Cleavable Additives for Deconstructable, Recyclable Polyurethane Thermosets

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Polyurethane (PU) thermosets are difficult to chemically recycle due to permanent cross-linking.
• Existing methods for PU deconstruction are often impractical, requiring complete precursor substitution.
• Cleavable additives (CAs) offer a promising, cost-effective alternative but haven't been explored in end-linked systems like PUs.

Purpose of the Study:

• To develop a generalizable theory for predicting minimum CA loading for end-linked network deconstruction.
• To experimentally validate the use of silyl ether-based CAs (BCSs and TCJs) in PU thermosets.
• To demonstrate the potential for PU circularity through additive-enabled deconstruction and repolymerization.

Main Methods:

• Development of a reverse gel-point theory to guide CA loading.
• Incorporation of bifunctional cleavable strands (BCSs) and trifunctional cleavable junctions (TCJs) into PU networks.
• Experimental validation of selective dissolution, material property tuning, and chemical repolymerization.

Main Results:

• A predictive theory for minimum CA loading was established.
• Low loadings (5-12 wt%) of BCSs and TCJs enabled selective PU dissolution.
• TCJs showed higher deconstruction efficiency, and combined additives allowed property tuning.
• Repolymerization of deconstructed PU fragments regenerated materials with retained mechanical performance over multiple cycles.

Conclusions:

• Cleavable additives are a viable strategy for enhancing the circularity of polyurethane thermosets.
• The developed theoretical framework provides a foundation for applying CAs to various end-linked polymer networks.
• This approach offers a practical route to recyclable polyurethane materials.