Coagulative Nucleation in the Copolymerization of Methyl Methacrylate–Butyl Acrylate under Monomer-Starved Conditions

Coagulative nucleation in the copolymerization of methyl methacrylate–butyl acrylate (MMA-BA) via semicontinuous emulsion heterophase polymerization (SEHP) under monomer-starved conditions in latexes with high solid content (50.0 wt %) and low concentrations of surfactant is reported. The SEHP technique allows the obtention of latex with high colloidal stability and has potential industrial application in polymer synthesis. High instantaneous conversions (>90%) and a high-ratio polymerization rate/addition rate (Rp/Ra) ≥ 0.9 were obtained at low times until the final copolymerization, which confirmed the starved conditions in the systems at the highest surfactant concentrations. The particle size exhibited a linear size increment at conversions between 0 and 40% induced by homogeneous nucleation, a transition region between 40 and 50%, and non-linear behavior at higher conversions by coagulative nucleation. These three behaviors were also observed in the particle surfactant coverage area (Sc), Z-potential, particle coagulation rate (dNp/dt) by the Smoluchowski model, final particle size (Dpz), and number particle (Np) through the reaction. By means of transmission electron microscopy (TEM) images, the onset of coagulation was observed from 50% of conversion until the end of the reaction. In addition, in both processes of copolymerization, tacticity was displayed (mainly syndiotacticity)

100 Cartas para Paulo Freire de quienes pretendemos Enseñar

Realizar un texto colectivo como “100 Cartas para Paule Freire de quienes pretendemos Enseñar”, es un desafío al reunir el aprehender desde el sentido profesional de la educación y con el espíritu de transformación, desde la educación como un espacio endógeno de revolución y exógeno a las comunidades y sociedades, en busca de un sentido de identidad. Hoy desde una crítica decolonial, antirracista, feminista y ecologica en la construcción de un sentido real que busque enfrentar el sistema hegemónico y destructivo que se ha impuesto con explotación, sangre y libertades de nuestro pueblo