Several basic physical properties of poly(thioether ketones) (PTEKs) were studied in comparison with corresponding ether analogs, poly(ether ketones) (PEKs), and various typical engineering plastics. The water absorption of PTEK (0.13%) was lower than that of the corresponding PEK (0.16%), probably because of the hydrophobic nature of the sulfide group. The dielectric breakdown strengths of PTEK and PEK were much greater than that of commercially available polymers. PTEK had higher dielectric breakdown strength than PEK. Although the volume resistivity of PEK considerably decreased after water absorption, that of PTEK remained high even after water absorption. wPTEK exhibited a remarkably high refractive index (n(D)(23) 1.66). alpha-Transition corresponding to T-g was observed at a high temperature (PTEK-1, 235degreesC; PTEK-2, 269degreesC) in the dynamic mechanical analysis. Young's modulus and tensile strength of PTEK were comparable to those of commercial high-performance polymers. PTEK also exhibited excellent flame resistance. Although the linear thermal expansion coefficient of PTEK was greater than that of PEEK, it was still within a practically acceptable level. (C) 2004 Wiley Periodicals, Inc.