Positive temperature coefficient of resistivity (PTCR) characteristics of poly(styrene-co-acrylonitrile) copolymer (SAN)/stainless steel (SS) powder (80 wt %) composites prepared by melt-mixing method has been investigated with reference to SAN/carbon black (CB) composites. The SAN/CB (10 wt %) composites showed a sudden rise in resistivity (PTC trip) at 125 degrees C, above the glass transition temperature (T-g) of SAN (T-g approximate to 107 degrees C). However, the PTC trip temperature of SAN/SS (80 wt %) composites appeared at 94 degrees C, well below the T-g of SAN. Addition of 1 phr of nanoclay increased the PTC trip temperature of SAN/CB (10 wt %) composites to 130 degrees C, while SAN/SS (80 wt %)/clay (1 phr) nanocomposites showed the PTC trip at 101 degrees C. We proposed that the mismatch in coefficient of thermal expansion (CTE) between SAN and SS played a key role that led to a disruption in continuous network structure of SS even at a temperature below the T-g of SAN. The dielectric properties study of SAN/SS (80 wt %) composites indicated possible use of the PTC composites as dielectric material. DMA results showed higher storage modulus of SAN/SS composites than the SAN/CB composites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012