Photo-Cross-Linking of Polymers

Since many polymers are to a certain degree photo-cross-linkable and photodegradable, the result of the overall reaction depends on the prevailing process, because cross-linking and degradation are competing processes. 

The photo-cross-linkability of a polymer depends not only on its chemical structure, but also on its molecular weight and the ordering of the polymer segments. Vinyl polymers, such as PE, PP, polystyrene, polyacrylates, and PVC, predominantly cross-link, whereas vinylidene polymers (polyisobutylene, poly-2-methylstyrene, polymethacrylates, and poly vinylidene chloride) tend to degrade. Likewise, polymers formed from diene monomers and linear condensation products, such as polyesters and polyamides, cross-link easily, whereas cellulose and cellulose derivatives degrade easily.  

There are several interesting applications reported in the literature, such as insulated wire and cable, UV cross-linking of drawn fibers, and tapes from ultra-high-molecular-weight polyethylene. Semi-interpenetrating networks (IPNs) from acrylates and polyurethanes are suitable as UV curable adhesives with high elasticity, good impact resistance, and excellent adhesion to a variety of substrates.  

The subject of photo-cross-linking is reviewed thoroughly by Ranby et al.  

Calvert, J. G., and Pitts Jr., J. N., Photochemistry, John Wiley Sons, New York (1966). 

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