Two anhydride-grafted isotactic polypropylene (PP) compatibilizers, HAC or high-anhydride compatibilizer (2.7 wt % grafted maleic anhydride) and LAC or low-anhydride compatibilizer (0.2 wt % anhydride), were compared in PP-rich blends with polyamide-66 (25 wt %). A previous article demonstrated that LAC imparted a much higher fracture strain than did HAC at similar anhydride concentrations. The present study shows that LAC is capable of cocrystallization with PP. HAC does not cocrystallize, but crystallizes as a second phase in binary PP/HAC blends studied by DSC and hot-stage microscopy. A cocrystallization model is proposed to explain the higher fracture strain of PP/LAC/PA blends. A separate phase crystallization model is proposed for PP/HAC/PA blends. The models are supported by peel tests, which demonstrate greater adhesion of PP with LAC than with HAC.