Derivatives of aryl ketones as visible sensitizers of photopolymerizable compositions

DETAILED DESCRIPTION I claim: 1.
A photopolymerizable composition comprising the components: (i) at least one nongaseous ethylenically unsaturated compound capable of forming a high molecular weight polymer by photoinitiated addition polymerization; (ii) at least one 2,4,5-triarylimidazolyl dimer initiator consisting of two 2,4,5-triarylimidazolyl radicals bound together by a single covalent bond; and (iii) at least one .
alpha.
,.
beta.
-unsaturated ketone sensitizer having the formula ##STR11## wherein R.
sup.
1 and R.
sup.
2 are each H, or R.
sup.
1 +R.
sup.
2 is --CH.
sub.
2 --; R.
sup.
3 is H, or R.
sup.
3 +R.
sup.
5 is selected from --CH.
sub.
2 --.
sub.
2, --CH.
sub.
2 --.
sub.
3, and --CH(CH.
sub.
3)CH.
sub.
2 C(CH.
sub.
3).
sub.
2 --; R.
sup.
4 is H, or R.
sup.
4 +R.
sup.
6 is selected from --CH.
sub.
2 --.
sub.
2 and --CH.
sub.
2 --.
sub.
3 ; R.
sup.
5 and R.
sup.
6 are alkyl groups of 1 to 5 carbon atoms, or together are selected from --CH.
sub.
2 --.
sub.
4 and --CH.
sub.
2 CH.
sub.
2 OCH.
sub.
2 CH.
sub.
2 --; R.
sup.
7, having a total of up to 8 carbon atoms, is selected from trimethylene and tetramethylene groups, unsubstituted, or substituted with 1 to 4 alkyl groups.
2.
A photopolymerizable composition according to claim 1 wherein the components are present in these amounts, by weight: 100 parts of (i), 0.
01 to 20 parts of (ii), and 0.
001 to 15 parts of (iii).
3.
A photopolymerizable composition according to claim 2 containing 1 to 10 parts of (iii).
4.
A photopolymerizable composition according to claim 1 comprising additionally a polymeric binder component, (iv).
5.
A photopolymerizable composition according to claim 4 wherein the binder is selected from at least one member of the group polyacrylate esters and poly-.
alpha.
-alkylacrylate esters containing carboxyl groups.
6.
A photopolymerizable composition according to claim 4 wherein the components are present in these amounts, by weight: (i) is 3 to 100 parts per 100 parts of (i) plus binder, (ii) is 0.
01 to 20 parts per 100 parts of (i) plus binder, (iii) is 0.
001 to 15 parts per 100 parts of (i) plus binder, and (iv) is 0 to 97 parts per 100 parts of (i) plus binder