Unlike poly(phenyl acrylate) (PPA), its isomer poly(vinyl benzoate) (PVBZ) is immiscible with poly(styrene-co-acrylonitrile) (SAN). The difference in miscibility behaviour of PPA and PVBZ towards SAN is also reflected in the heats of mixing (Delta H-m) of the low-molecular-weight analogues of the respective blend components at compositions corresponding to phi(SAN) = 0.92 in the blend. It turns out that propionitrile, the hydrogenated monomer of polyacrylonitrile (PAN), is very unsuitable as an analogue of the latter. In contrast, acetonitrile, having a solubility parameter closer to PAN, is a fairly acceptable analogue of PAN as far as miscibility of the latter with PPA is concerned in the PAN-rich region, phi(PAN) > 0.7.