Solvent-Free Synthesis of Acetal-Containing Polyols for Use in Recyclable Polyurethanes

Polyurethanes (PUs) are used in a large variety of applications due to their broad range of chemical and mechanical properties. Recently, the recyclability of PU has also gained much attention. The recyclability of PU materials can be improved greatly by introducing cleavable acetal bonds. We first present a solvent-free synthesis of acetal-containing polyols via the polyaddition of various diols and divinyl ethers using heterogeneous catalysts. The use of a heterogeneous catalyst such as aluminosilicate K10 and Siral 70 allows for simple filtration of the reaction mixture, yielding pure polyol and enabling reuse of the recovered catalyst. The acetal-containing polyol obtained from 1,4-butanediol (B14) and 1,4-butanediol divinyl ether (B14 DVE) was reacted with 4,4′-methylene diphenyl diisocyanate (4,4′-MDI) to prepare acetal-containing thermoplastic polyurethane materials. These materials can be depolymerized under acidic (soft phase) and basic conditions (hard phase), allowing for 90% recovery of the precursor diol and 83% recovery of the isocyanate precursor. This work shows that both the synthesis and recycling of polyurethanes are possible under mild and industrially applicable conditions.