Radical Homopolymerization of Arylsulfonylated α-Olefins to Synthesize Polysulfones - a "SO2-free" Approach

Traditionally, α-olefins have been regarded as non-homopolymerizable substrates in textbook examples. However, they have the ability to copolymerize with sulfur dioxide, leading to the creation of alternating copolymers. These commodity poly(olefin sulfone)s exhibit a wide array of applications. Nevertheless, the synthesis process involving sulfur dioxide pose considerable hazards and practical difficulties. In this study, we report on the "SO2-free" radical homopolymerization of sulfonyl α-olefin monomers, resulting in the production of ABC sequence-controlled poly(vinylbenzothiazole-olefin-sulfone)s. This unique radical polymerization process is enhanced by 1,4/1,5-aryl migration, facilitated by the sulfonyl radicals involved in propagation. This demonstrated aryl group migration radical polymerization opens up new possibilities for synthesizing polysulfones with unprecedented main chain sequences and structures, which hold great promise as candidates for innovative polymeric materials.

Sequence-Controlled Copolymerization of Structurally Well-Defined Multinuclear Zinc Acrylate Complexes and Styrene

The copolymerization of two or more monomers produces polymeric materials with unique properties that cannot be achieved with homopolymers. However, precise control over the polymer sequence remains challenging because the sequence is determined by the inherent reactivity of comonomers. Therefore, only limited methods using modified monomers or supramolecular interactions are reported. In this study, the sequence control of acrylate-styrene copolymerization using multinuclear zinc complexes is reported. The copolymerization of the zinc acrylate complex with a polymeric sheet-like structure and styrene in benzene affords a copolymer with a higher content of acrylate triad than calculated for the statistical random model, whereas tetranuclear zinc acrylate (TZA) affords a copolymer with fewer adjacent acrylate sequences. The copolymer with a higher content of acrylate triad exhibits a lower glass transition temperature because of the higher mobility of the longer polystyrene segments. These results highlight the promise of multinuclear zinc acrylate complexes as monomers for sequence-controlled copolymerization.

Radical Homopolymerization of Linear α-Olefins Enabled by 1,4-Cyano Group Migration

α-Olefins are valued and abundant building blocks from fossil resources. They are widely used to provide small-molecule or polymeric products. Despite numerous advantages of radical polymerization, it has been well-documented as textbook knowledge that α-olefins and their functionalized derivatives cannot be radically homopolymerized because of the degradative chain transfer side reactions. Herein, we report our studies on the homopolymerization of thiocyanate functionalized α-olefins enabled by 1,4-cyano group migration under radical conditions. By this approach, a library of ABC sequence-controlled polymers with high molecular weights can be prepared. We can also extend this strategy to the homopolymerization of α-substituted styrenic and acylate monomers which are known to be challenging to achieve. Overall, the demonstrated functional group migration radical polymerization could provide new possibilities to synthesize polymers with unprecedented main chain sequences and structures. These polymers are promising candidates for novel polymeric materials.

Bidirectional Iterative Approach to Sequence-Defined Unsaturated Oligoesters

Herein, we describe the development of a new strategy for the synthesis of unsaturated oligoesters via sequential metal- and reagent-free insertion of vinyl sulfoxonium ylides into the O-H bond of carboxylic acid. Like two directional coupling of amino acids (N- to C-terminal and C- to N-terminal) in peptide synthesis, the present approach offers a strategy in both directions to synthesize oligoesters. The sequential addition of the vinyl sulfoxonium ylide to the carboxylic acids (acid iteration sequence) in one direction and the sequential addition of the carboxylic acids to the vinyl sulfoxonium ylide (ylide iteration sequence) in another direction yield (Z)-configured unsaturated oligoesters. To perform this iteration, we have developed a highly regioselective insertion of vinyl sulfoxonium ylide into the X-H (X = O, N, C, S, halogen) bond of acids, thiols, phenols, amines, indoles, and halogen acids under metal-free reaction conditions. The insertion reaction is applied to a broad range of substrates (>50 examples, up to 99% yield) and eight iterative sequences. Mechanistic studies suggest that the rate-limiting step depends on the type of X-H insertion.

Homopolymer-block-Alternating Copolymers Composed of Acrylamide Units: Design of Transformable Divinyl Monomers and Sequence-Specific Thermoresponsive Properties

In this work, we synthesized an acrylamide-based terpolymer that is a block copolymer composed of an AB alternating copolymer and a C homopolymer. The key to the unprecedented achievement is rational design of an acrylate-acrylamide divinyl monomer carrying CF₃-substituted salicylic acid ester bonds (AAm-CF₃) to realize the efficient and selective cyclopolymerization as well as the quantitative transformation of the resultant cyclorepeating units. The selectivity in the cyclopolymerization and the pendant transformation ability were evaluated through reactivity ratios of the corresponding model monomers and quantitative aminolysis reactions of the model compound. The cyclopolymerization via the photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process with a macrochain-transfer agent and subsequent aminolysis reaction afforded the homopolymer-block-alternating copolymer. The sequence-controlled terpolymer exhibited a very unique thermal response behavior in water that was strikingly different from the corresponding sequence-uncontrolled terpolymers, such as homopolymer-block-statistical copolymers and all statistical terpolymers, despite the fact that the structure cannot be distinguished by ¹H NMR.

Sidechain Metallopolymers with Precisely Controlled Structures: Synthesis and Application in Catalysis

Inspired by the cooperative multi-metallic activation in metalloenzyme catalysis, artificial enzymes as multi-metallic catalysts have been developed for improved kinetics and higher selectivity. Previous models about multi-metallic catalysts, such as cross-linked polymer-supported catalysts, failed to precisely control the number and location of their active sites, leading to low activity and selectivity. In recent years, metallopolymers with metals in the sidechain, also named as sidechain metallopolymers (SMPs), have attracted much attention because of their combination of the catalytic, magnetic, and electronic properties of metals with desirable mechanical and processing properties of polymeric backbones. Living and controlled polymerization techniques provide access to SMPs with precisely controlled structures, for example, controlled degree of polymerization (DP) and molecular weight dispersity (Đ), which may have excellent performance as multi-metallic catalysts in a variety of catalytic reactions. This review will cover the recent advances about SMPs, especially on their synthesis and application in catalysis. These tailor-made SMPs with metallic catalytic centers can precisely control the number and location of their active sites, exhibiting high catalytic efficiency.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

2,5-Dimethylfuran/Acrylonitrile as Latent Monomer for Sequence-Controlled Copolymer and Sequence-Dependent Thermo-Responsivity

Sequence control has attracted increasing attention for its ability of regulating polymer property and performance. Herein, the sequence-controlled polymer containing acrylonitrile (AN) is achieved by using 2,5-dimethylfuran/acrylonitrile adduct as a latent monomer. The temperature-dependent retro Diels-Alder reaction is engaged in controlling the release of AN during RAFT polymerization, that is, regulating the instant AN concentration via a non-invasive and in situ manner. Such control over the instant AN concentration and particularly the molar ratio of comonomer pair leads to the simultaneous change of monomer units in "living" polymeric chain, thus resulting in the sequence-controlled polymeric structures. By delicately manipulating the polymerization temperature, diverse sequence-on-demand structures of AN-containing copolymers, such as poly(AN/methyl methacrylate), poly(AN/styrene), poly(AN/butyl acrylate), poly(AN/N,N-dimethylacrylamide), and poly(AN/N-isopropylacrylamide) are created. Meanwhile, this study presents an initial attempt in tuning the thermal responsivity of poly(AN/N-isopropylacrylamide), which is closely correlated to the sequence of polymer structure. More importantly, the polymer with averagely distributed AN units results in the higher thermal sensitivity. Therefore, the synthetic strategy proposed in this work offers a promising platform for accessing the sequence-controlled copolymers containing AN structures, thus expanding the investigation on the relationship between the polymer structures and correlated properties.

Dependence of the liquid crystalline properties on the exactly controlled single-site functionalized density of mesogens focused on the alternating copolymer model

Fluorinated liquid crystal polymers (FLCPs) with an alternating sequence of mesogenic moieties within their backbones were precisely constructed.

Regulation of tectonic sequences in chain-folding-directed monodisperse isomeric oligomers precisely tailored by Ugi-hydrosilylation orthogonal cycles

Monodisperse discrete oligomers with a tailored sequence of linkages within their backbones, which has been defined as a tectonic sequence, were precisely constructed through Ugi-4CRs coupled to hydrosilylation orthogonal cycles.

Unprecedented Sequence Control and Sequence-Driven Properties in a Series of AB-Alternating Copolymers Consisting Solely of Acrylamide Units

Herein, we report a method to synthesize a series of alternating copolymers that consist exclusively of acrylamide units. Crucial to realizing this polymer synthesis is the design of a divinyl monomer that contains acrylate and acrylamide moieties connected by two activated ester bonds. This design, which is based on the reactivity ratio of the embedded vinyl groups, allows a "selective" cyclopolymerization, wherein the intramolecular and intermolecular propagation are repeated alternately under dilute conditions. The addition of an amine to the resulting cyclopolymers afforded two different acryl amide units, i.e., an amine-substituted acryl amide and a 2-hydroxy-ethyl-substituted acryl amide in alternating sequence. Using this method, we could furnish ten types of alternating copolymers; some of these exhibit unique properties in solution and in the bulk, which are different from those of the corresponding random copolymers, and we attributed the differences to the alternating sequence.

Stereoisomeric furan/maleimide adducts as latent monomers for one-shot sequence-controlled polymerization

Two stereoisomeric latent monomers were used for one-shot sequence-controlled polymerization to create diverse sequence structures.

AB-alternating copolymers via chain-growth polymerization: synthesis, characterization, self-assembly, and functions

In this review, four topics on alternating copolymers synthesized via chain-growth polymerization are reviewed: (1) how to control the alternating sequence; (2) sequence analysis; (3) self-assembly; and (4) functions.

Living Cyclocopolymerization through Alternating Insertion of Isocyanide and Allene via Controlling the Reactivity of the Propagation Species: Detailed Mechanistic Investigation

Living cyclocopolymerization through the alternating insertion of an isocyanide and allene into palladium-carbon bond was developed based on the controlling the reactivity of the propagation species using bidentate ligands. We revealed that the rate of the presented cyclocopolymerization was depended on the ligands of Pd-initiator. When the palladium-methyl complexes having appropriate cis-chelating ligand, such as 1,3-bis(diphenylphosphino)propane (dppp), were used as initiator, the cyclocopolymerization of bifunctional aryl isocyanides (1) that contain both isocyano and allenyl moieties polymerized to afford poly(quinolylene-2,3-methylene)s with controlled molecular weight and narrow molecular weight distributions. The resulting polymer was characterized by ¹H and ¹³C NMR analyses, which clearly showed that the terminal moiety of the polymer formed well-defined organopalladium complex as the resting state for the polymerization, which could undergo further polymerization; not only cyclocopolymerization with 1 but also homopolymerization of simple aryl isocyanide. In the analysis of the cyclocopolymerization mechanism, we conclusively demonstrated that the insertion reaction of isocyanide is the rate-determination step in the cyclocopolymerization, which proceeds via a five-coordinate intermediate with a geometrical change. The cis-chelating ligand controls the site interchange reaction, which dominates the reactivity of propagation species.

Synthetic mimics of cyclic antimicrobial peptides via templated ring-opening metathesis (TROM)

We utilized a templated ring-opening metathesis (TROM) strategy to synthesize a series of precision macrocyclic olefins, each containing two, three or four repeating units of a cyclooctene with pendant carboxylic acid side chains.

Synthesis of a well-defined alternating copolymer of 1,1-diphenylethylene and tert-butyldimethylsilyloxymethyl substituted styrene by anionic copolymerization: toward tailored graft copolymers with controlled side chain densities

Well-defined alternating copolymers comprising 1,1-diphenylethylene (DPE) and styrene derivative having sterically bulky tert-butyldimethylsilyloxymethyl group at the meta position (St-TBS) were successfully synthesized.

Controlled polymerizations using metal-organic frameworks

This short review focuses on recent developments in polymerization reactions using metal-organic frameworks (MOFs). MOFs are crystalline porous materials that are able to tune their frameworks, enabling their use as promising media for polymerization. The precise design of the MOF structure is key to controlling polymerizations, allowing for the regulation of not only primary but also higher-order structures.

Cyclopolymerizations: Synthetic Tools for the Precision Synthesis of Macromolecular Architectures

Monomers possessing two functionalities suitable for polymerization are often designed and utilized in syntheses directed to the formation of cross-linked macromolecules. In this review, we give an account of recent developments related to the use of such monomers in cyclopolymerization processes, in order to form linear, soluble macromolecules. These processes can be activated by means of radical, ionic, or transition-metal mediated chain-growth polymerization mechanisms, to achieve cyclic moieties of variable ring size which are embedded within the polymer backbone, driving and tuning peculiar physical properties of the resulting macromolecules. The two functionalities are covalently linked by a "tether", which can be appropriately designed in order to "imprint" elements of chemical information into the polymer backbone during the synthesis and, in some cases, be removed by postpolymerization reactions. The two functionalities can possess identical or even very different reactivities toward the polymerization mechanism involved; in the latter case, consequences and outcomes related to the sequence-controlled, precision synthesis of macromolecules have been demonstrated. Recent advances in new initiating systems and polymerization catalysts enabled the precision syntheses of polymers with regulated cyclic structures by highly regio- and/or stereoselective cyclopolymerization. Cyclopolymerizations involving double cyclization, ring-opening, or isomerization have been also developed, generating unique repeating structures, which can hardly be obtained by conventional polymerization methods.

Sequence-regulated copolymerization based on periodic covalent positioning of monomers along one-dimensional nanochannels

The design of monomer sequences in polymers has been a challenging research subject, especially in making vinyl copolymers by free-radical polymerization. Here, we report a strategy to obtain sequence-regulated vinyl copolymers, utilizing the periodic structure of a porous coordination polymer (PCP) as a template. Mixing of Cu2+ ion and styrene-3,5-dicarboxylic acid (S) produces a PCP, [Cu(styrene-3,5-dicarboxylate)] n , with the styryl groups periodically immobilized along the one-dimensional channels. After the introduction of acrylonitrile (A) into the host PCP, radical copolymerization between A and the immobilized S is performed inside the channel, followed by decomposing the PCP to isolate the resulting copolymer. The predominant repetitive SAAA sequence in the copolymer is confirmed by monomer composition, NMR spectroscopy and theoretical calculations. Copolymerization using methyl vinyl ketone also provides the same type of sequence-regulated copolymer, showing that this methodology has a versatility to control the copolymer sequence via transcription of PCP periodicity at the molecular level.

Synthesis of copolymers with an exact alternating sequence using the cationic polymerization of pre-sequenced monomers

Alternating copolymers of styrene/methyl vinyl ether and styrene/vinyl alcohol were synthesized. The effect of an alternating sequence on the fluorescence emissions of the products was investigated.

Sequence-definition from controlled polymerization: the next generation of materials

An overview is given on the state-of-the-art in synthesis of sequence-controlled and sequence-defined oligomers and polymers.

Synthesis of a sequence-controlled in-chain alkynyl/tertiary amino dual-functionalized terpolymer via living anionic polymerization

A dual-functionalized sequence-defined terpolymer was synthesized via living anionic polymerization; meanwhile its kinetic characteristics and sequence structure were investigated in detail via the in situ¹H NMR method.

Facile synthesis of advanced gradient polymers with sequence control using furan-protected maleimide as a comonomer

Diverse advanced gradient polymers, including simultaneous, hierarchical, di-blocky, symmetrical, and tri-blocky gradient polymers, were facilely fabricated by applying furan protected maleimide as a co-monomer.

Defining the Field of Sequence-Controlled Polymers

Over the last ten years, the development of synthetic polymers containing controlled monomer sequences has become a prominent topic in fundamental and applied polymer science. This emerging area is particularly broad and combines classical polymer chemistry tools with techniques imported from other domains such as biology, biochemistry, organic synthesis, engineering, and bioanalytics. Consequently, it also generates new structures, terminologies, and applications that are not within the traditional scope of polymer science. The term "sequence-controlled polymers" (SCPs) was recently proposed as a generic name to describe all these recent trends. However, since the field of SCPs has been growing very rapidly in recent literature, it is urgent to accurately define its scientific frontiers. In this important context, this review is an attempt to define, rationalize, and classify the field of SCPs. In particular, all synthetic approaches that have been reported for the synthesis of SCPs are discussed and categorized. In addition, the characterization tools, properties, and potential applications of these new polymers are described herein. Overall, this review serves as a reference guide for understanding the burgeoning field of SCPs.

Cyclopolymerization of Cleavable Acrylate-Vinyl Ether Divinyl Monomer via Nitroxide-Mediated Radical Polymerization: Copolymer beyond Reactivity Ratio

Cyclopolymerization of a divinyl monomer, where two different vinyl groups, that is, acrylate and vinyl ether, are connected via an ester bond, was performed under diluted condition with nitroxide-meditated radical polymerization (NMP). Both vinyl groups were consumed at almost same rate under suitable condition, although the inherent cross-propagation ability between the two vinyl groups are pretty low in radical copolymerization. Furthermore, the polymerization was controlled to some extent to give polymers of unimodal molecular weight distributions. The results obviously differed from copolymerization and homopolymerization with vinyl monomers that constitutes the divinyl monomer, 2-methoxyethyl acrylate and 2-acetoxyethyl vinyl ether. Structural analyses indicated formation of the cyclopolymer but the cyclo-efficiency was imperfect indicating that some units of olefinic dangling were incorporated. Eventually, the ester bonds of the cyclo units were cleaved to convert into the copolymer consisting of acrylic acid and 2-hydroxy ethyl vinyl ether and the composition ratio (DP_acryl/DP_VE) was 55:45. The copolymer showed higher glass transition temperature than that estimated from the composition ratio and T_g values of the homopolymers, which is likely due to the formation of quasi-cyclopolymer between carboxylic acid and hydroxy groups aligned in alternating fashion.

Synthesis and Functionalization of Periodic Copolymers

For the copolymerization of non-conjugated olefins and maleimides, it is known that under certain conditions periodic ABA monomer sequences are formed. In this work, such a copolymerization is used to create polymers which have defined (periodic) monomer sequences and can be functionalized after polymerization. The copolymerization of pentafluorophenol (PFP) active esters of 4-pentenoic acid and perillic acid with N-phenyl maleimide (PhMI) was studied in 1,2-dichloroethane (DCE) and 1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol (HFPP). In DCE and for the copolymerization of the PFP ester of 4-pentenoic acid and PhMI in HFPP, polymers were formed where the active esters were separated by at least one PhMI unit. The average number of separating PhMI units can be controlled by varying the feed ratio of the monomers. For the copolymerization of the PFP ester of perillic acid in HFPP, a preference for the formation of periodic copolymers was observed, where active esters were preferably separated from each other by a maximum of two PhMI moieties. Therefore, the copolymerization of said active ester containing monomers with PhMI provides a platform to create polymers in which reactive moieties are distributed along the polymer chain in different fashions. The active esters in the non-conjugated vinyl monomers could be used in a post-polymerization functionalization step to create functionalized polymers with defined monomer sequences in a modular way.

Sequence-coded ATRP macroinitiators

Sequence-defined oligourethanes were transformed into ATRP initiators and used for the synthesis of precision macromolecular architectures.