Photocrosslinking of Polymers

This is actually an ancient art that dates back to the days of the Babylonians who pho-tocrosslinked pitch for decorative purposes. History aside, however, Minsk et alP rmy be the first chemists who synthesized a photocrosslinkable polymer, poly(vinylcinnamate). The crosslinking reactions can be illustrated as follows  

A detailed discussion of various photoreactions belongs in a book on photochemistry. The following are merely a few brief comments on the background of the reactions that occur in photocrosslinkings to aid those not familiar with the subject. 

When a quantum of light interacts with a molecule in the ground state, the eneigy is absorbed by that molecule and an electron is promoted to a higher eneigy level. The molecule in the process attains an excited state. This phenomenon obeys four laws of organic photochemistry, as was stated by Rino  

Photochemical changes take place only because light is absorbed by the system. 

One photon or one quantum of light activates only one molecule. 

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The photocrosslinking of polymer materials continues to be attractive in many applications for electronic, electrical, insulation and property enhancements. iV-isopropylacrylamide with di-methylmaleinimidoacrylamide has been crosslinked to produce thermally sensitive nano-gels. These gels, made in micellar media, exhibited major changes in the hydrodynamic diameter in the vicinity of the phase-transition temperature of the polymer, with increases of temperature, micellar concentration and chromophore content all decreasing... 

Several studies have appeared on the photocrosslinking of polymers by diazides. jjjggg include polyphenylenes and poly(phenylquinoxoalines). ... 

Photocrosslinking of Polymers with Light-Sensitive Groups... 

Show the reactions of photocrosslinking of polymers bearing azide groups. 

J. L. R. Williams, Photopolymerization and photocrosslinking of polymers, Fortschr. Chem. Forschg. 13, 111 (1969). 

The synthezised photopolymers, A and B, have glass transition temperatures (Tg) of 134 °C and 138 °C, respectively. Due to the thermal radiation of the lamp the polymer films were heated to approx. 80 C, nevertheless during irradiation the photocrosslinking was still carried out in the glassy state. The Tg of the polymers plays an important role in the photocrosslinking of polymer films. When the irradiation was performed at temperatures below Tg the rate of crosslinking decreased due to the reduced mobility of the chromophores. 

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