Tackling the Thermodynamic Stability of Low-Ceiling Temperature Polymers for the Preparation of Tough and Chemically Recyclable Thermoplastic Polyurethane-Urea Elastomers

Abstract

Thermoplastic polyurethane-ureas (TPUUs) from biobased, depolymerizable polyesters are promising as high-value polymeric materials for a circular economy. We demonstrate the bulk room temperature polymerization of β-methyl-δ-valerolactone (βMVL) using HCl (as a solution in ether) as a simple acid catalyst to prepare low molar mass polyols. One of the key challenges of poly(β-methyl-δ-valerolactone) (PβMVL) is the non-negligible equilibrium monomer concentration ([M]eq) at room temperature and above. To mitigate the consequences of residual monomer that results from βMVL polymerization, we utilize strategies including (i) rapid distillation to rid the polymer of residual monomer, (ii) sequestration of remaining monomer with diamines to prepare diamidodiols in situ along with the polyol, which can subsequently be used directly as chain extenders in TPUU syntheses, or (iii) the copolymerization of βMVL with lactone monomers that exhibit a higher ceiling temperature to prepare copolymers with varying degrees of crystallinity, improved thermal stability, and reduced residual βMVL content. The aliphatic polyols can then be used as soft-segments in a one-pot approach to prepare TPUUs by reacting with isophorone diisocyanate and chain extending with water. The resulting TPUUs are tough, elastic materials that can be chemically recycled by depolymerization to βMVL, which can be used to prepare new TPUUs with comparable properties.