Addition-fragmentation oligomers

A polymerizable composition comprising:

• an addition-fragmentation oligomer;
• at least one free-radically polymerizable monomer;
• and
• an initiator,
• wherein the addition-fragmentation oligomer is of the formula:
• wherein
• RA is non-directionally a 1-methylene-3,3-dimethyl propyl group,
• RB is a hydrocarbyl group, wherein at least two RA and/or RB groups are substituted with a pendent functional group D that bonds or etches a substrate to which it adheres;
• X1 is —O— or NR5—, where R5 is H or C1-C4 alkyl;
• Z comprises an ethylenically unsaturated polymerizable group;
• y is 0 or 1;
• and
• x is 0 to 60,
• wherein the D group that bonds or etches a substrate is selected from monophosphate, phosphonate, phosphonic acid, hydroxamic acid, carboxylic acid, acetoacetate, anhydride, isonitrile, silyl, disulfide, thiol, amino, sulfinic acid, sulfonic acid, and phosphine groups.