Since the effect of dextran, as a plasma expander, differs wide1y according to its molecular weight, the dextran solutions of various molecular weight has been studied by light scattering and viscosity methods. According to the Zimm plot method, the weightaverage molecular weight, M
w, radius of gyration, R
g, and second virial coefficient, A
2, were obtained for (1) solutions dissolved at 25°, (2) the solutions heated at 80° for 2 hr and (3) mixed solutions of two polymers dissolved at 25°. The relation of A
2=4.90×10
^<-2>M
-0.426 between A
2 and M
w is obtained in common for (1) to (3). R
g for the case (1), on the other hand, decreased at first with increase of M
w and reached a minimum at M
w=110000 and then increased at M
w=2500000. For the case (2), the value of R
g increased by heating. For the case (3), R
g was larger than the values expected from those of both components. The data for cases (2) and (3) are expressed by the equation R
g=1.67×10
-7M
w0.187. The relation [η]=6.95×10
-4M
w0.493 was also obtained for the intrinsic viscosity [η] of these solutions. It is concluded that the dextran molecules are dissolved in more extended state in aqueous solution when the solutions are heated or when the sample is a mixture of dextrans of different molecular weight.
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