SEC Analysis Research Articles

Synthesis and cross-linking behavior of biobased polyesters composed of bi(furfuryl alcohol)

Furfuryl alcohol is a biobased chemical obtained from inedible biomass that could potentially become a viable alternative for petroleum-based chemicals. In this study, we have coupled furfuryl alcohol to bi(furfuryl alcohol) (BFA), which can act as a bifunctional monomer. A single-crystal X-ray diffraction analysis of BFA revealed that the bifuran moiety adopts a rigid structure due to the anti-parallel and co-planar geometry of the two π-conjugated furan rings. BFA was subsequently polymerized with succinic anhydride to poly(bifurfurylene succinate) (PBFS). The alpha relaxation temperature (Tα) and melting temperature (Tm) of bifuran-containing PBFS are higher than those of polyesters containing mono-furan rings. The cross-linking reaction of PBFS with bismaleimide afforded cross-linked PBFS, which exhibited increased Tα and mechanical strength due to the restriction in mobility that results from the formation of the cross-linking points. The 1H NMR spectra and SEC analysis revealed that the cross-linked PBFS was a ladder-type polymer.

Telechelics Based on Catalytic Alternating Ring-Opening Metathesis Polymerization.

We describe a protocol to synthesize alternating telechelic ROMP copolymers of 7-oxa-norbornene derivatives and cycloalkenes under catalytic conditions. These copolymers were synthesized using Grubbs' second-generation catalyst. The sterically less hindered backbone double bonds of the resulting alternating copolymers facilitate the chain transfer (secondary metathesis) reactions. In the presence of symmetrical chain transfer agents (CTA), alternating copolymers could be synthesized catalytically. This procedure allows the synthesis of telechelic polymers based on potentially functional 7-oxa-norbornene derivatives under thermodynamic equilibrium conditions. The molar mass of the alternating copolymer was controlled by the monomer to CTA ratio. The end group of the copolymers synthesized in the catalytic manner was addressed by the CTA functionality, yielding telechelic copolymers in excellent yields. 1H NMR spectroscopy, MALDI-ToF mass spectrometry, and SEC analysis confirmed the chemical identity of the alternating telechelic copolymers with excellent control over the molar mass.

Controlled copolymerization of 1‐octene and butyl methacrylate via RAFT and their nonisothermal model‐free thermokinetic decomposition study

ABSTRACTReversible addition fragmentation chain transfer (RAFT) copolymerization of 1‐octene and butyl methacrylate (BMA) was carried out for the first time using 4‐cyano‐4‐(phenylcarbonothioylthio)pentanoic acid as RAFT agent in N,N′‐dimethyl formamide. Poly(1‐octene‐co‐BMA) copolymers with well‐controlled molecular weights and narrow molecular weight distribution were obtained throughout the polymerization. The copolymers have been well characterized by different analytical techniques such as SEC, FT‐IR, NMR, SEM, AFM, XRD, and TG analyses. FT‐IR and NMR analyses confirmed the synthesis of poly(1‐octene‐co‐BMA) copolymers. SEM and AFM analyses demonstrated the wavy‐lamellar morphological structure of the copolymers. Thermogravimetric analysis revealed good thermal stability of poly(1‐octene‐co‐BMA) copolymers synthesized via RAFT mediated polymerization. The thermokinetic parameters were evaluated by adopting model‐free methods of Friedman and Flynn–Wall–Ozawa using the nonisothermal thermogravimetric data. The multivariate nonlinear regression analysis established the most appropriate kinetic model and the corresponding kinetic parameters of thermal decomposition of poly(1‐octene‐co‐BMA) copolymers were also calculated. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2093–2103

Synthesis of well‐defined hairy polymer microspheres by precipitation polymerization and surface‐initiated atom transfer radical polymerization

ABSTRACTA variety of polymer microspheres were successfully synthesized by the surface‐initiated atom transfer radical polymerization (SI‐ATRP) of monomers by using monodisperse polymer microsphere having benzyl halide moiety as a multifunctional polymeric initiator. First, a series of monodisperse polymer microsphere having benzyl chloride with variable monomer ratio (P(St‐DVB‐VBC)) were synthesized by the precipitation polymerization of styrene (St), divinylbenzene (DVB), and 4‐vinylbenzyl chloride (VBC). Next, hairy polymer microspheres were synthesized by the surface‐initiated ATRP of various monomers with P(St‐DVB‐VBC) microsphere as a multifunctional polymeric initiator. The hair length determined by the SEC analysis of free polymer was increased with the increase of M/I. These hairy polymer microspheres were characterized by SEM, FT‐IR, and Cl content measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1296–1304

Programmed Polymer Folding with Periodically Positioned Tetrafunctional Telechelic Precursors by Cyclic Ammonium Salt Units as Nodal Points.

A programmed polymer folding process has been demonstrated by employing a pair of periodically positioned tetrafunctional, linear telechelic poly(THF)s having 5-membered cyclic ammonium salt groups, i.e., N-ethyl or N-phenylpyrrolidinium groups at both chain ends, and N, N-dialkylpyrrolidinium groups at the two interior positions, accompanying two units of a dicarboxylate counteranion to balance the charges, Ia and Ib, respectively. The electrostatic self-assembly and covalent fixation process has subsequently been applied, to cause the ring-opening reaction of the pyrrolidinium units by carboxylate counteranions under dilution. The obtained doubly cyclized polymer products, IIa from Ia and IIb from Ib, were characterized by 1H NMR and by a MALDI-TOF mass technique, to indicate the formation of polymeric constitutional isomers of either manacle-, 8-, or θ-form. The SEC peak deconvolution analysis of IIa showed the preferential formation of the manacle-form isomer over the 8- and the θ-form counterparts, to accord with the polymer folding of Ia, having the equivalent chemical reactivity of the linking groups, directed by the spatial distance between the folding points. On the other hand, the relevant SEC analysis of IIb showed the predominant formation of the 8-form isomer, consistent with the polymer folding of Ib promoted by the enhanced chemical reactivity of the N-phenylpyrrolidinium end groups over the interior N, N-dialkylpyrrolidinium groups.

Facile Synthesis of Functional Poly(ε-caprolactone) via Janus Polymerization

Functionalized aliphatic polyesters attract increasing attentions as biocompatible and biodegradable polymers with broad applications in biological science. In this contribution, we propose a facile and controllable synthetic technique for functional poly(ε- caprolactone) (PCL) via Janus polymerization, which comprises cationic ring-opening copolymerization (ROP) of ε-caprolactone (CL) with 3,3-bis(chloromethyl) oxacyclobutane (CO) and (coordinated) anionic ROP of CL at a single propagating chain by rare earth metal triflates (RE(OTf)3) and propylene oxide, thus generating block copolymers in one step. The compositions of the copolymers of poly(CLb-( CL-r-CO)) can be modulated by various RE(OTf)3. Scandium triflate catalyzes Janus polymerization to yield the copolymers containing the highest CO contents among all the RE(OTf)3 catalysts used with complete conversion of CL. The chlorine in CO repeating units is ready to be transferred into azide group which affords the modification sites to react with 9-ethynyl-9-fluorenol and mPEG-alkyne, respectively, via copper(I)-catalyzed azide-alkyne cycloaddition reaction with quantitative conversions of azides, as confirmed by FTIR analyses. According to NMR and SEC analyses, copolymers (PCC-g-PEG) bearing a homo-PCL block and a PEG-grafted block of poly(CO-co-CL) demonstrate well-defined chemical structures. The investigations on thermal properties reveal the strong phase separation between PCL and PEG blocks. The amphiphilic PCC-g-PEG is able to self-assemble into micelles in aqueous solution while cylindrical and lamellar morphologies are observed in bulk. We provide an efficient protocol to synthesize functional PCL combining onestep Janus polymerization and precise post-polymerization click reaction.

Radical polymerization in the presence of peroxide and reducing agent monomer for branched polymers

ABSTRACTIn this article, we report the radical polymerization in the presence of peroxide and commercially available or designed reducing agent monomer (RAM) for the preparation of branched poly(methyl methacrylate)s (PMMAs). The reaction behavior of the RAM was studied by NMR. Triple‐detection SEC (TD‐SEC) analysis was used to confirm the branching structure of the prepared PMMAs and to investigate the influence of peroxide concentration and RAM concentration on molecular weight and branched structure. The obtained branched PMMAs exhibited high molecular weights and relatively narrow polydispersities at high conversion of MMA. Interestingly, a significant increase in molecular weight and degree of branching of the obtained polymers are observed in higher BPO concentration, these results are quite different from that reported in the literature. The unique radical polymerization mechanism in the RAM/BPO redox‐initiated radical polymerization system resulted in branched PMMAs with high molecular weights at relatively high RAM and BPO concentrations. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 833–840

Inhibitor-Induced Dimerization of an Essential Oxidoreductase from African Trypanosomes.

Trypanosomal and leishmanial infections claim tens of thousands of lives each year. The metabolism of these unicellular eukaryotic parasites differs from the human host and their enzymes thus constitute promising drug targets. Tryparedoxin (Tpx) from Trypanosoma brucei is the essential oxidoreductase in the parasite's hydroperoxide-clearance cascade. In vitro and in vivo functional assays show that a small, selective inhibitor efficiently inhibits Tpx. With X-ray crystallography, SAXS, analytical SEC, SEC-MALS, MD simulations, ITC, and NMR spectroscopy, we show how covalent binding of this monofunctional inhibitor leads to Tpx dimerization. Intra- and intermolecular inhibitor-inhibitor, protein-protein, and inhibitor-protein interactions stabilize the dimer. The behavior of this efficient antitrypanosomal molecule thus constitutes an exquisite example of chemically induced dimerization with a small, monovalent ligand that can be exploited for future drug design.

Structural and Rheological Properties of Pectins Extracted from Industrial Sugar Beet By-Products.

In this work, the efficient extraction of pectin from sugar beet by-products (pressed, ensiled and dried pulp), by using an acid method or a commercial cellulose, is accomplished. The extraction method had an impact on the pectin monomeric composition, mainly in xylose, arabinose, and galacturonic acid content, as determined by GC-FID. FTIR and SEC analyses allowed the determination of similar degrees of methoxylation and molecular weights, respectively, in the extracted pectins. The acid extraction of pectin in the ensiled by-product led to the highest yield (19%) with a galacturonic acid content of 46%, whereas the application of the enzymatic extraction method resulted in a lower yield (13%) but higher galacturonic acid content (72%). Moreover, the stability in aqueous solution as well as the emulsifying activity index was higher for pectin extracted by the acid method, whereas the viscosity was higher in pectin extracted by the enzymatic method. To the best of our knowledge, this is the first study analyzing the physicochemical properties and exploring the potential reuse of ensiled and dried by-products from sugar beet industry for the extraction of pectin to be further used in the food and pharmaceutical areas.

Value-adding of organosolv lignin: Designing mechanically robust UV-resistant polymeric glass via ARGET ATRP

Most lignin-based materials reported so far exhibit poor mechanical properties which still differ from the requirements of commercialization. Here, organosolv lignin was selected as raw materials and a series of lignin-graft-poly(methyl methacrylate) (OL-g-PMMA) copolymers were prepared via activators regenerated by electron transfer for atom transfer radical polymerization (ARGET ATRP). FT-IR, 1H NMR, and SEC analyses confirmed that PMMA chains have been successfully grafted onto organosolv lignin. Thermal analysis indicated that the lignin core could help increase the glass transition temperatures as well as thermal stability of OL-g-PMMA copolymers. More importantly, the introduction of lignin not only improved the mechanical properties of PMMA, but also induced UV resistance properties. This novel approach can be generalized to design natural biomass based copolymers with desired mechanical properties.

Preparation of gelatin beads treated with glucose and glycerol

Abstract Gelatin is employed in pharmaceutical applications because of its biodegradability, biocompatibility and low toxicity. However, it may be necessary to promote gelatin crosslinking in order to develop drug release systems and extend release times. SEC analyses are used here for the first time to monitor the evolution of molar mass distributions of gelatins during treatment with glycerol and glucose in dispersed media. Unambiguous experimental evidence of gelatin crosslinking in presence of sugars and glycerol has yet to be presented. SEC results indicate that average molar masses decrease during gelatin treatment, while FT-IR analyses indicate that gelatins are subject to structural modifications during processing, which can explain the decrease of gelatin solubility after treatment. The results presented here indicate the importance of using SEC techniques to monitor gelatin crosslinking, as they seemingly contradict previously published results that make use of indirect measures for this purpose.

Retraction Note to: Bacterial conversion of depolymerized Kraft lignin

The authors have retracted this article [1] because due to a mistake in the laboratory, SEC analyses of some of the lignin samples used had already been published as part of another article [2]. The data in the section “Characterization of depolymerized lignin streams” was therefore inaccurately presented as new, and part of the materials and methods section was incorrect. To avoid confusion this article has been retracted and the authors have been given the opportunity to resubmit their corrected data. All authors agree to this retraction.

Synthetic construction of sugar-amino acid hybrid polymers involving globotriaose or lactose and evaluation of their biological activities against Shiga toxins produced by Escherichia coli O157:H7.

Synthetic assembly of sugar moieties and amino acids in order to create "sugar-amino acid hybrid polymers" was accomplished by means of simple radical polymerization of carbohydrate monomers having an amino acid-modified polymerizable aglycon. Amines derived from globotriaoside and lactoside as glycoepitopes were condensed with known carbobenzyloxy derivatives, including Z-Gly, Z-l-Ala and Z-β-Ala, which had appropriate spacer ability and a chiral center to afford fully protected sugar-amino acid hybrid compounds in good yields. After deprotection followed by acryloylation, the water-soluble glycomonomers were polymerized with or without acrylamide in the presence of a radical initiator in water to give corresponding copolymers and homopolymers, which were shown by SEC analysis to have high molecular weights. Evaluation of the biological activities of the glycopolymers against Shiga toxins (Stxs) was carried out, and the results suggested that glycopolymers having highly clustered globotriaosyl residues had high affinity against Stx2 (KD = 2.7∼4.0 µM) even though other glycopolymers did not show any affinity or showed very weak binding affinity. When Stx1 was used for the same assay, all of the glycopolymers having globotriaosyl residues showed high affinity (KD = 0.30∼1.74 µM). Interestingly, couple of glycopolymers having lactosyl moieties had weaker binding affinity against Stx1. In addition, when cytotoxicity assays were carried out for both Stxs, glycopolymers having highly clustered globotriaosyl residues showed higher affinity than that of the copolymers, and only highly clustered-type glycopolymers displayed neutralization potency against Stx2.

Synthesis of plant oil-based amide copolymethacrylates and their use as viscosity index improvers

Polymeric materials derived from fatty acids (FA)s were synthesized through free radical polymerization and evaluated as viscosity index improvers (VII) in an organic triglyceride lube oil (OTO). For this purpose, various FA-based copolymers were designed to own a reduced solubility at low temperature in OTO which can be gradually improved by increasing temperature. Different fatty amide methacrylates were chosen for their poorly oil-miscible repeating units while fatty ester methacrylates, 2-(methacryloyloxy)ethyl oleate (MAEO) and 2-(methacryloyloxy)ethyl 4-(dodecylthio)oleate (MAEOSC12), were used as oil-miscible comonomers for providing copolymers with a minimum of solubility in the lube oil. All copolymers were synthesized with a 50:50 M feed ratio and were fully characterized through 1H NMR, SEC, DSC, and TGA analyses. Then, rheological study of oil-copolymer blends revealed that copolymers containing –NH function were able to have a higher impact on oil viscosity at high than at low temperatures suggesting the coil copolymer expansion. This improvement of thickening power with temperature in OTO was further optimized by increasing the copolymer molecular weight, dispersity, concentration, pendant aliphatic chain length or by adding an additional aliphatic chain in the copolymer backbone. Moreover, copolymer additions in OTO did not disturb the initial Newtonian behavior of OTO at −30 °C which corresponds to the lube oil pour point.

Degradation of cellulose in NaOH and NaOH/urea aqueous solutions by ultrasonic irradiation

Ultrasonic degradation of cellulose with low molecular weight in NaOH and NaOH/urea solutions was investigated at 20 and 500 kHz frequencies by measuring the solution viscosity. The viscosity decreased with sonication time. A small difference in viscosity ratio which is defined as the ratio of specific viscosity of solution after and before sonication was observed for the longer sonication. The degrees of the polymerization were reduced from 230 to 150 for 30 min sonication at 20 kHz and for 120 min sonication at 500 kHz. From XRD measurement, it was estimated that the crystallinity after sonication was the same as that before sonication. The crystallinity structure after sonication corresponded to Cellulose II. The yield of water-soluble components after ultrasonic irradiation was 20 wt% at 20 kHz in NaOH solutions and 30 wt% for 720 min at 500 kHz in NaOH/urea solution. Oligosaccharides and their derivative were detected by the SEC analysis of water-soluble components after sonication.

Topologically Reversible Transformation of Tricyclic Polymer into Polyring Using Disulfide/Thiol Redox Chemistry

A polyring capable of reversible growth and dissociation is synthesized from a tricyclic polystyrene (PS) prepared by combining atom transfer radical polymerization of a 4-arm star-shaped PS and azide–alkyne click reactions. In the preparation of the tricyclic PS, a coupling agent containing a disulfide linkage is used in the click cyclization reaction. The reduction of the disulfide linkage in the tricyclic PS results in an 8-shaped PS with thiol groups which on oxidation leads to a high molecular weight polyring. The topology transformation between the polymers occurs via reversible redox reaction of disulfide/thiol. The high molecular weight of the polyring is realized due to the formation of flexible S–S linkage between the 8-shaped PSs. Their structures are confirmed by FT-IR, 1H NMR, SEC, and MALDI-TOF MS analyses. In addition, molecular weight control of the polyring according to polymer concentration has been confirmed through SEC analysis.

Synthesis and characterization of well-defined poly(2-deoxy-2-methacrylamido-d-glucose) and its biopotential block copolymers via RAFT and ROP polymerization

Well-defined homopolymers of 2-deoxy-2-methacrylamido-d-glucose (MAG) were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization using 4-cyanopentanoic acid-4-dithiobenzoate as chain transfer agent (CTA) and 2,2′-azobisisobutyronitrile (AIBN) as initiator. The effect of polymerization conditions such as molar ratio of RAFT agent to initiator and monomer to RAFT agent on conversion and molecular mass characteristics of prepared polymers was estimated. Kinetics of the polymerization under various reaction conditions was studied as a function of time and conversion using in situ1H NMR spectroscopy. The living character of polymerization was demonstrated by carriyng out the further chain extension experiments using isolated PMAG-CTA as a macroRAFT agent. For that, the PMAG with higher molecular weight, as well as block copolymer with acrylic acid were synthesized and characterized using 1H NMR and SEC analysis. A novel amphiphilic copolymer representing a hybrid of glycopolymer and polypeptide fragments was synthesized using RAFT and ring-opening polymerization (ROP). In this case, dithiobenzoate end-group of PMAG was transformed via simultaneous reduction and in situ thiol capping reaction by cysteamine hydrochloride into amino functionality suitable for polymerization of N-carboxyanhydrides (NCA). Two block copolymers of MAG with poly-l-phenylalanine (PPhe) differed with hydrophobic block length were synthesized, characterized and used for preparation of particles via copolymer self-assembly. The hydrodynamic diameter, morphology and cytotoxicity of polymer particles based on PMAG-b-PPhe were evaluated using DLS, TEM and MTT-assay, respectively. Moreover, the encapsulation of model compound (fluorescent dye rhodamine 6G) inside PMAG-b-PPhe micelles, as well as its release, were also tested.

Coupling Multi Angle Light Scattering to Ion Exchange chromatography (IEX-MALS) for protein characterization

Multi-angle light scattering coupled with size exclusion chromatography (SEC-MALS) is a standard and common approach for characterizing protein mass, overall shape, aggregation, oligomerization, interactions and purity. The limited resolution of analytical SEC restricts in some instances the accurate analysis that can be accomplished by MALS. These include mixtures of protein populations with identical or very similar molecular masses, oligomers with poor separation and short peptides. Here we show that combining MALS with the higher resolution separation technique ion exchange (IEX-MALS) can allow precise analyses of samples that cannot be resolved by SEC-MALS. We conclude that IEX-MALS is a valuable and complementary method for protein characterization, especially for protein systems that could not be fully analyzed by SEC-MALS.

Modified α,α'-trehalose and d-glucose: green monomers for the synthesis of vinyl copolymers.

Allyl saccharide/vinyl copolymers were synthesized using renewable feedstocks (α,α′-trehalose and d-glucose) to obtain ‘green monomers’. Properly designed synthetic procedures were used to obtain copolymers with high purity and without protection/deprotection steps in agreement with the principles of green chemistry and industrial sustainability. The use of saccharide derivatives as monomers allowed products to be obtained that showed high affinity and compatibility for the cellulosic substrates, like paper or wood, and that were suitable for applications like adhesion or consolidation in the field of cultural heritage. All reaction products were characterized by FT-IR and NMR spectroscopies and SEC analyses, while thermal properties were evaluated by DSC analyses.

Influence of Chain Topology (Cyclic versus Linear) on the Nucleation and Isothermal Crystallization of Poly(l-lactide) and Poly(d-lactide)

Ring closure click chemistry methods have been used to produce cyclic c-PLLA and c-PDLA of a number-average molecular weight close to 10 kg/mol. The effects of stereochemistry of the polymer chains and their topology on their structure, nucleation, and crystallization were studied in detail employing wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), polarized light optical microscopy (PLOM), and standard and advanced differential scanning calorimetry (DSC). The crystal structures of linear and cyclic PLAs are identical to each other, and no differences in superstructural morphology could be detected. Cyclic PLA chains are able to nucleate much faster and to produce a higher number of nuclei in comparison to linear analogues, either upon cooling from the melt or upon heating from the glassy state. In the samples prepared in this work, a small fraction of linear or higher molecular weight cycles were detected (according to SEC analyses). The presence of such “impurities” retards spher...