Abstract
Excited Triplet States of Organic Molecules and Reactive Free Radicals in Polymers
Highlights
Free-radical photopolymerization (UV-cure) of organic coatings is a very important process that has been used for more than half a century
The radical pairs (RP) formed in reaction (1) either decays in the polymer cage or radicals escape into the polymer bulk, as per (Scheme 1) shown below
The cured coating is subjected to destruction initiated in particular by the residual PI and possibly by carbonyl compounds formed during autoxidation. (Here we talk about processes which last years.) cage effect value and its dependence upon the degree of photopolymerization and properties of a polymer are very important for practice [7,8] It was demonstrated that the value of depends in particular upon the free volume of a polymer Vf and the glass transition temperature of a polymer Tg [3,9]
Summary
Free-radical photopolymerization (UV-cure) of organic coatings is a very important process that has been used for more than half a century. Academic and industrial researchers study the basics of this complex process [1,2,3,4] In this mini review we will briefly consider the important role of low MW free radicals of photoinitiators (PIs) and the excited triplet states of PIs in photopolymerization. Residual PIs in the cured coatings and other low MW photoreactive species in the cured coatings/polymers lead to a negative effect: photodecomposition of polymers outdoors, poor weatherability.
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