Modeling the Effect of Polymer Composition on Ionic Aggregation in Poly(propylene glycol)-Based Ionenes

Ionenes are polymers that contain a small fraction of charged groups in their backbone. These form ionic aggregates that act like reversible cross‐links, conferring interesting material properties to the system. Here, poly(propylene glycol)‐based ammonium ionenes are modeled containing varying amounts of alkyl groups, referred to as hard segments. Experimental results show that hard segment content strongly affects the temperature at the onset of flow, which is related to the dissociation of ionic aggregates. This study aims to show the ionic aggregation and microscopic morphology and how these relate to polymer relaxation behavior. Therefore, we perform molecular dynamics simulations using a simple coarse‐grained model of the system. The aggregate morphology and dynamics as a function of hard segment content is quantified and related to experimental observations. Coarse‐grained molecular dynamics shows ionic aggregation and microphase segregation in segmented ionenes. The model represents ammonium ionenes containing both aliphatic and polypropylene glycol (PPG) segments. Systems with a low amount of PPG (snapshot at right) have more significant microphase segregation and more ordered ionic aggregates; these features correspond to slower relaxation and a broader distribution of relaxation times.