Proton NMR study of molecular motion in bulk and in highly drawn fiber polyamide-6

Abstract

Abstraet. The proton motion in bulk and highly drawn fiber polyamide-6 has been studied by field cycling relaxometry and proton line shape measurements. The dips in the T~ dispersion allowed for the determination of the ~4N quadrupole coupling tensor. The fact that only one set of Z4N nuclear quadrupole resonance lines has been found shows that all N-H groups in nylon-6 are H-bonded. A striking difference in the main line width transition and the low-frequency molecular dynamics has been observed between a slowly cooled "bulk'" polyamide-6 sample and a rapidly cooled and highly drawn "fiber" sample by wide line proton nuclear magnetic resonance line shape and spin-lattice relaxation time measurements. This result is consistent with the picture that shearing melt processing procedures, such as spinning, plant stable and long-lived crystallization nuclei into the amorphous phase which impose additional motional constraints on the surroundings and inhibit the self-diffusion process.

Confinement-Induced Change in Chain Topology of Ultrathin Polymer Fibers

“…In order to investigate the nanoconfinement effect in the amorphous region of the NFs, the molecular mobility of the NFs was evaluated through measurements of the spin–lattice relaxation time in the laboratory frame, T 1 , using 1 H solid-state NMR. The spin–lattice relaxation is induced by the reptation-like displacement of the nylon-6 amorphous chains; thus, the amorphous structure can be analyzed through T 1 measurements. , The spin–lattice relaxation behaviors of the NFs were fitted using a double-exponential decay model, and the T 1 value for the double-exponential decay process was obtained using the following equation: where M e is the intensity of the excited spin at equilibrium (τ ≥ 5 T 1 ) and M τ is the intensity of the excited spin at the delay time (τ). Component A, which exhibited rapid decay initially, was related to spin diffusion, while component B originated from the spin–lattice relaxation induced by the molecular motion of the chains. , Therefore, the T 1,B value was suitable for evaluating the molecular mobility of the amorphous chains in the NFs.…”

“…The spin−lattice relaxation is induced by the reptation-like displacement of the nylon-6 amorphous chains; thus, the amorphous structure can be analyzed through T 1 measurements. 54,55 The spin−lattice relaxation behaviors of the NFs were fitted using a doubleexponential decay model, and the T 1 value for the doubleexponential decay process was obtained using the following equation:…”

Nuclear spin relaxtion in liquids and gases

“…An increase in 5-coordinated Al is also observed. Blinc et al 106 studied the proton motion in bulk and highly drawn fiber polyamide-6 by field cycling relaxometry and proton line shape measurements. The dips in the T, dispersion allowed for the determination of the nitrogen-14 quadrupole coupling tensor.…”

Electron paramagnetic resonance of stressed fibre nylon 6: annealing effects

“…It is well known [1] that modifying the boundary conditions to which the polymer has been exposed during solidification may lead to completely different macroscopic properties and different glass transition temperatures [5]. fibres and cast products, for instance, exhibit orders of magnitude of different mechanical properties.…”

“…The difference is due to the reduction of structural defects upon drawing and the inhibition of selfdiffusion owing to the super-structure induced by thermomechanical treatment. The results of this EPR study are to be compared with the wide line transition observed by proton NMR [5] in nylon 6.…”