ISSN:
1435-1536
Keywords:
Chain length dependence
;
self-diffusion
;
NMR pulsedfield gradient technique
;
melt
;
polyethylene
;
polystyrene
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The self-diffusion coefficients in melts of polyethylene fractions and polystyrene standards were measured by the NMR pulsed field gradient technique and compared with those measured by other techniques. The data agree very well if one takes into account the molar mass distribution of the samples and the free volume of the matrix. For molar masses much higher than the critical molar massM c, reptation is confirmed,D ∼M −2 holds. BelowM e=Mc/2 the self-diffusion coefficients corrected for constant free volume show approximately the dependenceD ∼M −1 confirming Rouse-like diffusion. This result was also obtained by investigating the self-diffusion of the molecules with different molar masses of a polyethylene fraction with a rather broad molar mass distribution aroundM e andM c, i. e. diffusion in a constant matrix. In the molar mass region betweenM c and about 3 ·M c the observed molar mass dependence of self-diffusion can be explained by tube formation. The constraint release model of Graessley seems to slightly overestimate the self-diffusion coefficients.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01412750
Permalink
