Multifunctional Biobased Comonomers for Flame-Retardant Polyamides with Superior Mechanical Properties

Efforts towards developing biobased chemicals primarily focus on generating molecules chemically analogous to those derived from petroleum. However, 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-6,6, a commodity polyamide that suffers from poor flame resistance. The conventional route to inhibit flammability involves blending the polymer with additives, an approach that comes with significant trade-offs on the mechanical properties of the final product compared to the parent polyamide. Herein, we address this limitation through synthesis of a novel multifunctional comonomer derived from renewably sourced trans-3-hexenedioic acid (t3HDA). t3HDA was subjected to a one-pot isomerization and functionalization strategy where the double bond migrates to render this molecule active for phospha-Michael-addition (MA) with 6-oxide6H-dibenz(1,2)oxaphosphorin (DOPO), a prominent halogen-free flame-retardant (FR). This monomer was introduced in the polyamide’s backbone through copolymerization and the obtained polymer was compared to physical mixtures containing proportionate amounts of DOPO and Nylon-6,6. Thermal and mechanical properties of the blends and the FR-grafted polymers were characterized through a suite of techniques that revealed superior crystallinity, thermal, and mechanical properties for the DOPO-tethered bio-advantaged polyamides relative to blends with comparable flame retardance. The synthesis strategy presented herein can be extended for a variety of functional groups for property-modified bio-advantaged polymers.