HOMEWORK 2
(Due to: 15.10.2015)
1.
The following measurements of osmotic pressure were made on a solution of poly(isobutylene) in cyclohexane at 25°C: c (kg/m
3
) 20 15 10 5
П (N/m 2
) 1578 992 528 203
Obtain the average molecular weight of the polymer.
2.
The following experimental measurements were made in an osmometer on solutions of a sample of polymer dissolved in benzene at 25 °C:
Conc. (g/ ml) Osmotic head (cm of solvent)
0.1925x10
-2
0.58
0.3850x10
-2
1.33
0.5965x10
-2
2.30
0.7825x10
-2 3.40
Given that the density of benzene at 25°C is 0.8737 g/ml and that the value of the gas constant is 84800 g cm/ deg-mole estimate the number average molecular weight.
3. A sample of poly (vinyl chloride) comprises 4 fractions as follows:
10 g of polymer of degree of polymerization:500
5 g of polymer of degree of polymerization:1000
1.0 g of polymer of degree of polymerization:2000
0.3 g of polymer of degree of polymerization:5000
Calculate the number and weight-average molecular weights for the sample (atomic weights;
H=1; C=12; Cl=35.5).
4.
Polymer samples A, B, and C are available, and it is suspected that the molecular weights of these samples may be in the ranges of 1000, 10.000 and 100.000 grams per mole, respectively. What methods may be used to determine the molecular weight of each of these samples? Discuss.