Alkyl-Substituted Polycaprolactone Poly(urethane-urea)s as Mechanically Competitive and Chemically Recyclable...

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Polymers

Background:

• Thermoplastic poly(urethane-urea) (TPUU) materials are versatile but often face challenges in recyclability.
• Incorporating poly(ε-caprolactones) (PCLs) as soft segments can influence TPUU properties.
• Alkyl substitution on PCLs offers a route to tune material performance and recyclability.

Purpose of the Study:

• To investigate the mechanical properties of TPUU materials with alkyl-substituted PCLs.
• To evaluate the chemical recyclability of these novel TPUU materials.
• To understand the influence of alkyl groups on PCL thermodynamics and TPUU performance.

Main Methods:

• Synthesis of poly(4-methylcaprolactone) (P4MCL) and poly(4-propylcaprolactone) (P4PrCL).
• Fabrication of TPUU materials via reaction with isophorone diisocyanate and chain extension with water.
• Mechanical testing (tensile properties, elastic recovery) and chemical recycling via ring-closing depolymerization.
• Thermodynamic analysis using Van't Hoff for polymerization.

Main Results:

• TPUU materials exhibited comparable or superior tensile properties to commercial polyester poly(urethanes).
• Enhanced elastic recovery was observed compared to PCL analogues due to the noncrystalline nature of P4MCL and P4PrCL.
• High yields of monomer recovery were achieved through reactive distillation depolymerization (240-260 °C, 25-140 mTorr) using ZnCl2 catalyst.
• Propyl group in P4PrCL led to a lower practical ceiling temperature (Tc).

Conclusions:

• Alkyl-substituted PCLs are effective soft segments for high-performance, recyclable TPUU materials.
• The developed depolymerization method allows for efficient monomer recovery, promoting a circular economy for TPUUs.
• The study demonstrates a pathway for designing advanced polymers with tailored mechanical and recycling characteristics.