Amine End Groups Research Articles

Fifth Generation Polyurethane Dendrimers Decorated with Protected Amine, Free Amine and Blocked Isocyanate End Groups: Synthesis and Electrolytic Performance to Increase the Efficiency of Dye‐Sensitized Solar Cell

AbstractFifth generation polyurethane dendrimers decorated with trifluoroacetamide, free amine and blocked isocyanate end‐groups were prepared and their structures were confirmed using FT‐IR, 1H and 19F‐NMR, MALDI‐TOF MS and size exclusion chromatography (SEC‐MALS) techniques. The hydrodynamic diameter and zeta potential of dendrimers were measured using dynamic light scattering (DLS) technique; the later parameter indicated that the dendrimer containing trifluoroacetamide end‐group (1) stabilized more in the medium. The effect of different end‐groups on photophysical, electrochemical and thermal properties of dendrimers were also evaluated; dendrimer with blocked isocyanate end‐groups (3) absorbed low light, showed two redox potential and exhibited glass transition temperature (Tg). All the dendrimers were used as electrolytes in combination with LiI for N719 dye‐sensitized solar cells (DSSCs) and found that the DSSC fabricated with blocked isocyanate‐terminated dendrimer (3) yielded nearly 2.5 times high power conversion efficiency (ɳ=8.04% upon illumination with 0.5 sun intensity) compared to the cell fabricated with only LiI electrolyte.

Complexes of end-functionalized polystyrenes carrying amine end-group with transition metals: association effects in organic solvents

Linear end-functionalized polystyrenes of different molecular weights bearing amino end-group (NPS) were synthesized by anionic polymerization high vacuum techniques. The polymers were exposed to copper and iron salts (CuCl2.2H2O and FeCl3.6H2O) to form complexes with specific metal/amino molar ratios. The thermal stability of these complexes was studied by Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG), whereas their solution behavior was studied by Low Angle Laser Light Scattering (LALLS), Dynamic Light Scattering (DLS) and dilute solution Viscometry. Extended aggregation phenomena of these complexes were observed in organic solvents. The association behavior was influenced by the molecular weight of the polymer chain, the metal/amine group molar ratio, the chemical nature of the metal and the polarity of the solvent. A complex situation was revealed by DLS showing the existence of equilibrium between aggregates and clusters. Under the influence of shear forces applied in the capillary tube of the viscometer the clusters are disrupted.

Cysteine-Modified Self-Assembling Peptides on Gold: The Role of the Head and Tail.

Molecular self-assembly consists of the spontaneous aggregation of molecules into a well-defined structure guided by noncovalent bonds. The self-assembly strategy is ubiquitous in nature and recently has been proposed as a nature-mimetic strategy in polymer science and biomaterial engineering. In this context, we aim at designing and testing innovative but simple chemical strategies to efficiently modify surfaces by exploiting minor modifications in the bioactive molecule functionalities, for example, introducing cysteine (Cys) as a terminal residue in self-assembling peptides (SAPs). In this work, we report the attenuated total reflection-Fourier transform infrared spectroscopy, synchrotron radiation-induced X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and time-of-flight secondary ion mass spectrometry investigation of self-assembled layers of oligopeptides anchored onto gold surfaces through cysteine residues, opportunely inserted in an SAP (EAK16-II) main chain in three different positions: at the amine end group, at the carboxyl end group, and at both terminal groups (i.e., a bidentate SAP). This study, which allowed us to individuate in the bidentate SAP the best candidate for the controlled production of ordered SAP layers on the gold substrate surface, is envisaged to open wide perspectives for efficient chemical modification of surfaces with biomolecules, leading to obtaining innovative bioactive materials for applications in the field of tissue engineering.

Synthesis of Hydrophilic Polyamide Copolymers Based on Nylon 6 and Nylon 46

Hydrophilic polyamide copolymers were successfully synthesized based on Nylon 6 and Nylon 46. This study aims to synthesize hydrophilic polyamides with moisture regain ability comparable to that of cotton. Random copolymers of nylon 6 and nylon 46 did not exhibit moisture regain rates higher than 6 %. A limited introduction of trifunctional monomer, diethylenetriamine (TA) produced the polyamides with higher mechanical strengths but failed to enhance the moisture regain. The incorporation of poly(ethylene oxide) oligomer with amine end groups increased the moisture regain but resulted in poor hydro-thermal and mechanical strength. A synergic effect was observed for copolymers which contain both nylon 46 units and PEO oligomer in regards to moisture regain capacity. Furthermore, the poor hydro-thermal and mechanical strength of Nylon/PEO segmented polyamides were drastically improved by the introduction of diethylenetriamine (TA). This study demonstrated that the polyamide copolymers comprising both PEO oligomer and TA unit record tensile moduli over 3 GPa and moisture regain rates of 8–10 wt%.

Adsorption of organic pollutants by amine functionalized mesoporous silica in aqueous solution. Effects of pH, ionic strength and some consequences of APTES stability

A mesoporous silica with MCM-41 type pore array was synthesized by hydrothermal method and then was functionalized with known amounts of 3-aminopropyltriethoxysilane (APTES) in order to study the selective adsorption towards several species/pollutants. Antibiotics doxycycline hydrochloride (DC) and norfloxacin (NFX), the dye methyl orange(MO) and the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) were used as adsorbates. The adsorption has been studied under different batch experimental conditions such as contact time, pH and ionic strength. The modification with APTES produced a decrease in the surface area of the solid and reversed the surface charge although did not change appreciably the mosoporosity and shape of the particles. This change in the charge strongly increased the adsorption of species that behave as anions in aqueous solution such as 2,4-D and MO. On the contrary, for species with several polar groups and charge-development the effect was very low and only detectable at specific pH. Electrostatic attractions between the protonated amine-end groups of APTES-SiO2 and the negative functional groups of 2,4-D and MO were the main responsible of the adsorption process. Partial hydrolysis of the supported coupling agent to regenerate silanol groups played an important role in decreasing the adsorption capacity of polar species and in the reuse capacity for adsorbing anionic species, i.e., the performance decreased up to 75% after four cycles of successive adsorption-desorption. Finding new methodology or functionalization agents to improve the silica surface reactivity should be the main goal of the researchers in the future. This work perhaps contributes with such perspectives.

Reduction‐responsive poly (ethylene glycol)‐dexamethasone biarm conjugate and its self‐assembled nanomicelles: Preparation, physicochemical characterization, and thiol‐triggered drug release

In this study, a reduction‐responsive poly (ethylene glycol)‐dexamethasone biarm conjugate was synthesized as intracellular targeted drug delivery carriers. The hydroxyl end group of methoxy poly (ethylene glycol) (mPEG) was modified to introduce a biarm structure with bioreducible disulfide bond and amine end groups. Dexamethasone (Dex) as a nuclear targeting moiety was conjugated to the amine end groups of mPEG biarm derivatives, mPEG‐(NH2)2 or mPEG‐(ss‐NH2)2, with or without bioreducible disulfide bonds. The bioreducible and nonreducible mPEG‐Dex biarm conjugates, R‐mPEG‐Dex and N‐mPEG‐Dex, were synthesized and characterized by various analytical methods, proton nuclear magnetic resonance (1H‐NMR), Fourier transform infraredspectroscopy (FT‐IR), dynamic light scattering (DLS), and fluorescence measurements. Amphiphilic mPEG‐Dex conjugates self‐assembled in aqueous solutions to form nanoparticles (NPs) with a size range of 130 to 150 nm, and their critical micelle concentrations (CMCs) were determined to be 12.4 and 15.3 mg/L, respectively, for bioreducible and nonreducible ones. The R‐mPEG‐Dex NPs maintained good colloidal stability in the presence of bovine serum albumin (BSA) for more than 1 week but demonstrated a significant change in colloidal stability in the presence of dithiothreitol (DTT). In DTT‐containing phosphate‐buffered saline (PBS), the bioreducible NPs showed not only reduction‐responsive destabilization with PEG shedding but also thiol‐dependent drug release profile. Our observations indicated that the R‐mPEG‐Dex NPs have a promising prospective as an efficient nanocarrier for intracellular targeted delivery of various anticancer drugs.

Fabrication of carbon fiber grafted with acyl chloride functionalized multi-walled carbon nanotubes for mechanical reinforcement of nylon 6,6

Carbon fiber (CF) grafted with acyl chloride functionalized multi-walled carbon nanotube (MWCNT), or (MWCNT-CF), was prepared by the reaction of aminopyrene (AP) adsorbed on CF (CF-AP) and 1-pyrenebutyric chloride (PBC) adsorbed on MWCNT (MWCNT-PBC). It is introduced that four kinds of PA66 composites, containing single incorporation of pristine CF, two-component incorporation of pristine CF and pristine MWCNT, two-component incorporation of PBC adsorbed CF (PBC-CF) and MWCNT-PBC, and single incorporation of MWCNT-CF were fabricated by melt extrusion, and their fatigue life and tensile and interfacial properties were explored. The residual PBC on the MWCNT of MWCNT-CF was reacted with the amine end group of PA66 during the melt extrusion process to produce PA66 grafted MWCNT-CF. When the content of total carbon fillers was fixed, PA66/MWCNT-CF and PA66/CF-PBC/MWCNT-PBC composites exhibited better fatigue life and tensile strength than PA66/pristine CF/pristine MWCNT composites owing to improved interfacial adhesion between PA66 and carbon fillers. Among the composites examined, the highest fatigue life and tensile strength of the PA66/MWCNT-CF composite were owing to the hierarchical structure of MWCNT-CF and optimal interfacial adhesion caused by chain entanglement between the PA66 grafted to MWCNT-CF and matrix PA66.

Toward superior applications of thermoplastic elastomer blends: double Tg increase and improved ductility

AbstractWith the aim of curbing air pollution and addressing climate change, the use of low density thermoplastic elastomers (TPEs) in transportation could be a useful way to lighten the vehicle weight. For that, melt blending of high performance rubber and thermoplastics is an attractive way of preparing high performance TPEs. In this work, several TPEs have been prepared by melt blending of hydrogenated acrylonitrile butadiene rubber (HNBR) with polyamide 6 (PA6), adding different amounts of carboxylated HNBR (XHNBR) as compatibilizer: 40/60/0, 40/42/18, 40/30/30 and 40/18/42 (PA6/HNBR/XHNBR). The resulting blends were investigated using melt rheological measurements, morphological observations (scanning electron microscopy and polarized optical microscopy), dynamic mechanical analysis, differential scanning calorimetry analysis and mechanical tests. A biphasic morphology was noted for all TPEs. An increase in XHNBR amount changes the morphology from dispersed to co‐continuous. This evolution is explained by the change in the melt rheological properties of the HNBR/XHNBR rubber phase. Moreover, the introduction of 42% XHNBR resulted in an increase in the glass transition temperature of both rubber and PA6 phases. This double Tg increase phenomenon was attributed to the interfacial interactions between the carboxyl groups in XHNBR and the amine end groups in PA6. Additionally, thermal analysis revealed a reduced crystallinity of PA6 in the blend, which corresponds to enhanced interfacial interactions. The interfacial adhesion and the co‐continuous morphology resulted in an improved ductility. This study reveals the possibility of obtaining TPE blends with tunable thermal and mechanical properties by controlling both interfacial interactions and morphology. © 2019 Society of Chemical Industry

A robust strategy for the synthesis of miktoarm star copolymers by combination of ROP and photoinitiated free radical polymerization

A novel approach for the synthesis of miktoarm star copolymers by the combination of ring opening polymerization (ROP) and Type II photopolymerization is described. The method pertains to the use of a multifunctional initiator, bearing primary hydroxyl and tertiary amine functionalities, for the sequential or simultaneous polymerization of vinyl and lactone monomers under mild conditions. In the first step, phosphazene base (P2-t-Bu) catalyzed ROP of ε-caprolactone is accomplished. Subsequently, thus obtained poly(ε-caprolactone) with amine end groups was used as co-initiator for the polymerization of methyl methacrylate by utilizing conventional Type II photoinitiators. The structures, molecular weight characteristics and thermal properties of the polymers are analyzed by NMR, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) measurements, respectively.

Supramolecular Networks from Block Copolymers Based on Styrene and Isoprene Using Hydrogen Bonding Motifs-Part 1: Synthesis and Characterization.

The combination of controlled anionic polymerization and subsequent introduction of hydrogen bonding groups was established to form thermo-reversible, supramolecular networks. Several polyisoprene-block-polystyrene-block-polyisoprene (ISI) copolymers—with polystyrene (PS) as the main block, and consequently giving the decisive material characteristics—were synthesized. The novel modification approach to post-functionalize the polyisoprene (PI) end-blocks and to introduce different motifs, which are able to form self-complementary hydrogen bonds, was attained. In the first step, hydroxylation was accomplished using 9-borabicyclo[3.3.1]nonane. Starting from the hydroxylated polymer, esterification with succinic anhydride was implemented to form an ester group with carboxylic end-group (-O-CO-CH2-CH2-COOH). In a second approach, 1,1’-carbonyldiimidazole was used as coupling agent to introduce various types of diamines (diethylenetriamine, triethylentetramine, and 2,6-diaminopyridine) to prepare urethane groups with amine end-group (-O-CO-NH-R-NH2). 1H NMR spectroscopy was used to confirm the successful synthesis and to calculate the degree of functionalization Df. Differential scanning calorimetry (DSC) showed a difference of the glass transition temperature Tg between unfunctionalized and functionalized block copolymers, but no greater influence between the different types of modification, and thus, on the Tg of the PS block. In temperature dependent FTIR spectroscopy, reversible processes were observed.

Redox‐Responsive Nanocomposites Composed of Graphene Oxide and Chlorin e6 for Photodynamic Treatment of Cholangiocarcinoma

The aim of this study is to synthesize graphene oxide (GO) nanocomposites conjugated with chlorin e6 (Ce6) and methoxy poly(ethylene glycol) (MePEG) using disulfide linkage for photodynamic treatment of cholangiocarcinoma (CCA) cells. Graphene oxide was conjugated with MePEG and cystamine (GO‐(NSSNH2)‐PEG). After that, amine end group was further conjugated with Ce6. Ce6 and MePEG conjugated GO nanocomposites (GO NP) were characterized and its photodynamic effect was studied with various CCA cells. In morphological observation, GO NP formed nano‐aggregates with small sizes less than 100 nm while GO itself showed typical sheet shape. Ce6 release from GO NP was faster in the presence of glutathione, indicating that GO NP has redox‐responsiveness. GO NP showed significantly higher intracellular Ce6 uptake ratio and produced higher amount of ROS than Ce6 itself. Then, GO NP resulted in increased anticancer activity against CCA cells compared to Ce6 itself. In animal study with SNU478 cell‐bearing mice, GO NP was properly concentrated in tumor tissue while Ce6 treatment showed relatively higher fluorescence intensity in liver than that of tumor tissue. Tumor growth was significantly inhibited by treatment of GO NP with irradiation compared to Ce6 treatment. GO NP showed redox‐responsiveness and increased photodynamic effect against CCA cells. We suggest GO NP as a promising candidate for photodynamic therapy (PDT) of CCA cells.

Amine functionalized polyglycerols obtained by copolymerization of cyclic carbonate monomers

Hyperbranched aliphatic polyethers containing hydroxyl and amine end groups were produced from glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one) and cyclic carbonate bearing phthalimide moieties. The new monomer N-[(2-oxo-1,3-dioxolan-4-yl)methyl]phthalimide was synthesized in a simple two-step, one-pot process. The structure of the monomer was proved by means of NMR, FTIR and X-ray techniques. Anionic polymerization of cyclic carbonate monomers, which proceeds with simultaneous decarboxylation, was performed using a simple catalyst - potassium carbonate and trimethylolpropane (TMP) or glycerol carbonate as an initiator. The polymerization conditions were investigated and optimized. The polymers were characterized by means of nuclear magnetic resonance, FTIR, MALDI-TOF, GPC and elemental analysis. It was shown that during the process of polymerization an intermediate - glycidol is formed and acts as initiator or monomer.

The Effect of End Group and Molecular Weight on the Yellowness of Polyetherimide

The effects of end group and molecular weight on the yellowness of telechelic polyetherimide (PEI) are investigated. Electron-withdrawing dianhydride end groups reduce the yellowness and increase the transparency of PEI regardless of the molecular weight. Electron-donating phenyl, amine, and phthalic end groups increase the yellowness of PEI but the effect depends on the molecular weight. As the molecular weight is increased, the yellowness of PEIs with electron-donating end groups initially decreases due to a decreasing end-group density and then increases due to an increasing probability of charge-transfer complex formation. The systematic study reveals the correlations among yellowness, end group, and molecular weight of PEIs. The correlations can be used for designing highly transparent PEIs and other high-performance polymers.

Novel Pentadecyl Phenol‐Tagged L‐Tryptophan Molecules: Synthesis, Self‐ Assembly and Liquid Crystalline Properties

AbstractThe paper describes the self‐assembly and liquid crystalline properties of pentadecylphenol tagged L‐tryptophan molecules having ester and amide functionality. We have synthesized a series of molecules having mono and ditryptophan moieties attached to pentadecylphenol through amide or ester linkage. The fluorescence properties of the Boc‐L‐tryptophan‐pentadecylphenol molecules were measured in methanol and found to aggregate beyond the critical aggregation concentration and self‐assembled to give spherical structures. Upon deprotection of Boc group, the amine end group got involved in extended hydrogen bonding and fibril like structures were developed. These molecules also showed liquid crystalline behavior in hydrogen bonding solvents such as benzyl alcohol and showed needle like crystals in tert‐butanol, as analyzed by polarized optical light microscopy.

Isocyanate-Free Approach to Water-Borne Polyurea Dispersions and Coatings.

Here, an isocyanate-free approach to produce polyureas from diamines and dicarbamates as monomers is reported. A side reaction limiting the molecular weight during the diamine/ dicarbamate polymerization, that is, N-alkylation of amine end groups, is investigated. Mitigation of the N-alkylation, either by enhancing the carbamate aminolysis rate or by substitution of dimethylcarbamates with more sterically hindered diethylcarbamates, affords polyureas with sufficiently high molecular weights to assure satisfactory mechanical properties. Stable polyurea dispersions with polyamines as internal dispersing agents are prepared, and the properties of the corresponding coatings are evaluated.

Structure-property relationships of crosslinked disulfonated poly(arylene ether sulfone) membranes for desalination of water

Controlled molecular weight poly(arylene ether sulfone) oligomers with aromatic amine end groups and systematically varied degrees of disulfonation were synthesized by direct polymerization of disulfonated and non-sulfonated 4,4′-dichlorodiphenylsulfone. The oligomers were crosslinked with a tetrafunctional epoxy curing agent in the membrane casting process. Water uptake and IEC were investigated to understand how the structure and ion content affected the fixed charge concentrations (moles of ions/L of sorbed water). The hydrated mechanical properties of these copolymer networks were also studied in light of their ion contents and water uptake. At similar IECs, membranes with shorter ∼5000 Da oligomers absorbed less water than those with ∼10,000 Da blocks. The salt permeabilities correlated with water uptake and fixed charge density. Among the crosslinked membranes, the one with the 10,000 Da oligomer and with 50% disulfonation (mB5-10) had an excellent combination of water uptake, hydrated mechanical properties, fixed charge density, and low salt permeability.

Optimized Removal of Acid Blue 62 from Textile Waste Water by SBA-15/PAMAM Dendrimer Hybrid Using Response Surface Methodology

SBA-15/PAMAM Nano adsorbent was synthesized by the proficiency of SBA-15 as an original compound, 3-chloropropyltrimethoxysilane as a bridge chemical compound and polyamidoamine dendrimer (PAMAM) in the role of a multifunctional amine end group for adsorption of acid blue 62 (AB62) from aqueous media. The synthesized adsorbent was characterized by transmission electron microscope, field emission scanning electron microscope and Fourier-transform infrared spectroscope. A response surface methodology was employed to evaluate the simple and amalgamated factors of the operating variables subtending initial pH (2–12), adsorbent dosage(0.01–0.03 g), contact time (5–120 min), initial dye concentration (40–600 ppm) and temperature (25–45 °C) to optimize the operating statues of the treatment method. These parameters were altered at five levels pursuant to the central composite design to appraise their effects on AB62 removal through analysis of variance. Analysis of variance represented a high coefficient of definition amount (R2 = 0.9999) and acceptable prediction quadratic polynomial model was concluded which ascertain the suitability of the model and a high correlation among the predicted and empirical amounts. Utmost color removal efficiency was auspicated and empirically accredited. The optimum conditions relied on acquired results for AB62 removal were at an initial pH of 2, adsorbent dosage of 0.03 g SBA-15/PAMAM, dye concentration of 40 mg l−1, time contact of 60 min and temperature of 25 °C.

In situ forming stereocomplexed and post-photocrosslinked acrylated star poly(ethylene glycol)-poly(lactide) hydrogels

Biodegradable acrylate end-group functionalized poly(ethylene glycol)-poly(lactide) (PEG-PLA) star block copolymer hydrogels were formed by the consecutive physical gelation through stereocomplexation of star shaped PEG-(PLLA)8 and PEG-(PDLA)8 enantiomers and UV photopolymerization. The 8-armed PEG-PLA star block copolymers were prepared by ring opening polymerization of lactide onto an amine end-group functionalized PEG with a molecular weight of 20kg/mol using stannous octoate as a catalyst. The degree of polymerization of the PLA blocks was 12 lactyl units and the end hydroxyl groups were reacted with acryloyl chloride to give the required acrylate end groups. Aqueous solutions of enantiomeric mixtures of the PEG-(PLA)8 macromonomers formed physically crosslinked hydrogels above a critical gel concentration of 4w/v%. Subsequent photopolymerization at 365nm in the presence of Irgacure 2959 resulted in gels with improved mechanical properties and hydrolytic stability. With 40% polymer mass loss after 45d in vitro, these hydrogels show excellent resistance against hydrolytic degradation and dissolution, which is believed to result from the combination of stable amide linkages between the PEG and PLA blocks and the high physical and chemical crosslink density owing to the star architecture.

Distinctive roles of silane coupling agents on the corrosion inhibition performance of graphene oxide in epoxy coatings

Abstract Although graphene oxide (GO) is an unique 2D material for improving the corrosion resistance of polymeric coatings, GO nanosheets easily form aggregates in polymer matrix which provide obstacles in front of achieving high protective coatings. The main goal of this research is to enhance the corrosion inhibiting performance of GO nanofiller in epoxy coatings via modifying the surface of GO sheets with silane coupling agents. We have employed 3-aminopropyl triethoxysilane (APTES) and 3-glysidyloxypropyl trimethoxysilane (GPTMS) as silane agents with amine and epoxy end-groups, respectively, to investigate the effect of silane type on the properties of nanocomposite coatings. The results reveal that silane functionalization of GO significantly improves the adhesion of coatings on metal substrate and increases the water contact angle on epoxy coatings. Although all the prepared nanocomposites show superior barrier properties via tortuousing the diffusion path of corrosive species in epoxy matrix, electrochemical analysis exhibit that incorporation of APTES-GO with amine end-groups more efficiently enhances the corrosion resistance of epoxy coating. The investigation offers new aspects for selecting the kind of silane agent for modifying GO sheets and developing epoxy coatings with high corrosion protection efficiency.

Fullerene as alligator clips for electrical conduction through anthracene molecular junctions

The conductance of a single molecule transport junction comprising anthracene molecular junction (AMJ) with fullerene as alligator clips was investigated using ab-initio density functional theory (DFT) in the Landauer–Imry regime of coherent tunnelling transport. In our previous research, we have already calculated the electrical transport properties of aromatic molecules with thiol, amine, hydroxyl and selenol end groups concluding the exceptional assistance in the formation of robust molecular junctions. In this article, we have presented the suitability of fullerene anchoring in coupling anthracene molecule with gold electrodes. AMJ with boron-20 (B-20) and C-20 alligator clips exhibited strongest conduction in contrast to nitrogen, oxygen, fluorine and neon alligator clips.