| dc.description.abstract | The large values of a, the M.H. exponent, suggest that these molecules are highly extended in the solvents studied. Application of S.F. and other existing theories like I.P. to calculate the unperturbed dimensions lead to very low values (i.e., low steric factor) and high values of a³ (Table 18), suggesting that these molecules are highly extended mainly due to unusual short-range interactions. The observed decrease of [?] with temperature is also in agreement with this trend.
However, if the high extension of these molecules in these solvents is mainly due to unusual solvent effect, then one can expect high A? and low (1) values. But, the A? values obtained by light scattering for these systems are very low and the (1) values are very high, opposite to that expected in good solvents.
Cellulose derivatives also exhibit high values of a and very low values of A? and a decrease of [?] with temperature, which have been interpreted as the typical properties of stiff chain polymers.
Kurata and Stockmayer, based on the large values of a³ obtained by applying Flory equation, concluded that these molecules are highly extended mainly due to the unusually favourable polymer-solvent interactions, rather than to short-range interactions. The recent theoretical studies suggest that the cellulosic chains assume large extensions mainly due to the unusual short-range interactions.
The present experimental data viz., low A? values, large (1) and high a values and decrease of [?] with T, suggest that the incorporation of AN in MMA might have introduced some stiffness in the chain. It is also thought that probably the S.F. equation or variants thereof may have to be modified for such systems. | |
