TO DETERMINE THE MOLECULAR MASS OF POLYSTYRENE FROM VISCOSITY MEASUREMENT

 

APPARATUS REQUIRED

Viscometer

 Polystyrene

 stopwatch

beakers

CHEMICALS REQUIRED

Toluene 1% polystyrene (1gm in 100 ml toluene

THEORY

The resistance which a liquid resist exerts known as viscosity. so it is reciprocal of fluidity. The apparatus used for determination of viscosity of liquid is known as Ostwald's viscometer. The molecular weight of the polymer can be determined by viscosity against of its own molecules is measurement

When solute is added to the pure solvent, viscosity same manner. of the solution increases. In the addition of polymer to the solvent increases its viscosity, over that of pure solvent. The specific viscosity is denoted by ηsp & is given by Coefficient of viscosity (η)sp = t2 -t1/t

where,

t1= flow time of solution

t2 = flow time of pure solvent

relation It was shown by Staudinger that an empirical exist between intrinsic viscosity and molectar weight of the polymer. ie [η] = K M°

Where 'k' and a are constants for a specific polymer in a specific solvent. Thus for polystyrene. we have

(η) = 11 x 10-8 M°/0.725

M=. [η]/(11 X 10-8)]. °/0.725

Now if C' be the concentration of the solute, then when the graph of 'n'infeversus 'C' is plotted, a straight line is obtained. The extrapolation of the line (i.e.C-O) gives the intercept equal to intrinsic viscosity.

PROCEDURE

1gm of polystyrene was kept in a beaker. About 50 ml of toluene was added to it & stirred fill all the polystyrene dissolved completely. Then the soin was made 100 ml transfering it inside a volumetric flask of 100 ml. Then. 20 ml solution was beaker similarly in 4 different beakers. of it was left as it was & other were by adding 5ml, 10ml & 15 ml toluene respectively Then the flow rate of all the dilutions including pure toluene were measured using Ostwald's is cometer Then the limiting viscosity & molecular mass of polystyrene was determined with the help of graph.

OBSERVATION AND CALCULATIONS

Now, from the graph of ηsp/c versus C, [(η)] = intact = 2.5 poise.

we have, molecular weight of polystyren e

(M) = [η /11×10-3] °/0.725 

       = 2.5÷11×10-3 °/0.725

      = 1779.95 gm/cm³

Results

 Hence the molecular mass was found to be 1779.95g/cm³

CONCLUSION

The molealer mass of polystyrene can be determined from viscosity measurement.