Allyl-terminated polystyrenes (PS macromonomers) were synthesized by quasiliving atom transfer radical polymerization (ATRP) of styrene followed by carbocationic chain end transformation with allyltrimethylsilane in the presence of titanium tetrachloride. Systematic investigations were carried out on metallocene/MAO-catalyzed copolymerization of PS macromonomers with propene by varying the molecular weight of the macromonomer, the type of catalyst, the polymerization temperature, and the propene pressure. The resulting poly(propene-g-styrene)(PP-g-PS) graft copolymers were analyzed by H-1 and C-13 NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry. Macromonomer incorporation, molecular weight, tacticity, and crystallinity of the resulting PP-g-PS copolymers were greatly influenced by the investigated parameters. The macromonomer incorporation depends mostly on the polymerization temperature. The highest comonomer incorporation (10.8 wt %) was achieved at the highest polymerization temperature, but at the same time the molecular weight decreases strongly with increasing polymerization temperature leading to graft copolymers with relatively low molecular weights. For the first time, the effect of well-defined PP-g-PS grafts was investigated on blending incompatible polypropylene with polystyrene. Surprisingly, it was found that PP-g-PS; graft copolymers with short PS side chains show a better compatibilization efficiency than those with long PS chains at comparable composition as scanning electron microscopic investigations on the morphology of blends indicate.