Low Degree Of Cross-linking Research Articles

N,N'-methylenebis(acrylamide)-crosslinked poly(acrylic acid) particles as doxorubicin carriers: A comparison between release behavior of physically loaded drug and conjugated drug via acid-labile hydrazone linkage.

N,N'-methylenebis(acrylamide) (MBA)-crosslinked poly(acrylic acid) (PAA) particles with low degree of cross-linking were synthesized using distillation precipitation polymerization. Size and size distribution of particles were obtained using dynamic light scattering and field emission scanning electron microscopy( and results showed that microspheres had a narrow size dispersity. Proton nuclear magnetic resonance results indicated that amount of cross-linker in structure of particles is a little more than the molar percentage of feeded MBA because of greater activity ratio of MBA than AA. pH-responsive behavior of samples was investigated using UV-vis. absorption at 480 nm where each sample showed a sudden deplete in UV absorbance at a peculiar pH. Synthesized particles were used as carriers of anti-cancer drug doxorubicin using two different approaches including physically loading of drug and drug conjugation via an acid-labile hydrazone linkage. Release results showed that in the first case, amount of released drug has an inverse relationship with the amount of cross-linker in the structure and also, by adding an acid-labile linkage, the amount of burst release decreased drastically. Also, the amount of released drug for conjugated systems was much lesser than particles with physically loaded drug. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 342-348, 2018.

Dehydration of 1-octanol to di-n-octyl ether in liquid phase with simultaneous water removal over ion exchange resins: Effect of working-state morphologies

The influence of the concentration of polar reactants and products on the working-state morphology of ion exchange catalysts has been investigated over different acidic ion-exchange resins for di-n-octyl ether (DNOE) synthesis from 1-octanol dehydration at 423–448K and atmospheric pressure in a batch reactor equipped with a Dean & Stark device. By removing water formed 1-octanol conversion was practically complete; the olefin formation being the main secondary reaction. When 1-octanol is completely consumed the working-state morphology of ion exchange resins changes, which influences the selectivities towards products. At this point, for microporous resins all reactions stop while with macroreticular ones DNOE decomposes and significant amounts of olefin dimers appears. The best selectivity to DNOE was found in gel-type and macroreticular resins with low crosslinking degree. Macroreticular resins with medium or high crosslinking give good results in olefin formation.

Effects of irradiation on polyethyleneterephthalate(PET) fibers impregnated with sensitizer

Polyethylene terephthalate(PET) is difficult to be irradiation cross-linked at low dose for the aromatic groups. In this paper, trimethylolpropane triacrylate (TMPTA) was incorporated in PET fibers to sensitize the cross-linking. Changes in PET fibers subjected to electron beam irradiation at dose up to 200 kGy and dose rate 12 kGy/s were investigated by gel content, scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, thermal gravimetric analysis and X-ray photoelectron spectroscopy. The gel content was 0.14% at dose of 60 kGy and it arrived at the maximum value 0.53% at 100 kGy. Irradiated fibers showed a decrease in the breaking strength and an increase in the elongation at break. The crystal form of PET fibers had not been changed and crystallinity decreased 28% with the increasing dose. The melting temperature shifted from the original 254.28 °C to 253.44 °C. The thermal stability and the amount of non-volatile residue at 800 °C increased at dose of 100 kGy. XPS analysis indicated that the number of C-C band increased to prove the occurring of cross-link. The surface of PET fibers got rougher after irradiation and the anti-dripping property had not been improved effectively for the low degree of cross-linking.

Metathesis Curing of Allylated Lignin and Different Plant Oils for the Preparation of Thermosetting Polymer Films with Tunable Mechanical Properties

Lignin and plant oils—two highly available renewable feedstocks—are cured via olefin metathesis to produce thermosetting polymer films with tunable mechanical properties. Therefore, an organosolv lignin, allylated in a recently described sustainable approach, is used. For the first time, unmodified plant oils are reacted with a lignin derivative. An increasing lignin content as well as an increasing amount of polyunsaturated fatty acids in the plant oil structure lead to higher Young's moduli and higher cross-linking density. Stress–strain measurements reveal ductile behavior of the prepared films. Only a lignin content over 70% leads to brittle materials. To improve the overall sustainability of this approach, dimethyl carbonate is investigated as sustainable solvent for film formation, leading to materials with similar Young's moduli and tensile strength, but lower degree of cross-linking if compared to the more volatile solvent dichloromethane.

Is quercetin an alternative natural crosslinking agent to genipin for long-term dermal scaffolds implantation?

As biocompatible matrices, porcine dermal scaffolds have limited application in tissue engineering due to rapid degradation following implantation. This study compared the physical, chemical and biomechanical changes that occurred when genipin and quercetin were used to crosslink dermal scaffolds and to determine whether quercetin could be used as an alternative to genipin. Physicochemical changes in the collagen were assessed using spectroscopic methods [X-ray diffraction analysis (XRD) and nuclear magnetic resonance (NMR) analysis]. The crosslinking reaction was evaluated by quantification of amino acids and the degree of this reaction by ninhydrin assay. Because the mechanical behaviour of the collagen matrices is highly influenced by crosslinking, the tensile strength of both sets of scaffolds was evaluated. The highest mechanical strength, stiffness, degree of crosslinking and changes in the packing features of collagen (measured by XRD) were achieved using genipin. Some of the results found in the quercetin-crosslinked scaffolds were possibly due to hydration and dehydration effects elicited by the solvents (phosphate-buffered saline or ethanol), as seen in the NMR results. In the quercetin-ethanol-crosslinked scaffolds, possible reorientation of the amino groups of the collagen molecule may have taken place. Therefore, depending on their proximity to the crosslinking reagent, different types and numbers of interactions may have occurred, inducing a higher crosslinking degree (as evidenced by the ninhydrin assay) and reduction in the free amino acids after reaction. Both crosslinking agents and solvents interfere in the physicochemical properties of collagen thereby inducing variations in the matrix structure. Quercetin-crosslinked scaffolds may have broader clinical application where a lower degree of crosslinking and stiffness is required. Copyright © 2016 John Wiley & Sons, Ltd.

On the efficiency of a hydrogel-based desalination cycle

Polyelectrolyte based hydrogels swollen in seawater can release partially desalinated water under compression, and hence can be used as desalination agents. We use a previously developed model for the swelling of a hydrogel based on earlier work by Katchalsky and Michaeli to analyse the thermodynamic costs of a full desalination cycle. We investigate salt concentrations from 0.6mol/l down to 10−3mol/l, thereby covering the full range from sea water to potable water, and investigate gels with varying crosslinking degree N and charge fraction α. Our results demonstrate that most efficient are either strongly charged gels with high degree of crosslinking, or gels with intermediate charge fraction and low crosslinking degree. Our analytical model allows us to extract the mechanical work needed to compress the gel, and ultimately to calculate the energy cost to desalinate water by using a hydrogel as a desalination agent. Our theoretical results suggest that hydrogels can compete in energy costs with other standard desalination methods.

Isolation and Characterization of 1,3-Bis(vinylbenzyl)thymine: Copolymerization with Vinylbenzyl Thymine Ammonium Chloride

A novel bioinspired molecule, 1,3-bis(vinylbenzyl)thymine (bisVBT), was isolated as a by-product during the synthesis of 1-(4-vinylbenzyl)thymine (VBT) and analyzed with various techniques: NMR, IR, and Single-Crystal X-ray Diffraction. In addition to embodying all the desired characteristics of VBT (i.e., having the ability to undergo a 2π+2π photodimerization reaction upon UV irradiation, a derivatization site, hydrogen bonding sites, and aromatic stacking ability) the bisVBT monomer has the added benefit of having two vinyl groups for cross-polymerization. Copolymerizing the bisVBT monomer with the charged monomer vinylbenzyl triethylammonium (VBA) chloride, different copolymers/terpolymers/cross-linked network were obtained, as it was shown by the absence of the vinyl resonance in the NMR spectra. Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) showed an indication of materials with low degree of cross-linking. A Gel Permeation Chromatography (GPC) method was improved to better characterize the molecular weight distributions of the cationic structures. Preliminary qualitative cross-linking studies were performed on bisVBT-VBA copolymers, and a comparison with VBT-VBA copolymers is presented.

Low dielectric material from novel core-fluorinated polybenzoxazine

Cross-linked polybenzoxazine with substantially reduced dielectric constant and loss factor (2.3 and 0.0041 at 10 kHz, respectively) based on a novel core-fluorinated bis(benzoxazine)-containing monomer with 1,4-tetrafluorobenzene dioxyphenylene central unit was prepared. Herewith, this fluorinated polybenzoxazine possesses low water absorption (0.5%) and high degree of cross-linking (98.5%).

Preparation and hydration characteristics of carbodiimide crosslinked lignite humic acids

Polar and apolar moieties of humic acids are spatially separated forming domains of different polarity. In this work, we tested the procedures to crosslink functional groups in polar domains of humic acids by using carbodiimide coupling and analyzed to which extent influenced the modification their hydration properties and stability. For this reason, we prepared eight derivatives of lignite humic acids using either water-soluble N-Ethyl-N′-(3-dimethylaminopropyl)carbodiimide (EDC) or water-insoluble N,N′-dicyclohexylcarbodiimide (DCC) under various conditions. Characterization of prepared derivatives showed that both methods lead to formation of crosslinked humic structures. Using of EDC resulted in lower degree of crosslinking, but better hydration properties. Higher moisture uptake and water holding capacity were observed in humic acids, which were pre-wetted prior to crosslinking for at least 24h. Although the EDC derivatives of humic acids contained only between 60 and 85% of original free carboxylic groups, they showed similar moisture uptake as parental humic acids by equilibration at relative humidities of both 94% and 76%. Under water-saturated conditions, the EDC derivatives showed faster swelling kinetics and reached almost the same water holding capacity as the original sample after 18days. However, both the EDC and DCC derivatives began to degrade already after 3–9days during swelling tests, which subsequently decreased their hydration. The results suggested that water holding capacity, swelling kinetics and moisture uptake of humic acids were not influenced significantly by the amount of polar groups, but also by their spatial arrangement and distribution.

Argon Plasma Treatment of Tapioca Starch Using a Semi-continuous Downer Reactor

To develop a novel modification process of tapioca starch using low-pressure argon plasma treatment in a large-scale production, a semi-continuous downer reactor was designed to provide a production rate of 0.1–0.5 kg per cycle. Physicochemical and rheological properties of plasma-treated starch were investigated in order to predict the phenomena occurred during the plasma treatment. Native tapioca starch (NTS) was plasma-treated for 1, 3, or 6 cycles, which were referred to as PTS-1, PTS-3, or PTS-6 samples, respectively. Plasma treatment of the NTS resulted in a significant decrease (P < 0.05) in paste clarity and Rapid Visco Analyzer (RVA) breakdown viscosity, and an increase in gel strength of starch. The PTS-1 had the lowest paste clarity of 39.85 %T at 650 nm and breakdown viscosity of 29.71 Rapid Visco Unit (RVU), and the highest gel strength, e.g., G′ = 5.47ω 0.32. With increasing the number of treatment cycles, i.e., the PTS-3 and PTS-6, the paste clarity and breakdown viscosity significantly increased (P < 0.05), while the gel strength decreased. The Fourier transform infrared (FTIR) spectroscopy via relative areas of C–O–C peaks indicated that the PTS-1 had a significant increase (P < 0.05) in the C–O–C cross-linked bonds compared to the NTS, but the effect of depolymerization could further suppress the cross-linking reaction when the number of treatment cycle was increased. Taking an advantage of a very short residence time (less than 0.3 s) in the plasma downer reactor, the semi-continuous process of starch modification could be developed for a commercial production of non-chemically modified starch with a relatively low degree of cross-linking.

Analysis of influence of fibre type and orientation on dynamic properties of polymer laminates for evaluation of their damping and self-heating

Abstract In the following study, the dynamic behaviour of polymer laminates reinforced by glass and carbon fibres with different orientations was considered for several excitation frequencies and elevated temperatures. The obtained dynamic moduli, loss factors and glass-transition temperatures were used for the evaluation of damping capabilities and the self-heating phenomenon. In order to evaluate the influence of a fibre type, additional studies for a pure matrix were carried out and used in the analysis as the reference. The obtained results show significant differences both in thermal and dynamic mechanical properties with respect to a fibre type and its orientation, which has a direct influence on the analysed self-heating and damping phenomena. The results of the present study could be used for the design of composite properties with respect to thermal degradation resulting from coupled thermomechanical loading conditions. Several hypotheses on the influence of a heating rate on estimation of the thermomechanical properties as well as structural degradation of composites in such conditions were presented with appropriate discussion and argumentation. The present study has a preliminary character. Furthermore, it is planned to perform such tests for specimens with a low cross-linking degree in order to analyse its influence on the resulting thermomechanical response of fibre-reinforced composite structures.

Cyclodextrin nanosponges to enhance the dissolution profile of quercetin by inclusion complex formation

ABSTRACTThe therapeutic potential of quercetin is mostly hampered by its low water solubility and poor absorption. The aim of this study was to enhance the dissolution rate of quercetin by molecular encapsulation with cyclodextrin nanosponges. The inclusion complexes were obtained by freeze-drying method. Inclusion complexes were characterized by Fourier Transformed Infrared Spectroscopy (FTIR), x-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), transmission electron microscopy (TEM), and dissolution testing. FTIR, XRD, and DSC studies confirmed the interactions of quercetin with nanosponges. TEM images revealed the spherical morphology of complexes. The dissolution of the drug nanosponge complex was significantly higher compared with the pure drug in simulated intestinal fluid (SIF; pH 6.8). The results indicated that the degree of cross-linking has the significant influence on dissolution. Nanosponges with lower degree of cross-linking released 91% of the drug within 45 min, whereas nanosponges with higher degree of cross-linking resulted in sustained release up to 24 h.

Characterization, molecular dynamics, and encapsulation ability of β-cyclodextrin polymers crosslinked by polyethylene glycol

A series of water-insoluble cyclodextrin polymers (CDP) was prepared by crosslinking β-cyclodextrin (CD) with polyethylene glycol diglycidyl ether (PEGDE). Similarly, a reference CDP was prepared using ethylene glycol diglycidyl ether (EGDE). Increasing the feed ratio of PEGDE to CD in the reaction mixture led to high degrees of crosslinking. Relaxation measurements revealed structural homogeneity among the CDPs, which exhibited mobilities that strongly depended on the chain lengths of the crosslinking agents. In addition, all the CDPs displayed high encapsulation abilities toward bisphenol A (BPA) in aqueous media. In particular, the CDP sample with a low degree of crosslinking by PEGDE showed the highest encapsulation ability toward BPA. In contrast, the CDP crosslinked by EGDE exhibited low encapsulation ability because its highly dense structure, which results from the short chain lengths of the crosslinking agents, hinders the penetration of BPA molecules.

Preparation of slightly crosslinked monodisperse poly(maleic anhydride-cyclohexyl vinyl ether-divinylbenzene) functional microspheres with anhydride groups via precipitation polymerization

Slightly crosslinked monodisperse poly(maleic anhydride-cyclohexyl vinyl ether-divinylbenzene) (MA-CHVE-DVB) microspheres were prepared via precipitation polymerization while using 2,2-azobisisobutyronitrile as an initiator in a mixture of methyl ethyl ketone and n-heptane without any stabilizer. The number-average diameter of the resultant poly(MA-CHVE-DVB) microspheres ranged from 0.478 to 1.386μm with a polydispersity index of 1.00 to 1.02 that depended on the feed ratios of the MA/CHVE/DVB monomers. The introduction of one electron donor monomer cyclohexyl vinyl ether strongly affected the yield, size, and morphology of these slightly crosslinked microspheres. Quinoline-type chelating resins were obtained after combining the poly(MA-CHVE-DVB) with 8-hydroxyquinoline; the adsorption properties of these materials were measured through their ability to remove Cu2+ ions from water. The poly(MA-CHVE-DVB) microspheres with low degrees of crosslinking provided more effective functional groups and therefore better ion removal capabilities. These slightly crosslinked microspheres may have applications in water treatment as well as in sensing and drug delivery.

Low energy 4f-5d transitions in lanthanide doped CaLaSiN3 with low degree of cross-linking between SiN4 tetrahedra

CaLaSiN3 samples doped with Eu, Yb, Sm, Ce and Pr have been prepared via solid-state reaction synthesis and the optical properties have been studied. Both Yb and Sm were only observed in the trivalent state due to the fact that their Ln2+ ground states are located inside or very close to the conduction band of the CaLaSiN3 host lattice. Doping with Ce3+ or Eu2+ resulted in a very low energy Ce3+ or Eu2+ 4f-5d absorption band around 1.9 eV (650 nm) and 1.4 eV (885 nm), respectively. The Ce3+ 5d-4f emission appeared to be quenched, just as the Eu2+ 5d-4f emission, which can be explained as the result of auto-ionization.

Mechanical and shape‐memory properties of poly(mannitol sebacate)/cellulose nanocrystal nanocomposites

ABSTRACTPolyesters based on polyols and sebacic acid, known as poly(polyol sebacate)s (PPS), are attracting considerable attention, as their properties are potentially useful in the context of soft‐tissue engineering applications. To overcome the drawback that PPSs generally display rather low strength and stiffness, we have pursued the preparation of nanocomposites based poly(mannitol sebacate) (PMS), a prominent example of this materials family, with cellulose nanocrystals (CNCs). Nanocomposites were achieved in a two‐step process. A soluble, low‐molecular‐weight PMS pre‐polymer was formed via the polycondensation reaction between sebacic acid and D‐mannitol. Nanocomposites with different CNC content were prepared by solution‐casting and curing under vacuum using two different profiles designed to prepare materials with low and high degree of crosslinking. The as‐prepared nanocomposites have higher stiffness and toughness than the neat PMS matrix while maintaining a high elongation at break. A highly crosslinked nanocomposite with a CNC content of 5 wt % displays a sixfold increase in Young's modulus and a fivefold improvement in toughness. Nanocomposites also exhibit a shape memory effect with a switch temperature in the range of 15 to 45 °C; in particular the materials with a thermal transition in the upper part of this range are potentially useful for biomedical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3123–3133

Characterization of 1,2,3-triazole crosslinked polymers based on azide chain-ends prepolymers and a dipolarophile curing agent as propellant binders: The effect of a plasticizer

The 1,2,3-triazole crosslinked polymers with potential use as a binder system in solid rocket propellants were prepared by mixing of an azide chain-ends diazide prepolymer, a dipolarophile curing agent, which act as a crosslinker, and a plasticizer at CC/N3 ratio of 1.1. A wide range of the plasticizer ratios were investigated: 0–300wt% for the polycaprolactone (PCP) and polycaprolactone ether (PCE) prepolymer based binders, and 0–500wt% for the polyethylene glycol (PEG) prepolymer based binder. Even at high amounts of plasticizer, sufficient initial reactivity and good conversion were obtained, however the increase of viscosity was considerably delayed. Crystalline domains of in the 1,2,3-triazole crosslinked polymers were effectively eliminated by the plasticizer. The tensile strength and modulus (100% and 300%, respectively) decreased with increasing of the amount of plasticizer whereas the elongation at the break was only modestly affected. PCP showed excellent elongation at the break compared to PEG at the same levels of plasticizer as well as good tensile strength. In contrast, the binder network prepared from the PCE prepolymer collapsed due to its low degree of crosslinking.

Self-Assembly of Polysaccharides Gives Rise to Distinct Mechanical Signatures in Marine Gels

Marine-gel biopolymers were recently visualized at the molecular level using atomic force microscopy (AFM) to reveal fine fibril-forming networks with low to high degrees of cross-linking. In this work, we use force spectroscopy to quantify the intra- and intermolecular forces within the marine-gel network. Combining force measurements, AFM imaging, and the known chemical composition of marine gels allows us to identify the microscopic origins of distinct mechanical responses. At the single-fibril level, we uncover force-extension curves that resemble those of individual polysaccharide fibrils. They exhibit entropic elasticity followed by extensions associated with chair-to-boat transitions specific to the type of polysaccharide at high forces. Surprisingly, a low degree of cross-linking leads to sawtooth patterns that we attribute to the unraveling of polysaccharide entanglements. At a high degree of cross-linking, we observe force plateaus that arise from unzipping, as well as unwinding, of helical bundles. Finally, the complex 3D network structure gives rise to force staircases of increasing height that correspond to the hierarchical peeling of fibrils away from the junction zones. In addition, we show that these diverse mechanical responses also arise in reconstituted polysaccharide gels, which highlights their dominant role in the mechanical architecture of marine gels.

Environment-friendly crosslinking of cornstarch by pentanedioic acid for stabilizing the viscosity of starch paste during warp sizing

Acid-thinned cornstarch was crosslinked with pentanedioic acid to different degrees to enhance viscosity stability of cooked starch paste for replacing the currently used toxic crosslinking agents such as formaldehyde and epichlorohydrin in the preparation of starch sizing agents. The degree of crosslinking was determined according to the stability, adhesion-to-fibers, film properties, desizability, and aerobic biodegradation of crosslinked starch. The degree of crosslinking showed significant effects on the stability, adhesion, desizability, and film properties, but was less sensitive to the biodegradation and wear loss of starch film. Suitable degree of crosslinking resulted in stable viscosity, good adhesion to fibers, strong and bending resistant film, and better desizability. Low degree of crosslinking could be utilized to increase the stability and improve usability of the starch used as warp sizing agent. The degree of crosslinking range (902-477 anhydroglucose units per crosslink) was recommended to stabilize the viscosity of cooked starch paste and improve the sizing properties of starch sizing agents.

Chemically cross-linked ultrathin electrospun poly(vinylidene fluoride-co-hexafluoropropylene) nanofibrous mats as ionic liquid host in electrochromic devices

In this work, ultrathin free-standing electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) nanofibrous mats are realized through the use of 1,3-diaminopropane as the chemical cross-linking agent. The cross-linking reaction occurs within the nanofibers as well as between the nanofibers that are in touch, forming relatively strong inter-fiber junctions and hence resulting in remarkable improvement in structural integrity of the electrospun mats with very small thickness. The chemically cross-linked electrospun mats are used as the host for 1-butyl-3-methylimidazolium tetrafluoroborate to prepare ionic liquid (IL)-based polymer electrolytes, and the effects of cross-linking on swelling and crystallization behaviors of the mats are studied. The results show that with a low degree of cross-linking, a high ionic conductivity of 2.6 mS/cm can be achieved, which is mainly due to the presence of a significant amount of free ILs in the interpenetrating pores of the mats. An electrochromic device is fabricated using this electrolyte to demonstrate the potential of the mat as IL host, especially its capability to greatly reduce IL consumption.