Synthesis and Application of Functional Group-Bearing Pyridyl-Based Initiators in Rare Earth Metal-Mediated Group Transfer Polymerization

The polymer class of poly(vinylphosphonates) offers a wide array of attractive features such as high biocompatibility, thermoresponsive behavior, and the option for the directed introduction of small molecules at the initial step of the polymerization. Through the latter, polymer conjugates consisting of targeting ligands, fluorophores, or pharmacologically active substances become feasible. However, the modification of such compounds for the utilization in postpolymerization functionalization is usually cumbersome due to their structural complexity. In this study, we considered this factor and envisioned a flexible platform of functional polymers via the introduction of initiators comprising reactive functionalities. Hence, a series of customized initiators with protected functional groups (O-tert-butyldimethylsilyl, 2,5-dimethylpyrrole, and STrityl) were synthesized and studied in the C-H bond activation with Cp2Y(CH2TMS)(THF). The positive outcome of the activation experiments allowed the use of these initiators in the rare earth metal-mediated group transfer polymerization (REM-GTP). The versatility of this approach was demonstrated by end-group analysis using electrospray ionization mass spectrometry (ESI-MS) and DOSY-NMR, confirming the incorporation of the individual end group in poly(diethyl vinylphosphonate) (PDEVP). On this basis, PDEVP with varying feed concentrations was generated and the protection groups were removed to release the reactive motif. Doing so eventually enabled the successful coupling of model compounds, namely, cholesteryl chloroformate and N-phenyl maleimide, which established a foundation in the direction of more sophisticated polymer conjugates involving complex and highly functional compounds.