Addition-fragmentation agents

1. An addition-fragmentation agent of the formula:

wherein

R 1 , R 2 and R 3 ar each independtly Z m -Q-, a (hetero)alkyl group or a (hetero)aryl group with the proviso that at least two of R 1 , R 2 and R 3 is Z m -Q-,

Q is selected from the group consisting of monohydroxyl-substituted alkylene, alkoxy-substituted alkylene and aryloxy-substituted alkylene;

Z is an ethylenically unsaturated polymerizable group selected from the group consisting of

m is 1 to 6;

each X 1 is independently —O— or —NR 4 —, where R 4 is H or C 1 -C 4 alkyl, and

n is 0.

2. The addition-fragmentation agent of claim 1 where Q is —CH 2 —CH(OH)—CH 2 —.

3. The addition-fragmentation agent of claim 1 wherein the R 1 —X 1 — and the R 3 —X 1 — groups are selected from the group consisting of H 2 C═C(CH 3 )C(O)—O—CH 2 —CH(OH)—CH 2 —O—, H 2 C═C(CH 3 )C(O)—O—CH(CH 2 OPh)-CH 2 —O—, and H 2 C═C(H)C(O)—O—CH 2 —CH(OH)—CH 2 —O—.

4. A method of making an addition-fragmentation agent of claim 1 comprising the step of reacting a compound of the formula:

wherein each of X 2 and X 3 comprises an electrophilic or nucleophilic functional group, and

n is 0;

with a compound of the formula:

wherein

A is a functional group that is co-reactive with functional groups X 2 and X 3 , R 4 is hydrogen, a C 1 to C 4 alkyl group, or aryl group; R 5 is a single bond or a divalent (hetero)hydrocarbyl linking group that joins the ethylenically unsaturated group to reactive functional group A, co-reactive with the X 2 and X 3 groups.

5. The method of claim 4 wherein the co-reactive functional group A is selected from the group consisting of hydroxyl, amino, and carboxyl, and the X 2 and X 3 groups comprise an epoxy group.

6. The method of claim 4 wherein the co-reactive functional group A is an epoxy group and the X 2 and X 3 are selected from the group consisting of hydroxyl, amino and carboxyl groups.

7. A polymerizable composition comprising:

a) a (meth)acrylic acid ester monomer;

b) a multifunctional (meth)acrylate;

c) optionally an acid functional ethylenically unsaturated monomer;

d) optionally a non-acid functional, ethylenically unsaturated polar monomer;

e) optionally a vinyl monomer; and

f) filler; and

g) 0.1 to 10 parts by weight, based on 100 parts by weight of a) to e), of an addition-fragmentation agent of the formula:

wherein

R 1 , R 2 and R 3 are each independently Z m -Q-, a (hetero)alkyl group or a (hetero)aryl group with the proviso that at least two of R 1 , R 2 and R 3 is Z m -Q-,

Q is selected from the group consisting of monohydroxyl-substituted alkylene, alkoxy-substituted alkylene and aryloxy-substituted alkylene;

Z is an ethylenically unsaturated polymerizable group selected from the group consisting of

m is 1 to 6;

each X 1 is independently —O— or NR 4 —, where R 4 is H or C 1 -C 4 alkyl, and n is 0.

8. The polymerizable composition of claim 7 comprising:

a) 85 to 100 parts by weight of an (meth)acrylic acid ester of non-tertiary alcohol;

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

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

d) 0 to 5 parts vinyl monomer; and

e) 0.01 to 5 parts of a multifunctional (meth)acrylate;

based on 100 parts by weight total monomer;

f) filler; and

0.1 to 10 parts by weight of the addition-fragmentation agent, based on 100 parts by weight of a) to e).

9. The polymerizable composition of claim 7 where Q is a monohydroxyl-substituted alkylene.

10. The polymerizable composition of claim 7 where Q is —CH 2 —CH(OH)—CH 2 —.

11. The polymerizable composition of claim 7 where Q is an aryloxy-substituted alkylene.

12. The polymerizable composition of claim 7 where Q is an alkoxy-substituted alkylene.

13. The addition-fragmentation agent of claim 7 wherein the R 1 —X 1 — and the R 3 —X 1 — groups are selected from the group consisting of H 2 C═C(CH 3 )C(O)—O—CH 2 —CH(OH)—CH 2 —O—, H 2 C═C(CH 3 )C(O)—O—CH(CH 2 OPh)-CH 2 —O—, and H 2 C═C(H)C(O)—O—CH 2 —CH(OH)—CH 2 —O—.

14. The polymerizable composition of claim 7 wherein the filler is present in amount of <50 wt. % relative to the amount of a) to e).

15. The polymerizable composition of claim 7 wherein filler is selected from the group consisting of silica, submicron silica, zirconia, submicron zirconia, and non-vitreous microparticles.

16. The polymerizable composition of claim 7 wherein filler is selected from the group consisting of nanosized silica particles, nanosized metal oxide particles, and combinations thereof.

17. An article comprising a substrate and the polymerized coating of the polymerizable coating of claim 7 on a surface thereof.