Single-Site, Organometallic Aluminum Catalysts for the Precise Group Transfer Polymerization of Michael-Type Monomers

End-functionalized polymers by controlled/living radical polymerizations: synthesis and applications

This review focuses on end-functionalized polymers synthesized by controlled/living radical polymerizations and the applications in fields including bioconjugate formation, surface modification, topology construction, and self-assembly.

C–H Bond Activation of Silyl-Substituted Pyridines with Bis(Phenolate)Yttrium Catalysts as a Facile Tool towards Hydroxyl-Terminated Michael-Type Polymers

Herein, silicon-protected, ortho-methylated hydroxy-pyridines were reported as initiators in 2-aminoalkoxy-bis(phenolate)yttrium complexes for rare earth metal-mediated group-transfer polymerization (REM-GTP) of Michael-type monomers. To introduce these initiators, C−H bond activation was performed by reacting [(ONOO)tBuY(X)(thf)] (X = CH2TMS, thf = tetrahydrofuran) with tert-butyl-dimethyl-silyl-functionalized α-methylpyridine to obtain the complex [(ONOOtBuY(X)(thf)] (X = 4-(4′-(((tert-butyldimethylsilyl)oxy)methyl)phenyl)-2,6-di-methylpyridine). These initiators served as functional end-groups in polymers produced via REM-GTP. In this contribution, homopolymers of 2-vinylpyridine (2VP) and diethyl vinyl phosphonate (DEVP) were produced. Activity studies and end-group analysis via mass spectrometry, size-exclusion chromatography (SEC) and NMR spectroscopy were performed to reveal the initiator efficiency, the catalyst activity towards both monomers as well as the initiation mechanism of this initiator in contrast to commonly used alkyl initiators. In addition, 2D NMR studies were used to further confirm the end-group integrity of the polymers. For all polymers, different deprotection routes were evaluated to obtain hydroxyl-terminated poly(2-vinylpyridine) (P2VP) and poly(diethyl vinyl phosphonate) (PDEVP). Such hydroxyl groups bear the potential to act as anchoring points for small bioactive molecules, for post-polymerization functionalization or as macroinitiators for further polymerizations.

Non-Innocent Methylene Linker in Bridged Lewis Pair Initiators

Deprotonation usually occurs as an unwanted side reaction in the Lewis pair polymerization of Michael acceptors, for which the conjugated addition of the Lewis base to the acid-activated monomer is the commonly accepted initiation mechanism. This has also been reported for B-P-based bridged Lewis pairs (BLPs) that form macrocyclic addition products. We now show that the formerly unwanted deprotonation is the likely initiation pathway in the case of Al-P-based BLPs. In a detailed study of a series of Al-P-based BLPs, using a combination of single-crystal diffraction experiments (X-ray and neutron) and mechanistic investigations (experimental and computational), an active role of the methylene bridge was revealed, acting as a base towards the α-acidic monomers. Additionally, the polymerization studies proved a living behavior combined with significantly high activities, narrow molecular mass distributions, and the possibility of copolymerization.