Toughening of Glassy Supramolecular Polymer Networks

A modular approach for the design of two-component supramolecular polymer (SMP) networks is reported. A series of materials was prepared by blending two (macro)monomers based on trifunctional poly(propylene oxide) (PPO) cores that were end-functionalized with hydrogen-bonding 2-ureido-4[1H]pyrimidinone (UPy) groups. One monomer was based on a PPO core with a number-average molecular weight (M_n) of 440 g mol^-1. The SMP formed by this building block is a glassy, brittle material with a glass transition temperature (T_g) of about 86 °C. The second monomer featured a PPO core with an M_n of 3000 g mol^-1. The SMP formed by this building block adopts a microphase-segregated morphology that features a rubbery phase with a T_g of -58 °C and crystalline domains formed by the UPy assemblies, which act as physical cross-links and melt around 90-130 °C. Combining the two components allows access to microphase-segregated blends comprised of a rubbery phase constituted by the high-M_n cores, a glassy phase formed by the low-M_n component, and a crystalline phase formed by UPy groups. This allowed tailoring of the mechanical properties and afforded materials with storage moduli of 37-609 MPa, tensile strengths of 2.0-5.4 MPa, and melt viscosities of as low as 11 Pa s at 140 °C. The materials can be used as reversible adhesives.