Exploring Self-Condensing Vinyl Polymerization of Inimers in Microemulsion To Regulate the Structures of Hyperbranched Polymers

Employing transfer-dominated branching radical telomerisation (TBRT) and atom transfer radical polymerisation (ATRP) to form complex polyester-polymethacrylate branched-linear star copolymer hybrids via orthogonal initiation

TBRT and ATRP are orthogonal initiation chemistries used in vinyl polymerisations. Here, we present the first combination of these techniques to readily create high molecular weight branched polyester macroinitiators capable of forming star copolymers from a range of methacrylate monomers.

Hydrophilic Poly(meth)acrylates by Controlled Radical Branching Polymerization: Hyperbranching and Fragmentation

Topology significantly impacts polymer properties and applications. Hyperbranched polymers (HBPs) synthesized via atom transfer radical polymerization (ATRP) using inimers typically exhibit broad molecular weight distributions and limited control over branching. Alternatively, copolymerization of inibramers (IB), such as α-chloro/bromo acrylates with vinyl monomers, yields HBPs with precise and uniform branching. Herein, we described the synthesis of hydrophilic HB polyacrylates in water by copolymerizing a water-soluble IB, oligo(ethylene oxide) methyl ether 2-bromoacrylate (OEOBA), with various hydrophilic acrylate comonomers. Visible-light-mediated controlled radical branching polymerization (CRBP) with dual catalysis using eosin Y (EY) and copper complexes resulted in HBPs with various molecular weights (M n = 38 000 to 170 000) and degrees of branching (2%-24%). Furthermore, the optimized conditions enabled the successful application of the OEOBA to synthesize linear-hyperbranched block copolymers and hyperbranched polymer protein hybrids (HB-PPH), demonstrating its potential to advance the synthesis of complex macromolecular architecture under environmentally benign conditions. Copolymerization of hydrophilic methacrylate monomer, oligo(ethylene oxide) methyl ether methacrylate (OEOMA500), and inibramer OEOBA was accompanied by fragmentation via β-carbon C-C bond scission and subsequent growth of polymer chains from the fragments. Furthermore, computational studies investigating the fragmentation depending on the IB and comonomer structure supported the experimental observations. This work expands the toolkit of water-soluble inibramers for CRBP and highlights the critical influence of the inibramer structure on reaction outcomes.

Preparation and Self-Assembly of pH-Responsive Hyperbranched Polymer Peptide Hybrid Materials

In recent years, the coupling of structurally and functionally controllable polymers with biologically active peptide materials to obtain polymer-peptide hybrids with excellent properties and biocompatibility has led to important research progress in the field of polymers. In this study, a pH-responsive hyperbranched polymer hPDPA was prepared by combining atom transfer radical polymerization (ATRP) with self-condensation vinyl polymerization (SCVP) using a three-component reaction of Passerini to obtain a monomeric initiator ABMA containing functional groups. The pH-responsive polymer peptide hybrids hPDPA/PArg/HA were obtained by using the molecular recognition of polyarginine (β-CD-PArg) peptide modified with β-cyclodextrin (β-CD) on the hyperbranched polymer, followed by the electrostatic adsorption of hyaluronic acid (HA). The two hybrid materials, h₁PDPA/PArg₁₂/HA and h₂PDPA/PArg₈/HA could self-assemble to form vesicles with narrow dispersion and nanoscale dimensions in phosphate-buffered (PB) at pH = 7.4. The assemblies exhibited low toxicity as drug carriers of β-lapachone (β-lapa), and the synergistic therapy based on ROS and NO generated by β-lapa had significant inhibitory effects on cancer cells.

Synthesis and Self-Assembly of Hyperbranched Multiarm Copolymer Lysozyme Conjugates Based on Light-Induced Metal-Free Atrp

In recent years, the coupling of structurally and functionally controllable polymers with biologically active protein materials to obtain polymer-protein conjugates with excellent overall properties and good biocompatibility has been important research in the field of polymers. In this study, the hyperbranched polymer hP(DEGMA-co-OEGMA) was first prepared by combining self-condensation vinyl polymerization (SCVP) with photo-induced metal-free atom transfer radical polymerization (ATRP), with 2-(2-bromo-2-methylpropanoyloxy) ethyl methacrylate (BMA) as inimer, and Di (ethylene glycol) methyl ether methacrylate (DEGMA) and (oligoethylene glycol) methacrylate (OEGMA, M_n = 300) as the copolymer monomer. Then, hP(DEGMA-co-OEGMA) was used as a macroinitiator to continue the polymerization of a segment of pyridyl disulfide ethyl methacrylate (DSMA) monomer to obtain the hyperbranched multiarm copolymers hP(DEGMA-co-OEGMA)-star-PDSMA. Finally, the lysozyme with sulfhydryl groups was affixed to the hyperbranched multiarm copolymers by the exchange reaction between sulfhydryl groups and disulfide bonds to obtain the copolymer protein conjugates hP(DEGMA-co-OEGMA)-star-PLZ. Three hyperbranched multiarm copolymers with relatively close molecular weights but different degrees of branching were prepared, and all three conjugates could self-assemble to form nanoscale vesicle assemblies with narrow dispersion. The biological activity and secondary structure of lysozyme on the assemblies remained essentially unchanged.

Toward Green Atom Transfer Radical Polymerization: Current Status and Future Challenges

Reversible-deactivation radical polymerizations (RDRPs) have revolutionized synthetic polymer chemistry. Nowadays, RDRPs facilitate design and preparation of materials with controlled architecture, composition, and functionality. Atom transfer radical polymerization (ATRP) has evolved beyond traditional polymer field, enabling synthesis of organic-inorganic hybrids, bioconjugates, advanced polymers for electronics, energy, and environmentally relevant polymeric materials for broad applications in various fields. This review focuses on the relation between ATRP technology and the 12 principles of green chemistry, which are paramount guidelines in sustainable research and implementation. The green features of ATRP are presented, discussing the environmental and/or health issues and the challenges that remain to be overcome. Key discoveries and recent developments in green ATRP are highlighted, while providing a perspective for future opportunities in this area.

Hyperbranched polymers as superior adsorbent for the treatment of dyes in water

The effective control on environmental pollutants is crucial for the proper management of diverse environmental systems (e.g., soil, water, and air). In this respect, the utility of various functional materials such as hyperbranched polymers (HPs) has been recognized due to their great potentil as adsorbent for the mitigation of numerous environmental pollutants. Here, we highlight the latest progress achieved in the design and construction of HPs with high adsorption potentials. We focus on adsorption mechanisms, functionalization methods, the role of functional groups in adsorption capacity, and the choice of HPs in adsorption of cationic and anionic dyes. Recent published reports are reviewed to quantify and qualify the removal efficiency of pollutants through adsorption. We also evaluate the adsorbing efficiency of the constructed HPs and compared their performance with other such systems. The utilization potential of new materials (magnetic, polar, and biological) is highlighted along with the methods needed for their preparation and/or modification (surface, end-group, and zwitterionic) for the construction of efficient adsorbing systems. Finally, the advantages and limitations of adsorbing systems are described along with the existing challenges to help establish guidelines for future research. This article is thus expected to offer new path and guidance for developing advanced HP-based adsorbents.

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...

Quantification of branching within high molecular weight polymers with polyester backbones formed by transfer-dominated branching radical telomerisation (TBRT)

New branched polymerisations offer previously inaccessible macromolecules and architectural understanding is important as it provides insight into the branching mechanism and enables the determination of structure–property relationships. Here we present a detailed inverse gated ¹³C NMR characterisation of materials derived from the very recently reported Transfer-dominated Branching Radical Telomerisation (TBRT) approach to quantify branching and provide an insight into cyclisation.

The characterisation and quantification of branching is key to understanding new complex macromolecules. Here we establish approaches to evaluate the unique and novel architectures formed by Transfer-dominated Branching Radical Telomerisation (TBRT).

Combining Hyperbranched and Linear Structures in Solid Polymer Electrolytes to Enhance Mechanical Properties and Room-Temperature Ion Transport

Polyethylene oxide (PEO)-based polymers are commonly studied for use as a solid polymer electrolyte for rechargeable Li-ion batteries; however, simultaneously achieving sufficient mechanical integrity and ionic conductivity has been a challenge. To address this problem, a customized polymer architecture is demonstrated wherein PEO bottle-brush arms are hyperbranched into a star architecture and then functionalized with end-grafted, linear PEO chains. The hierarchical architecture is designed to minimize crystallinity and therefore enhance ion transport via hyperbranching, while simultaneously addressing the need for mechanical integrity via the grafting of long, PEO chains (M_n = 10,000). The polymers are doped with lithium bis(trifluoromethane) sulfonimide (LiTFSI), creating hierarchically hyperbranched (HB) solid polymer electrolytes. Compared to electrolytes prepared with linear PEO of equivalent molecular weight, the HB PEO electrolytes increase the room temperature ionic conductivity from ∼2.5 × 10^–6 to 2.5 × 10⁻⁵ S/cm. The conductivity increases by an additional 50% by increasing the block length of the linear PEO in the bottle brush arms from M_n = 1,000 to 2,000. The mechanical properties are improved by end-grafting linear PEO (M_n = 10,000) onto the terminal groups of the HB PEO bottle-brush. Specifically, the Young’s modulus increases by two orders of magnitude to a level comparable to commercial PEO films, while only reducing the conductivity by 50% below the HB electrolyte without grafted PEO. This study addresses the trade-off between ion conductivity and mechanical properties, and shows that while significant improvements can be made to the mechanical properties with hierarchical grafting of long, linear chains, only modest gains are made in the room temperature conductivity.

Hyperbranched Bisphosphonate-Functional Polymers via Self-Condensing Vinyl Polymerization and Postpolymerization Multicomponent Reactions

The synthesis of hyperbranched aminobisphosphonic acid polymers via reversible addition-fragmentation chain transfer (RAFT) self-condensing vinyl polymerization is reported. A novel acrylamide-functional chain transfer monomer is synthesized and characterized by ¹ H and ¹³ C NMR spectroscopy, elemental analysis, and mass spectrometry. The monomer is subsequently copolymerized with an acrylamide monomer bearing a pendent amine group to create hyperbranched amine-functional polymers with degrees of branching dictated by changing the reaction stoichiometry. The aminobisphosphonate functional group is introduced via a 3-component Kabachnik-Fields reaction. An alternate functionalization of the amine polymers to create acid-degradable imine hydrogels is also employed. This work demonstrates the application of multicomponent reactions to RAFT-derived hyperbranched polymers and provides a new route to previously inaccessible polymers.

Influence of the Architecture of Soft Polymer-Functionalized Polymer Nanoparticles on Their Dynamics in Suspension

The behavior of nanogels in suspension can be dramatically affected by the grafting of a canopy of end-tethered polymer chains. The architecture of the interfacial layer, defined by the grafting density and length of the polymer chains, is a crucial parameter in defining the conformation and influencing the dynamics of the grafted chains. However, the influence of this architecture when the core substrate is itself soft and mobile is complex; the dynamics of the core influences the dynamics of the tethered chains, and, conversely, the dynamics of the tethered chains can influence the dynamics of the core. Here, poly(styrene) (PS) particles were functionalized with poly(methyl acrylate) (PMA) chains and swollen in a common solvent. NMR relaxation reveals that the confinement influences the mobility of the grafted chain more prominently for densely grafted short chains. The correlation time associated with the relaxation of the PMA increased by more than 20% when the grafting density increased for short chains, but for less than 10% for long chains. This phenomenon is likely due to the steric hindrance created by the close proximity to the rigid core and of the neighboring chains. More interestingly, a thick layer of a densely grafted PMA canopy efficiently increases the local mobility of the PS cores, with a reduction of the correlation time of more than 30%. These results suggest an interplay between the dynamics of the core and the dynamics of the canopy.

Blocking ACAT-1 Activity for Tumor Therapy with Fluorescent Hyperstar Polymer-Encapsulated Avasimible

Targeting the distinct cholesterol metabolism of tumor cells is proposed as a novel way to treat tumors. Blocking acyl-CoA cholesterol acyltransferase-1 (ACAT-1) by the inhibitor avasimible (Ava), which elevates intracellular free cholesterol levels, is shown to effectively induce apoptosis. However, Ava faces disadvantages of poor water solubility, a short half-life, and no capability for fluorescence detection, which have greatly limited its application. Herein, a fluorescent hyperstar polymer (FHSP) is developed to encapsulate Ava to improve its ability to inhibit HeLa cells and K562 cells. The results of this study show that the obtained Ava-FHSP micelles possess a high drug loading capacity of 22.7% and bright green fluorescence. Ava and Ava-FHSP are cytotoxic to both HeLa and K562 cells and cause reductions in cell size, nuclear lysis, and chromatin condensation and hindered proliferation of both cell types by causing S phase cell cycle arrest. Further mechanistic analysis indicates that Ava-FHSP reduces the protein and messenger RNA expression of ACAT-1 and significantly increases intracellular free cholesterol levels, which can increase endoplasmic reticulum stress and finally cause cell apoptosis. All these results suggest that this fluorescent hyperstar polymer represents a potential therapeutic tumor strategy by changing the cholesterol metabolism of tumor cells.

Preparation of hyperbranched polymers by oxa-Michael addition polymerization

Hyperbranched polymers with high molecular weights were synthesized by t-BuP₂-catalyzed oxa-Michael addition polymerization of trifunctional hydroxyl and diacrylate monomers.

Expanding the monomer scope of linear and branched vinyl polymerisations via copper-catalysed reversible-deactivation radical polymerisation of hydrophobic methacrylates using anhydrous alcohol solvents

The use of anhydrous alcohols for Cu-catalysed reversible-deactivation radical polymerisation of a wide range of hydrophobic methacrylates has been explored in detail.

Photo-controlled release of metal ions using triazoline-containing amphiphilic copolymers

Photo-controlled release of metal ions can be achieved by denitrogenation of triazoline from the micelles of amphiphilic copolymer, and has potential applications for biomedicines.

Cationic Hyperbranched Polymers with Biocompatible Shells for siRNA Delivery

Cationic hyperbranched polymers (HBP) were prepared by self-condensing vinyl polymerization of an atom transfer radical polymerization (ATRP) inimer containing a quaternary ammonium group. Two types of biocompatible shells, poly(oligoethylene glycol) methacrylate (polyOEGMA) and poly(2-(methylsulfinyl) ethyl methacrylate) (polyDMSO), were grafted respectively from HBP core to form core-shell structures with low molecular weight dispersity and high biocompatibility, polyOEGMA-HBP and polyDMSO-HBP. Both of the structures showed low cytotoxicity and good siRNA complexing ability. The efficacy of gene silencing against Runt-related transcription factor 2 ( Runx2) expression and the long-term assessment of mineralized nodule formation in osteoblast cultures were evaluated. The biocompatible core-shell structures were crucial to minimizing undesired cytotoxicity and nonspecific gene suppression. polyDMSO-HBP showed higher efficacy of forming polyplexes than polyOEGMA-HBP due to shell with lower steric hindrance. Overall, the gene silencing efficiency of both core-shell structures was comparable to commercial agent Lipofectamine, indicating long-term potential for gene silencing to treat heterotopic ossification (HO).

Hyperbranched Glycopolymers of 2-(α-d-Mannopyranose) Ethyl Methacrylate and N,N'-Methylenebisacrylamide: Synthesis, Characterization and Multivalent Recognitions with Concanavalin A

A series of novel hyperbranched poly[2-(α-d-mannopyranosyloxy) ethyl methacrylate-co-N,N'-methylenebisacrylamide] (HPManEMA-co-MBA) are synthesized via a reversible addition fragmentation polymerization (RAFT). The dosage ratios of linear and branch units are tuned to obtain different degree of branching (DB) in hyperbranched glycopolymers. The DB values are calculated according to the content of nitrogen, which are facilely determined by elemental analysis. The lectin-binding properties of HPManEMA-co-MBA to concanavalin A (ConA) are examined using a turbidimetric assay. The influence of defined DB value and molecular weight of HPManEMA-co-MBA on the clustering rate is studied. Notably, HPManEMA-co-MBAs display a low cytotoxicity in the MTT assay, thus are potential candidates for biomedical applications.

Synthesis and characterisation of highly branched polyisoprene: exploiting the “Strathclyde route” in anionic polymerisation

This work aimed at developing a synthetic route towards highly branched poly(isoprene) from commercially available raw materials, in good yield and devoid of microgelation, i.e., to prepare a completely soluble polymer via the versatile technique anionic polymerisation. The polymerisations were conducted under high vacuum conditions using sec-butyllithium as initiator at 50 °C in toluene. Toluene served both as a solvent and as a chain-transfer agent. The polar modifier used was tetramethylethylenediamine (TMEDA), and a commercial mixture of divinylbenzene (DVB) was employed as the branching agent for the “living” poly(isoprenyl)lithium anions. The nature of the reaction was studied on the TMEDA/Li ratio as well as the DVB/Li ratio. The obtained branched polymers were characterised by triple detection size exclusion chromatography (SEC), proton nuclear magnetic resonance spectroscopy (¹H NMR), differential scanning calorimetry (DSC) and melt rheology. Broad molecular weight distributions have been obtained for the highly branched polymer products. ¹H NMR spectroscopy reveals the dominance of 3,4-polyisoprene microstructure. It was found that the complex viscosities and dynamic moduli of the branched samples were much lower compared to their linear counterparts. The results conform with earlier findings by the “Strathclyde team” for radical polymerisation systems. This methodology has the potential of providing soluble branched vinyl polymers at low cost using the readily available raw materials.

Copolymerisation of isoprene and divinylbenzene was achieved in toluene via anionic chain transfer polymerization to yield highly branched polymers with good solution and rheological properties.

Development of Excipient-Free Freeze-Dryable Unimolecular Hyperstar Polymers for Efficient siRNA Silencing

We designed a unimolecular hyperstar polymer for efficient small interfering RNA (siRNA) delivery that can be processed under repeated lyophilization and reconstitution without the need of any excipient. The hyperstar polymer contains a biodegradable hyperbranched core and is bound to siRNA through its thousands of cationic arms that radiate from its core. The siRNA/hyperstar complexes showed siRNA transfection efficiency that was superior to that of Lipofectamine2000 in regard to the gene for human Cu, Zn superoxide dismutase 1 (SOD1), whose mutation causes familial amyotrophic lateral sclerosis. More importantly, hyperstar polymers as unimolecular containers minimized the multipolymer cross-interaction during lyophilization, and this maintained the uniquely high transfection efficiency of the siRNA/hyperstar complexes after repeated freeze-drying and reconstitution without the conventional need for excipient.

Cationic branched polymers for cellular delivery of negatively charged cargo

Receptor-independent cellular uptake of small molecule therapeutics is limited by their physical interaction with the negatively charged surface of cellular membranes. Passive diffusion through the hydrophobic membrane bilayer follows this process. Unless specific carriers exist in the biological membrane, such interactions limit therapeutics to those that are hydrophobic with modest positive charge at physiological pH. Small negatively charged molecules are therefore not efficient as therapeutics. To enable delivery of such molecules into eukaryotic cells, cationic branched polymers with tetraalkylammonium pendant groups were synthesized by copolymerization of a functional monomer (glycidyl methacrylate) with degradable and non-degradable divinyl crosslinkers in the presence of an efficient chain transfer agent, CBr4, followed by reaction of the multiple pendant epoxide groups and most of the alkyl bromide chain ends with amines. Cationic branched polymers with covalently attached fluorescent labels entered human cancerous and non-cancerous cells. The non-labeled analogues were able to carry anionic cargo (carboxyfluorescein) into the cells, while no uptake was observed in the absence of the cationic carriers. Most of the polymers were not significantly toxic at the concentrations used. This pilot study showed that cellular uptake of anionic small molecules can be promoted even in the absence of natural uptake mechanisms.

Preparation of hyperstar polymers with encapsulated Au25(SR)18 clusters as recyclable catalysts for nitrophenol reduction

A robust approach is developed to prepare hyperstar polymer-Au₂₅(SR)₁₈ nanocomposites for catalysis. The synthesis started with atom transfer radical copolymerization of an inimer with a cyclic disulfide-containing methacrylate monomer in a microemulsion to produce hyperbranched copolymers with high molar mass, low polydispersity, and a vital fraction of dangling disulfide groups. The core-shell structured hyperstar polymers were then prepared using hyperbranched copolymers as macroinitiators to polymerize oligo(ethylene glycol) methyl ether methacrylate (M_n = 500) and grow the radiating arms. The hyperstar polymers with disulfide groups were proved to efficiently encapsulate Au₂₅(SR)₁₈ nanoclusters through ligand exchange without destroying the fine structure of the Au₂₅(SR)₁₈ clusters. The obtained hyperstar-Au₂₅(SR)₁₈ nanocomposites showed great stability with no size change after a three-month shelf storage. They were used as efficient catalysts for the catalytic reduction of 4-nitrophenol by NaBH₄, showing convenient recovery and reuse without losing catalytic efficiency.

Effect of Linear-Hyperbranched Amphiphilic Phosphate Esters on Collagen Fibers

The surfactants of the linear-hyperbranched phosphate esters (PAMAM_Gn-3-Ps) have been constructed through random multibranching esterification of lauroyl chloride and phosphate ester as a branching agent. Subsequently, a series of surfactant products were obtained. Benefiting from the amphiphilic structure with the hydrophilic core and many hydrophobic tails, PAMAM_Gn-3-Ps were able to self-assemble into nanomicelles in aqueous media. Importantly, the polymers show low critical micelle concentrations (CMCs) and small particle sizes. Here, PAMAM_G1-3-P was applied in the collagen fibers of leather to improve the fibers' distance and mechanical property of collagen fibers. Additionally, the polymers display significant flexibility, which could replace ordinary fatliquor in the future. The result provides a new application of using linear-hyperbranched amphiphilic phosphate esters into traditional leather materials to enhance the performance of collagen fibers.

Radical polymerization in the presence of a peroxide monomer: an approach to branched vinyl polymers

In this paper, we report radical polymerization in the presence of a peroxide monomer for the preparation of branched vinyl polymers.

Preparation of water-soluble hyperbranched polymers with tunable thermosensitivity using chain-growth CuAAC copolymerization

Thermoresponsive hyperbranched polymers with dangling oligo(ethylene oxide) chain on every monomer unit were constructed using the chain-growth copper-catalyzed azide–alkyne cycloaddition (CuAAC) copolymerization of two AB₂-F monomers.

Synthesis of acid-degradable hyperbranched polymers by chain-growth CuAAC polymerization of an AB3 monomer

The first synthesis of acid-degradable hyperbranched polymers using chain-growth CuAAC click polymerization of an AB₃ monomer.

Formation of long sub-chain hyperbranched poly(methyl methacrylate) based on inhibited self-cyclization of seesaw macromonomers

Well-defined hyperbranched PMMA almost without self-cyclization was obtained through a click reaction, facilitated by a high concentration, good solvent and disubstituted chain ends.

Synthesis of well-defined core–shell nanoparticles based on bifunctional poly(2-oxazoline) macromonomer surfactants and a microemulsion polymerization process

Surface-functional nanoparticles have been fabricated by utilizing bifunctional poly(2-oxazoline) macromonomers as surfactants in a microemulsion process.

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.