The effects uncompatibilized immiscible polymer blend compositions on the T-g of the amorphous polymer were studied in the systems polystyrene/polypropylene (PS/PP), polystyrene/high density polyethylene (PS/PE) and polycarbonate/high density polyethylene (PC/PE). In the two similar systems of PS/PP and PS/PE, the T-g of PS increased with decreasing PS percentage in the blends. This variation in glass transition is attributed to the polymer domain interactions resulting from the different morphologies of various blend compositions. Experiments were conducted to study these effects by preparing blends with various polymers that varied the relationship between the T-g of the amorphous polymer and the crystallization behavior of the semicrystalline polymer. Results show that the variation in amorphous component T-g with composition depends strongly on the physical state of the semicrystalline domains. Whereas the T-g of PS in PS/PE blends changed with composition, the T-g of PC in the PC/PE blend did not change with composition. (c) 2006 Elsevier Ltd. All rights reserved.