(680a) Synthesis of Block Carbon Nanotubes and Their Use As Compatibilizers in Immiscible Polymer Blends

A new method to synthesize block nanotubes, i.e. nanotubes with varying chemistry along their lengths, in a scalable manner is described and one example is shown where these nanotubes strengthen polymer-polymer interfaces. The synthetic method relies on the incorporation of nitrogen atoms selectively within the nanotube structure during growth. By rapidly changing the reaction environment, blocks of nitrogen functionality along the length of the nanotube result. Without further modification, we found that the different chemistries did not cause the tubes to partition into different phases in a variety of polymer blends; in the case of interest for this study both tube chemistries would cause the tubes to partition to the poly(methyl methacrylate) phase in a polystyrene/poly(methyl methacrylate) (PS/PMMA) interface blend. Hence, the change in local electronic environment and radical scavenging property of the nanotube near the nitrogen atoms was used to selectively polymerize styrene from the nanotube wall where nitrogen is incorporated. An asymmetric double cantilever beam test was used to determine the ability of these tubes to compatibilize the PS/PMMA interface. Fracture toughnesses increased monotonically with increasing diblock carbon nanotube concentration and maximum values were like those for block copolymer reinforced interfaces while single-chemistry nanotubes showed no reinforcing effect. However, the abrupt increase in fracture toughness with added compatibilizer indicative of a transition to crazing was not found consistent with nanotubes suppressing crazing in homopolymers. Scanning electron microscopy images of the fractured surfaces show agglomerates of carbon nanotubes present which are likely limiting the efficacy of carbon nanotubes at toughening the interface.