Studies On Synthesis And Heat Conduction Properties Of Polystyrene/Graphene Composite

Thermal conductive materials are widely used, especially the field of heat dissipation problem of the national economy and defense industry has become increasingly obvious and growing, the research and development of new efficient thermal conductive materials become very urgent. Polymer materials are qualitative light, easy processing, good corrosion resistance and mechanical properties, and they are expected to replace the traditional metal materials. This thesis mainly synthesized PS chains with uniform molecular chain length through the reversible addition fragmentation chain transfer(RAFT) polymerization. And then we used graphene as fillers to prepare polystyrene/graphene(PG) composites in different way. We studied the bonding degree between PS matrix and graphene; filler content and matrix molecular chain length on the influence of thermal conduction properties of PG composites.The main results were as follows:(1) The “grafting to” strategy of covalent-grafting technique in in-situ compounding was adopted to prepare PG composites through RAFT polymerization and grafted PS chain on the surface of graphene at the same time. The research showed that the thermal property of PG increased glass transition temperature(Tg) by about 1.5 °C in comparison with that of neat PS, and the grafting density of PG composites was about 0.18 chains per 100 carbons with 10 wt% graphene sheets loading. The thermal conductivity(λ) improved from 0.150 W·m-1·K-1 of neat PS to 0.250 W·m-1·K-1 of PG composites. The thermal property of PG composites increased due to the homogeneous dispersion and ordered arrangement of graphene sheets in PS matrix and the formation of PG composites.(2) The “grafting to” strategy of covalent-grafting technique in in-situ compounding was adopted to prepare PG composites with different graphenen filler content. The hot-pressing process made graphene directional arrangement in the polymer matrix. The research shows that the thermal conductivity of PG composites increased with the increasing of graphene content. The thermal conductivity of PG composites with 10 wt% graphene loading was enhanced by 66 % to 0.244 W·m-1·K-1 compared with 0.147 W·m-1·K-1 of pure PS. The thermal diffusivity(α) of PG composites increased with the increasing of filler content in the direction of through-plane. And the α of in-plane direction was almost ten times higher than that of in through-plane direction. And both of them changed slowly in function of graphene loadings. This anisotropic property may be caused by the ordered arrangement of graphene sheets and PS chains after PG composites were hot-pressed. At the same time, the research shows that the thermal conductivity of PG composites decreased with the increasing of PS chain length. The thermal conductivity of PG composites with PS matrix with a number-average molecular weight(Mn) of 473156 g·mol-1 was decreased to 0.144 W·m-1·K-1 compared with 0.159 W·m-1·K-1 of PG composites with PS matrix with Mn of 25973 g·mol-1. This was due to the more favourable grafting structure between the shorter PS grafted chains with graphene led to lower thermal resistance.