1378
YOSHINORI TOYOSHIMA AND HIROSHI FUJITA
Application of the Archibald Ultracentrifugal Method for the Study of Dilute Polymer Solutions. 111. Effects of Polydispersity and Nonideality
by Yoshinori Toyoshima and Hiroshi Fujita Department of Polumer Science, Osaka University, Osaka, J a p a n
(Received December 3, 1968)
Sedimentation measurements of the Archibald type were performed on methyl ethyl ketone (MEK) solutions a t 25’ and cyclohexane solutions at 35’ of two polystyrene samples. One sample was a conventional polydisperse polystyrene, and the other a narrow distribution one pQpared by anionic polymerization, but both had comparable weightaverage molecular weights M,. The apparent molecular weight Mapp(t),evaluated at the meniscus of the solution, changed with time t in the qualitative fashion predicted by a theory of Fujita, et al. That is, (i) M a p p ( t ) was independent of time when the solute was monodisperse and its solution was under %-conditions; (ii) Mapp(t)increased with time when the solute was monodisperse and its solution was positively nonideal (ie., the second virial coefficient was positive) ; (iii) M a p p ( t ) decreased with time when the solute was polydisperse and its solution was under %-conditions. I n cyclohexane a t 3 5 O , plots of n/jrapp-l us. co were horizontal over the range of co studied, regardless of the heterogeneity of solute, where Map, is the value of Mapp(t)at t = 0 and c g is the initial concentration of the solution. This plot for the polydisperse solute in M E K at 25’ gave a curve of upward curvature, but the corresponding plot for the monodisperse solute in the same solvent was linear over the entire range of co studied (
