Alkyl-Substituted Polycaprolactone Poly(urethane-urea)s\nas Mechanically Competitive and Chemically Recyclable Materials

We\nreport the mechanical performance and chemical recycling advantages\nof implementing alkyl-substituted poly(ε-caprolactones) (PCLs)\nas soft segments in thermoplastic poly(urethane-urea) (TPUU) materials.\nPoly(4-methylcaprolactone) (P4MCL) and poly(4-propylcaprolactone)\n(P4PrCL) were prepared, reacted with isophorone diisocyanate, and\nchain-extended with water to form TPUUs. The resulting materials’\ntensile properties were similar or superior to a commercially available\npolyester thermoplastic poly(urethane) and had superior elastic recovery\nproperties compared to a PCL analogue due to the noncrystalline nature\nof P4MCL and P4PrCL. Additionally, monomers were recovered from the\nTPUU materials in high yields via ring-closing depolymerization using\na reactive distillation approach at an elevated temperature and a\nreduced pressure (240–260 °C, 25–140 mTorr) with\nzinc chloride (ZnCl<sub>2</sub>) as the catalyst. The thermodynamics\nof polymerization were estimated using Van’t Hoff analyses\nfor 4MCL and 4PrCL; these results indicated that the propyl group\nin 4PrCL results in a lower practical ceiling temperature (<i>T</i><sub>c</sub>) for P4PrCL.