Random Copolymers Research Articles

Toughening mechanism of α/β core-shell structure for high toughness polypropylene random copolymer

Weak interfaces can impede crack propagation in rigid natural materials containing small amounts of organic compounds. Inspired from this, we start from the core-shell structured isotactic propylene (iPP)/polypropylene random copolymers (PPR) homocomposites and construct serval kinds of interfaces to study the toughening mechanisms by applying the crystallization epitaxies of PPR on iPP. Through molecular chain diffusion and crystallization epitaxy, derived models from microscopic core-shell structured crystals in the homocomposites to macroscopic layer-by-layer assemblies with different interfaces are established to magnify the role that each layer plays during crack initiation and propagation. As a result, the ductile β-PP interface can decrease crack tip strength so that a further step of crack initiation is triggered in the composite laminates with a fold of fracture energy consumption compared to the laminates with weak or rigid interfaces. At last, we come back to the core-shell structured homocomposites and toughen them with an improve in impact toughness from ∼10.8 to ∼18.2 kJ/m2 by manipulating the content of ductile interfaces. This work provides a novel research routine and a new toughening mechanism toward the toughening of PP and can be extended to study the fracture mechanisms of other toughening systems with core-shell structures.

Preparation of acrylate-cationic monomer block copolymers by RAFT and their flotation oil removal properties

With the development of oilfields, the liquid volume of oily wastewater gets larger. Thus, more efficient flotation agents must be developed. In this regard, cationic polyacrylates with amphiphilic structures are potentially efficient flotation agents. Many studies have explored the effect of monomer type on flotation performance. However, there is a lack of investigations on the effect of block sequences on flotation performance. In this paper, acrylates (including methyl acrylate (MA) and ethyl acrylate (EA)) and cationic monomers (including acryloxyethyl trimethyl ammonium chloride (DAC), methylacryloxyethyl trimethyl ammonium chloride (DMC) and acryloxyethyl benzyl dimethyl ammonium chloride (DBC)) were used as raw materials, random, diblock and triblock copolymers were prepared through free radical polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The effect of the copolymer sequence on flotation performance was studied, and triblock copolymer P(DBC-b-MA-b-DBC) had better flotation performance than those of other copolymers. The synthesis conditions of P(DBC-b-MA-b-DBC) were successively optimized using the single-factor and response surface methods, and the optimal synthesis conditions were obtained as follows: monomer concentration of 51 wt%, the first section m(DBC): the second section m(MA): the third section m(DBC) = 1.5:1:1.5, initiator concentration of 0.28 wt%, reaction time of each section of 2 h, and reaction temperature of 73 °C. Under flotation temperature of 25 °C, P(DBC-b-MA-b-DBC) concentration of 70 mg/L, aeration flow rate of 2.0 L/min and flotation time of 10 min, the oil removal of oily wastewater with initial oil content of 822 mg/L reached 96.5 %. The results of the study can provide reference for the research and development of oily wastewater treatment agents.

The Crystallization Morphology and Conformational Changes of Polypropylene Random Copolymer Induced by a Novel β-Nucleating Agent.

The crystal morphology and conformational changes during crystallization of a polypropylene random copolymer (PPR) are the basis for understanding its crystallization process. In this work, novel rare-earth β-nucleating agent WBN-28 was directly added into PPR to induce β-crystallization. The results of differential scanning calorimetry (DSC) showed that it has an excellent β-crystal-induced effect. The β-crystal content could surpass 85%, calculated from wide-angle X-ray diffraction (WAXD) data. The morphology of the β-crystal and α-crystal was intuitively observed via a polarizing optical microscope (POM). The β-crystallites were interconnected to naturally develop plate-like crystalline regions possessing a certain size, and the α-crystallites with sufficient thicknesses possessed a cross-hatched phenomenon. The bundle-like supramolecular structure of the β-crystal induced by WBN-28 was further observed via a scanning electron microscope (SEM). The conformational changes in the crystallization process of PPR were resolved via high-resolution infrared spectroscopy to understand its β-crystallization in depth. The conformational changes during the crystallization of PPR were found to be different from those of the isotactic polypropylene homopolymer (PPH); they had their own characteristics. This will provide guidance for understanding the β-crystallization of PPR in depth.

Improved thermoelectric properties by copolymerization of conducting with insulating monomers on carbon nanotubes

In the present work, development of carbon nanotube (CNT)/poly(conducting-co-insulating monomer) structures was proposed to improve the thermoelectric (TE) performance in CNT/polyaniline (PANI) composites. To check the validity of this idea, we prepared multiwalled carbon nanotube (MWNT)/poly(aniline-co-acrylonitrile) composites by in-situ inverted emulsion copolymerization, and applied secondary doping with camphorsulfonic acid in m-cresol medium prior to the investigation of TE properties. The samples were characterized by FT-IR, UV–Vis, 1H NMR, DSC, GPC, CHNS elemental analysis, intrinsic viscosity, SEM, XRD, electrical resistance, Seebeck coefficient, thickness, and Hall measurements. We report that nitrile groups were hydrolyzed during the polymerization reactions to provide a polymer structure exhibiting aniline, acrylamide, acrylic acid, and glutarimide groups. Further, the poly(aniline-co-acrylonitrile) that prepared in the present work were random copolymers. Importantly, we found that 30 % MWNT/70 % poly(90ANI-co-10AN) composite exhibited a 63 % higher power factor (PF) of 5.48 μW/mK2 (σ: 225 S/cm, S: 15.6 μV/K) at 35 °C than that of 30 % MWNT/70 % PANI, which exhibited a PF of about 3.37 μW/mK2 (σ: 238 S/cm, S: 11.9 μV/K). This was ascribed to the decrease of carrier concentration together with the increase of carrier mobility in the 30 % MWNT/70 % poly(90ANI-co-10AN) composite as compared to the 30 % MWNT/70 % PANI.

Supra-biological performance of immobilized enzymes enabled by chaperone-like specific non-covalent interactions

Designing complex synthetic materials for enzyme immobilization could unlock the utility of biocatalysis in extreme environments. Inspired by biology, we investigate the use of random copolymer brushes as dynamic immobilization supports that enable supra-biological catalytic performance of immobilized enzymes. This is demonstrated by immobilizing Bacillus subtilis Lipase A on brushes doped with aromatic moieties, which can interact with the lipase through multiple non-covalent interactions. Incorporation of aromatic groups leads to a 50 °C increase in the optimal temperature of lipase, as well as a 50-fold enhancement in enzyme activity. Single-molecule FRET studies reveal that these supports act as biomimetic chaperones by promoting enzyme refolding and stabilizing the enzyme’s folded and catalytically active state. This effect is diminished when aromatic residues are mutated out, suggesting the importance of π-stacking and π-cation interactions for stabilization. Our results underscore how unexplored enzyme-support interactions may enable uncharted opportunities for using enzymes in industrial biotransformations.

Phosphorus-containing stereocontrolled polyhydroxyalkanoates by yttrium-mediated ring-opening copolymerization of β-lactones

Poly(3-hydroxybutyrate) (PHB) polymers functionalized with pendent diphenyl-phosphinate moieties were prepared by the simultaneous ring-opening copolymerization (ROCOP) of racemic or enantiopure β-butyrolactone (rac- or (S)-BPLMe, respectively) with racemic-(4-oxooxetan-2-yl)methyl diphenylphosphinate (rac-BPLOP). The reactions were mediated by yttrium catalysts which tunable ancillary structure enabled preparing copolymers containing syndio-enriched (Pr up to 0.84; Pr is the probability of racemic linkage), atactic (Pr ∼ 0.50) and highly isotactic (Pr < 0.06) poly(BPLMe) (P(BPLMe), aka PHB for polyhydroxybutyrate) segments, starting from rac-BPLMe or (S)-BPLMe, respectively, as assessed by detailed NMR analyses of the copolymer samples. The amount of BPLOP incorporated within the P[(BPLMe)x-co-(BPLOP)y] samples were in line with the initial comonomer loadings (1.8–8.1 mol% vs. 2–10 mol%). The ROCOP was rather well-controlled affording linear α-isopropoxy, ω-crotonyl telechelic and cyclic random copolymers with Mn,NMR up to 15,000 g.mol−1 and ÐM = 1.34–1.95. Detailed MALDI and high-resolution ESI mass spectrometric analyses evidenced the formation of three major series of macromolecules, namely the cyclic one and two linear ones end-capped with an α-isoproxy and either an ω-hydroxy or a ω-crotonate groups; for each of these series, the populations containing y = 0, 1 or 2 BPLOP repeating units were unambiguously distinguished. The thermal characteristics of the P[(BPLMe)x-co-(BPLOP)y] copolymers were investigated by DSC and TGA, revealing in comparison to those of the parent PHB homopolymers, tunable features as a function of their molar mass, tacticity and BPLOP content.

Nanogel-type nano-objects from a random polyelectrolyte through intermolecular cross-linking

Polyelectrolyte nanogel-like nano-objects were synthesized from poly((2-dimethylamino) ethyl methacrylate-co-oligoethylene glycol methacrylate), P(DMAEMA-co-OEGMA), random copolymers through covalent cross-linking with the hydrophobic 1,12-dibromododecane difunctional quaternizing agent, with varying degrees of cross-linking, corresponding to different dimethylamino group molar conversions to quaternized, permanently cationic amino groups. Physicochemical characterization, employing dynamic and electrophoretic light scattering (DLS, ELS), along with fluorescence spectroscopy (FS) measurements under various solution conditions elucidated distinct self-assembled structures of the formed polymer networks, most probably due to the utilization of the hydrophilic random copolymers as precursor macromolecules. The nanogels demonstrated pH responsiveness and temperature sensitivity, advantageous for applications requiring controlled release or environmental adaptability, while the stability under high ionic strength conditions indicated their resilience in complex physiological environments and varying salinities. Furthermore, Nanogel 2, displaying a balanced response to environmental factors, was successfully complexed with protein ovalbumin (OVA). The produced OVA/Nanogel 2 complexes maintained their size under high salt concentrations and sustained colloidal stability over time, even under ultrasound exposure. Further characterization through Cryo-TEM and ATR-FTIR spectroscopy highlighted the efficient complexation of OVA, revealing varying co-assembled structures, including irregular nano-objects consisting of thread-like structures and sphere-like morphologies comprised of branched-like internal structures, dependent on the protein concentration. We expect that such hybrid nanostructures may be promising for enzyme immobilization and as vaccine-delivering vehicles with special morphologies.

Linearly-Changed Thermal Behavior and Depressed Brill Transition in Long-Chain Polyamides Substituted by Methyl Side Groups.

Side substitution is an effective way of functionalizing and modifying the properties of polyamides. Meanwhile, side substitution would significantly influence the crystallization kinetics and polymorphic phase transition of polyamides, which, however, has not been well elucidated. Herein, we synthesized the side-substituted long-chain polyamides with various content of methyl pendent groups and investigated their crystallization and phase transition behaviors. We find that the thermal parameters of side-substituted polyamides vary linearly with the side group content, analogous to the isomorphic crystallization of random copolymers. All the solution-crystallized polyamides experience the α-γ Brill transition during heating, with the Brill transition temperature linearly decreasing as the side group content increases. Intriguingly, the γ-α transition of polyamides during cooling is suppressed with the presence of side methyl groups due to the difficulty in H-bond reorganization and gauche-trans conformational changes. This work has demonstrated the critical role of side substitution in the polymorphic crystallization and phase transition of long-chain polyamides.

Terpolymer Containing a meta-Octyloxy-phenyl-Modified Dithieno[3,2-f:2',3'-h]quinoxaline Unit Enabling Efficient Organic Solar Cells.

With the rapid development of small-molecule electron acceptors, polymer electron donors are becoming more important than ever in organic photovoltaics, and there is still room for the currently available high-performance polymer donors. To further develop polymer donors with finely tunable structures to achieve better photovoltaic performances, random ternary copolymerization is a useful technique. Herein, by incorporating a new electron-withdrawing segment 2,3-bis(3-octyloxyphenyl)dithieno[3,2-f:2',3'-h]quinoxaline derivative (C12T-TQ) to PM6, a series of terpolymers were synthesized. It is worth noting that the introduction of the C12T-TQ unit can deepen the highest occupied molecular orbital energy levels of the resultant polymers. In addition, the polymer Z6 with a 10% C12T-TQ ratio possesses the highest film absorption coefficient (9.86 × 104 cm-1) among the four polymers. When blended with Y6, it exhibited superior miscibility and mutual crystallinity enhancement between Z6 and Y6, suppressed recombination, better exciton separation and charge collection characteristics, and faster hole transfer in the D-A interface. Consequently, the device of Z6:Y6 successfully achieved enhanced photovoltaic parameters and yielded an efficiency of 17.01%, higher than the 16.18% of the PM6:Y6 device, demonstrating the effectiveness of the meta-octyloxy-phenyl-modified dithieno[3,2-f:2',3'-h]quinoxaline moiety to build promising terpolymer donors for high-performance organic solar cells.

Effect of Repeat Unit’s Composition Ratio on the Properties of a Random Copolymer: A Molecular Dynamics Simulation Study

For thermosetting resins the degree of cross-linking plays a crucial role in the dielectric properties of the resin. In our previous works we confirmed this by simulating the relationship between the dielectric properties of poly(2-(4-benzocyclobutenyl)-divinylbenzene (DVB-S-BCB)) and the degree of cross-linking. In our research described here, we constructed a novel random copolymer with all-hydrocarbon structure based on poly(DVB-S-BCB) by introducing styrene (St) as the second polymerization monomer, thus controlling the number of cross-linking sites in the polymer. The effect of changes in St monomer content (number of cross-linking points) in the polymer chains, i.e. DVB-S-BCB and St, on the dielectric properties of the cured resins was investigated by molecular dynamics simulations. The simulation results showed that increasing the St monomer content in the copolymer, decreasing the cross-linking points, led to an increase in the dielectric constant of the cured resin, in addition to which the copolymer exhibited excellent thermo-mechanical properties. We also tested resin samples prepared by the experimental method and compared them with the simulated data, confirming the reliability of the results within acceptable error limits.

The role of photo‐catalytically synthesized poly (N‐vinyl pyrrolidone‐methyl methacrylate)/CuO‐rGO nanocomposite as a filler for the reinforcement for epoxy system

AbstractThis study demonstrates the effective copolymerization of N‐Vinyl pyrrolidone and methyl methacrylate using reduced graphene oxide adorned with copper oxide nanoparticles (CuO‐rGO) acting as a catalyst when exposed to blue LED irradiation to generate random copolymer hybrid system of P(NVP‐co‐MMA/CuO‐rGO). We investigated the effects of this copolymer hybrid system of P(NVP‐co‐MMA/CuO‐rGO) on the mechanical, thermal and antibacterial properties of epoxy (DEGBA‐DETDA) composite. By employing two different concentrations of CuO nanoparticle, we assessed the reinforcement capability of the synthesized copolymer‐nanoparticle hybrid within an epoxy matrix. We observed that the composite sample comprising P(NVP‐co‐MMA/CuO‐rGO), having 0.5% of CuO‐rGO (Cu002) with respect to the epoxy concentration resulted in significant enhancements in fracture toughness. Further mechanical properties and thermal properties of the composite samples were studied using DMA, DSC and TGA. Microstructural properties and Mechanisms of toughening are elucidated through the examination of SEM images depicting the fracture surfaces. Moreover, the hybrid composites exhibited notable antibacterial activity against both E. coli and S. aureus compared to control. These findings highlight the copolymer hybrid P(NVP‐co‐MMA/CuO‐rGO) system's role as a multifunctional filler, enhancing epoxy composites' durability, functionality, and antibacterial performance. Our work advances the field of composites by showcasing the customized use of nanoparticle‐enhanced copolymers to improve material properties, providing valuable insights for the development of next‐generation composite materials.Highlights Achieved novel copolymerization of N‐Vinyl pyrrolidone and methyl methacrylate. CuO‐rGO successfully facilitates P(NVP‐co‐MMA/CuO‐rGO) nanocomposite formation. P(NVP‐co‐MMA/CuO‐rGO) nanocomposite proved as an effective filler for epoxy. P(NVP‐co‐MMA/CuO‐rGO) reinforced epoxy enhances toughness by 143% over neat epoxy Reinforced epoxy showed better efficacy against E. coli &amp; S. aureus versus control.

Synthesis of random copolymers of styrene and arylamino substituted styrenes and their sensitivities towards nitroaromatics

AbstractRandom copolymers of styrene and substituted styrenes bearing arylamino substituents as fluorophore units have been obtained. Their photophysical properties have been investigated by measuring absorption and emission spectra as in solutions as solid‐state. All copolymers proved to possess absolute quantum yields up to 0.39 in solution and up to 0.05 in solid‐state, depending on their fluorophore substituents. Fluorescence studies have shown that these copolymers show a highly sensitive response towards a diversity of nitroaromatic compounds, both in solutions and in a vapor phase. The detection limits for these compounds towards model nitroaromatic explosives in dichloromethane solution proved to be in the range from 10−6 to 10−7 mol/L. The fluorescent materials prepared by electrospinning of synthesized copolymers have been evaluated as sensor materials for detecting nitrobenzene vapor for our hand‐made sniffer with detection limits of 0.5 ppm during 100‐s exposure to the vapor.

Design and Synthesis of Comb‐Like Bisulfonic Acid Proton Exchange Membrane with Regulated Microstructure

AbstractThe design and synthesis of proton exchange membranes (PEMs) with controllable microstructure and sulfonation degree play a crucial role in enhancing their performance and expanding their application. In this study, the disulfonic acid monomer is designed and prepared to synthesize the comb‐like disulfonic PEMs with controllable ion exchange capacity. The results show that the side chain structure and more concentrated sulfonic acid groups facilitate the aggregation of sulfonic acid groups in the polymer, improve the microphase separation morphology of PEMs, and increase the ionic conductivity. The proton conductivity of the DS‐PXIDI‐60 membrane is approximately 300 mS cm−1. The PEMs with controllable microstructure are prepared by introducing comonomers, including 9,9‐dimethylxanthrene, biphenyl, and p‐terphenyl, with different reactivity, spatial structure, and solubility. Biphenyl is copolymerized to form a copolymer with an alternating structure, and 9, 9‐dimethylxanthrene is copolymerized to form a random copolymer. In addition, it is worth noting that p‐terphenyl is copolymerized to form a microblock structure of the copolymer, with more excellent comprehensive properties. DS‐PXITp‐60 exhibits better performance than Nafion 212 in redox­flow batteries and fuel cells. Therefore, such molecular design and synthesis strategies provide a reference guide for the development of high‐performance PEMs.

Synthesis of a New Random Copolymer Based on Glycidyl Nitrate and Tetrahydrofuran: A Thermal, Kinetic, and Theoretical Study

Synthesis of a New Random Copolymer Based on Glycidyl Nitrate and Tetrahydrofuran: A Thermal, Kinetic, and Theoretical Study

Hybrid Dynamic Covalent Network-Based Protecting Layer for Stable Li-Metal Batteries.

Metallic lithium (Li) is considered as the "Holy Grail" anode material for next-generation energy storage systems due to its extremely high theoretical capacity and low electrochemical potential. Before the commercialization of the Li electrode, dendritic Li growth and the unstable solid electrolyte interphase layer should be conquered. Herein, a hybrid covalent adaptable polymer network (HCAPN) is prepared via the random copolymerization of poly(ethylene glycol) methyl ether methacrylate and -acetoacetoxyethyl methacrylate, followed by chemical cross-linking with polyethylenimine (PEI) and amine-modified silicon dioxide (SiO2). Such a hybrid network, where PEI and amine-modified SiO2 formed a vinylogous urethane-based dynamic covalent bond with the copolymer, respectively, shows improved mechanical properties, solvent resistance, and excellent healability/recyclability. As the protecting layer on the Li electrode, the assembled HCAPN@Li||HCAPN@Li symmetric cell shows a long cycle life of 800 h with low overpotential at a current density of 1 mA cm-2, and superior electrochemical performance can be achieved in the HCAPN@Li||LiFePO4 full cell (capacity retention of 77% over 400 cycles at 1.5 C) and HCAPN@Li||NCM811 cell (capacity retention of 79% after 300 cycles). Surface morphology analysis is also performed for physical insight into their role as protecting layer. This work provides a new perspective for constructing a hybrid dynamic covalent network-based polymer protecting layer for inhibiting Li dendrite growth.

Synthesis of full bio‐based, fast degradable, and high strength copolyesters: Poly(butylene succinate‐sebacicate‐salicylicate‐malicate)

AbstractThe presence of petroleum‐based monomers in the backbone of poly(butylene succinate‐co‐adipate) (PBSA) restricts its application in light of increasingly stringent environmental regulations. In this study, a novel full bio‐based biodegradable random copolymer poly(butylene succinate‐sebacicate‐salicylicate‐malicate) (PBSSeSa‐c‐M) was designed and synthesized. The comprehensive study encompassed the structural alterations, properties, and degradation resulting from the inclusion of salicylicate sebacicate and malicate units. The incorporation of salicylic acid effectively enhanced the tensile modulus of the copolymer, due to the effect of rigid benzene ring. Meanwhile, the addition of sebacic acid regulated the degradation rate. The introduction of malic acid significantly improved the rheological properties, endowing the copolymer with exceptional processability. The obtained high molecular weight PBSSeSa‐c‐M exhibited outstanding film‐blowing processability with an intrinsic viscosity of 1.58 dL/g and melt flow rate of 7.34 g/10 min. The tensile modulus reaches 235.43 MPa that is comparable to commercial PBSA. Besides, the degradation of PBSSeSa‐c‐M reaches 18.92% over 4 weeks, far higher than that of PBSA. In conclusion, this work provides a design and synthesis for a new kind of biodegradable copolyester that satisfies the requirement of rapid degradation in single‐use plastics.

Clusterization-triggered emission, stimulus-responsiveness, and DNA polyplex formation of poly(vinylamine)-based chiral block and random copolymers

Random and block copolymers exhibiting clusterization-triggered emission (CTE) and consisting of vinylamine (VAm) and methylated N-acryloyl-L-threonine (AThrOMe) were developed. They showed unique stimulus-responsiveness and polyplex-formation-induced changes in emission properties. The random and block copolymers, P(VAm-co-AThrOMe) and PVAm-b-PAThrOMe, contained no traditional fluorescent aromatic molecules, whereas the aggregation of VAm units within the assembled structures appeared to be a powerful tool for achieving enhanced fluorescence signals. The concentration-, wavelength-, and solvent-polarity-dependent emission behaviors of the VAm/AThrOMe copolymers could be tuned by implementing a rational molecular design (random or block sequence). The assembled structures and chiroptical and emission properties in response to external stimuli (temperature change and addition of salt and urea) in an aqueous solution were investigated using dynamic light scattering, circular dichroism, and fluorescence measurements. Selective interactions of DNAs with the VAm units in the VAm/AThrOMe copolymers were evaluated by performing agarose gel electrophoresis; these interactions affected the assembled structures and chiroptical and CTE properties. The comonomer sequence, external stimuli, and interactions with DNAs affected the aggregated states of the VAm unit in the copolymers, thereby showing that CTE behaviors can be manipulated in future sensing applications.

Antimicrobial peptide glatiramer acetate targets Pseudomonas aeruginosa lipopolysaccharides to breach membranes without altering lipopolysaccharide modification

Antimicrobial peptides (AMPs) are key components of innate immunity across all domains of life. Natural and synthetic AMPs are receiving renewed attention in efforts to combat the antimicrobial resistance (AMR) crisis and the loss of antibiotic efficacy. The gram-negative pathogen Pseudomonas aeruginosa is one of the most concerning infecting bacteria in AMR, particularly in people with cystic fibrosis (CF) where respiratory infections are difficult to eradicate and associated with increased morbidity and mortality. Cationic AMPs exploit the negatively charged lipopolysaccharides (LPS) on P. aeruginosa to bind and disrupt bacterial membrane(s), causing lethal damage. P. aeruginosa modifies its LPS to evade AMP killing. Free-LPS is also a component of CF sputum and feeds pro-inflammatory cycles. Glatiramer acetate (GA) is a random peptide co-polymer—of glycine, lysine, alanine, tyrosine—used as a drug in treatment of multiple sclerosis (MS); we have previously shown GA to be an AMP which synergises with tobramycin against CF P. aeruginosa, functioning via bacterial membrane disruption. Here, we demonstrate GA’s direct binding and sequestration/neutralisation of P. aeruginosa LPS, in keeping with GA’s ability to disrupt the outer membrane. At CF-relevant LPS concentrations, however, membrane disruption by GA was not strongly inhibited. Furthermore, exposure to GA did not result in increased Lipid A modification of LPS or in increased gene expression of systems involved in AMP sensing and LPS modification. Therefore, despite the electrostatic targeting of LPS by GA as part of its activity, P. aeruginosa does not demonstrate LPS modification in its defence.

Efficient triisopropylsilylethynyl-substituted benzo[1,2-b:4,5-b′]dithiophene-based random terpolymers enable non-fullerene organic solar cells with enhanced efficiency

Recent work has highlighted the pivotal role of ternary random polymers in the development of efficient high-performance polymer donors for organic solar cells (OSCs) and most of these D-A copolymer donors are so far constituted of an equal proportion of D and A-units. In this contribution, we report series of PM6-based ternary random terpolymers with unequal D- and A-units, namely, PM-TIPS10, PM-TIPS20 and PM-TIPS20, respectively by adding the 10%, 20% and 30% of simple and low-cost triisopropylsilylethynyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT-TIPS) unit as second donor (D1) unit in polymer backbone based on D1-A-D2-A molecular design. Ascribed from the structural similarity of the two building blocks in the terpolymer backbone, these polymers showed orderly molecular packing, broadened light absorption, and the face-on orientation of the active layer to facilitate charge transport. Additionally, the new polymers displayed much deeper highest occupied molecular orbital (HOMO) energy levels than host PM6 polymer, which helped in enhancing the open circuit voltage (Voc) in the PM-TIPS-based OSCs. As a result, when combined with BTP-eC9 acceptor unit, PM-TIPS10 and PM-TIPS20 displayed best efficiency of 16.7 and 16.5% with a small energy loss of 0.484 and 0.473 eV, producing overall superior device parameters compared to PM6-based devices tested parallelly (PCE of 15.7%). This study reveals the correlation between introduction of the BDT-TIPS unit on polymer properties and photovoltaic performance and thus contributes to the design of high-PCE polymer donors by adapting a ternary random copolymerization strategy.

Electrical Chain Rearrangement: What Happens When Polymers in Brushes Have a Charge Gradient?

Under the influence of electric fields, the chains in polyelectrolyte brushes can stretch and collapse, which changes the structure of the brush. Copolymer brushes with charged and uncharged monomers display a similar behavior. For pure polyelectrolyte and random copolymer brushes, the field-induced structure changes only the density of the brush and not its local composition, while the latter could be affected if charges are distributed inhomogeneously along the polymer backbone. Therefore, we systematically study the switching behavior of gradient polyelectrolyte brushes in electric fields for different solvent qualities, grafting densities, and charges per chain via coarse-grained molecular dynamics simulations. Similar to random copolymers and pure polyelectrolytes, these brushes show a mixed-phase transition: intermediate states between fully stretched and collapsed are characterized by a bimodal chain-end distribution. Additionally, we find that the total charge of the brush plays a key role in the critical field required for a complete transition. Finally, we find that gradient polyelectrolyte brushes are charge-enriched at the brush-solvent interface under stretched conditions and charge-depleted under collapsed conditions, allowing for control over the local composition and thus the surface charge of the brush due to the inhomogeneous charge along the grafted chains.