Ultraviolet activated substances

[Ez4u2cit]

I recently purchased a bonding agent that is activated by an ultraviolet light (provided as part of the package). After three seconds of exposure to the UV light, the liquid substance turns rock hard. I believe they use the same process with modern dental fillings. Can anyone explain what is the physics/chemistry involved in this reaction.

 

[Bystander]

Polymerization. You want more detail?
https://en.wikipedia.org/wiki/Polymerization

 

[Ez4u2cit]

Thanks. I was looking for the actual mechanism whereby the UV light induces the polymerization.

 

[Kevin McHugh]

The UV light creates a free radical. Then the monomers polymerize via free radical polymerization.

 

[Ez4u2cit]

So why UV light? Is this strictly because it is short wavelength/high energy. In which case, would x-rays work?

 

[Kevin McHugh]

No, the frequencies of X-rays are too high. The freqeuncy of the incident radiation has to be resonant with the electrons in the bond.