Reactive multi-arm polymers having branched end groups

A system comprising:

• (a) a first composition comprising a multi-arm polymer comprising three or more polymer arms, wherein a first portion of the polymer arms comprises a reactive end group selected from the group consisting of imidazole esters, imidazole carboxylates, benzotriazole esters, or imide esters, and wherein a remaining portion of the polymer arms comprises a branched end group that comprises between 3 and 7 branches, each comprising a covalently attached monocyclic or multicyclic aromatic structures that comprises (i) a plurality of C1-C4-hydroxyalkyl groups and (ii) a plurality of radiopaque functional groups or a plurality of radionuclide groups, wherein the first portion of the polymer arms corresponds to between 60% and 95% of a total number of the polymer arms in the first composition and wherein the second portion of the polymer arms corresponds to between 40% and 5% of the total number of the polymer arms in the first composition;
• and
• (b) a second composition comprising a multifunctional compound that comprises reactive functional groups selected from the group consisting of amine groups and thiol groups that are reactive with the reactive end group such that a crosslinked reaction is formed.