Aqueous Gel Permeation Chromatography Research Articles

Synthesis of a hydrosoluble reversible addition‐fragmentation chain transfer agent and application in the preparation of micro/nano‐polyacrylamide gel dispersions

AbstractA hydrosoluble reversible addition‐fragmentation chain transfer (RAFT) agent named S‐(2‐propionic acid)‐S′‐(2‐methylpropionic acid) trithiocarbonate (PAMPATTC) is successfully synthesized. Then the micro/nano‐polyacrylamide gel dispersions are prepared via one‐pot RAFT polymerization in water to solve the problems of complicated preparation process and particle size control of common profile‐controlling and flooding agents. The structure of the RAFT agent is characterized and confirmed by fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H‐NMR). The effects of different reaction conditions on the properties of polyacrylamide gel dispersions are studied. The polymer dispersity index (PDI) of the polyacrylamide gel dispersions is tested by aqueous gel permeation chromatography, confirming the activity characteristics of RAFT polymerization. The rheological characteristics of the polyacrylamide gel dispersions and liner polyacrylamide are characterized. Compared with the liner polyacrylamide at similar viscosities, it is confirmed that the polyacrylamide gel dispersions were closer to Newtonian fluid, especially at high shear rates and the increasing amount of RAFT agent. The viscoelasticity tests under frequency scanning further confirm that the polyacrylamide gel dispersions are successfully synthesized via aqueous RAFT polymerization. The particle sizes are measured to show that the particle size of the polyacrylamide gel dispersions is micro/nano‐scale. The micromorphology of polyacrylamide gel dispersions is determined to indicate the irregular spherical structure, confirming that the micro‐particles are indeed formed by the aggregation of nano‐particles.

Adsorption of poly(vinyl alcohol) on gel permeation chromatography columns depends on the degree of hydrolysis

Both fully (98%) and partially (88%) hydrolyzed poly(vinyl alcohol) (PVA) are characterized by aqueous gel permeation chromatography (GPC) coupled with multi-angle laser light scattering. Polymer adsorption on hydrophilic GPC columns is observed for partially hydrolyzed PVA but not for fully hydrolyzed PVA, which is driven by the hydrophobic interactions between the residual acetate groups on PVA and the stationary phase. Desorption of these partially hydrolyzed PVA chains from the packing materials is monitored by decay of the light scattering signal. It is found that the desorption of these polymer chains from porous particles is non-exponential and follows stretched exponential kinetics with index 0.36. It is also shown that asymmetric flow field flow fractionation can be successfully used for the molar mass characterization of PVA, irrespective of the degree of hydrolysis.

Quantitative analysis of products from lignin depolymerisation in high-temperature water

Different types of lignin have been depolymerized via oxidative cleavage in sub- and supercritical water. As expected, a wide range of products of different structure and molecular weight have been obtained. Instead of analysing them one by one, we believe that it is equally useful and much more feasible to determine certain global parameters such as type of aromatic substituents, OH functionality or molecular weight distribution, particularly if the objective is to obtain a mixture of compounds with a particular application. To this end, each sample (products of lignin depolymerisation) was fractionated according to its solubility in water and ethyl acetate and the yield of the different fractions was determined. Then each fraction was analysed using CHNS elemental analysis; 31P- and 13C NMR and aqueous Gel Permeation Chromatography (GPC). Important conclusions about the effect of the reaction on the lignin structure can be deduced. These conclusions agree with previous observations found in literature. Based on these conclusions, some further insights have been proposed.

Synthesis, characterisation, and in vitro cellular uptake kinetics of nanoprecipitated poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(2-(diisopropylamino)ethyl methacrylate) (MPC-DPA) polymeric nanoparticle micelles for nanomedicine applications

Nanoscience offers the potential for great advances in medical technology and therapies in the form of nanomedicine. As such, developing controllable, predictable, and effective, nanoparticle-based therapeutic systems remains a significant challenge. Many polymer-based nanoparticle systems have been reported to date, but few harness materials with accepted biocompatibility. Phosphorylcholine (PC) based biomimetic materials have a long history of successful translation into effective commercial medical technologies. This study investigated the synthesis, characterisation, nanoprecipitation, and in vitro cellular uptake kinetics of PC-based polymeric nanoparticle micelles (PNM) formed by the biocompatible and pH responsive block copolymer poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(2-(diisopropylamino)ethyl methacrylate) (MPC-DPA). Atom transfer radical polymerisation (ATRP), and gel permeation chromatography (GPC) were used to synthesise and characterise the well-defined MPC100-DPA100 polymer, revealing organic GPC, using evaporative light scatter detection, to be more accurate than aqueous GPC for this application. Subsequent nanoprecipitation investigations utilising photon correlation spectroscopy (PCS) revealed PNM size increased with polymer concentration, and conferred Cryo-stability. PNM diameters ranged from circa 64–69 nm, and increased upon hydrophobic compound loading, circa 65–71 nm, with loading efficiencies of circa 60 % achieved, whilst remaining monodisperse. In vitro studies demonstrated that the PNM were of low cellular toxicity, with colony formation and MTT assays, utilising V79 and 3T3 cells, yielding comparable results. Investigation of the in vitro cellular uptake kinetics revealed rapid, 1 h, cellular uptake of MPC100-DPA100 PNM delivered fluorescent probes, with fluorescence persistence for 48 h. This paper presents the first report of these novel findings, which highlight the potential of the system for nanomedicine application development.

Promoting cell adhesion on slippery phosphorylcholine hydrogel surfaces

The growing interest in regenerative medicine has created a need for superior polymer matrices that suit multiple physical, mechanical, and biological requirements. While the phospholipid bilayer of a cell membrane is considered optimal for interacting with biologics, polymeric materials composed of 2-methacryloyloxyethyl phosphorylcholine (MPC) offer a cell membrane-like synthetic alternative. In this work, thiol-containing phosphorylcholine polymers were synthesized by radical copolymerization of a lipoic acid-functionalized methacrylate with MPC. The canonical cell adhesion oligopeptide (GRGDS) was incorporated into the polymers by copolymerization of a GRGDS-containing methacrylamide prepared by solid phase peptide synthesis. The relative amounts of phosphorylcholine, lipoic acid and oligopeptide were controlled by the monomer feed ratios, and the polymers were characterized by NMR spectroscopy and aqueous gel permeation chromatography (GPC). These multifunctional polymers formed hydrogels rapidly (<10 minutes) by Michael addition when poly(ethylene glycol)diacrylate (PEGDA) was added at pH 9 - an initiator-free gelation performed in a completely aqueous environment. Two cell lines, live mouse skeletal muscle myoblasts (C2C12) and human ovarian cancer (SKOV3) cells, were observed to specifically attach, spread and proliferate only on hydrogels containing the GRGDS peptide sequence, with a notable dependence on peptide concentration. The remarkable hydrophilicity and biocompatibility attributed to polyMPC combined with the facile gelation conditions of these polymers affords a platform of new bio-cooperative materials suitable for cell studies.

Determination of Caprolactam and Residual Vinyl Caprolactam Monomer in Soluplus by Mixed Mode Gel Permeation Chromatography

Soluplus, a graft copolymer of polyethylene glycol, vinyl caprolactam and vinyl acetate, is designed to solubilize poorly soluble active pharmaceutical ingredients. A straightforward aqueous gel permeation chromatography method that exploits both size exclusion and adsorption modes of separation was used to separate and quantify the related residual vinyl caprolactam monomer and caprolactam impurity present in Soluplus. This methodology offers a single step analysis of caprolactam and the residual vinyl caprolacatam monomer, yielding similar results to reversed-phase chromatography measurements, which are time-consuming and may involve multi-step sample preparation. The results of this study demonstrate that gel permeation chromatography provides a viable option to traditional reversed-phase chromatography in the quantitative analysis of residual caprolactam and vinyl caprolactam monomers and can be extended to other monomer-polymeric systems.

Anisotropic Self-Assembling Micelles Prepared by the Direct Dissolution of PLA/PEG Block Copolymers with a High PEG Fraction

A series of polylactide-poly(ethylene glycol) (PLA-PEG) block copolymers with a high PEG fraction were synthesized by the ring-opening polymerization of L- or D-lactide in the presence of mono- or dihydroxyl PEG using nontoxic zinc lactate as a catalyst. Micelles were then prepared by direct dissolution of the obtained water-soluble copolymers in an aqueous medium without heating or using any organic solvents. Large anisotropic micelles instead of conventional spherical ones were observed from a transmission electron microscopy examination. Various parameters influencing the structure of the novel micelles were considered, such as the copolymer chain structure, molar mass, PEG fraction, copolymer concentration, and stereocomplexation between L- and D-PLA blocks. Anisotropic micelles were obtained for both diblock and triblock copolymers but vanished with increasing molar mass of the copolymers. The morphology of micelles strongly depends on the PEG fraction. Anisotropic micelles were found only in an intermediate EO/LA ratio range in which a higher PEG fraction leads to a higher length/width ratio of micelles. Stereocomplexation between L- and D-PLA or a lower concentration disfavors the formation of anisotropic micelles. Under appropriate concentrations, spherical and anisotropic micelles coexist in the same micellar solution. Moreover, it was found that anisotropic micelles are susceptible to further self-assemble into more organized complex aggregates. Similar results were obtained from light scattering and aqueous gel permeation chromatography measurements. A novel model is proposed to explain the formation of anisotropic micelles and the effects of various parameters on the structure of micelles in an aqueous medium.

Direct Synthesis of Poly(potassium 3-sulfopropyl methacrylate) Cylindrical Polymer Brushes via ATRP Using a Supramolecular Complex With Crown Ether

A supramolecular complex between an ionic monomer 3-sulfopropyl methacrylate (SPMAK) and crown ether 18-crown-6 (18C6) has been employed to prepare a strong anionic cylindrical polyelectrolyte brush poly(potassium 3-sulfopropyl methacrylate) (PSPMAK) by atom transfer radical polymerization (ATRP) in polar solvent dimethyl sulfoxide (DMSO). This strategy solved the problem of the solubilities of the incompatible hydrophobic poly-initiator and hydrophilic ionic monomer. The formation of the PSPMAK brush is well proven by (1) H NMR, aqueous gel permeation chromatography (GPC), dynamic light scattering (DLS), static light scattering (SLS), atomic force microscopy (AFM), and cryogenic transmission electron microscopy (cryo-TEM) measurements. Cleavage of the side chains and further analysis reveal that the initiating efficiency of the polymerization is as low as 0.35.

Aggregation behavior of self-assembling polylactide/poly(ethylene glycol) micelles for sustained drug delivery

A series of diblock copolymers were synthesized by ring-opening polymerization of l- or d-lactide in the presence of monomethoxy poly(ethylene glycol) (mPEG) with molar masses of 2000 and 5000. The aggregation behavior of the resulting water soluble PLA/PEG diblock copolymers in aqueous medium was studied with dynamic and static light scattering (DLS and SLS), in combination with aqueous gel permeation chromatography (GPC). The average hydrodynamic radius ( R h) of l-PLA/PEG and d-PLA/PEG mixed micelles is lower than that of l-PLA/PEG single micelles due to the stereocomplexation effect between l-PLA and d-PLA blocks. It is also confirmed that the micelle size increases with increasing temperature and hydrophobic block length, but decreases after salt addition. Aqueous GPC and SLS were used to evaluate the molecular weight ( M w) and aggregation number ( N agg) of the micelles. Mixed micelles present lower N agg than single copolymer micelles due to stereocomplexation. N agg decreases with increasing hydrophobic block length, and decreases upon addition of NaCl, in agreement with a more compact structure. In contrast, N agg increases with elevating temperature. The average radius of gyration ( R g) and R g/ R h ratio data show that both increase with increasing temperature, suggesting that micelles exhibit a compact hard-sphere structure at 15 °C and a swollen structure at 35 °C. As the temperature increases from 15 °C to 35 °C, the second virial coefficient ( A 2) of PLA/PEG copolymers turns from negative to positive, which means that water changes from poor solvent to good solvent. The fact that the average density ( ρ) of PLA/PEG micelles decreases with increasing temperature confirms that micelles exhibit a looser structure at higher temperatures due to water swelling effect. The higher ρ value of mixed micelles as compared to single micelles also confirms a more compact structure of the former. In addition, due to the much higher N agg and lower R h, PLA/PEG2000 micelles present higher ρ value than PLA/PEG5000 ones.

Synthesis and Characterization of Polyolefin-graft-oligopeptide Polyelectrolytes

Novel polyelectrolytes consisting of hydrophobic polyolefin backbones and charged oligopeptide grafts have been synthesized and characterized. Oligopeptide-containing monomers were prepared by solid-phase peptide synthesis (SPPS) and then polymerized by ring-opening metathesis polymerization (ROMP). Copolymerization of the peptide-functionalized monomers with charge neutral cyclic olefins (i.e., poly(ethylene glycol)-substituted) gave polymers with varying charge density. These graft copolymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, organic and aqueous gel permeation chromatography (GPC), and light scattering. Light scattering indicated that the oligopeptide-functionalized polyolefins could be tailored to form extended, pearl-like, or multimolecular structures, depending on the composition and density of the grafts.

Structural modification and characterization of lignosulfonate by a reaction in an alkaline medium for its incorporation into phenolic resins

AbstractWe studied the enhancement of lignin reactivity in an alkaline medium, using sodium hydroxide in a microreactor set. The chemical composition and structural characterization of the reacted lignosulfonate in terms of the phenolic hydroxyl groups, aromatic protons, weight‐average molecular weight, number‐average molecular weight, and lignosulfonate content of all reacted lignins were determined. The techniques that we used were ultraviolet spectroscopy, proton nuclear magnetic resonance spectroscopy, and aqueous gel permeation chromatography. Using response surface methodology, we studied how the temperature and reaction time affected the lignin properties. The reaction conditions were temperatures between 116 and 180°C and reaction times between 18 and 103 min. Modeled response surfaces showed that the two factors affected the lignin properties within the studied ranges. The phenolic hydroxyl groups, aro matic protons, and lignosulfonate content increased when the severity of the treatment increased. The weight‐average molecular weight, number‐average molecular weight, and solid yield (%) decreased when the severity of the treatment increased. The reactivity of the modified lignins was studied with a formaldehyde reactivity test: more severe conditions produced greater improvements in the formaldehyde reactivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3286–3292, 2006

Highly Protein-Resistant Coatings from Well-Defined Diblock Copolymers Containing Sulfobetaines

Three well-defined diblock copolymers of poly(sulfobetaine methacrylate) [poly(SBMA)] and poly(propylene oxide) (PPO) were synthesized by the sequential addition of SBMA monomer to fixed amounts of PPO using an atom transfer radical polymerization method and varying poly(SBMA) lengths. These copolymers were characterized by 1H NMR and aqueous gel permeation chromatography. These copolymers were physically adsorbed onto a surface plasmon resonance (SPR) sensor surface covered by methyl-terminated self-assembled monolayers, followed by the in situ evaluation of protein adsorption on the adsorbed copolymers. It is found that the behavior of the protein adsorption depends on the molecular weight of the copolymers. Results show that the diblock copolymers containing poly(SBMA) can be highly protein resistant when surface SBMA densities are well controlled. Thus, copolymers containing zwitterionic groups are ideal for resisting protein adsorption when the surface density of zwitterionic groups is controlled.

Biomimetic Stimulus-Responsive Star Diblock Gelators

Novel biomimetic gelators with star diblock copolymer architectures have been synthesized by atom-transfer radical polymerization (ATRP). Two types of trifunctional ATRP initiator were used to polymerize 2-(methacryloyloxy)ethyl phosphorylcholine [MPC] at 20 degrees C, followed by sequential monomer addition of various tertiary amine methacrylates or mixtures thereof. Poor living character was achieved using an amide-based trifunctional initiator, but the analogous triester initiator gave reasonably well-defined thermo-responsive and pH-responsive star diblock copolymers. The most effective thermo-responsive gelators were obtained by the statistical terpolymerization of 2-(dimethylamino)ethyl methacrylate [DMA], 2-(diethylamino)ethyl methacrylate [DEA], and a monomethoxy-capped poly(propylene oxide) methacrylate [PPOMA], whereas pH-responsive gelators were prepared using 2-(diisopropylamino)ethyl methacrylate [DPA] as the second monomer. Star diblock copolymer gelators that were both thermo-responsive and pH-responsive were obtained by the statistical copolymerization of DMA with DPA. Copolymer compositions were assessed by 1H NMR spectroscopy, and the molecular weight distributions of the three-arm star MPC homopolymer precursors were assessed by aqueous gel permeation chromatography. Static light scattering was used to obtain weight-average molecular weights of selected star diblock copolymers and rheological measurements and variable-temperature 1H NMR were used to probe the onset of gelation.

Physicochemical Characterization of Konjac Glucomannan

Four commercial konjac glucomannan (KGM) samples and a glucomannan derived from yeast were characterized by aqueous gel permeation chromatography coupled with multi angle laser light scattering (GPC-MALLS). Disaggregation of aqueous glucomannan solutions through controlled use of a microwave bomb facilitated reproducible molar mass distribution determination alleviating the need for derivatization of the polymer or the use of aggressive solvents. Further characterization was undertaken by use of capillary viscometry and photon correlation spectroscopy (PCS). The weight average molecular masses (M(w)) determined were in the region of 9.0 +/- 1.0 x 10(5) g mol(-1) for KGM samples and 1.3 +/- 0.4 x 10(5) g mol(-1) for the yeast glucomannan. The values determined for KGM in aqueous solution are in agreement with those reported for KGM in aqueous cadoxen. The degradation of samples observed upon autoclaving has been quantified by GPC-MALLS and intrinsic viscosity determination, allowing comparison with reported Mark-Houwink parameters. Shear flow experiments were undertaken for a range of KGM solutions of concentration 0.05 to 2.0% using a combination of controlled stress and controlled strain rheometers. The concentration dependence of the zero shear specific viscosity was determined by analysis of the data using the Ellis model. The dependence of the zero shear specific viscosity on the coil overlap parameter was defined and interpretation discussed in terms of the Martin and Tuinier equations.

Oxidation and metal-ion affinities of a novel cyclic tetrasaccharide

The cyclic tetrasaccharide, cyclo-{→6)-α- d-Glc p-(1→3)-α- d-Glc p-(1→6)-α- d-Glc p-(1→3)-α- d-Glc p-(1→}, was oxidized in high yield to a dicarboxylic acid, cyclo-{→6)-α- d-Glc p-(1→3)-α- d-Glc pA-(1→6)-α- d-Glc p-(1→3)-α- d-Glc pA-(1→}. The parent and oxidized compound were then screened for the ability to form stable complexes with 20 metal cations. Ion-exchange thin-layer chromatography was utilized to survey binding in aqueous and 50% methanolic solutions. The screening identified Pb 2+, Fe 2+ and Fe 3+ as forming strong metal chelates with the oxidized cyclic tetrasaccharide. The stoichiometry of the oxidized cyclic tetrasaccharide and Pb 2+ complex was determined to be 1:1 using aqueous gel-permeation chromatography. Perturbations between the free and complexed structure were examined using NMR spectroscopy. Molecular simulations were used to identify a probable structure of oxidized cyclic tetrasaccharide complexed with Pb 2+.

Synthesis and aqueous solution properties of novel sugar methacrylate-based homopolymers and block copolymers.

We report the facile preparation of a range of novel, well-defined cyclic sugar methacrylate-based polymers without recourse to protecting group chemistry. 2-Gluconamidoethyl methacrylate (GAMA) and 2-lactobionamidoethyl methacrylate (LAMA) were prepared directly by reacting 2-aminoethyl methacrylate with D-gluconolactone and lactobionolactone, respectively. Homopolymerization of GAMA and LAMA by atom transfer radical polymerization (ATRP) gave reasonably low polydispersities as judged by aqueous gel permeation chromatography. A wide range of sugar-based block copolymers were prepared using near-monodisperse macroinitiators based on poly(ethylene oxide) [PEO], poly(propylene oxide) [PPO], or poly(e-caprolactone) [PCL] and/or by sequential monomer addition of other methacrylic monomers such as 2-(diethylamino)ethyl methacrylate [DEA], 2-(diisopropylaminoethyl methacrylate [DPA], or glycerol monomethacrylate [GMA]. The reversible micellar self-assembly of selected sugar-based block copolymers [PEO23-GAMA50-DEA100, PEO23-LAMA30-DEA50, PPO33-GAMA50, and PPO33-LAMA50] was studied in aqueous solution as a function of pH and temperature using dynamic light scattering, transmission electron microscopy, surface tensiometry, and 1H NMR spectroscopy.

Water‐soluble polymers with tunable temperature sensitivity: Solution behavior

Water‐soluble polymers with tunable temperature sensitivity: Solution behavior

Templating of inorganic nanoparticles by PAMAM/PEG dendrimer–star polymers

Poly(amidoamine) (PAMAM) dendrimers with amine endgroups (PAMAM–NH 2) are converted to starlike copolymers by grafting of monofunctional poly(ethylene glycol) (PEG) ‘arms’ onto the dendrimer endgroups. Generation 4, 7, and 10 dendrimers are converted to 60-arm, 235-arm, and 750-arm PAMAM/PEG stars, respectively. The dendrimer–stars are studied as polymer templates for stabilization of gold and cadmium sulfide nanoparticles of 1–6 nm diameter. PAMAM/PEG star templating reactions are studied by aqueous gel permeation chromatography, ultraviolet–visible absorption spectroscopy, fluorescence spectroscopy, and transmission electron microscopy. PAMAM/PEG stars effectively control nanoparticle size in the same way as PAMAM–NH 2 dendrimers. However, PAMAM/PEG stars are miscible with a wider range of solvents and with selected polymers (e.g. polymethyl methacrylate). Potential applications of dendrimer–inorganic hybrid materials (solution-phase catalysis, additives for polymer blends) could benefit from the versatile solubility of PAMAM/PEG stars.

Synthesis and aqueous solution characterization of amphiphilic diblock copolymers containing carbazole

A series of near-monodisperse diblock copolymers of 2-( N-carbazolyl)ethyl methacrylate and 2-(dimethylamino)ethyl methacrylate (DMAEMA) of relatively low molecular weights (2600–24,000 g mol −1) were synthesized by group transfer polymerization using tetrahydrofuran (THF) as a solvent. The molecular weight distributions and compositions of all the copolymers were obtained using gel permeation chromatography (GPC) in THF and proton nuclear magnetic resonance ( 1H NMR) spectroscopy, respectively. Differential scanning calorimetry and thermal gravimetric analysis provided low glass transition temperatures ( T gs) of about 60 °C and decomposition temperatures between 320 and 450 °C for the copolymers, respectively. The three copolymers with the highest DMAEMA content were water-soluble below pH 7. Aqueous GPC at pH 3 showed that the water-soluble block copolymers formed micelles with apparent number average molecular weights above 100,000 g mol −1.

Aqueous Gel Permeation Chromatographic Methods for Technical Lignins

The molecular weights and molecular weight distributions of lignosulfonates and soda lignins were determined by aqueous gel permeation chromatography (GPC). The elution behavior of the samples, was investigated in detail to evaluate the non-size-exclusive effect in the aqueous GPC system. The ionic strength and pH are thought to be the main factors influencing the accuracy and the reliability of measurements. Solutions of 0.1M NaNO3 with pH 7 or 0.1 M NaNO3 with pH 12 were shown to be optimum for determining the molecular weight of lignosulfonate and alkali lignin. Accuracy of the method was checked by comparing the data obtained by aqueous GPC with that from vapor pressure osmometry (VPO).