Reprocessable polymer networks can undergo structural rearrangement via dynamic chemistry under proper conditions, making them a promising candidate for recyclable crosslinked materials, e.g., rubber tires. This research field has been focusing on a variety chemistries. However, there has been lack of fundamental physical theory explaining the relationship between relativet levels of dynamic linkages vs. permanent linkages between crosslinks and reprocessability. Based on the classical Flory-Stockmayer analysis on network gelation, we developed a related analysis for reprocessable polymer networks in order to quantitatively predict the critical condition for reprocessability. Our theory indicates that it is unnecessary for all bonds to be dynamic to make the resulting network reprocessable. As long as there is no percolated permanent network in the system, the material can fully rearrange. To experimentally validate our theory, we used a thiol-epoxy network model system with various dynamic linkage compositions. The stress relaxation behavior of resulting materials supports our theoretical prediction: only 50 % of linkages between crosslinks need to be dynamic for a tri-arm polymer network to be reprocessable. This analysis provides the first fundamental theoretical platform for designing and evaluating reprocessable polymer networks and indicates that the presence of permanent linkages between crosslinks, if below a critical level, is not a hindrance to reprocessability of dynamic polymer networks and associated robust property recovery.

What level of dynamic linkages relative to permanent linkages between crosslinks allows for reprossability of polymer networks with robust recovery of properties: A Flory-Stockmayer analysis

254th National Meeting (2017)

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