Blended vinylogous urethane/urea vitrimers derived from aromatic alcohols†
Vitrimers belong to the class of covalent adaptable networks and are cross-linked polymers, which undergo dynamic, associative exchange reactions under thermal treatment, making these networks permanent as well as dynamic. In this work a feasible synthesis route for the acetoacetylation of aromatic alcohols, which expands the selection of acetoacetate monomers for the synthesis of vitrimers, is introduced. Bisphenol-A, resorcin, 2,7-naphthalenediol and 1,1,1-tris(4-hydroxyphenyl)ethane are chosen as examples for commercially relevant di- and trifunctional alcohols used for countless applications, e.g. epoxy resins, phenolic resins and polyester-networks, which are in general not reprocessable. In contrast, aromatic alcohols provide the basis for the prepared vitrimers, representing a reprocessable alternative to the established materials. Model studies are conducted to enlighten the undergoing condensation, substitution and transamination reactions in the emerging vinylogous urethane/urea mixtures, investigating solvent and catalyst effects and determining activation energies. Utilizing the findings from the model studies for the preparation of vitrimers, 16 elastomeric and thermosetting blended poly(vinylogous urethane/urea) networks are prepared by bulk/solvent polymerization, showing short stress-relaxation times of up to 0.7 s at 130 °C and activation energies of ca. 45–150 kJ mol−1 with a broad range of material properties. Moreover, the materials show remarkable reprocessing, reshaping, shape-memory and self-healing properties.