DNP NMR spectroscopy of cross-linked organic polymers: rational guidelines towards optimal sample preparation #DNPNMR
Tanaka, Shinji, Wei-Chih Liao, Atsuko Ogawa, Kazuhiko Sato, and Christophe Copéret. “DNP NMR Spectroscopy of Cross-Linked Organic Polymers: Rational Guidelines towards Optimal Sample Preparation.” Physical Chemistry Chemical Physics 22, no. 6 (2020): 3184–90.
Cross-linked polystyrenes (PS) are an important class of polymers, whose properties are strongly dependent on incorporated functionalities, for which detailed understanding of their structure remains a challenge. Here, we develop a rational guideline for dynamic nuclear polarization (DNP) sample formulation for cross-linked PS to interrogate their structure. We show that the DNP enhancement on a series of cross-linked PS bearing alkylammonium groups as prototypical organic polymers correlates with the polymer swelling properties in both apolar and polar formulations (TEKPol/1,1,2,2-tetrachloroethane and AMUPol/dimethyl sulfoxide). This work provides guidelines to easily optimize DNP formulation using a simple swelling test and enables natural abundance 15N NMR to be recorded on a series of PS-supported quaternary alkylammonium salts, allowing a detailed structural analysis.