Separation of poly(acrylic acid) salts according to topology using capillary electrophoresis in the critical conditions

Particle Dynamics in Colloid-Polymer Mixtures with Different Polymer Architectures

Nonadsorbing polymers are widely used as thickening agents for colloids. A quantitative description of the structure and dynamics of such colloid-polymer mixtures is crucial to reveal the mechanisms accounting for the desired mechanical properties. We use confocal microscopy to study colloids with three types of commonly used polymers with different architectures: linear, subgranular cross-linked, and branched microgels. All three thickeners give rise to heterogeneous colloidal dynamics, characterized by non-Gaussian displacement distributions. However, while the ensemble-averaged particle dynamics in these materials are very similar, the underlying individual particle dynamics are not. Linear polymers give rise to depletion attraction and the formation of colloidal gels, in which the majority of particles are immobilized, while a few weakly bound particles have much higher mobility. By contrast, the branched and cross-linked polymers thicken the continuous phase of the colloid, squeezing the particles into dense pockets, where the mobility is reduced and requires more cooperative rearrangements.

Degree of branching in poly(acrylic acid) prepared by controlled and conventional radical polymerization

Poly(acrylic acid)s, PAAs and poly(sodium acrylate)s, PNaAs were characterized in detail.

Characterization of oligo(acrylic acid)s and their block co-oligomers

Oligo(acrylic acid), oligoAA are important species currently used industrially in the stabilization of paints and also for the production of self-assembled polymer structures which have been shown to have useful applications in analytical separation methods and potentially in drug delivery systems. To properly tailor the synthesis of oligoAA, and its block co-oligomers synthesized by Reversible-Addition Fragmentation chain Transfer (RAFT) polymerization to applications, detailed knowledge about the chemical structure is needed. Commonly used techniques such as Size Exclusion Chromatography (SEC) and Electrospray Ionization-Mass Spectrometry (ESI-MS) suffer from poor resolution and non-quantitative distributions, respectively. In this work free solution Capillary Electrophoresis (CE) has been thoroughly investigated as an alternative, allowing for the separation of oligoAA by molar mass and the RAFT agent end group. The method was then extended to block co-oligomers of acrylic acid and styrene. Peak capacities up to 426 were observed for these 1D CE separations, 10 times greater than what has been achieved for Liquid Chromatography (LC) of oligostyrenes. To provide a comprehensive insight into the chemical structure of these materials ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy was used to provide an accurate average chain length and reveal the presence of branching. The chain length at which branching is detected was investigated with the results showing a degree of branching of 1% of the monomer units in oligoAA with an average chain length of 9 monomer units, which was the shortest chain length at which branching could be detected. This branching is suspected to be a result of both intermolecular and intramolecular transfer reactions. The combination of free solution CE and NMR spectroscopy is shown to provide a near complete elucidation of the chemical structure of oligoAA including the average chain length and branching as well as the chain length and RAFT agent end group distribution. Furthermore, the purity in terms of the dead chains and unreacted RAFT agent was quantified. The use of free solution CE and ¹H NMR spectroscopy demonstrated in this work can be routinely applied to oligoelectrolytes and their block co-oligomers to provide an accurate characterization which allows for better design of the materials produced from these oligomers.

Rapid and Quantitative De-tert-butylation for Poly(acrylic acid) Block Copolymers and Influence on Relaxation of Thermoassociated Transient Networks

The synthesis of charged polymers often requires the polymerization of protected monomers, followed by a polymer-analogous reaction to the polyelectrolyte product. We present a mild, facile method to cleave tert-butyl groups from poly(tert-butyl acrylate) blocks that yields poly(acrylic acid) (pAA) blocks free of traces of the ester. The reaction utilizes a slight excess of HCl in hexafluoroisopropanol (HFIP) at room temperature and runs to completion within 4 h. We compare deprotection in HFIP with the common TFA/DCM method and show that the latter does not yield clean pAA. We show the effect of complete tert-butyl cleavage on a ABA triblock copolymer, where poly(N-isopropylacrylamide) (pNIPAM) is A and pAA is B, by means of viscosimetry, DLS, and SAXS on solutions above overlap. The pNIPAM blocks dehydrate, and their increased self-affinity above the lower critical solution temperature (LCST) results in network formation by the triblocks. This manifests itself as an increase in viscosity and a slowing down of the first-order correlation function in light scattering. However, this stickering effect manifests itself exclusively when the pAA block is tert-butyl-free. Additionally, SAXS shows that the conformational properties of tert-butyl-free pAA copolymers are markedly different from those with residual esters. Thus, we illustrate a surprising effect of hydrophobic impurities that act across blocks and assert the usefulness of HCl/HFIP in pAA synthesis.

Determination of molecular size parameters and quantification of polyacrylic acid by high performance size-exclusion chromatography with triple detection

Synthetic polyelectrolytes are a broad class of vaccine adjuvants. Among them, polyacrylic acid (PAA), a polyanionic polymer, is currently evaluated by Sanofi Pasteur. As chain length is considered to be a critical quality attribute for adjuvant properties of PAA, measurement of precise and accurate molecular size parameters is important for these polymers. In the field of synthetic polymer chemistry, methods for determination of molecular size parameters are well defined. Specifically, high performance size-exclusion chromatography (HPSEC) with multi-detection system is a method of choice. This paper describes the development of HPSEC method to well characterize and precisely quantify PAA in different adjuvant formulations. A first set of characterizations were made, with determination of dn/dc coefficient, which enabled the determination of weight- and number-average molecular weight, viscosimetric radius, and intrinsic viscosity. In-depth characterization was also made with branching study through the use of Mark-Houwink parameter determination. The quantification method was also evaluated according to validation method-like criteria: limit of detection and limit of quantification, repeatability, accuracy, and specificity with recombinant surface glycoprotein gB from human cytomegalovirus (CMV-gB) as model antigen.

Capillary Electrophoresis to Monitor Peptide Grafting onto Chitosan Films in Real Time

Free-solution capillary electrophoresis (CE) separates analytes, generally charged compounds in solution through the application of an electric field. Compared to other analytical separation techniques, such as chromatography, CE is cheap, robust and effectively requires no sample preparation (for a number of complex natural matrices or polymeric samples). CE is fast and can be used to follow the evolution of mixtures in real time (e.g., chemical reaction kinetics), as the signals observed for the separated compounds are directly proportional to their quantity in solution. Here, the efficiency of CE is demonstrated for monitoring the covalent grafting of peptides onto chitosan films for subsequent biomedical applications. Chitosan's antimicrobial and biocompatible properties make it an attractive material for biomedical applications such as cell growth substrates. Covalently grafting the peptide RGDS (arginine - glycine - aspartic acid - serine) onto the surface of chitosan films aims at improving cell attachment. Historically, chromatography and amino acid analysis have been used to provide a direct measurement of the amount of grafted peptide. However, the fast separation and absence of sample preparation provided by CE enables equally accurate yet real-time monitoring of the peptide grafting process. CE is able to separate and quantify the different components of the reaction mixture: the (non-grafted) peptide and the chemical coupling agents. In this way the use of CE results in improved films for downstream applications. The chitosan films were characterized through solid-state NMR (nuclear magnetic resonance) spectroscopy. This technique is more time-consuming and cannot be applied in real time, but yields a direct measurement of the peptide and thus validates the CE technique.

Quantifying the Heterogeneity of Chemical Structures in Complex Charged Polymers through the Dispersity of Their Distributions of Electrophoretic Mobilities or of Compositions

The complexity of synthetic and natural polymers used in industrial and medical applications is expanding; thus, it becomes increasingly important to improve and develop methods for their molecular characterization. Free-solution capillary electrophoresis is a robust technique for the separation and characterization of both natural and synthetic complex charged polymers. In the case of polyelectrolytes, free-solution capillary electrophoresis is in the "critical conditions" (CE-CC): it allows their separation by factors other than molar mass for molar masses typically higher than 20000 g/mol. This method is thus complementary to size-exclusion chromatography (SEC). SEC is widely used to determine molar mass distributions and their dispersities. Utilizing CE-CC, an analogous calculation of dispersity based on the distributions of electrophoretic mobilities was derived and the heterogeneity of composition or branching in different polysaccharides or synthetic polymers was obtained in a number of experimental cases. Calculations are based on a ratio of moments and could therefore be compared to simulations of polymerization processes, in analogy to the work performed on molar mass distributions. Among four possible types of dispersity, the most precise values were obtained with the calculation analogous with the dispersity of molar mass distribution Mw/Mn. In addition, the dispersity value allows conclusions based on a single value: the closer the dispersity is to 1, the more homogeneous the polymer is in terms of composition or branching. This approach allows the analysis of dispersity of important molecular attributes of polymers other than molar mass and aims at improving the overall molecular characterization of both synthetic and natural polymers. The dispersity can also be monitored online while performing a chemical reaction within the CE instrument.

Cellular Response to Linear and Branched Poly(acrylic acid)

Poly(acrylic acid-co-sodium acrylate) (PNaA) is a pH-responsive polymer with potential in anticancer drug delivery. The cytotoxicity and intracellular effects of 3-arm star, hyperbranched and linear PNaA were investigated with L1210 progenitor leukemia cells and L6 myoblast cells. Free solution capillary electrophoresis demonstrated interactions of PNaA with serum proteins. In a 72 h MTT assay most PNaAs exhibited a IC50 between 7 and 14 mmol L(-1), showing that precipitation may be a sufficient purification for PNaA dilute solutions. Dialyzed 3-arm star and hyperbranched PNaA caused an increase in L6 cell viability, challenging the suitability of MTT as cytotoxicity assay for PNaA. Fluorescent confocal microscopy revealed merging of cellular lipids after exposure to PNaA, likely caused by serum starvation.

Separation and Characterization of Synthetic Polyelectrolytes and Polysaccharides with Capillary Electrophoresis

The development of macromolecular engineering and the need for renewable and sustainable polymer sources make polymeric materials progressively more sophisticated but also increasingly complex to characterize. Size-exclusion chromatography (SEC or GPC) has a monopoly in the separation and characterization of polymers, but it faces a number of proven, though regularly ignored, limitations for the characterization of a number of complex samples such as polyelectrolytes and polysaccharides. Free solution capillary electrophoresis (CE), or capillary zone electrophoresis, allows usually more robust separations than SEC due to the absence of a stationary phase. It is, for example, not necessary to filter the samples for analysis with CE. CE is mostly limited to polymers that are charged or can be charged, but in the case of polyelectrolytes it has similarities with liquid chromatography in the critical conditions: it does not separate a charged homopolymer by molar mass. It can thus characterize the topology of a branched polymer, such as poly(acrylic acid), or the purity or composition of copolymers, either natural ones such as pectin, chitosan, and gellan gum or synthetic ones.