Triple Detection Size Exclusion Chromatography Research Articles

Investigation of the microrheological properties of the branched polystyrene using 2-(2-bromoisobutyryloxy) ethyl methacrylate as the inimer

ABSTRACT A novel functional inimer 2-(2-bromoisobutyryloxy)ethyl methacrylate(BiBEM) both with the double bond and bromide was designed and synthesised. The branched polystyrene (PS) was prepared by the atom transfer radical polymerisation (ATRP), using BiBEM as inimer (initator) and CuBr complexed with bipyridine as catalysts in toluene at 80°C. The molecular weight and the branching degree of the polystyrene were analysed by using triple detection size-exclusion chromatography (TD-SEC) and the storage modulus in a wide and high-frequency range of polystyrene microrheological properties were studied by the diffusive wave spectroscopy (DWS). By adjusting the ratio of inimer to catalysts, a series of branched polystyrene polymers with different molecular weight and branching degree were obtained. The increase of the BiBEM concentration led to a higher degree of branching, while higher molecular weight and broader molecular weight distribution are accompanied. The branched polystyrene showed low storage modulus and lower chain entanglement compared to linear analogues.

Insight into the Alcohol-Free Ring-Opening Polymerization of TMC Catalyzed by TBD.

We report herein a study on the alcohol-free, ring-opening polymerization of trimethylene carbonate (TMC) in THF, catalyzed by 1,5,7-triazabicyclo [4.4.0] ec-5-ene (TBD) with ratios nTBD/nTMC ranging between 1/20 and 1/400. In all cases, the reaction proceeds very rapidly, even faster than in the presence of alcohol initiators, and provides PTMC with molecular weights up to Mn = 34,000 g mol−1. Characterization of the obtained PTMC samples by MALDI-TOF mass spectrometry, triple detection size exclusion chromatography and 1H NMR spectroscopy reveals the presence of both linear and cyclic polymer chains.

Branched polymers through redox emulsion polymerization using peroxide monomer as the branching agent

AbstractRedox emulsion polymerization to branched vinyl polymers in the presence of 2‐(tert‐butylperoxy)ethyl methacrylate (BPEMA), ferrous sulfate, and sodium formaldehyde sulfoxylate (SFS) is reported in this paper. The peroxide monomer BPEMA containing alkyl peroxide was designed for high stability during preparation and storage. Nuclear magnetic resonance spectroscopy (NMR), Raman, and triple‐detection size‐exclusion chromatography (TD‐SEC) measurements were used to reveal the polymerization procedure and provide evidence of branching structure. In the case of polymerization at St100‐BPEMA1.0‐FeSO4 0.5‐SFS0.2, the molecular weight increased and decreased with conversion below and above 75% monomer conversion, respectively. The decreasing of molecular weight with monomer conversion came from the increased viscosity of the micelle, which makes it difficult for the formed macromolecules containing vinyl group to participate into polymerization. Finally, the molecular weight reached a value of Mn. SEC = 439,200 g/mol at 92.2% conversion. In addition, the Zimm branching factor, g', also decreased and increased with conversion below and above 60% conversion, respectively, and then the g' finally attends a value of 0.41, showing high degree of branching. Branched poly(methyl methacrylate) was also prepared through this strategy, showing a versatile approach to branched vinyl polymers.

Effect of microstructure on chain flexibility and glass transition temperature of polybenzofulvene

Polybenzofulvene (PBF) is a polydiene with a very high glass transition temperature (Tg), which makes it a potential candidate for use as the hard block for high-temperature thermoplastic elastomer applications. The Tgs of polydienes are known to be related to chain flexibility. However, no studies have been reported that correlate the chain flexibility to the microstructure of PBF. Herein, we present a study of solution properties of linear PBFs with narrow molacular weight dispersity and having 1,2-addition ranging from 23% to 99%. The materials were prepared by living anionic polymerization under different conditions. Specifically, the chain flexibility as defined by the Flory's characteristic ratio, C∞, and dependence of chain flexibility on microstructure by combined measurements of intrinsic viscosity and molecular weight using triple-detector size exclusion chromatography (SEC) is studied. The persistence lengths (lp) and chain diameters (dB) were also estimated using the touched-bead wormlike chain model. To the best of our knowledge, the characteristic ratio of PBF is found to be the highest of all polydienes that have been reported so far.

Preparation of Starch Citrates Using Solvent Free Reaction and Comparison with Aqueous and Ethanol Mediated Reactions

AbstractCorn starch is modified with citric acid (2.5% w/w) in aqueous, alcoholic media and in solid solid reaction (dry heat condition without any solvent). Degree of substitution is similar for both treatments, independent of use of solvent but higher than for dry heated starch citrate. Apparent amylose content of all starch citrates is higher than for native starch. Molecular weight, as determined by triple detection size exclusion chromatography, also decreases, demonstrating hydrolysis of chains. As a consequence, starch citrate prepared using dry heating and ethanol, as compared to aqueous media, show drastic reduction in pasting viscosity. X‐ray diffraction pattern and morphology of the produced starch granules remain unaltered in all three reaction types. Starch citrates prepared using solvent less reactions show similar characteristics as that of conventional hydrolysis performed using concentrated hydrochloric acid. However, the solid solid hydrolytic reaction process using citric acid is far more environmental friendly and less costly than typical conventional hydrolysis processes. The present study is not only useful for starch systems but more generally for studying reactions in, for example, gums and cellulose.

Study of mechanical properties in relation to microrheological behaviour of polystyrenes with different polymer chain structures

ABSTRACTThe random-branched and the star-like branched polystyrenes were prepared by atom transfer radical polymerization (ATRP). Then the random-branched polystyrene and star-like polystyrene were blended with the linear polystyrene. The structure and properties of the polymers were characterized by triple detection size exclusion chromatography (TD-SEC), diffusing wave spectroscopy (DWS), differential scanning calorimetry (DSC) andmechanical property testing. The results showed that the tensile strength of the industrial-grade polystyrene blended with the branched polymer decreased with the amount of branched polystyrene. But it was increased when the high storage modulus of BPS was used by keeping the BPS amount constant. The glass transition temperature of the industrial-grade polystyrene blended with the branched polymer decreased with increased amount of the BPS. For an example, the glass transition temperature of the polystyrene blend dropped by 1.87°C when 5wt% of the BPS was added to the blend.

Evolution of Single Chain Conformation for Model Comb-Like Chains with Grafting Density Ranging from 0 to ∼100% in Dilute Solution.

This work aims to experimentally clarify how the single chain conformation evolves as a function of grafting density for model comb-like chains in dilute solution in the whole density regime. Via a combination of rational design, precise synthesis and accurate characterization, we obtained four sets of PPANb-g-PS30-σ comb-like samples with well-defined architectures and accurately extracted their molecular parameters by triple detection size exclusion chromatography (TD-SEC). With these samples in hand, we quantified how the excluded volume interaction and chain conformation evolve with the grafting density (σ) in the whole density regime. Three main findings are reported: (i) the graft-graft excluded volume interaction is not ignorable even in the low σ-regime; (ii) contrary to theoretical predictions, both the excluded volume interaction and the chain conformation are found to be Nb-dependent; (iii) both Rg ∼ σ1/3 and [η] ∼ σ0 are experimentally confirmed for comb-like chains from different σ and Nb, signifying a unique 3D mass-size growth pattern and a quasi-3D fractal feature. The obtained results help clarify some long-existed controversial issues in the field.

Comprehensive branching analysis of star-shaped polystyrenes using a liquid chromatography-based approach.

The comprehensive branching analysis of complex polymers is still a challenge in advanced polymer analysis. Average branching information (average number and length of branches) can be obtained by spectroscopic methods, mainly NMR spectroscopy. The determination of the branching distribution, i.e., the concentration of macromolecules with a given number of branches, however, requires fractionation. Typically, size exclusion chromatography is used that separates the complex mixture with regard to molecular size in solution and not strictly with regard to the number of branches. In the present approach, model star-shaped polystyrenes were synthesized with a pre-determined architecture to give theoretical three-arm, four-arm, and six-arm structures. The branched samples were compared with a linear analogue of comparable molar mass known not to contain branching. Triple detector size exclusion chromatography with refractive index, multiangle light scattering, and online viscometer detection was used to determine absolute molar masses, radii of gyration, and branching distributions of the star-shaped polymers. 1H-NMR was used to calculate the average functionality and a reasonable agreement between the results of the two methods was obtained. Thermal gradient interaction chromatography and solvent gradient interaction chromatography were employed to separate the complex reaction products according to chemical composition (number of branches) and to resolve by-products. The separation capabilities of the two chromatographic techniques were compared and evaluated. Comprehensive two-dimensional liquid chromatography was used to separate the polydisperse star-shaped polystyrenes with regard to both branching and molar mass. Graphical abstract.

Hyperbranched Multicyclic Polymer Built from Tailored Multifunctional Monocyclic Prepolymer.

A simple and efficient method to construct a hyperbranched multicyclic polymer is introduced. First, a tailored trithiocarbonate with two terminal anthracene units and three azide groups is successfully synthesized, and this multifunctional trithiocarbonate is used as chain transfer agent (CTA) to afford anthracene-telechelic polystyrene (PS) via reversible addition-fragmentation chain transfer (RAFT) polymerization. After that, linear PS is irradiated under 365 nm UV light to achieve the cyclization process. The monocyclic polymer further reacts with sym-dibenzo-1,5-cyclooctadiene-3,7-diyne via "A2 +B3 " strategy based on a self-accelerating click reaction to produce hyperbranched multicyclic polymer. The structures and properties of the polymers are characterized by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), UV-vis spectrophotometry, and triple-detection size-exclusion chromatography (TD-SEC). The number of monocyclic units of the resultant hyperbranched multicyclic polymer reaches about 21 based on multi-angle laser light scattering (MALLS) measurements. The plot of intrinsic viscosity versus molecular weight reveals that the α value of the unique hyperbranched multicyclic polymer is lower than both hyperbranched polymers and cyclic polymers.

Influence of Grafting Density and Distribution on Material Properties Using Well-Defined Alkyl Functional Poly(Styrene-co-Maleic Anhydride) Architectures Synthesized by RAFT

Poly(styrene-co-maleic anhydride) copolymers (PSMA) with controlled number and distribution of maleic anhydride (MAnh) units were synthesized by reversible addition–fragmentation chain transfer polymerization using chain-transfer agents (CTA) suitable for industrial scale processes. Linear- and star-shaped alternating PSMA polymers were prepared in a single-step synthesis, while a one-pot sequential chain-extension strategy was utilized to prepare diblock, multiblock, and multisite copolymer architectures. A library of grafted PSMAs with controlled density and distribution of side chains was achieved by the subsequent grafting of long aliphatic alcohol chains (C22) to the MAnh units. The influence of structure, composition, and long alkyl chain addition on PSMAs behavior in solution was studied with triple-detection size exclusion chromatography, while their thermal properties were examined by thermogravimetric analysis and differential scanning calorimetry. Overall, the side chain density and distributio...

PPEylation of proteins: Synthesis, activity, and stability of myoglobin-polyphosphoester conjugates

Protein-polymer conjugates are used to treat several diseases. PEGylation, i.e. the modification with poly(ethylene glycol) (PEG) is the currently used strategy. However, due to its non-biodegradability, the design of effective and degradable conjugates is of both academic and industry potential. We present the preparation and studies of the activity and stability of novel biodegradable myoglobin-polyphosphoester conjugates. Poly(ethyl ethylene phosphate) (PEEP) is a water-soluble polyphosphoester, which had been reported to be biocompatible and biodegradable. PEEP is a promising candidate as a degradable substitute for the “gold standard” PEG, which can cause long-term effects, as it is not degradable. PEEPylated conjugates with a variable degree of polymer grafting were synthesized, characterized (with online triple detection size exclusion chromatography, mass spectrometry, and gel electrophoresis), and compared with PEGylated analogs. We highlight differences in how the structure, the number, and the length of the polymer influence the properties of the conjugates. Overall, the analyses conducted (including activity assay, calorimetry, and fluorimetry measurements) show that the covalent attachment of the polymer does not irrevocably affect the protein’s features under physiological conditions, suggesting the potential of this new class of polymers for the design of a new generation of fully degradable conjugates.

Rheological characterization of long-chain branched poly(lactide) prepared by reactive extrusion in the presence of allylic and acrylic coagents

Reactive extrusion of poly(lactide) (PLA) is implemented to introduce branching, through grafting of multifunctional coagents in the presence of free-radicals. Two types of coagents, allylic and acrylate-based, are compared by analyzing the melt-state linear viscoelastic properties, in combination with triple detection size-exclusion chromatography. The coagent-modified PLA compounds exhibit substantially higher zero shear viscosity, pronounced shear thinning, and higher activation energies for flow when compared to the neat linear PLA. The accompanying increases in the molar mass, broadening of the dispersity, and appearance of high molar mass tails are attributed to the presence of branched architectures. The pronounced deviations from the linear Mark–Houwink plot suggest that long-chain branched structures are generated through the combination of the trifunctional coagents with the PLA macroradicals. The allylic coagent, triallyl mesate (TAM) is substantially more effective in introducing branched structures at low concentrations. On the other hand, the highly reactive acrylate-based coagents are prone to oligomerization in the presence of peroxide resulting in a separate phase, leading to reduced branch density compared to TAM.

Multi detection in Size-Exclusion Chromatography of electron beam irradiated Ethylene Norbornene Copolymers

Ethylene Norbornene Copolymers (ENCs) belong to the Cyclic Olefin Copolymers (COC) family and are used in numerous industrial fields. The goal of this paper is to compare the behavior under electron beam radiation of three grades of ENCs. Several radiation doses have been tested: 25 kGy to simulate sterilization dose and higher doses (75 and 150 kGy) to emphasize the electron beam effect on polymer ageing.By using Triple Detection (Refractometer/Laser Scattering/Viscometer) Size-Exclusion Chromatography, we wanted to study more accurately the evolution of ENCs under radiation than the previous studies available. Thanks to Triple detection, molecular weights were calculated without being dependent of calibration standards, branching was evidenced as the major effect of electron beams on those materials over a dose of 25 kGy, and long chain branching and branching chains frequencies were also calculated.This study focuses on the effect of additive concentration and norbornene (NB) content and a trend has merged: for a same NB content, the higher the phenolic antioxidant concentration, the less crosslinked was the copolymer with the dose. By increasing NB content, radiation effects were minimized.

Structure-properties relationships in isosorbide-based polyacetals: Influence of linear or cyclic architecture on polymer physicochemical properties

A linear biobased polyacetal was prepared from the reaction between isosorbide and methylene chloride according a one step procedure. Cyclic polyacetal was obtained using the previous linear polymer as precursor. The respective architectures of both polymers and their chemical compositions were carefully established using 1H NMR and MALDI-TOF spectroscopies. Their molecular weight characteristics were defined using a triple detection size exclusion chromatography while their thermal characteristics were investigated by the conduction of calorimetric and thermogravimetric experiments. The registering of the thermomechanical properties of each kind of isosorbide-based polyacetal showed that the cyclic polymer was the only one able to show a rubbery plateau. This peculiarity was justified by calculation of the threshold value above which entanglements were possible.

Preparation and Properties of Branched Polystyrene through Radical Suspension Polymerization.

Radical solvent-free suspension polymerization of styrene with 3-mercapto hexyl-methacrylate (MHM) as the branching monomer has been carried out using 2,2′-azobisisobutyronitrile (AIBN) as the initiator to prepare branched polymer beads of high purity. The molecular weight and branching structure of the polymers have been characterized by triple detection size exclusion chromatography (TD-SEC), proton nuclear magnetic resonance spectroscopy (1H-NMR), and Fourier transform infrared spectroscopy (FTIR). The glass transition temperature and rheological properties have been measured by using differential scanning calorimetry (DSC) and rotational rheometry. At mole ratios of MHM to AIBN less than 1.0, gelation was successfully avoided and branched polystyrene beads were prepared in the absence of any solvent. Branched polystyrene has a relatively higher molecular weight and narrower polydispersity (Mw.MALLS = 1,036,000 g·mol−1, Mw/Mn = 7.76) than those obtained in solution polymerization. Compared with their linear analogues, lower glass transition temperature and decreased chain entanglement were observed in the presently obtained branched polystyrene because of the effects of branching.

Degradable Polyphosphoester-Protein Conjugates: "PPEylation" of Proteins.

Pharmacokinetic properties determine the efficacy of protein therapeutics. The covalent attachment of poly(ethylene glycol) (PEG) extends the half-life of such biologicals to maintain a therapeutically effective concentration over a prolonged period of time and improves administration and compliance. A major obstacle of these polymer-protein conjugates is the chemical stability of the PEG preventing its metabolism and leading to side effects. Instead, we propose the PPEylation, that is, the conjugation of degradable poly(phosphoester)s (PPE) to proteins, in order to generate fully biodegradable polymer-protein conjugates. The structure of the PPEylated protein conjugates was verified with mass spectrometry and size exclusion chromatography. They were compared to structural analogues, except classical, PEGylated proteins, and exhibit comparable bioactivity, but avoiding any nondegradable polymer in the conjugate. We proved the degradation of the protective polymer shell surrounding the conjugate in aqueous environments at physiological conditions by online triple detection size exclusion chromatography and gel electrophoresis. We believe that this research will provide an attractive alternative for future drug design with implications for the clinical use of biologicals.

Characterising protein/detergent complexes by triple-detection size-exclusion chromatography.

BackgroundIn vitro investigations of membrane proteins usually depend on detergents for protein solubilisation and stabilisation. The amount of detergent bound to a membrane protein is relevant to successful experiment design and data analysis but is often unknown. Triple-detection size-exclusion chromatography enables simultaneous separation of protein/detergent complexes and protein-free detergent micelles and determination of their molar masses in a straightforward and absolute manner. Size-exclusion chromatography is used to separate different species, while ultraviolet absorbance, static light scattering, and refractive index measurements allow molar mass determination of protein and detergent components.ResultsWe refined standard experimental and data-analysis procedures for challenging membrane-protein samples that elude routine approaches. The general procedures including preparatory steps, measurements, and data analysis for the characterisation of both routine and complex samples in difficult solvents such as concentrated denaturant solutions are demonstrated. The applicability of the protocol but also its limitations and possible solutions are discussed, and an extensive troubleshooting section is provided.ConclusionsWe established and validated a protocol for triple-detection size-exclusion chromatography that enables the inexperienced user to perform and analyse measurements of well-behaved protein/detergent complexes. More experienced users are provided with an example of a more sophisticated analysis procedure allowing mass determination under challenging separation conditions.

Vinyl pivalate Propagation Kinetics in Radical Polymerization

Radical propagation kinetics of the bulk homopolymerizations of vinyl pivalate (VPi) and vinyl benzoate (VBz) have been studied using pulsed‐laser polymerization (PLP) combined with size exclusion chromatography (SEC). As part of the study, the Mark–Houwink para­meters of poly(VPi) and poly(VBz) in tetrahydrofuran are determined using a triple detector SEC. The observed significant increase (by ≈ 20%) of the bulk VPi propagation rate coefficient (kp) as pulse repetition rate is increased from 200 to 500 Hz is similar to that reported for vinyl acetate (VAc). Data collected in the temperature range of 25–85 °C for VPi is well fit by the Arrhenius relation ln(kp/L mol−1 s−1) = 15.73−2093(T/K). The activation energy is similar to that found for vinyl acetate (VAc), with kp values higher by ≈ 50%. PLP studies in ethyl acetate and in heptane find no substantial solvent effect on VPi or VAc kp values. Attempts to measure the propagation kinetics of VBz by PLP are not successful, suggesting that significant radical stabilization occurs for the system. Small‐scale batch poly­merization experiments demonstrate relative polymerization rates of these vinyl ester monomers that are consistent with the PLP results. image

A simple route to vinyl-functionalized hyperbranched polymers: Self-condensing anionic copolymerization of allyl methacrylate and hydroxyethyl methacrylate

Vinyl-functionalized hyperbranched polymers (HBPs) have attracted much attraction because their pendant vinyl groups can be further modified for a required application. However, the syntheses of these polymers are difficult, because the cross-linking is inevitable during the polymerization reaction. The present work reports a new, facile, one-step strategy for the synthesis of vinyl-functionalized HBPs via the self-condensing anionic copolymerization of commercially available allyl methacrylate and hydroxyethyl methacrylate with a monomer conversion approaching 100% at room temperature. The hyperbranched structures were confirmed by triple-detection size exclusion chromatography. The pendent vinyl groups of the resulting polymer were successfully modified by a “thiol-ene” reaction. This method provides a facile approach for preparing vinyl-functionalized HBPs with excellent monomer conversions under mild conditions, and will be useful in materials chemistry.

New Insight into the ATRP of Monovinyl and Divinyl Monomers

New insights are provided into the atom transfer radical polymerizations of styrene with 1,6‐bismaleimidohexane, tri‐ethylene glycol dimethacrylate (tri‐EGDMA), and divinyl benzene (DVB) as branching agents. Gas chromatography, proton nuclear magnetic resonance spectroscopy, and triple detection size exclusion chromatography are used to analyze the polymerizations and the polymers. The polymerizations and molecular weights of polymers differ because of the different levels of intramolecular cyclization and initiator efficiencies (IEs) among the three polymerization systems. High IE increases polymerization rate and restrains gelation, thereby facilitating preparation of branched polymers with high molecular weights. Polymers in the tri‐EGDMA system exhibit the lowest molecular weight and the broadest polydispersity because of some evident primary chain residues, whereas polymers in the DVB system show the highest molecular weight because of the low amount of the primary chain residues and high IE. The absence of branching monomer units in the primary chain residue of all these polymerizations is confirmed. image