M. Pilar Tarazona

Polymer characterization by size-exclusion chromatography with multiple detection☆

Size-exclusion chromatography with coupled multiangle light scattering and differential refractometry detectors has been used to obtain molecular mass and radius of gyration distributions of polydisperse polymer samples. From these data the scaling law between dimensions and the absolute molecular mass is obtained with just one sample of each polymer. Three different kinds of polymers are presented: polystyrene which serves as reference polymer, polyphosphazenes which behave abnormally in solution and poly(ethylene oxide) which is soluble in water. Since the relationship between dimensions and molecular mass depends on the extent of interactions between chain segments and solvent molecules, the scaling law provides information about the solution properties of the polymer.

Combination of SEC/MALS experimental procedures and theoretical analysis for studying the solution properties of macromolecules.

Size-exclusion chromatography (SEC) with dual detection, i.e., employing refractive index (RI) and multiangle light-scattering (MALS) detectors, has been applied to study the solution properties of two very different polymer-solvent systems at 25 degrees C: poly(N-vinylcarbazole) (PVCz) in an organic solvent THF that is a very good solvent and a system under theta conditions that is formed by polyvinylpyrrolidone (PVP) in water containing a 0.1 M concentration of NaNO(3). In both cases, the analysis of a single highly polydisperse sample obtained by free radical polymerization is enough for obtaining molecular weight and radius of gyration calibration curves, molecular weight distributions (MWD) (and thus, molecular weight averages), molecular dimensions, scaling laws coefficients and unperturbed dimensions. Extrapolation to theta conditions produces values of the characteristic ratio of the unperturbed dimensions C(n)=(o)/nl(2)=15.9 and 14, respectively, for PVCz and PVP. Unperturbed dimensions are also theoretically calculated with different models such as Kuhn equivalent chain, worm-like chain and rotational isomeric states model. Conformational parameters required for this last model were taken from the literature in the case of PVCz; however, they are calculated by molecular dynamics simulations in the case of PVP. Theoretical values obtained with the RIS model are in good agreement with the experimental results.

Analysis of copolymers of styrene and methyl methacrylate using size exclusion chromatography with multiple detection

Size exclusion chromatography (SEC) with differential refractive index (RI), multiangle light scattering (MALS) and UV detectors has been used to obtain information about copolymers of styrene (S) and methyl methacrylate (MMA). Homopolymers PS and PMMA having broad molecular weight distributions, mixtures of PS and PMMA homopolymers, and copolymers containing different weight fractions of S and MMA units were studied. Molecular weight distributions, molecular dimensions and scaling laws are reported for these systems. The behavior of the random copolymers is very different from that exhibited by the heterogeneous mixtures of homopolymers. Thus, the results obtained for the copolymers can be explained by assuming that these molecules have homogeneous distributions of S and MMA units along their chains. On the contrary, the mixtures produce the results that would be expected from heterogeneous combinations of different molecules. The SEC technique offers the possibility of determining the composition of random copolymers and discriminating among random copolymers (having homogeneous distributions of units) and block copolymers.

The use of molecular dynamics for the study of solution properties of guar gum

Size exclusion chromatography with dual detection, i.e., employing a refractive index, concentration sensitive, detector together with a multiangle light scattering detector which is sensitive to molecular size, has been applied to study the solution properties of guar gum in water with different concentrations of K2SO4 at 25 °C. The analysis of a single highly polydisperse sample is enough for obtaining calibration curves for molecular weight and radius of gyration and the scaling law coefficients. The influence of the ionic strength on the conformational properties of the polymer can also be analyzed. Moreover, unperturbed dimensions can be obtained by extrapolation of the values measured in a good solvent. The value of the characteristic ratio of the unperturbed dimensions thus obtained is Cn=〈r2〉0/nl2≈19±1. A theoretical analysis is also included. Thus, molecular dynamics procedures were employed to analyze the conformational properties of an oligomer of guar gum under different conditions; namely, st...

Solution properties of polyphosphazenes containing 2,2′-dioxybiphenyl groups

Abstract Dilute solution properties of four different polyphosphazenes containing 2,2′-dioxybiphenyl groups have been studied by size exclusion chromatography, using simultaneously multiangle light scattering and differential refractive index detectors. The polymers present broad molecular weight distributions and the dependence of the dimensions, i.e. radius of gyration, of the polymers on the molecular weight is discussed. Moreover, scaling laws and unperturbed dimensions have been calculated for the fractions with high molecular weight. The polymers behave as random coil chains, the characteristic ratios are in the range 12–17 in good accord with the results reported for other polyphosphazenes.

Interaction of gold nanoparticles with Doxorubicin mediated by supramolecular chemistry

A copolymer containing β-cyclodextrin, catechol and polyethylene glycol groups in its side chain was designed for the in situ synthesis and coating of gold nanoparticles (Au@PEG-CD NPs). These platforms were designed as a smart carrier and traceable delivery probe of the chemotherapeutic Doxorubicin drug (Dox). The coated polymer forms stable complexes with Dox in water with a high binding constant (K=2.3×10(4) M(-1) at 25°C), which is one hundred times greater than those reported for its complexation with native βCD. Therefore, Au@PEG-CD NPs were able to load 0.01 mg of the drug per mg of NP and to release up to 60% of it in 48 h at 37°C. In addition, Au@PEG-CD NPs had the capacity to act as a quencher of Dox fluorescence when it was complexed with βCD in the NP organic shell. This feature allows the Dox release to be tracked by monitoring the recovery of its fluorescence in real time. Therefore, the Dox release kinetics and the influence of temperature on the thermal stability of Dox/CD complexes on Au@PEG-CD NP were investigated. The increase in temperature favors the dissociation of the complexes and subsequent Dox release from the NP. The first order rate constant for drug releasing was 1.1×10(-2) min(-1) with a half-life time of 63 min at 37°C. Finally, the great potential of the carrier/probe double nature of Au@PEG-CD NPs was demonstrated in real time inside HeLa cells.

Dilute solution properties of poly(dianilino phosphazene)

Poly(dianilino phosphazene) has been synthesized from hexachlorocyclotriphosphazene by two different methods, bulk and solution. Several fractions, with polydispersity ratio ranging from 1.8 to 2.4, were obtained by fractional precipitation and characterized by viscometry and size exclusion chromatography (s.e.c.) using simultaneously refractive index and multi-angle light scattering detectors. From these data the solution behaviour of the polymer is discussed.

Versatile Tetrablock Copolymer Scaffold for Hierarchical Colloidal Nanoparticle Assemblies: Synthesis, Characterization, and Molecular Dynamics Simulation

A unique combination of molecular dynamics (MD) simulation and detailed size exclusion chromatography-multiangle light scattering (SEC-MALS) analysis is used to provide important a priori insights into the solution self-assembly of a well-defined and symmetric tetrablock copolymer with two acrylic acid (AA) outer blocks, two polystyrene (PS) inner blocks, and a trithiocarbonate (TTC) central group, prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. SEC-MALS experiments show that the copolymer forms aggregates in both tetrahydrofuran and N,N-dimethylformamide (DMF), even in the presence of different salts, but not in 1,4-dioxane (dioxane). Combined with MD simulations, these results indicate that the AA units are the main cause of aggregation through intermolecular hydrogen bonding, with additional stabilization by the central TTC. The block copolymer chains self-assemble in dioxane by adding cadmium acetate, originating flowerlike inverse micelles with a cadmium acrylate core and the TTC groups in the outer surface of the PS corona. The micelles were used as nanoreactors in the templated synthesis of a single cadmium selenide (CdSe) quantum dot (QD) in the core of each micelle, whereas the shell TTC groups can be converted into thiol functions for further use of these units in hierarchical nanostructures. Only in dioxane where simulations and SEC-MALS suggest an absence of copolymer aggregates prior to cadmium acetate addition do well-dispersed and highly luminescent CdSe QDs form by templated synthesis. These results provide valuable insights into the self-assembly of RAFT copolymers in different solvent systems as it relates to the preparation of emissive QDs with polymer-spaced thiol functionality for binding to gold nanostructures.

Contribution of Size Exclusion Chromatography, Light Scattering, Viscometry, and Conductimetry to the Study of Solution and Gel Properties of a Cationic Polyelectrolyte

Abstract Solution properties of a cationic polyelectrolyte poly (acrylamide-co-diallyldimethylammonium) were studied by size exclusion chromatography with double detection (differential refractive index and light scattering), viscometry, and electrical conductimetry, in water containing different ionic salts. These techniques allow not only the determination of molecular weights, molecular dimensions, and scaling law coefficients, but also study the influence of the counterion on the unperturbed dimensions of the chain. Moreover, swelling properties of crosslinked gel samples of this copolymer, both in pure water and water containing ionic salts, were also studied. The swelling degree is also sensitive to the nature of the anion of the salt and there is a direct correlation between the solution properties of the linear samples and the swelling behaviour of their crosslinked counterparts. Thus, measurements of the polymer in aqueous solution can be used to anticipate the swelling behaviour of the corresponding hydrogel.

Correlation between solution and gel properties of copolymers of acrylamide and diallyldimethylammonium chloride

Abstract Several copolymers formed by acrylamide and diallyldimethyl ammonium chloride containing different fractions of charged diallyl residues, x, were synthesized. Solution properties of linear samples of these copolymers were studied by size exclusion chromatography coupled to differential refractive index and light scattering detectors, which allowed the determination of molecular weight averages, molecular dimensions, scaling law coefficients, and unperturbed dimensions. The results were compared with those of the corresponding homopolymers i.e., polyacrylamide and poly(diallyldimethylammonium chloride). On the other hand, crosslinked samples of the copolymers were prepared and their swelling in water was studied. The correlation between the solution properties of the linear samples and the swelling behaviour of their crosslinked counterparts can be illustrated through the relationship between the characteristic ratio of the unperturbed dimensions and the equilibrium degree of swelling since both magnitudes exhibit a similar dependence on x. Moreover, this dependence is not linear and it passes through a maximum at ca. x ≈ 0.5.