Research Article Biocompatible and Biodegradable Ultrafine Nanoparticles of Poly(Methyl Methacrylate-co-Methacrylic Acid) Prepared via Semicontinuous Heterophase Polymerization: Kinetics and Product Characterization Henned Saade, 1 María de Lourdes Guillén, 1 Judith Cabello Romero, 1 Jesús Cepeda, 1 Anna Ilyna, 2 Salvador Fernández, 1 Francisco Javier Enríquez-Medrano, 1 and Raúl Guillermo López 1 1 Departamentos de Procesos de Polimerizaci´ on y S´ ıntesis de Pol´ ımeros, Centro de Investigaci´ on en Qu´ ımica Aplicada, Blvd. Enrique Reyna No. 140, 25294 Saltillo, COAH, Mexico 2 Departamento de Nanobiociencias, Facultad de Ciencias Qu´ ımicas, Universidad Aut´ onoma de Coahuila, Blvd. V. Carranza y Jos´ e C´ ardenas Vald´ es S/N, 25280 Saltillo, COAH, Mexico Correspondence should be addressed to Ra´ ul Guillermo L´ opez; guillermo.lopez@ciqa.edu.mx Received 24 August 2016; Accepted 31 October 2016 Academic Editor: Sajjad Haider Copyright © 2016 Henned Saade et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Ultrafne nanoparticles, less than 10 nm in mean diameter, of the FDA approved copolymer methyl methacrylate- (MMA-) co- methacrylic acid (MAA), 2/1 (mol/mol), were prepared. Te method used for the preparation of these particles stabilized in a latex containing around 11% solids includes the dosing of the monomers mixture on a micellar solution preserving monomer starved conditions. It is thought that the operation at these conditions combined with the hydrophilicity of MMA and MAA units favors the formation of ultrafne particles; the propagation reaction carried out within so small compartments renders copolymer chains rich in syndiotactic units very likely as consequence of the restricted movements of the end propagation of the chains. Because of their biocompatibility and biodegradability as well as their extremely small size these nanoparticles could be used as vehicles for improved drug delivery in the treatment of chronic-degenerative diseases. 1. Introduction The copolymer methyl methacrylate- (MMA-) co-methacrylic acid (MAA), 2/1 (mol/mol), is a biodegradable material long time approved by the FDA, which is used for the elaboration of drug-loaded pills because of its water solubility at pH > 7 [1]. Tis copolymer is marketed under the commercial name of Eudragit S-100 (ES-100) [1]. Many literature studies have documented the preparation of drug-loaded micro- and nanoparticles making use of ES-100. Te processes involved usually include the dissolution of a drug-copolymer mixture in a suitable solvent which is subsequently evaporated to fnally obtain the drug-copolymer particles. Tese particles usually show mean diameters in the order of hundred nanometers [2–11]; the exception is the work of Dai et al. [3] who obtained drug-loaded nanoparticles with 37 nm in mean diameter, as measured by quasi-elastic light scattering (QLS). It is noticeable that none of these processes include the polymerization step. In fact, reports on preparation of poly(MMA-co-MAA) 2/1 mol/mol nanoparticles via poly- merization were not found in our literature search. Tis is at odds with the increased potential of smaller particles as drug carriers, which could be produced by an appropriate polymerization method. In accordance with literature, drug- loaded polymeric nanoparticles with diameters of less than 50 nm and, more specifcally, ranging 10–30 nm are very attractive. Tey would show the ability to cross through the intestine wall and enter the blood stream [12]; because of their smallness, their ability to circumvent the immunological system would be increased allowing its circulation in the Hindawi Publishing Corporation International Journal of Polymer Science Volume 2016, Article ID 7674620, 8 pages http://dx.doi.org/10.1155/2016/7674620