Modified End Groups Research Articles

Halogen-Functionalized Hole Transport Materials with Strong Passivation Effects for Stable and Highly Efficient Quasi-2D Perovskite Solar Cells.

The performance of quasi-two-dimensional (Q-2D) perovskite solar cells (PSCs) strongly depends on the interface characteristics between the hole transport material (HTM) and the perovskite layer. In this work, we designed and synthesized a series of HTMs with triphenylamine-carbazole as the core structure and modified end groups with chlorine and bromine atoms. These HTMs show deeper highest occupied molecular orbital energy levels than commercial HTMs. This reduced energy band mismatch between the HTM and perovskite layer facilitates efficient charge extraction at the interface. Moreover, these HTMs containing halogen atoms on the end groups could form halogen bonding with the Pb2+ ions at the buried interface of the perovskite layer, effectively passivating defects to suppress nonradiative recombination. Additionally, halogen bonding also contributes to the formation of vertically oriented perovskite crystals with a high quality. By incorporation of chlorohexane-substituted HTMs, the resultant Q-2D PSCs exhibited the highest power conversion efficiency of 21.07%. Furthermore, the devices show improved stability, retaining 97.2% of their initial efficiency after 1100 h of continuous illumination.

A brominated M3 based non-fullerene acceptor: synthesis, material and photovoltaic properties

A non-fullerene acceptor with modified end groups was synthesized and shows benefits in charge carrier mobility and photovoltage in organic solar cells.

Mitochondria-Targeting Multimodal Phototheranostics Based on Triphenylphosphonium Cation Modified Amphiphilic Pillararenes and A-D-A Fused-Ring Photosensitizers.

Tumor-targeting phototheranostics has gradually developed as a powerful tool for the precise diagnosis and treatment of cancer. However, the designs of tumor-targeting phototheranostics agents with excellent multimodal phototherapy and fluorescence imaging (FLI) capability, as well as very few components, are still scarce and challenging for cancer treatment. Herein, a mitochondria-targeting multimodal phototheranostics system has been constructed by combining a designed amphiphilic pillararene WP5-2PEG-2TPP and the A-D-A fused-ring photosensitizer F8CA5. WP5-2PEG-2TPP is constructed by attaching the triphenylphosphonium cations to our previously reported dual PEG-functionalized amphiphilic pillararene, which can self-assemble into regular spherical nanocarriers with outstanding mitochondria targeting and water solubility. The A-D-A photosensitizer F8CA5 containing two methyl cyanoacetate group modified end groups displays superior photothermal conversion ability and dual type I/II photodynamic activity as well as strong NIR fluorescence emission. Through their strong union, multifunctional mitochondria-targeting phototheranostics agent F8CA5 NPs were obtained to be applied into FLI-guided synergistic photothermal and type I/II photodynamic therapy. As a result, F8CA5 NPs show good mitochondria-targeting and phototherapy effects in various tumor cells. Not only that, they can combat tumor hypoxia, which hinders the efficacy of photodynamic therapy. Therefore, this work provides a creative ideal for the construction of multifunctional tumor-targeting phototheranostic agents with excellent performance.

Completely non-fused ring acceptors with low non-radiative energy loss enabled by end-group modulation

Four non-fused-ring electron acceptors with modified end groups, namely FC8-0F, FC8-1F, FC8-2F and FC8-2Cl, were designed and synthesized. Among them, the FC8-2Cl-based OSC exhibits a remarkable PCE of 13.28% with low energy loss.

Organic solar cells based on non-fullerene acceptors of nine fused-ring by modifying end groups

Abstract A series of small molecule acceptors (SMAs) based on a benzodithiophene-pyrrolobenzothiadiazole-based nine fused-ring core and different end groups of 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (2FIC), 3-(dicyanomethylene)indian-1-one (IC) and 2-(3-ethyl-4-oxo-thiazolidin-2-ylidene) malononitrile (RCN) have been designed and synthesized. The SMAs X94FIC, X9IC, X9Rd and X9T4FIC were chosen as electron acceptors with blending the donor polymer PBDB-T to prepare the organic solar cells (OSCs) and investigate photoelectric performance. Surprisingly, X94FIC showed an excellent photo-response up to 1000 nm, while X9IC and X9T4FIC also possess a photo-response to 900 nm. A power conversion efficiency (PCE) of 7.08% was obtained for the active layers PBDB-T:X94FIC. This result demonstrates that small molecule acceptor containing the nine fused-ring core and the end group with di-fluorine atoms is promising candidate for the development of high performance non-fullerene OSCs.

Benefits and Limitations of Adding Hyperbranched Polymers to Dental Resins

Volumetric shrinkage reduction is a constant challenge in the improvement of dental resins. The inclusion of hyperbranched polymers (HBPs) with modified functionalities (hydroxyl, propionate, and methacrylate) instead of conventional dimethacrylate monomers has the potential to reduce shrinkage, but can also affect other properties. The null hypothesis was that the addition of HBPs (from 5 to 40 mass%) to a 50/50 mass% Bis-GMA/TEGDMA mixture reduces shrinkage without affecting degree of conversion, elastic modulus, glass transition temperature, Wallace hardness (before/after ethanol storage), and viscosity. This hypothesis was rejected, since HBP incorporation significantly affected most properties either negatively or positively. When HBP amounts in the resin were increased, the following general trends were observed: Volumetric shrinkage decreased significantly (p < 0.0001), down to about one-third of the control value at 40% HBP; Wallace hardness (both before and after ethanol) and viscosity increased progressively, while elastic modulus showed a parabolic profile, with a maximum at 10% HBP; and finally, degree of conversion and glass transition temperature were relatively stable, regardless of the HBP content. These results indicate that HBPs with modified end groups might be interesting substitutes for Bis-GMA/TEGDMA.

Stability of Amphiphilic Dendrimers at the Water/Air Interface

By means of atomistic molecular dynamics simulations, we investigate the structure and stability of alkyl-modified polyamido-amide (PAMAM) dendrimers at the air/water interface as a function of the number and the relative position of the modified end groups. We find that the PAMAM dendrimer with all terminal groups functionalized is more stable at the interface than the Janus dendrimer where only half the amine groups are modified. This result is explained in terms of softness of the dendrimer molecule which adapts its conformation to maximize the favorable amide-water contacts segregating the alkyl chains and increasing the structural order of the "hydrophilic core". We interpret the stability of the molecule at the interface also in terms of particle wettability and energy components. We verify that the atomistic model follows the prediction of the thermodynamic analytical theory adopting an oblate or prolate shape and orientating its longest axis parallel to the normal to the interface. These results indicate that monolayers of fully functionalized molecules could be as stable as (or more stable than) those self-assembled from proper Janus molecules.

In vivo biostability of polyether polyurethanes with fluoropolymer and polyethylene oxide surface modifying endgroups; resistance to metal ion oxidation

Polyether polyurethanes are subject to oxidation catalyzed by, and through direct (redox) reaction with transition metal ions (metal ion oxidation, MIO). The source of the ions is corrosion of metallic parts within an implanted device. A Shore 80A polyether polyurethane was modified with fluoropolymer (E80AF) or polyethylene oxide (E80AP) surface modifying end groups (SME). The SME migrates to the surface to form a covalently bonded monolayer, while maintaining the bulk properties of the polyurethane. In vitro tests in H(2)O(2) solution indicated that both SME's accelerated MIO. Tubing samples containing cobalt mandrels were implanted in the subcutis of rabbits for up to 2 years. In vivo, E80AF significantly slowed the rate of visible degradation, but did not prevent MIO. E80AP had virtually identical visual performance to the unmodified control in vivo. Infrared spectroscopy and molecular weight correlated well with visual appearance. When cracks were seen, polyether soft segment oxidation was occurring. Both E80AP and the control developed severe loss of molecular weight in vivo. The changes were much less severe for E80AF. Thus, contrary to in vitro test results, the PEO SME had no effect at all on MIO resistance, while the fluoropolymer SME produced a significant improvement in biostability.

In vivobiostability of shore 55D polyether polyurethanes with and without fluoropolymer surface modifying endgroups

Polyether polyurethanes are subject to autooxidation and environmental stress cracking (ESC) because of interactions with lysosomal oxygen-free radicals. Oxidation can also be catalyzed by and caused by direct (redox) reaction with transition metal ions (metal ion oxidation, MIO). The source of the ions is corrosion of metallic parts within an implanted device. A previous study on a Shore 80A polyether polyurethane modified with fluoropolymer surface modifying end groups demonstrated improved biostability over unmodified controls. We predicted that this could be extrapolated to the inherently more biostable Shore 55D version (E55DF). While it is difficult to demonstrate significant biodegradation in the harder polymers within a reasonable time frame, we did see excellent biologic autooxidation and ESC resistance for both E55DF and its unmodified Shore 55D (P55D) control. E55DF was slightly, but significantly more resistant to MIO than P55D. This was particularly evident in molecular weight distributions with P55D exhibiting a large decrease in number average molecular weight compared to no change for E55DF. Both were markedly superior to the softer Shore 80A control. It does appear that one can extrapolate accelerated in vivo biostability results with the softer polymers to their harder analogues.

In vivo biostability of polyether polyurethanes with fluoropolymer surface modifying endgroups: Resistance to biologic oxidation and stress cracking

A series of Shore 80A polyether polyurethanes were synthesized with from 0 to 6% fluoropolymer surface modifying endgroups (SME) to provide the bulk properties of the polyurethane with the surface properties of the fluoropolymer. It was theorized that the fluoropolymer would migrate to the surface, forming a monolayer barrier to the oxidants and crack-driving agents released by macrophages and foreign body giant cells in vivo. In a 12-week biostability screening test, samples strained to 400% elongation appeared to be highly stable. In a longer-term study, the fluoropolymer SME significantly delayed, but did not completely prevent the onset of microcracking and the development of environmental stress cracking in strained samples. Even so, the 4 and 6% SME polymers explanted at 2 years performed significantly better than the control. FTIR analysis did not correlate with SME concentration, but increased hydrogen-bonding index and loss of aliphatic ether (autoxidation) did correlate with the visual appearance and density of microcracks. Significant molecular weight reductions were seen for the SME-free control, but were small (within instrumental error) for the polymers with SME. The use of fluoropolymer as a SME does appear to be warranted as a means to improve polyether polyurethane biostability.

Macrophage behavior on surface-modified polyurethanes

Adherent macrophages and foreign body giant cells (FBGCs) are known to release degradative molecules that can be detrimental to the long-term biostability of polyurethanes. The modification of polyurethanes using surface modifying endgroups (SMEs) and/or the incorporation of silicone into the polyurethane soft segments may alter macrophage adhesion, fusion and apoptosis resulting in improved long-term biostability. An in vitro study of macrophage adhesion, fusion and apoptosis was performed on polyurethanes modified with fluorocarbon SMEs, polyethylene oxide (PEO) SMEs, or poly(dimethylsiloxane) (PDMS) co-soft segment and SMEs. The fluorocarbon SME and PEO SME modifications were shown to have no effect on macrophage adhesion and activity, while silicone modification had varied effects. Macrophages were capable of adapting to the surface and adhering in a similar manner to the silicone-modified and unmodified polyurethanes. In the absence of IL-4, macrophage fusion was comparable on the modified and unmodified polyurethanes, while macrophage apoptosis was promoted on the silicone modified surfaces. In contrast, when exposed to IL-4, a cytokine known to induce FBGC formation, silicone modification resulted in more macrophage fusion to form foreign body giant cells. In conclusion, fluorocarbon SME and PEO SME modification does not affect macrophage adhesion, fusion and apoptosis, while silicone modification is capable of mediating macrophage fusion and apoptosis. Silicone modification may be utilized to direct the fate of adherent macrophages towards FBGC formation or cell death through apoptosis.

Carboxylic acid end group modification of poly(butylene terephalate) in supercritical fluids

Carboxylic acid end groups of poly(butylene terephalate) (PBT) granules were modified with an excess of 1,2-epoxybutane in supercritical CO 2 and in supercritical and subcritical mixtures of CO 2 with 10 mol% 1,4-dioxane. Temperatures of 120 and 180 °C and pressures of 60, 150 and 300 bar were applied. Best results were obtained for the modification in scCO 2 containing 10 mol% 1,4-dioxane at 180 °C. The carboxylic acid end group concentration was reduced from 44 mmol/kg to approximately 10 mmol/kg, which resulted in a significantly enhanced hydrolytic stability. This was demonstrated by measuring, both for unmodified and for 1,2-epoxybutane blocked PBT, the intrinsic viscosity as a function of hydrolysis time as well as the number and weight average molecular weights ( M ̄ n and M ̄ w ) before and after hydrolysis. After the modification, some PBT granules appeared more brittle than the unmodified PBT granules. The crystallinity proved to be enhanced by the plasticising effect of CO 2/1,4-dioxane at 180 °C. No indications were obtained that the 1,2-epoxybutane modified end groups exhibit a nucleating effect on the PBT crystallisation.

Combined experimental and theoretical investigations of clay–polymer nanocomposites: intercalation of single bifunctional organic compounds in Na+-montmorillonite and Na+-hectorite clays for the design of new materials

This paper reports a study of the intercalation of single bifunctional poly(ethylene oxide)- and poly(propylene oxide)-based compounds, with and without modified end groups, in Na+-montmorillonite and Na+-hectorite clays as the starting point for the design of new non-exfoliated clay–polymer materials. The terminal functional groups employed on intercalated poly(ethylene oxide) and poly(propylene oxide) include acrylate, methacrylate and amine functions. For some of the monomers, in situ polymerisation was observed. Attempts to rationalise these behaviours are made on the basis of atomistic grand canonical Monte Carlo, canonical Monte Carlo and molecular dynamics simulations. Poly(ethylene oxide) diacrylate monomers, for which in situ polymerisation was observed, interact more strongly with the Na+-montmorillonite clay layers than the other monomers.

Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry

Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.

Study of the thermal degradability of poly(α‐methylstyrene) with modified end groups

AbstractTo induce degradabilities in polymers in response to environmental conditions, endm odification reactions of poly(α‐methylstyrene) (PMS) derivatives were carried out. 2‐Phenylallyl halide derivatives such as 2‐phenylallyl bromide, 2‐(p‐tolyl)allyl bromide, and α‐trifluoromethylstyrene were found to be suitable end‐modification agents. For example, the ω‐2‐phenylallyl‐PMS derivative was prepared with almost quantitative functionality by the reaction of the living PMS derivative with 2‐phenylallyl bromide. In a similar way, ω‐3,3‐difluoro‐2‐phenylallyl‐ and ω‐2‐(4‐toly)allyl‐PMS derivatives were synthesized. Based on thermogravimetric analysis, the onset of the degradation temperature of the endmodified PMS derivatives decreased in the following order: ω‐hydrogen‐ &gt; ω‐3,3‐difluoro‐2‐phenylallyl‐ &gt; ω‐2‐phenylallyl‐ &gt; ω‐2‐(p‐tolyl)allyl‐PMS. Actually, the onset temperature of ω‐2‐(p‐tolyl)allyl‐PMS derivatives was 50°C lower than that of ω‐H‐PMS derivatives. These results indicate that the active species is produced effectively at the endunsaturated bond, which initiates depolymerization of the polymer at rather low temperatures. Therefore, it is concluded that a 2‐phenylallyl substituent at the end of the PMS chain induces effective degradation through a radical mechanism.

Application of mass spectrometry to copolymers of ethylenes and propylene oxides. I. Structural analysis

AbstractMass spectra of linear copolymers of ethylene and propylene oxides show features which are characteristic of the two monomers. Interpretation of the spectra of samples with and without modified end groups allows them to be classified as either random or blocked in structure and, in the latter case, permits determination of the order in which blocks are incorporated. Within a limited molecular weight range, the method can lead to a full determination of the distribution of molecular weights in the samples.

Chemical and Enzymatic Studies of Deoxyribonucleic Acid Covalently Linked to Ficoll

Abstract Nucleotides and polynucleotides with terminal phosphoryl groups can be covalently linked in a carbodiimide reaction to water-soluble polysaccharides such as Ficoll and dextran. Small, dialyzable nucleotides can be converted to nondialyzable macromolecules of high molecular weight. Hybrid molecules of polynucleotides and polysaccharides have novel properties such as a reduced density in cesium chloride and modified end groups. Nucleotides and polynucleotides attached to Ficoll have been used in enzymatic studies of deoxyribonuclease, polynucleotide kinase, and DNA polymerases.