Discrete macromolecular constructs via the Diels–Alder “Click” reaction

Photoinduced Electron Transfer Reactions for Macromolecular Syntheses

Photochemical reactions, particularly those involving photoinduced electron transfer processes, establish a substantial contribution to the modern synthetic chemistry, and the polymer community has been increasingly interested in exploiting and developing novel photochemical strategies. These reactions are efficiently utilized in almost every aspect of macromolecular architecture synthesis, involving initiation, control of the reaction kinetics and molecular structures, functionalization, and decoration, etc. Merging with polymerization techniques, photochemistry has opened up new intriguing and powerful avenues for macromolecular synthesis. Construction of various polymers with incredibly complex structures and specific control over the chain topology, as well as providing the opportunity to manipulate the reaction course through spatiotemporal control, are one of the unique abilities of such photochemical reactions. This review paper provides a comprehensive account of the fundamentals and applications of photoinduced electron transfer reactions in polymer synthesis. Besides traditional photopolymerization methods, namely free radical and cationic polymerizations, step-growth polymerizations involving electron transfer processes are included. In addition, controlled radical polymerization and "Click Chemistry" methods have significantly evolved over the last few decades allowing access to narrow molecular weight distributions, efficient regulation of the molecular weight and the monomer sequence and incredibly complex architectures, and polymer modifications and surface patterning are covered. Potential applications including synthesis of block and graft copolymers, polymer-metal nanocomposites, various hybrid materials and bioconjugates, and sequence defined polymers through photoinduced electron transfer reactions are also investigated in detail.

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.

Best of both worlds: Diels–Alder chemistry towards fabrication of redox-responsive degradable hydrogels for protein release

Poly(ethylene glycol)-based redox-responsive hydrogels have been preparedviathe Diels–Alder reaction between a furan-containing hydrophilic copolymer and a disulfide-containing bis-maleimide based crosslinker.

Maleimide-functionalized poly(2-ethyl-2-oxazoline): synthesis and reactivity

Poly(2-ethyl-2-oxazoline)s end-functionalized with a maleimide moiety were prepared from azide-terminated PEtOx_x-N₃viacopper-catalyzed azide–alkyne cycloaddition (CuAAC) with an alkyne-bearing maleimide (MI).

Doubly-dynamic-covalent polymers composed of oxime and oxanorbornene links

Two sets of reversible covalent linkages distributed in series along a polymer backbone were used to prepare a new class of doubly dynamic-covalent polymers capable of reversibly dissociatingviatwo distinct pathways.

Fabrication of Thiol-Ene "Clickable" Copolymer-Brush Nanostructures on Polymeric Substrates via Extreme Ultraviolet Interference Lithography

We demonstrate a new approach to grafting thiol-reactive nanopatterned copolymer-brush structures on polymeric substrates by means of extreme ultraviolet (EUV) interference lithography. The copolymer brushes were designed to contain maleimide functional groups as thiol-reactive centers. Fluoropolymer films were exposed to EUV radiation at the X-ray interference lithography beamline (XIL-II) at the Swiss Light Source, in order to create radical patterns on their surfaces. The radicals served as initiators for the copolymerization of thiol-ene "clickable" brushes, composed of a furan-protected maleimide monomer (FuMaMA) and different methacrylates, namely, methyl methacrylate (MMA), ethylene glycol methyl ether methacrylate (EGMA), or poly(ethylene glycol) methyl ether methacrylate (PEGMA). Copolymerization with ethylene-glycol-containing monomers provides antibiofouling properties to these surfaces. The number of reactive centers on the grafted brush structures can be tailored by varying the monomer ratios in the feed. Grafted copolymers were characterized by using attenuated total reflection infrared (ATR-IR) spectroscopy. The reactive maleimide methacrylate (MaMA) units were utilized to conjugate thiol-containing moieties using the nucleophilic Michael-addition reaction, which proceeds at room temperature without the need for any metal-based catalyst. Using this approach, a variety of functionalities was introduced to yield polyelectrolytes, as well as fluorescent and light-responsive polymer-brush structures. Functionalization of the brush structures was demonstrated via ATR-IR and UV-vis spectroscopy and fluorescence microscopy, and was also indicated by a color switch. Furthermore, grafted surfaces were generated via plasma activation, showing a strongly increased wettability for polyelectrolytes and a reversible switch in static water contact angle (CA) of up to 18° for P(EGMA-co-MaMA-SP) brushes, upon exposure to alternating visible and UV-light irradiation.

Hydrosilylation as an efficient tool for polymer synthesis and modification with methacrylates

Hydrosilylation is a well-established reaction for the preparation of organo-silicon compounds, in which vinyl groups react with silanes (Si–H) usually catalysed by late transition metal complexes, most often Pt(ii) complexes.

Well-defined polymethylene-based block co/terpolymers by combining anthracene/maleimide diels–alder reaction with polyhomologation

Well-defined co/terpolymers of polymethylene (PM) with poly(d,l-lactide) (PLA), polycaprolactone (PCL) and polyethylene glycol (PEG) were synthesized by combining polyhomologation, anionic ring opening polymerization and anthracene(Ant)/maleimide(MI) Diels–Alder reaction.

Homopolymer bifunctionalization through sequential thiol–epoxy and esterification reactions: an optimization, quantification, and structural elucidation study

In this study, we probe various aspects of a post-polymerization double-modification strategy involving sequential thiol–epoxy and esterification reactions for the preparation of dual-functional homopolymers.

Ready access to end-functional polystyrenes via a combination of ARGET ATRP and thiol–ene chemistry

Bromine end-groups of ATRP polystyrenes were converted into terminal alkene groupsviaa facile synthetic strategy. Subsequently, a light-induced radical thiol–ene reaction was employed for the functionalization of the terminal double bonds.

Model Diels-Alder Studies for the Creation of Amphiphilic Cross-Linked Networks as Healable, Antibiofouling Coatings

Diels-Alder (DA) chemistry was used in the construction of amphiphilic cross-linked polymer networks comprised of furan-functionalized hyperbranched fluoropolymers and maleimide-functionalized linear poly(ethylene glycol)s, which were designed as antibiofouling coatings capable of repair. Discrete molecules and a linear polymer analog were studied as model systems to understand the nature of the thermally reversible [4 + 2] cycloaddition reaction involving a tetrafluorobenzylfuranyl ether unit, which was part of the structure for the incorporation of the DA functionalities into the composite network materials. Atomic force microscopy confirmed the complex, nanoscopically resolved topography needed for antibiofouling. Bright field and fluorescence imaging monitored healing at damage sites as well as the ability of the coatings to resist protein adsorption.