Defence of doctoral thesis: Linnea Cederholm – Thermodynamic Toolkit for Chemical Recycling to Monomer

The design of polymeric materials for a circular economy is, to a largeextent, a challenge of thermodynamics. The work presented in this thesishas explored the thermodynamic features of ring-opening polymerizationand ring-closing depolymerization, to develop polymeric materials andrecycling strategies for chemical recycling to monomer.First, statistical copolymerization was explored as a tool for internal endcapping,in order to enhance the thermodynamic stability of an aliphaticpolyester. However, a drawback of the improved thermodynamic stabilitywas a negative impact on the recyclability. Next, the solvents effect on thethermodynamic equilibrium was studied. It was found that, apart from thedecreasing effect that dilution had on the ceiling temperature as aconsequence of the increased entropy, the properties of the solventstrongly influenced the equilibrium. This was studied for three differentsix-membered cyclic monomers, two lactones and one carbonate, whereceiling temperature of the more polar monomers where more influencedby the solvent effect. This solvent effect was used to realize chemicalrecycling to monomer of polylactide via ring-closing depolymerization,with high conversion and high selectivity. Finally, three different A–B–Atype block copolymers were designed. The influence of block componentson the mechanical properties and recyclability was investigated, showingthat the midblock chemical structure had a strong impact on the Young’smodulus, the elongation at break, as well as the on the ring-closingdepolymerization behavior.

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