Synthesis and characterization of an interpolyelectrolyte complex based on Eudragit E100 and L100 copolymers

Abstract

In recent decades, copolymers based on methacrylic acid (MAA) and methyl(ethyl)methacrylate have been widely used as auxiliary components in drugs, especially in those for peroral administration. In the international market, the most popular materials of this kind are those produced by the Roehm Pharma (Germany) on the basis of copolymers of MAA and methyl methacrylate (MMA) under the trade name Eudragit. The list of these MAA – MMA copolymers includes virtually all kinds of materials necessary for the production of drugs absorbed in the stomach (E grade) and in different parts of the intestine (L and S grades), and special grades (RL, RS, and RL) are available for the production of drugs with controlled release [1]. Despite this broad spectrum of products, investigations aimed at increasing the range of applications of Eudragit copolymers in drug technology are currently in progress [2]. Since most of the aforementioned copolymers are polyelectrolytes, one possible way of modification of their structure is via inclusion of such polymers into so-called interpolyelectrolyte complexes (IPCs). This is achieved through scientifically justified selection of oppositely charged polymers – polycations and polyanions – constituting such systems [3, 4]. According to specification of the Roehm Pharma products, Eudragits of the E grade (representing copolymers of dimethylaminomethyl methacrylate and neutral esters of methacrylic acid) dissolve at pH 6 (due to ionization of the carboxy groups) and are recommended for obtaining enteric-soluble coatings [1]. At first glance, interaction between these copolymers is impossible, which probably explains the absence of published data on the formation of IPCs between two grades of Eudragit. Only a few papers were devoted to IPCs between Eudragits and some other oppositely charged polyelectrolytes [2, 4]. Sometimes, only the fact of such complexation was established, while the conditions of formation and compositions of IPCs were not studied in sufficient detail [5]. As is known, the interpolyelectrolyte reaction between weak polyelectrolytes is possible both in acid media (via charging a polyacid in the positive chain of the polycation) and in basic media (via charging a polyamine in the negative chain of the polyanion) [3]. The aforementioned grades of Eudragit dissolve at pH 6.0 and, under such conditions, both E and L type copolymers are ionized to a rather low extent. Nevertheless, despite the low density of charge, we believe that (taking into account the possibility of charging one component on the other), the formation of IPCs between these copolymers is possible. The aim of this study was to determine the conditions of formation, the composition, and the structural features of IPCs between Eudragit E (polycation) and Eudragit L (polyanion).