What chemical in hairspray makes the hair "hold"?

Dear gee3929-ga 

Hair spray is a solution of a polymer in a liquid. The solution
reaches the hair in a fog of tiny droplets. When they strike they join
up coating the hair thinly with the polymer. It evaporates almost
instantly it touches the hair. As it dries it welds or bonds between
the strands of hair.
Different types of hair spray are sold, for use on different types of
hair. They differ in the formulation of
the holding polymer used, and also in the way the spray is produced.
One common polymer used in hairspray is a silicone called
polydimethylsiloxane. Another is polyvinylpyrrolidone. A detailed
explanation can be found on: http://www.psrc.usm.edu/macrog/nvp.htm
and try the main page for further information on polymers
http://www.psrc.usm.edu/macrog/index.htm
For general reading on hairspray:
http://www.pg.com/science/haircare/hair_twh_121.htm?rc=-5
For more on polymers:
http://scifun.chem.wisc.edu/chemweek/polymers/polymers.html
The BASF Group discusses research on new polymers in hairspray.
http://www.basf.de/en/corporate/innovationen/fakten/polymerforschung/Weg_zur_Innovation/Luviset.htm?id=V00--f1z*Rh**bsf500

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hairspray chemical OR chemicals OR chemistry hold
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polymers hairspray
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