Exercise $3$: Influence of the solvent on viscosity

The intrinsic viscosity of poly$($vinyl acetate$)$ fractions was measured in a series of

solvents at increasing temperatures. The intrinsic viscosities are given in $m\frac{L}{g}.$ the parameters of the Mark$-$Houvink law are given for each solvent and temperature in the last two columns.

$1-$ How can we explain qualitatively the fact that we observe

simultaneously an increase in a and K with temperature?

$2-$To give this explanation a quantitative character, calculate, at each

temperature, from viscosimetric data, the ratio $R\frac{g_{}^2}{M}$ or $R{g}_{}^{(2)is\text{t}\text{h}\text{e}\text{r}\text{a}\text{d}\text{i}\text{u}\text{s}of\text{g}\text{y}\text{r}\text{a}\text{t}\text{i}\text{o}\text{n}\text{u}\text{n}\text{d}\text{e}\text{r}\text{t}\text{h}\text{e}\text{c}\text{o}\text{n}\text{d}\text{i}\text{t}\text{i}\text{o}\text{n}\text{s}}\backslash$theta $.$We will take the Flox$-$Flory law. Deduce the length of the statistical link.

$3-$Compare the undisturbed dimensions obtained:

has. At the same temperature in two solvents. Comment

b$.$ At different temperatures in the same solvent. Is the observed variation compatible with that expected for a chain with a valence angle and symmetrical hindered rotation potential on the valence cone.

Could a variation of inverse sign also be observed? how to interpret it$?$

$4-$Based on the data obtained for the largest molar mass in

acetone, calculate the variation of the expansion coefficient a of the chain with the

temperature. How can we interpret it$?$