Photochemical reaction crosslinking

These polymers need to be made photosensitive for use as photoresists and this is achieved by the incorporation of bisazide sensitisers. On exposure to light the photochemical reaction induced by the bisazide results in rapid crosslinking of the polymer rendering it insoluble in the developing solvent. 

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. 

Thiadiazoles readily undergo photochemical reactions (see Section 4.24.3.1) which have been utilized in polymer chemistry. For instance, polymers of type (46), formed by condensation of bisphenol epichlorohydrin copolymers and a l,2,3-thiadiazole-4-carboxylic acid, undergo photochemically induced crosslinking (70SST(1)444). This type of process is useful in the printing and electronic industries. 

The Excited States of Poly(vinyl cinnamate) and their Photochemical Reactivities. The photochemical reaction of PVCi is believed to be Intermolecular crosslinking of the polymer chains by the formation of the four-membered ring from the central double bonds of cinnamoyl-oxy groups( ), and it is known that many experimental results from the photochemical reaction are interpreted well(6) if we can postulate that the reaction is the concerted cycloaddition according to the Woodward-Hoffmann s rule(lB). This means that the four-membered ring... 

Guillet et al. (52) have shown that solar photochemical reactions can be carried out using crosslinked poly(ethylenevinyl acetate) (EVA) beads as a solvent. The beads can be exposed in solar ponds and the products recovered by extraction. Figure 12 shows data on the rate of photolytic conversion of the a-(o-tolyl)aceto-phenone when exposed in the solid bead and in benzene solution. Identical rates and quantum yields were observed in both media, showing that the rate of cyclizations of this type are independent of the internal viscosity of the medium. 

The photoerosslinking reaetion was followed by observing ehanges in the ultraviolet and infrared absorption speetra. It was shown that the simple photochemical reaction occurs stochiometrically upon irradiation. Also, an absorption band was observed at 1500 cm" in the infrared region of the irradiated and crosslinked polymer. This band is due to N=N stretching vibration of the azo group. Based on that, Tsuda concluded the crosslinking reaction takes place by dimerization, as expected... 

Photochemistry teaches that absorbed light causes photochemical reactions, such as crosslinking or degradation. 

Sunlight (UV) Induction of photochemical reactions. MW reduction (brittleness). Crosslinking (could impair biodegradability). Germicidal effect. Reduction of microbial population on irradiated surface. 

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