Chain Extension Process Research Articles

Deciphering the reduction of antibiotic resistance genes (ARGs) during medium-chain fatty acids production from waste activated sludge: Driven by inhibition of ARGs transmission and shift of microbial community

Medium-chain fatty acids (MCFAs) production from waste activated sludge (WAS) by chain extension (CE) is a promising technology. However, the effects and mechanisms of CE process on the fate of antibiotic resistance genes (ARGs) remain unclear. In this study, the results showed that the removal efficiency of ARGs was 81.15 % in CE process, suggesting its efficacy in reducing environmental risks. Further, the observed decrease in mobile genetic elements (MGEs) indicated that CE process restricted the horizontal gene transfer (HGT). Complementing this, the increase in soluble organic matters and extracellular 16 S rDNA confirmed that MCFAs production caused bacterial damage. Decreased intracellular ARGs and increased extracellular ARGs further revealed that MCFAs production impaired ARGs hosts, thereby limiting the vertical gene transfer (VGT) of ARGs. Shift of microbial community combined with co-occurrence network analysis demonstrated that functional bacteria without host potential for ARGs were enriched, but potential ARGs and MGEs hosts decreased, showing the role of functional bacterial phylogeny and selection pressure of MCFAs in reducing ARGs. Finally, partial least squares path model was used to systematic verify the mechanism of ARGs removal in CE process, which was attributed to the inhibition of ARGs transmission (HGT and VGT) and shift of microbial community.

Target Recognition Initiated Self-Assembly-Based Signal Amplification Strategy for Sensitive and Colorimetric Staphylococcus aureus Detection and Diagnosis of Skin Infection.

Staphylococcus aureus (S. aureus), as a Gram-positive bacterium, is commonly encountered in various infectious diseases, such as acute skin and soft tissue infections. Despite that many efforts have been made, sensitive and reliable quantitative determination of S. aureus remains a huge challenge. Here, we depict a novel colorimetric approach for sensitive and accurate detection by combining allosteric probe-based target recognition and chain extension-based dual signal recycling. The single-strand DNA (ssDNA) products generated by the chain extension process lead to the liberation of G-quadruplex sequences, which can fold into active DNAzyme under the assistance of hemin. The active DNAzyme can work as peroxidase mimics to catalyze the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS2-)-H2O2 system, causing the color change of the system. Eventually, the method exhibits a wide detection range from 103cfu/mL to 106cfu/mL. The limit of detection of the approach was determined 232cfu/mL. Considering the robust capability of the approach in S. aureus detection, we believe that it will be a potential alternative tool for biomedical research and clinical molecular diagnostics.

One-pot synthesis of hyperbranched polymers via visible light regulated switchable catalysis

Switchable catalysis promises exceptional efficiency in synthesizing polymers with ever-increasing structural complexity. However, current achievements in such attempts are limited to constructing linear block copolymers. Here we report a visible light regulated switchable catalytic system capable of synthesizing hyperbranched polymers in a one-pot/two-stage procedure with commercial glycidyl acrylate (GA) as a heterofunctional monomer. Using (salen)CoIIICl (1) as the catalyst, the ring-opening reaction under a carbon monoxide atmosphere occurs with high regioselectivity (>99% at the methylene position), providing an alkoxycarbonyl cobalt acrylate intermediate (2a) during the first stage. Upon exposure to light, the reaction enters the second stage, wherein 2a serves as a polymerizable initiator for organometallic-mediated radical self-condensing vinyl polymerization (OMR-SCVP). Given the organocobalt chain-end functionality of the resulting hyperbranched poly(glycidyl acrylate) (hb-PGA), a further chain extension process gives access to a core-shell copolymer with brush-on-hyperbranched arm architecture. Notably, the post-modification with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) affords a metal-free hb-PGA that simultaneously improves the toughness and glass transition temperature of epoxy thermosets, while maintaining their storage modulus.

Design, Preparation and Properties of Polyurethane Dispersions via Prepolymer Method.

A waterborne polyurethane dispersion for foamed synthetic leather base was designed and prepared using prepolymer method. There are many variables in the emulsification and chain-extension process of waterborne polyurethane (WPUR) dispersions prepared by prepolymer method. This work thoroughly evaluated the impacts of the steps of adding emulsified water, the temperature of the prepolymer and emulsified water, and concentration of ammonia water on WPUR dispersions by investigating the particle sizes/distributions and the mechanical stability. Changes in the temperature of the prepolymer and emulsified water, the concentration of ammonia water, and the step of adding emulsified water showed great impacts on the appearance and particle size of dispersions. Decreasing the temperature of the prepolymer and emulsified water and increasing the dilution ration of H2O to ethylenediamine (EDA) led to safe emulsification and dispersions with good appearance and narrow particle size distributions can be prepared. Surprising results were obtained by adding emulsified water in two steps, WPUR dispersions with a small particle size, narrow particle distribution and excellent tensile properties can be obtained. The optimized WPUR1 was applied to prepare water-based synthetic leather base after mechanical foaming, and the base presented the desired high performance, such as high folding resistance and peel strength.

Preparation and Characterization of Waterborne Polyurethane with Unique Nanoparticles by Controlling Water

A facile method, focusing on emulsification, chain extension and dispersion process in preparing waterborne polyurethane, was developed to prepare emulsion with rod-like nanoparticles. The facile method involves a water addition procedure by in situ generated water to react with polyurethane prepolymer instead of the external water addition process. As a comparison, waterborne polyurethane was synthesized through the external water addition process. According to the characterization methods including FTIR, 1H-NMR, TEM and water swelling experiments, it is suggested there are two kinds of hydrogen bonds interactions in hard/soft domain of the novel polyurethane, and the phase separation of hard/soft domains increases significantly. The morphology of the two polyurethanes was quite different (nanorods and spherical particles, respectively), presenting a different surface property. In addition, the water swelling of the novel polyurethane indicates that it holds significant potential application as degradable material.

Improving Recycled Poly(lactic Acid) Biopolymer Properties by Chain Extension Using Block Copolymers Synthesized by Nitroxide-Mediated Polymerization (NMP).

The aim of this contribution is to assess the use poly(styrene-co-glycidyl methacrylate-b-styrene) copolymers synthesized by nitroxide mediated polymerization (NMP) as chain extenders in the recycling of poly(lactic acid) biopolyester. Concisely, the addition of such block copolymers during the melt processing of recycled poly(lactic acid) (rPLA) leads to important increases in the viscosity average molecular weight of modified polymeric materials. Molar masses increase from 31,000 g/mol for rPLA to 48,000 g mol−1 for the resulting rPLA/copolymer blends (bPLA). Fortuitously, this last value is nearly the same as the one for pristine PLA, which constitutes a first piece of evidence of the molar mass increase of the recycled biopolymer. Thermograms of chain extended rPLA show significant decreases in cold crystallization temperature and higher crystallinity degrees due to the chain extension process using NMP-synthesized copolymers. It was found that increasing epoxide content in the NMP-synthesized copolymers leads to increased degrees of crystallinity and lower cold crystallization temperatures. The rheological appraisal has shown that the addition of NMP synthesized copolymers markedly increases complex viscosity and elastic modulus of rPLA. Our results indicate that P(S-co-GMA)-b-S) copolymers act as efficient chain extenders of rPLA, likely due to the reaction between the epoxy groups present in P(S-co-GMA)-b-PS and the carboxyl acid groups present in rPLA. This reaction positively affects viscometric molar mass of PLA and its performance.

Research on the Problems and Countermeasures of Suzhou "Single Window" Construction of Trade Facilitation

At present, under the background of the increasing tide of "anti-globalization" and China's open economy of higher standards, it is of great practical significance for Suzhou to promote the construction of "single window" of trade facilitation. Therefore, based on the current situation of promoting the construction of "single window" for trade facilitation, this paper concludes that there are some problems, such as business coverage is limited, system functions are imperfect; information interconnection and intercommunication should be strengthened; the overflow function of "single window" is insufficient, the recognition degree need to be improved; the cross regional construction lags behind, and the integration of customs clearance in the Yangtze River Delta has not yet been realized. Furthermore, the article puts forward three countermeasures and suggestions, including clarifying the functional orientation of the construction of "single window" with local characteristics in Suzhou; providing intelligent and integrated value-added services in combination with industrial chain extension and supply chain process; and promoting the "interconnection" of Yangtze River Delta and actively seeking for complementary and docking resources.

When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D3.

A simple, mild and efficient method to prepare HSi- or HOSi-telechelic, high-molecular-weight polydimethylsiloxane polymers (to 41,600 g·mol−1) using the one-shot hydrolysis of MHMH is reported; titration of the water allowed for higher molecular weights (to 153,900 g·mol−1). The “living” character of the chain extension processes was demonstrated by adding a small portion of MHMH and B(C6F5)3 (BCF) to a first formed polymer, which led to a ~2-fold, second growth in molecular weight. The heterogeneous reaction reached completion in less than 30 min, much less in some cases, regardless of whether it was performed neat or 50 wt% in dry toluene; homogeneous reactions in toluene were much slower. The process does not involve traditional redistribution, as judged by the low quantities (<3%) of D4 produced. However, it is not possible to avoid Chojnowski metathesis from MHDDMH giving D3, which occurs competitively with chain extension.

Preparation of aramid-based epoxy resin from low-grade aramid.

Low-grade aramid fibers, an unavoidable by-product in the industrialized process of aramid fiber production, are difficult to utilize and harmful to the environment. In this study, low-grade aramid fibers were recycled to assemble a high-quality epoxy resin through an epoxidation modification. Triggered by the epichlorohydrin, the molecular configuration of the low-grade aramid fibers was altered through crosslinking and chain-extension processes. bisphenol-A epoxy resin (E-51) with 5% aramid-based epoxy resin cured product exhibited improved mechanical and thermal properties, outperforming pure E-51 and pure aramid. This improvement is caused by the increased percentage of epoxide groups and flexible ether bonds. This work opens up new possibilities to maximize the reclamation of low-grade aramid fibers, which currently poses an obstacle in waste recycling.

Carbon chain extension processes in cryogenic environments: UV-assisted growth of polyynic nitriles in solidified rare gases

As demonstrated in recent years, polyynic nitriles may photochemically arise from smaller unsaturated chain species in an apparently rigid environment of a cryogenic rare gas matrix. Here I summarize the highlights of respective research that has advanced the spectroscopic description of R–(C≡C)n–C≡N molecules (R = H, CN or CH3).

Thermal stability of RAFT-based poly(methyl methacrylate): A kinetic study of the dithiobenzoate and trithiocarbonate end-group effect

Thermal stability of dithiobenzoate- (DB) and trithiocarbonate- (TC) terminated poly(methyl methacrylate) (PMMA) synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization is systematically studied under dynamic heating and prolonged isothermal treatment at 100–180 °C. It is demonstrated that in the presence of functional end-groups the onset of mass loss can be shifted relative to conventional PMMA, either toward higher (PMMA-DB) or lower (PMMA-TC) temperatures. Irrespective of the polymer molar mass, a loss of PMMA chain-end functionality clearly manifests itself upon 24 h of isothermal treatment at 120 °C for DB end-groups and already at 100 °C for TC ones. At 120 °C (for PMMA-TC) and 140 °C (for PMMA-DB) the ability of both polymers to serve as macromolecular RAFT agents in the chain extension processes ceases almost completely. The kinetics of functional end-groups elimination depends on their chemical nature. In the case of DB-groups, the reaction is of the first order, whereas TC-groups containing two CS bonds demonstrate more complex degradation kinetics. We propose a two-step mechanism of TC-group elimination, which enables interpretation of the observed experimental data.

Effect of chain topological structure on the crystallization, rheological behavior and foamability of TPEE using supercritical CO2 as a blowing agent

Thermoplastic polyether ester elastomer (TPEE) has been reacted with different multi-functional group modifiers, such as 2,2′-bis(2-oxazoline) (2,2′-BOZ) and triglycidyl isocyanurate (TGIC), to create long chain TPEE and highly branched TPEE respectively by reactive processing. Both chain extension and branching processes could improve the complex viscosity and modulus, but TPEE with a branched structure showed distinguished strain-hardening behavior. The branched structure can also accelerate crystallization processes. In the foaming process, TPEE with branched chains have a higher expansion ratio, higher cell density and wider foaming window when compared with TPEE with long chains. The branched structure can prevent cells from collapsing to obtain foamed TPEE with high expansion ratios ranging from 1.5 folds to 16 folds, cell diameters ranging from 3 μm to 13 μm and a cell density between 3.6×108 cells/cm3 and 7.1×109 cells/cm3.

Studies on Influence of the Size of Waterborne Polyurethane Nanoparticles on Coating Performance

Abstract Waterborne polyurethanes are extensively utilized as in coatings and adhesive applications because of their outstanding performance as solventless system. To achieve such a product with almost no or minimum volatile organic compounds, water is the best choice to utilize as a solvent medium in coating formulations to eliminate organic solvents from the final products. During the synthesis of the waterborne polyurethanes, the particle size of final dispersion products depends on many factors like NCO:OH content, the concentration of acid, synthesis conditions, chain extension process etc. In this research work using the prepolymer mixing process and changing NCO:OH content, flame retardant waterborne polyurethane dispersions (FWBPUD) were prepared from phosphorous containing polyester polyol and isophorone diisocyanate (IPDI). These prepolymers were neutralized by triethylamine followed by the addition of predefined quantity of water. Diethylenetriamine was used as a chain extender. These FWBPUs were further coated on various substrates. Characterization was done using Fourier transform infrared and Nuclear magnetic resonance spectroscopy. The average particle size of the dispersions was characterized by Microtrac-analyser. An influence of the size of waterborne polyurethane nanoparticles on the coating performance was described by scratch resistance, pencil hardness, adhesion (cross-hatch), flexibility 1/4“ mandrel test, chemical resistance and solvent resistance test. Due to the presence of phosphorous moiety, these FWBPUs also show flame retardancy which was investigated by limiting oxygen index (LOI) and UL-94 test methods. The FWBPU dispersions were stable for 8 months.

Investigating the effect of multi-functional chain extenders on PLA/PEG copolymer properties

Biodegradable copolymers polylactic acid-co-poly ethylene glycol (PLA-co-PEG) were synthesized at a specific volume ratio (PLA/PEG) (80/20) using direct melt polycondensation without solvent. The effects of an oligomeric chain extender (CE) on the mechanical, molecular weight, thermal stability, and degradation were evaluated. The copolymers were tailored by introducing classes of CE contents (0.25, 0.5, 0.075, 1.0, 1.25, and 1.5wt%) (styrene- glycidyl acrylate copolymer). Apparently, the mechanical properties of copolymers were enhanced in the presence of CE. A long chain branch structure has led to a slight improvement of tensile strength to reach 70MPa at CE 1.25%, compared with 60MPa for neat PLA. A significant increase of 17% was observed for the elongation at break of copolymers after addition of CE 1.25%. In addition, the impact strength increased to 7.9KJ/m2 in the ranges of CE 1–1.25%. Melt flow index dramatically reduces with the addition of CE contents. Gas Permeation Chromatography (GPC) showed that the addition of CE 1.25% has resulted in increasing the PLA molecular weight to 132.569kDa with a broad molecular weight distribution, MWD (2.066), and bimodal distribution. Differential Scanning Calorimetric (DSC) results revealed that the chain extension process improved glass transition temperature (Tg) 62°C, melting temperature (Tm) 161°C, and crystallinity (X%) 34.9% as a result of CE 1.25%. Thermal gravimetric analyses (TGA) results indicated that the CEs have a positive effect on the enhancement of thermal stability. Moreover, Scanning Electron Microscopic (SEM) showed that the compatibility and interfacial adhesion between the PLA and PEG chains were enhanced in the existence of the CE contents. The weight loss of the copolymer during 30days of degradation time was 28%, while the weight loss of CE 1.5% was only 3% during the same time interval.

The effects of two-step reactive processing on the properties of recycled poly(ethylene terephthalate)

A simple approach for preparing recycled poly(ethylene terephthalate) (r-PET) with excellent processability and melt strength has been developed in this research. To increase the intrinsic viscosity of r-PET, a two-step chain extension process using a combination of SAG-008 and tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) was investigated. To evaluate the chain extension degree of the modified r-PET, its intrinsic viscosity (IV) and rheological properties were characterized, and found to be correlated to the long-chain branches and molecular weight. The results indicated that the combination of SAG-008 and TGDDM at the optimized conditions provided the highest IV of 1.18 dl/g while controlling the gel formation to a low value. The increases in storage modulus, loss modulus and complex viscosity revealed the enhancement of melt strength and viscoelasticity of r-PET. The differential scanning calorimetry results showed that the crystallinity was reduced with the addition of chain extenders. On the other hand, stepwise annealing method from room temperature to crystal melting temperature promoted the crystallization, which was confirmed by wide-angle X-ray diffraction measurement.

New Class of Alkoxyamines for Efficient Controlled Homopolymerization of Methacrylates.

Despite significant efforts, the design of alkoxyamines for polymerization of methacrylic monomers in a well-controlled fashion with good retention of the active chain ends remains a challenge. Herein, the facile synthesis of several alkoxyamines, which are capable of achieving this long sought-after goal, is reported. Controlled homopolymerization of methyl methacrylate is achieved as determined by a linear increase in molecular weight with conversion and first-order rate plots for various alkoxyamine concentrations. The versatility of the alkoxyamines is further exemplified by the ability to control the homopolymerization of styrene and by synthesis of a block copolymer of a second methacrylate in an efficient chain extension process.

Fluorescently labeled degradable thermoplastic polyurethane elastomers: Visual evaluation for the degradation behavior

ABSTRACTThermoplastic polyurethane elastomers (TPU) were synthesized with isophorone diisocyanate (IPDI) as the rigid segment, poly(lactic‐co‐glycolic acid) (PLGA‐PEG‐PLGA) diol as soft segment, and 1,4‐butanediol (BDO) as the chain extender. During the chain extension process, three kinds of fluorescent monomers 4‐(2‐hydroxyethylamino)−1,8‐naphthoyl‐(2‐hydroxyethyl)imide (HNHI), 1,5‐dihydroxy naphthalene (DHN), and dicoumarin (DIC) were introduced to get the fluorescently labeled degradable TPUs. The structure and degradation properties of the TPUs were characterized in detail. The results showed that there was no significant effect found on average molecular weight, mechanical properties, and glass transition temperature of polyurethane by introducing 0.001% (wt) weight percent of fluorescence monomers. The degradation behavior of fluorescent‐tagged thermoplastic elastomer has been characterized with fluorescence microscopy. Results showed that polyurethane elastomers, in which fluorescence monomers especially HNHI were introduced by chemical reaction, had more homogeneous and stable fluorescence intensity than that with fluorescence monomers introduced by post blending. This work also provides a promising visual characterization approach to monitor degradation behavior of degradable TPUs for tissue engineering applications or drug delivery system. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42519.

Obez Kişilerde Plazma Yağ Asit Kompozisyonu, Desatüraz ve Elongaz Enzim Aktivitelerinin Değerlendirilmesi

Obesity is associated with an increased risk of insulin resistance, diabetes, hyperlipidemia, hypertension and elevated circulating fatty acids. Some of those abnormalities may be caused by an altered fatty acid metabolism. Increased plasma fatty acids in obese individuals may contribute to accelerate of β-oxidation and may also affect insulin sensivity. Fatty acid composition is used as an indicator of disease risk, because its alteration has been related to metabolic disease and cardiovascular disease. Desaturase are involved in the endogenous synthesis of polyunsaturated fatty acids. The delta 9, 6 and 5 desaturases introduce a double bond at specific positions on long chain fatty acids. Fatty acids of the enzymes responsible for chain extension process is called the elongase. In this paper, we review estimated, addressing the recent studies, plasma fatty acid composition, desaturase and elongase activity in obese people

Chain extension of dimer fatty acid- and sugar-based polyurethanes in aqueous dispersions

The chain extension process of renewable waterborne polyurethane dispersions (WBPUDs) prepared from a dimer fatty acid-based diisocyanate (DDI) and isosorbide (IS), using dimethylolpropionic acid (DMPA) as the internal dispersing agent, was investigated. Ethylene diamine (EDA), adipic dihydrazide (ADH) and water were evaluated as chain extenders. Other variables such as the chain extension temperature, the sequence of addition of the chain extender with respect to the dispersion step and the utilization of a catalyst (triethylamine, TEA) were investigated as well. It was found that EDA extended the NCO-functional prepolymer chains at both 30 and 50°C, independent of the moment of its addition. A limited extent of chain extension by ADH was observed, which was thought to be caused by the low solubility of ADH in the solvent 2-butanone, used for the prepolymer synthesis. ADH chain extension only took place after removal of the 2-butanone. Water chain extension was observed at temperatures ranging from 50°C to 70°C. A good balance was found at 50°C, where a stable dispersion with a relatively high molecular weight, a small particle size and a narrow particle size distribution were obtained. The usage of TEA during the dispersion process promoted the water chain extension reaction, however, at the cost of dispersion stability. An increased DMPA level has shown to improve the dispersion stability. Dispersion-cast poly(urethane urea) films were found to be thermally stable up to 249°C (5wt% mass loss) and had Tg values around room temperature.

Stereoselective synthesis of 1-C-alkyl iminogalactitol derivatives, potential chaperones for galactosidase-linked LSDs: a real challenge

1-C-Alkyl iminogalactitol derivatives are highly desirable target compounds as potential pharmacological chaperones for the treatment of galactosidase-linked lysosomal storage disorders (LSDs). The synthesis of such compounds from d-galactose by a C-1 chain extension process by way of an open-chain 6-amino d-gulo nonulose intermediate was complicated by unexpected deoxygenation reactions leading to 3-deoxy iminogalactitol derivatives and epimers; an alternative, stereocontrolled synthesis from an l-tagatose derivative by C-6 chain-extension was therefore developed, which involved addition of organometallic reagents onto t-butanesulfinylimine intermediates in the key step.