Molecular Weight Polydispersity Research Articles

A Titanium–Organic Framework: Engineering of the Band-Gap Energy for Photocatalytic Property Enhancement

A visible-light-responsive metal–organic framework based on titanium hexameric cluster and high conjugation system of organic linker building block termed MOF-902 was synthesized and fully characterized. The photocatalytic properties of MOF-902 were investigated in the polymerization reaction with various monomers such as methyl methacrylate (MMA), benzyl methacrylate (BMA), and styrene (St), respectively. Gel permeation chromatography (GPC) analysis results demonstrated the high performance of MOF-902 as a catalyst, affording polymer products with high molecular weight (Mn) and low polydispersity index (PDI). The photocatalytic efficiency of MOF-902 in the polymerization transformation obviously exceeds other catalysts such as MOF-901, UiO-66, UiO-66-NH2, MIL-125(Ti), MIL-125-NH2(Ti), and commercial P25-TiO2.

Facile preparation of a novel nickel-containing metallopolymer via RAFT polymerization

While the metallocene polymers were comprehensively studied, other metallopolymers are rarely explored. The major challenge is the lack of a synthetic platform for the preparation of metal coordinated derivatives, monomers, and polymers. Therefore, the development of a facile synthesis of new metal coordinated monomers and polymers is critically needed. A novel successfully synthesized methacrylate-containing nickel complex is reported in this communication. Controlled RAFT polymerizations are further carried out to prepare a series of side-chain nickel containing polymers with different molecular weight and narrow Polydispersity Index (PDI). This new metallopolymer performs specific electrochemical and excellent thermal properties. This study provides a novel and convenient strategy to prepare metallopolymer with controllable molecular weight, which has potential applications in assembled, catalytic and magnetic materials.

Simultaneous Chain-Growth and Step-Growth Polymerization of Methoxystyrenes by Rare-Earth Catalysts.

The simultaneous chain-growth and step-growth polymerization of a monomer is of great interest and importance because it can produce unique macromolecules which are difficult to prepare by other means. However, such a transformation is usually difficult to achieve in one polymerization system because chain-growth polymerization and step-growth polymerization proceed by different reaction mechanisms. Reported here is the simultaneous chain-growth and step-growth polymerization of para- and meta-methoxystyrenes catalyzed by half-sandwich rare-earth alkyl complexes, and the step-growth polymerization proceeds by the C-H polyaddition of anisyl units to vinyl groups. This unprecedented transformation affords a new family of macromolecules containing unique alternating anisole-ethylene sequences. In contrast to para- and meta-methoxystyrenes, ortho-methoxystyrene exclusively undergo syndiospecific, living chain-growth polymerization by continuous C=C bond insertion to give perfect syndiotactic poly(ortho-methoxystyrene) with high molecular weight and narrow polydispersity (rrrr >99 %, Mn up to 280 kg mol-1 , Mw /Mn <1.10).

Simultaneous Chain‐Growth and Step‐Growth Polymerization of Methoxystyrenes by Rare‐Earth Catalysts

AbstractThe simultaneous chain‐growth and step‐growth polymerization of a monomer is of great interest and importance because it can produce unique macromolecules which are difficult to prepare by other means. However, such a transformation is usually difficult to achieve in one polymerization system because chain‐growth polymerization and step‐growth polymerization proceed by different reaction mechanisms. Reported here is the simultaneous chain‐growth and step‐growth polymerization of para‐ and meta‐methoxystyrenes catalyzed by half‐sandwich rare‐earth alkyl complexes, and the step‐growth polymerization proceeds by the C−H polyaddition of anisyl units to vinyl groups. This unprecedented transformation affords a new family of macromolecules containing unique alternating anisole‐ethylene sequences. In contrast to para‐ and meta‐methoxystyrenes, ortho‐methoxystyrene exclusively undergo syndiospecific, living chain‐growth polymerization by continuous C=C bond insertion to give perfect syndiotactic poly(ortho‐methoxystyrene) with high molecular weight and narrow polydispersity (rrrr &gt;99 %, Mn up to 280 kg mol−1, Mw/Mn &lt;1.10).

Crystalline Polyesters from CO2 and 2-Butyne via α-Methylene-β-butyrolactone Intermediate

The selective transformation of carbon dioxide into useful chemicals has attracted much attention in recent decades due to the economic and environmental benefits arising from the utilization of renewable source. Nevertheless, the reactions on incorporating CO2 into polymeric materials are very limited. The copolymerization of CO2 and alkynes to synthesize degradable polyesters is a thermodynamically unfavorable process, since the propagation step involving CO2 is a major obstacle. Herein, we report a strategy to conquer the thermodynamic and kinetic barriers for the copolymerization of CO2 and 2-butyne via α-methylene-β-butyrolactone (MβBL) intermediate. Subsequent ring-opening polymerization of the lactone intermediate mediated by achiral Salen aluminum complexes afforded syndiotactic-enriched polyesters with controllable molecular weight and narrow polydispersity. Notably, the resultant syndiotactic-enriched poly(MβBL) is a typical semicrystalline material. The present method provides access to a new c...

Composition and structure of an antioxidant acetic acid lignin isolated from shoot shell of bamboo (Dendrocalamus Latiforus)

Bamboo shoot shell (BSS), which contains a large amount of insoluble fibre and lignin, is the main agricultural waste from the production of bamboo shoots. To utilize this waste in a value-added manner, the acetic acid lignin (AL) fraction from BSS was extracted via a combination of hot water pre-treatment and acetic acid post-treatment in the present study. The chemical composition, structural characteristics, and antioxidant activity of AL were investigated and compared to the corresponding milled wood lignin (MWL). The results showed that AL had a higher yield (74%) and lower content of associated carbohydrates (2.96%) than MWL (5.16%). GPC analysis revealed that AL possessed a moderate molecular weight (Mw=2789Da) and narrow polydispersity index (Mw/Mn=1.54). Structural characterization via FT-IR, 1H NMR, 2D-HSQC, and 31P NMR indicated that AL from BSS was a typical HSG-type lignin and was partially acylated at the γ-carbon of the side chain by p-coumarate. Moreover, the bonds between lignin units were predominately β-O-4⿲ linkages. Compared to MWL, AL possessed a characteristically higher phenolic hydroxyl group content and S/G ratio. In terms of the DPPH radical scavenging activity, ABTS radical cation scavenging activity and ferric reducing antioxidant power, AL showed stronger antioxidant activity than MWL and was superior to the commercial synthetic antioxidant BHT. In summary, by applying a modified two-step procedure, which included hot water pre-treatment and acetic acid extraction, AL from BSS was effectively extracted, and the antioxidant potential of AL was characterized.

RAFT polymerization and dually responsive behaviors of terpyridine-containing PNIPAAm copolymers in dilute solutions

Introduction of new components is an effective way to gain new functionalities and to regulate the properties of responsive polymers. In the present work, a RAFT polymerization approach to terpyridine-containing poly(N-isopropyl acrylamide) (PNIPAAm) copolymers was developed and the dually responsive behavior of the obtained polymer to temperature variation and metal ions in dilute solutions were investigated. By utilizing RAFT polymerization, the molecular weight polydispersity index of the polymer can be reduced compared with the traditional free radical polymerization method. Due to the coexistence of thermosensitive component and terpyridine, the synthesized polymer is thermosensitive and metal ion sensitive. Further titration investigation revealed that this polymer may be utilized as a water-soluble and colorimetric sensor for Fe2+ and Fe3+ and the obvious color change from a colorless state to a purple state makes the polymer a potential sensor to detect Fe2+ and Fe3+ macroscopically by naked eye. Overall, the terpyridine-containing poly(N-isopropyl acrylamide) copolymers may enrich the family of terpyridine-containing polymers and provide some clues for developing new multi-responsive and multi-functional polymers.

Synthesis, structure and methyl methacrylate polymerization of cobalt(II), zinc(II) and cadmium(II) complexes with N,N′,N-bidentate versus N,N′,N-tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines

Mononuclear Co(II), Zn(II) and Cd(II) complexes derived from bidentate or tridentate N,N′,N-bis((1H-pyrazol-1-yl)methyl)amines (Ln = LA, LB), where LA is N,N-bis((1H-pyrazol-1-yl)methyl)-3-methoxypropan-1-amine and LB is 3-methoxy-N,N-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)propan-1-amine, have been synthesized and characterized. The geometry at Co(II) and Cd(II) for [LACoCl2], [LBCoCl2] and [LBCdBr2] with N,N′,N-tridentate ligands (Ln = LA, LB) can be described as a distorted trigonal bipyramid achieved by coordinative interaction of Npyrazole, two halides and the nitrogen of amine moiety. However, the molecular structure of four-coordinate [LAZnCl2] can be best described as tetrahedral, resulting in an eight-membered chelate ring. [LACoCl2] polymerized methyl methacrylate in the presence of modified methylaluminoxane at 60 °C and resulted in poly(methylmethacrylate) (PMMA) with higher molecular weight and narrower polydispersity index compared to the other synthesized complexes. However, all the synthesized complexes yielded syndiospecific PMMA, characterized using 1H NMR spectroscopy, with ca. 0.70.

Validation of a high-performance size-exclusion chromatography method to determine and characterize β-glucans in beer wort using a triple-detector array

Beer wort β-glucans are high-molecular-weight non-starch polysaccharides of that are great interest to the brewing industries. Because glucans can increase the viscosity of the solutions and form gels, hazes, and precipitates, they are often related to poor lautering performance and beer filtration problems. In this work, a simple and suitable method was developed to determine and characterize β-glucans in beer wort using size exclusion chromatography coupled with a triple-detector array, which is composed of a light scatterer, a viscometer, and a refractive-index detector. The method performances are comparable to the commercial reference method as result from the statistical validation and enable one to obtain interesting parameters of β-glucan in beer wort, such as the molecular weight averages, fraction description, hydrodynamic radius, intrinsic viscosity, polydispersity and Mark-Houwink parameters. This characterization can be useful in brewing science to understand filtration problems, which are not always explained through conventional analysis.

Antioxidant and Adsorption Properties of Bioinspired Phenolic Polymers: A Comparative Study of Catechol and Gallol

Polyphenols, which by the Quideau definition are plant-derived chemicals with two or more phenolic groups, have attracted interest because of their antioxidant activity, adsorption on universal substrates, and biocompatibility. Most polyphenols include gallol groups in their chemical structures, which has inspired us to synthesize gallol-functionalized polymers. We report the reversible addition–fragmentation chain transfer polymerization of 3,4,5-trimethoxystyrene using cyanomethyl dodecyl trithiocarbonate as the chain transfer agent. This method produces well-defined polymers with a wide range of molecular weight (from 5.4 to 53.4 kg mol–1) and low polydispersity index (Mw/Mn < 1.3). Subsequent demethylation of poly(3,4,5-trimethoxystyrene) (PTMS) yields poly(3,4,5-trihydroxystyrene) (polyvinylgallol, PVGal). These newly synthesized polymers exhibit greater antioxidant activities than widely used catechol-functionalized polymers based on the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), 2,2′-azinobis(3-...

Rapid copolymerization of carbon dioxide and propylene oxide catalyzed by double metal cyanide complexes in an ultrasonic field

Sonochemistry as a clean, efficient and environmentally friendly synthetic method has shown great potential in the chemical synthesis. In this work, poly (propylene carbonate) (PPC) was successfully obtained from carbon dioxide (CO2) and propylene oxide (PO) by using Zn-Co and Zn-Fe double metal cyanides (DMCs) as catalyst with the sonochemistry method. With FTIR, 1H NMR and GPC analysis, PPCs prepared in the ultrasonic field have high yield, high molecular weight and wide polydispersity index (PDI). It is proven to be effective for the copolymerization of CO2 and PO with the sonochemistry method.

Alkylammonium AlPO-kanemite as support for tuning catalytic activity of metallocene: In situ preparation of polyethylene nanocomposites

Several alkylammonium-AlPO-kanemites were prepared to display a range of interlayer distances due to the presence of variable n-butyl/n-dodecylammonium concentrations. Zirconocene and titanocene dichlorides reacted with these layered materials to produce new supported metallocene catalysts. The characterization of these materials confirmed their formation and the presence of the anchored metallocene on the solid support. This study aimed to test these samples for the first time as catalysts for ethylene polymerization for verification of the influence of the metallocene supports with tunable interlayer distances on the catalytic behavior and for in situ production of nanocomposites. The data showed that the highly active new supported systems reaches values of activity comparable to that obtained by analogous homogeneous system. The increase in the interlayer space acted to increase the activity, showing that the possibility of change the interlayer space is a tool to control the activity. Polymers obtained by the supported catalysts presented higher molecular weight and lower polydispersities index than that synthetized with homogeneous catalyst. The ethylene polymerization promoted the exfoliation of the alkylammonium-AlPO-kanemite layers in the polymer matrix, characterizing the formation of a nanocomposite. Compared to the pristine polymer, the presence of inorganic fillers in the polymer matrix increased the melting temperature of the nanocomposite.

Influence of molecular-weight polydispersity on the glass transition of polymers.

It is well known that the polymer glass transition temperature T_{g} is dependent on molecular weight, but the role of molecular-weight polydispersity on T_{g} is unclear. Using molecular-dynamics simulations, we clarify that for polymers with the same number-average molecular weight, the molecular-weight distribution profile (either in Schulz-Zimm form or in bimodal form) has very little influence on the glass transition temperature T_{g}, the average segment dynamics (monomer motion, bond orientation relaxation, and torsion transition), and the relaxation-time spectrum, which are related to the local nature of the glass transition. By analyzing monomer motions in different chains, we find that the motion distribution of monomers is altered by molecular-weight polydispersity. Molecular-weight polydispersity dramatically enhances the dynamic heterogeneity of monomer diffusive motions after breaking out of the "cage," but it has a weak influence on the dynamic heterogeneity of the short time scales and the transient spatial correlation between temporarily localized monomers. The stringlike cooperative motion is also not influenced by molecular-weight polydispersity, supporting the idea that stringlike collective motion is not strongly correlated with chain connectivity.

Design a Highly Reactive Trifunctional Core Molecule To Obtain Hyperbranched Polymers with over a Million Molecular Weight in One-Pot Click Polymerization

We present the first one-pot one-batch synthesis of hyperbranched polymers with over a million molecular weight and low polydispersity in the copper-catalyzed alkyne–azide cycloaddition (CuAAC) polymerization of AB2 monomer. In contrast to the traditional triazido core molecule that failed to produce high molecular weight polymer, a novel tris-triazoleamine-based B3 molecule was designed, which complexed with CuI catalyst and activated the azido reactivity in both B3 and B3-containing polymers. The polymerization demonstrated linear increase of polymer molecular weights with the feed ratio of [AB2]0:[B3]0 with no need of slow monomer addition. At the same time, a higher ratio of [CuI]0:[B3]0 showed no influence on molecular weight but significantly increased the polymerization rate and produced hyperbranched polymers with higher degree of branching. The one-pot polymerization using [AB2]0:[B3]0:[Cu]0 = 2700:1:10 produced hyperbranched polymers with molecular weight Mn = 1.01 × 106 and polydispersity Mw/Mn...

Cobalt(II) complexes containing N′-substituted N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine ligands: The formation of four-coordinate or five-coordinate complexes as a function of the N′-substitution group in N,N′,N-bis((1H-pyrazol-1-yl)methyl)amine

N,N-bis((1H-pyrazol-1-yl)methyl)(cyclohexyl)methanamine (LA), N,N-bis((1H-pyrazol-1-yl)methyl)-2,6-diethylbenzenamine (LB), N,N-bis((1H-pyrazol-1-yl)methyl)-4-bromobenzenamine (LC), N,N-bis((1H-pyrazol-1-yl)methyl)cyclohexanamine (LD), N,N-bis((1H-pyrazol-1-yl)methyl)(furan-2-yl)methanamine (LE), N,N-bis((1H-pyrazol-1-yl)methyl)-2-methoxyethanamine (LF), and N,N-bis((1H-pyrazol-1-yl)methyl)-3-(methylthio)propan-1-amine (LG) with [CoCl2·6H2O] in ethanol yield a novel series of Co(II) chloride complexes; i.e. [LnCoCl2] (Ln=LA–LG), respectively. The molecular structures of [LnCoCl2] (Ln=LA–LC) and [LnCoCl2] (Ln=LD–LG) exist as monomeric four-coordinated and five-coordinated complexes, respectively. [LnCoCl2] (Ln=LA–LC) showed a distorted tetrahedral geometry involving non-coordination of the nitrogen atom of the N′-substitution amine moiety and the Co(II) centre, resulting in the formation of an eight-membered chelate ring. The geometry at each Co(II) centre in [LnCoCl2] (Ln=LD–LG) were best described as a distorted trigonal bipyramid involving coordination of the nitrogen atom of the N′-substitution amine group and the Co(II) centre. Specifically, a distorted trigonal bipyramid was achieved in [LDCoCl2] through a coordinative interaction of the nitrogen atom of the cyclohexylamine unit and the Co(II) atom with an σ plane of symmetry based on the bond length of Co–Ncyclcohexylamine [2.466(4)Å]. Moreover, [LDCoCl2] showed the highest activity for methyl methacrylate (MMA) polymerization in the presence of modified methylaluminoxane (MMAO) at 60°C and yielded poly(methylmethacrylate) (PMMA) with a high molecular weight (Mw) and narrower polydispersity index (PDI) compared to the other Co(II) complexes. However, all Co(II) complexes produced syndiotactic (PMMA), characterised using 1H NMR spectroscopy, with ca. 0.70.

Diluting ferric carboxymaltose in sodium chloride infusion solution (0.9% w/v) in polypropylene bottles and bags: effects on chemical stability

ObjectivesThis study was designed to assess the physicochemical stability of colloidal ferric carboxymaltose solution (Ferinject) when diluted and stored in polypropylene (PP) bottles and bags for infusion.MethodsTwo batches of ferric...

Understanding lignin treatment in dialkylimidazolium-based ionic liquid–water mixtures

The treatment of enzymatically hydrolyzed lignin (EHL) in dialkylimidazolium-based ionic liquid (IL)–water mixtures (50–100wt% IL content) was investigated at 150°C for 3h. pH, IL type, and IL content were found to greatly influence the degradation of lignin and the structure of regenerated lignin. 1-Butyl-3-methylimidazolium methylsulfonate–water mixtures with low pH facilitated lignin depolymerization but destroyed the regenerated lignin substructure. Regenerated lignin with low molecular weight and narrow polydispersity index (2.2–7.7) was obtained using a 1-butyl-3-methylimidazolium acetate-based system. Water addition inhibited lignin depolymerization at 50–100wt% IL content, except for 70wt% 1-butyl-3-methylimidazolium chloride–water mixture. Compared with pure IL treatment, obvious differences were observed in the breakdown of inter-unit linkages and ratio of syringyl to guaiacyl units in regenerated lignin with IL–water treatment.

Visible-Light-Induced Living Radical Polymerization (LRP) Mediated by (salen)Co(II)/TPO at Ambient Temperature

Visible-light-induced living radical polymerization of acrylates (MA, nBA, tBA), acrylamides (DMA, AMO), and vinyl acetate (VAc) at ambient temperature mediated by (salen)Co(II)/TPO was described. Effects of light intensity, feeding ratio of monomer and equivalent of TPO for the polymerization of MA were investigated. Well-defined homopolymers and block polymers with predetermined molecular weight and narrow polydispersity were obtained under mild conditions. The mechanism of the polymerization was proposed based on polymerization behavior and polymer structure analysis. The (salen)Co(II)/TPO system was suitable for both conjugated and unconjugated monomers under mild conditions.

Enhanced Charge Transfer Doping Efficiency in J-Aggregate Poly(3-hexylthiophene) Nanofibers

Charge transfer doping efficiencies of π-stacked poly(3-hexylthiophene) (P3HT) aggregate nanofibers are studied using spectroscopic and electron microscopy probes. Solution dispersions of self-assembled P3HT nanofibers are doped in the ground electronic state by adding varying amounts (w/w%) of the strong charge transfer dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ). Careful control of self-assembly conditions allows us to select either the H- and J-aggregate limiting forms, which differ primarily in the degree of purity (i.e., molecular weight fractionation) and nanomorphology. Electron paramagnetic resonance (EPR), electronic absorption, and Raman spectroscopy of F4-TCNQ–:P3HT+ species are then used to track doping efficiency with dopant loading. J-aggregate nanofibers exhibit over an order of magnitude larger doping efficiencies than polymorphic H-aggregate nanofibers. The higher purity and order of the former promote intrachain polaron delocalization whereas disorder arising from greater molecular weight polydispersity in the latter instead lead to polaron localization resulting in charge transfer complex formation. Interestingly, J-aggregate nanofiber EPR signals decrease significantly after ∼25% F4-TCNQ loading which we attribute to increased antiferromagnetic coupling between delocalized hole polarons on neighboring P3HT chains leading to spinless interchain bipolarons. Raman spectra excited on resonance with NIR F4-TCNQ–:P3HT+ absorption transitions also reveal quinoid distortions of the P3HT backbone in J-aggregates. We propose that self-assembly approaches to control aggregate packing and purity can potentially be harnessed to achieve long-range, anisotropic charge transport with minimal losses.

Abundance and characteristics of lignin liquid intermediates in wood (Pinus ponderosa Dougl. ex Laws.) during hot water extraction

The objective of this research was to investigate the effects of the conditions of hot water extraction (HWE) on abundance, properties, and structure of lignin depolymerization products. HWE of extracted softwood (ponderosa pine) was conducted using temperatures from 140 to 320 °C for 90 min. HWE materials were then subjected to a soxhlet extraction process using dichloromethane (DCM). The composition and molecular weight of this DCM-soluble material was conducted using semi-quantitative Py-GC/MS and ESI/MS, which showed that this material is rich in lignin with low molecular weight (<1200 g mol−1) and low polydispersity (∼1.4). The highest yield of this material (∼4.2%) was obtained in material processed at 260 °C. Py-GC/MS of the solid fraction after the DCM process showed a progressive reduction of products of the pyrolysis of lignin as the HWE temperature increased. This finding suggests that the lignin content in the solid decreased due in part to migration from the cell walls and middle lamella to the particles surfaces, particularly the inner surface of the cells. SEM and AFM techniques helped to visualize the ability of this DCM-soluble extract to adhere to cellulosic fibers. Therefore, this lignin-rich material presents properties that depend on the conditions of the operation. Results indicate that during HWE it is possible to control the process parameters to limit or increase the amount of DCM-soluble lignin and its properties as required for downstream processes.