Overcoming the Tradeoff Between Processability and Mechanical Performance of Elastomeric Vitrimers

TLDR

Vitrimers are polymer networks with dynamic covalent bonds that allow reconfiguration while maintaining a constant number of bonds, yet their melt viscosity decreases with temperature, making them harder to process than typical thermoplastics and creating a tradeoff between processability and mechanical performance. This study introduces a strategy to overcome that tradeoff in elastomeric vitrimers. The approach cross‑links a functionalized low‑glass‑transition polymer matrix with an incompatible high‑glass‑transition polymer bearing complementary pendant groups, creating microphase separation, restricting dynamic cross‑linking at interfaces, and selecting a hard‑phase Tg between use and processing temperatures. Microphase‑separated materials produced by reactive extrusion exhibit superior tensile strength and creep resistance at room temperature and improved processability at high temperature compared to conventional homogeneous vitrimers.

Abstract

Vitrimers are polymer networks with dynamic covalent bonds that allow the network to reconfigure its connectivity while maintaining a constant number of chemical bonds at all temperatures. The melt viscosity of vitrimers thus gradually decreases with temperature. This behavior makes vitrimers more difficult to process than typical thermoplastics using conventional processing techniques, such as extrusion. Although many strategies have been reported to address this issue, it remains challenging to overcome a key tradeoff between improving the processability or the mechanical performance. Herein, this work presents a new strategy for overcoming this tradeoff in the context of elastomeric vitrimers. The approach entails the cross‐linking of a functionalized low‐glass transition ( T g ) polymer matrix with an incompatible high‐ T g polymer featuring pendant groups with complementary reactivity. When compared to a conventional homogeneous vitrimer, the microphase‐separated materials prepared by reactive extrusion present improved tensile properties and creep resistance at room temperature while also exhibiting enhanced processability at high temperature. These enhanced properties are a consequence of the combination of the phase separation between the soft and hard phases, the restriction of dynamic cross‐linking reactions within the interfacial zones, and the judicious selection of the T g of the hard phase to be in between the use and processing temperatures.