Characterization of poly(phenylacetylene) (PPA) samples produced using Rh(I) complexes featuring hemilabile phosphine ligands by size exclusion chromatography, multiangle light scattering (SEC-MALS), or asymmetric flow field flow fractionation (A4F)-MALS has revealed that some of these PPA samples contain a mixture of linear and branched polymer. The occurrence and extent of branching is dependent on both catalyst structure and polymerization conditions. The levels of branching are consistent with either terminal branching through copolymerization of macromonomer or chain transfer to polymer, where the branched species are less reactive toward further polymerization than the linear chains. The MM dependence of B, the number of branches per molecule, or lambda, the number of branches per 1000 repeat units, suggests that the latter explanation may be correct, but further work is needed.