One-Step Synthesis and Properties of P4HB Based Thermoplastic Polyurethane Elastomers

A series of depolymerizable and recyclable thermoplastic polyurethanes (TPU) were synthesized through a one-step method using poly(4-hydroxybutyrate) (P4HB) as the soft segment and different diisocyanates and 1,4-butanediol (BDO) as the hard segment. The effects of feed ratio, P4HB molecular weight, chain extender content, and isocyanates on the properties of P4HB based TPU (P4HB-TPU) were studied, and the controllable depolymerization and monomer recovery of P4HB-TPU were also investigated. The thermal properties, mechanical properties, and thermal decomposition recovery of P4HB-TPU were studied using Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, uniaxial mechanical stretching, and other testing methods to illustrate the relationship between polyurethane structure and properties. Results show that when n(—NCO)/n(—OH) is 1.1, tensile strength of P4HB-TPU can reach 37.8 MPa with comparable mechanical performance to commercial TPU. With increase of molecular weight, the P4HB segment started to crystallize and thus caused transition of P4HB-TPU from elastic to plastic polyurethane. The increase of BDO content can improve the mechanical properties of P4HB-TPU to a certain extent, and use of cyclic symmetric isocyanates can effectively improve the tensile strength of materials. Notably, the P4HB-TPU can use Sn(Oct)₂ at 170 ℃, 200 Pa that be depolymerized into γ-BL monomer and achieved a monomer recovery rate of approximately 98%.