Enzyme-catalyzed polymerizations at higher temperatures: Synthetic methods to produce polyamides and new poly(amide-co-ester)s

Novozyme-435 (N-435) catalyzed polycondensation reaction between different aliphatic (oligo)esters and diamines by precipitation polymerization at elevated temperatures yields various particulate polyamides and poly(amide-co-ester)s. The reaction between diethylsebacate (DES) and 1,8-diaminooctane (DAO) at 60 °C in dried toluene leads to a low Mn polyamide (NMR: Mn = 520 g mol−1 GPC: Mn = 2000 g mol−1 with Mw/Mn = 1.3). An improved three-step procedure with an adjusted temperature profile and an optimized amount of enzyme in dried diphenyl ether, yields 97% amide bond formation and a polymer with increased molecular mass (NMR: Mn = 5380 g mol−1, GPC: Mn = 4960 g mol−1 with Mw/Mn = 3.5). Three step ring-opening and polycondensation reactions between a cyclic ester (ethylene tridecanedioate) with three different diamines were also performed in dried toluene to obtain the corresponding polyamides. Here, diamine with higher alkyl chain length, i.e. 1,12-diaminododecane shows higher activity towards N-435 catalyzed amide bond formation and therefore the produced nylon-12,13 has higher molecular weight (GPC: Mn = 8250 g mol−1 and Mw/Mn = 5.8) compared to the other nylons. By adopting the three step synthetic protocol, a new series of poly(amide-co-ester)s with Mn up to 17,550 g mol−1 were produced. Melting and thermal degradation behaviors of these copolymers are compared with pure nylon-8,10 and polyester by DSC and TGA. The microstructure of the synthesized polyamides with different end groups was investigated by MALDI-TOF MS analysis while the particles’ morphology was studied by TEM analysis.