<p>The effect of chain structure of polystyrene (PS) on the phase morphology and quiescent coalescence behavior of polypropylene/polystyrene (PP/PS) blends was investigated by dynamic rheological properties measurements and optical microscopy. The results indicate that the chain structure of PS significantly influences its entanglement and relaxation behavior, determining the dispersion state and coalescence kinetics upon melt annealing. For linear polystyrene (lPS) and three-arm star-shaped polystyrene (sPS), lower molar mass correlates with lower melt viscosity and a more favorable viscosity ratio between the dispersed phase and the matrix. This results in finer dispersion and a higher coalescence rate driven by enhanced chain mobility. When comparing linear and branched PS with close molar mass, the finer dispersion and higher coalescence rate of branched PS are ascribed to the better chain mobility resulting from the existence of short branched chains. However, comb-like branched polystyrene (cPS) demonstrates pronounced chain entanglement compared to lPS and sPS, as evidenced by the absence of viscous flow transition. Although the high bulk viscosity of cPS tends to hinder coalescence, the dense side chains create significant steric hindrance at the interface, leading to reduced interdiffusion with PP chains. This lack of interfacial entanglement facilitates interfacial slip and accelerates the drainage of the matrix film between droplets. Consequently, this interfacial dynamic mechanism dominates over the bulk viscous resistance, leading to a remarkable elevation in the coalescence rate for PP/cPS blends.</p>