Photopolymerizable composition stabilized with nitrogen-containing aromatic compounds

DETAILED DESCRIPTION OF THE INVENTION More in detail, the photopolymerizable composition of this invention comprises at least one photopolymerizable ethylenically unsaturated compound containing a photoinitiator in an amount sufficient to initiate photopolymerization and a stabilizing amount of a nitrogen-containing aromatic compound having the formula ##STR1## wherein A is a carbon or nitrogen; R.
sup.
1 and R.
sup.
2 are (a) independently selected hydrogen or --X--R.
sup.
5 where X is zero, oxygen, sulfur, N.
dbd.
N, S--S, --R.
sup.
6 or N--R.
sup.
6 where R.
sup.
6 is hydrogen or alkylene of 1 to 6 carbon atoms, and R.
sup.
5 is phenyl or pyridyl with the proviso that both R.
sup.
1 and R.
sup.
2 cannot be hydrogen; or (b) together with the ring carbon atoms in the formula adjacent to R.
sup.
1 and R.
sup.
2 form a radical having the formula ##STR2## where R.
sup.
7 and R.
sup.
8 are independently selected hydrogen hydroxyl, nitroso or pyridylazo, and Y is nitrogen or carbon; or ##STR3## where Z is oxygen, sulfur, or NR.
sup.
9 where R.
sup.
9 is hydrogen or alkyl of 1 to 6 carbon atoms; and R.
sup.
3 and R.
sup.
4 are independently selected hydrogen, hydroxyl, or an alkali metal salt thereof; with the further proviso that said compound must contain at least one nitrogen.
Illustrative of the nitrogen-containing aromatic compounds having the formula I are 2,2'-dipyridyl; 2,3'-dipyridyl; 3-hydroxy-2,2'-dipyridyl; 2-hydroxy-2',3-dipyridyl; 2-hydroxy-2',4-dipyridyl; 2,2'-dihydroxy-2,2'-dipyridyl; 3,3'-dihydroxy-2,2'-dipyridyl; 2-(2' hydroxyphenyl) pyridyl; 4-hydroxy-2,2'-dipyridyl; 2,2'-azobis-pyridyl; 2-pyridylazobenzene; 1-(2-pyridylazo)-2-naphthol; 2-(phenylazo)-pyridine; phenyl, 2-pyridyl disulfide; 2,2'-dipyridyl disulfide; 8-hydroxyquinoline; 2,8'-dihydroxyquinoline; 2 nitroso-1-naphthol; 1 nitroso-2-naphthol; 1-(2-pyridylazo)-3-naphthol; 1-(2-pyridylazol)-2 naphthol; 2-mercapto-benzimidazole; 2-mercapto-(benzoxazole); 2-mercapto-2-(benzthiazole); 2-mercapto -1-methyl benzimidazole; etc.
The nitrogen-containing aromatic compounds I are known compounds; many of them are commercially available