SWCNT Induced Crystallization in an Amorphous All-Aromatic Poly(ether imide)

We have selected two amorphous all-aromatic poly(ether imide)s with similar chemical structures but with different backbone geometries as matrices for SWCNT-based nanocomposites. Up to 4.4 vol %, SWCNTs could be incorporated using an in situ polymerization method. Nanocomposites prepared from aBPDA-P3, a nonlinear matrix polymer with a T-g of 230 degrees C, remains amorphous, and the presence of the SWCNTs reduces the T-g by 11 degrees C. No effect on E' or stress-strain behavior was observed. 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 concentrations as low as 0.1 vol %. XRD and TEM measurements show that the SWCNTs become embedded in a highly crystalline polymer matrix. The result is a significant change in thermomechanical properties. The polymer T-g was increased by 12 degrees C, from 196 to 208 degrees C, and due to the induced crystallinity, the modulus above T-g showed a dramatic increase. The neat polymer fails at T-g, but the 4.4 vol % nanocomposite shows a storage modulus of 1 GPa at 280 degrees 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 determines 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 has been shown to develop a semicrystalline morphology in the presence of SWCNTs. Steric factors in aBPDA-P3 seem to inhibit favorable pi-pi interactions and prevent the polymer chains from adapting low-energy conformations that readily interact with the SWCNT surface.