Estudo da copolimerização em mini emulsão de metacrilato de metila/metacrilato de etila / Study of methyl methacrylate/ethyl methacrylate in mini emulsion copolimerization

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Reduction of volatile organic compounds (VOC) usage is a constant environmental demand. Polymeric aqueous emulsion of low surfactant contends produced from direct miniemulsion synthesis are used with advantages to replace organic solvents media as well as aqueous emulsions of high surfactant concentration. Water as continuous phase and organic monomers with low solubility in water are used. This emulsion can be thermodynamically or kinetically stabilized by surfactant agents and / or hydrophobic agents. In free radical miniemulsion polymerization the stabilized organic site acts as a reactor, forming a kinetically stable polymeric dispersion. Depending on the emulsion preparation technique and polymerization rates, at the end of polymerization, several mean particle diameters (Dp) and several size particle distributions (DSD) are possible. Among the emulsion polymerization techniques, miniemulsion polymerization stands out, since kinetic stabilization allows to reduce the need for different types and large amounts of surfactants, where the reaction sites are the monomer droplets formed from scission of the monomer phase or by fusion of even smaller droplets, kinetically stabilized by surfactants and hydrophobic agents resulting in nanoparticles. The water media allow outstanding heat transfer rates as well as mass transfer rates that do not interfere in conversion rates from moderate to high. On this work, a methacrylate polymer based with specific physical properties for the development of materials for Dentistry application, drove the choice of the copolymer obtained from methyl methacrylate (MMA) and ethyl methacrylate (EMA) monomers as they reactivity ratios were: 1.08 and 0.98, respectively, which theoretically would allow obtaining a statistical or random copolymer. Polymerization temperature effect (50, 60 and 80oC) on: overall conversion and kinetic reaction, Dp, DSD, glass transition temperature (Tg) and melting temperature (Tf) of the obtained copolymer, were studied using gravimetric analysis, laser spectrometry spreading (LSS) and differential scanning calorimetry (DSC). The synthesized copolymer at 60o C was also characterized by Fast Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance analysis (NMR) for verification of copolymer organic functions, and gel permeation chromatography (GPC) to determine distribution and mean molar mass. The addition of hydrophobic agent and the use of ultrasound, made possible to obtain volumetric particle diameter as low as 280 nm and polydispersity of 1.60 with average molar mass of 2.16 x 106 g/mol. From the polymer characterization (RMN, FTIR e DSC) it was possible to conclude that a random or alternating copolymer was obtained, as expected

ASSUNTO(S)

nanoparticulas metacrilatos ethyl methacrylate polimerização em emulsão methil methacrylate copolimerização copolimerization mini emulsion nanoparticles

ACESSO AO ARTIGO

Documentos Relacionados