Fragmentation Chain Transfer Polymerization Research Articles

Effects of Molecular Structures of Poly(styrene-co-octadecyl maleimide) as a Flow Improver for the Model Crude Oil with a Relatively High Content of Asphaltenes

Poly(styrene-co-maleic anhydride)s (SMAs) with different compositions and molecular weight were synthesized through the reversible addition–fragmentation chain transfer polymerization technique. SMAs were converted to poly(styrene-co-octadecyl maleimide)s (SNODMIs) by amidation with octadecyl amine and subsequent imidization. SNODMIs with octadecyl branches were evaluated as flow improvers in the model crude oil with a high content of asphaltenes. The effects of molecular structures, including molecular weight, branch content, and imidization degree, on the effectiveness of SNODMI in reducing the viscosity and yield stress and improving the morphologies of asphaltene particles were thoroughly investigated using a rotational rheometer with parallel plate geometry and a polarizing microscope with a hot stage, respectively. It has been found that efficacy of SNODMI in reducing the viscosity and yield stress of the model crude oil increases with an increasing branch content of SNODMI. (alt)SNODMI with the highest branch content, approximately 45 mol %, achieved the best performance. Too high or too low molecular weight is not beneficial for SNODMI to improve the flow ability of the model crude oil. The appropriate molecular weight (Mₙ = 3500 Da) is required to achieve the optimal effectiveness. The optimal imidization degree of SNODMI is 100% and is independent of the branch content. The addition of SNODMI in a real crude oil has reduced the viscosity and yield stress by more than 90%.

Nonbiofouling Coatings Using Bottlebrushes with Concentrated Polymer Brush Architecture.

Concentrated polymer brushes (CPBs) are known to suppress biofouling phenomena, such as protein adsorption and cell adhesion. However, a cumbersome process is needed for their synthesis. Here, we report a simple and versatile method for fabricating nonbiofouling coatings that uses well-defined bottlebrushes instead of CPBs. First, a macroinitiator, poly[2-(2-bromoisobutyryloxy)ethyl methacrylate] (PBIEM), was synthesized by reversible addition-fragmentation chain transfer polymerization. Then, poly[poly(ethylene glycol) methyl ether methacrylate] was grafted from PBIEM through atom transfer radical polymerization to form well-defined bottlebrushes. By controlling the graft chain length, two types of bottlebrushes could be prepared, namely those with a semi-dilute polymer brush (SDPB) structure or a CPB structure on the surface of the outermost layer. Crosslinked films of the bottlebrushes were prepared on silicon wafers by spin-coating and subsequent radical coupling. Importantly, the CPB-type bottlebrush films showed significantly better nonbiofouling characteristics than those of the SDPB-type bottlebrush films.

Dextran based amphiphilic self-assembled biopolymeric macromolecule synthesized via RAFT polymerization as indomethacin carrier

This work demonstrates a facile pathway to develop a biopolymer based amphiphilic macromolecule through reversible addition–fragmentation chain transfer (RAFT) polymerization, using dextran (a biopolymer) as starting material. Also, a new hydrophobic monomer [2-methyl-acrylic acid 1-benzyl-1H-[1,2,3] triazol-4-ylmethyl ester (MABTE)] has been synthesized using methacrylic acid via “click” approach. The resultant copolymer displays controlled radical polymerization characteristics: narrow polydispersity (Ð) and controlled molecular weight as obtained through advanced polymer chromatography (APC) analysis. In aqueous solution, the copolymer can proficiently be self-assembled to provide micellar structure, which has been evidenced from field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) analyses. The in-vitro cytotoxicity study illustrates the nontoxic nature of the copolymer up to 100 μg/mL polymer concentration. The copolymer has been found to be worthy as an efficient carrier for the sustained release of hydrophobic drug: Indomethacin (IND).

P(MMA‐co‐HPMA)‐b‐POEGMA copolymers: synthesis, micelle formation in aqueous media and drug encapsulation

AbstractWe report the synthesis and the micellar self‐assembly in aqueous media of novel amphiphilic block copolymers. The copolymers consist of a poly[(methyl methacrylate)‐co‐(hydroxypropyl methacrylate)] statistical copolymer block and a poly[oligo(ethylene glycol) methyl ether methacrylate] block, and were synthesized by reversible addition–fragmentation chain transfer polymerization. The amphiphilic P(MMA‐co‐HPMA)‐b‐POEGMA block copolymers contain monomers of differing polarity and in varying ratios. Furthermore, HPMA segments are chosen in order to enhance hydrogen bonding interactions within the core of spherical micelles formed by the copolymers in aqueous media, as evidenced by light scattering and fluorescence spectroscopy studies. The amphiphilic copolymers are able to encapsulate the hydrophobic drugs curcumin and indomethacin as found using light scattering and spectroscopic methods. © 2021 Society of Industrial Chemistry.

Cross-Linked Polymer Brushes Containing N-Halamine Groups for Antibacterial Surface Applications.

Microbial contamination is a significant issue in various areas, especially in the food industry. In this study, to overcome microbial contamination, cross-linked polymer brushes containing N-halamine were synthesized, characterized, and investigated for antibacterial properties. The cross-linked polymer brushes with different N-halamine ratios were synthesized by in-situ cross-linking methods with reversible addition−fragmentation chain transfer (RAFT) polymerization using a bifunctional cross-linker. The RAFT agent was immobilized on an amine-terminated silicon wafer surface and utilized in the surface-initiated RAFT polymerization of [N-(2-methyl-1-(4-methyl-2,5-dioxoimidazolidin-4-yl)propane-2-yl)acrylamide] (hydantoin acrylamide, HA), and N-(2-hydroxypropyl)methacrylamide) (HPMA) monomers. Measurement of film thickness, contact angle, and surface morphology of the resulting surfaces were used to confirm the structural characteristics of cross-linked polymer brushes. The chlorine content of the three different surfaces was determined to be approximately 8–31 × 1013 atoms/cm2. At the same time, it was also observed that the activation–deactivation efficiency decreased during the recharge–discharge cycles. However, it was determined that the prepared N-halamine-containing cross-linked polymer brushes inactivated approximately 96% of Escherichia coli and 91% of Staphylococcus aureus. In conclusion, in the framework of this study, high-performance brush gels were produced that can be used on antibacterial surfaces.

Simple and feasible design of a polymeric nanoparticle for efficient anticancer drug delivery

In this paper, we present a simple and feasible drug self-assembled delivery system with pH responsiveness and targeting function for cancer therapy. The drug delivery system is composed of an anticancer drug and an amphiphilic random copolymer based on phenylboronic acid, galactose, and polyethylene glycol monomethyl ether acrylate molecules and achieved through reversible addition–fragmentation chain transfer polymerization. The micelles present targeting function by introducing galactose molecules and show pH sensitivity on the basis of the interactions between phenylboronic acid and galactose molecules. Particle size, transmission electron microscopy, and drug release assays show the pH-responsive behavior of micelles at pH 6.0. Cellular uptake assay demonstrates that micelles can internalize HepG2 cells via receptor-mediated interaction. In addition, the drug-loaded micelles can considerably inhibit cancer cell proliferation as indicated by in vivo antitumor assay. The synthesized micelles may facilitate the development of valid drug delivery systems for cancer therapy.

Nano-Assemblies from Amphiphilic PnBA-b-POEGA Copolymers as Drug Nanocarriers.

The focus of this study is the development of highly stable losartan potassium (LSR) polymeric nanocarriers. Two novel amphiphilic poly(n-butyl acrylate)-block-poly(oligo(ethylene glycol) methyl ether acrylate) (PnBA-b-POEGA) copolymers with different molecular weight (Mw) of PnBA are synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization, followed by the encapsulation of LSR into both PnBA-b-POEGA micelles. Based on dynamic light scattering (DLS), the PnBA30-b-POEGA70 and PnBA27-b-POEGA73 (where the subscripts denote wt.% composition of the components) copolymers formed micelles of 10 nm and 24 nm in water. The LSR-loaded PnBA-b-POEGA nanocarriers presented increased size and greater mass nanostructures compared to empty micelles, implying the successful loading of LSR into the inner hydrophobic domains. A thorough NMR (nuclear magnetic resonance) characterization of the LSR-loaded PnBA-b-POEGA nanocarriers was conducted. Strong intermolecular interactions between the biphenyl ring and the butyl chain of LSR with the methylene signals of PnBA were evidenced by 2D-NOESY experiments. The highest hydrophobicity of the PnBA27-b-POEGA73 micelles contributed to an efficient encapsulation of LSR into the micelles exhibiting a greater value of %EE compared to PnBA30-b-POEGA70 + 50% LSR nanocarriers. Ultrasound release profiles of LSR signified that a great amount of the encapsulated LSR is strongly attached to both PnBA30-b-POEGA70 and PnBA27-b-POEGA73 micelles.

Succinimidyl Carbonate-Based Amine-Reactive Polymer Brushes: Facile Fabrication of Functional Interfaces

Polymeric coatings that can undergo effective functionalization with ligands and (bio)molecules necessary for intended applications are widely employed to engineer functional interfaces. Herein, amine-reactive polymer brushes are fabricated using a succinimidyl group-activated carbonate monomer, and their facile post-polymerization functionalization is demonstrated through ligand-mediated protein immobilization and detection. Copolymer brushes containing varying amounts of the reactive monomer and an ethylene glycol-based methacrylate comonomer were obtained using surface-mediated reversible addition fragmentation chain transfer polymerization. Post-polymerization functionalization of the thus-obtained copolymer brushes with a fluorine-containing amine, namely, 4-(trifluoromethyl)benzylamine, demonstrated highly efficient functionalization at ambient temperature. To demonstrate possible applications, polymer brushes functionalized with a bioactive ligand, namely, biotin, were used to detect the target protein, streptavidin. The biotin–streptavidin interaction on brushes could also be employed to conjugate protein-coated quantum dots. Importantly, comparison of the attachment of 4-(trifluoromethyl)benzylamine on activated carbonate group-containing brushes with reaction of the same molecule on traditional active ester-based brushes demonstrated higher extent of conjugation to carbonate brushes. Finally, orthogonal functionalization of the copolymer brushes with an amino-functionalized molecule and a maleimide-containing fluorescent dye in spatial control using microcontact printing was demonstrated. One can envision that the facile fabrication and efficient functionalization of succinimidyl carbonate-based amine-reactive brushes afford an attractive platform for applications using functional interfaces for diagnostic purposes.

Upper Critical Solution Temperature Behavior of pH-Responsive Amphoteric Statistical Copolymers in Aqueous Solutions.

Amphoteric statistical equivalent copolymers (P(2VP/NaSS)n) composed of 2-vinylpyridine (2VP) and anionic sodium p-styrenesulfonate (NaSS) were prepared via reversible addition–fragmentation chain transfer polymerization. The degrees of polymerization (n) were 19 and 95. The monomer reactivity ratio, time conversion profile, and 1H nuclear magnetic resonance diffusion-ordered spectra suggested that the copolymerization of 2VP and NaSS provided statistical or near to random copolymers. P(2VP/NaSS)n exhibited an upper critical solution temperature (UCST) in acidic aqueous solutions on the basis of the charge interactions between the protonated cationic 2VP and anionic NaSS units. With an increase in pH value, the interaction was weakened because of the deprotonation of the 2VP units, thus reducing the UCST. At high [NaCl], the electrostatic interactions among the polymers were weakened because of the screening effect, and again, the UCST was reduced. With an increase in polymer concentration, the intra- and interpolymer interactions increased because of some entanglement, and the UCST consequently increased. Electrostatic interactions among the polymer chains with high molecular weight occurred easier than those among the low-molecular-weight polymer chains, which increased the UCST. The UCST also increased when deuterium oxide was used instead of hydrogen oxide, which was due to the isotopic effect. Hence, the UCST of P(2VP/NaSS)n can be adjusted according to the desired application.

Preparation, crystallization and thermo-oxygen degradation kinetics of poly(lactic acid)/fulvic acid-g-poly(isoprene) grafting polymer composites

In order to graft poly(isoprene) on the surface of fulvic acid (FA), fulvic acid-g-poly(isoprene) grafting polymer (FA-g-PI) was synthesized by reversible addition–fragmentation chain transfer polymerization. Because FA-g-PI became more hydrophobic, the static contact angle of FA-g-PI was 67°, which was increased by 37° compared with FA. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis showed that PI was grafted onto the FA. Furthermore, FA-g-PI was used as a modifier to melt blend with PLA to prepare poly(lactic acid)/fulvic acid-g-poly(isoprene) grafting copolymer composites (PLA/FA-g-PI). The mechanical performance results presented that the impact strength, tensile strength and elongation at break of PLA/FA-g-PI (0.3 wt%) reached 18.8 kJ/m2, 81.5 MPa and 18.47%, respectively, which were increased by 97.8%, 3.6% and 5.0% compared with PLA. The scanning electron microscopy analysis of impact fracture for PLA/FA-g-PI (0.3 wt%) also clearly showed that PLA/FA-g-PI (0.3 wt%) had the typical toughness fracture morphology feature. The results of differential scanning calorimetry and polarized optical microscope analysis indicated that the addition of FA-g-PI reduced the crystallite size during PLA crystallization. The kinetics of thermo-oxygen degradation by Kissinger method showed that the apparent activation energy of PLA/FA-g-PI (0.3 wt%) composites was increased from 153.73 kJ/mol to 179.17 kJ/mol, which was shown that FA-g-PI improved the thermal stability of PLA. Moreover, the reaction order showed that FA-g-PI had little effect on the PLA thermo-oxygen degradation reaction kinetic order under the air atmosphere.

V-Shaped amphiphilic polymer brushes grafted on cellulose nanocrystals: Synthesis, characterization and properties

Cellulose nanocrystals (CNCs) were modified using an amphiphilic triblock copolymer [poly(2-(dimethylamino) ethyl methacrylate)-b-poly(glycidyl methacrylate)-b-poly(2,2,3,4,4,4-hexafluorobutyl acrylate) (PDMAEMA-b-PGMA-b-PHFBA)] bearing epoxy functionalities located in middle segment of PGMA, which were used to react with the hydroxyl groups on the surface of the CNCs. The triblock copolymer was synthesized via a reversible addition fragmentation chain transfer (RAFT) polymerization reaction between 2-(dimethylamino) ethyl methacrylate, glycidyl methacrylate and 2,2,3,4,4,4-hexafluorobutyl acrylate, and characterized using 1H-NMR spectroscopy and size exclusion chromatography (SEC). The successful modification of the CNCs was demonstrated by means of FT-IR, TGA, TEM, XRD and XPS. In addition, the surface properties of the modified CNCs were studied using water contact angle and surface tension studies. When compared with the pristine CNCs, the modified CNCs exhibited a higher contact angle and lower surface tension. Good dispersion of the modified CNCs was observed in different polar solvents, such as water, THF, DMF, CHCl3 and toluene. The modified CNCs exhibited pH responsive properties, which were measured using dynamic light scattering (DLS). In addition, the stability of Pickering emulsions stabilized by PDMAEMA-g-CNC-g-PHFBA decreased with time or increasing pH. The droplet size increased gradually upon increasing the pH. This work provides a method to design sophisticated CNC-based materials, which benefit from both the intrinsic properties of the CNCs and the new characteristics conferred by the multifunctional grafted chains.

Enhancing the Mechanical Properties of Matrix‐Free Poly(Methyl Acrylate)‐Grafted Montmorillonite Nanosheets by Introducing Star Polymers and Hydrogen Bonding Moieties

AbstractMatrix‐free nanocomposite films of poly(methyl acrylate) (PMA) and montmorillonite (MMT) nanosheets that imitate the microscopic structure of nacre are developed and their mechanical properties are studied in detail via tensile testing. The exfoliated MMT nanosheets are grafted with PMA via a grafting‐through radical addition–fragmentation chain transfer polymerization in presence of a surface‐anchored ionic monomer. The mechanical properties are precisely tailored a) via the variation of the degree of polymerization of the surface‐grafted polymer, illustrating the impact of chain entanglement and the MMT content on the performance of the material, and b) via cross‐linking of the surface‐grafted polymer, either by partial change of the polymer topology from linear to star‐shape or by the introduction of hydrogen‐bonding units within the polymer. These experiments demonstrate the strong influence of the chain mobility of the surface‐grafted polymer on the mechanical properties of the nanocomposite material.

Design of Hydrogels with Thermoresponsive Crosslinked Domain Structures via the Polymerization-Induced Self-Assembly Process and Their Thermoresponsive Toughening in Air

We designed a hydrogel with a thermoresponsive crosslinked domain (CD) structure, which expressed thermoresponsive toughening in an isochoric manner in air. The responsive behavior of conventional thermoresponsive hydrogels is usually a macroscopic volume change along with water transfer to and from the outside of the polymer network. In order to expand the scope of thermoresponsive hydrogels, a network design that requires no external water for thermoresponsive transition has been demanded. To this end, we focused on the polymerization-induced self-assembly process for the direct synthesis of gels with designed domains and performed reversible addition–fragmentation chain transfer polymerization of N-isopropylacrylamide in water at a high temperature using a bifunctional macro-chain transfer agent, yielding a transparent gel. The structural analysis of the obtained gel revealed that dispersed CDs reversibly swelled and shrunk in response to temperature change in air without aggregation. Such an internal structural change induced the increase of elastic modulus and elongation at a high temperature.

HPMA-Based Copolymers Carrying STAT3 Inhibitor Cucurbitacin-D as Stimulus-Sensitive Nanomedicines for Oncotherapy.

The study describes the synthesis, physicochemical properties, and biological evaluation of polymer therapeutics based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers intended for a tumor-targeted immuno-oncotherapy. Water-soluble linear and cholesterol-containing HPMA precursors were synthesized using controlled reversible addition–fragmentation chain transfer polymerization to reach molecular weight Mn about 2 × 104 g·mol−1 and low dispersity. These linear or self-assembled micellar conjugates, containing immunomodulatory agent cucurbitacin-D (CuD) or the anticancer drug doxorubicin (Dox) covalently bound by the hydrolytically degradable hydrazone bond, showed a hydrodynamic size of 10–30 nm in aqueous solutions. The CuD-containing conjugates were stable in conditions mimicking blood. Importantly, a massive release of active CuD in buffer mimicking the acidic tumor environment was observed. In vitro, both the linear (LP-CuD) and the micellar (MP-CuD) conjugates carrying CuD showed cytostatic/cytotoxic activity against several cancer cell lines. In a murine metastatic and difficult-to-treat 4T1 mammary carcinoma, only LP-CuD showed an anticancer effect. Indeed, the co-treatment with Dox-containing micellar polymer conjugate and LP-CuD showed potentiation of the anticancer effect. The results indicate that the binding of CuD, characterized by prominent hydrophobic nature and low bioavailability, to the polymer carrier allows a safe and effective delivery. Therefore, the conjugate could serve as a potential component of immuno-oncotherapy schemes within the next preclinical evaluation.

Nonionic UCST-LCST Diblock Copolymers with Tunable Thermoresponsiveness Synthesized via PhotoRAFT Polymerization.

Nonionic double thermoresponsive diblock copolymers with both upper critical solution temperature (UCST) and lower critical solution temperature (LCST) phase transitions are synthesized via eco-friendly photoiniferter reversible addition-fragmentation chain transfer polymerization. While the biocompatible random copolymer of di(ethylene glycol) methyl ether methacrylate and oligo(ethylene glycol) methacrylate accounts for the LCST transition, the block of polymethacrylamide from an easily accessible monomer with low health hazard is responsible for the UCST transition. Temperature-dependent dynamic light scattering measurements confirm the formation of micellar aggregates in water at the temperatures below UCST- and above LCST-type cloud points. Additionally, the temperature interval between UCST and LCST, where both blocks are dissolved, can be tailored by varying the comonomer ratio in the random copolymer block. With these unique advantages, the presented work introduces a new polymer system for the design of schizophrenic polymers.

Thermal Properties and Self-Assembly Behaviors of Triblock Copolymers Consisting of PEG Segment and Acrylamide-Based Block Bearing Alkyl Side Chains Prepared by RAFT Method

A new series of hybrid triblock copolymers (TBCs) based on hard–soft–hard segments are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization using a macroinitiator p...

RAFT Emulsion Polymerization for (Multi)block Copolymer Synthesis: Overcoming the Constraints of Monomer Order

Synthesis of (multi)block copolymers using reversible addition–fragmentation chain transfer (RAFT) polymerization generally suffers from the limitation that the order of the blocks must be considered. Herein, syntheses of block copolymers by RAFT polymerization using trithiocarbonate RAFT species are conducted as solution, miniemulsion, and emulsion polymerizations to demonstrate that the issue of monomer order for styrene and butyl methacrylate can be largely overcome in emulsion polymerization under carefully chosen conditions. The presence of monomer droplets in emulsion polymerization—in addition to polymer particles that constitute the locus of polymerization—leads to a reduction in the ratio of RAFT end groups to monomer at the locus of polymerization. Consequently, fragmentation of the RAFT adduct radical in the “backward” (“wrong”) direction is associated with fewer monomer additions, thus minimizing the impact of this undesired kinetic event. It is demonstrated that RAFT emulsion polymerization can be exploited to prepare an alternating pentablock copolymer composed of methacrylates (with 10 mol % styrene) and styrene without consideration of monomer order, thereby significantly broadening the scope of RAFT polymerization for multiblock copolymer synthesis.

RAFT polymerization mediated core-shell supramolecular assembly of PEGMA-co-stearic acid block co-polymer for efficient anticancer drug delivery.

In this work, core–shell supramolecular assembly polymeric nano-architectures containing hydrophilic and hydrophobic segments were synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. Herein, polyethylene glycol methyl ether methacrylate (PEGMA), and stearic acid were used to synthesize the poly(PEGMA) homopolymer and stearyl ethyl methacrylate (SEMA), respectively. Then, PEGMA and SEMA were polymerized through controlled RAFT polymerization to obtain the final diblock copolymer, poly(PEGMA-co-SEMA) (BCP). Model anticancer drug, doxorubicin (DOX) was loaded on BCPs. Interestingly, efficient DOX release was observed at acidic pH, similar to the cancerous environment pH level. Significant cellular uptake of DOX loaded BCP50 (BCP50-DOX) was observed in MDA-MB-231 triple negative breast cancer cells and resulted in a 35 fold increase in anticancer activity against MDA MB-231 cells compared to free DOX. Scanning electron microscopy (SEM) imaging confirmed the apoptosis mediated cellular death. These core–shell supramolecular assembly polymeric nano-architectures may be an efficient anti-cancer drug delivery system in the future.

Synthesis, aqueous solution behavior and self-assembly of a dual pH/thermo-responsive fluorinated diblock terpolymer

The synthesis of fluorinated dual-responsive block terpolymers via sequential reversible addition–fragmentation chain transfer (RAFT) polymerization is presented.

Screening RAFT agents and photocatalysts to mediate PET-RAFT polymerization using a high throughput approach

We report a high throughput approach for the screening of RAFT agents and photocatalysts to mediate photoinduced electron/energy transfer-reversible addition–fragmentation chain transfer (PET-RAFT) polymerization.