Messung der Selbstdiffusion im System Polystyrol‐Benzol; Temperatur‐, Konzentrations‐ und Molekulargewichtsabhängigkeit

Abstract

ZUSAMMENFASSUNG:Die Selbstdiffusion des Benzols und des Polystyrols im System Benzol-Polystyrol wird mit Hilfe der Spin-Echo-Technik in Abhlngigkeit von der Temperatur, der Konzentration und dem Molekulargewicht untersucht. Aus der Temperaturabhlngigkeit des Selbstdiffusionskoeflizienten werden Aktivierungsenergien als Funktion der Konzentration und des Molekulargewichtes bestimmt. Die Konzentrationsabhangigkeit wird aufgrund der Vorstellungen uber die behinderte Diffusion und in Anlehnung an die Theorie des Freien Volumens nach Fujita diskutiert. Das berechnete Freie Volumen zeigt bei ungefihr 50 "C ein ausgepragtes Maximum, das sich mit abnehmendem Molekulargewicht abschwacht. Die beobachtete Zunahme des Freien Volumens kann auf Anderungen in der Beweglichkeit der Phenylseitengruppen zuruckgefuhrt yerden. Die Temperaturabhangigkeit des Freien Volumens zeigt Hinweise auf den Glasubergang. SUMMARY:Self-diffusion of benzene and polystyrene in the system benzene-polystyrene is studied by means of spin-echo-technique as function of temperature, concentration and polymer molecular weight. From the dependence of temperature the activation energies are calculated as function of concentration and molecular weight. The concentration dependence is discussed in terms of restricted diffusion and the Fujita Free-Volume-Theory. The computed free volume shows a significant maximum at 50°C. This effect may be attributed to a change in the mobility of the phenyl side groups of polystyrene and is vanishing with decreasing molecular weight. The free-volume-temperature curves are giving references to the glass transition.

Self-diffusion of polystyrene in solution 1. Experimental results of the NMR pulsed field gradient technique

“…Possible changes in the motional mechanisms with varying polymer concentration and molar mass are disregarded. Another possibility is to postulate that the monomeric friction coefficient ~o is proportional to the friction coefficient of the solvent ~1 at the same concentration, which can be easily obtained from the solvent self-diffusion coefficient [6,24]. Since the motional mechanisms of the solvent molecules and the monomeric units are different, we prefer the former proportionality, although the concentration dependences of ~1 and 7"2 1 are very similar.…”

Deuteron NMR relaxation and molecular motion of polystyrene in solution

“…It should be noted that Kosfeld et a1. 20,21) have performed an extensive study of solvent self diffusion in concentrated polystyrene solutions. The apparent activation energies of the diffusion coefficients increase rapidly with increasing concentration, thus reflecting the decrease of segment mobility.…”

Small-Molecule Probe Diffusion in Polymer Solutions: Studies by Taylor Dispersion and Phosphorescence Quenching

“…46 In this study, a comprehensive investigation of the effects of size, shape, and flexibility on the translational diffusion of small molecule probes in polymer solutions has been undertaken. Sixteen probes with molar volumes ranging from about 70 to over 400 cm 3 /mol have been studied in solutions up to 400-700 g/L in polymer content. To accomplish this study, two complementary and relatively little-employed techniques are used to obtain information on diffusion: Taylor dispersion [47][48][49][50][51][52][53][54][55] and phosphorescence quenching.…”

“…The diffusion of small molecules in polymer solutions has been a subject of considerable study over several decades. − Knowledge of diffusion in polymer−solvent systems is of practical concern. For example, the solvent self-diffusion coefficient, D s , is of interest in designing devolatilization equipment that removes residual toxic species such as monomers and solvents from polymer products .…”