Poly(lactic acid) (PLA) is an important polymer because of its significant biocompatibility and biodegradability. Supported H3PW12O40 (H3PW) on activated carbon was utilized for the catalytic polymerization of D,L-lactic acid, resulting in blends of PLA. The stability of the polymer was monitored by thermogravimetry (TGA), and the decomposition temperature (Td) was used to determine the optimal production conditions (i.e., temperature of 180 °C for 15 h; 0.1 wt. % catalyst; 20 wt. % H3PW/carbon calcined at 400 °C). The best catalyst was reused three times with good activity and recovery (95 %) and was analyzed to confirm the consistency of its Keggin structure, dispersion, and acidity, which are important parameters that affect the catalyst’s activity. The obtained polymer was characterized by gel permeation chromatography (GPC), Fourier-transform infrared spectroscopy (FT-IR), 1H/13C nuclear magnetic resonance (NMR) spectroscopy, specific optical rotation ([α]D25), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The average molar mass of the polymer was 17,400 g mol?1. Blends of poly(lactic acid) with 85 % poly(L-lactic acid) stereospecific isomer were obtained.
Graphical Abstract Stereoselective synthesis of 85 % PLLA from polymerization of d,l-lactic acid using 12-tungstophosphoric acid supported on carbon as a catalyst
Blend membranes were prepared by incorporating two types of polyethylene glycol (PEG) (molecular masses of 400 and 1000 g mol?1) into three grades of poly(ether-block-amide) (PEBAX), namely PEBAX 1074, PEBAX 1657, and PEBAX 2533. The PEGs, which were used as blending agents, were employed at mass fractions ranging from 10 to 40 wt.% based on the mass of PEBAX. The gas separation performance of each neat or blend membrane, comprising its CO2 and CH4 permeabilities and its ideal CO2/CH4 selectivity, was studied at room temperature (25 °C) and at pressures of 2–8 bar. X-ray diffraction (XRD) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analyses were used to determine the crystallinities of and the chemical bonds in the prepared membranes, respectively. Scanning electron microscopy (SEM) was also utilized to observe the morphologies of the membranes. The results obtained from experimental investigations showed that the incorporation of low molecular mass PEG significantly increased the permeability but only slightly affected the ideal CO2/CH4 selectivity, while the incorporation of high molecular mass PEG decreased the permeability considerably but sharply increased the ideal CO2/CH4 selectivity. This behavior intensified as the polyether content of the PEBAX was decreased.
A series of salicylaldimine ligands 2-tert-butyl-6-((2,4-bis(diphenylmethyl)-8-arylnaphthalen)imine)-phenol (L1: Aryl =4-tBu-phenyl; L2: Aryl = p-tolyl; L3: Aryl = phenyl; L4: 4-CF3-phenyl) and the corresponding neutral salicylaldimine nickel complexes (Ni1-Ni4) were prepared and characterized. In ethylene polymerization at 20 °C, these nickel complexes are highly active, with activities of up to 6.88 × 105 g·mol?1·h?1. Moreover, the molecular weight of the polyethylene could reach up to 8.1 × 105. Comparing with the classic salicylaldimine nickel complexes Ni5 at 20 °C, complexes Ni1 with the 4-tBu-phenyl substituent demonstrated 8 times higher activity and 35 times higher polyethylene molecular weight.
The main objective of this study was to prepare thin film nanofibrous composite (TFNC) membranes based on self-support nanofibrous mats. To this end, polyethylene terephthalate nanofibrous supports were produced by electrospinning technique and subsequently heat treatment was performed to increase mechanical stability of the mats. Then, interfacial polymerization procedure was applied for preparation of TFNC nanofiltration membranes. For comparison, the thin film composite (TFC) nanofiltration membrane was prepared by the same conditions based on polyethersulfone ultrafiltration membrane prepared through phase inversion method. Chemical structure, morphology and mechanical properties were studied by using ATR-FTIR, SEM and tensile tests, respectively. Also, filtration performance was investigated by water flux, rejection, water contact angle and MWCO determination. Results showed that the TFNC nanofiltration membrane had higher salt rejection and four times higher water flux than the TFC nanofiltraion membrane (Na2SO4 rejection and pure water flux were (93 ± 3)%, (34 ± 2.3) L./m2h and (67 ± 4)%, (8 ± 0.9) L./m2h for TFNC and TFC, respectively). At the end, the filtration performance of PET TFNC-NF membrane was compared with other nanofibrous nanofiltration membranes.
The CO2 capturing and sequestration are of importance in environmental science. A new type of microporous coordination polymer (Ni/PAPy) with secondary amine groups has been successfully prepared. Taking advantage of the synergistic effect of metal-electrostatic and hydrogen bonding interactions between the Ni/PAPy network and CO2 molecules, the CO2 uptake capacity of the microporous coordination polymer reaches up to 4.82 mmol g?1 (1.0 bar, 273 K) with the high selectivities (CO2/N2?=?83, CO2/CH4?=?16), making the Ni/PAPy a promising microporous material for application of CO2 uptake and separation. For comparison, the microporous coordination polymer without secondary amine groups (Ni/PPy) is also prepared.
Graphical Abstract Taking advantage of the synergistic effect of metal-electrostatic and hydrogen bonding interactions between the Ni/PAPy network and CO2 molecules, the Ni/PAPy can be considered as a promising microporous material for application of CO2 uptake and separation.
Polyimde (PI) samples with different molecular weights were synthesized. Based on SEC coupled with multidetectors measurement and Yamakawa-Fujii-Yoshizaki (YFY) model, eight soluble samples with absolute Mw from 40,600 g/mol to 197,000 g/mol are chosen and applied to investigate the influence of molecular weight on scaling exponents and critical concentrations at 20–45 °C in dilute, semidilute unentangled, and semidilute entangled solutions. Most of the scaling exponents are higher than the theoretical values in three concentration regions, and scaling exponent increases with molecular weight; overlap concentration (C*) increases and entanglement concentration (Ce) decreases with molecular weight. Considering bead-bead interaction, corrected bead-spring model can explain the related results. Finally, the relationship among C*, Ce, and molecular weight is established at different temperatures (from 20 °C to 45 °C), and two linear equations are available at each temperature. Thus, both C* and Ce are calculated at a fixed molecular weight. And from C/C* and C/Ce ratios, the morphology of PI fiber during electrospinning can be controlled. These results are helpful to guide the preparation of polyimide solutions for different processing.
Graphical abstract Different molecular weight soluble polyimide (PI) was synthesized and the relationship between scaling exponent (calculated from the relationship between specific viscosity and concentration) and molecular weight in different concentration ranges was established. It is found that most of the scaling exponents are higher than the theoretical values in three concentration regions, and scaling exponent increases with molecular weight. Moreover, overlap concentration (C*) increases and entanglement concentration (Ce) decreases with molecular weight, and its reason is discussed. Finally, the relationship among C*, Ce, and molecular weight is established, which is helpful in guiding the preparation of polyimide solution for different processing.
We present a first report for developing stimulus responsive hydrogels via free radical aqueous polymerization technique using Acrylic acid (AAc), methacrylic acid (MAAc) and diethylaminoethyl methacrylate (DEAEMA). The morphological aspects of poly(AAc-co-DEAEMA) (pAcD) and poly(MAAc-co-DEAEMA) (pMcD) were investigated to delineate the relevant mechanism of hydrogel formation for better understanding of their mechanical behaviour. The formulated hydrogels were found to have a structural framework comprising inter-connected nanogels and continuous outer skin with macroporous interiors. An abrupt increase in the peak intensities specific to the polymer and a simultaneous decrease in the water related peaks in the attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra exhibited the phenomenon of phase separation, whereas peaks of proton nuclear magnetic resonance (1HNMR) revealed hydrogen bonding and electrolytic complexation between the monomers. Biocompatibility is the hallmark for any drug carrier and was evaluated by both in vitro and in vivo testing. Administration of the prepared hydrogels to rat models did not cause any significant affect on the vital organs.
Graphical abstract Graphical representation showing macroporous interior with interlocked nanoglobules as stable building blocks in pAcD gels with high in-vitro and in-vivo biocompatibility
Methanol permeation and conductivity of membrane materials are important factors to evaluate the feasibility of application as proton exchange membranes (PEMs) in direct methanol fuel cell (DMFC). The methanol permeation values of these composite membranes based on ionic liquids of trifluoroacetic propylamine (TFAPA) and the disubstituted imidazolium cations with different anions were summarized, and the methanol permeation behaviors were investigated in this work. Although these polymer/ionic liquid composite membranes displayed satisfactory conductivities, the relative selectivity values of conductivity to methanol permeability were lower than the value of Nafion® membrane. Moreover, polymerized ionic liquids (PILs) membranes showed the strong ability to hinder methanol permeation with a value around 10?11 cm2/s at 10 M methanol solution. The maximum relative selectivity value reached (2.23–1.76) × 106 S·s/cm3 for PVC-MIMCl membrane, which was near two orders of magnitude higher than the reported 2.47 × 104 S·s/cm3 for Nafion-117 membrane at 2 M methanol solution.
The G0 and G1 polyurethane dendrimers terminated with 3–12 atom transfer radical polymerization (ATRP) initiators were prepared using single and dual functional ATRP reagents and their structures were confirmed using FT-IR, 1H–NMR, HR-MS and SEC-MALLS techniques. 4-Vinylpyridine was polymerized using the G1 dendritic initiators to obtain six- and twelve-arm star poly(4-vinylpyridine)s (STAR-P1 and STAR-P2). The absolute molecular weight and PDI of star polymers were in the order of 105 and 1.23–1.24 respectively. Hydrolysis leading to degradation of inner polyurethane core of the star polymers yielded more narrow dispersed poly(4-vinylpyridine) chains and the SEC-MALLS data of these chains confirm the accurate control on number of arms. Both of the polymers were doped with KI/I2 along with N3-dye to work as efficient polymer electrolytes for dye sensitized solar cell (DSSC). The increment in the conductivity of doped STAR-P1 was very significant and reached 2.415 mS/m from 0.0066 mS/m of dopant salt. The current-voltage characteristics of these doped polymer electrolytes measured under simulated sun light with AM 1.5 at 40 mW/cm2 yielded energy conversion efficiency (η) of 5.13% and 1.90% for STAR-P1 and STAR-P2 respectively and these values also significantly high compared to 1.09% corresponds to current-voltage curve of the device fabricated without the polymers.
Graphical abstract Star poly(4-vinylpyridine)s were prepared using novel dendritic ATRP initiators and used as electrolytes for dye sensitized solar cell (DSSC); one of the cells showed 5.13% energy conversion efficiency.
In the present study, synthesis of poly(AAm-co-AMPS)/Na-MMT hydrogel nanocomposite with different amount of bis[2-(methacryloyloxy)ethyl] phosphate as a crosslinker was successfully carried out for the removal of crystal violet (CV), methylene blue (MB) and methyl red (MR) from aqueous solution. Hydrogel nanocomposite was characterized by FT-IR, SEM, EDS, XRD and TGA analysis. Several important parameters were investigated to obtain maximum adsorption capacity. Adsorption behavior of hydrogel nanocomposite was investigated for the adsorption of dyes and it was found to remove about 80% for CV, 89% for MB and 51% for MR in 50 mg/L of dyes solutions at pH 7 and about 86% for CV, 93% for MB and 23% for MR at pH 12. Kinetic studies revealed that the applicability of pseudo-first-order and pseudo-second-order model for the adsorption of CV, MB and MR. The adsorption isotherm was studied in 25, 35, 45 and 55 °C using Langmuir, Freundlich, Temkin and Jovanovic models and the adsorption data were well described by Freundlich isotherm model. Hydrogel nanocomposite showed 155, 176 and 113 mg/g maximum adsorption capacity for CV, MB and MR respectively. Negative values of ΔG0 for all three dyes suggested the feasibility of dyes removal and support for spontaneous adsorption of CV, MB and MR on hydrogel nanocomposite. Desorption of dyes from the dye loaded hydrogel nanocomposite was simply done in ethanol. The results indicate that the prepared poly(AAm-co-AMPS)/Na-MMT hydrogel nanocomposite is an efficient adsorbent with high adsorption capacity for the aforementioned dyes.
The polyurethane pressure sensitive adhesive (PUPSA) films have been prepared on polypropylene sheets with coating bars. The topographical information of the dried films is investigated using phase images by using Atomic Force Microscope (AFM) in tapping mode. The film develops a segmental architecture by using different compositions. Various samples of PUPSA comprising of polypropylene glycol PPG (Mn?=?425, 1000, 2000 and 2700 g-mol?1) and hydroxyl terminated polybutadiene HTPB (Mn?=?1984 and 2912 g-mol?1) along with three different isocyanates: 1,6 hexane diisocyanate (HDI), isophorone diisocyanate (IPDI) and hexamethylene diisocyanate (H12MDI) have been used for capturing the images through AFM. The samples contained 40 wt.% of solid content containing different nature of macrodiols and diisocyanate. Due to varying composition, dispersion in domain area along with different contour and dimension has been observed in the images. Apparently, there seems no correlation of spherulites and lamellae in different domains. However, the properties imparted by high molecular weight HTPB resulted in non-adhesive stiff material.
A method for the synthesis of particle brushes by grafting polylactic acid onto TiO2 nanoparticle is reported. The efficiency of grafting was enhanced by combining azeotropic separation of water with polycondensation in a single pot. PLA/TiO2 brushes synthesized with different ratio of lactic acid and TiO2 were characterized by various techniques such as FT-IR, XRD, TEM, XPS, 1H and 13C NMR. TEM analysis indicates that the sizes of TiO2 nanoparticles are between 2 and 8 nm. DLS was used to determine overall size of particle brush and average size varied between 59.68–65.83 nm. Zeta potential measurement indicated high stability of water dispersed particles brushes with measured values of ?30.1 to ?37.1 mV for brushes prepared with PLA/TiO2 ratio of 50:1 and 20:1 respectively. The DSC and TGA analysis showed that PLA/TiO2 nanocomposites have good thermal stability.
In this study, the effect of crosslinking conditions was investigated to obtain insoluble poly(ethylene oxide) (PEO) nanofiber mats having an ultraviolet (UV) initiating and crosslinking agent, pentaerythritol triacrylate (PETA), with various ratios in the presence or absence of UV irradiation at 366 nm. At first, PEO nanofibers were electrospun from 400,000 and 600,000 g/mole molecular weights of PEO and they were compared in terms of diameter and fiber morphology. Whereas applied voltage in the range of 10–25 kV had no significant effect on the fiber morphology, fiber diameters varied by voltage. An increase in the flow rate from 0.25 to 1.00 mL h?1 had an effect in favor of fabricating thicker fibers. The effect of distance to collector on the diameter and morphology was not distinctive. Fibers having irregular morphology and beads appeared with increasing the polymer concentration from 4 to 8 % w/v. Prior crosslinking, electrospinning process at selected conditions was applied to the PEO (600,000) including PETA and PEO-PETA nanofibers were obtained. Besides PETA concentration and UV application, drying conditions before UV irradiation were also found effective to obtain stable fibers in aqueous media. PEO nanofibers electrospun in the presence of 10 % PETA (w/w), dried for 8 days at 37 °C in an air atmosphere and then, irradiated with UV for 50 min were found most stable in aqueous media. However, crosslinking was also achieved in the absence of UV.
One low density polyethylene (LDPE) resin with high-speed extrusion coating property is fractionated through solvent gradient fractionation (SGF) technique using 1,2,4-trimethylbenzene (TMB) and ethyl cellosolve (ECS) as good/poor solvent pair at 115 °C. The pristine sample and its fractions are characterized by high-temperature gel permeation chromatography (HT-GPC) coupled with triple detectors (refractive index RI, light scattering LS, viscometer VIS), 13C–nuclear magnetic resonance spectroscopy (13C–NMR), differential scanning calorimetry (DSC) and successive self-nucleation/annealing (SSA) thermal fractionation. By adjusting the ratio of good/poor solvent, the obtained fractions show their molecular weight from 1.58?×?103 g/mol to 4.76?×?105 g/mol. It is found that the fractions with high molecular weight (fractions 10–13) occupy about 55.85% in resin. Particularly, the molecular weight distribution (MWD) of most fractions is in the range of 1.1–1.2. Each fraction contains more short chain branch (SCB) and less long chain branch (LCB) simultaneously. With increasing the molecular weight, the branching content shows no regular change. The lowest SCB and total branch content regions correspond to molecular weight 1.97?×?104 to 4.10?×?104 g/mol. The melting and crystallization temperatures of fractions firstly increase and then decrease with the molecular weight. The crystallinity decreases gradually from 51.7% to 31.1%. In the SSA thermal fractionation, each fraction shows a broad range of endotherm with multiple melting peaks in DSC curve corresponding to the different methylene sequence length (MSL) (Ln and Lw). The longest Ln (Lw) region occurs in the molecular weight of 8.95?×?103 to 3.14?×?104 g/mol. The relationship between chain microstructure and properties is also discussed.
Graphical Abstract One coating LDPE resin is effectively fractionated by solvent gradient fractionation using TMB/ECS as good/poor solvent pair according to molecular weight. The component with high molecular weight is more than that with low molecular weight. Higher molecular weight and LCB improve the melt strength synergetically, and suitable component with low molecular weight provides better flowability.
In this study, we synthesized an imidazolium iodide–containing hyperbranched polymer ionic liquid (HPIL) for use as the gel electrolyte of dye-sensitized solar cells (DSSCs). We incorporated HPIL at various contents (4, 8, and 15 wt%) in a solvent-free ionic liquid (1-propyl-2,3-dimethylimidazolium iodide and 1-ethyl-3-methylimidazolium tetrafluoroborate)–based quasi-solid gel electrolyte (IL-A) and a solvent (3-methoxypropionitrile)-based fluid gel electrolyte (IL-B). After fabricating N719 dye–based DSSCs incorporating the HPIL/IL-A and HPIL/IL-B gel electrolytes, we recorded the electrochemical impedance spectra and measured the photovoltaic (PV) performance of these devices. In the dark, the DSSCs incorporating HPIL exhibited higher charge recombination resistances at the interface between TiO2/dye and the electrolyte. This high recombination resistance suppressed the dark current and improved the PV performance of the devices incorporating HPIL. The DSSCs fabricated from the HPIL/IL-B gel electrolyte displayed higher photo-conversion efficiency, while those fabricated from the HPIL/IL-A gel electrolyte provided superior operational stability. Under AM 1.5 illumination (100 mW cm?2), we measured a photo-conversion efficiency of 7.18 %, a short-circuit current density of 16.09 mA cm?2, an open-circuit voltage of 0.69 V, and a fill factor of 0.65 for the DSSC incorporating the gel electrolyte HPIL/IL-B (4:96, w/w). The DSSC incorporating the gel electrolyte HPIL/IL-A (15:85, w/w) exhibited good operational stability, retaining approximately 93 % of its original efficiency after 500 h.
Graphical abstract An imidazolium iodide-containing hyperbranched polymer ionic liquid HPIL was synthesized for use as the gel electrolyte of dye-sensitized solar cells.
Polyaniline/Multiwalled carbon nanotubes (PANI/MWCNTs) nanocomposite was prepared via liquid-liquid interfacial polymerization method. The morphology studies of the nanocomposite using SEM and TEM techniques confirmed the presence of PANI as aggregates along with MWCNTs and X-ray diffraction studies indicated the presence of graphitic planes of MWCNTs along with PANI in semi-crystalline emeraldine salt form. The PANI/MWCNTs nanocomposite electrode exhibited specific capacitance (Cs) of 1551 F/g at a scan rate of 2 mV/s in aqueous 1 M H2SO4 in a potential window of 0–1.2 V. The material exhibited good cycle life with 95% capacitance retention in a life cycle test conducted at 5 A/g for 1000 cycles. Further, an asymmetric supercapacitor device (ASD) was fabricated using PANI/MWCNTs as positive and activated carbon as negative electrodes in aqueous 1 M H2SO4. The ASD exhibited a Cs of 142 F/g at a scan rate of 5 mV/s in a wide potential range of 0–1.6 V. The device offered high energy and power densities of 29 Wh/Kg and 7.3 kW/Kg respectively and also demonstrated an excellent cyclic stability by retaining 97% of its initial capacitance after 5000 cycles at high current density of 20 A/g.
A series of new waterborne polyurethanes (WPUs) was successfully prepared by the prepolymer process from the bio-renewable sources hydroxytelechelic natural rubber (HTNR with MW 3000 g mol?1) and hydroxylated rubber seed oil (HRSO), with DMPA fixed at 5.6 wt%. The effects of ratio of HTNR and HRSO (ranging from 1.00/0 to 0.10/0.90) and of hydroxyl value (OHV) of HRSO (200 or 270 mgKOH/g) on final properties were studied. It was found that the particle size of WPU increased significantly with both HRSO/HTNR ratio and OHV of HRSO. Chemical structure of the WPU films was confirmed by FT-IR. The water uptake, mechanical, dynamic mechanical properties and thermal stability of WPU film improved with both HRSO content and OHV of HRSO, while swelling in THF decreased. All these WPU films had similar Tg. This article reports novel green biobased WPU with promising applications as adhesive for shoe industries.
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