Toughening and Stiffening in Thermoreversible Diels-Alder Polymer Network Blends

Abstract

The thermophysical properties, mechanical behavior, andhealingperformance of Diels-Alder-based polymer networks can be tunedwidely by changing the molar mass, functionality, and stoichiometricratio of the multifunctional diene (e.g., furan) and dienophile (e.g.,maleimide) monomers. Blending furan-functionalized monomers with ahigh and low molar mass opens a new dimension in tuning the propertiesof the resulting reversible polymer network blends (RPNBs), containingdifferent ratios of elastomeric and thermoset phases, with low andhigh crosslink densities and glass transitions below and above roomtemperature, respectively. Increasing the thermoset content up to20 wt % raises the gel transition temperature (T (gel)), relaxation time (tau), rubbery plateau modulus, ultimatestress, and Young's modulus of the stiffened elastomers, whilethe strain at fracture and self-healing efficiency remained mostlyunchanged. Conversely, the addition of up to 20 wt % of the elastomerphase drastically toughens the thermosets because of stress dissipation,which can suppress the stress concentration in the phase-separatednetwork blends. The blends showed higher stress and strain at breakwhile retaining similar Young's moduli. The toughness increasesup to an order of magnitude at 50 wt %, compared to the pure thermoset.The phase-separated morphologies were evidenced by the presence ofthe T (g)'s of the pure networks inDSC and DMA.