A series of well-defined polystyrene-supported tertiary phosphine ligands were prepared by copper-catalyzed atom transfer radical polymerization (ATRP), involving direct copolymerization of styrene and 4-diphenylphosphinostyrene (or 4-styryldiphenylphosphine, SDPP). Copolymerization of the two monomers at different molar ratios showed a decreasing level of control as the SDPP molar fraction (fSDPP) increased. A satisfactory level of control was achieved for fSDPP≤0.25 such that there was a constant concentration of growing “living chains”, and linear Mn growth with conversion and low dispersity. Copper-free polymers with different chain lengths were prepared and tested as polymeric ligands in the rhodium-catalyzed hydroformylation of 1-octene. The polymeric ligands yielded higher linear/branched selectivity and lower activity relative to PPh3 at the same P/Rh ratio. The selectivity increased slightly as a function of the polymer chain length.