Polymer–multiwalled carbon nanotube composite films were fabricated using two types of polymer matrices, namely poly(vinyl alcohol), (PVA) and chlorinated polypropylene. In the first case, the PVA was observed to form a crystalline coating around the nanotubes, maximising interfacial stress transfer. In the second case the interface was engineered by covalently attaching chlorinated polypropylene chains to the nanotubes, again resulting in large stress transfer. Increases in Young's modulus, tensile strength, and toughness of × 3.7, × 4.3, and × 1.7, respectively were observed for the PVA‐based materials at less than 1 wt.‐% nanotubes. Similarily for the polypropylene‐based composites, increases in Young's modulus, tensile strength and toughness of × 3.1, × 3.9, and × 4.4, respectively, were observed at equivalent nanotube loading levels. In addition, a model to describe composite strength was derived. This model shows that the tensile strength increases in proportion to the thickness of the interface region. This suggests that composite strength can be optimized by maximising the thickness of the crystalline coating or the thickness of the interfacial volume partially occupied by functional groups.

Multiwalled carbon nanotubes have been functionalized using n-butyllithium and then covalently bonded to a chlorinated polypropylene. The following addition of the polymer-grafted nanotubes to the chlorinated polypropylene polymer matrix resulted in significant increase of mechanical properties. As nanotube content is increased to 0.6 vol %, Young's Modulus increased by a factor of 3, while both the tensile strength and the toughness increased by factors of 3.8 and 4, respectively. This covalent functionalization enables us to get an efficient dispersion and excellent interfacial stress transfer, potentially leading to new ultra-strong polymer composite materials.

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