Synthesis and characterization of graft copolymers by photoinduced CuAAC click chemistry

Revisiting poly(vinyl chloride) reactivity in the context of chemical recycling

Poly(vinyl chloride) (PVC) is one of the highest production volume polymers due to its many applications, and it is one of the least recycled due to its chemical structure and frequent formulation with additives. Developing efficient PVC recycling techniques would enable PVC waste to be reused or repurposed in other processes. Within this context, the literature on PVC modification offers considerable insight into versatile reaction pathways, potentially inspiring new approaches for repurposing PVC waste into value-added products. This perspective provides an overview of PVC functionalization through a lens of chemical recycling, discussing various PVC reactivity trends and their applications with a critical assessment and future outlook of their recycling implications.

Electrochemical Characterization of Redox Probes Confined in 3D Conducting Polymer Networks

In this manuscript we present a versatile platform for introducing functional redox species into tailor‐made 3D redox polymer networks. Electrochemical characterization based on cyclic voltammetry is applied to verify the immobilization of the redox species within the conducting networks. Ultimately this strategy shall be extended to (photo)electrocatalytic applications which will profit from the conducting polymer matrix. Soluble precursor copolymers are synthesized via radical copolymerization of vinyltriphenylamine (VTPA) with chloromethylstyrene (CMS) in different ratios, whereas CMS is subsequently converted into azidomethylstyrene (AMS) to yield poly(VTPA‐co‐AMS) copolymers. Spin‐coating of poly(VTPA‐co‐AMS) on gold electrodes yields thin films which are converted into stable polymer network structures by electrochemical crosslinking of the polymer chains via their pendant triphenylamine groups to yield N,N,N′,N′‐tetraphenylbenzidine (TPB) crosslinking points. Finally, the resulting redox‐active, TPB‐crosslinked films are functionalized with ethynylferrocene (EFc) as a representative redox probe using a click reaction. Main experimental tools are polarization modulation infrared reflection absorption spectroscopy and scan rate dependent cyclic voltammetry. Especially the latter proves the successful conversion and the immobilization of redox probes in the polymer matrix. The results are compared with the reference system of azide‐terminated self‐assembled monolayers on gold substrates, allowing to distinguish between free and immobilized EFc species.

Light-Triggered Click Chemistry

The merging of click chemistry with discrete photochemical processes has led to the creation of a new class of click reactions, collectively known as photoclick chemistry. These light-triggered click reactions allow the synthesis of diverse organic structures in a rapid and precise manner under mild conditions. Because light offers unparalleled spatiotemporal control over the generation of the reactive intermediates, photoclick chemistry has become an indispensable tool for a wide range of spatially addressable applications including surface functionalization, polymer conjugation and cross-linking, and biomolecular labeling in the native cellular environment. Over the past decade, a growing number of photoclick reactions have been developed, especially those based on the 1,3-dipolar cycloadditions and Diels-Alder reactions owing to their excellent reaction kinetics, selectivity, and biocompatibility. This review summarizes the recent advances in the development of photoclick reactions and their applications in chemical biology and materials science. A particular emphasis is placed on the historical contexts and mechanistic insights into each of the selected reactions. The in-depth discussion presented here should stimulate further development of the field, including the design of new photoactivation modalities, the continuous expansion of λ-orthogonal tandem photoclick chemistry, and the innovative use of these unique tools in bioconjugation and nanomaterial synthesis.

Advances in Internal Plasticization of PVC: Copper-Mediated Atom-Transfer Radical Polymerization from PVC Defect Sites To Form Acrylate Graft Copolymers

Internally plasticized PVC copolymers were prepared by grafting PVC with butyl acrylate and 2-(2-ethoxyethoxy)ethyl acrylate by atom-transfer radical polymerization, resulting in well-behaved polymers with a wide range of glass transition temperatures (–54 °C to 54 °C). When the grafted side chains made up more than 50% of the polymer by weight, the glass transition temperatures were below 0 °C. The covalent attachment of the plasticizing grafts requires one simple procedure starting from commercial PVC, making this strategy an industrially relevant and environmentally friendly alternative to the use of conventional small-molecule plasticizers.

A Survey of Strain-Promoted Azide-Alkyne Cycloaddition in Polymer Chemistry

Highly efficient reactions that enable the assembly of molecules into complex structures have driven extensive progress in synthetic chemistry. In particular, reactions that occur under mild conditions and in benign solvents, while producing no by-products and rapidly reach completion are attracting significant attention. Amongst these, the strain-promoted azide-alkyne cycloaddition, involving various cyclooctyne derivatives reacting with azide-bearing molecules, has gained extensive popularity in organic synthesis and bioorthogonal chemistry. This reaction has also recently gained momentum in polymer chemistry, where it has been used to decorate, link, crosslink, and even prepare polymer chains. This survey highlights key achievements in the use of this reaction to produce a variety of polymeric constructs for disparate applications.

The emerging applications of click chemistry reactions in the modification of industrial polymers

Click chemistry reactions have been applied to the modification of major industrial polymers by analysing the synthetic approaches and the resulting material properties.

A new synthetic pathway based on one-pot sequential aza-Michael addition and photoCuAAC click reactions

A solvent-free process is described for the synthesis of tailor-made molecules from a one-pot, two-step approach combining aza-Michael addition and photoinduced copper(i) catalysed azide–alkyne (photo-CuAAC) reactions. After the first reaction between an amine and an acrylate, cycloaddition between an azide and an alkyne is activated by light irradiation in the presence of a copper complex. The kinetics of the aza-Michael addition and photo-CuAAC reaction were investigated by liquid state ¹H NMR spectroscopy and real-time Fourier transform infrared spectroscopy. This new process represents a well-defined spatio-temporal pathway to the synthesis of bespoke intermediate molecules for various applications.

A solvent-free process is described for the synthesis of tailor-made molecules from a one-pot, two-step approach combining aza-Michael addition and photoinduced copper(i) catalysed azide–alkyne (photo-CuAAC) reactions.

Copper Ligand and Anion Effects: Controlling the Kinetics of the Photoinitiated Copper(I) Catalyzed Azide-Alkyne Cycloaddition Polymerization

The kinetics of photoinduced copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) polymerizations were assessed as a function of copper(II) amine-based ligands. Copper(II) bromide ligated with 1,1,4,7,10,10-hexamethylenetetramine (HMTETA) exhibited the fastest kinetics in both Norrish type(I) and type(II) photoinitiating systems. A characteristic induction period is observed with these polymerizations and is manipulated by adding an external tertiary amine in Norrish Type(II) photoinitating systems or by changing the anion of the copper(II) salt. Halides, specifically bromide and chloride, exhibit the fastest kinetics with the smallest induction period in comparison with organic anions, such as bistriflimide and triflate. The temporal control of the photo-CuAAC polymerization is affected by pre-ligation of the copper catalyst, by the presence of certain anions such as acetate, and by specific ligands such as tetramethylethylenediamine (TMEDA).

Photocatalysis in organic and polymer synthesis

This review, with over 600 references, summarizes the recent applications of photoredox catalysis for organic transformation and polymer synthesis. Photoredox catalysts are metallo- or organo-compounds capable of absorbing visible light, resulting in an excited state species. This excited state species can donate or accept an electron from other substrates to mediate redox reactions at ambient temperature with high atom efficiency. These catalysts have been successfully implemented for the discovery of novel organic reactions and synthesis of added-value chemicals with an excellent control of selectivity and stereo-regularity. More recently, such catalysts have been implemented by polymer chemists to post-modify polymers in high yields, as well as to effectively catalyze reversible deactivation radical polymerizations and living polymerizations. These catalysts create new approaches for advanced organic transformation and polymer synthesis. The objective of this review is to give an overview of this emerging field to organic and polymer chemists as well as materials scientists.

Nonmigrating Equivalent Substitutes for PVC/DOP Formulations as Shown by a TG Study of PVC with Covalently Bound PEO-PPO Oligomers

Monoamino functionalized ethylenoxide (EO)/propylenoxide oligomers (Jeffamine) are linked chemically to poly(vinyl chloride) (PVC) using trichlorotriazine chemistry in order to prepare nonmigrating internally plasticized materials. The dependence of the plasticizer efficiency on both the number of anchoring points to the chains and the PVC/plasticizer compatibility is investigated using oligomers of different molecular weight and hydrophilic-hydrophobic balance. Hydrophilic oligomers (containing predominantly EO) of molecular weights between 2000 and 5000 g mol^-1 exhibit excellent plasticizer efficiency, nearly identical to di-2-ethylhexylphthalate (DOP) in conventional PVC/DOP mixtures and may therefore be used as nonmigrating equivalents for DOP.

Synthesis of self-curable polysulfone containing pendant benzoxazine units via CuAAC click chemistry

Synthesis, characterization, and properties of new thermally curable polysulfone containing benzoxazine moieties in the side chain were investigated. First, chloromethylation and subsequent azidation processes were performed to form polysulfone containing pendant clickable azide groups. Independently, antagonist 3,4-dihydro-3-(prop-2-ynyl)-2H-benzoxazine was prepared by using paraformaldehyde, phenol and propargylamine. The following copper(I) catalyzed azide-alkyne cycloaddition click reaction was applied to obtain self-curable polysulfone with pendant benzoxazine units. The polymer and intermediates at various stages were characterized by ¹H-NMR, ¹³C-NMR and FT-IR spectroscopies. The thermal properties and curing behavior of final polymer were investigated by differential scanning calorimetry and thermal gravimetric analysis. Compared to the neat polysulfone, the obtained polymers exhibited thermally more stable polymers.

Reversible Regulation of Thermoresponsive Property of Dithiomaleimide-Containing Copolymers via Sequential Thiol Exchange Reactions

The facile and efficient functionalization of thermoresponsive polymers based on sequential, reversible thiol-exchange reactions is reported. Well-defined dithiomaleimide-containing polymers have been synthesized via Cu(0)-mediated SET-LRP and characterized by ¹H NMR and size exclusion chromatography (SEC). The resulting thermosensitive copolymers were subsequently reacted with various thiols to demonstrate the applicability of the strategy, and the thiol-exchange reaction was found to be very fast and efficient. The cloud point of the prepared copolymers can be continually and reversibly tuned, and desirable functionality can be dynamically exchanged upon sequential addition of functional thiol reagents. Through the substitution by thioglucose, an ON-to-OFF switch for fluorescence of the copolymers along with the generation of a glycopolymer was achieved.

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.

Cross-linking and postfunctionalization of polymer films by utilizing the orthogonal reactivity of 7,7,8,8-tetracyanoquinodimethane

Spontaneous radical copolymerization of poly(7,7,8,8-tetracyanoquinodimethane) and α-chloromethylstyrene followed by click postfunctionalization produces colored and redox-active cross-linked polymer films.

Effective ascorbate-free and photolatent click reactions in water using a photoreducible copper(II)-ethylenediamine precatalyst

The search for copper catalysts able to perform effectively click reactions in water in the absence of sodium ascorbate is an active area of current research with strong potential for applications in bioconjugation. The water-soluble and photoreducible copper(II)-EDA (EDA = ethylenediamine) complex 1, which has two 4-benzoylbenzoates acting as both counterion and photosensitizer, has been synthesized and characterized by different techniques including single crystal X-ray diffraction. Highly efficient photoreduction was demonstrated when solutions of 1 in hydrogen atom donating solvents, such as THF or MeOH, were exposed to UVA radiation (350-400 nm) provided by a low pressure mercury lamp (type TLC = thin-layer chromatography, 365 nm), or by a 23 W fluorescent bulb, or by ambient/sunlight. In water, a much poorer hydrogen atom donating solvent, the photoreduction of 1 proved inefficient. Interestingly, EPR studies revealed that complex 1 could nonetheless be effectively photoreduced in water when alkynes were present in solution. The catalytic activity of 1 for click reactions involving a range of water-soluble alkynes and azides, in particular saccharides, was tested under various illumination conditions. Complex 1 was found to exhibit a photolatent character, the photogenerated copper(I) being very reactive. On irradiating aqueous reaction mixtures containing 1 mol % of 1 at 365 nm (TLC lamp) for 1 h, click reactions were shown to proceed to full conversion.

Dibenzoyldiethylgermane as a visible light photo-reducing agent for CuAAC click reactions

A highly active, versatile and visible light-responsive system for CuAAC click reaction using the dibenzoyldiethylgermane photoinitiator with Cu(ii) has been developed.

The Suzuki coupling reaction as a post-polymerization modification: a promising protocol for construction of cyclic-brush and more complex polymers

The Suzuki coupling reaction was utilized as a highly efficient post-polymerization modification for modular construction of cyclic-brush polymers and other more complex polymers.