Reversible Chain Transfer Research Articles

A Stochastic FRET Study on the Core Dimension of Polystyrene-block-Poly(Polyethylene Glycol Monomethyl Ether Acrylate) Micelles.

Polystyrene-b-poly(polyethylene glycol monomethyl ether acrylate) (PSt-b-PPEGA) copolymers featuring pyrene and perylene as the Förster resonance energy transfer (FRET) donor (denoted as D-BCP) and acceptor (denoted as A-BCP), respectively, were synthesized via the reversible addition and fragmentation chain transfer (RAFT) polymerization. These copolymers were then used to form DA-mixed micelles via a dialysis method. The micelles consisted of D-BCP (mole fraction fD = 0.04), A-BCP (fA = 0.04), and label-free PSt-b-PPEGA (fN = 0.92). The decrease in fluorescence intensity of pyrene in the micelles confirmed the occurrence of FRET, with an observed efficiency of 0.32. A Monte Carlo approach was employed to estimate the expected FRET efficiency, assuming the random fractional distribution of D-BCP and A-BCP, along with the random spatial distribution of pyrene and perylene within the micellar core. The observed FRET efficiency suggested a core radius (Rc) of 0.95R0, where R0 was the Förster critical distance. With R0 calculated to be 3.2 nm based on Förster theory, Rc was determined to be approximately 3.0 nm, aligning closely with the dried-out core radius estimated from aggregation number and polystyrene density. This stochastic FRET methodology was further applied to investigate the swelling behavior of the polymer micelles in a mixture of N,N-dimethylformamide (DMF) and water. Dynamic light scattering analysis revealed minimal change in core dimension below 60 vol % DMF content. However, FRET analysis provided a deeper insight, showing an increase in core radius with DMF content up to 20 vol %, followed by saturation up to 50 vol %, offering a more comprehensive understanding of the micelle swelling behavior.

Efficient synthesis of the cyclo-olefin copolymers at high temperature and pressure in a homogeneous mini-tubular reactor

Ethylene-norbornene copolymer (ENC) is one of the most representative cyclo-olefin copolymer (COC). Both the amorphous and semi-crystalline ENCs were efficiently synthesized by the homogeneous solution copolymerization of ethylene (E) and norbornene (NB) using rac-Et(Ind)2ZrCl2/triisobutylaluminium/(Ph3C)B(C6F5)4 ternary catalyst system in a visualized mini-tubular reactor under high temperature (90–130 °C) and given pressure (24 bar). An ultra-high activity of 7.6 × 108 g/(molZr h), as well as considerable efficiency of 14.1 kgENC/gZr was achieved in time of only 30 s at E/NB molar ratio of 3:1. Moreover, a quench-labeling method using 2-thiophenecarbonyl chloride (TPCC) was adopted to calculate the high proportion of active center [C*]/[Zr]. The novel strategy was proposed for preparation of the block semi-crystalline ENC elastomers with excellent tensile performance and high transparency via reversible chain transfer based on spatiotemporal concentration distribution in a mini-tubular reactor.

ZIF-8-mediated block copolymer micelles and its application in drug delivery

Block copolymer micelles have been widely used in drug delivery. Great efforts have been made to optimize the function of block copolymer micelles and further enhance their bioavailability. We propose a means of embedding ZIF-8 in block copolymer micelles to regulate its stability for improving the drug release kinetics. The block copolymer poly (2-(diisopropyl amino-ethyl methacrylate)-block-poly (vinylimidazole-co-poly (ethylene glycol) methyl methacrylate) (PDPA18-b-P(Vim18-co-P(EG)5MA21) (PDPV) bearing imidazole moiety was synthesized through reversible addition-cracking chain transfer (RAFT) polymerization. PDPV can self-assemble into micelles in aqueous solution and then be loaded with doxorubicin (DOX) to obtain DOX@PDPV, followed by Zn coordination to anchor ZIF-8 to the PVim moiety in DOX@PDPV to obtain the final drug delivery system DOX@PDPV@ZIF-8 hybrids. The DOX@PDPV@ZIF-8 hybrids can avoid the influence of the critical micelle concentration (CMC) on it, which was further prevent the premature leakage of DOX under physiological conditions. Furthermore, the pH-responsive properties of PDPA and ZIF-8 facilitated enabled the effective release of DOX in weakly acidic tumor environments. In vitro studies also confirmed that DOX@PDPV@ZIF-8 improved DOX accumulation in cells, leading to the inhibition of cancer cell growth. Therefore, the integrated design provided a promising strategy to regulate the stability of block copolymer micelles, improve drug release kinetics, and ultimately inhibit the growth of cancer cell.

Proton transfer anionic polymerization with C-H bond as the dormant species.

Living anionic polymerization-the most common living polymerization and the one with the longest history-generally requires stringent, water-free conditions and one metal initiator per polymer chain. Here we present the proton transfer anionic polymerization of methacrylates using acidic C-H bonds as the dormant species that are activated by base catalysts. The polymerization mechanism involves reversible chain transfer or termination of the growing enolate species. A weakly acidic compound, such as an alkyl isobutyrate, serves as the initiator or chain-transfer agent in the presence of a bulky potassium base catalyst to produce a polymer chain and, thereby, diminishes the metal compound per chain ratio. An added alcohol serves as a reversible terminator to tame the propagation. End-functionalized, star, block and graft polymers are easily accessible from compounds with C-H bonds.

Facile and efficient in-situ end-functionalization of neodymium-based polybutadiene by isocyanate via a coordinative chain transfer polymerization strategy

Tapping facile and efficient strategies for in-situ end-functionalization of polydiene elastomers has been pursued for scientists for decades. This has been especially prominent for Ziegler-Natta type catalytic systems, because they hold great potential for future large-scale industrializations. In this report, through using a newly emerged method of coordinative chain transfer polymerization (CCTP), we introduce a simple and convenient method to efficiently end-functionalize neodymium-based polybutadienes by in-situ addition of isocyanate or isothiocyanate compounds. These two types of substrates performed high reactivities with η1-allyl-Al capped polybutadienyl chain-ends, that were generated from fast and reversible chain transfer reactions, giving high functionalization efficiencies (up to 97.1 %). The high functionalization efficiencies were also applicable to isocyanate or isothiocyanate substrates bearing different functionalities, showing a broad scope capability. Moreover, such a functionalization process was not influenced by the viscosities of the reaction system, as revealed from the kinetic studies that linear relationship was obtained between Mns and various [BD]/[Nd] ratios, implying again the high reactivities of the isocyanate or isothiocyanate compounds. Due to the incorporation of amide or thioamide functional group into the chain-ends, the corresponding polybutadienes showed much improved surface properties and performed higher mechanical properties than unfunctionalized counterparts for raw rubber matrix. Regarding the vulcanizate, chain-end functional groups could also result in much improved filler dispersion and stronger interaction between rubber and filler particles, which eventually gave rise to better mechanical properties, inducing higher tensile strength, more toughness, and greater tear strength.

A single-step extraction and immobilization of soybean lipolytic enzymes by using a purpose-designed copolymer of styrene and maleic acid as a membrane lysis agent

Approaches aiming to recover proteins without denaturation represent attractive strategies. To accomplish this, a membrane lysis agent based on poly(styrene-alt-maleic acid) or PSMA was synthesized by photopolymerization using Irgacure® 2959 and carbon tetrabromide (CBr4) as a radical initiator and a reversible chain transfer agent, respectively. Structural elucidation of our in-house synthesized PSMA, so-called photo-PSMA, was performed by using NMR spectroscopy. The use of this photo-PSMA in soybean enzyme extraction was also demonstrated for the first time in this study. Without a severe cell rupture, energy input or any organic solvent, recovery of lipolytic enzymes directly into nanometric-sized particles was accomplished in one-step process. Due to the improved structural regularity along the photo-PSMA backbone, the most effective protective reservoir for enzyme immobilization was generated through the PSMA aggregation. Formation of such reservoir enabled soybean enzymes to be shielded from the surroundings and resolved in their full functioning state. This was convinced by the increased specific lipolytic activity to 1,950 mU/mg, significantly higher than those of sodium dodecyl sulfate (SDS) and the two commercially-available PSMA sources (1000P and 2000P). Our photo-PSMA had thus demonstrated its great potential for cell lyse application, especially for soybean hydrolase extraction.

Synthesis and characterization of styrene‐maleic acid block copolymers with acrylic and methacrylic acids for potential use in membrane protein extraction

AbstractStyrene‐maleic acid (SMA) block copolymers with acrylic acid (AA) and methacrylic acid (MAA) were synthesized via a 3‐step process comprising: (1) photopolymerization of styrene and maleic anhydride in solution to yield an alternating styrene‐maleic anhydride (SMAnh) copolymer, (2) copolymerization of SMAnh with AA and MAA to yield SMAnh‐b‐AA and SMAnh‐b‐MAA block copolymers, and (3) base‐catalyzed hydrolysis of the anhydride groups to yield water‐soluble SMA‐b‐AA and SMA‐b‐MAA block copolymers. Copolymer compositions and average molecular weights were determined by the synthesis methodology used in which reversible chain transfer was a key component. Copolymer characterization was carried out by a combination of techniques, namely: ATR‐FTIR, 1H‐NMR, dilute‐solution viscometry, GPC, DSC, and TGA. These novel SMA block copolymers have been designed with a view to their use in membrane protein (MP) extraction from plant extracts and other naturally occurring substances of potential therapeutic value. The main function of the AA or MAA blocks is to widen the operational pH range of SMA in terms of (a) maintaining its water solubility at low pH and (b) stabilizing its MP assemblies in solution.

Imidazole-mediated stability of block copolymer micelles and its application in drug delivery

Block copolymer micelles have emerged as a safer alternative for delivering drugs in biomedical applications. Recent studies have shown that the stability of these micelles can significantly impact the efficiency of drug delivery. Here, we propose a method to regulate the stability of block copolymer micelles by introducing a third monomer. Specifically, we synthesized the block copolymer PDPA18-b-P(Vim18-co-P(EG)5MA21) through reversible addition-cracking chain transfer (RAFT) polymerization based on PDPA19-b-P(P(EG)5MA)18. The diblock three-component copolymer is a unique copolymer, in which the hydrophilic block being doped the third monomer with pH-sensitive property, resulting in distinctive physiological properties. Both PDPA18-b-P(Vim18-co-P(EG)5MA21) and PDPA19-b-P(P(EG)5MA)18 can self-assemble into micelles with a core-shell structure. In the case of PDPA19-b-P(P(EG)5MA)18 micelles, the solvophobic PDPA19 block forms the core, while the solvophilic P(P(EG)5MA)18 block forms the shell. To regulate the stability of the block copolymer micelles, an imidazole intermediate layer with pH-responsiveness is introduced between PDPA core and P(P(EG)5MA) shell. The introduction of the imidazole monomer affect the stability of block copolymer micelles and the release kinetics of drugs. We validated that these PDPA18-b-P(Vim18-co-P(EG)5MA21) micelles exhibit higher stability under neutral conditions and show enhanced drug release in mildly acidic conditions compared to PDPA19-b-P(P(EG)5MA)18 micelles. Overall, this report demonstrates that copolymerization of imidazole monomer is a powerful approach to mediated the stability of block copolymer micelles for drug delivery applications.

Synthesis and modification of copolymers of stearyl methacrylate and maleic anhydride and study of their effect on low-temperature characteristics of diesel fuel

Polymer-analogous transformations have been used to modify copolymers of stearyl methacrylate with maleic anhydride synthesized under radical polymerization conditions using reversible chain transfer agents of various structures. It has been established that copolymer of stearyl methacrylate with maleic anhydride modified by 25% with octanol-1 has a high depressant effect for a pour point of minus 19°С and at the same time significantly reduces both the cloud point values and the maximum filterability temperature of diesel fuel. In this regard, the obtained modified copolymers may be of interest in terms of their practical use as fuel additives.

Pyrazole carbodithiolate-driven iterative RAFT single-additions.

In this Communication, we comprehensively investigated substituent effects relevant to iterative reversible activation fragmentation chain transfer (RAFT) single unit monomer insertion (SUMI) reactions. Through the use of the pyrazole carbodithiolate (PCDT) "Z-group" as the chain transfer component in RAFT SUMI, we show the importance of "Z-group" effects and its interplay with "R-group" (the carbon-centred radical precursor) effects. We also expanded the scope of RAFT SUMI to new monomer types and sequences thereof. As such, the C-S bond dissocation/reformation steps were found to be crucial factors in SUMI, and it was found that general substituent effects must be wholistically examined for every step of this reaction. This stands in contrast with conventional knowledge of RAFT polymerisation, where the main consideration is often centred around the propagation stage, i.e., the key C-C bond formation step. Indeed, contrary to SUMI, the latter characteristic was observed in the analogous alternating copolymerisation.

SYNTHESIS OF COPOLYMERS OF STEARYLMETHACRYLATE AND STEARYLACRYLATE WITH N-SUBSTITUTED ACRYLAMIDES IN THE PRESENCE OF REVERSIBLE CHAIN TRANSFER AGENTS AND STUDY OF THEIR EFFECT ON THE LOW-TEMPERATURE PROPERTIES OF DIESEL FUEL

The features of copolymerization of stearylacrylate (SA) and stearylmethacrylate with N-isopropylacrylamide and N,N-dimethylacrylamide in the presence of dibenzyltrithiocarbonate and 2-cyanoisopropyldodecyltrithiocarbonate as agents of reversible chain transfer have been studied. The choice of agents of reversible chain transfer (RAFT-agents) is due to the fact that sulfur-containing compounds with cyanoisopropyl radicals are most effective in the polymerization of methacrylic monomers, while benzyltrithiocarbonates are more active in the polymerization of acrylic monomers, as well as styrene and acrylonitrile. It has been established that polymerization of stearyl methacrylate (SMA) in the presence of RAFT-agents proceeds without a gel effect up to a high conversion. At the same time, although polystеarylmethacrylate samples are characterized by relatively high values of polydispersity coefficients (Mn/Mw) for controlled radical polymerization processes, they are nevertheless somewhat lower than for polymers of similar conversion synthesized in the absence of chain transfer agents. It has been shown that the process of copolymerization of stearyl acrylate and stearylmethacrylate with N-isopropylacrylamide and N,N-dimethylacrylamide in the presence of dibenzyltrithiocarbonate and 2-cyanoisopropyldodecyltrithiocarbonate proceeds without gelation to high conversions. The synthesized copolymers are characterized by a relatively narrow molecular weight distribution: the polydispersity coefficients of polymer samples vary from 1.18 to 1.57 in the case of using N-isopropylacrylamide and from 1.21 to 1.47 when using N,N-dimethylacrylamide as a comonomer to higher alkyl acrylates, which is typical for processes of radical polymerization proceeding in a controlled manner. At the same time, the synthesized copolymers exhibit a significant depressant effect when they are introduced into diesel fuel at a concentration of 1600 ppm. It has been established that copolymers of stearylmethacrylate and stearylacrylate with polar nitrogen-containing monomers have a more effective effect on the low-temperature properties of diesel fuel than homopolymers of stearylmethacrylate and stearylacrylate. At the same time, additives based on copolymers of stearylmethacrylate with N-isopropylacrylamide with a composition of 70/30 mol.% and stearylacrylate with N-isopropylacrylamide with a composition of 20/80 mol.% had the most significant effect on the low-temperature characteristics of the fuel.

Nitrogen-Doped Graphene Quantum Dots as Electrochemiluminescence-Emitting Species for Sensitive Detection of KRAS G12C Mutation via PET-RAFT.

The levels of KRAS G12C point mutation is recognized to be closely related to the earlier diagnosis of non-small cell lung cancer (NSCLC). Here, based on nitrogen-doped graphene quantum dots (NGQDs) and photo-induced electron/energy transfer reversible addition-fragment chain transfer (PET-RAFT) signal amplification strategy, we fabricated a novel electrochemiluminescence (ECL) biosensor for the detection of KRAS G12C mutation for the first time. NGQDs as ECL-emitting species with cathodic ECL were prepared by a simple calcination method. Firstly, KRAS G12C mutation DNA, i. e., target DNA (tDNA), was captured by specific identification with hairpin DNA (hDNA). Then, PET-RAFT was initiated by blue light, and large numbers of monomers were successfully polymerized to form controllable polymer chains. Lastly, massive NGQDs was introduced via amidation reaction with N-(3-aminopropyl)methacrylamide hydrochloride (APMA), which significantly amplified the ECL signal intensity. Under optimal conditions, this biosensor achieved a good linear relationship between ECL intensity and logarithm of the levels of KRAS G12C mutation in the range from 10 fM to 10 nM. Moreover, this strategy exhibited high selectivity and excellent applicability for KRAS G12C mutation detection in the serum samples. Therefore, this biosensor has great potential in clinical diagnosis and practical application.

Preparation and controllable heavy oil viscosity reduction performance of pH-responsive star block copolymers

In this study, a series of S-PHEDM star block copolymers of hydrophilic N-hydroxyethyl acrylamide (HEAm) and pH-responsive N,N-dimethylaminoethyl methacrylate (DMAEMA) were synthesized by reversible addition-fragment chain transfer (RAFT) copolymerization for the controllable viscosity reduction of heavy oil. The structures and average molecular weights of the star polymers were characterized by FT-IR spectra, 1H NMR spectra and GPC measurements. The aggregation behavior and oil/water interfacial properties of S-PHEDM were studied using DLS, TEM and IFT measurements in aqueous solutions with various pH values. The properties of heavy oil emulsions formed by S-PHEDM were monitored under different pH conditions using Turbiscan Lab measurements and optical microscopy at ambient temperature, and cyclic regulation of emulsion stability was successfully achieved through regular adjustments of pH values in oil/water mixing systems. Then, S-PHEDM was applied to the field of heavy oil viscosity reduction. Therein, S-PHEDM-2 achieved a degree of viscosity reduction of 99.88% at a dosage of 1000 mg·L−1 for heavy oil (ηapp, 50 °C = 85820 mPa·s) under alkaline conditions. The dehydration rate of the formed emulsion was 25.58% after standing for 1 h. When the heavy oil mixing system was adjusted to acidic, the heavy oil emulsion demulsified rapidly and achieved a dehydration rate of 90.7% within 1 h. The flexible transformation between viscosity reduction and oil–water separation for the heavy oil/water mixing system by adjusting the pH values provided a new idea to enhance efficiency and reduce costs during heavy oil recovery.

Cationic β‐Scission of C−H and C−C Bonds for Selective Dimerization and Subsequent Sulfur‐Free RAFT Polymerization of α‐Methylstyrene and Isobutylene

AbstractA series of exo‐olefin compounds ((CH3)2C(PhY)−CH2C(=CH2)PhY) were prepared by selective cationic dimerization of α‐methylstyrene (αMS) derivatives (CH2=C(CH3)PhY) with p‐toluenesulfonic acid (TsOH) via β‐C−H scission. They were subsequently used as reversible chain transfer agents for sulfur‐free cationic RAFT polymerization of αMS via β‐C−C scission in the presence of Lewis acid catalysts such as SnCl4. In particular, exo‐olefin compounds with electron‐donating substituents, such as a 4‐MeO group (Y) on the aromatic ring, worked as efficient cationic RAFT agents for αMS to produce poly(αMS) with controlled molecular weights and exo‐olefin terminals. Other exo‐olefin compounds (R−CH2C(=CH2)(4‐MeOPh)) with various R groups were prepared by different methods to examine the effects of R groups on the cationic RAFT polymerization. A sulfur‐free cationic RAFT polymerization also proceeded for isobutylene (IB) with the exo‐olefin αMS dimer ((CH3)2C(Ph)−CH2C(=CH2)Ph). Furthermore, telechelic poly(IB) with exo‐olefins at both terminals was obtained with a bifunctional RAFT agent containing two exo‐olefins. Finally, block copolymers of αMS and methyl methacrylate (MMA) were prepared via mechanistic transformation from cationic to radical RAFT polymerization using exo‐olefin terminals containing 4‐MeOPh groups as common sulfur‐free RAFT groups for both cationic and radical polymerizations.

Cationic β-Scission of C-H and C--C Bonds for Selective Dimerization and Subsequent Sulfur-Free RAFT Polymerization of α-Methylstyrene and Isobutylene.

A series of exo-olefin compounds ((CH3)2C(PhY)-CH2C(=CH2)PhY) were prepared by selective cationic dimerization of α-methylstyrene (αMS) derivatives (CH2=C(CH3)PhY) with p-toluenesulfonic acid (TsOH) via β-C-H scision. They were subsequently used as reversible chain transfer agents for sulfur-free cationic RAFT polymerization of αMS via β-C-C scission in the presence of Lewis acid catalysts such as SnCl4. In particular, exo-olefin compounds with electron-donating substituents, such as a 4-MeO group (Y) on the aromatic ring, worked as efficient cationic RAFT agents for αMS to produce poly(αMS) with controlled molecular weights and exo-olefin terminals. Other exo-olefin compounds (R-CH2C(=CH2)(4-MeOPh)) with various R groups were prepared by different methods to examine the effects of R groups on the cationic RAFT polymerization. A sulfur-free cationic RAFT polymerization also proceeded for isobutylene (IB) with the exo-olefin αMS dimer ((CH3)2C(Ph)-CH2C(=CH2)Ph). Furthermore, telechelic poly(IB) with exo-olefins at both terminals was obtained with a bifunctional RAFT agent containing two exo-olefins. Finally, block copolymers of αMS and MMA were prepared via mechanistic transformation from cationic to radical RAFT polymerization using exo-olefin terminals containing 4-MeOPh groups as common sulfur-free RAFT groups for both cationic and radical polymerizations.

Versatile Production of Multivariate, Hyperdimensional End Group and Main Chain Functionalized Polyolefins.

The (stereoselective) living coordinative copolymerization of 1-alkenes with 4-aryl-1,6-heptadienes, in both the absence and presence of multiple equivalents of a reversible chain transfer agent, is established as a highly versatile strategy for production of multivariate hyperdimensional functionalized semi-crystalline or amorphous polyolefins that optionally possess either mono- or difunctionalized (telechelic) end-groups in combination with a programmable level of incorporation of orthogonal functional groups within the main-chain. The non-conjugated diene comonomers are readily obtained from a diverse range of aryl carboxaldehyde precursors through a one-step bis-allylation process. These results serve to provide a new platform for exploring the science and technology of a vast new landscape of functionalized classes of polyolefins that are now accessible in practical and scalable quantities.

Versatile Production of Multivariate, Hyperdimensional End Group and Main Chain Functionalized Polyolefins

AbstractThe (stereoselective) living coordinative copolymerization of 1‐alkenes with 4‐aryl‐1,6‐heptadienes, in both the absence and presence of multiple equivalents of a reversible chain transfer agent, is established as a highly versatile strategy for production of multivariate hyperdimensional functionalized semi‐crystalline or amorphous polyolefins that optionally possess either mono‐ or difunctionalized (telechelic) end‐groups in combination with a programmable level of incorporation of orthogonal functional groups within the main‐chain. The non‐conjugated diene comonomers are readily obtained from a diverse range of aryl carboxaldehyde precursors through a one‐step bis‐allylation process. These results serve to provide a new platform for exploring the science and technology of a vast new landscape of functionalized classes of polyolefins that are now accessible in practical and scalable quantities.

RAFT Synthesis and Characterization of Poly(Butyl-co-2-(N,N-Dimethylamino)Ethyl Acrylates)-block-Poly(Polyethylene Glycol Monomethyl Ether Acrylate) as a Photosensitizer Carrier for Photodynamic Therapy.

Polymer micelles are promising drug delivery systems for highly hydrophobic photosensitizers in photodynamic therapy (PDT) applications. We previously developed pH-responsive polymer micelles consisting of poly(styrene-co-2-(N,N-dimethylamino)ethyl acrylate)-block-poly(polyethylene glycol monomethyl ether acrylate) (P(St-co-DMAEA)-b-PPEGA) for zinc phthalocyanine (ZnPc) delivery. In this study, poly(butyl-co-2-(N,N-dimethylamino)ethyl acrylates)-block-poly(polyethylene glycol monomethyl ether acrylate) (P(BA-co-DMAEA)-b-PPEGA) was synthesized via reversible addition and fragmentation chain transfer (RAFT) polymerization to explore the role of neutral hydrophobic units in photosensitizer delivery. The composition of DMAEA units in P(BA-co-DMAEA) was adjusted to 0.46, which is comparable to that of P(St-co-DMAEA)-b-PPEGA. The size distribution of the P(BA-co-DMAEA)-b-PPEGA micelles changed when the pH decreased from 7.4 to 5.0, indicating their pH-responsive ability. The photosensitizers, 5,10,15,20-tetrakis(pentafluorophenyl)chlorin (TFPC), 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (TFPP), protoporphyrin IX (PPIX), and ZnPc were examined as payloads for the P(BA-co-DMAEA)-b-PPEGA micelles. The encapsulation efficiency depended on the nature of the photosensitizer. TFPC-loaded P(BA-co-DMAEA)-b-PPEGA micelles exhibited higher photocytotoxicity than free TFPC in the MNNG-induced mutant of the rat murine RGM-1 gastric epithelial cell line (RGK-1), indicating their superiority for photosensitizer delivery. ZnPc-loaded P(BA-co-DMAEA)-b-PPEGA micelles also exhibited superior photocytotoxicity compared to free ZnPc. However, their photocytotoxicity was lower than that of P(St-co-DMAEA)-b-PPEGA. Therefore, neutral hydrophobic units, as well as pH-responsive units, must be designed for the encapsulation of photosensitizers.

Controllable Synthesis of Heterofunctionalized Polyethers via Intramolecular Phosphonium Bisborane Lewis Pair-Catalyzed Immortal Ring-Opening Polymerization

A metal-free phosphonium bisborane Lewis pair (PBB-Br) was demonstrated to realize the immortal ring-opening polymerization (iROP) of propylene oxide (PO) under mild conditions with alcohols as chain-transfer agents (CTAs). Narrow dispersed poly(propylene oxides) (PPOs) with controllable molecular weights predicted from the [PO]0/([PBB-Br]0 + [CTAs]0) molar ratio were obtained in quantitative conversion. These findings indicated the iROP feature of PBB-Br-catalyzed PO polymerization. The rapid, reversible, and quantitative chain transfer assured the iROP characteristic for an intramolecular Lewis pair catalyst PBB-Br, so various well-defined heterofunctionalized PPOs were easily produced. All the α,ω-difunctionalized PPOs were carefully characterized. Density functional theory (DFT) calculations reveal that the chain transfer to the CTA process is almost barrierless (0.8 kcal mol–1) and thermodynamically favorable as compared to chain propagation. Moreover, PPO-based block copolyethers were easily obtained in one-pot using epoxide mixtures. This research demonstrated that the delicately designed intramolecular synergistic Lewis pair offered a powerful and controllable method to prepare various heterofunctionalized PPO samples with high values.

Facilely Control Grafting Density and Side Chain Composition of Bottlebrush Polymer.

Control over polymer architecture and composition is essential for disclosing structure-property relationships and developing high-performance materials. Herein, a new method is successfully developed to synthesize bottlebrush polymer (BP) with controllable graft density and side chain composition by "grafting-from" strategy using in situ halogen exchange and reversible chain transfer catalyzed polymerization (RTCP). The main chain of the BP is first synthesized by the polymerization of methacrylates containing alkyl bromide as a side group. Then, the alkyl bromine is quantitatively converted to alkyl iodide with sodium iodide (NaI) via in situ halogen exchange to efficiently initiate the RTCP of methacrylates. By adjusting the input amount of NaI and monomers in sequence, BP named PBPEMA-g-PMMA/PBzMA/PPEGMEMA which contains three different kinds of polymer side chains including hydrophilic PPEGMEMA, hydrophobic PMMA, and PBzMA is synthesized with narrow molecular weight distribution (Mw /Mn ≤1.36). The grafting density and the chain length of each polymer side chain are well controlled by the addition of NaI in batches and following RTCP. Moreover, the obtained BP self-assembled into spherical vesicles in aqueous with hydrophilic coronal structure, core region, and the hydrophobic wall between the former two, which enables to wrap hydrophobic pyrene and hydrophilic Rhodamine 6G separately or simultaneously.