Photoinitiated degradation

The photoinitiated degradation of a typical melamine cross-linked acrylic enamel studied by using this technique will be discussed. 

Photophysical processes involved in the photodegradation and photoinitiated degradation are ... 

In order to protect polymers against thermal oxidation, it is necessary to add thermostabilizers and/or antioxidants, which themselves contain many chromophoric groups, which can further photoinitiate degradation of the polymer. 

In practice the kinetics of photoinitiated degradation of polymers are more... 

In the photoinitiated degradation, it is important to find the optimum photoinitiator concentration for the most effective initiation of polymer degradation. 

Dye photoinitiated degradation of polymers is a phenomenon commonly known in industry as phototendering, and has been described in a number of pubhcations [49, 86, 1307, 1446, 1787, 1804]. 

Polyvinyl chloride has been modified by photochemical reactions in order to either produce a conductive polymer or to improve its light-stability. In the first case, the PVC plate was extensively photochlorinated and then degraded by UV exposure in N2. Total dehydrochlorination was achieved by a short Ar+ laser irradiation at 488 nm that leads to a purely carbon polymer which was shown to exhibit an electrical conductivity. In the second case, an epoxy-acrylate resin was coated onto a transparent PVC sheet and crosslinked by UV irradiation in the presence of both a photoinitiator and a UV absorber. This superficial treatment was found to greatly improve the photostability of PVC as well as its surface properties. 

Many papers have been published on positive electron-beam resists. These resists are mostly polymers which are degraded upon electron-beam irradiation. The resulting lower molecular weight polymer in the exposed area can be selectively removed by a solvent under certain developing conditions. The development is accomplished by the difference in the rate of dissolution between the exposed and unexposed areas, which is a function of the molecular weight of the polymer. Recently, Willson and his co-workers reported the new type of positive resist, poly(phthalaldehyde), the exposure of which in the presence of certain cationic photoinitiators resulted in the spontaneous formation of a relief image without any development step (/). 

From the studies described above, it was concluded that the presence of unreacted photoinitiator in a cured polymer initiates a free radical degradation of the polymer upon irradiation with UV light. It was further concluded that the rate of degradation is dependent on the structure of the initiator and the initiator concentration. 

Muggli et al. (1998) and others discussed the polymerization behavior of a new class of dimethacrylated anhydride monomers that react to form highly cross-linked degradable networks using different photoinitiation schemes. Polymerizations occurred in seconds to minutes depending on the initiating conditions, and conversions in excess... 

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