- As we have discussed, co-solvency and co-non-solvency are important effects to understand when we talk about thermodynamic aspects of polymer dissolution. We have also talked about water and ethanol acting as cosolvents at room temperature for dissolving poly(methyl methacrylate) and acting as co-non-solvents for PNIPAM.a) Explain why water and ethanol are acting as cosolvents for the PMMA system; that is, why a mixture of water and ethanol is able to dissolve PMMA. Sketch chemical structures while explaining.
b) Let us consider a small experiment: assume that we have used two solvent mixtures with water-to-ethanol ratios varying as 60:40 and 40:60. An osmotic pressure technique was employed with both these systems at room temperature (298 K) and the data obtained for PMMA is given below in Table 1. The solvent (mixture) density varies as 0.931 g/cm3 and 0.887 g/cm3 for 60:40 and 40:60 mixtures.
Table 1. Concentration versus osmotic head data for poly with different ratios of solvent mixture (water to ethanol).
(i) Determine the molecular weight of the polymer and the second virial
coefficient (A2) in each mixture of solvents. Assume that A3 and subsequent
coefficients are negligible.
(ii) Based on the obtained data, which solvent mixture is a good solvent for
(iii) Looking at the molecular weights, A2 values, and osmotic data, are the
obtained results reasonable? Justify your choice with proper reasoning.
(iv) Are these ideal or non-ideal solutions? Explain.
- Mark-Houwink equation-based question:
A) Explain the Mark-Houwink relationship and its significance in calculating the molecular weight of a polymer.
B) When does the Flory equation is similar to the Mark-Houwink equation?