Size Exclusion Chromatography Traces Research Articles

Controlling the Chain Folding for the Synthesis of Single-Chain Polymer Nanoparticles Using Thermoresponsive Polymers

Synthetic polymer single-chain nanoparticles (SCNPs) are an emerging new class of nanomaterials that possess similar folded structures as natural proteins. However, most SCNPs reported so far are p...

Macropropagation Rate Coefficients and Branching Levels in Cationic Ring-Opening Polymerization of 2-Ethyl-2-oxazoline through Prediction of Size Exclusion Chromatography Data

A systematic kinetic study of the isothermal cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EtOx) in acetonitrile initiated by methyl tosylate under microwave irradiation (353-413 K) for a target degree of polymerization of 100 is reported as a basis for kinetic Monte Carlo simulations with parameters tuned based on monomer conversion and chain length data. It is highlighted that the size-exclusion chromatography (SEC) trace is needed to properly tune the less known macropropagation rate coefficient, which is related to the incorporation of enamine-terminated polymer chains resulting from chain transfer to monomer and which determines the contribution of linear and branched chains. A model-based design is applied to identify the reaction temperatures that lead to an optimum between the reaction time and control over molecular properties. A linear relationship is derived, which can be used to reliably assess the mass fraction of branched chains at sufficiently high monomer conversions based on the measurement of the location of the inflection point for the high molar mass part of the SEC trace.

Functional Polycarbonate of a d-Glucal-Derived Bicyclic Carbonate via Organocatalytic Ring-Opening Polymerization.

Herein, we demonstrate the synthesis of a bicyclic carbonate monomer of a d-glucal derivative, which originated from the natural product d-glucose, in an efficient three-step procedure and its ring-opening polymerization (ROP), initiated by 4-methylbenzyl alcohol, via organocatalysis. The ROP behavior was studied as a function of time, catalyst type, and catalyst concentration by using size exclusion chromatography (SEC) and nuclear magnetic resonance (NMR) spectroscopy. Using a cocatalyst system of 1,8-diazabicyclo[5.4.0]undec-7-ene and 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexyl-2-thiourea (5 mol %) afforded poly(d-glucal-carbonate) (PGCC) with almost complete monomer conversion (ca. 99%) within 1 min, as analyzed by 1H NMR spectroscopy, and a monomodal SEC trace with dispersity of 1.13. The resulting PGCCs exhibited amorphous characteristics with a relatively high glass transition temperature at ca. 69 °C and onset decomposition temperature at ca. 190 °C, as analyzed by differential scanning calorimetry and thermogravimetric analysis, respectively. This new type of potentially degradable polymer system represents a reactive functional polymer architecture.

Syntheses of triblock bottlebrush polymers through sequential ROMPs: Expanding the functionalities of molecular brushes

Syntheses of triblock bottlebrush polymers through sequential ROMPs: Expanding the functionalities of molecular brushes

Organocatalyzed ring‐opening polymerization of cyclic butylene terephthalate oligomers

ABSTRACTIn this study, various organic compounds, with different activation modes, have been tested as catalysts for the ring‐opening polymerization (ROP) of cyclic butylene terephthalate oligomers (CBT) in bulk at 210 °C, using tert‐butylbenzyl alcohol (tBnOH) as initiator. Among them, 1,3,5‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) appeared to be the most efficient, achieving high monomer conversions in short reaction times (within minutes). Analysis by size‐exclusion chromatography (SEC) of the poly(butylene terephthalate) (PBT) synthesized using this catalyst also showed that the polymerization follows the expected theoretical Mn trend for molecular weights up to 50 kg·mol−1. Chain‐end fidelity relatively to the alcohol initiator has been confirmed by MALDI‐TOF mass spectroscopy, which showed that all polymer chains possess the tert‐butylbenzyl moiety as chain‐end. Finally, to demonstrate the potential of this system for the synthesis of PBT‐based block copolymers, a monomethyl ether poly(ethylene glycol) (PEG) of 5000 g·mol−1 has been employed as initiator for the ROP of CBT. A PEO‐b‐PBT block copolymer of 15,000 g·mol−1 could thus been obtained, as confirmed by the shift of the SEC traces towards higher molecular weights and the same diffusion coefficient determined for 1H NMR signals of the PEO block and the PBT block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 1611–1619

Well-Defined Cyclic Triblock Terpolymers: A Missing Piece of the Morphology Puzzle.

Two well-defined cyclic triblock terpolymers, missing pieces of the terpolymer morphology puzzle, consisting of poly(isoprene), polystyrene, and poly(2-vinylpyridine), were synthesized by combining the Glaser coupling reaction with anionic polymerization. An α,ω-dihydroxy linear triblock terpolymer (OH-PI1,4-b-PS-b-P2VP-OH) was first synthesized followed by transformation of the OH to alkyne groups by esterification with pentynoic acid and cyclization by Glaser coupling. The size exclusion chromatography (SEC) trace of the linear terpolymer precursor was shifted to lower elution time after cyclization, indicating the successful synthesis of the cyclic terpolymer. Additionally, the SEC trace of the cyclic terpolymer produced, after cleavage of the ester groups, shifted again practically to the position corresponding to the linear precursor. The first exploratory results on morphology showed the tremendous influence of the cyclic structure on the morphology of terpolymers.

A Useful Methodology for Determining the Compaction Degree of Single‐Chain Nanoparticles by Conventional SEC

The folding/collapse of linear single chains to single‐chain nanoparticles (SCNPs) is a field of intense activity. Current synthetic methods allow obtaining from sparse SCNP morphologies in solution – resembling those observed in intrinsically disordered proteins – to compact SCNP conformations, more akin to those displayed by globular enzymes. A useful characterization technique in the field of SCNPs is “conventional” size‐exclusion chromatography (SEC) with differential refractive index (DRI) detection, providing rapid and convincing evidence of SCNP formation through comparison of the SEC traces of the precursor and the SCNPs. Upon SCNP formation, a noticeable shift of the SEC curve toward longer retention times (i.e., lower hydrodynamic sizes) is observed. However, quantitative information embedded in the SEC curve about the actual “compaction degree” of the SCNPs has not yet been extracted to distinguish between sparse and globular SCNPs. Here, a useful methodology for quantifying the compaction degree of SCNPs by SEC with conventional DRI detector is introduced allowing: i) construction of theoretical SEC curves corresponding to the collapse of a linear precursor having a log‐normal molecular weight distribution to either sparse or globular SCNPs and ii) analysis of experimental SEC curves to estimate the actual morphology of synthetic SCNPs in solution.

Derivation of the molecular weight distributions from size exclusion chromatography

Size exclusion chromatography (SEC) is one of the most used analytical methods in chemistry to determine the molecular weight distribution of macromolecules, including natural and synthetic polymers. With the advent of ‘living’ radical polymerization, Researchers now have the capability to produce polymers with a wide range of chemical compositions and architectures. In many cases, SEC is the only method available for analysis of the polymer. Here, we provide a derivation of the three molecular weight distributions from the raw concentration detector response data. The derivations are given in an easy to follow procedure. A method is derived to determine the molecular weight averages from the SEC data. A case study is then provided to demonstrate the insight that SEC can provide into the types of polymer species, and unlock mechanistic information from the SEC traces that may otherwise be overlooked.

Intra‐Chain Photodimerization of Pendant Anthracene Units as an Efficient Route to Single‐Chain Nanoparticle Fabrication

An efficient route to architecturally defined, sub-20 nm soft nanoparticles fabricated from single polymer chains via intramolecular photodimerization of pendant anthracene units is presented. Photodimerization is confirmed by the disappearance of the characteristic anthracene π-π* absorption peak at ≈ 360 nm measured by UV-vis spectroscopy. Size exclusion chromatography (SEC) with UV, multi-angle light scattering (MALS), and viscometric detection confirms that as photodimers form, the chains fold to form nanoparticles, demonstrated by shifts in the SEC traces to longer retention times as a function of increased irradiation time. These shifts indicate a reduction in hydrodynamic radius, corroborated and quantified by viscometric data. MALS detector traces reveal the presence of a small amount of chain-chain coupling during this process, but confirm that this is primarily a single-chain phenomenon. Electron microscopy provides visual confirmation of nanoparticle formation.

Polystyrene–organoclay nanocomposites produced by in situ activators regenerated by electron transfer for atom transfer radical polymerization

Abstract A newly developed initiation system, activators regenerated by electron transfer (ARGET), was employed to synthesize polystyrene-organoclay nanocomposites via atom transfer radical polymerization (ATRP). ARGET ATRP was applied since it is carried out at significantly low concentrations of the catalyst and environmentally acceptable reducing agents. Conversion and molecular weight evaluations were performed using gravimetry and size exclusion chromatography (SEC), respectively. According to the findings, addition of clay content resulted in a decrease in conversion and molecular weight of nanocomposites. However, an increase of polydispersity index is observed by increasing nanoclay loading. The living nature of the polymerization is revealed by 1H NMR spectroscopy and extracted data from the SEC traces. X-ray diffraction (XRD) analysis shows that organoclay layers are disordered and delaminated in the polymer matrix and exfoliated morphology is obtained. Thermogravimetric analysis (TGA) shows that thermal stability of the nanocomposites is higher than the neat polystyrene. A decrease in glass transition temperature of the samples by increasing organoclay content is observed by differential scanning calorimetry (DSC). Transmission electron microscopy (TEM) reveals that clay layers are partially exfoliated in the polymer matrix containing 2 wt% of organomodified montmorillonite (PSON 2) and a dispersion of partially exfoliated clay stacks is formed.

Visualizing the efficiency of rapid modular block copolymer construction

The quantification of the efficient ultra-rapid modular synthesis of block copolymersviatwo-dimensional chromatography and a comparably accurate, low-cost deconvolution of size exclusion chromatography traces is reported. Cyclopentadienyl-capped poly(methyl methacrylate) (PMMA, 97% functionality) and a series of pyridin-2-yldithioformate-capped poly(isobornyl acrylate)s (PiBoA, 93–95% functionality) were synthesiszed via atom transfer radical polymerization (ATRP) and reversible addition fragmentation chain transfer (RAFT) polymerization respectively. The corresponding block copolymers were generated by simply stirring a chloroform solution of PMMA, PiBoA and acidic catalyst for 10 min at ambient temperature. The crude block copolymer mixtures were directly analyzed by size exclusion chromatography (SEC), liquid adsorption chromatography at critical conditions (LACCC) and 2D LACCC-SEC to visualize the efficiency of the ultra rapid conjugation reaction. The quantitative analysis via the 2D LACCC-SEC yielded the composition of the block copolymer mixtures which were in excellent agreement with predicted values, thus indicating quantitative conjugation efficiency. In all cases, the crude block copolymer mixtures contained at least 94 wt% block copolymer. Furthermore, a low-cost deconvolution method that may be applied to conventional SEC traces was found to provide comparable composition data.

Free radical copolymerization of methyl substituted stilbenes with maleic anhydride

Stilbene-maleic anhydride is a well-known donor–acceptor comonomer pair which undergoes free radical copolymerization to form an alternating copolymer. A series of methyl substituted stilbenes were synthesized and copolymerized with maleic anhydride. A conversion versus time study was undertaken to understand the methyl substituent effect on copolymerization rates. Methyl substituents on the phenyl ring of stilbene can change the reactivity of stilbene by changing the resonance stability of the propagating radical and steric hindrance in the propagation step and thereby change the copolymerization rate. Methyl substituted stilbene-maleic anhydride copolymers were determined by quantitative 13C 1D NMR to be alternating copolymers. Size exclusion chromatography (SEC) measurements showed that the weight-average molecular weights of these copolymers varied from 3000 to over 1,000,000 g/mol. Interchain aggregation was observed in poly(( E)-4-methylstilbene- alt-maleic anhydride) by dynamic light scattering (DLS). The SEC trace for poly(( E)-4-methylstilbene- alt-maleic anhydride) exhibited bimodal peaks. No glass transition temperature or crystalline melting temperature was observed between 0 °C and 250 °C by differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) showed that these polymers have 5% weight loss around 290 °C.

Well-Defined Protein−Polymer Conjugates via in Situ RAFT Polymerization

Biotechnology, biomedicine, and nanotechnology applications would benefit from methods generating well-defined, monodisperse protein-polymer conjugates, avoiding time-consuming and difficult purification steps. Herein, we report the in situ synthesis of protein-polymer conjugates via reversible addition-fragmentation chain transfer polymerization (RAFT) as an efficient method to generate well-defined, homogeneous protein-polymer conjugates in one step, eliminating major postpolymerization purification steps. A water soluble RAFT agent was conjugated to a model protein, bovine serum albumin (BSA), via its free thiol group at Cys-34 residue. The conjugation of the RAFT agent to BSA was confirmed by UV-visible spectroscopy, matrix-assisted laser desorption ionization--time of flight (MALDI-TOF), and 1H NMR. BSA-macroRAFT agent was then used to control the polymerization of two different water soluble monomers, N-isopropylacrylamide (NIPAAm) and hydroxyethyl acrylate (HEA), in aqueous medium at 25 degrees C. The growth of the polymer chains from BSA-macroRAFT agent was characterized by size exclusion chromatography (SEC), 1H NMR, MALDI-TOF, and polyacrylamide gel electrophoresis (PAGE) analyses. The controlled character of the RAFT polymerizations was confirmed by the linear evolution of molecular weight with monomer conversion. The SEC analyses showed no detectable free, nonconjugated polymer formation during the in situ polymerization. The efficiency of BSA-macroRAFT agent to generate BSA-polymer conjugates was found to be ca. 1 by deconvolution of the SEC traces of the polymerization mixtures. The structural integrity and the conformation-related esterase activity of BSA were found to be unaffected by the polymerization conditions and the conjugation of the polymer chain. BSA-poly(NIPAAm) conjugates showed hybrid temperature-dependent phase separation and aggregation behavior. The lower critical solution temperature values of the conjugates were found to increase with the decrease in molecular weight of poly(NIPAAm) block conjugated to BSA.

Synthesis and characterisation of poly(sodium 4-styrenesulfonate) combs

A series of poly(sodium 4-styrenesulfonate) (NaPSS) combs has been synthesized. Architecturally and molecularly well-defined polystyrene combs were initially produced with the branch molecular mass fixed at 30,000g/mol, the average number of branches being the major variable. Conditions were established whereby linear polystyrene (PS) synthesized via anionic polymerization was chloromethylated using zinc (II) chloride, side-reactions such as Friedel–Crafts alkylation being suppressed. An excess of diphenylethylene-capped polystyryllithium (PSLi) was then reacted with the functionalized backbone to yield materials having long chain branches. The polystyrene combs were then reacted with sulfuric acid to yield water-soluble poly(styrenesulfonic acid) combs and subsequently neutralized with sodium hydroxide to give the corresponding sodium 4-styrene sulfonate species. The extent of sulfonation was determined via titration and nuclear magnetic resonance spectroscopy (NMR). Aqueous triple-detector size exclusion chromatography (SEC) was used to characterize the sulfonated combs. Although the SEC traces were monomodal and the Mn values agreed well with the expected values, an increase in the polydispersity index compared to the polystyrene combs may reflect the susceptibility of the sulfonation reaction to cross-linking.

General Solution to the Band-Broadening Problem in Polymer Molecular Weight Distributions

A method is developed for overcoming the problem of band broadening (where a sample which is monodisperse in molecular weight elutes over a range of elution volumes) in order to obtain accurate molecular weight distributions of polymers using size exclusion chromatography (SEC). It is proved that the SEC signal from an exponential number distribution (as obtained from free-radical polymerization under certain conditions) has the same functional form at the maximum, irrespective of band broadening. This leads to a method for quantifying the band broadening from any SEC trace, and hence for deconvoluting the trace to obtain the true distribution—by free-radical polymerization one should synthesize ‘standards’ which have exponential distributions and then carry out least-squares fitting to find the corresponding broadening function. The new method opens the way for mechanistic understanding and rate parameters to be obtained from the full detail that has hitherto been inaccessible in molecular weight distributions.

An Alternative Synthetic Approach toward Dendritic Macromolecules: Novel Benzene-Core Dendrimers via Alkyne Cyclotrimerization

An Alternative Synthetic Approach toward Dendritic Macromolecules: Novel Benzene-Core Dendrimers via Alkyne Cyclotrimerization

Molar Mass Distributions and Hydrodynamic Interactions in Random Copolyesters Investigated by Size Exclusion Chromatography/Matrix-Assisted Laser Desorption Ionization

Matrix-assisted laser desorption ionization−time-of-flight mass spectrometry (MALDI−TOF MS) was used in combination with size exclusion chromatography (SEC) to characterize a series of copolyesters with butylene adipate (BA), butylene succinate (BSu), and butylene sebacate (BSe) units. These copolyesters, synthesized by condensation polymerization from 1,4-butanediol and dimethyl esters, have flexible chains, are random, and do possess a homogeneous composition. The SEC fractionation of these polymers allowed to collect numerous fractions that were then analyzed by MALDI−TOF. The mass spectra of these nearly monodisperse fractions allowed the computation of the corresponding molar masses (MM). The calibrated SEC traces could then be used to compute average MM and molar mass distribution of the unfractionated samples. Furthermore, the SEC/MALDI data allowed an estimate of the effect of the hydrodynamic interactions of comonomers A and B along the copolymer chain and a comparison with the theoretical predic...

Ethylene polymerization catalysts from supported organotransition metal complexes: III. Support interactions

During the polymerization of ethylene, supported chromium catalysts display a strong interaction with the carrier, which affects the molecular weight of the polyethylene produced at a site. As a consequence, size exclusion chromatography (SEC) of the polymer sometimes provides evidence for different types of sites. In this study organochromium compounds and chromium oxide were deposited onto aluminas, aluminophosphates, and silicas treated in various ways. SEC traces of the resultant polymers suggest interaction of the Cr with Al, P, Si, and Ti.