Graft Chains Research Articles

Bidispersity Improves the Toughness and Impact Resistance of Star-Polymer Thin Films.

Branched polymer architectures are used to tune the mechanical properties of impact-resistant thin films through parameters, such as chain length and grafting density. While chain dispersity affects molecular properties, such as interpenetration and entanglements, structure-property relationships accounting for dispersity are challenging to obtain experimentally and are often neglected in computational models. We employ molecular dynamics simulations to model the high-rate tensile elongation and nanoballistic impact of thin films composed of bidisperse star polymers with varying arm lengths. We find that, at fixed molecular weight, high dispersity can significantly enhance the toughness and impact resistance of the films without decreasing their elastic modulus. Bidisperse stars with fewer longer arms are less entangled, but stretch and interpenetrate for longer times during crazing, leading to increased toughness. These findings highlight controlled dispersity as a design strategy to improve the mechanical properties of polymer composites across Pareto fronts.

Molecular brushes with long polyfluorene backbones and polymethacrylic acid side chains: Luminescent properties and self‐organization in solutions

AbstractA series of molecular brushes with a polyfluorene (PF) backbone and polymethacrylic acid side chains of varying lengths were prepared by atom transfer radical polymerization. The structure and composition of the synthesized compounds were confirmed by 1H NMR and IR spectroscopy. Effect of the length of the backbone on spectral and conformational parameters of the macromolecules in solutions was analyzed. The grafting density of side chains was about 90%. Spectral methods have been used to determine the dependence of side chain grafting on the luminescent properties of polymer solutions, including quantum yields. It was shown that an optimal length of polymethacrylic acid side chains provides solubility of the polymer brushes. Solutions of PF‐graft‐polymethacrylic acid complexes with the model substance curcumin were investigated. It was established that the molecular brushes containing curcumin form monomolecular micelles. Molecular brushes with zinc phthalocyanine, potential systems for photodynamic, and photothermal therapy, were studied.

Regulatable endothermic behavior of one-chain-tethered sliding graft copolymers as novel solid-solid phase change materials

Sliding graft copolymer (SGC) is a polyrotaxane (PR) composed of a poly(ethyelene glycol) (PEG) axle and α-cyclodextrins (α-CDs) substituted with polymer graft-chains. We have previously reported a sharp-endothermic phase transition of SGCs, which was expected due to the high mobility of graft chains by the mechanical linkage of PRs. To examine this hypothesis, SGCs with well-defined structures were prepared. PRs consisting of monoazidated α-CD and PEG were grafted with monomethoxy poly(ethylene glycos)s (mPEGs) via click chemistry. The SGC bearing shortest graft chains (mPEG750) did not exhibit endotherm, whereas those with side chains of mPEG2000 and mPEG4000 underwent endothermic phase transition. However, values of the transition temperatures and those of melting enthalpies were lower than those of unmodified mPEGs. Unlike our previous report, the SGCs synthesized here contained densely-packed α-CDs, which were capable of rotational movement but not translational movement. The endothermic peak observed for the present SGC is relatively broader than that observed for our previous SGC, which suggests that the mobility of α-CDs were critical to induce sharp-endothermic phase transition.

Chitosan-β-cyclodextrin composite flocculants dual-drive for efficient microalgae harvesting: Structural evidences, dehydration process, E-DLVO model behavior and biomass utilization

Flocculation is one of the promising methods for harvesting microalgae. In this study, a series of grafted cationic chitosan-cyclodextrin composite flocculants (CTS/β-CDs) with different structural properties were prepared from chitosan and cyclodextrin. The results showed that the harvesting efficiency of CTS/β-CD-1 for C. vulgaris reached 99.91%. The chain type of polymeric flocculants with moderate graft chain lengths (L = 10–20) and tighter branched chain density distribution (D = 1.0–1.8) was favorable for C. vulgaris harvesting. The addition of CTS/β-CDs caused the discrete C. vulgaris cells to be flocculated and aggregated, and the reorganization of particles resulted in larger particles after flocculation, improving the dewatering performance of microalgae flocs. CTS/β-CDs had no significant inhibitory effect on the extraction of lipids, proteins and carbohydrates, and did not affect the extraction and quality of fatty acid methyl esters, and the re-cultivation experiments of the harvested water showed that chitosan-based flocculant was able to effectively reduce the cost of microalgae harvesting. Electrostatic interactions and bridging were the main harvesting mechanisms between CTS/β-CD-1 and C vulgaris. E-DLVO modeling suggested that flocculation is mainly a result of electrostatic and acid-base interactions when the distance between particles is small. At higher pH, the harvesting efficiency of CTS/β-CD-1 with C. vulgaris decreased. The study contributes to a better understanding of the structure–activity relationship between the structural characteristics of flocculants and the harvesting performance.

Nanostructures of etherified arabinoxylans and the effect of arabinose content on material properties

To further our understanding of a thermoplastic arabinoxylan (AX) material obtained through an oxidation-reduction-etherification pathway, the role of the initial arabinose:xylose ratio on the material properties was investigated. Compression molded films with one molar substitution of butyl glycidyl ether (BGE) showed markedly different tensile behaviors. Films made from low arabinose AX were less ductile, while those made from high arabinose AX exhibited elastomer-like behaviors. X-ray scattering confirmed the presence of nanostructure formation resulting in nano-domains rich in either AX or BGE, from side chain grafting. The scattering data showed variations in the presence of ordered structures, nano-domain sizes and their temperature response between AX with different arabinose contents. In dynamic mechanical testing, three transitions were observed at approximately −90 °C, −50 °C and 80 °C, with a correlation between samples with more structured nano-domains and those with higher onset transition temperatures and lower storage modulus decrease. The mechanical properties of the final thermoplastic AX material can therefore be tuned by controlling the composition of the starting material.

Brownian dynamics simulations of bottlebrush polymers in dilute solution under simple shear and uniaxial extensional flows.

We study the dynamics of bottlebrush polymer molecules in dilute solutions subjected to shear and uniaxial extensional flows using Brownian dynamics simulations with hydrodynamic interaction (HI). Bottlebrush polymers are modeled using a coarse-grained representation, consisting of a set of beads interacting pairwise via a purely repulsive potential and connected by finitely extensible nonlinear springs. We present the results for molecular stretching, stress, and solution viscosity during the startup of flow as well as under steady state as a function of side chain length while keeping the backbone length fixed. In extensional flow, the backbone fractional extension and the first normal stress difference decrease with an increase in side chain length at a fixed Weissenberg number (Wi). Using simulation results both in the presence of and in the absence of HI, we show that this is primarily a consequence of steric interaction resulting from the dense grafting of side chains. In shear flow, we observe a shear-thinning behavior in all cases, although it becomes less pronounced with increasing side chain length. Furthermore, nonmonotonicity in the backbone fractional extension is observed under shear, particularly at high Wi. We contextualize our simulation results for bottlebrush polymers with respect to existing studies in the literature for linear polymers and show that the unique dynamical features characterizing bottlebrush polymers arise on account of their additional molecular thickness due to the presence of densely grafted side chains.

Surface hydrophobization of hydrogels via interface dynamics-induced network reconfiguration

Effective and easy regulation of hydrogel surface properties without changing the overall chemical composition is important for their diverse applications but remains challenging to achieve. We report a generalizable strategy to reconfigure hydrogel surface networks based on hydrogel–substrate interface dynamics for manipulation of hydrogel surface wettability and bioadhesion. We show that the grafting of hydrophobic yet flexible polymeric chains on mold substrates can significantly elevate the content of hydrophobic polymer backbones and reduce the presence of polar groups in hydrogel surface networks, thereby transforming the otherwise hydrophilic hydrogel surface into a hydrophobic surface. Experimental results show that the grafted highly dynamic hydrophobic chains achieved with optimal grafting density, chain length, and chain structure are critical for such substantial hydrogel surface network reconfiguration. Molecular dynamics simulations further reveal the atomistic details of the hydrogel network reconfiguration induced by the dynamic interface interactions. The hydrogels prepared using our strategy show substantially enhanced bioadhesion and transdermal delivery compared with the hydrogels of the same chemical composition but fabricated via the conventional method. Our findings provide important insights into the dynamic hydrogel–substrate interactions and are instrumental to the preparation of hydrogels with custom surface properties.

Tuning the water intrinsic permeability of PEGDA hydrogel membranes by adding free PEG chains of varying molar masses.

We explore the effect of poly(ethylene glycol) (PEG) molar mass on the intrinsic permeability and structural characteristics of poly(ethylene glycol) diacrylate PEGDA/PEG composite hydrogel membranes. We observe that by varying the PEG content and molar mass, we can finely adjust the water intrinsic permeability by several orders of magnitude. Notably, we show the existence of maximum water intrinsic permeability, already identified in a previous study to be located at the critical overlap concentration C* of PEG chains, for the highest PEG molar mass studied. Furthermore, we note that the maximum intrinsic permeability follows a non-monotonic evolution with respect to the PEG molar mass and reaches its peak at 35 000 g mol-1. Besides, our results show that a significant fraction of PEG chains is irreversibly trapped within the PEGDA matrix even for the lowest molar masses down to 600 g mol-1. This observation suggests the possibility of covalent grafting of the PEG chains onto the PEGDA matrix. CryoSEM and AFM measurements demonstrate the presence of large micron-sized cavities separated by PEGDA-rich walls whose nanometric structures strongly depend on the PEG content. By combining our permeability and structural measurements, we suggest that the PEG chains trapped inside the PEGDA-rich walls induce nanoscale defects in the crosslinking density, resulting in increased permeability below C*. Conversely, above C*, we speculate that partially trapped PEG chains may form a brush-like arrangement on the surface of the PEGDA-rich walls, leading to a reduction in permeability. These two opposing effects are anticipated to exhibit molar-mass-dependent trends, contributing to the non-monotonic variation of the maximum intrinsic permeability at C*. Overall, our results demonstrate the potential to fine-tune the properties of hydrogel membranes, offering new opportunities for separation applications.

Polypyrrole fabricated Laponite RD conductive nanocomposites: influence of grafting efficiency on structural and conductive properties.

In the present work novel conductive organic-inorganic nanocomposites were produced by grafting of pyrrole monomer onto silanized Laponite RD utilizing emulsion graft polymerization. Influence of some important factors like concentration of monomer, initiator and surfactant were investigated on grafting efficiency. Grafting of polypyrrole chains onto modified Laponite RD was verified by Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscope (SEM) revealed the spherical particles of nanocomposite with average diameter of 271.5 nm. XRD pattern showed that molecular framework of pure polypyrrole almost remains same in nanocomposite. Surface area and pore volume of Laponite RD, measured by Brunauer-Emmett-Teller (BET) analysis, was also altered indicating effective grafting of polypyrrole chains onto modified substrate. Maximum grafting efficiency (%), determined gravimetrically, was 87.3% at monomer, initiator, and surfactant concentrations of 1.50, 1.00, and 0.50% respectively. Prepared nanocomposites with grafting efficiency of 87.3% have displayed maximum electrical conductivity of 0.23 × 10-2 Scm-1. These nanocomposites can be used for manifold applications like biomedical and energy storage devices.

Effect of Surface Properties of Nanoparticles on the Crystallization Behavior of Polypropylene/Polypropylene‐g‐Silica Nanocomposites

AbstractIn order to investigate the effect of surface properties of nanoparticles (NPs) on the crystallization behavior of nanocomposite, three kinds of silica (SiO2) NPs are dispersed in isotactic polypropylene (iPP) matrix by solution blending method. Specifically, the poor compatibility between inorganic bare SiO2 NPs and organic PP matrix triggers the formation of aggregates and induces the fractionated crystallization with two crystallization peaks at higher particle loading (Φ), i.e., main crystallization peak (MCP) and low temperature crystallization peak (LCP, always located at 124.0 °C). Once short PP chains (0.9 × 104 g mol−1) are grafted onto the surface of SiO2 NPs, the nanocomposites with all Φ only exhibit a single MCP which is attributed to the strong interfacial interaction. With the increase of grafting chain length (9 × 104 g mol−1), the more stretched conformation of grafting chains can provide numerous heterogeneous nucleation sites and significantly accelerate the crystallization rate of PP chains near the surface of SiO2 NPs, which lead to the formation of an extra high temperature crystallization peak (HCP, almost kept constant at 133.0 °C). The occurrence of various crystallization peaks implies that the surface properties of nanoparticles play a vital role in the nucleation ability of nanoparticles.

Development of nanoparticles based on amphiphilic cyclodextrins for the delivery of active substances

Although amphiphilic cyclodextrin derivatives (ACDs) serve as valuable building blocks for nanomedicine formulations, their widespread production still encounters various challenges, limiting large-scale manufacturing. This work focuses on a robust alternative pathway using mineral base catalysis to transesterify β-cyclodextrin with long-chain vinyl esters, yielding ACD with modular and controlled hydrocarbon chain grafting. ACDs with a wide range of degrees of substitution (DS) were reliably synthesized, as indicated by extensive physicochemical characterization, including MALDI-TOF mass spectrometry. The influence of various factors, including the type of catalyst and the length of the hydrocarbon moiety of the vinyl ester, was studied in detail. ACDs were assessed for their ability to form colloidal suspensions by nanoprecipitation, with or without PEGylated phospholipid. Small-angle X-ray scattering and cryo-electron microscopy revealed the formation of nanoparticles with distinct ultrastructures depending on the DS: an onion-like structure for low and very high DS, and reversed hexagonal organization for DS between 4.5 and 6.1. We confirmed the furtivity of the PEGylated versions of the nanoparticles through complement activation experiments and that they were well tolerated in-vivo on a zebrafish larvae model after intravenous injection. Furthermore, a biodistribution experiment showed that the nanoparticles left the bloodstream within 10 h after injection and were phagocytosed by macrophages.

Characterization of well‐defined PHEMA‐based bottlebrushes with controlled chain length and grafting density

AbstractBottlebrushes with controlled horizontal‐ and vertical‐axis scales, which have a high density of graft chains on their main chains, are useful as a nanomaterial. The properties of bottlebrushes depend on the polymer‐type, ‐chain length, and grafting density. We fabricate well‐defined bottlebrushes based on poly(2‐hydroxyethyl methacrylate) (PHEMA) using the grafting from method. Macroinitiators with different compositions of an atom transfer radical polymerization (ATRP) initiator group are prepared, and two bottlebrushes are consequently synthesized by ATRP of HEMA with the macroinitiator: a concentrated bottlebrush with graft chains on the repeating units and a semi‐dilute bottlebrush with graft chains on approximately 10%. The hydrodynamic and gyration radii of the concentrated‐ and semi‐dilute bottlebrushes are Rh = 9.2 nm (Rg = 24.9 nm) and Rh = 69.1 nm (Rg = 130 nm), respectively. The shape factors (Rg/Rh) of these bottlebrushes indicate both solid‐rods. The virial coefficient of semi‐dilute bottlebrush, calculated from static light scattering measurements, is higher than that of concentrated bottlebrush, owing to the flexibility and solvation structure. The grafting density play a more prominent role than the graft‐chain length in the excluded volume effect of the bottlebrush. These results provide useful insights for the construction of polymethacrylate‐based bottlebrushes with specific hydrodynamic properties.

A novel phosphorylated hyper-crosslinked porous polymer for efficient uranium adsorption in water

As the nuclear resource industry rapidly progresses, efficient adsorbents play a vital role in separating and eliminating uranium from aqueous solutions. Herein, 9,9-dimethyl-fluorenylphosphonic acid was designed as a phosphate functional monomer and the triptycene as a rigid backbone monomer. Through the “knitting” strategy, a novel triptycene-based phosphorylated hyper-crosslinked porous polymer (TPP-DFP) was obtained by the above monomers. The resulted polymer TPP-DFP has a high BET surface area of 1397.62 m2/g with a rich porosity. The porous polymer TPP-DFP was the first time used for uranium adsorption from water and showed outstanding adsorption performance. The maximum uranium adsorption capacity of TPP-DFP was 414.26 mg/g, which was higher than that of most of other porous adsorbents. In the presence of impurity ions such as Ca2+, Mg2+, Al3+, Co2+, Ni2+, V5+, NO3−, CO32− etc., TPP-DFP exhibited high selectivity (Su up to 99%) for uranium. In addition, TPP-DFP has excellent reusability, and the removal percentage of uranium can reach more than 95% after 5 adsorption–desorption cycles. According to the XPS experiment, the mechanism of interaction between TPP-DFP and U(VI) was mainly due to the complex formed by the phosphate functional groups and U(VI). The theory DFT calculation indicated a 1:2 ratio of U(VI) and phosphate functional group on the two-distinct graft chain, which was consistent with the experimental results. Accordingly, the “knitting” polymerization technique showed potential for preparation effective adsorbents for uranium extraction from water.

Tuning moduli of hybrid bottlebrush elastomers by molecular architecture

Polymeric elastomers made of bottlebrush chains are soft, solvent-free materials with precisely controllable moduli by network topology. However, fabrication methods of bottlebrush networks with precisely programmable topology are lacking. The aim of this study is to achieve precise control over the modulus of hybrid elastomers containing bottlebrush and linear strands by integrating a versatile experimental synthesis approach with Molecular Dynamics (MD) simulations. In this study, polydimethylsiloxane (PDMS) networks (G′=10−328 kPa) are made by crosslinking prepared and purified bottlebrush molecules where the precursors, side chains and backbone, are synthesized using well-controlled living anionic polymerization. This approach allows independent programming of the crucial topological parameters of bottlebrushes, such as length of both sides chain and backbone and grafting density. In addition to this versatile synthesis, MD simulations reveal the influence of network defects inevitably present in all polymer networks. This novel combining of fabrication method and simulation yields experimentally-measured structural shear and Young's moduli which are in better agreement with theoretical predictions. Importantly, these bottlebrush-containing networks have no solvent or additives and notably, by removing ungrafted side chains impurities before network formation, results in soft, solvent-free elastomers with Young's moduli as low as E∼30 kPa with adhesiveness far lower than commercial silicone products of similar stiffness.

Density functional approach to wetting behavior of water on solid surfaces modified by grafting of chains and their mixtures

We apply a classical density functional theory for associating fluids to study wetting of a simple model of water and graphite-like solid surface chemically modified by the grafting of chains and their mixtures. The grafting points are randomly distributed on the surface. The chain molecules consist of tangentially bonded spherical segments. We explore adsorption of water on such complex substrates and evaluate different projections of the wetting phase diagrams dependent on grafting density, chains length and composition of grafted chains mixture. Besides, the contact angle dependence on temperature is obtained and discussed. If the total grafting density is high enough, the prewetting line splits into two lines that join at a triple point. Each of the lines is associated with changes in the predominant configuration of segments of grafted chains. The role of attractive interaction of water with segments of chains is explored. Despite the qualitative similarity of the phase diagrams of one- and two-component grafted chains, the behavior of chain molecules during phase transitions may be different. The chains of one kind can stretch, while those of the second - can collapse. Such behavior corresponds to the “vertical separation” of the chains. Trends of this phenomenon are studied in detail.

A general strategy for designing complex brush architecture using star‐like polymeric grafts

AbstractSynthetic control over the shape, size, and interactions between nanoscale building blocks remains an open challenge in self‐assembly. Here, we propose to engineer triblock, star‐like polymers to design patterning on nanoparticles. We developed a theory that characterizes the structural organization of grafted polymers as a function of parameters such as grafting density, chain length, block fractions, and core shape/sizes. Stripe‐like patterning and corner/edge patch formation on arbitrarily shaped cores are readily accessible using our framework, all of which can be a priori predicted. Lastly, we employ assembly simulations to show that the resulting particles provide tighter control over structural and orientational orderings during self‐assembly. More importantly, they offer a way to pattern directional interactions that can override face–face alignment tendencies intrinsic to each core geometry. Our theory, therefore, creates a new handle for tuning nanoscale synthesis, enabling designs of complex building blocks that can target novel assemblies for materials fabrication.

Synthesis and Evaluation of Antifungal and Antibacterial Abilities of Carbon Nanotubes Grafted to Poly(2-hydroxyethyl methacrylate) Nanocomposites.

Developing nanomaterials with the capacity to restrict the growth of bacteria and fungus is of current interest. In this study, nanocomposites of poly(2-hydroxyethyl methacrylate) (PHEMA) and carbon nanotubes (CNTs) functionalized with primary amine, hydroxyl, and carboxyl groups were prepared and characterized. An analysis by Fourier-transform infrared (FT-IR) spectroscopy showed that PHEMA chains were grafted to the functionalized CNTs. X-ray photoelectron spectroscopy suggested that the grafting reaction was viable. The morphology of the prepared nanocomposites studied by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) showed significant changes with respect to the observed for pure PHEMA. The thermal behavior of the nanocomposites studied by differential scanning calorimetry (DSC) revealed that the functionalized CNTs strongly affect the mobility of the PHEMA chains. Tests carried out by thermogravimetric analysis (TGA) were used to calculate the degree of grafting of the PHEMA chains. The ability of the prepared nanocomposites to inhibit the growth of the fungus Candida albicans and the bacteria Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli was evaluated. A reduced antifungal and antibacterial capacity of the prepared nanocomposites was determined.

Nanostructure Explains the Behavior of Slippery Covalently Attached Liquid Surfaces.

Slippery covalently-attached liquid surfaces (SCALS) with low contact angle hysteresis (CAH, <5°) and nanoscale thickness display impressive anti-adhesive properties, similar to lubricant-infused surfaces. Their efficacy is generally attributed to the liquid-like mobility of the constituent tethered chains. However, the precise physico-chemical properties that facilitate this mobility are unknown, hindering rational design. This work quantifies the chain length, grafting density, and microviscosity of a range of polydimethylsiloxane (PDMS) SCALS, elucidating the nanostructure responsible for their properties. Three prominent methods are used to produce SCALS, with characterization carried out via single-molecule force measurements, neutron reflectometry, and fluorescence correlation spectroscopy. CO2 snow-jet cleaning was also shown to reduce the CAH of SCALS via a modification of their grafting density. SCALS behavior can be predicted by reduced grafting density, Σ, with the lowest water CAH achieved at Σ≈2. This study provides the first direct examination of SCALS grafting density, chain length, and microviscosity and supports the hypothesis that SCALS properties stem from a balance of layer uniformity and mobility.

Nanostructure Explains the Behavior of Slippery Covalently Attached Liquid Surfaces

AbstractSlippery covalently‐attached liquid surfaces (SCALS) with low contact angle hysteresis (CAH, &lt;5°) and nanoscale thickness display impressive anti‐adhesive properties, similar to lubricant‐infused surfaces. Their efficacy is generally attributed to the liquid‐like mobility of the constituent tethered chains. However, the precise physico‐chemical properties that facilitate this mobility are unknown, hindering rational design.This work quantifies the chain length, grafting density, and microviscosity of a range of polydimethylsiloxane (PDMS) SCALS, elucidating the nanostructure responsible for their properties. Three prominent methods are used to produce SCALS, with characterization carried out via single‐molecule force measurements, neutron reflectometry, and fluorescence correlation spectroscopy. CO2 snow‐jet cleaning was also shown to reduce the CAH of SCALS via a modification of their grafting density. SCALS behavior can be predicted by reduced grafting density, Σ, with the lowest water CAH achieved at Σ≈2. This study provides the first direct examination of SCALS grafting density, chain length, and microviscosity and supports the hypothesis that SCALS properties stem from a balance of layer uniformity and mobility.

Supramolecular Liquid Crystal Carbon Dots for Solvent-free Direct Ink Writing.

Recent years have witnessed the major advances of nanolights with extensive exploration of nano-luminescent materials like carbon dots (CDs). However, solvent-free processing of these materials remains a formidable challenge, impeding endeavors to develop advanced manufacturing techniques. Herein, in response to this challenge, liquid crystallization is demonstrated as a versatile and robust approach by deliberately anchoring flexible alkyl chains on the CDs surface. Alkyl chain grafting on the CDs surface is observed to substantially depress the common aggregation-caused quenching effect, and results in a shift of self-assembly structure from the crystalline phase to smectic liquid crystalline phase. The liquid crystalline phase transition temperature is ready to adjust by varying the alkyl chain length, endowing low temperature (< 50°C) melt-processing capabilities. Consequently, the first case of direct ink writing (DIW) with liquid crystal (LC) carbon dots is demonstrated, giving rise to highly emissive objects with blue, green and red color fluorescence, respectively. Another unexpected finding is that the DIW with LC inks dramatically outperforms the DIW with isotropic inks, further highlighting the significance of LC processing. The reported approach herein not only exhibits a fundamental advance by imparting LC functions to CDs, but also promises technological utility in DIW-based advanced manufacturing. This article is protected by copyright. All rights reserved.