Addition-fragmentation oligomers having high refractive index groups

1. An addition-fragmentation oligomer of the formula

wherein

R A is

R B a (hetero)hydrocarbyl group, wherein at least 50% of the R B units are substituted with a high refractive index group,

X 1 is —O— or NR 5 —, where R 5 is H or C 1 -C 4 alkyl;

Z comprises an ethylenically unsaturated polymerizable group;

y is 0 or 1;

x is 0 or 1.

2. The addition-fragmentation oligomer of claim 1 , wherein at least 75% of the R B units are substituted by a high refractive index group.

3. The addition-fragmentation oligomer of claim 1 , wherein the high refractive index group is selected from benzyl, 2-, 3-, and 4-biphenyl, 1-, 2, 3-, 4-, and 9-fluorenyl, 4-(1-methyl-1-phenethyl)phenoxyethyl; phenylthio; 1-, 2-, 3- and 4-napthyl, 1- and 2-naphthylthio; 2,4,6-tribromophenoxy; 2,4-dibromophenoxy; 2-bromophenoxy; 1-, and 2-naphthyloxy; 3-phenoxy-; 2-, 3- and 4-phenylphenoxy; 2,4-dibromo-6-sec-butylphenyl; 2,4-dibromo-6-isopropylphenyl; 2,4-dibromophenyl; pentabromobenzyl and pentabromophenyl.

4. The addition-fragmentation oligomer of claim 1 derived from A compounds of the formula:

R 1 —O—CO—R A —CO—O—R 1 , wherein R A is a 1-methylene-3,3-dimethylpropyl group and R 1 is H, alkyl, aryl or R FG , where R FG is an aryl or an alkyl further substituted with a nucleophilic or electrophilic functional group.

5. The addition-fragmentation oligomer of claim 4 derived from B compounds of the formula:

X 2 —R B —X 2 , wherein R B is a (hetero)hydrocarbyl group and X 2 is functional group reactive with the functional groups of the A compound.

6. The addition-fragmentation oligomer of claim 5 wherein the compound of the formula X 2 —R B —X 2 is selected from difunctional epoxides, diols, aziridines, isocyanates and diamines.

7. The addition-fragmentation oligomer of claim 1 where x+y is 0 to 2.

8. The addition-fragmentation oligomer of claim 1 where x+y is 1 to 2.

9. A polymerizable composition comprising the addition-fragmentation oligomer of claim 1 , at least one free-radically polymerizable monomer, and an initiator.

10. The polymerizable composition of claim 9 comprising:

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

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 to 100 parts of a multifunctional (meth)acrylate;

based on 100 parts by weight total monomer a) to d), and

f) 0.1 to 12 parts by weight of the addition-fragmentation oligomer, based on 100 parts by weight of a) to e), and

g) an initiator.

11. The polymerizable composition of claim 10 further comprising 0.01 to 100 parts of a multifunctional (meth)acrylate based on 100 parts by weight total monomer a) to d).

12. The polymerizable composition of claim 9 further comprising an inorganic filler.

13. An article comprising the cured polymerizable composition of claim 9 on a substrate.

14. A method of bonding two substrates together comprising the steps of coating the polymerizable composition of claim 9 to a surface of one or both substrates, contacting the coated surfaces, optionally with pressure, and curing the polymerizable compositions.

15. A hardcoat composition comprising one or more multifunctional (meth)acrylate monomers or (meth)acrylate oligomers, and the addition-fragmentation oligomer of claim 1 .

16. The hardcoat composition of claim 15 comprising:

a) 0.1-10 wt. % of the addition fragmentation oligomer;

b) 20-80 wt. % of multifunctional (meth)acrylate monomers and/or multifunctional (meth)acrylate oligomers,

c) 0 to 25 wt. % range of (meth)acrylate diluent, (0-25 wt. %); and

d) 20 to 75 wt. % of silica.

17. A curable dental composition comprising:

a) at least one dental resin comprising at least two ethylenically unsaturated group;

b) an addition-fragmentation oligomer of claim 1 ; and

c) optionally an inorganic oxide filler.

18. The dental composition of claim 17 wherein the inorganic oxide filler comprises nanoparticles.