Synthesis, Characterization and Thermal Stability Study of Styrene-based Ionomers I) Programmed Heating Experiments (10 oC/min to 500 oC)

Ionomers are generally described by copolymers having either acrylic or methacylic acid as one component and the other component is mostly either ethylene or styrene. The objective of this research was to study the thermal behaviour and stability of ionomers of styrene with some alkali metal acrylates. These materials have been synthesized by neutralization of the respective copolymer containing 40 mole percent acrylic acid with sodium and potassium hydroxides in acetone medium.The copolymer of styrene–acrylic acid was made by solution polymerization in methanol using 2,2’-azobisbutyronitrile (AIBN) as initiator under nitrogen blanket at 60 oC. Copolymer composition was calculated from the monomer feed concentration. The ionomer samples were characterized using FTIR technique. Thermal behaviour of the ionomers has been studied under programmed heating in dynamic nitrogen atmosphere by using differential thermal analysis (DTA) and thermogravimetry (TG) and in vacuo using thermal volatilization analysis (TVA) techniques supported by product analysis. The thermal behaviour of the sodium and potassium salts of styrene-acrylic acid copolymer is found to be rather similar. Infrared spectroscopy, mass spectrometry and GC-MS techniques were used to examine the degradation products from TVA degradation. Quantitative measurements of the main product fractions under normal TVA conditions have been made. It is found that the main decomposition of the styrene-acrylic acid salts copolymers starts at about 350 oC and reaches maximum at 450 oC.