Scalable Frontal Oligomerization: Insights from Advanced Mass Analysis

Linear oligomers of dicyclopentadiene (DCPD) are reactive precursors for thermoplastic and thermoset materials. Unlike the foul-smelling parent monomer, oligomers composed of DCPD are odorless. With appropriate modification of the end-group or backbone chemistry, telechelic DCPD oligomers have potential utility as cross-linkers and as macromonomer precursors for block and graft copolymers. Most existing methods to produce oligo-DCPD, however, require solvent, are relatively slow, and necessitate air-free techniques. Here we show that frontal ring-opening metathesis oligomerization (FROMO) of neat DCPD and other norbornene derivatives rapidly generates hundreds of grams of material in minutes with catalyst loadings of 0.5 mM. This energy-efficient catalytic process utilizes the heat generated by the reaction to self-propagate oligomerization throughout the liquid monomer. FROMO employs a terminal olefin (e.g., styrene) in which a cross-metathesis reaction (i.e., chain transfer) competes with ring-opening metathesis (i.e., propagation). Kendrick mass analysis enables rapid identification and assignment of all the chain-end types present and quantifies the degree of branching resulting from the infrequent cyclopentene ring-opening reaction. This analytical technique also detects oligomer species derived from trace impurities in the monomer or chain-transfer agent that are otherwise difficult to observe with other characterization methods. The obtained oligomers possess well-defined chain-ends and molecular weight distributions.双环戊二烯（dicyclopentadiene, DCPD）的线性低聚物是热塑性与热固性材料的反应型前驱体。与气味刺鼻的母体单体不同，DCPD基低聚物无异味。通过对端基或主链化学结构进行适当修饰，遥爪型DCPD低聚物可作为交联剂以及嵌段、接枝共聚物的大分子单体前驱体，具备潜在应用价值。然而，现有多数制备DCPD低聚物的方法均需使用有机溶剂，反应速率相对缓慢，且必须采用无氧操作技术。本研究证实，纯DCPD与其他降冰片烯衍生物的前沿开环易位低聚反应（frontal ring-opening metathesis oligomerization, FROMO）可在数分钟内快速合成数百克产物，催化剂负载量仅为0.5 mM。该节能催化过程借助反应自身释放的热量，使低聚反应在液态单体中自蔓延进行。FROMO体系采用端基烯烃（如苯乙烯），其中交叉易位反应（即链转移）与开环易位反应（即链增长）相互竞争。肯德里克质量分析（Kendrick mass analysis）可快速识别并归属所有存在的链端类型，同时量化由偶发环戊烯开环反应引发的支化程度。该分析技术还可检测到源自单体或链转移剂中痕量杂质的低聚物物种，而这类物种通过其他表征手段通常难以被观测到。最终得到的低聚物具备结构明确的链端与分子量分布。