Supramolecular polymers (SPs) consist of monomeric building blocks that associate via directional, non-covalent interactions such as hydrogen-bonding or metal-ligand complexation into macromolecular assemblies. Due to the transient, reversible nature of these bonds, SPs are susceptible to external stimulation and they can be (temporarily) disassembled back into the monomeric species via triggers such as heat or light. Changing the mechanical properties of SP materials by an external stimulus is particularly interesting in the context of healable materials or debonding-on-demand adhesives. However, the development of SP materials whose mechanical properties are comparable to their covalently linked counterparts has remained challenging. We here report the synthesis and characterization of a family of SP networks based on trifunctional building blocks carrying three quadruple hydrogen-bonding ureido-4-pyrimidinone (UPy) groups. Three monomers based on polypropylene oxide (PPO) cores of different molecular weights (ca. 440 – 5000 g/mol) were used. While the SP based on 440-PPO-UPy3 formed a brittle glassy material with a glass transition temperature (Tg) at 84 °C, both 3000-PPO-UPy3 and 5000-PPO-UPy3 adopted phase separated morphologies, with a crystalline phase formed by the UPy-dimers melting around 95–113 °C, and a rubbery phase with a Tg around -60 °C. At room temperature, the latter two materials display Young’s moduli of 28 and 14 MPa, a tensile strength of 1.6 and 0.7 MPa, and a strain at break of 9 and 6%, respectively. Moreover, the various building blocks can be combined to create blends with attractive property combinations. In particular, blending of 440-PPO-UPy3 with higher molecular weight cores allowed a significant increase in both toughness and stiffness. Thus, the combination of these characteristics and the low melt-viscosity affords materials with promising mechanical performance, adhesive properties and attractive (de)bonding-on-demand capabilities that may be useful for a wide range of applications.

Stimuli-responsive supramolecular polymer adhesives exhibiting high toughness and stiffness

256th National Meeting (2018)

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