A polymer composition is provided with a multi-modal molecular weight distribution of a halo-containing polymer. The halo-containing polymer is has multi-functional phosphine linkages at less than 10% of halo sites of the halo-containing polymer that were available before multi-functional phosphine linking. A process for producing a polymer composition having a multi-modal molecular weight distribution involves dispersing a multi-functional phosphine compound in a halo-containing polymer, the halo-containing polymer comprising a total number of available halo sites, and reacting the multi-functional phosphine compound with the halo-containing polymer at an elevated temperature to produce the polymer composition in which less than 10% of the total number of available halo sites are reacted with the phosphine compound to provide multi-functional phosphine linkages in the halo-containing compound.