Kinetic and Thermomechanical Analysis of Hydrophobic-Hydrophilic Copolymer Thermosets Synthesized via Free-Radical Polymerization

The synthesis of a crosslinked copolymer of hydrophobic and hydrophilic monomers, diglycidyl ether of bisphenol A vinyl ester (VE), and 2-acrylamido 2-methyl 1-propane sulfonic acid (AMPS) respectively, is discussed. A methodology for real-time monitoring of the copolymerization reaction using transmission mode near infrared (NIR) spectroscopy was employed that resolves overlapping peaks associated with the reactive double bonds. The influence of solvent, monomer ratio, and initiator concentration on the kinetic behavior of the system was investigated. The method of Mayo and Lewis was used to provide a qualitative understanding of the microstructure being formed. At low conversions (<15%) and within the compositions of interest, greater VE homopolymerization as compared with AMPS homopolymerization was observed and the product of the reactivity ratios (r(AMPS).r(VE)) was close to 0.5, suggesting the formation of a moderately random copolymer structure. Thermo-mechanical analysis shows large concentrations of AMPS had a plasticizing effect on the network structure. Solvent removal using supercritical carbon dioxide and thermal drying were compared, and the drying technique were shown to have an effect on the glass transition temperature (T-g), with the lowest T-g being 146 degrees C for supercritically dried samples and 121 degrees C for thermally dried systems. Gel permeation chromatography shows that there is a significant fraction of an unbound mobile phase within the network structure that might be acting as a plasticizing agent for the copolymer structure. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115:1419-1427, 2010