Structure-Morphology-Property Relationships of Polyolefin Ionomers

• Daniel Sayler, Material Science, University of Delaware

• Alex Balzer, Chemical Engineering, University of Delaware
• Elizabeth Kellstedt, Chemistry, University of North Carolina at Chapel Hill

 Ionomers have been previously shown to be beneficial for use in mixed plastic waste. These polymers with ions dispersed along the backbone are believed to cause the formation of ion clusters that behave similarly to crosslinks. Our goal was to to study how these ionomers affect the structure-morphology-property relationships within a single polymer type. To do this, high density polyethylene (HDPE) was functionalized using a post polymerization modification (PPM) functionalization, hydrolysis of acyl phosphonated polyethylene, and ionization of carboxylic acid. This process resulted in an addition of a carboxylate ionic group with a sodium counterion. This was repeated four times, yielding four different ionomers with varying mol % concentrations of the functionized groups: 0.4%, 0.7%, 1.0%, and 1.4%. Each of these ionomers, along with the base HDPE, were characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and rheology. TGA showed a small decrease in the degradation temperatures of the samples as the mol % increased. Similarly, DSC revealed a similar decrease in melting and recrystallization temperatures across the samples. Rheology demonstrated a significant increase in complex viscosity and zero rate viscosity from the base HDPE to even the lowest ionomer mol %, as well as a subsequent smaller increase as the mol % increased across the samples. These trends point to evidence of these ion clusters, and their significant influence on the mechanical and thermal properties of the ionomers.