The research problem

Polymer materials, both commodity and engineering polymers (e.g. PP, HDPE, Nylon) are used in a wide range of applications due to their good processing properties and the ease at which they can be scaled, as well as their low cost of production. However, they

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are typically electrically and thermally insulating and mostly only suitable for non-load bearing components which limits their use. Applications which require high electrical and thermal conductivity combined with enhanced mechanical strength and stiffness tend to resort to metals to fulfil their needs (e.g. copper, steel). In the modern age of sustainability, efficiency and high cost of production, new materials are sought after which meet certain criteria such as; high electrical and thermal conductivity, high mechanical strength and stiffness, lightweight, low cost of production, scalable and longevity. In the last three decades, polymer materials have provided many of these solutions in terms of low cost and scalability which has led to their wide scale use ranging from packaging to consumer electronics. However, further improvements to polymers are possible if additional functionalities can be added to the matrix material. Thus, there is the need for an additional component which has very different properties to those of the neat polymer. The addition of nanometre scale particles to polymer systems has attracted substantial interest due to the possibility of producing composites with exceptional electrical, thermal and mechanical properties with the addition of only a small weight/volume percentage of nanofiller (<5 wt%). Polymer encapsulation has been commonly selected as the system of choice when looking to magnify the outstanding properties of nanomaterials and has generated a new field of materials science known as ‘nanocomposites’. Polymer composites reinforced with

nanoscale inclusions differ greatly from the traditional particulate and fibre-reinforced composites, where challenges including dispersion, distribution and interfacial adhesion become more of a stumbling block. One of the key advantages of reducing the reinforcement size from the micro-meter to the nano-meter scale is to offer multi-functional properties in contrast to traditional composites which are focused on primarily on improvements in mechanical properties (stiffness and strength). Carbon nanotubes (CNTs) and graphene are cylindrical and sheet shaped nanostructures made entirely of carbon. CNTs are referred to as 1D graphitic carbon allotropes because of their high aspect ratios (ratio of length to diameter). Graphene is referred to as a 2D graphitic carbon allotrope because it represents a single layer of graphite and it is a single atom thick. Graphene is a single-atom-thick sheet of carbon atoms arranged in a hexagonal lattice and has been reported to be the world’s

thinnest, strongest and stiffest material, as well as being an excellent conductor of both heat and electricity.3 _{CNTs have been shown to be thermally stable up to 2800 °C, to have a}

thermal conductivity twice that of diamond and electron mobilities over a thousand times higher than copper wire. In addition, CNTs possess a high elastic modulus, in the order of

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~1 TPa. Graphene also has many similar properties to that of CNTs. On their own, it can be difficult to utilise the exceptional properties of these carbon nanofillers due to their nanoscale as they are difficult to handle and produced in powder form. It makes sense to combine the outstanding properties of nanofillers with commodity and engineering polymers, e.g. poly(propylene), poly(amide) to produce composites which can be easily processed and moulded. It has been theorised that the outstanding properties of carbon nanomaterials can be optimised if the nanofillers are homogenously dispersed and distributed within the polymer matrix. There is a preference for the formation of a network structure to be achieved at a low percolation threshold to optimise the electrical and thermal conductivity of the unfilled polymer. Mixing nanofillers with thermoplastics is typically performed under solvent-free conditions using extrusion however, the thermodynamics of mixing is not favourable and prevents the two systems from mixing effectively and homogenously. The aromatic, highly electronic, sp2 _{hybridized structure of nano-fillers have extremely poor}

compatibility with the neutral, sp3 _{hybridized structure of poly(propylene) (PP). A range of}

methods can be used to functionalise graphitic fillers including, covalent functionalisation

comprising of ‘grafting to’ and ‘grafting from’ the surface of the nano-filler. Extensive research into covalent functionalisation of graphitic nanofillers has been conducted and a review of literature has indicated improvements in the properties of the composite materials are possible (see chapter 2). For example, polymer grafting to the surface has rendered the fillers soluble in a wide range of solvents and improved their interfacial compatibility with polymer matrices. However, it is the hexagonal sp2 _{arrangement of carbon atoms that gives}

graphitic nanofillers their exceptional properties and the introduction of covalent bonds on the surface introduces defects which will inevitably reduce the maximum potential for the filler to reinforce the composite. The process of covalent functionalisation destroys the regular sp2 _{structure reducing the intrinsic properties of these fillers. Additionally, industry}

will only seek to use graphitic nanofillers with their existing infrastructure if the improvement in properties justifies the added cost. From a composites perspective, the covalent functionalisation strategy is not regarded as the optimal approach. Moreover, any covalent functionalisation will only add to the cost of an already very expensive nano-filler.

The non-covalent functionalisation strategy is regarded as a more optimal approach whereby there is no attachment of functional groups to the graphitic nanofiller surface which preserves the intrinsic properties. Polymers containing pyrene derivatives have been investigated for non-covalent functionalisation however, studies have been limited to solvent

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based systems. This project seeks to develop a polymer based compatibiliser which can promote non-covalently, compatibility between graphitic nanofillers and the polymer matrix (using e.g. CH-π and π-π interactions) during melt mixing in the extruder.2-5 _{To the best of}

my knowledge, there have been no investigations into the use of controlled living radical polymerisation techniques (RAFT and Cu(0)-mediated LRP), to synthesise polymers which are thermally stable for processing with PP in an extruder, designed to non-covalently functionalise MWCNTs and GNPs, through the use of either CH-π and/or π-π interactions.

In addition, studies correlating the poly(acrylate) (compatibiliser) structure and architecture to the properties of the composite have not been performed extensively. It has however been known that long chain alkyl polyacrylates demonstrate high solubility within PP from the research by ICI ltd.