Moore Oliver B, Hanson Polly-Ann, Comerford James W, Pellis Alessandro, Farmer Thomas J
Green Chemistry Centre of Excellence, Department of Chemistry, University of York, York, United Kingdom.
Front Chem. 2019 Jul 15;7:501. doi: 10.3389/fchem.2019.00501. eCollection 2019.
Bio-based platform molecules such as itaconic, fumaric, and muconic acid offer much promise in the formation of sustainable unsaturated polyester resins upon reaction with suitable diols and polyols. The C=C bonds present in these polyester chains allows for post-polymerization modification and such moieties are conventionally utilized in curing processes during the manufacture of coatings. The C=C modification sites can also act as points to add useful pendants which can alter the polymers final properties such as glass transition temperature, biodegradability, hardness, polarity, and strength. A commonly observed modification is the addition of secondary amines via an aza-Michael addition. Conventional procedures for the addition of amines onto itaconate polyesters require reaction times of several days as a result of undesired side reactions, in particular, the formation of the less reactive mesaconate regioisomer. The slow reversion of the mesaconate back to itaconate, followed by subsequent amine addition, is the primary reason for such extended reaction times. Herein we report our efforts toward finding a suitable catalyst for the aza-Michael addition of diethylamine onto a model substrate, dimethyl itaconate, with the aim of being able to add amine onto the itaconate units without excessive regioisomerization to the inactive mesaconate. A catalyst screen showed that iodine on acidic alumina results in an effective, heterogeneous, reusable catalyst for the investigated aza-Michael addition. Extending the study further, itaconate polyester was prepared by (CaL-B) via enzymatic polytranesterification and subsequently modified with diethylamine using the iodine on acidic alumina catalyst, dramatically reducing the required length of reaction (>70% addition after 4 h). The approach represents a multidisciplinary example whereby biocatalytic polymerization is combined with chemocatalytic modification of the resultant polyester for the formation of useful bio-based polyesters.
诸如衣康酸、富马酸和粘康酸等生物基平台分子在与合适的二醇和多元醇反应形成可持续的不饱和聚酯树脂方面具有很大的潜力。这些聚酯链中存在的碳碳双键允许进行后聚合改性，并且这些部分通常在涂料制造过程的固化过程中使用。碳碳双键改性位点还可以作为添加有用侧基的位点，这些侧基可以改变聚合物的最终性能，如玻璃化转变温度、生物降解性、硬度、极性和强度。一种常见的改性方法是通过氮杂迈克尔加成添加仲胺。由于不期望的副反应，特别是形成反应性较低的中康酸区域异构体，将胺添加到衣康酸酯聚酯上的传统方法需要几天的反应时间。中康酸缓慢地转化回衣康酸，随后进行胺添加，是反应时间延长的主要原因。在此，我们报告了我们为寻找一种合适的催化剂用于将二乙胺氮杂迈克尔加成到模型底物衣康酸二甲酯上所做的努力，目的是能够在衣康酸酯单元上添加胺而不会过度区域异构化为无活性的中康酸。催化剂筛选表明，酸性氧化铝负载的碘是用于所研究的氮杂迈克尔加成的有效、多相、可重复使用的催化剂。进一步扩展研究，通过酶促聚酯交换反应由（CaL - B）制备衣康酸酯聚酯，随后使用酸性氧化铝负载的碘催化剂用二乙胺进行改性，显著缩短了所需的反应时间（4小时后加成>70%）。该方法代表了一个多学科的实例，即生物催化聚合与所得聚酯的化学催化改性相结合以形成有用的生物基聚酯。
