Multidimensional Characterization of α,ω-Telechelic Poly(ε-caprolactone)s via Online Coupling of 2D Chromatographic Methods (LC/SEC) and ESI-TOF/MALDI-TOF-MS

Abstract

The focus of the current study is the development of chromatographic methods to understand the end-group modification of poly(ε-caprolactones) (pCLs) prepared via azide/alkyne “click” chemistry. In order to prove the efficiency of the “click” reaction with increasing molar mass of the pCLs, a detailed characterization method via several multidimensional chromatographic techniques (2D LC/SEC, coupled to mass spectrometry) was developed. In particular, we have investigated the separation of low molar mass pCLs (Mn ≤ 35 000 g·mol–1) using a gradient elution chromatographic method (eluent: ACN/THF) monitoring the end-group functionalization of the separated polymers online via ESI-TOF and/or MALDI-TOF mass spectrometry, the latter coupled via a transfer module sprayer (TM sprayer). Because of the poor solubility of high molar mass pCLs (Mn above 35 000 g·mol–1), a second chromatographic method was employed, enabling the separation of end-group-functionalized pCLs up to a molar mass of 115 400 g·mol–1. Based on the critical solution conditions of the polymers, different solvent compositions and chromatographic columns were investigated in an isocratic mode to determine the critical conditions of α,ω-dihydroxy-telechelic pCLs. Finally, the critical conditions were optimized on a silica gel modified aminopropyl column (NUC-NH2) using a solvent mixture ratio of DCM/THF of 92/8 at 35 °C. A combination of the developed LCCC methods with SEC revealed the chemical composition as well as the molar mass of all of the modified pCLs, from the low molar mass polymers up to Mn = 115 400 g·mol–1.