Department of Chemistry, The University of Akron, Akron, OH 44325, USA.
Department of Chemistry, Tulane University, New Orleans, LA 70118, USA.
Analyst. 2022 May 17;147(10):2089-2096. doi: 10.1039/d2an00208f.
Macrocyclic poly(glycidyl phenyl ether) (pGPE) synthesized zwitterionic ring opening polymerization is typically contaminated by chains with linear and tadpole architecture. Although mass spectrometry (MS) analysis can readily confirm the presence of the linear byproduct, due to its unique mass, it is unable to differentiate between the cyclic and tadpole structures, which are constitutional isomers produced by backbiting reactions in monomeric or dimeric chains, respectively. To overcome this problem, ultraperformance reversed-phase liquid chromatography interfaced with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS) was employed. The separation achieved by UPLC revealed that the tadpole isomer elutes before the cyclic structure because of the increased polarity afforded by its distinctive substituents. The ratio of tadpole to cyclic species increased with the degree of polymerization, in agreement with the synthetic method used, as the potential for forming tadpole structures by backbiting is entropically favored in longer polymer chains. Once separated, the two isomers could be independently characterized by tandem mass spectrometry. The macrocyclic and tadpole species exhibit unique fragmentation patterns, including structurally diagnostic fragments for each structure.
通过开环聚合合成的大环聚（缩水甘油基苯基醚）（pGPE）通常会被具有线性和蝌蚪状结构的链所污染。虽然质谱（MS）分析可以很容易地确认线性副产物的存在，但由于其独特的质量，它无法区分环状和蝌蚪状结构，这两种结构是由单体或二聚体链中的回咬反应分别产生的结构异构体。为了解决这个问题，采用了超高效反相液相色谱-电喷雾串联质谱（UPLC-ESI-MS/MS）。UPLC 实现的分离表明，由于其独特取代基赋予的增加极性，蝌蚪状异构体在环状结构之前洗脱。蝌蚪与环状物质的比例随着聚合度的增加而增加，这与所使用的合成方法一致，因为在较长的聚合物链中，通过回咬形成蝌蚪状结构的可能性在熵上是有利的。一旦分离，这两种异构体就可以通过串联质谱独立进行表征。大环和蝌蚪状物质表现出独特的碎裂模式，包括每种结构的结构诊断片段。
