Isocyanate- and Solvent-Free Route to Thermoplastic Poly(amide-urea) Derived from Renewable Resources

This study reports on tailoring biobased aliphatic poly(amide-urea) (PAU) thermoplastics by means of reactive extrusion requiring neither the use of diisocyanate monomers nor time-consuming PAU polycondensation in a separate step prior to melt processing. Key intermediate is N,N'-carbonyl-biscaprolactam (CBC), which enables rapid and temperature-programmable polycondensation of biobased diamines and difunctional aminoamides (AA) derived from diamines and dicarboxylic acids. Within a few minutes during melt processing using a twin-screw extruder, CBC-mediated advancement of biobased diaminoamides affords high molecular weight PAU. Whereas PAUs derived from short-chain AAs are stiff and brittle materials with high melting temperatures close to thermal decomposition; the incorporation of AAs derived from sebacic acid and dimer fatty acid renders urea-functional thermoplastics flexible and processable. Hence, the variation of oligomethylene segment lengths by incorporating short- and long-chain AA building blocks in CBC-mediated melt-phase polycondensation governs PAU melting temperature (124-249 degrees C), Young's modulus (100-1900 MPa), tensile strength (6-51 MPa), and elongation at break (0.3-230%).