Established and emerging strategies for polymer chain‐end modification

Abstract

The development of "controlled" and "living" polymerization processes with high end-group fidelity has enabled an unprecedented range of polymeric materials with specific chainend functionality to be prepared. This highlight provides an overview of available strategies and evaluation of recent approaches for the chain-end functionalization of polymers prepared through controlled chain-growth polymerizations. As a tribute to Professor Robert B. Grubbs on the occasion of his 75th birthday, we also take this opportunity to highlight methods for the chain-end modification of polymers prepared by ring-opening metathesis polymerization within the broader context of functional group tolerant, living polymerizations. Finally, we focus attention toward new directions in polymer chain-end modifications, describing existing gaps in current strategies, and detailing recently reported protocols that show significant improvements over traditional methods.

Desulfurization–bromination: direct chain-end modification of RAFT polymers

“…10 To demonstrate the synthetic versatility of PS-Br obtained via RAFT, the Br chain-end was reacted with excess sodium azide to furnish the azide-terminated polymer (Figure 6a). Analysis by 1 H NMR indicated complete disappearance of peaks at 4.5 ppm corresponding to PS-Br and the emergence of new peaks at 3.9 ppm corresponding to the protons adjacent to the azide in PS-N 3 , suggestive of quantitative conversion to the desired end group (Figure 6b).…”

“…9 Three main strategies exist for the incorporation of specific end groups into polymers: (1) the use of functional initiators, (2) specific termination reactions, or (3) through the post-polymerization modification of residual reactive functional groups. 10 Post-polymerization modification is often the preferred method, enabling the preparation of a range of materials with different chain-ends from a common polymer precursor. When combined with CRPs, these approaches can be used to prepare a diverse range of polymers with control over molar mass, dispersity ( Đ ) and molecular architecture, while also incorporating reactive chemical functionality for further modification.…”

“…10 This is predominantly a result of the synthetic versatility enabled by halide substitution reactions. 12,13 The conversion of RAFT chain-ends to the corresponding bromides would therefore expand the scope of possible chain-end modifications of RAFT polymers, while also allowing conversion between RAFT and ATRP processes.…”

PET‐RAFT as a facile strategy for preparing functional lipid–polymer conjugates

“…Controlled radical polymerization offers a promising route to functional lipid–polymer conjugates that address many of these drawbacks . Prior synthetic approaches to lipid–polymer conjugates have been based on traditional reversible addition‐fragmentation chain transfer (RAFT) strategies with preliminary studies showing efficient insertion into the phospholipid bilayers of cells or liposomes .…”

How good is CuAAC “click” chemistry for polymer coupling reactions?

“…Of all the reactions that were designated with “click” status, the copper(I) catalyzed azide–alkyne cycloaddition (CuAAC) is considered by many to be the gold standard. Its popularity can be attributed in part to the highly orthogonal nature between azides and alkynes as well as the ease of introducing the functional groups onto molecules/macromolecules by both nucleophilic and electrophilic processes . In the fields of biological science, the CuAAC reaction has been employed for the conjugation of proteins, carbohydrates, and antibodies to macromolecules; viral and bacterial cell surface labeling; and the preparation of cyclic polypeptide and polysaccharide analogs.…”