Preparation of Block Copolymer Latex Nanocomposites By Reverse Atom Transfer Radical Polymerisation and Reverse Addition Fragmentation Transfer Polymerisation Methods.

Polymer composites containing carbon nanotube (CNT) networks have undergone extensive study over the last few years. Electronic conductance in these films relies on a connected network of nanotubes or by saturation of CNT's into the polymer matrix. As CNT's are expensive the drive has been to reduce the loading of the CNT's by formation of a percolating network involving the dispersion of the NT's using a surfactant within a homogeneous (solvent based system), a heterogeneous system (latex dispersion) or within the polymer melt. Recent studies on latex systems and polymer blends have revealed that lower NT loadings can be achieved by a concept known as 'Double Percolation' where the threshold is controlled by the morphology of the polymers as well as the polymer size. In this way the percolation threshold may be reduced by preferentially dispersing the NT's into the more miscible minor phase.
This concept of double percolation is being applied to copolymers where the major and minor blocks can be produced in a latex (controlled morphology) using radical polymerisation methods such as RAFT (Reverse Addition Fragmentation Transfer) and R-ATRP (Reverse Addition Transfer Radical Polymerisation) followed by dispersion of the CNT's therein. Owing to studies by Van den Brande and Van Mele1, Koning et. al.2,3 and Hermant4; several candidate co-polymers have been identified. Notably copolymers of polystyrene, poly-t-butylmethacrylate, polymethylmethacrylate, polydimethylsiloxane and poly(2-dimethylamino)ethyl methacrylate.
Although some of these copolymer systems have been studied significantly using RAFT and ATRP there are still significant challenges that remain in producing well tailored blocks within a latex system. In this work a three-way strategy is discussed for the synthesis of these block copolymers as candidates for the formation of CNT composite films. Of these challenges the most significant are producing well defined PDMS copolymers in latex systems, reducing the amount/effect of surfactants in the system, improving PS conversion in R-ATRP latex systems and maintaining good control over block lengths and PDI to ensure meaningful comparison to homopolymer and blend systems.