Pendant Polymers Research Articles

Antioxidant Polymers with Phenolic Pendants for the Mitigation of Cellular Oxidative Stress.

Overproduction of reactive oxygen species (ROS) in cells is a major health concern as it may lead to various diseases through oxidative damage of biomolecules. Commonly used traditional small molecular antioxidants (polyphenols, carotenoids, vitamins, etc.) have inadequate efficacy in lowering excessive levels of ROS due to their poor aqueous solubility and bioavailability. In response to the widespread occurrence of antioxidant polyphenols in various biorenewable resources, we aimed to develop water-soluble antioxidant polymers with side chain phenolic pendants. Four different types of copolymers (P1-P4) containing phenyl rings with different numbers of hydroxy (-OH) substituents (0: phenylalanine, 1: tyrosyl, 2: catechol, or 3: gallol) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization with a desired molar mass (8500-10000 g/mol) and a narrow dispersity (Đ ≤ 1.3). After successful characterizations of P1-P4, their in vitro antioxidant properties were analyzed by different methods, including 2,2-diphenyl-1-picrylhydrazyl (DPPH•), 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS•+), 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl (TMB), and β-carotene (βC) assays. Our results revealed that the gallol pendant polymers can effectively scavenge ROS. Furthermore, electron paramagnetic resonance (EPR) spectroscopy with DPPH• also confirmed the radical quenching ability of the synthesized polymers. The gallol pendant polymers, at a well-tolerated concentration, could effectively penetrate the macrophage cells and restore the H2O2-induced ROS to the basal level. Overall, the present approach demonstrates the efficacy of water-soluble antioxidant polymers with gallol pendants toward the mitigation of cellular oxidative stress.

Crosslinking through acyl hydrazone formation by reacting water soluble polyurethanes derived from ketone diol comonomers and those containing hydrazide pendant groups

Fully water-based formulations are gaining traction with the sustainability initiative for various applications. In this regard, producing the components required for making these formulations by eliminating toxic reagents is highly desirable. Hydrazone formation is widely used as a non-hazardous curing process in coating applications. Generally, carbonyl compounds that are used in the hydrazone forming reaction are nearly exclusively derived from vinyl polymers. This article describes a facile process for making carbonyl group containing diols and keto group containing water-soluble polymers therefrom by step growth or condensation polymerization. A water-soluble polymeric hydrazide was prepared by DCC coupling reaction between hydrazine hydrate and a polyurethane bearing pendant carboxylic acid group. The aqueous solutions of keto group containing, and hydrazide pendant polymers were mixed and coated on glass slides. Subsequently, the acyl hydrazone formation was studied under static heating in a hot air oven and a dynamic condition provided by blowing air under ambient conditions with a hair dryer. The dynamic nature of the latter process more than compensated the absence of direct heating to induce drying and hydrazone formation sequentially as studied by FT-IR spectroscopy. The cured slides were stable to water and were sensitive to weakly acidic aqueous solutions (about pH 3) formed by dissolving citric acid in water. The keto group containing diols enabled the hydrazone formation in polymer pairs entirely derived from step growth polymerization. As step growth or condensation polymers potentially offer both degradability and recycling through the cleavage of labile bonds prevailing in the polymer backbone, these keto group containing diols are preferable alternatives to keto group containing vinyl monomers commonly used for making hydrazones.

Influence of Backbone on the Performance of Pendant Polymer Electrode Materials in Li-ion Batteries.

Pendant polymers are a promising class of electrode materials due to their synthetic simplicity, derivation from sustainable feedstocks, and potentially benign synthesis. These materials consist of a redox-active pendant tethered to a polymer backbone, which mitigates dissolution during electrode cycling. To date, an extensive number of pendant groups have been studied within the context of metal-ion batteries. However, the choice of the polymer backbone and its impact on the electrode performance have been relatively understudied. In this work, we use a postpolymerization modification approach to synthesize a series of viologen-bearing redox-active pendant polymers with similar molecular weights but three distinct chemical backbones, namely, polyacrylamide, polymethacrylamide, and polystyryl. By evaluating the polymers in lithium-ion batteries, we show that the polymer backbone has a significant influence on electrode performance and behavior. Specifically, the polymethacrylamide displays slower kinetics than the other two polymers, resulting in lower capacities, particularly at high cycling rates. Furthermore, the charge storage mechanism is dependent on the nature of the backbone: the polyacrylamide shows a significant capacitive contribution to charge storage, while the polystyryl does not. The difference in performance between the polymer electrode materials is ascribed to a difference in chain mobility and packing within the electrode films. Overall, this work shows that the fundamental properties of the polymer backbone are critical to the design of high-performance polymer electrodes.

Front Cover: Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self‐Assembly (ChemSusChem 23/2021)

The Front Cover shows how the supramolecular interaction between pendant polymers can play a role in controlling the electronic properties in perovskite-based electronics such as solar cells and photodetectors. More information can be found in the Full Paper by J. Lim, M.-S. Kim, W. Jang, et al.

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly.

Invited for this month's cover is the group of Jin Kuen Park and Dong Hwan Wang at two different universities in South Korea. The image shows how the supramolecular interaction between pendant polymers can play a role in controlling the electronic properties in perovskite-based electronics such as solar cells and photodetectors. The Full Paper itself is available at 10.1002/cssc.202101785.

Contrasting the Charge Carrier Mobility of Isotactic, Syndiotactic, and Atactic Poly((N-carbazolylethylthio)propyl methacrylate).

Isotactic nonconjugated pendant electroactive polymers (NCPEPs) have recently shown potential to achieve comparable charge carrier mobilities with conjugated polymers. Here we report the broader influence of tacticity in NCPEPs, using poly((N-carbazolylethylthio)propyl methacrylate) (PCzETPMA) as a model polymer. We utilized the thiol-ene reaction as an efficient postpolymerization functionalization method to achieve pendant polymers with high isotacticity and syndiotacticity. We found that a stereoregular isotactic polymer showed ∼100 times increased hole mobility (μh) as compared to both atactic and low molecular weight syndiotactic PCzETPMA, achieving μh of 2.19 × 10-4 cm2 V-1 s-1 after annealing at 120 °C. High molecular weight syndiotactic PCzETPMA gave ∼10 times higher μh than its atactic counterpart, comparable to isotactic PCzETPMA after annealing at 150 °C. Importantly, high molecular weight syndiotactic PCzETPMA showed a dramatic increase in μh to 1.82 × 10-3 cm2 V-1 s-1 when measured after annealing at 210 °C, which surpassed the well-known conjugated polymer poly(3-hexylthiophene) (P3HT) (μh = 4.51 × 10-4 cm2 V-1 s-1). MD simulations indicated short-range π-π stacked ordering in the case of stereoregular isotactic and syndiotactic polymers. This work is the first report of charge carrier mobilities in syndiotactic NCPEPs and demonstrates that the tacticity, annealing conditions, and molecular weight of NCPEPs can strongly affect μh.

Facile Synthesis of Tertiary Amine Pendant Polymers by Cu0-Mediated ATRP under Aqueous Conditions

Cu0-mediated atom transfer radical polymerization (ATRP) in aqueous media is extended to tertiary amine-pendant methacrylate polymers with poly([2-dimethylamino]ethyl methacrylate) (PDMAEMA) servin...

Versatile Pendant Polymer for Selective Charge Carrier Transport via Controlling the Supramolecular Self-Assembly.

Polyvinyl carbazole (P0)-based pendant polymers were synthesized by modifying carbazole motifs with pyrene derivatives (P1 and P4) to manipulate the bandgap and frontier orbital energy levels. To establish the electronic properties of pendant polymers according to structural differences, the polymers were utilized as additional hole transport layers in planar-type perovskite solar cells and organic photovoltaic cells. When P4 with thiophene-pyrene pendant was used as hole transport layer, all device parameters, except open-circuit voltage, were significantly improved in comparison with P0 and P1 (conjugated with t-butyl pyrene derivatives). Since P4 had more electrically conductive thiophene units than benzene units with fewer alkyl groups, the supramolecular assembly of P4 was found to be more favorable in electronic devices. Furthermore, devices with P4 demonstrated lower dark current than others, which could potentially be useful for charge carrier transport and sensitive photo detecting devices.

Potential for Disruption with Organic Magnesium-Ion Batteries

Bryony McAllister earned her BSc in Chemistry from the University of Victoria in 2015. She is currently an NSERC CGS-D doctoral student in the Seferos Lab in the Chemistry Department at the University of Toronto. Her current research focuses on the design of organic conjugated and pendant polymers for high-voltage supercapacitors and batteries. Luke Kyne obtained his HBSc in Chemistry and Psychology as a C. David Naylor Scholar at the University of Toronto in 2018. As an NSERC USRA and SOUSCC Award recipient, Luke has been investigating the applications of novel organic cathode materials in lithium- and magnesium-ion batteries as a member of the Seferos Lab. Tyler Schon received his BSc in chemistry from the University of Western Ontario in 2012 and completed his PhD at the University of Toronto in 2017, under the supervision of Prof. Seferos, where he developed novel organic polymers for energy storage devices. Tyler is currently CEO of Pliant Power Devices, a company he co-founded in 2017 commercializing sustainable battery technology. Dwight Seferos is a Professor of Chemistry, Chemical Engineering, and the Canada Research Chair in Polymer Nanotechnology at the University of Toronto. Seferos has authored or coauthored over 100 publications, holds numerous patents, and has been recognized by many national and international awards including the DuPont Young Professor Award, Alfred P. Sloan Research Fellowship, CSC Strem Chemical Award, and ACS Harry Gray Award.

Self-assembly of amphiphilic block pendant polymers as microphase separation materials and folded flower micelles

Herein, we created amphiphilic polymers bearing hydrophilic/hydrophobic block pendants as a new class of self-assembled materials for microphase separation in the solid state and folded flower micelles in water.

Converging the Hole Mobility of Poly(2-N-carbazoylethyl acrylate) with Conjugated Polymers by Tuning Isotacticity

Nonconjugated electroactive polymers (also known as pendant or side-chain electroactive polymers) promise several potential advantages relative to conjugated polymers including enhanced mechanical durability, greater stability and synthesis via living polymerization techniques. However, most previous examples suffer from low charge carrier mobility. Here, using poly(2-N-carbazoylethyl acrylate) (PCzEA) as a model polymer, we investigate the ability of side-chain tacticity to influence hole mobility. Specifically, we investigated polymers with dyad isotacticity (m) ranging from ∼45 to ∼95% synthesized by several methods including free radical polymerization and anionic polymerization. We found that the hole mobility (μh) measured via the space charge limited current (SCLC) technique increased proportionally to the increasing isotacticity from 2.11 × 10-6 cm2 V-1 s-1 (m = 45.5%) to 4.68 × 10-5 cm2 V-1 s-1 (m = 94.7%) in unannealed samples and that mobilities could be boosted as high as 2.74 × 10-4 cm2 V-1 s-1 (m = 94.7%) with thermal annealing, which rivaled the well-known conjugated polymer poly(3-hexylthiophene) (P3HT) (μh = 5.8 × 10-4 cm2 V-1 s-1). As such, we report here clear experimental evidence that control of side chain tacticity can enhance charge carrier mobility in nonconjugated pendant electroactive polymers, converging with mobilities typically only observed in conjugated polymers.

Solvents Effects on Film Morphologies and Memory Behavior of a Perylenediimide-Containing Pendent Polymer.

The large polydispersity index of functional pendant polymers has hindered their application in semiconductors. Herein, a novel pendant polymer with perylenediimide (PDI) in the side chains was successfully synthesized through ring-opening metathesis polymerization (ROMP) with a very low polydispersity index. The synthesized polymers were spin-coated on indium tin oxide (ITO) substrate by using a mixture of 1,2-dichlorobenzene (o-DCB) and methanol (MeOH) solvents. The surface morphologies and intermolecular π-π stacking of the fabricated film could be adjusted through tuning of the ratio of o-DCB and MeOH, and thus, the sandwich-structured device of ITO/polymer/aluminum exhibited different electrical behavior. The threshold voltages of the devices decreased as the MeOH content was increased from 0 to 30 % (v/v); however, the device changed from being unrewritable to rewritable if the MeOH content was increased to 40 %; a probable mechanism for this process is discussed. It is hoped that this new idea of synthesizing narrow polydispersity index pendant polymers, and the fabrication of high-quality films through the use of a mixture of solvents could allow high-performance memory devices to be prepared in the future.

Organocatalytic Synthesis and Evaluation of Polycarbonate Pendant Polymer:β-Cyclodextrin-Based Nucleic Acid Delivery Vectors

A family of mPEG-b-polycarbonate (mPEG-PC) diblock pendant polymers were synthesized from trimethylene carbonate and other cyclic carbonate monomers bearing hydrophobic guest ligands via organocatalytic ring-opening polymerization using 1,4,5-triazabicyclo[4.4.0]dec-5-ene catalyst or 1,8-diazabicyclo[5.4.0]undec-7-ene/thiourea cocatalyst. Diblock copolymers composed of a methoxypoly(ethylene oxide) (mPEG) block and a polycarbonate block containing either homopolymer or mixed polycarbonates (PC) were prepared by homopolymerization or copolymerization of the cyclic carbonate monomers in the presence of mPEG2000 or mPEG5000 initiator to give materials having a tunable pendant group density along the polycarbonate backbone. Polycarbonate blocks targeting the 2.4–10 kDa range were prepared with good molecular weight control and modest polydispersities (averaging ∼1.3). Complexation of plasmid DNA with β-cyclodextrin–polyethylenimine2.5 kDa produced nanoparticle cores that were then coated with the mPEG–PC dibl...

Synthesis, characterization, and cytotoxicity studies of novel pendant polymers: Amino acid β-cyclodextrin-conjugated poly(ε-lysine) derivatives

ABSTRACTA series of novel pendant polymers, composed of a poly(ε-lysine) (ε-PL) (w: 4,000 g mol−1) main chain and three kinds of amino acid β-cyclodextrin (CD) derivatives, were prepared by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide-assisted synthesis and characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray power diffraction, and scanning electron microscopy. Cytotoxicity and moisture absorption of the pendant polymers were also tested. Compared with ε-PL, all the pendant polymers exhibited lower moisture absorption and cytotoxicity. The synthesis method of the pendant polymers is simple, feasible, and has good practicability. We suggest these polymers have potential applications in many fields, especially in gene delivery vector and drug delivery systems.

Bio‐Derived Polymers for Sustainable Lithium‐Ion Batteries

Biologically derived organic molecules are a cost‐effective and environmentally benign alternative to the widely used metal‐based electrodes employed in current energy storage technologies. Here, the first bio‐derived pendant polymer cathode for lithium‐ion batteries is reported. The redox moiety is flavin and is derived from riboflavin (vitamin B2). A semi‐synthetic methodology is used to prepare the pendant polymer, which is composed of a poly(norbornene) backbone and pendant flavin units. This semi‐synthetic approach reduces the number of chemical transformations required to form this new functional material. Lithium‐ion batteries incorporating this polymer have a 125 mAh g−1 capacity and an ≈2.5 V operating potential. It is found that charge transport is greatly improved by forming hierarchical structures of the polymer with carbon black, and new insight into electrode degradation mechanisms is provided which should be applicable to polymer electrodes in general. This work provides a foundation for the use of bio‐derived pendant polymers in sustainable, high‐performance lithium‐ion batteries.

Conjugated fluorene-moiety-containing pendant polymers for the dispersion of single-wall carbon nanotubes: polymer wrapping abilities and electrical properties

We report a new strategy to disperse single-wall carbon nanotubes (SWNTs) via conjugated moiety-containing pendant polymers, poly(2-vinylpyridine)-co-poly(9,9-dihexyl-2-(4-vinylphenyl)-9H-fluorene) (P2VP-co-P(StFl)). The polymer composition ratio and molecular weight were varied to control the SWNT dispersion. The P(St-Fl) segments were adsorbed to the surface of the de-bundled SWNTs through π–π interaction, while the P2VP segments surrounded the outer surfaces of the SWNTs to enhance their solubility and stability. A low-voltage field-effect transistor (FET) was fabricated using a P(St-Fl)-wrapped SWNT network, SWNTs wrapped with P2VP79-co-P(St-Fl)347, and hafnium oxide as the active layer, gate electrode, and dielectric, respectively. The field-effect mobility of the fabricated device was as high as 0.82 cm2 V−1 s−1 on average, with an ON/OFF ratio over 104 under a −5 V bias. This study highlights the tailored wrapping power of pendant polymers, as well as the tunable electrical conducting/semiconducting properties of SWNTs for FET device applications. The wrapping abilities of comb-like polymers with pendant conjugated fluorine moieties and their tunable electrical properties of SWNTs were discussed. It is found that longer side-chain-conjugated fluorene segments in homopolymer (P(St-Fl)300, 7) can strongly bind to the SWNTs surfaces through π–π interaction and its copolymer (P2VP79-co-P(St-Fl)347, 5a) lead to predominant dispersion of SWNTs due to the flexibility of P2VP for further increasing the solubility. Thus, SWNTs wrapped by 5a after thermal annealing can be selected as a gate electrode, whereas the spin-coated SWNTs wrapped by 7 can be as a semiconductor for the FET channel, resulting in a mobility of 0.82 cm2 V−1s−1, a threshold voltage of 0.35 V and an ON/OFF ratio of 2.8 × 104.

Side‐Chain Amino‐Acid‐Derived Cationic Chiral Polymers by Controlled Radical Polymerization

There is an increased interest in incorporation of naturally occurring amino acid/peptide moieties into the synthetic polymeric chain. Because of functional group diversity in amino acids, it is possible to synthesize a large variety of well‐defined functional amino‐acid/peptide‐based optically active polymers with varied polymer length, composition, and architectures using available controlled/living polymerization techniques. The amino acid inclusion into the synthetic polymer chains may offer several advantages such as (a) functional group availability which not only results in improved hydrophilicity and possible interactions with proteins and genes but also facilitates further modification with bioactive molecules, (b) introduces chirality, and (c) makes room for noncovalent interactions to form hierarchical superstructures. From the long past, amino acids have been extensively incorporated in the main chain of biodegradable polymers, and their biological importance have been evaluated. Besides, various side‐chain amino‐acid/peptide‐bearing polymers have been synthesized and used for different purposes. In this article, utilization of different controlled/living polymerization methods to prepare various side‐chain amino acid/peptide pendant polymers will be discussed, mainly focusing on cationic chiral polymeric architectures and 3D gel networks by reversible addition–fragmentation chain transfer polymerization. image

Effect of Pendant Group on pDNA Delivery by Cationic-β-Cyclodextrin:Alkyl-PVA-PEG Pendant Polymer Complexes

We have previously shown that cationic-β-cyclodextrin:R-poly(vinyl alcohol)-poly(ethylene glycol) (CD+:R-PVA-PEG) pendant polymer host:guest complexes are safe and efficient vehicles for nucleic acid delivery, where R = benzylidene-linked adamantyl or cholesteryl esters. Herein, we report the synthesis and biological performance of a family of PVA-PEG pendant polymers whose pendant groups have a wide range of different affinities for the β-CD cavity. Cytotoxicity studies revealed that all of the cationic-β-CD:pendant polymer host:guest complexes have 100-1000-fold lower toxicity than branched polyethylenimine (bPEI), with pDNA transfection efficiencies that are comparable to bPEI and Lipofectamine 2000. Complexes formed with pDNA at N/P ratios greater than 5 produced particles with diameters in the 100-170 nm range and ζ-potentials of 15-35 mV. Gel shift and heparin challenge experiments showed that the complexes are most stable at N/P ≥ 10, with adamantyl- and noradamantyl-modified complexes displaying the best resistance toward heparin-induced decomplexation. Disassembly rates of fluoresceinated-pDNA:CD(+):R-PVA-PEG-rhodamine complexes within HeLa cells showed a modest dependence on host:guest binding constant, with adamantyl-, noradamantyl-, and dodecyl-based complexes showing the highest loss in FRET efficiency 9 h after cellular exposure. These findings suggest that the host:guest binding constant has a significant impact on the colloidal stability in the presence of serum and cellular uptake efficiency, whereas endosomal disassembly and transfection performance of cationic-β-CD:R-poly(vinyl alcohol)-poly(ethylene glycol) pendant polymer complexes appears to be controlled by the hydrolysis rates of the acetal grafts onto the PVA main chain.

α-amino acid pendant polymers as endosomal pH-responsive gene carriers

In order to prepare gene carriers responsive to an endosomal pH, amino groups of linear poly(allylamine) (PAA) or poly(L-lysine) (PLL) were coupled with a-carboxyl groups of α-amino acids (Gly, His, Lys, Arg, and Orn). Acid-base titration indicated that Lys-, Arg-, and Orn-pendant polymers had both strongly basic groups and endosomal pH-responsive α-amino groups. These polymers, like PAA and PLL, formed stable complexes with DNA. Lys-, Arg-, and Orn-pendant polymers were effective transfection reagents independent of the backbone polymers. The pH-responsive α-amino groups enhanced transfection activity as shown by the observation that acetylation of the α-amino group resulted in a considerable loss in transfection activity. These results strongly suggested a lysosomotropic activity of the α-amino groups. Among the α-amino acid-pendant polymers tested, the Orn-pendant polymer exhibited the highest transfection activity/toxicity index. Since PLL with α-amino acid-pendants is composed of naturally occurring amino acids, it is expected to be biodegradable, and these reagents have promise as gene carriers. Open image in new window

Band-gap tuning of pendant polymers for organic light-emitting devices and photovoltaic applications

The preparation of a series of novel polymers comprising pendant electro-active “push–pull” chromophores and their performance in solution-processed organic electronic devices is described. The design of the electro-active pendant chromophores was based on the well-known motif of cyano-substituted poly( p-phenylenevinylene). Optical band-gap engineering within this series of polymers was achieved by varying the conjugation length and the electron donor/acceptor functionalities of the pendant chromophores. The introduction of a cyanoimine group into the electro-active pendant module resulted in a marked narrowing of the optical band-gap compared with the other electro-active pendant chromophores investigated in this work. Bulk heterojunction solar cell devices comprising these polymers were prepared by solution processing blends of each polymer with [6,6]-phenyl-C 61-butyric acid methyl ester, and their performance was evaluated by measuring power conversion efficiencies. The best-performing solar cell in this series exhibited a power conversion efficiency of 0.29% and a maximum incident photon-to-current conversion efficiency of 22% and was produced using the polymer in which the electro-active chromophore comprised the cyanoimine group.