Poly(aramid silicone) (PAS) multiblock copolymers were synthesized by the low-temperature solution polycondensation of isophthaloyl dichloride (IPC) and two diamines, diamino poly(dimethyl siloxane) (PDMS; number-average molecular weight = 1680) and 3,4'-diaminodiphenylether (3,4'-DAPE), in tetrahydrofuran/dimethylacetamide (2/1 v/v). Two synthetic methods for the control of the PAS sequence were used: a one-step synthesis that presumably gave PAS with a random sequence and the polymerization of 3,4'-DAPE with a presynthesized dimer, IPC-PDMS-IPC (two-step synthesis), that presumably gave PAS with an alternating sequence of 3,4'-DAPE and PDMS segments. In a H-1 NMR study of the amide protons of the 3,4'-DAPE component in PAS, the relative length of the 3,4'-DAPE segment of randomly sequenced PAS to that of ideally sequenced PAS could be estimated. The glass-transition temperatures of the 3,4'-DAPE and PDMS segments of random PAS were 152-234 and -104 to -117 degreesC, respectively, whereas the alternating PAS sequences showed no glass transition for the 3,4'-DAPE segments. A tensile test indicated that randomly sequenced PAS behaved like a rubber-toughened material at lower PDMS contents and like a thermoplastic elastomer at higher PDMS contents, whereas the alternately sequenced PAS behaved like a very soft rubber, showing a high value of elongation at the breaking point. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 841-852, 2003.