Example problem PBL Polymers: Case of polyurethanes in hairsprays

Rina and Betty are students of chemical engineering department.  They are barely used hairspray for their hairstyle. When they are assigned to make a report on polymer in daily lives application, they are interested to have small investigation on hairspray. In BASF website, they read this following article:

Women have high expectations, including when it comes to fixing their favorite hairstyle with hairspray. They also expect their hairstyle to keep as long as possible, but of course it should remain natural and flexible. The hairspray should dry quickly but be easy to brush and wash out again in the evening.
Eco-friendliness is another requirement for hairsprays. The new BASF polymer for hair cosmetics, hairsprays can meet these requirements perfectly. The polymers of the polyurethanes class give hair a flexible hold. They are also specially adapted to produce environmentally friendly hairsprays in which water replaces many of the organic solvents. But besides the need for a flexible hold, polymers have to meet other criteria too: they have to interact smoothly with the other hairspray components: the solvent and the propellant. Products containing water as solvent are particularly well received by consumers because of their ecological safety, and indeed legal regulations in many countries now limit the amount of volatile organic compounds (VOC).
As the water content of the hairspray increases, the viscosity rises dramatically and the sprayability suffers. The polymer films are tackier and leave much more visible residue on the hair on brushing out. Completely new polymers therefore had to be found for use in hairsprays with a high water content. Thorough studies of the different polymer classes finally declared the polyurethane family to be the winner.
Polyurethanes have a modular structure. This means that the starting materials (available in BASF) can be varied in numerous ways, allowing the product properties to be selectively designed. Each of the components used has a particular function to perform. Some components are responsible for the property “hard”, others for “soft”, while other polar components make the polymer water soluble. The special feature of polyurethane: the solution viscosity in water is much lower than for conventional acrylate-based polymers and provides improved sprayability.

The functional polymers are shapeless, inconspicuous, often invisible, yet have now become an indispensable feature of everyday life. A main characteristic of these polymers is their extreme efficiency: major effects can be achieved using even the smallest amounts; functional polymers thus behave like polymeric active ingredients. Since functional polymers thus have a large number of different functions, their chemical structures are highly variable and can be assembled from anionic, cationic and neutral monomers.

Rina and Betty are starting to make a concept map to get the whole picture of this polymer. They will use this concept map to make a report on polyurethanes. As they open and read the polymer textbook on related topics, they found that they should learn also on some principles to give more understanding on polymer solution characteristics such as polyurethanes for hairsprays.


  1. What are the criteria of polymers used in hairspray?
  2. Why did BASF declare that polyurethane family to be the winner of polymers for use in hairsprays with high water content?
  3. Why functional polymers become essential in our daily lives and contribute significantly to our standard of living? Give some examples.
  4. How do solvents affect the conformation of polymer in solution ?
  5. How do you describe the polymerization of polyurethane from 1,4 buthanediol and buthyldiisocianate?
  6. How Flory-Huggins polymer-solvent interaction parameter  can be used to account for  the equilibrium thermodynamic properties of polymer solution? When the use of Flory-Huggins lattice theory is least satisfactory ?
  7. How do you determine the solubility parameter for polyurethane and its solvents? Are there any criteria for polymer solvents? Can you determine (and give examples) the good solvents for polyurethane?
  8.    is Flory-Huggins polymer-solvent interaction parameter, which characterizes polymer-solvent interactions, how do you determine this parameter for solution of polyurethane (Mn = 2.5×105 g mol-1) in toluene given that vapor pressure measurements showed that the activity coefficient of solvent in a solution with volume fraction of polymer (2) = 0.250 is 0.989. The ratio of the molar volume of the polymer to molar volume of solvent is defined as x.  How do you describe about this dilute polymer solution based on its value of   ?


  1. Billmeyer, F.W, Textbook of Polymer Science, 3rd ed., Wiley and Sons, NewYork.
  2. Young, R.J. and Lovell, P.A, Introduction to Polymers, 2nd ed.,Chapman and Hall, London.
  3. Harper, C.A, Handbook of Plastics, Elastomers, and Composites, 3rd ed., McGraw-Hill, New York.

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