The role of crystallinity in SWCNT-polyetherimide nanocomposites

Two all-aromatic, high-performance poly(etherimide)s ODPA-P3 (I) and BPDA-P3 (II) are studied as a function of SWCNT loading. Polyetherimide I is amorphous but SWCNTs nucleate crystallization during imidization to produce a nanocomposite (nc-I) with SWCNTs embedded in the crystals. This crystalline interphase, with a radial thickness of ∼8 nm, results in a substantial reinforcement efficacy. Melting the interphase and cooling nc-I yields an amorphous nanocomposite with an interphase thickness (3.6 nm) that is smaller and has a lower reinforcement efficacy. Polyetherimide II was used as a reference since SWCNTs reside in the amorphous fraction of its nanocomposite. Consequently, the reinforcement efficiency of the semi-crystalline nc-II and its amorphous analog (prepared by heating above the crystal melting point and cooling) remains unchanged. A crystalline interphase surrounding SWCNT-reinforced poly(etherimide)s appears to be critical in obtaining high reinforcement efficacies. Most high-performance polyimides and poly(etherimide)s are prepared using a thermal imidization step. Our work emphasizes that care has to be taken in selecting the final imidization temperature to avoid melting the crystalline interphase if one is targeting high modulus materials.