9 - Experimental Methods

Abstract

In this chapter test procedures are provided to determine the properties of both the precursor form as well as the final ionomer. Most important among these properties are equivalent weight (EW) and melt flow (MF). Infrared spectra are very useful for many purposes: to determine equivalent weight (EW), to follow the chemical reactions of the functional groups, and to check the completeness of hydrolysis are just a few examples of how they can be utilized. Polymer precursors, sulfonyl fluoride, and carboxylic ester, can be hydrolyzed using solutions of sodium or potassium hydroxide. The solution can be aqueous or a mixture of an organic solvent, such as dimethyl sulfoxide (DMSO) and water to increase the rate of hydrolysis. The sulfonyl fluoride precursor form can undergo reactions with many reagents. In discussing ion exchange equilibrium, it is frequently necessary to express the concentration of ions in the polymer phase, requiring somewhat arbitrary assumptions of the volume of electrolyte occupying the polymer phase. Titration is used to calibrate other analytical methods. Its major limitation is the difficulty of drying the polymer in the proton form to a known water content value. A number of titrations of samples of different EWs can form the basis of a calibration curve for the faster infra red analysis of the precursor resin. Next to EW of an ionomer the melt flow (MF) of precursor polymer is an important characteristic of an ionomer. It can be conveniently be determined by a device called a melt indexer.