Taking plastics with a pinch of salt: Polyester-based polyelectrolyte complexes: from synthesis to decomplexation

Large amounts of plastic are polluting marine ecosystems and continue to accumulate due to the remarkable chemical and physical stability of conventional plastics. As current collection, reuse, and recycling strategies have proven insufficient to address this problem, it is essential to develop alternative approaches to prevent further accumulation of plastic in the oceans. This thesis investigates polyester-based polyelectrolyte complexes (PECs) as a potential solution, incorporating an on-demand trigger that enables the material to dissolve upon leaking into the ocean. PECs are formed by mixing aqueous solutions of oppositely charged polyelectrolytes. The ionic interactions between these polymers are reversible and can be cleaved by exposure to charged molecules, such as the salt present in seawater, which weakens the ionic crosslinks and eventually dissolves the complex. Additionally, incorporating a polyester backbone into the polyelectrolytes could further enable (bio)degradation of the dissolved PEC, providing a viable end-of-life scenario. The main aspect of this work revolves around the synthesis of polyester-based polyelectrolytes. Melt polycondensation and ring-opening polymerization strategies were employed, making predominant use of biobased monomers. First, we demonstrate a synthetic route toward polyester-based PECs via melt polycondensation. The resulting PEC exhibits reduced brittleness compared to state-of-the-art vinyl-based PECs. Furthermore, the lower charge density along the polymer backbone enables processing at reduced temperatures and without the need for plasticizers. When exposed to a seawater mimic, the polyester-based PEC dissolves within 30 minutes. Subsequently, we explore ring-opening polymerization of lactones as an alternative route towards polyester-based polyelectrolytes, allowing improved control of the polydispersity. Through systematic post-modification of the ring-opened lactones, we examine the effects of charge density and hydrophobicity of the polyelectrolytes on the complexation behavior, and the resulting thermomechanical properties are highlighted. By combining polyelectrolytes of varying charge densities and hydrophobicities, the salt resistance, glass transition temperature, and tensile properties of the PECs can be systematically tuned. Overall, this thesis presents synthetic strategies for polyester-based polyelectrolytes, with an emphasis on structure-property relationships. The findings advance the understanding of polyester polyelectrolyte synthesis and elucidate the influence of charge density and hydrophobicity on material properties.