Polymer-particle interfacial effect on the bond exchange rate of vitrimer composites

Recently, polymer networks with dynamic covalent bonds, called vitrimers or covalent adaptable networks, have attracted significant attention for their reprocessability owing to the transient characteristics of the dynamic bonds in crosslinked networks. For enhancing mechanical properties, highly tunable silica particles can lead to widened possibilities of chemical reactions on polymer-particle interfaces. Also, the tunable structures of the crosslinked network will allow control of the relaxation behavior of the crosslinked network to improve reprocessability. However, the covalently crosslinked or confined polymer-particle interface will alter the resulting properties abruptly.

In order to understand the bulk reprocessability of multicomponent composite systems, we need to deconvolute the interfacial effect of polymer-particle interface from bulk polymer-polymer domains. We designed mechanically resilient and reprocessable polymer composites by introducing surface-functionalized silica particles as a dual tunable moiety. We modify the surface of particles with functionalities that allow them to dynamically crosslink into the network themselves and study the kinetics of crosslinking and degradation. We use Aza-Michael adducts with the silica particles modified to have amine surface functional groups. The trimethylolpropane triacrylate (TMPTA) and various molecular amine crosslinkers form a dynamic covalent crosslinking network and particles are added that also bond with the resin through the additional Aza-Michael reaction. We examine how the functionalized particles affect not only the bond exchange rates of the composites but also detect how the polymer-particle interface impacts the overall bond exchange rates and mechanical properties. In addition to the insights gained by designing new composite systems with dynamically bonding particles, our studies of polymer-particle and polymer-polymer interfaces will play a large role in moving this work towards applications.