# Enzymatic Synthesis of Biobased Polyesters and Polyamides
## 3 Polyamides
Actually, nylon 6,6 is the first example of aliphatic polyamides, which was firstly produced in the laboratory by Carothers and Hill at DuPont in 1930. After that, this polyamide was prepared by DuPont as nylon 6,6 fiber on 28 February 1935, and then produced at full-scale in July 1935. Regarding nylon 6, it was firstly developed by [PERSON] at IG Farbenindustrie in 1938, for the purpose of reproducing the properties of nylon 6,6 without violating the patents [70; 71]. At present, 66% of nylon 6 production is used as fibers, 30% is applied as engineering thermoplastics, and the rest 10% is consumed as films. For nylon 6,6, 55% of the current production is used as fibers, and the remainder is applied as engineering thermoplastics. Other nylons like nylon 4,10, nylon 6,12, nylon 10,10, nylon 11 and nylon 12 are commonly used as high performance materials [72]. Semi-aromatic polyamides consist of both aliphatic and aromatic fragments in the polymer main chain. Especially, polyphthalamides (PPAs), a type of semi-aromatic polyamides, are defined by ASTM D5336 as \"polyamides in which at least 55 mol % of the carboxylic acid portion of the repeating unit in the polymer chain is comprised by a combination of terephthalalc acid (TPA) and isophthal acid (IPA)\" [73]. Compared to aliphatic polyamides, semi-aromatic polyamides are much stiffer, rendering the polyamides with higher mechanical strength and better thermal resistance. In addition, semi-aromatic polyamides possess many other merits such as high heat chemical/abrasion/corrosion resistance, good dimensional stability, superior processing characteristics and direct bonding to many elastomers. Semi-aromatic polyamides can be used as thermal engineering materials and high performance materials, which have found various applications in many areas, for example, in marine, automotive industry, oil industry, electronics, machinery, domestic appliances, medical devices, personal care, and so on. Examples of semi-aromatic polyamides are PA 6,T, poly(nonamethylene terephthalalamide) (PA 9,T), and poly(decamethylene terephthalalamide) (PA 10,T). They are commercially produced by many companies such as DuPont (Zytel(r)HTN, PA 6,T), Solvay (Amodel(r), PA 6,T), EMS-GRIVORY (Grilamid(r)HT, PA 6,T), Mitsui (ARLEN(r), PA 6,T/6,6), Kuraray (Genesta(r), PA 9,T), and Evonik (VESTAMID(r)HTplus, PA 6,T/X or PA 10,T/X) [74; 72]. Aromatic polyamides are normally referred to wholly aromatic polyamides, or aramids in which at least 85% of the amide linkages are directly attached to two aromatic groups [73; 75; 76]. Due to the amide linkages and the rigid aromatic structures, the stiff rod-like aromatic polyamide chains interact with each other by strong and highly directional hydrogen bonds and \(\pi\)-\(\pi\) stackings. Therefore, aromatic polyamides possess outstanding thermal and mechanical resistance, and excellent chemically inert property, but a poor solubility and processability. Aromatic polyamides are high performance materials that are used as advantageous replacement for metals or ceramics, cut-resistant, flame resistant and high-tensile strength synthetic fibers and coatings, bullet-proof body arm, protective clothing, electrical insulation materials, sealing materials, composites, and so on. Examples of aromatic polyamides are PPPTA and poly(\(m\)-phenylene isophthalamide) (PMPI). These two aramids are the most well-known commercially available aromatic polyamides, with the trademark of Kevlar(r) (DuPont) and Nomex(r) (DuPont), respectively. Besides, some aromatic polyamides display liquid crystalline properties. For example, the solid-state PPPT (Kevlar(r), DuPont, Wilmington, DE, USA) is an example of main chain lyotropic liquid crystal polymers [55]. Similar to polyesters, polyamides can be generally synthesized via two methods: (1) step-growth polycondensation of diacids/diesters with diamines, or \(\omega\)-amino acids/esters; and (2) ring-opening polymerization of lactams.