Sequential Monomer Research Articles

Photo‐Mediated RAFT Step‐Growth Polymerization With Diacrylate Monomers: Investigating Versatility and Oxygen Tolerance

AbstractPhotomediated reversible addition fragmentation chain transfer (RAFT) step‐growth polymerization is performed using a trithiocarbonate‐based chain transfer agent (CTA) and acrylate‐based monomers both with and without a photocatalyst. The versatility of photo‐mediated RAFT step‐growth is demonstrated by one‐pot synthesis of a graft copolymer via sequential monomer addition. Furthermore, oxygen‐tolerant photo‐mediated RAFT step‐growth is demonstrated, facilitated by the appropriate selection of photocatalyst and solvent pair (zinc tetraphenyl porphyrin [ZnTPP] and dimethyl sulfoxide [DMSO]), enabling ultralow volume polymerization under open‐air conditions.

Transcription factors ERα and Sox2 have differing multiphasic DNA- and RNA-binding mechanisms.

Many transcription factors (TFs) have been shown to bind RNA, leading to open questions regarding the mechanism(s) of this RNA binding and its role in regulating TF activities. Here, we use biophysical assays to interrogate the k on, k off, and K d for DNA and RNA binding of two model human TFs, ERα and Sox2. Unexpectedly, we found that both proteins exhibit multiphasic nucleic acid-binding kinetics. We propose that Sox2 RNA and DNA multiphasic binding kinetics can be explained by a conventional model for sequential Sox2 monomer association and dissociation. In contrast, ERα nucleic acid binding exhibited biphasic dissociation paired with novel triphasic association behavior, in which two apparent binding transitions are separated by a 10-20 min "lag" phase depending on protein concentration. We considered several conventional models for the observed kinetic behavior, none of which adequately explained all the ERα nucleic acid-binding data. Instead, simulations with a model incorporating sequential ERα monomer association, ERα nucleic acid complex isomerization, and product "feedback" on isomerization rate recapitulated the general kinetic trends for both ERα DNA and RNA binding. Collectively, our findings reveal that Sox2 and ERα bind RNA and DNA with previously unappreciated multiphasic binding kinetics, and that their reaction mechanisms differ with ERα binding nucleic acids via a novel reaction mechanism.

Synthesis and Characterization of All-Acrylic Tetrablock Copolymer Nanoparticles: Waterborne Thermoplastic Elastomers via One-Pot RAFT Aqueous Emulsion Polymerization.

Reversible addition-fragmentation chain transfer (RAFT) aqueous emulsion polymerization is used to prepare well-defined ABCB tetrablock copolymer nanoparticles via sequential monomer addition at 30 °C. The A block comprises water-soluble poly(2-(N-acryloyloxy)ethyl pyrrolidone) (PNAEP), while the B and C blocks comprise poly(t-butyl acrylate) (PtBA) and poly(n-butyl acrylate) (PnBA), respectively. High conversions are achieved at each stage, and the final sterically stabilized spherical nanoparticles can be obtained at 20% w/w solids at pH 3 and at up to 40% w/w solids at pH 7. A relatively long PnBA block is targeted to ensure that the final tetrablock copolymer nanoparticles form highly transparent films on drying such aqueous dispersions at ambient temperature. The kinetics of polymerization and particle growth are studied using 1H nuclear magnetic resonance spectroscopy, dynamic light scattering, and transmission electron microscopy, while gel permeation chromatography analysis confirmed a high blocking efficiency for each stage of the polymerization. Differential scanning calorimetry and small-angle X-ray scattering studies confirm microphase separation between the hard PtBA and soft PnBA blocks, and preliminary mechanical property measurements indicate that such tetrablock copolymer films exhibit promising thermoplastic elastomeric behavior. Finally, it is emphasized that targeting an overall degree of polymerization of more than 1000 for such tetrablock copolymers mitigates the cost, color, and malodor conferred by the RAFT agent.

Controlled “one-pot” block copolymerization of β-butyrolactone and oxiranes via quantitative active centers transformation

The synthesis of block copolymers of oxiranes and β-butyrolactone based on a method of sequential monomer addition was developed. The anionic controlled polymerization of protected glycidol - ethoxyethyl glycidyl ether (EEGE) and β-butyrolactone (BBL) was used. By quantitatively transforming the hydroxyl groups at the ends of the polyoxirane chains to the carboxylate centers, a one-pot synthesis was possible without further purification of the intermediates. The main part of the study was directed toward verifying the degree of precision of the transformation step and copolymer synthesis and clarifying the role of hydroxyl groups potentially present during the polymerization of BBL. It was also found that the presence of a small excess of anhydride during the transformation reaction did not affect the subsequent synthesis steps. The use of a macroinitiator in the form of poly(ethylene glycol) allowed us to obtain well-defined block copolymers of oxiranes and BBL of di-, tri- and pentablock structures.

Synthesis of poly(2-isopropyl-2-oxazoline)-b-poly(2-phenyl-2-oxazoline)-b-poly(2-isopropyl-2-oxazoline) and its self-assembly into polymersomes: Temperature-dependent aqueous solution behavior

This study reports on synthesis of poly(2-isopropyl-2-oxazoline)-b-poly(2-phenyl-2-oxazoline)-b-poly(2-isopropyl-2-oxazoline) (PiPOX-b-PPhOX-b-PiPOX) by a three-step sequential monomer addition through cationic ring opening polymerization (CROP). Self-assembly of PiPOX-b-PPhOX-b-PiPOX was triggered through solvent shifting or double emulsion methods, resulting in formation of polymersomes with hydrophilic and temperature-responsive PiPOX inner/outer coronae and hydrophobic PPhOX membrane. Double emulsion method provided smaller polymersomes with greater colloidal stability. Increasing the temperature of the polymersome solution led to formation of polymersome clusters and this transition was found to be irreversible. Glucose oxidase (GOx) encapsulated polymersomes were used as nanoreactors for GOx/horseradish peroxidase (HRP) cascade reactions. The increase in the rate of the enzymatic reaction with increasing temperature was found to be smaller for the encapsulated enzymes compared to free enzymes.

Studies on polyoxymethylene dimethyl ethers production from dimethoxymethane and 1,3,5-trioxane over [formula omitted

Polyoxymethylene dimethyl ethers (OMEs) with physical properties similar to those of diesel has received significant attention as green additives for soot emission suppression. Herein, series of SO42-/ZrO2–TiO2 catalysts were developed for OMEs production from dimethoxymethane (DMM) and 1,3,5-trioxane through sequential formaldehyde monomer insertion into CO bond of DMM. Not Lewis but Brønsted acid sites were identified to be active for the decomposition of 1,3,5-trioxane into formaldehyde unit, however, both of them are effective for the chain propagation of DMM via formaldehyde unit insertion into CO bond. Kinetic studies indicated each chain growth step exhibited the same parameters and activation barrier on corresponding Brønsted and Lewis acid sites due to the same reaction mechanism and very similar chemical structure of OMEs. Also, the catalytic stability investigation suggested the deactivation behavior was derived from the carbon deposition, and the decay factor could be exponentially correlated with the amount of coke accumulation.

Innenrücktitelbild: Swelling‐induced Mechanochromism in Multinetwork Polymers (Angew. Chem. 9/2023)

The swelling force exerted by solvents in polymer gels is revealed to trigger mechanochemical reactions, as reported by Takuma Watabe and Hideyuki Otsuka in their Research Article (e202216469). A multinetwork strategy based on sequential monomer swelling and polymerization processes makes the original network sensitive to mechanical stimuli. A slight volume expansion caused by swelling leads to the activation of mechano-responsive linkers in the first network, exhibiting a notable color change.

Multistep sequence-controlled supramolecular polymerization by the combination of multiple self-assembly motifs

The precise sequence control of polymer chain is an important research topic of polymer chemistry. Although some methods such as iterative synthesis and supramolecular polymerization have been developed to fabricate sequence-controllable polymer, it is still a great challenge to consecutively prepare multiple supramolecular polymers with different sequence structures. In this work, through the reasonable utilization of assembly motifs, we integrated multiple host-guest recognitions and metal coordination interactions to prepare different sequence-controlled supramolecular polymers by a multistep assembly strategy. This research provides inspiration for the design and preparation of supramolecular polymers with different sequence structures.

Synthesis and Ring-Opening Metathesis Polymerization of o-Dialkoxy Paracyclophanedienes.

The highly strained ortho-diethylhexyloxy [2.2]paracyclophane-1,9-diene (M1) can be synthesized by ring contraction of a dithia[3.3]paracyclophane using a benzyne-induced Stevens rearrangement. This paracyclophanediene undergoes ring-opening metathesis polymerization to give well-defined 2,3-dialkoxyphenylenevinylene polymers with an alternating cis/trans alkene stereochemistry and controllable molecular weight. Fully conjugated block copolymers with electron-rich and electron-deficient phenylene vinylene polymer segments can be prepared by sequential monomer additions. These polymers can be readily isomerized to the all-trans stereochemistry polymer. The optical and electrochemical properties of these polymers were investigated by theory and experiment.

Degradable terpolyesters synthesized from a monomer mixture mediated by a heterometallic complex: Defined monomer- and stereo-sequences

Copolymers provide a feasible platform to extend the structures of polymeric material, and the control of architecture (such as monomer sequence and stereo sequence) plays a critical role in tailoring specific properties. Herein, a heterometallic (Salph Zn)2-Ho complex was screened out for the synthesis of architecture-defined block terpolymers from a monomer mixture of epoxide, cyclic anhydride and l-lactide (LLA). The polymerization in one-pot firstly underwent ring-opening copolymerization reaction producing completely alternating ester linkage, and then transformed to LLA polymerization with trace stereoerrors, forming block polyesters with a semicrystalline segment and an amorphous segment. The polymerization was “immortal” with the ability to synthesize sequence-defined multiblock polyesters by sequential monomer addition. Furthermore, DSC traces revealed that the obtained block polyesters exhibited distinct thermal properties stemming from each segment. The melting temperature of block terpolymer was increased to 207.6 °C facilitated by the stereocomplexes of PLA segment.

Phase Diagram of Tapered Copolymers Based on Isoprene and Styrene

AbstractAlthough several phase diagrams of block copolymers prepared by sequential monomer addition are known today, the phase diagrams of the corresponding tapered copolymers have not been reported in detail and this despite the industrial importance of the latter. A phase diagram based on a series of tapered diblock copolymers is reported, generated by the sec‐butyllithium initiated statistical anionic copolymerization of styrene and isoprene in cyclohexane. This affords copolymers with polyisoprene volume fractions, f, in the range of 0.43 < f < 0.82 and total molar mass in the range of 46–160 kg mol–1. The phase diagram consists of lamellae, hexagonally packed cylinders, weakly ordered hexagonally packed cylinders (CYL), and perforated (PL) as well as irregular bicontinuous morphologies. The phase state in the tapered copolymers bears some similarities and several distinct differences in comparison to the respective copolymers prepared by conventional sequential monomer addition. It is shown that the weakly ordered CYL/PL morphologies comprise a large part of the phase diagram that is significantly extended in comparison to diblock copolymers prepared sequentially. On the other hand, the composition range for the bicontinuous morphologies is similar in the two systems (0.64 < fPI < 0.68).

Toughening Poly(l-lactide) Blends: Effectiveness of Sequence-Controlled Six-Arm Star-Branched Block Copolymers of Poly(l-lactide) and Poly(ε-caprolactone).

Well-defined six-arm star-branched bio-degradable block copolymers of l-lactide and ε-caprolactone were prepared using controlled ring-opening polymerization and a sequential monomer addition method using dipentaerythritol as the initiator core and organocatalysts at low temperatures in solution. Sequence of enchainment was changed by reversing the order of monomer addition giving, either, a crystalline PLA block or an amorphous PCL block as the outer segment. Well-defined six-arm poly(ε-caprolactone-b-l-lactide, 6s-PCL-b-PLA) block copolymers were obtained with a range of segment molecular weights. However, in the case of six-arm poly(l-lactide-b-ε-caprolactone, 6s-PLA-b-PCL), disruption of the block structure was observed on account of competing transesterification reactions accompanying a chain-growth reaction. Such sequence-controlled block copolymers showed interesting phase morphologies, as evidenced by differential scanning calorimetry (DSC) studies. 6s-PCL-b-PLA showed two glass-transition temperatures and two melting temperatures characteristic of the amorphous and crystalline blocks. 6s-PCL-b-PLA and 6s-PLA-b-PCL with different segment chain lengths were solution blended (10 wt %) with a commercially sourced PLA. All the blends were highly transparent. The structure and properties of the blend were examined by DSC, measurement of mechanical properties, and scanning electron microscopy. The results show that a phase-separated 6s-PCL-b-PLA copolymer results in two- to three-fold improvement in tensile toughness without the loss of modulus. A possible hypothesis for the mechanism of tensile toughness in the blend has been proposed.

ABC-Type Triblock Copolyacrylamides via Copper-Mediated Reversible Deactivation Radical Polymerization.

The aqueous Cu(0)-mediated reversible deactivation radical polymerization (RDRP) of triblock copolymers with two block sequences at 0.0 °C is reported herein. Well-defined triblock copolymers initiated from PHEAA or PDMA, containing (A) 2-hydroxyethyl acrylamide (HEAA), (B) N-isopropylacrylamide (NIPAM) and (C) N, N-dimethylacrylamide (DMA), were synthesized. The ultrafast one-pot synthesis of sequence-controlled triblock copolymers via iterative sequential monomer addition after full conversion, without any purification steps throughout the monomer additions, was performed. The narrow dispersities of the triblock copolymers proved the high degree of end-group fidelity of the starting macroinitiator and the absence of any significant undesirable side reactions. Controlled chain length and extremely narrow molecular weight distributions (dispersity ~1.10) were achieved, and quantitative conversion was attained in as little as 52 min. The full disproportionation of CuBr in the presence of Me6TREN in water prior to both monomer and initiator addition was crucially exploited to produce a well-defined ABC-type triblock copolymer. In addition, the undesirable side reaction that could influence the living nature of the system was investigated. The ability to incorporate several functional monomers without affecting the living nature of the polymerization proves the versatility of this approach.

Methacrylate and Styrene Block Copolymer Synthesis by Cu‐Mediated Chain Extension of Acrylate Macroinitiator in a Semibatch Reactor

AbstractA process for the well‐controlled growth of acrylates by Cu‐mediated polymerization has been developed, with macroinitiator synthesized continuously in a copper tubular reactor and subsequently chain‐extended in a semibatch reactor without additional copper. Extending this process to methacrylates and styrene, however, has proven difficult due to a significant reduction in reaction rate. This barrier has been overcome by chain‐extending the low molecular weight (Mn of 760 g mol–1) poly(methyl acrylate) macroinitiator with methacrylates and styrene using PMDETA (N,N,N′,N″,N″‐pentamethyldiethylenetriamine) as ligand. Methyl methacrylate conversions of >80% at 70 °C and diethylene glycol methyl ether methacrylate conversions of >90% at room temperature are achieved in 4 h, with the same room temperature conditions successfully applied for controlled chain extensions with butyl methacrylate. Although styrene conversions are slightly lower (60–70%) over 4 h at 85 °C, the rates achieved are substantially higher than achieved in other studies. Hydrophobic–hydrophilic triblock structures are produced through sequential monomer feeds to the semibatch reactor, keeping total reaction time to less than 5 h. The ability to incorporate methacrylates and/or styrene into structured block polymers greatly extends the range of products that can be efficiently synthesized with low copper levels by this process.

Controlled block-polymerization of styrene, divinylbenzene and ethylene oxide. Intermolecular cross-linking towards well-defined miktoarm copolymer stars

• Synthesis of well-defined miktoarm copolymer stars. • Control over the molecular weight and composition for both arm species. • Controlled polymerization of poly(divinylbenzene). • Intermolecular cross-linking of linear triblock terpolymers. A novel approach for the synthesis of miktoarm copolymer stars with divinylbenzene cross-linked core, via anionic polymerization is reported. This synthetic route gives access to polymers, characterized by low dispersity values and improved structural homogeneity for both arm species. Specifically, miktoarm copolymer stars of A n B n type, with cross-linked divinylbenzene (DVB) core and arms of polystyrene (PS) and poly(ethylene oxide) (PEO), are synthesized via anionic polymerization and sequential monomer addition, employing high vacuum techniques. Analytically, the first step involves the synthesis of a triblock terpolymer PS- b -PDVB- b -PEO. Then, in the presence of a free radical initiator the pending vinyl groups of the middle DVB block cross-link intermolecularly, leading to the final miktoarm copolymer star. The novelty of the proposed synthetic route, lies in the potassium alkoxide co -initiator, which is responsible for the controlled polymerization of both DVB and EO in one pot, without the need for end group modification between the two steps. Concerning the final polymer, there are numerous benefits advancing from this synthetic protocol, such as the control of the molecular characteristics of both arms, as well as the easily confirmed structural integrity of the precursor triblock which is inherited to the resulting miktoarm star. For comparison reasons, another batch of (PS)(PEO) miktoarm copolymers was synthesized, following the “in-out” synthetic route. For this reason, styrene was polymerized using s -BuLi, which is used as macroinitiator for the polymerization/cross-linking of DVB, resulting PS star with DVB cross-linked core. With the addition of EO, in the presence of p4 t -Bu phosphazene base, PEO arms are polymerized, initiating from the core’s active cites outwards.

Palladium-Catalyzed Living/Controlled Vinyl Addition Polymerization of Cyclopropenes.

Despite the various utilities of cyclopropenes (CPEs) in organic synthesis and ring-opening metathesis polymerization (ROMP), their vinyl addition polymerization has been sporadically explored, and the corresponding living/controlled polymerization remains a formidable challenge. The major obstacle is the intrinsic instability of the intermediate and the kinetic barrier for propagation. Herein a living/controlled vinyl addition polymerization of 3-methyl-3-carboxymethyl CPEs, catalyzed by [Pd(π-allyl)Cl]2 ligated by a sulfinamide bisphosphine ligand, is demonstrated. A plot of the number-average molecular weight (Mn) versus the conversion was found to be linear during the polymerization, with the molecular weight dispersity (Mw/Mn) remaining narrow. The Mn values increased linearly with the increase in the initial feed ratio of monomer to catalyst. Furthermore, controlled block copolymerization via sequential monomer addition was successful. All of these points corroborate the living nature of this polymerization. The synergistic coordination action of the catalyst ligand and the lateral carbonyl group in the cyclopropene moiety plays a key role in achieving the efficient polymerization in a living/controlled manner.

Pathway Complexity in Supramolecular Porphyrin Self-Assembly at an Immiscible Liquid-Liquid Interface.

Nanostructures that are inaccessible through spontaneous thermodynamic processes may be formed by supramolecular self-assembly under kinetic control. In the past decade, the dynamics of pathway complexity in self-assembly have been elucidated through kinetic models based on aggregate growth by sequential monomer association and dissociation. Immiscible liquid–liquid interfaces are an attractive platform to develop well-ordered self-assembled nanostructures, unattainable in bulk solution, due to the templating interaction of the interface with adsorbed molecules. Here, we report time-resolved in situ UV–vis spectroscopic observations of the self-assembly of zinc(II) meso-tetrakis(4-carboxyphenyl)porphyrin (ZnTPPc) at an immiscible aqueous–organic interface. We show that the kinetically favored metastable J-type nanostructures form quickly, but then transform into stable thermodynamically favored H-type nanostructures. Numerical modeling revealed two parallel and competing cooperative pathways leading to the different porphyrin nanostructures. These insights demonstrate that pathway complexity is not unique to self-assembly processes in bulk solution and is equally valid for interfacial self-assembly. Subsequently, the interfacial electrostatic environment was tuned using a kosmotropic anion (citrate) in order to influence the pathway selection. At high concentrations, interfacial nanostructure formation was forced completely down the kinetically favored pathway, and only J-type nanostructures were obtained. Furthermore, we found by atomic force microscopy and scanning electron microscopy that the J- and H-type nanostructures obtained at low and high citric acid concentrations, respectively, are morphologically distinct, which illustrates the pathway-dependent material properties.

A study of protein aggregation activators in molecular complexes of cationic porphyrins and chlorin with BSA

Protein aggregation in the human body can cause a number of diseases, which makes it essential to study protein aggregation paths and mechanisms in order to find methods to treat them. This work is a continuation of the series of studies aimed at finding compounds capable of triggering protein aggregation in solutions. The aim of this work was to find a correlation between the structure, thermodynamic stability of BSA complexes with cationic macroheterocycles (MHC) and propensity of albumin complexes for aggregation, as well as the hydrodynamic properties of protein solutions. Meso-tetra-(N-methyl-4-pyridyl)porphine tetraiodide (TMPyP4), meso-tetra-(N-methyl-3-pyridyl)porphine tetraiodide (TMPyP3) and meso-tetra-(N-methyl-3-pyridyl)bacteriochlorin tetra tosylate (BC) trigger different types of BSA aggregation, depending on their localization in the albumin globule. When macroheterocycles are localized inside an albumin globule, they trigger sequential monomer addition, with both monomer structures and aggregates of medium and large sizes present in the solution. If a macroheterocycle is localized on the surface of a protein globule, protein aggregation is caused by the formation of macroheterocycle complexes with two or more globules.

One-Pot Synthesis of Supertough, Sustainable Polyester Thermoplastic Elastomers Using Block-Like, Gradient Copolymer as Soft Midblock

It remains challenging to synthesize supertough thermoplastic elastomers (TPEs) since the stretchability and tensile strength are mutually exclusive. Here, we report a one-pot strategy for the prep...

Synthesis of Di-Block Copolymers Poly (propylene ox-ide)-block-Poly (9-(2,3-epoxypropyl) Carbazole) via Sequential Addition of Monomers in One Pot.

Polypropylene oxide (PPO) and poly(9-(2,3-epoxypropyl) carbazole) (PEPK) di-block copolymers are prepared in one pot via sequential monomer addition by using i-PrONa/i-Bu3Al as an anionic catalytic system. An almost 100% monomer conversion is obtained, and the length of each block is controlled through the monomer/catalyst ratio used. Copolymer molecular weights are quite close to theoretical values calculated assuming the formation of one polymer chain per catalyst; therefore, it is hypothesized that the polymerization reaction proceeds with a living character. The synthesis appears to be particularly efficient and versatile. The calorimetric properties of copolymers obtained in this work are remarkable, since they show two distinct Tg values, corresponding to the PPO and PEPK blocks. The optical measurements of di-block copolymers show more analogous features than those of PEPK homopolymer. Copolymer solution emission spectra just exhibit isolated carbazole fluorescence, whereas in the solid state, film spectra show excimer fluorescence.