Macromolecular Coupling in Seconds of Triazolinedione End-Functionalized Polymers Prepared by RAFT Polymerization

Dual Function of β-hydroxy Dithiocinnamic Esters: RAFT Agent and Ligand for Metal Complexation

The reversible addition-fragmentation chain-transfer (RAFT) process has become a versatile tool for the preparation of defined polymers tolerating a large variety of functional groups. Several dithioesters, trithiocarbonates, xanthates, or dithiocarbamates have been developed as effective chain transfer agents (CTA), but only few examples have been reported, where the resulting end groups are directly considered for a secondary use besides controlling the polymerization. We here demonstrate that β-hydroxy dithiocinnamic esters represent a hitherto overlooked class of materials, which were originally designed for the complexation of transition metals but might as well act as reversible CTA. Modified with a suitable leaving group (R-group), these vinyl conjugated dithioesters indeed provide reasonable control over the polymerization of acrylates, acrylamides, or styrene via the RAFT process. Kinetic studies revealed linear evolutions of molar mass with conversion, while different substituents on the aromatic unit had only a minor influence. Block extensions prove the livingness of the polymer chains, although extended polymerization times may lead to side reactions. The resulting dithiocinnamic ester end groups are still able to form complexes with platinum, which verifies that the structural integrity of the end group is maintained. These findings open a versatile new route to tailor-made polymer bound metal complexes. This article is protected by copyright. All rights reserved.

RAFT-Based Polymers for Click Reactions

The parallel development of reversible deactivation radical polymerization and click reaction concepts significantly enriches the toolbox of synthetic polymer chemistry. The synergistic effect of combining these approaches manifests itself in a growth of interest to the design of well-defined functional polymers and their controlled conjugation with biomolecules, drugs, and inorganic surfaces. In this review, we discuss the results obtained with reversible addition–fragmentation chain transfer (RAFT) polymerization and different types of click reactions on low- and high-molar-mass reactants. Our classification of literature sources is based on the typical structure of macromolecules produced by the RAFT technique. The review addresses click reactions, immediate or preceded by a modification of another type, on the leaving and stabilizing groups inherited by a growing macromolecule from the chain transfer agent, as well as on the side groups coming from monomers entering the polymerization process. Architecture and self-assembling properties of the resulting polymers are briefly discussed with regard to their potential functional applications, which include drug delivery, protein recognition, anti-fouling and anti-corrosion coatings, the compatibilization of polymer blends, the modification of fillers to increase their dispersibility in polymer matrices, etc.

1,2-Disubstituted 1,2-Dihydro-1,2,4,5-tetrazine-3,6-dione as a Dynamic Covalent Bonding Unit at Room Temperature

Dynamic covalent bonds are useful tools in a wide range of applications. Although various reversible chemical reactions have been studied for this purpose, the requirement for harsh conditions, such as high temperature and low or high pH, to activate generally stable covalent bonds limits their potential applications involving biomolecules or household utilization. Here, we report the design, synthesis, characterization, and dynamic covalent bonding properties of 1,2-disubstituted 1,2-dihydro-1,2,4,5-tetrazine-3,6-dione (TETRAD). Hetero-Diels-Alder reactions of TETRAD with furan derivatives and their retro-reactions proceeded rapidly at room temperature under neutral conditions, enabling a chemically induced sol-gel transition system.

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.

The bright and the dark side of the sphere: light-stabilized microparticles

We introduce degradable microparticles, synthesized from prepolymers in a precipitation-like polymerization. The narrow disperse particles are stabilized with continuous irradiation of green light and can be spontaneously degraded in the dark.

Mass spectrometry as a tool to advance polymer science

In contrast to natural polymers, which have existed for billions of years, the first well-understood synthetic polymers date back to just over one century ago. Nevertheless, this relatively short period has seen vast progress in synthetic polymer chemistry, which can now afford diverse macromolecules with varying structural complexities. To keep pace with this synthetic progress, there have been commensurate developments in analytical chemistry, where mass spectrometry has emerged as the pre-eminent technique for polymer analysis. This Perspective describes present challenges associated with the mass-spectrometric analysis of synthetic polymers, in particular the desorption, ionization and structural interrogation of high-molar-mass macromolecules, as well as strategies to lower spectral complexity. We critically evaluate recent advances in technology in the context of these challenges and suggest how to push the field beyond its current limitations. In this context, the increasingly important role of high-resolution mass spectrometry is emphasized because of its unrivalled ability to describe unique species within polymer ensembles, rather than to report the average properties of the ensemble.

Multi-olefin containing polyethers and triazolinediones: a powerful alliance

Multi-functional polyethers with ene or diene moieties were prepared via the polymerisation of tailored functional glycidyl ether monomers to create a platform for click chemistry with triazolinediones (TADs).

Ultrafast Tailoring of Carbon Surfaces via Electrochemically Attached Triazolinediones

The straightforward coupling between a triazolinedione (TAD) unit and citronellyl derivatives via an Alder-ene reaction has been exploited to tailor the physicochemical surface properties of glassy carbon (GC) surfaces in an ultrafast and additive-free manner. For this purpose, we first covalently grafted a TAD precursor onto GC via electrochemical reduction of an in situ generated diazonium salt, which was then electrochemically oxidized into the desired GC-bonded TAD unit. A kinetic study of the modification of this reactive layer with an electroactive ferrocene probe proved that a complete functionalization was obtained in merely 1 minute. Further modification experiments with a fluorinated probe demonstrated that the surface properties can be swiftly tailored on demand. The different modification steps, as well as the efficiency of this strategy, were investigated by electrochemistry, contact angle goniometry, and X-ray photoelectron spectroscopy analysis.

One-Enzyme Triple Catalysis: Employing the Promiscuity of Horseradish Peroxidase for Synthesis and Functionalization of Well-Defined Polymers

We demonstrate a new concept in polymer chemistry that the promiscuity of enzymes, as represented by horseradish peroxidase, can be employed for RAFT polymerization and thiol-ene and Diels-Alder reactions to synthesize well-defined functional polymers, via three different catalytic reactions mediated by one single enzyme.

Tyrosine-Triazolinedione Bioconjugation as Site-Selective Protein Modification Starting from RAFT-Derived Polymers

The electrophilic aromatic substitution (S_EAr) reaction of triazolinediones (TADs) with the phenol moiety of tyrosine amino acid residues is a potent method for the site-selective formation of polymer-protein conjugates. Herein, using poly(N,N-dimethylacrylamide) (pDMA) and bovine serum albumin (BSA) as model reagents, the performance of this tyrosine-TAD bioconjugation in aqueous solutions is explored. At first, reversible addition-fragmentation chain transfer (RAFT) polymerization with a functional urazole, a precursor for TAD, chain transfer agent is used for the synthesis of a TAD end-functionalized pDMA. Eventually, the BSA ligation efficiency and selectivity of this polymer was evaluated in different aqueous solvent mixtures using SDS-PAGE and mass spectroscopy after trypsin digestion.

Controlling thermal reactivity with different colors of light

The ability to switch between thermally and photochemically activated reaction channels with an external stimulus constitutes a key frontier within the realm of chemical reaction control. Here, we demonstrate that the reactivity of triazolinediones, powerful coupling agents in biomedical and polymer research, can be effectively modulated by an external photonic field. Specifically, we show that their visible light-induced photopolymerization leads to a quantitative photodeactivation, thereby providing a well-defined off-switch of their thermal reactivity. Based on this photodeactivation, we pioneer a reaction manifold using light as a gate to switch between a UV-induced Diels-Alder reaction with photocaged dienes and a thermal addition reaction with alkenes. Critically, the modulation of the reactivity by light is reversible and the individually addressable reaction pathways can be repeatedly accessed. Our approach thus enables a step change in photochemically controlled reactivity, not only in small molecule ligations, yet importantly in controlled surface and photoresist design.

Click and Click-Inspired Chemistry for the Design of Sequence-Controlled Polymers

During the previous decade, many popular chemical reactions used in the area of "click" chemistry and similarly efficient "click-inspired" reactions have been applied for the design of sequence-defined and, more generally, sequence-controlled structures. This combination of topics has already made quite a significant impact on scientific research to date and has enabled the synthesis of highly functionalized and complex oligomeric and polymeric structures, which offer the prospect of many exciting further developments and applications in the near future. This minireview highlights the fruitful combination of these two topics for the preparation of sequence-controlled oligomeric and macromolecular structures and showcases the vast number of publications in this field within a relatively short span of time. It is divided into three sections according to the click-(inspired) reaction that has been applied: copper-catalyzed azide-alkyne cycloaddition, thiol-X, and related thiolactone-based reactions, and finally Diels-Alder-chemistry-based routes are outlined, respectively.

Design of a thermally controlled sequence of triazolinedione-based click and transclick reactions

The reaction of triazolinediones (TADs) and indoles is of particular interest for polymer chemistry applications, as it is a very fast and irreversible additive-free process at room temperature, but can be turned into a dynamic covalent bond forming process at elevated temperatures, giving a reliable bond exchange or 'transclick' reaction. In this paper, we report an in-depth study aimed at controlling the TAD-indole reversible click reactions through rational design of modified indole reaction partners. This has resulted in the identification of a novel class of easily accessible indole derivatives that give dynamic TAD-adduct formation at significantly lower temperatures. We further demonstrate that these new substrates can be used to design a directed cascade of click reactions of a functionalized TAD moiety from an initial indole reaction partner to a second indole, and finally to an irreversible reaction partner. This controlled sequence of click and transclick reactions of a single TAD reagent between three different substrates has been demonstrated both on small molecule and macromolecular level, and the factors that control the reversibility profiles have been rationalized and guided by mechanistic considerations supported by theoretical calculations.

SuFEx – a selectively triggered chemistry for fast, efficient and equimolar polymer–polymer coupling reactions

The synergy between controlled radical polymerization methods and click chemistry enables the design of complex and well-defined materials.

Preparation of Janus nanoparticles from block copolymer thin films using triazolinedione chemistry

A nanostructured thin film obtained from a polystyrene-block-poly(4-vinylpyridine) diblock copolymer was used as a template to produce Janus-type nanoparticles via triazolinedione-ene click chemistry.

1,3-Dipolar and Diels–Alder cycloaddition reactions on polyester backbones possessing internal electron-deficient alkyne moieties

A polyester containing electron deficient internal alkyne units derived from acetylene dicarboxylic acid in the main backbone was employed as a polymeric platform in copper free cycloaddition reactions.