New family of unsaturated polyamides from novel long-chain biomass-derived diacids
A new class of bio-based aliphatic unsaturated polyamides (PA) is synthesized from C16-rich monounsaturated diacid (C16:1 diacids). C16:1 diacids are derived from fermented biomass intermediates through multistep purifications and hydrolysis. In this regards, we start with a biomass derived feedstock from REG Life Science LLC. The feedstock is a mixture of a variety of saturated and unsaturated C14 to C18 fatty acid methyl esters (FAMEs), fatty diacid dimethyl esters (FDADEs), ω-hydroxyl fatty methyl esters (ω-OH FAMEs) and ω-1 hydroxyl fatty methyl esters (ω-1 OH FAMEs). We aim at extraction of FDADEs to use as the precursor for polyamide production. FDADEs is of our interest as they have ester groups on both ends of their molecule that makes them a great candidate for poly-condensation reaction. However, the other fractions possess only one ester group and act as the chain terminator in the reaction which drastically reduce the reaction conversion and lead to significant decrease in the polymer molecular weight. Therefore, here we develop a separation method to achieve FDADEs with the highest purity to reach a high degree of conversion in the polymerization reaction. The final FDADEs are a mixture of saturated and unsaturated diesters with the chain length from C14 to C18 while the dominated fraction is C16:1 diester. The diester moiety in FDADEs are converted to diacid through a basic hydrolysis. The diacid mixture is dominated by mono-unsaturated diacid with the aliphatic chain length of 16 (C16:1 diacid). The presence of a double bond in the center of the C16:1 diacid is a bio-advantage which distinguishes this diacid from petroleum-based dicarboxylic C16:0 acids.
This bio-advantaged diacid is then utilized to synthesize a new unsaturated homo-polyamide PA6u16. The polymer properties are compared with PA6,16 made from petroleum-based C16 diacid. Moreover, two series of new co-polyamides namely PA6,6-co-PA6u16(x) and PA6,12-co-PA6u16(x) are made by copolymerization of PA6u16 with PA6,6 and PA6,12 respectively. The copolymers are designed to retain the desired thermal and mechanical characteristics of petroleum-based PA6,6 and PA6,12 while spawning the double bond along the polymer backbone. This provides opportunities to add material features such as super-hydrophobicity, corrosion resistance, and flame retardancy by polymer or monomer functionalization.