Molecular Mobility In Polymers Research Articles

NMR studies of molecular mobility in uniaxially stretched oriented polymers

AbstractThe effect of elasticlike uniaxial tension on molecular mobility in polymers have been studied over a wide temperature range using the broad‐line NMR technique. The studies were carried out on oriented semicrystalline samples of nylon 6, poly(ethylene terephthlate), polypropylene, polyethylene, polyoxymethylene, poly(vinyl alcohol), and polytetrafluorethylene. Above the low‐temperature transition the NMR spectra are reversibly transformed under tension. Increases in the second moments of the spectra are attributed to weaker molecular motion in stressed polymers. The only exception is polypropylene, in which the reverse, i.e., enhancement of molecular mobility, can be observed in a certain temperature range. In the spectra of polymers stretched above the glass transition temperature the narrow component decreases, thus indicating inhibition of micro‐Brownian motion, a phenomenon we call “mechanical vitrification.” Such mechanical vitrification is proved to result from reduction in the number of possible tie‐chain conformations in the non‐crystalline regions and not from closer packing of chains. In discussing the results we use the experimental data on the reduction of the number of gauche isomers under tension (on average, one transition of a gauche link to the trans state causes at least five methylene groups in the main chain to become immobile). The results of studies of molecular mobility in stretched polymers are used for more accurate definition of the mechanisms of molecular motion at different temperatures. A method for evaluation of the energy of intermolecular interactions which hinder small‐scale motion at low temperature is suggested.

An investigation of molecular mobility in polymers under rubbing contact

The results of investigations into the molecular mobility of polymer materials are reported. Under frictional interaction, certain structural variations take place in the surface layers and influence the molecular mobility; the effect of loading, the speed of the relative sliding and the material of the counterface are discussed.

Molecular mobility in polymers under cyclic loading

Using the NMR method the authors have investigated thermal molecular movement in polymers under the conditions of fatigue tests. They have found that the increase in molecular mobility under cyclic loading (cycle frequency 1–10 Hz) is due only to general self-heating of the polymer. Heating of the specimens as a result of hysteresis heat release takes place uniformly throughout the volume.

The effect of the solvent on molecular mobility in polymer concentrates

The molecular mobility (MM) of polar groups present in poly- p-chlorostyrene in two thermodynamically differing solvents, i.e. a “good” solvent such as toluene, and a “poor” one such as isopropylbenzene, was studied. It was found that the MM parameters in concentrated polymer solutions depend only on the volume fraction of the polymer present, and are independent of the thermodynamic quality of the solvent. The effect of this quality will be evident at moderate polymer concentrations at φ 2<0·4. The MM will be larger in a good solvent. The differences in the concentration dependence of the parameters characterizing the MM in the 2 solvents enabled us to come to some conclusions about the structure present in the solution within this concentration range.

On the Motion of Polymer Molecules Studied by the Electrochromism Method

Abstract It is shown that electrochromism, i.e., changes in spectral characteristics of dye solutions in an electric field, may be used to investigate the molecular mobility of polymers. The method is compared with others (NMR, ESR, and luminescence).

Molecular mobility in polymers with long-chain side groups

Molecular mobility in polymers with long-chain side groups