Synthesis and characterization of thermoreversible K-Ionomers based on butyl rubber: a simple one-step crosslinking method and a novel crosslinking system

A simple one-step thermoreversible polymer crosslinking method and a novel reversible ionic crosslinking system (maleic anhydride and KOH) have been developed which is performed on high physical mechanical properties and valuable reversibility. The system involves the acid–base reaction of maleic anhydride with potassium hydroxide to form ionic thermoreversible cross-linking network. A series of ionic thermoreversible cross-linking butyl rubber which is called K-ionomers are obtained as a function of the ratio of KOH to maleic anhydride by simple one-step solution method. The ratio is held at 5:1, the degrees of neutralization is up to 70 % that reprocessibility is possible. X-ray diffraction (XRD) shows the presence of microphase-separated aggregates for K-ionomer that act as physical cross-links which are responsible for its outstanding mechanical property and valuable reversiblity. Very high mechanical property in tensile strength up to 5 Mpa was obtained. The reversibility of K-ionomers is investigated in detail by Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Hot stage microscopy. ATR-FTIR results show a desired shift back from carboxylate reacted with carboxylic acid to cyclic anhydrides and KOH depending on heating. Hot stage microscopy shows that the reprocessibility of K-ionomer is detected up to 169 °C.