Effect Of End Groups Research Articles

Synthesis of copolymers with cyclodextrin as pendants and its end group effect as superplasticizer

In this paper, the efficient approach for the synthesis of β-cyclodextrin (CD) based functional monomers was described. Based on the monovinyl β-CD monomer (GMA-EDA-CD), a new type poly(AA-co-GMA-EDA-CD) (PCDs) copolymer bearing pendent CD groups was synthesized and used as superplasticizer. Their chemical compositions were characterized by FT-IR, NMR, MALDI-TOF and GPC. The effects of PCDs on dispersion and adsorption in cement mortars were detailed discussed. The results indicated that PCD copolymers behaved excellent dispersion ability and strong retarding effect. PCD2 with molar ratio (%) for monomer (AA:GMA-EDA-CD=80:20) had the best dispersion and dispersion maintaining abilities, which were mainly attributed to the synergistic effects of steric hindrance and electrostatic repulsive force, and the retarding effect of PCD copolymers resulted from steric hindrance repulsion of CD pendants and the large number of hydroxyl groups, which affected the hydration reaction of cement.

Theoretical investigation of substitution and end-group effects on poly(p-phenylene vinylene)s

Semi-empirical AM1 and ZINDO/S, as well as density function theory (DFT) method B3LYP/6-31G(d) quantum chemical calculations were carried out to study the electronic structures and optical properties of poly(p-phenylene vinylene) derivatives (PPVs) with 10 and 11 phenylene rings in the backbone. The calculations suggest that the assembly of alternate incorporation of CN and alkoxy substituted phenylene rings in the PPV backbone could be a good way to construct organic semiconductors with low HOMO/LUMO energy band-gaps. The effect of the end-group on the electronic structures and optical properties of the conjugated polymer was investigated by the calculated UV-Vis and UPS spectra. It was demonstrated that the aldehyde and phosphate end-groups have limited effects on the photophysical properties in the UV-visible range.

Lubricant Flow and Evaporation Model for Heat-Assisted Magnetic Recording Including Functional End-Group Effects and Thin Film Viscosity

The lubricant covering a hard disk in a heat-assisted magnetic recording drive must be able to withstand the writing process in which the disk is locally heated several hundred degrees Celsius within a few nanoseconds to reduce the coercivity of the media and allow writing of data. As a first step in modeling a robust lubricant, we have developed a simulation tool based on continuum theory that incorporates previously proposed variations of viscosity and an additional component of disjoining pressure due to functional end-groups with film thickness. Here we apply this simulation tool to a conventional perfluoropolyether lubricant, Zdol 2000, for which there exists experimental data. The simulation tool can be used equally well for other lubricants once their properties become known. Simulations at small length and time scales that are unobservable with current experimental capabilities are performed. We investigate the effect of the total disjoining pressure and thin film viscosity on evaporation and lubricant flow for different initial thickness. For films thicker than 1 nm, the inclusion of polar disjoining pressure suppresses the lubricant thickness change due to evaporation and thermocapillary shear stress compared with cases without this component. Thin film viscosity is an important property to consider for thinner lubricants. We also consider how lubricant depletion depends on laser spot size and thermal spot maximum temperature. The smaller spot profiles exhibit side ridges due to thermocapillary shear stress while the larger spot profiles show no side ridges, only a trough due to evaporation. The lubricant depletion zone width and depth increase with increasing thermal spot maximum temperature.

Retraction Note: Plasma protein adsorption to zwitterionic poly (carboxybetaine methacrylate) modified surfaces: chain chemistry and end-group effects on protein adsorption kinetics, adsorbed amounts and immunoblots

Protein–surface interactions are crucial to the overall biocompatability of biomaterials, and are thought to be the impetus towards the adverse host responses such as blood coagulation and complement activation. Only a few studies hint at the ultra-low fouling potential of zwitterionic poly(carboxybetaine methacrylate) (PCBMA) grafted surfaces and, of those, very few systematically investigate their non-fouling behavior. In this work, single protein adsorption studies as well as protein adsorption from complex solutions (i.e. human plasma) were used to evaluate the non-fouling potential of PCBMA grafted silica wafers prepared by nitroxide-mediated free radical polymerization. PCBMAs used for surface grafting varied in charge separating spacer groups that influence the overall surface charges, and chain end-groups that influence the overall hydrophilicity, thereby, allows a better understanding of these effects towards the protein adsorption for these materials. In situ ellipsometry was used to quantify the adsorbed layer thickness and adsorption kinetics for the adsorption of four proteins from single protein buffer solutions, viz, lysozyme, α-lactalbumin, human serum albumin and fibrinogen. Total amount of protein adsorbed on surfaces differed as a function of surface properties and protein characteristics. Finally, immunoblots results showed that human plasma protein adsorption to these surfaces resulted, primarily, in the adsorption of human serum albumin, with total protein adsorbed amounts being the lowest for PCBMA-3 (TEMPO). It was apparent that surface charge and chain hydrophilicity directly influenced protein adsorption behavior of PCBMA systems and are promising materials for biomedical applications.

Effect of Functional Groups on the Sensing Properties of Silicon Nanowires toward Volatile Compounds

Molecular layers attached to a silicon nanowire field effect transistor (SiNW FET) can serve as antennas for signal transduction of volatile organic compounds (VOCs). Nevertheless, the mutual relationship between the molecular layers and VOCs is still a puzzle. In the present paper, we explore the effect of the molecular layer's end (functional) groups on the sensing properties of VOCs. Toward this end, SiNW FETs were modified with tailor-made molecular layers that have the same backbone but differ in their end groups. Changes in the threshold voltage (ΔVth) and changes in the mobility (Δμh) were then recorded upon exposure to various VOCs. Model-based analysis indicates that the interaction between molecular layers and VOCs can be classified to three main scenarios: (a) dipole-dipole interaction between the molecular layer and the polar VOCs; (b) induced dipole-dipole interaction between the molecular layers and the nonpolar VOCs; and (c) molecular layer tilt as a result of VOCs diffusion. Based on these scenarios, it is likely that the electron-donating/withdrawing properties of the functional groups control the dipole moment orientation of the adsorbed VOCs and, as a result, determine the direction (or sign) of the ΔVth. Additionally, it is likely the diffusion of VOCs into the molecular layer, determined by the type of functional groups, is the main reason for the Δμh responses. The reported findings are expected to provide an efficient way to design chemical sensors that are based on SiNW FETs to nonpolar VOCs, which do not exchange carriers with the molecular layers.

Effects of chemical structure and chain end groups on the thermal stability of new silsesquioxanes with methacrylate and/or vinyl units

The paper reports the synthesis of new silsesquioxanes with methacrylate and/or vinyl units, obtained by combining the sol–gel technique with radical polymerization in the presence of 2,2′-azobis(2-methylpropionitrile) as initiator and a cationic surfactant, cetyltrimethylammonium bromide. The thermal behaviour was investigated through simultaneous thermogravimetric and differential scanning calorimetry analysis (TG/DSC) coupled on-line with Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS), as well as by pyrolysis and gas chromatography–mass spectrometry (GC–MS). The aim of the investigation consists in drawing useful information on the influence of both chemical structure and chain end double bonds and silanol units on the resistance of such compounds against thermal degradation.

Cellulose degradation in alkaline media upon acidic pretreatment and stabilisation

The present study reports on a revised kinetic model for alkaline degradation of cellulose accounting for primary peeling/stopping reactions as well as for alkaline hydrolysis followed by secondary peeling. Oxalic acid pretreated cotton linters was utilised as the model substrate for the prehydrolysis-soda anthraquinone process. The main emphasis was investigating the effect of end-group stabilising additives such as sodium borohydride (BH), anthraquinone (AQ), and anthraquinone-2-sulphonic acid sodium salt (AQS) on the rates of the yield loss reactions. BH and AQS ensured a cellulose yield gain of 13% and 11%, respectively, compared to the reference. Both stabilisation agents decreased the content of the reducing end groups in the samples, while in the case of AQS stabilisation a 25% increase in carboxyl group content compared to the reference was also observed. As expected, the addition of end group stabilisers resulted in a significant decrease in the peeling-to-stopping rate constants ratio.

Elucidating the smectic A-promoting effect of halogen end-groups in calamitic liquid crystals

Two isometric series of chloro-terminated 5-alkoxy-2-(4-alkoxyphenyl)pyrimidine mesogens QL8-m/n and QL9-m/n (m + n = 16), with the chloro-terminated alkoxy chain tethered to either the pyrimidine ring or the phenyl ring, were synthesized and their liquid crystalline properties characterized by polarized optical microscopy and differential scanning calorimetry. Based on the analysis of mesogenic properties and correlations to electrostatic potential isosurfaces calculated at the B3LYP/6-31G* level, we present evidence suggesting that the SmA-promoting effect of chloro end-groups is not due to strong polar interactions at the layer interfaces, as previously postulated in the literature. Instead, the evidence suggests that the SmA-promoting effect is due to the electron-withdrawing effect of the chloro end-group, which should reduce electrostatic repulsion between alkoxy chains and, consequently, increase van der Waals interactions between aromatic cores in the orthogonal SmA phase.

Facile tuning of plasmon bands in hollow silver nanoshells using mild reductant and mild stabilizer

Hollow silver nanoshells with tunable plasmon bands have been synthesized using Ag2O nanoparticles at an optimized temperature of 20 °C. The plasmon peak has been tuned in a wide range from 460 nm to 605 nm employing a combination of mild reductant and a mild stabilizer, hydrazine hydrate and sodium citrate, respectively. In contrast, the combination of strong reductant and strong stabilizer, NaBH4 and hydrophilic thiols, resulted in limited plasmon tunability (455-510 nm). The differential behaviour is attributed to the change in dynamics of the diffusion-reaction process. For thiols, the effect of free end-groups was quite evident as plasmon peak shifted from 449 nm to 470 nm on replacing thioglycolic acid (HS-CH2-COOH) with mercaptoethanol (HS-CH2-CH2-OH). Transmission electron microscopy (TEM) revealed that the aspect ratio [outer diameter (d)/shell thickness (t)] was 2.8 (d: 40.0 ± 1.6 nm, t: 14.0 ± 1.3 nm) and 5 (d: 84 ± 2.3 nm, t: 16.8 ± 1.9 nm) for the nanoshells exhibiting a plasmon peak at 460 nm and 605 nm, respectively. The crystal phase of nanoshells was found to be face centered cubic (fcc) as deduced from HR-TEM and electron diffraction data. Using the same Ag2O template, morphological transformation from non-porous to mesoporous has also been achieved by simply reversing the order of addition.

Positively Charged Dendron Micelles Display Negligible Cellular Interactions

PEGylated dendron-based copolymers (PDC) with different end-group functionalities (-NH(2), -COOH, and -Ac) were synthesized and self-assembled into dendron micelles to investigate the effect of terminal surface charges on size, morphology, and cellular interactions of the micelles. All of the dendron micelles exhibited similar sizes (20-60 nm) and spherical morphologies, as measured using dynamic light scattering and transmission electron microscopy, respectively. The cellular interactions of dendron micelles were evaluated using confocal microscopy and flow cytometry. Surprisingly, although amine-terminated dendrimers are known to strongly interact with cells non-specifically, all of the surface-modified dendron micelles exhibited charge-independent low-levels of cellular interaction. The unexpected results, particularly from the amine-terminated dendron micelles, could be attributed to: i) minimal end-group effects, as each PDC has an approximately 10-fold lower charge-number-to-molecular-weight ratio compared to the dendrimer; and ii) intra- and intermolecular hydrogen bonding between positively charged terminal groups with poly(ethylene glycol) (PEG) backbones, which leads to the sequestration of the charges, as demonstrated by atomistic molecular dynamics simulations. With the narrow size distribution, uniform morphologies, and low levels of non-specific cellular interactions, the dendron micelles offer a promising drug delivery platform.

New insights into the effects of molecular weight and end group on the temperature-induced phase transition of poly(N-isopropylacrylamide) in water

In an attempt to clarify issues related to the molecular weight dependence of the phase transition of poly(N-isopropylacrylamide) (PNIPAM) in water, we prepared a library of PNIPAM samples of well-controlled molecular weight (7000 to 45000 g/mol) bearing identical groups on each chain end. The polymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N-isopropylacrylamide (NIPAM) with a bifunctional chain tranfer agent and further end group modification. The effects of the end group chemical structure, hydroxyethyl (HE), propargyl (Pr), chloroethyl (CE), n-butyl (nBu), n-hexyl (nHe), and isobutylsulfanylthiosulfanyl (IBS) on the phase transition temperature of aqueous PNIPAM solutions were investigated by high-sensitivity differential scanning calorimetry (HS-DSC), yielding the enthalpy ΔH and the endotherm maximum temperature (TM), and turbidimetry, providing the cloud point (TCP) of each solution. The TCP and TM of the PNIPAM sample of lowest molar mass (Mn 7,000 g/mol, 0.5 g/L) ranged, respectively, from 38.8 to 22.5 °C and 42.2 to 26.0 °C, depending on the structure of the end-group, whereas ΔH showed no strong end-group dependence. The phase transition of all polymers, except α,ω-di(n-butyl-PNIPAM), exhibited a marked dependence on the polymer molar mass.

Effect of End Groups on Optoelectronic Properties of Poly(9,9-dioctylfluorene): A Study with Hexadecylfluorenes as Model Polymers

Monodisperse hexadecyl(9,9-dioctylfluorene)s F16, BrF16, and BF16, which comprise H, Br, and boronic pinacol ester end groups, respectively, were synthesized, and the effect of these end groups on the photophysical, electrochemical, and electroluminescent properties of the polymers were investigated. The end groups have no noticeable effect on the energy levels of the polymers. F16 and BrF16 show high photoluminescence (PL) quantum yields (Phi s) in both solution and film states. Film PL Phi s (Phi(film)s) of F16 and BrF16 are 0.72 and 0.79, respectively. These values are about 1.4-1.5 times of that of BF16 and poly(9,9-dioctylfluorene) (PFO) prepared by Suzuki polycondensation. Moreover, Phi(film)s of F16 and BrF16 were kept almost the same after thermal annealing at 120 degrees C in both air and argon atmospheres. By contrast, the Phi(film)s of BF16 and PFO dramatically decreased to 0.25 and 0.2.9 after thermal annealing at 120 degrees C in air. Polymer light-emitting diodes (PLEDs) were fabricated. F16, BrF16, and PFO exhibited maximum luminance efficiencies of 0.60, 0.27, and 0.39 cd.A(-1), respectively; while that of BF16 was as low as 0.024 cd.A(-1). Meanwhile, green emission was observed for devices of BrF16, BF16, and PFO, but not for devices of F16. Electron- and hole-only devices were fabricated for elucidating the effect of end groups on charge transporting properties of the polymers. While Br is a mild hole-trapper, boronic ester group traps both holes and electrons, resulting in severely unbalanced hole- and electron-transport. Our results indicate that boronic ester end groups have a detrimental effect on the optoelectronic properties of polyfluorenes larger than Br.

Mechanism of ion transport in PEO/LiTFSI complexes: Effect of temperature, molecular weight and end groups

The conductivity and viscosity of PEO/LiTFSI complexes are determined as a function of temperature, molecular weight (Mn) and the end group nature in view of the design of future polymer electrolytes. The results show the crucial role of the end groups on the dynamics of polymers at low Mn. A new method is proposed to estimate the glass transition temperature variation as function of Mn and end groups using conductivity data. The conductivity and viscosity plotted at constant friction factor follow a master curve which suggests that the main impact of end groups is to modify the available free volume which governs in turn the segmental dynamics. The anion and cation conductivities are separated using the cationic transport number obtained by pfg-NMR. Finally, an empirical equation based on Rouse dynamics taking into account the effect of the end groups is proposed. It reproduces with a good degree of accuracy the conductivities over the whole temperature and Mn ranges. In agreement with molecular dynamic simulations, at high Mn the limiting step is the jump of the lithium ion from one coordination site to another and is not influenced by the dynamics of the PEO chain reptation, whereas at low Mn the transport is mainly ensured by a vehicular mechanism.

Effects of polymer end groups on the drying rates of phase separating coatings

The effect of chain end groups on the drying of phase separating polymer blends was investigated for different functionally terminated poly(dimethyl siloxane) (PDMS). The drying rates of a PDMS/cellulose acetate butyrate (CAB) blend in methyl ethyl ketone (MEK) or isopropyl acetate (IA) were measured using the gravimetric method. The weight loss curves revealed that the addition of dihydroxyl-terminated PDMS significantly increased the drying rate in a particular range of solvent concentrations. On the contrary, monoglycidyl-ether-terminated and monohydroxyl-terminated PDMS showed suppressed evaporation and particular transitions between suppressed and enhanced drying modes, respectively. The drying enhancement was especially observed in cases where the separating polymer domains were developed through a film, regardless of the surface activities of PDMS. These facts imply that the interfaces between the domains act as diffusion paths for solvent molecules, and thus guide the transportation of solvent from the interior to the surface.

End-Group-Induced Charge Transfer in Molecular Junctions: Effect on Electronic-Structure and Thermopower

We analyze triphenyl molecules coupled to gold electrodes through five different end groups to understand the effect of end groups on the thermoelectric properties of molecular junctions. Our investigation suggests that end-group-mediated charge transfer between the molecule and electrodes plays an important role in the resulting thermoelectric properties. We find that the direction of charge transfer, which is governed by the electronegativity of the end-group functionalized molecule, is strongly correlated to the degree of reorganization of frontier molecular orbitals (HOMO–LUMO). In particular, isocyanide, nitrile, and amine end-group molecular junctions, with charge (electron) transfer out of the molecule, exhibit a strong overall downward shift in the energies of frontier molecular orbitals, whereas thiol and hydroxyl end-group molecular junctions, with charge transfer into the molecule, exhibit a smaller overall downward shift. Finally, our study shows that the sign of the thermopower of molecular j...

RETRACTED ARTICLE: Plasma Protein Adsorption to Zwitterionic Poly (Carboxybetaine Methacrylate) Modified Surfaces: Chain Chemistry and End-Group Effects on Protein Adsorption Kinetics, Adsorbed Amounts and Immunoblots

Protein-surface interactions are crucial to the overall biocompatability of biomaterials, and are thought to be the impetus towards the adverse host responses such as blood coagulation and complement activation. Only a few studies hint at the ultra-low fouling potential of zwitterionic poly(carboxybetaine methacrylate) (PCBMA) grafted surfaces and, of those, very few systematically investigate their non-fouling behavior. In this work, single protein adsorption studies as well as protein adsorption from complex solutions (i.e. human plasma) were used to evaluate the non-fouling potential of PCBMA grafted silica wafers prepared by nitroxide-mediated free radical polymerization. PCBMAs used for surface grafting varied in charge separating spacer groups that influence the overall surface charges, and chain end-groups that influence the overall hydrophilicity, thereby, allows a better understanding of these effects towards the protein adsorption for these materials. In situ ellipsometry was used to quantify the adsorbed layer thickness and adsorption kinetics for the adsorption of four proteins from single protein buffer solutions, viz, lysozyme, α-lactalbumin, human serum albumin and fibrinogen. Total amount of protein adsorbed on surfaces differed as a function of surface properties and protein characteristics. Finally, immunoblots results showed that human plasma protein adsorption to these surfaces resulted, primarily, in the adsorption of human serum albumin, with total protein adsorbed amounts being the lowest for PCBMA-3 (TEMPO). It was apparent that surface charge and chain hydrophilicity directly influenced protein adsorption behavior of PCBMA systems and are promising materials for biomedical applications.

Poly(butylene/diethylene glycol succinate) multiblock copolyester as a candidate biomaterial for soft tissue engineering: Solid-state properties, degradability, and biocompatibility

A multiblock bioresorbable copolyester, poly(butylene/diethylene glycol succinate), was synthesized by reactive blending, and it was used, together with the corresponding poly(butylene succinate) homopolymer, to form films and to fabricate biomimetic electrospun scaffolds. The poly(butylene/diethylene glycol succinate) scaffold had a more pronounced elastomeric behavior than poly(butylene succinate). It also underwent hydrolytic degradation faster than poly(butylene succinate) since the incorporated diethylene glycol succinate units rendered the copolymer more hydrophilic than poly(butylene succinate). The films degraded faster than electrospun samples due to the autocatalytic effect of carboxylic end-groups. The biodegradable poly(butylene/diethylene glycol succinate) scaffold supported the growth and preserved the cardiac phenotype markers of H9c2 cells, demonstrating its potential utility in soft tissue engineering applications.

Effects of End-Groups on Properties of Hyperbranched Polyether

In order to investigate influence of end-groups on thermodynamic property and viscosity of hyperbranched polyether. Three series of hyperbranched polyethers with three different end-groups were studied. These three groups are: hydroxyl, acetate and stearic acid ester. The result confirms the complicated effect of end-groups on properties of hyperbranched polymer. When end-groups change from polar groups of hydroxyl to non-polar groups of acetate, glass transition temperature reduced about 50°C, viscosity reduced sharply too. Glass transition temperature and viscosity all increase with generation rise. When end-groups change from acetate to stearic acid ester, corresponding hyperbranched polyether change from amorphous to crystalline. The crystallization stemmed from long chain structure of end-group, which is easy to form crystalline, its crystalline region molten become main thermodynamic transformation, and obscure the glass transition.

Effects of nanoparticle surface-coupled peptides, functional endgroups, and charge on intracellular distribution and functionality of human primary reticuloendothelial cells

The medical use of nanoparticles (NPs) has to consider their interactions with the cells of the reticuloendothelial system. In this study the authors used gold nanorods coated by PEG chains bearing peptides or charged functional groups to study their influence on the uptake, subcellular distribution, and activation of human primary reticuloendothelial cells: monocytes, macrophages (MΦ), immature and mature dendritic cells (DC), and endothelial cells (EC). We found that beside MΦ and immature DC also EC internalize large quantities of NPs and observed an increased uptake of positively charged particles. Most notably, NPs accumulated in the MHC II compartment in mature DC that is involved in antigen processing. Furthermore, surface-coupled peptide sequences RGD and GLF altered the activation profile of DC, and modulated cytokine release in both DC and MΦ in a cell specific manner. These data suggest that the charge of NPs mainly influences their uptake, whereas conjugated peptides alter cell functions. From the Clinical EditorIn this paper the interactions between RES cells and nanoparticles is investigated, concluding that in the case of gold nanorods charge determines uptake characteristics, whereas conjugated peptides determine their function.

Synthesis and the effect of hydrophobic dodecyl end groups on pH-responsive micellization of poly(acrylic acid) and poly(ethylene glycol) triblock copolymer in aqueous solution

A pH-responsive triblock copolymer of poly(acrylic acid)-b-poly(ethylene glycol)-b-poly(acrylic acid) containing hydrophobic dodecyl end groups (C12H25-PAA-b-PEG-b-PAA-C12H25) with narrow molecular weight distribution (M w/M n = 1.30) was synthesized via reversible addition-fragmentation chain transfer polymerization of acrylic acid (AA). Poly(ethylene glycol) (PEG) capped with S-1-dodecyl-S′-(α,α′-dimethyl-α″-acetic acid) trithiocarbonate (DDATC) end groups was used as the macro chain transfer agent (PEG macro-CTA) and 2,2′-azobisisobutyronitrile (AIBN) as initiator for monomer acrylic acid. The effect of the hydrophobic dodecyl end groups on pH-sensitive self-association of C12H25-PAA-b-PEG-b-PAA-C12H25 in aqueous solution was investigated by fluorescence spectroscopy, dynamic light scattering and atomic force microscope. At pH ≥5.5, the solution behavior of C12H25-PAA-b-PEG-b-PAA-C12H25 is like polyelectrolyte in aqueous solution, and the effect of dodecyl end groups is negligible. At pH <5.0, the hydrophobic dodecyl end groups contribute dominantly to the pH-sensitive micellization and result in the formation of micelles with stronger hydrophobicity and larger size at low concentration (critical micelle concentration is 0.062 g/L). In the range of pH 2.5–3.5, the steady (R h ≈ 35.0 nm) and narrow size distributed micelles (polydispersity index, PDI < 0.2) can be obtained. The micelles formed by C12H25-PAA-b-PEG-b-PAA-C12H25 triblock copolymer in acidic solution are expected to have a core–shell–corona structure, where the hydrophobic dodecyl groups form the core, and weak hydrophobic PAA/PEG hydrogen-bonded complexes form the shell and the uncomplexed PAA, and PEG chain segments form the corona.