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We have studied by single-crystal X-ray diffraction the structure of a cyclic trimer model of nylon 11 (IUPAC name: 1,13,25-triazacyclohexatriacontane-2,14,26-trione). The crystal is organized in layers of hydrogen-bonded rings similar to nylon lamellar crystals. The rings fold both at the amide and methylene regions. Neighbor layers show van der Waals contacts among similar turns, either methylene/methylene or amide/amide. A new type of fold has been found, which includes an amide group and a methylene unit. Such folds may coexist in nylon lamellar crystals with conventional turns similar to the β-turn found in proteins. The orientation of up and down chains in the crystal is different from the orientation usually assumed for nylon 11, which suggests an alternative unit cell for nylon 11. We also include an analysis of the vertical displacement of hydrogen bonded layers found by different authors in nylon 11, which shows that it may vary between zero and three methylene units. In the trimer crystal we f...

Two crystalline structures for nylon 5,6 have been studied by transmission electron microscopy, electron diffraction, and X-ray diffraction. A γ form or an α-like phase can be obtained as a functio...

We have synthesized, by the active esters method, several polyamides (nylons) n,3 with n = 4−6, 8, 9, and 12. We have studied these polymers and another group of similar polymers obtained from carbon suboxide. The methods used involve IR and NMR spectroscopies, calorimetry, electron diffraction and microscopy, and X-ray diffraction. These polymers show structural polymorphism, in the sense that powder samples prepared directly after polymer synthesis have a poorly ordered structure that is different from that found in single crystals and oriented films. Single crystals have been obtained by solution crystallization; they usually have irregular shapes and borders. Electron diffraction of single crystals shows that the molecular chains pack in a quasi-hexagonal rectangular cell. Electron and X-ray diffraction of oriented films shows that the molecules pack in either an orthorhombic or a monoclinic unit cell, depending on the parity of n. The molecules are linked by a unique network of hydrogen bonds, with t...

We have determined the structure of acetyl-(glycyl-e-aminocaproyl 2 -NH-propyl) by X-ray diffraction methods as a model of nylon 2/6. The structure obtained confirms the tendency of glycine copolyamides to adopt a structure similar to polyglycine II with hydrogen bonds in three different directions. Our results also show that the e-aminocaproyl residue adopts a conformation in which its two terminal peptide groups form hydrogen bonds with an angle of about 120 o . This observation might be of interest in order to understand the polymorphism of nylon 6

We analyze the conformation of the two forms (hexagonal and tetragonal) of the title compound with the linked-atom least-squares (LALS) methodology applied to X-ray data previously reported and with AMBER energy optimization algorithms. We conclude that both helical forms are right handed, with very similar conformational angles, and report their coordinates. The transition between both forms appears to be mainly determined by the side chain interactions.

Etude sur des lamelles obtenues par cristallisation a partir de solutions diluees. Traitement de monocristaux entre 100 et 270 o C. Transition hexagonale-tetragonale