Encapsulation of Montmorillonite by RAFT-mediated emulsion polymerization for the preparation of nanostructured films with anisotropic properties

Author(s)

Rodrigo Duarte Silva

• Document type: Doctoral Thesis
• Press: Lorena.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI)
• Defense date: 2017-03-06

Examining board members

Amilton Martins dos Santos; Fábio Herbst Florenzano; Reinaldo Giudici; Mauricio Pinheiro de Oliveira

• Advisor: Amilton Martins dos Santos

Abstract

This work describes the synthesis of hybrid polymer latexes containing natural Montmorillonite clay (MMT) by reversible addition-fragmentation chain transfer (RAFT)-mediated surfactant-free emulsion polymerization. Firstly, amphiphilic copolymers with different structures and compositions were prepared by RAFT polymerization in solution and characterized by hydrogen nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC). The interaction between these copolymers (referred to as macroRAFT agents) and the MMT surface was studied by experimental adsorption isotherms, which were adjusted by theoretical adsorption models. MacroRAFT agents based on acrylic acid (AA), poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA) displayed affinity for MMT as shown by the \"L-type\" (Langmuir) isotherms obtained. The hybrid latexes prepared using these macroRAFT agents were analyzed by transmission electron microscopy at cryogenic temperatures (cryo-TEM), which revealed polymer-decorated MMT platelets. The adsorption isotherms of cationic macroRAFT agents based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), PEGA and BA were of the \"H-type\" (high affinity). These RAFT macroRAFT agents allowed the preparation of stable dispersions of MMT/macroRAFT agents complexes, which was verified by dynamic light scattering analysis (DLS), and their use in the synthesis of hybrid latexes led to the formation of a polymer layer surrounding the MMT platelets. Nanocomposite films obtained from stable cationic latexes of poly(methyl methacrylate-co-n-butyl acrylate)/MMT showed better thermal stability and better mechanical properties than polymer films prepared without addition of clay as shown, respectively, by the results of thermogravimetric analysis (TG) and dynamic mechanical analysis (DMA) of the final materials. (AU)

• FAPESP's process: 11/20533-8 - Encapsulation of montmorillonite through RAFT controlled radical polymerization in emulsion for the production of nanostructured films with anisotropic properties
• Grantee: Rodrigo Duarte Silva
• Support Opportunities: Scholarships in Brazil - Doctorate