Leveraging the bio-enabled muconic acid platform via phospha-Michael-addition: intrinsically flame-retardant nylon-66/DOPO copolymers†

Efforts towards developing biobased chemicals primarily focus on generating molecules chemically analogous to those derived from petroleum. The compositional uniqueness of biomass can also be leveraged to reinvigorate the chemical industry with novel multifunctional molecules. We demonstrate the value and potential of these new compounds in the case of Nylon-66, a commodity polyamide that suffers from poor flame resistance. The conventional route to inhibit flammability involves blending the polymer with additives, which improves flame retardance but has mechanical property trade-offs. Herein, we address these limitations through the synthesis of a novel multifunctional comonomer derived from renewably sourced trans-3-hexenedioic acid (t3HDA). t3HDA was subjected to a one-pot isomerisation and functionalisation strategy where the alkene migrates to render this molecule active for phospha-Michael-addition (MA) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a halogen-free flame-retardant (FR). This DOPO-functional counit was polymerised into Nylon-66 copolymers and compared with physical blends of DOPO and Nylon-66 using a suite of thermomechanical techniques; analysis revealed comparable crystallinity, flame retardance, and thermomechanical properties for the DOPO-functionalised bio-advantaged polyamides. The synthesis strategy presented herein can be extended to a variety of functional groups and novel properties, a platform for creating bespoke bio-advantaged polymers.