Polycarbonate resins containing at least one divalent chain unit of the formula: ##STR1## wherein E represents a trivalent hydrocarbon radical, or a trivalent halogen-substituted hydrocarbon radical, are transitory cross-linkers prepared by thermal degradation of the corresponding acid esters (the ester group being removable under conditions of the degradation by a beta-elimination mechanism). Cross-linked polycarbonate resins exhibit enhanced fire-resistance, especially non-dripping. The cross-linkers are useful to cross-link any resin having a group reactive with a carboxyl group.