Mechanical properties at the sub-micrometric length scale (hardness and elastic modulus) from instrumented indentation testing are often extracted assuming linear elasticity in the initial portion of the unloading curve. The method is nowadays widely accepted as a convenient tool to interpret depth-sensing data; however, it is a matter of controversy when applied to porous polymeric materials due to their time-dependent behavior. More recently, Loubet and co-workers applied continuous stiffness measurements (CSM), consisting of superimposing a small oscillation to the quasi-static component of loading, to the study of the mechanical properties of polymers and proposed a new model to account for the apparent increase in the contact area detected at the first stages of contact.

The present works offers a comparative study between the Loubet’s model using CSM and the procedure yielding a single reading from the onset of unloading. A wide range if ionic-exchange resins with different functional group’s nature and morphology in terms of pore diameter have been investigated. The most important equations employed for each method will be presented and the advantages and disadvantages of employing one procedure or the other are discussed in detail. The differences found between the results obtained from both approaches are discussed in relation to the nature and degree of the porous polymeric resin. Finally, the mechanical properties in terms of hardness and elastic modulus will be correlated with the main thermic and chemical properties determined by using thermogravimetric analysis and differential scanning calorimetry and Fourier-Transfer infrared, respectively.