Computational Characterization of Nylon 4, a Biobased and Biodegradable Polyamide Superior to Nylon 6

Abstract

This study is an attempt to develop a theoretical methodology to elucidate or predict the structural characteristics and the physical properties of an isolated polymeric chain and its crystalline state precisely and quantitatively. To be more specific, conformational characteristics of a biobased and biodegradable polyamide, nylon 4, in the free state have been revealed by not only ab initio molecular orbital calculations on its model compound but also nuclear magnetic resonance experiments for the model and nylon 4. Furthermore, the crystal structure and solid-state properties of nylon 4 have been elucidated by density functional theory calculations with a dispersion force correction under periodic boundary conditions. In the free state, the nylon 4 chain forms intramolecular N–H···O=C hydrogen bonds, which force the polymeric chain into distorted conformations including a number of gauche bonds, whereas nylon 4 crystallizes in the fully extended all-trans structure (α form) that is stabilized by intermolecular N–H···O=C hydrogen bonds. The intermolecular interaction energy (Δ E CP ) in the crystal was accurately calculated via a counterpoise (CP) method contrived here to correct the basis set superposition error, and the ultimate crystalline modulus ( E b ) in the chain axis ( b axis) direction at 0 K was also evaluated theoretically. The results were compared with those obtained from the α and γ crystalline forms of nylon 6, and, consequently, the superiority of nylon 4 to nylon 6 in thermal stability and mechanical properties was indicated: the Δ E CP and E b values are, respectively, −214 cal g –1 and 334 GPa (nylon 4), −191 cal g –1 and 316 GPa (α form of nylon 6), and −184 cal g –1 and 120 GPa (γ form of nylon 6). In conclusion, nylon 4 is expected to be put to practical use as a tough environmentally friendly polyamide.

Structure–Property Relationships of Poly(glycolic acid) and Poly(2-hydroxybutyrate)

“…In our previous studies, , the counterpoise (CP) method , to correct for the basis set superposition error (BSSE) of polymer crystals was developed to evaluate interchain interaction energies. Here, the methodology has also been applied to the PGA crystal.…”

“…The PGA crystal was structurally optimized at the B3LYP-D/6-31G­(d,p) level and compared with that determined by X-ray diffraction . The interchain interaction (cohesive) energy was evaluated via the counterpoise (CP) method for the basis set superposition error (BSSE) correction − and compared with those of other typical polymers. The stiffness and compliance tensors and Young’s moduli of PGA crystal were calculated and compared with those of other polymers.…”

Thermal and Mechanical Properties of Poly(methylene oxide) Polymorphs Unraveled by Periodic Density Functional Theory

“…Interchain Cohesive Energy and the Basis Set Superposition Error (BSSE). In a previous study, 35 we have developed a counterpoise (CP) method 28,36 to correct for the basis set superposition error (BSSE) of polymer crystals. In this study, the BSSEs of t-PMO and o-PMO were evaluated by the method.…”

An Integrated Cofactor/Co‐Product Recycling Cascade for the Biosynthesis of Nylon Monomers from Cycloalkylamines

“…Similarly, 6‐aminohexanoic acid (6‐AmHA) can be cyclized into ϵ ‐caprolactam by employing suitable ring‐cyclizing enzymes, serving as valuable alternative starting material to obtain nylon 6 [6–8] . Nylon 4, 5 and 6 are polyamides that can be used for the engineering of plastics, tire cords, carpeting, and food‐packaging materials, owing to their superior thermal and mechanical properties [7c–d] . To date, many biocatalytic approaches for the production of ω‐AAs have been developed.…”