Sustainable, Malleable, and Recyclable Castor Oil-Derived Poly(urethane urea) Networks with Tunable Mechanical Properties and Shape Memory Performance Based on Dynamic Piperazine–Urea Bonds

Castor oil (CO)-derived polyurethanes (PUs), denoted CPUs, are drastically limited because they cannot be reprocessed, reshaped, or recycled and because they show low strength, poor toughness, and insufficient functionality due to their permanently cross-linked structure with a high cross-link density and a soft backbone. Herein, we developed novel reversible piperazine–urea bonds (PaUBs) from inexpensive piperazines and isocyanates and incorporated the PaUBs into CPUs to fabricate sustainable and reprocessable poly(urethane urea) covalent adaptable networks (CANs). We synthesized the CANs from CO, N-(2-hydroxyethyl) piperazine (HEP), and 4-methylenedicyclohexyl diisocyanate (HMDI) via a catalyst- and solvent-free approach. The CANs showed variable tensile behavior over a wide range from a soft elastomer to tough and hard plastics. They also exhibited excellent malleability, stable reprocessability, and multiple recyclability, in which their original properties were recovered after several thermal recycling or remolding cycles. The CANs possessed excellent shape memory performance and reconfigurability, allowing them to be reprocessed into various complex shapes without using a mold. The advanced sustainable CANs based on dynamic PaUBs have great potential application as alternatives to traditional fossil-derived elastomers and plastics.