Photo-degradation of poly(neopentyl isophthalate). Part II: Mechanism of cross-linking

Depth-resolved infrared microscopy and UV-VIS spectroscopy analysis of an artificially degraded polyester-urethane clearcoat

“…13 shows that the evolution of the concentration of several chemical species occurs via specific gradients close to the coating surface and in a more uniform fashion in the bulk of the coating. Previous studies on the mechanisms of photodegradation in PNI coatings in aerobic conditions indicate the simultaneous occurrence of photolytic cleavage of ester bonds, chain breaking reactions along oxidative pathways and the recombinative formation of crosslinks [19,21]. The initially non-crosslinked thermoplast is increasingly converted into a crosslinked gel.…”

“…Aside from that the results for this band are rather noisy due to its low absorbance in the infrared spectrum, its large change can be explained by the fact that this vibration is sensitive to several changes that can take place in its neighbourhood during photodegradation. The 828 cm À1 band decreases upon the loss of a substituted carbonyl on the 1-or on the 3-position of the IPA residue, but also disappears when phenyl rings are converted into biphenyl structures due to recombination reactions [19].…”

Data on Specific Polymers

“…356 The mechanism of crosslinking of PNI during photodegradation in nitrogen atmosphere was investigated. 357 The gel formed had the highest density near the coating surface. 357 The crosslink density was non-homogeneous across the coating thickness with the highest density near the coating surface.…”

“…357 The gel formed had the highest density near the coating surface. 357 The crosslink density was non-homogeneous across the coating thickness with the highest density near the coating surface. 357 3 .…”

“…357 The crosslink density was non-homogeneous across the coating thickness with the highest density near the coating surface. 357 3 . Each group is highly diverse because of chain irregularities (branches), unsaturations, molecular weight variations, and components added during the polymerization reaction to influence basic mechanical properties and durability.…”