Facile Synthesis of Hyperbranched and Star-Shaped Polymers by RAFT Polymerization Based on a Polymerizable Trithiocarbonate

Fluorinated hydrogel nanoparticles with regulable fluorine contents and T2 relaxation times as 19F MRI contrast agents

Medical imaging contrast agents that are able to provide detailed biological information have attracted increasing attention. Among the new emerging imaging contrast agents, ¹⁹F magnetic resonance imaging contrast agents (¹⁹F MRI CAs) are extremely promising for their weak background disturbing signal from the body. However, to prepare ¹⁹F MRI CAs with a long T₂ relaxation time and excellent biocompatibility in a simple and highly effective strategy is still a challenge. Herein, we report a new type of ¹⁹F MRI hydrogel nanocontrast agents (¹⁹F MRI HNCAs) synthesized by a surfactant-free emulsion polymerization with commercial fluorinated monomers. The T₂ relaxation time of ¹⁹F MRI HNCA-1 was found to be 25-40 ms, guaranteeing its good imaging ability in vitro. In addition, according to an investigation into the relationship between the fluorine content and ¹⁹F MRI signal intensity, the ¹⁹F MRI signal intensity was not only determined by the fluorine content in ¹⁹F MRI HNCAs but also by the hydration microenvironment around the fluorine atoms. Moreover, ¹⁹F MRI HNCAs demonstrated excellent biocompatibility and imaging capability inside cells. The primary exploration demonstrated that ¹⁹F MRI HNCAs as a new type of ¹⁹F MRI contrast agent hold potential for imaging lesion sites and tracking cells in vivo by ¹⁹F MRI technology.

A Study on the Dual Thermo- and pH-Responsive Behaviors of Well-Defined Star-like Block Copolymers Synthesize by Combining of RAFT Polymerization and Thiol-Ene Click Reaction

A series of stimuli-responsive star-like block copolymers are synthesized via the combination of reversible addition, fragmentation chain transfer (RAFT) polymerization, and photo-initiated thiol-ene (PITE) click reaction. The controllable block ratio and block sequence, narrow distribution of molecular weight, and customized arm numbers of the star-shaped copolymers reveal the feasibility and benefits of combination of RAFT polymerization and PITE click reaction for synthesis of well-defined star-like (co)polymers. A clear insight into the relationship among the arm number, block sequence, and block ratio of the star-like block copolymers and their stimuli-responsive aggregation behavior was achieved via dynamic light scattering and UV-vis spectroscopy study. Notably, the star-like poly(acrylic acid)-b-poly(2-(dimethylamino) ethyl methacrylate) (star-PAA-b-PDMAEMA) shows higher lower critical solution temperature (LCST) compared to star-PDMAEMA-b-PAA with the same arm number and block ratio due to the inner charged PAA segments at pH > IEP. In addition, for star-like PAA-b-PDMAEMA, higher PAA content enhances the hydrophilicity of the polymer in basic solution and leads to the LCST increase, except for star-PAA1-b-PDMAEMA4 at pH = 9.0 (≈IEP). For star-PDMAEMA-b-PAA, the PAA content shows minimal effect on their LCSTs, except for the polymer in solution with pH = 9.5, which is far from their IEP. The star-like block copolymers with well-defined structure and tunable composition, especially the facile-controlled block sequence, bring us a challenging opportunity to control the stimuli-responsive properties of star-like block copolymers.

Synthesis and Visualization of bottlebrush-shaped segmented hyperbranched polymers

Visualization of single molecular morphology provides an intuitive evidence to understand the relationships of molecular structure-synthetic method. Herein, by combining the architectural features of molecular bottlebrush (MBB) and segmented hyperbranched...

Facile synthesis and self-assembly behaviors of biodegradable amphiphilic hyperbranched copolymers with reducible poly(caprolactone) grafts

A reducible hydrophobic macromonomer, HEMA-g-PCL, developed herein provides a facile yet robust strategy for biodegradable amphiphilic hyperbranched copolymers.

Multi-responsive poly(oligo(ethylene glycol)methyl methacrylate)-co-poly(2-(diisopropylamino)ethyl methacrylate) hyperbranched copolymers via reversible addition fragmentation chain transfer polymerization

Multi-responsive P(OEGMA-co-DIPAEMA) hyperbranched copolymers are synthesized via RAFT polymerization. The copolymers form different aggregates in aqueous media depending on solution pH, temperature and copolymer composition.

Facile One-Pot Synthesis of Hyperbranched Glycopolymers in Aqueous Solution via a Hydroxy/Cu(III) Redox Process

In this study, a self-condensing vinyl copolymerization/redox (SCVP/Redox) system was constructed to prepare hyperbranched poly(methyl-6-O-methacryloyl-α-D-glucoside) by using Cu(III) as the initiator in aqueous solution, in which the –OH group in C-2, C-3 and C-4 position on pyranose rings could be initiated by Cu(III). The branched and linear units were clearly distinguished by nuclear magnetic resonance (¹H NMR) to estimate the degree of branching (DB). When the ratio of Cu(III) to monomer fixed at 0.5:1, the DB value reached 0.32, which was higher than the product initiated by Ce(IV). Moreover, the inhibition activity of the products on amyloid fibrillation was investigated by using the hen egg-white lysozyme (HEWL) as a model based on the difference of the initiation sites. The results showed that the –OH groups in C-4 position might play an important role in this process.

Polymer-encapsulation of iron oxide clusters using macroRAFT block copolymers as stabilizers: tuning of the particle morphology and surface functionalization

We report the successful synthesis of superparamagnetic latex particles with a high fraction of magnetic materials and a fast magnetic response. Commercial fatty acid-modified iron oxide (IO) nanoparticles were first assembled into spherical clusters through an emulsification/solvent evaporation method. The resulting particles were stabilized with poly(2-dimethylaminoethyl methacrylate)-b-polystyrene (PDMAEMA-b-PS) amphiphilic block copolymers obtained by RAFT, and used as seeds in the emulsion copolymerization of styrene and divinylbenzene (DVB), used as cross-linking agent. The latter revealed to be key in preserving the integrity of the clusters during the emulsion polymerization reaction, and a minimum amount (i.e. 10 wt%) was necessary to obtain stable latexes composed of a core of densely packed IO nanoparticles surrounded by a thin polymer shell. DVB also had a strong influence on the particle morphology as the core-shell morphology of the composite particles could be tuned with either a smooth polymer shell or a raspberry-like surface by adjusting the DVB-to-monomer weight ratio and the feeding conditions. The amphiphilic macroRAFT not only provides colloidal stability to the magnetic latexes, but also offers a versatile platform for the design of composite particles with tailored surface properties by an appropriate choice of the hydrophilic block. Our strategy was thus successfully extended to poly(acrylic acid)-b-polystyrene (PAA-b-PS) copolymers, leading to PAA-stabilized composite particles. Both kinds of IO-encapsulated particles showed superparamagnetic properties (magnetizations at saturation of 35 and 31 emu g-1 for PDMAEMA and PAA systems, respectively), and could thus find interesting applications as magnetic carriers in the biological field due to their thermo- (for PDMAEMA) and pH- (for PDMAEMA and PAA) responsive properties.

Hyperbranched Zwitterionic Polymer-Functionalized Underwater Superoleophobic Microfiltration Membranes for Oil-in-Water Emulsion Separation

Inspired by mussel adhesion chemistry, a kind of hydrophilic poly(vinylidene fluoride) (PVDF) microfiltration membrane with underwater superoleophobicity was prepared using thiolated hyperbranched zwitterionic poly(sulfobetaine methacrylate) (HPS) as a nanoscale surface modifier. The HPS was first synthesized via reversible addition fragmentation chain transfer (RAFT) copolymerization and followed by sulfonation reaction and then coated onto polydopamine (PD) adhesive PVDF membranes via thiol-mediated Michael addition reaction. The successful and uniform coating of HPS onto the membrane surface was demonstrated by X-ray photoelectron spectroscopy and by using an energy dispersive X-ray detector. The surface micro-nano morphology and increased roughness of the PD/HPS-modified (M-PD/HPS) membrane were also investigated by using a field emission scanning electron microscope and an atomic force microscope. The M-PD/HPS membrane could be wetted completely by water, and the underwater oil contact angles were about 160°, indicating the M-PD/HPS membrane has excellent hydrophilicity and underwater superoleophobicity. Compared with the pure PVDF membrane, the M-PD/HPS membrane for hexane-in-water emulsion separation exhibited an enhanced water filtration flux of 10 707 L m^-2 h^-1 (0.1 MPa), and the oil rejection ratio was above 99.9%. Besides, the excellent antifouling ability and recyclable properties of the M-PD/HPS membranes would make them suitable for long-time use. Thus, the approach of mussel adhesion chemistry employing the RAFT-mediated nanosized hyperbranched zwitterionic polymers as postmodification reagents showed a good application prospect in purification of oily waste water and oil recovery.

Starlike Branched Polyacrylamides by RAFT Polymerization-Part I: Synthesis and Characterization

Starlike branched polyacrylamides (SB-PAMs) were synthesized using reversible addition-fragmentation chain transfer copolymerization of acrylamide (AM) and N,N'-methylenebis(acrylamide) (BisAM) in the presence of 3-(((benzylthio) carbonothioyl)thio)propanoic acid as a chain transfer agent, followed by chain extension with AM. The amount of incorporated BisAM in the core and the amount of AM during chain extension have been systematically varied. Core structures were achieved by incorporation of total monomer ratios [BisAM]/[AM] ranging from 0.010 to 0.143. The obtained macromolecular chain transfer agents had weight average molecular weights in the range of (2.2-7.8) × 103 Da and polydispersity indices between 1.2 and 15.1. Kinetic experiments were performed to investigate the extent of control of polymerization. Finally, the expansion of the core structures by chain-extension polymerization resulted in the successful preparation of high molecular weight SB-PAMs with apparent molecular weights ranging from 19 to 1250 kDa.

One-Pot Synthesis of Dual-Responsive Hyperbranched Polymeric Prodrugs Using an All-in-One Chain Transfer Monomer

Over the past decades, tremendous progress has been advanced in the preparation of hyperbranched polymers (HPs), especially for the one-pot synthesis of segmented HPs by using self-condensing vinyl polymerization based on controlled living radical polymerization techniques. However, the fabrication of hyperbranched polymeric prodrugs (HPPs) still requires multistep postpolymerization conjugations, which generally suffer from low and uncontrolled conjugation efficacy of drug molecules due to the steric hindrance, low yields because of multistep synthesis, and scale-up difficulties attributed to batch-to-batch variations. To further address these issues and provide a highly straightforward and robust strategy toward HPPs, we reported in this study the one-pot preparation of dual-responsive hyperbranched polymeric prodrugs (DRHPPs) using an all-in-one chain transfer monomer that integrates a drug molecule with both acidic pH- and reduction-sensitive links. The resulting DRHPPs with precisely regulated drug loading content and great therapeutic efficacy offered a highly promising platform for efficient anticancer drug delivery.

Synthesis of hypergrafted poly[4-(N,N-diphenylamino)methylstyrene] through tandem anionic-radical polymerization of radical-inimer

In this paper, we present a tandem anionic-radical approach for synthesizing hypergrafted polymers. We prepared 4-(N,N-diphenylamino)methylstyrene (DPAMS) as a new radical-based inimer. Linear PDPAMS was prepared through anionic polymerization. Hypergrafted PDPAMS was synthesized through the self-condensing vinyl polymerization of DPAMS with linear PDPAMS. The linear backbone of PDPAMS, which incorporated latent radical initiating sites, served as a ‘hyperlinker’ to link hyperbranched side chains. The molecular weights of hypergrafted polymers increased as the length of the linear backbone chain increased. The hypergrafted structure of the resulting polymer was confirmed using a conventional gel permeation chromatograph apparatus equipped with a multiangle light scattering detector, nuclear magnetic resonance, differential scanning calorimetry, and thermogravimetric analysis. This strategy can be applied to synthesize other complex architectures based on hyperbranched polymers by changing the structure of a polymer backbone through anionic polymerization.

Star-Shaped Thermoresponsive Polymers with Various Functional Groups for Cell Sheet Engineering

This study demonstrates the facile preparation of poly(N-isopropylacrylamide) (PNIPAM)-immobilized Petri dishes by drop-casting a star-shaped copolymer of hyperbranched polystyrene (HBPS) possessing PNIPAM arms (HBPS-g-PNIPAM) functionalized with polar groups. HBPS was synthesized via reversible addition-fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP), and HBPS polymers with different terminal structures were prepared by changing the monomer structure. HBPS-g-PNIPAM was synthesized by the grafting of PNIPAM from each terminal of HBPS. To tune the cell adhesion and detachment properties, polar functional groups such as carboxylic acid and dimethylamino groups were introduced to HBPS-g-PNIPAM. Based on surface characterization using scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements, the advantage of the hyperbranched structure for the PNIPAM immobilization was evident in terms of the uniformity, stability, and thermoresponsiveness. Successful cell sheet harvesting was demonstrated on dishes coated with HBPS-g-PNIPAM. In addition, the cell adhesion and detachment properties could be tuned by the introduction of polar functional groups.

Facile preparation of hyperbranched glycopolymers via an AB3* inimer promoted by a hydroxy/cerium(iv) redox process

The facile preparation of hyperbranched glycopolymers was performed without protecting group chemistry, where the methyl-6-O-methacryloyl-α-d-glucoside (6-O-MMAGlc) monomer was adopted as an AB₃*-type inimer.

Light- and pH-dually responsive dendrimer-star copolymer containing spiropyran groups: synthesis, self-assembly and controlled drug release

Dendrimer-star copolymer containing spiropyran groups could self-assemble into micelles and presented light- and pH-dually responsive properties.

Radiant star nanoparticle prodrugs for the treatment of intracellular alveolar infections

Radiant star nanoparticle prodrugs were synthesized in a two-step process by first homopolymerizing RAFT transmers followed by copolymerization from the hyperbranched polymer core.

Facile construction of a hyperbranched poly(acrylamide) bearing tetraphenylethene units: a novel fluorescence probe with a highly selective and sensitive response to Zn2+

Thermo-responsive hyperbranched copoly(bis(N,N-ethyl acrylamide)/(N,N-methylene bisacrylamide)) (HPEAM-MBA) was synthesized by using reversible addition–fragmentation chain-transfer polymerization (RAFT). Interestingly, the zinc ion (Zn²⁺) was found to have a crucial influence on the lowest critical solution temperature (LCST) of the thermo-responsive polymer. The tetraphenylethylene (TPE) unit was then introduced onto the backbone of the as-prepared thermo-responsive polymer, which endows a Zn²⁺-responsive “turn-off” effect on the fluorescence properties. The TPE-bearing polymer shows a highly specific response over other metal ions and the “turn-off” response can even be tracked as the concentration of Zn²⁺ reduces to 2 × 10⁻⁵ M. The decrement of fluorescence intensity was linearly dependent on the concentration of Zn²⁺ in the range of 4–18 μmol L⁻¹. The flexible, versatile and feasible approach, as well as the excellent detection performance, may generate a new type of Zn²⁺ probe without the tedious synthesis of the moiety bearing Zn²⁺ recognition units.

A novel fluorescent HPEAM-TPEAH, possessing a highly selective and sensitive response to Zn²⁺, was synthesized using RAFT.

Tuning thermoresponsive network materials through macromolecular architecture and dynamic thiol-Michael chemistry

Synthesis of precision polymers crosslinked with dynamic thiol-Michael adducts is developed, and the materials are characterized to determine structure–property relationships.

Nano-Star-Shaped Polymers for Drug Delivery Applications

With the advancement of polymer engineering, complex star-shaped polymer architectures can be synthesized with ease, bringing about a host of unique properties and applications. The polymer arms can be functionalized with different chemical groups to fine-tune the response behavior or be endowed with targeting ligands or stimuli responsive moieties to control its physicochemical behavior and self-organization in solution. Rheological properties of these solutions can be modulated, which also facilitates the control of the diffusion of the drug from these star-based nanocarriers. However, these star-shaped polymers designed for drug delivery are still in a very early stage of development. Due to the sheer diversity of macromolecules that can take on the star architectures and the various combinations of functional groups that can be cross-linked together, there remain many structure-property relationships which have yet to be fully established. This review aims to provide an introductory perspective on the basic synthetic methods of star-shaped polymers, the properties which can be controlled by the unique architecture, and also recent advances in drug delivery applications related to these star candidates.

RAFT polymerization to form stimuli-responsive polymers

Stimuli-responsive polymers respond to a variety of external stimuli, which include optical, electrical, thermal, mechanical, redox, pH, chemical, environmental and biological signals. This paper is concerned with the process of forming such polymers by RAFT polymerization.

From seleno-mediated radical polymerization to seleno-containing branched polymers and dynamic hydrogel

A protocol of introducing redox responsive Se–Se bond into well-defined hydrogel backbone.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Light and Temperature as Dual Stimuli Lead to Self-Assembly of Hyperbranched Azobenzene-Terminated Poly(N-isopropylacrylamide)

Hyperbranched poly(N-isopropylacrylamide)s (HBPNIPAMs) end-capped with different azobenzene chromophores (HBPNIPAM-Azo-OC₃H₇, HBPNIPAM-Azo-OCH₃, HBPNIPAM-Azo, and HBPNIPAM-Azo-COOH) were successfully synthesized by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using different azobenzene-functional initiators. All HBPNIPAMs showed a similar highly branched structure, similar content of azobenzene chromophores, and similar absolute weight/average molecular weight. The different azobenzene structures at the end of the HBPNIPAMs exhibited reversible trans-cis-trans isomerization behavior under alternating UV and Vis irradiation, which lowered the critical solution temperature (LCST) due to different self-assembling behaviors. The spherical aggregates of HBPNIPAM-Azo-OC₃H₇ and HBPNIPAM-Azo-OCH₃ containing hydrophobic para substituents either changed to bigger nanorods or increased in number, leading to a change in LCST of -2.0 and -1.0 °C, respectively, after UV irradiation. However, the unimolecular aggregates of HBPNIPAM-Azo were unchanged, while the unstable multimolecular particles of HBPNIPAM-Azo-COOH end-capped with strongly polar carboxyl groups partly dissociated to form a greater number of unimolecular aggregates and led to an LCST increase of 1.0 °C.

Matrices for combined delivery of proteins and synthetic molecules

With the increasing advancement of synergistic, multimodal approaches to influence the treatment of infectious and non-infectious diseases, we witness the development of enabling techniques merging necessary complexity with leaner designs and effectiveness. Systems- and polypharmacology ask for multi-potent drug combinations with many targets to engage with the biological system. These demand drug delivery designs for one single drug, dual drug release systems and multiple release matrices in which the macromolecular structure allows for higher solubilization, protection and sequential or combined release profiles. As a result, nano- and micromaterials have been evolved from mono- to dual drug carriers but are also an essential part to establish multimodality in polymeric matrices. Surface dynamics of particles creating interfaces between polymer chains and hydrogels inspired the development not only of biomedical adhesives but also of injectable hydrogels in which the nanoscale material is both, adhesive and delivery tool. These complex delivery systems are segmented into two delivery subunits, a polymer matrix and nanocarrier, to allow for an even higher tolerance of the incorporated drugs without adding further synthetic demands to the nanocarrier alone. The opportunities in these quite novel approaches for the delivery of small and biological therapeutics are remarkable and selected examples for applications in cancer and bone treatments are discussed.

Hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) via RAFT self-condensing vinyl polymerization

We report the first synthesis of hyperbranched poly(N-(2-hydroxypropyl) methacrylamide) (HB-PHPMA) using reversible addition–fragmentation chain transfer (RAFT) self-condensing vinyl polymerization (SCVP).

Hyperbranched polymers via RAFT self-condensing vinyl polymerization

RAFT-mediated self-condensing vinyl polymerization is a promising synthetic tool to create well-defined hyperbranched polymers.