaldehyde, and they could find various applications, e.g., intermediate containers, furniture, domestic flooring, shelving, general construction, etc.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pretreatment on lignocellulosic biomass was developed, which leads to an increased average fiber aspect ratio. A natural binder can also be added continuously after fiber refining, leading to bio-based fiberboards with improved mechanical properties after hot pressing of the obtained extruded material.

双螺丝挤压工艺，以生产可再生纤维板

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as ...

工程学

Fractionation of Lignocellulosic Biomass using the OrganoCat Process

The shift from a petroleum-based to a more sustainable and bio-based economy requires the development of new refinery concepts to maintain the supply of raw materials and energy. For these novel and sustainable biorefinery concepts, it is important to use catalysts and solvents that are aligned with the principles of Green Chemistry. Therefore, the implementation of biogenic alternatives can be a promising solution. The lignocellulose pretreatment and fractionation process presented herein-OrganoCat-is an integrated fractionation of lignocellulose into its main components using biogenic acids such as 2,5-furandicarboxylic acid as catalyst. Hemicelluloses and other non-cellulosic polysaccharides are selectively depolymerized by the diluted acid and dissolved, while the crystalline cellulose remains in the solid pulp. In the presence of a second organic phase consisting of biogenic 2-methyltetrahydrofuran, disentangled lignin is extracted in situ. The process allows for the efficient fractionation of the three main components-lignin, cellulose, and non-cellulosic sugars. This helps to focus on the quality of the lignin, the improvement of enzymatic hydrolysis of the cellulose-enriched pulp, and the mild non-cellulosic sugar extraction with low degradation.

OrganoCat is a method for the pretreatment and fractionation of lignocellulose under mild conditions into lignin, fermentable sugars, and cellulose pulp. In a biogenic, biphasic solvent system of water and 2-methyltetrahydrofuran with 2,5-furancarboxylic acid as catalyst, the OrganoCat products are separated in situ for straightforward product recovery.

使用有机催化工艺分馏木质纤维素生物质

The shift from a petroleum-based to a more sustainable and bio-based economy requires the development of new refinery concepts to maintain the supply of ...

Ultrafast Lignin Extraction from Unusual Mediterranean Lignocellulosic Residues

Pretreatment is still the most expensive step in lignocellulosic biorefinery processes. It must be made cost-effective by minimizing chemical requirements as well as power and heat consumption and by using environment-friendly solvents. Deep eutectic solvents (DESs) are key, green, and low-cost solvents in sustainable biorefineries. They are transparent mixtures characterized by low freezing points resulting from at least one hydrogen bond donor and one hydrogen bond acceptor. Although DESs are promising solvents, it is necessary to combine them with an economic heating technology, such as microwave irradiation, for competitive profitability. Microwave irradiation is a promising strategy to shorten the heating time and boost fractionation because it can rapidly attain the appropriate temperature. The aim of this study was to develop a one-step, rapid method for biomass fractionation and lignin extraction using a low-cost and biodegradable solvent. 
In this study, a microwave-assisted DES pretreatment was conducted for 60 s at 800 W, using three kinds of DESs. The DES mixtures were facilely prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBDs): a monocarboxylic acid (lactic acid), a dicarboxylic acid (oxalic acid), and urea. This pretreatment was used for biomass fractionation and lignin recovery from marine residues (Posidonia leaves and aegagropile), agri-food byproducts (almond shells and olive pomace), forest residues (pinecones), and perennial lignocellulosic grasses (Stipa tenacissima). Further analyses were conducted to determine the yield, purity, and molecular weight distribution of the recovered lignin. In addition, the effect of DESs on the chemical functional groups in the extracted lignin was determined by Fourier-transform infrared (FTIR) spectroscopy. The results indicate that the ChCl-oxalic acid mixture affords the highest lignin purity and the lowest yield. The present study demonstrates that the DES-microwave process is an ultrafast, efficient, and cost-competitive technology for lignocellulosic biomass fractionation.

Deep eutectic solvent-based, microwave-assisted pretreatment is a green, fast, and efficient process for lignocellulosic fractionation and high-purity lignin recovery.

超高速利格宁从不寻常的地中海木质细胞残留物中提取

Pretreatment is still the most expensive step in lignocellulosic biorefinery processes. It must be made cost-effective by minimizing chemical requirements ...

Quantitative 31P NMR Analysis of Lignins and Tannins

The development of sustainable biorefinery products is confronted, among others, with the challenge of lignin and tannin valorization. These abundant, renewable aromatic biopolymers have not been widely exploited due to their inherent structural complexity and high degrees of variability and species diversity. The lack of a defined primary structure for these polyphenols is further compounded with complex chemical alterations induced during processing, eventually imparting a large variety of structural features of extreme significance for any further utilization efforts.
Consequently, a protocol for the rapid, simple, and unequivocal identification and quantification of the various functional groups present in natural polyphenols, is a fundamental prerequisite for understanding and accordingly tailor their reactivity and eventual utility.
Quantitative 31P NMR offers the opportunity to rapidly and reliably identify unsubstituted, o-mono substituted, and o-disubstituted phenols, aliphatic OHs, and carboxylic acid moieties in lignins and tannins with broad application potential.
The methodology consists of an in situ quantitative lignin or tannin labeling procedure using a suitable 31P containing probe, followed by the acquisition of a quantitative 31P NMR spectrum in the presence of an internal standard. The high natural abundance of the 31P nucleus allows for small amounts of the sample (~30 mg) and short NMR acquisition times (~30-120 min) with well-resolved 31P signals that are highly dependent on the surrounding chemical environment of the labeled OH groups.

Quantitative 31P NMR Analysis of Lignins and Tannins

31P NMR is a powerful tool for the structural elucidation of polyphenols. This fast, easy, precise, quantitative, and highly reproducible analytical procedure, that allows for the quantification and differentiation of the different types of hydroxy, phenolic, and carboxylic groups in lignins and tannins has now become a routine analytical tool.

利格宁和单宁的定量 31P NMR 分析

The development of sustainable biorefinery products is confronted, among others, with the challenge of lignin and tannin valorization. These abundant, ...

Depolymerizable Olefinic Polymers Based on Fused-Ring Cyclooctene Monomers

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. Achieving a closed-loop polymer economy via chemical recycling to monomer (CRM) is one such promising route. Our group recently reported a new CRM system based on polymers prepared by ring-opening metathesis polymerization (ROMP) of trans-cyclobutane fused cyclooctene (tCBCO) monomers. This system offers several key advantages, including the ease of polymerization at ambient temperatures, quantitative depolymerization to monomers under mild conditions, and a broad range of functionalities and thermomechanical properties. Here, we outline detailed protocols for the preparation of tCBCO-based monomers and their corresponding polymers, including the preparation of elastic polymer networks and compression molding of linear thermoplastic polymers. We also outline the preparation of high ring strain E-alkene tCBCO monomers and their living polymerization. Finally, the procedures for the depolymerization of linear polymers and polymer networks are also demonstrated.

Here, we describe protocols for the preparation of trans-cyclobutane fused cyclooctenes (tCBCO),&#160;their polymerization to prepare depolymerizable olefinic polymers, and the depolymerization of these polymers under mild conditions. Additionally, protocols for the preparation of depolymerizable networks and compression molding of rigid linear plastics based on this system are described.

基于熔环环辛烯单体的可解聚烯烃聚合物

The growing consumption of synthetic polymers and the accumulation of polymer waste have led to a pressing need for new routes to sustainable materials. ...