Date Published: April 16, 2018
Publisher: Springer Berlin Heidelberg
Author(s): Catalina Fuentes, Joel Castillo, Jose Vila, Lars Nilsson.
The use of polymers for the delivery of drugs has increased dramatically in the last decade. To ensure the desired properties and functionality of such substances, adequate characterization in terms of the molar mass (M) and size is essential. The aim of this study was to evaluate the changes in the M and size of PVP-b-PAMPS when the amounts of the synthesis reactants in the two-step radical reaction were varied. The determination of the M and size distributions was performed by an asymmetric flow field-flow fractionation (AF4) system connected to multiangle light scattering (MALS) and differential refractive index (dRI) detectors. The results show that the M of the polymers varies depending on the relative amounts of the reactants and that AF4-MALS-dRI is a powerful characterization technique for analyzing polymers. Using AF4, it was possible to separate the product of the first radical reaction (PVP-CTA) into two populations. The first population had an elongated, rod-like or random coil conformation, and the second had a conformation corresponding to homogeneous spheres or a microgel structure. PVP-b-PAMPS had only one population, which had a rod-like conformation. The molar masses of PVP-CTA and PVP-b-PAMPS found in this study were higher than those reported in previous studies.
In recent decades, the use of polymers as a means of drug delivery has increased. Polymeric micelles have become an attractive option because of their capability to protect and extend the lifetime of a drug. Polymeric micelles can be divided in two categories: hydrophobically assembled micelles and polyion complex micelles, where cationic and anionic segments form polyion complex micelles. In the present study, PVP (poly-vinylpyrrolidone) acts as the hydrophilic nonionic segment and PAMPS (poly-2-acrylamido-2-methyl-1-propanesulfonic acid) as the polyanion segment for the synthesis of PVP-b-PAMPS . In this sense, the use of PVP in polymeric micelles has been demonstrated to form microgels, which showed no toxicity when they were used in saline solutions as a blood extender [2, 3]. In addition, PVP-b-PAMPS in combination with PEG-b-P4VP could be used as a drug delivery system .
In this study, the change in Mw when the amounts of the reactants were varied during each radical reaction, which yielded PVP-CTA and PVP-b-PAMPS, was determined using AF4-MALS-dRI. For the first radical reaction, PVP-CTA was separated in two populations by AF4. The first population displayed an elongated, rod-like or random coil conformation, and the second population had a very different conformation, which scaled constantly in relation to M, potentially suggesting the presence of supramolecular aggregates. The presence of supramolecular aggregates has, to the best of our knowledge, not been reported previously in other studies on the same polymer. Additionally, it was found that different Mw values of PVP-CTA could be obtained by manipulating the amount of AIBN, whereas DMP did not have a large effect on Mw. In addition, the variation in the amount of VP showed no clear relationship with Mw.