We have selected two amorphous all-arom. poly(ether imide)s with similar chem. structures but with different backbone geometries as matrixes for SWCNT-based nanocomposites. Up to 4.4 vol. %, SWCNTs could be incorporated using an in situ polymn. method. Nanocomposites prepd. from aBPDA-P3, a nonlinear matrix polymer with a Tg of 230 °C, remains amorphous, and the presence of the SWCNTs reduces the Tg by 11 °C. No effect on E’ or stress-strain behavior was obsd. When ODPA-P3 was used as the matrix, the SWCNTs appear to be highly compatible with this more linear polymer host. The SWCNTs act as a nucleating agent at concns. as low as 0.1 vol. %. X-ray diffraction and TEM measurements show that the SWCNTs become embedded in a highly cryst. polymer matrix. The result is a significant change in thermomech. properties. The polymer Tg was increased by 12 °C, from 196 to 208 °C, and due to the induced crystallinity, the modulus above Tg showed a dramatic increase. The neat polymer fails at Tg, but the 4.4 vol. % nanocomposite shows a storage modulus of 1 GPa at 280 °C. Stress-strain measurements show a noticeable improvement in strain and toughness at low SWCNT loadings (0.1-0.3 wt. %), which is indicative of good stress transfer between the SWCNTs and polymer matrix. At higher loadings the yield strength increases from 80 to 126 MPa at 4.5% strain. Our findings show that the poly(ether imide) backbone geometry dets. whether the polymer is good host for SWCNTs. The more linear ODPA-P3 is able to maximize its interaction with the SWCNT surface. To the best of our knowledge, this is the first time that an amorphous polymer was shown to develop a semicryst. morphol. in the presence of SWCNTs. Steric factors in aBPDA-P3 seem to inhibit favorable π-π interactions and prevent the polymer chains from adapting low-energy conformations that readily interact with the SWCNT surface. [on SciFinder(R)]