Photolabile barbiturate compounds

1. A polymerizable composition comprising a polymerizable component, and a redox initiation system comprising:

a) a transition metal complex that participates in a redox cycle;

b) an oxidizing agent;

c) a photolabile reducing agent of the formula:

wherein

R 1 , R 2 and R 3 are each independently H, C 1-18 hydrocarbyl; and

a) R Photo is a photolabile group;

and optionally a quaternary ammonium halide.

2. The polymerizable composition of claim 1 , wherein the photolabile group R photo is selected from phenacyl groups, 2-alkylphenacyl groups, ethylene-bridged phenacyl groups, p-hydroxyphenacyl groups, benzoin groups, o- or p-nitrobenzyl groups, o-nitro-2-phenethyloxycarbonyl groups, coumarin-4-yl methyl groups, benzyl groups, o- or p-hydroxylbenzyl groups, o- or p-hydroxynapthyl groups, 2,5-dihydroxyl benzyl groups, 9-phenylthioxanthyl, 9-phenylxanthyl groups, anthraquinon-2-yl groups, 8-halo-7-hydroxyquinoline-2-yl methyl groups, and pivaloylglycol groups.

3. The polymerizable composition of claim 1 wherein the transition metal complex is of the formula:

[ML p ] n+ A − , wherein M is a transition metal that participates in a redox cycle,

L is a ligand, A- is an anion, n is the formal charge on the transition metal having a whole number value of 1 to 7, and p is the number of ligands on the transition metal having a number value of 1 to 9.

4. The polymerizable composition of claim 3 wherein M is selected from Cu, Fe, Ru, Cr, Mo, Pd, Ni, Pt, Mn, Rh, Re, Co, V, Au, Nb and Ag.

5. The polymerizable composition of claim 1 wherein the redox initiator system is present in the composition in amounts, from 0.05 to about 10 parts by weight, based on 100 parts by weight of the polymerizable component of the polymerizable composition.

6. The polymerizable composition of claim 1 wherein further comprising a secondary reducing agent selected from tertiary amines; aromatic sulfinic salts; thioureas; and mixtures thereof.

7. The polymerizable composition of claim 1 wherein the oxidizing agent of the redox initiator system is selected from persulfuric acid and salts thereof; peroxides, hydroperoxides; transition metals, perboric acid and salts thereof, permanganic acid and salts thereof, perphosphoric acid and salts thereof, and mixtures thereof.

8. The polymerizable composition of claim 1 comprising more than one oxidizing agent.

9. The polymerizable composition of claim 1 wherein the polymerizable component comprises:

i) 85 to 100 parts by weight of an (meth)acrylic acid ester;

ii) 0 to 15 parts by weight of an acid functional ethylenically unsaturated monomer;

iii) 0 to 10 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer;

iv) 0 to 5 parts vinyl monomer; and

v) 0.1 to 5 parts of a multifunctional (meth)acrylate;

vi) 0.1 to 10 parts by weight of the redox initiator system, based on 100 parts by weight of i) to v).

10. The polymerizable composition of claim 9 further comprising 0.01 to 5 parts of a multifunctional (meth)acrylate.

11. The polymerizable composition of claim 1 wherein the polymerizable component comprises:

i) up to 100 parts by weight of an (meth)acrylic acid ester;

ii) 0 to 15 parts by weight of an acid functional ethylenically unsaturated monomer;

iii) 0 to 15 parts by weight of a non-acid functional, ethylenically unsaturated polar monomer;

iv) 0 to 5 parts vinyl monomer;

v) 0 to 100 parts of a multifunctional (meth)acrylate, relative to 100 parts i)-iv);

and

vii) the redox initiator system (including the transition metal complex, oxidant and photolabile reductant) in amounts from about 0.1 weight percent to about 5.0 weight percent, relative to 100 parts total monomer i)-v).

12. The polymerizable composition of claim 1 further comprising 1-35 parts by weight of a toughening agent, relative to 100 parts by weight of the polymerizable component of the polymerizable composition.

13. The polymerizable composition of claim 1 wherein the transition metal complex is Cu(II) naphthenate.

14. The polymerizable composition of claim 1 , wherein the polymerizable ethylenically unsaturated component comprises a reactive oligomer having pendent polymerizable groups, and wherein the reactive oligomer comprises:

a) greater than 50 parts by weight of (meth)acrylate ester monomer units;

b) 0.5 to 10 parts by weight of monomer units having a pendent, free-radically polymerizable functional groups,

c) 0 to 20 parts by weight of other polar monomer units, wherein the sum of the monomer units is 100 parts by weight.

15. A multilayer article comprising the polymerizable composition of claim 1 on a substrate.

16. The multilayer article of claim 15 wherein the substrate is a release liner.

17. The multilayer article of claim 15 wherein the substrate is a tape backing.