Two dimensional 2 D) MoS 2 known for its scalability, high carrier mobility and tunable bandgap, has enabled many novel electronic and optoelectronic devices. Wafer scale synthesis of high quality 2 D MoS 2 films is crucial to their industry applications Alkali halide assisted chemical vapor deposition (CVD) can achieve large scale growth of 2 D MoS 2 while the residual alkali is detrimental to device performance. Here, we develop a contamination free polymer promoter to realise large scale clean growth of 2 D MoS 2. We tune the reactant concentrations and enable promoter dominated nucleation, which leads to large single crystal MoS 2 flakes 20 μ m as well as millimeter sized monolayered films of high crystal quality. The controllability of the growth will facilitate the development of 2D MoS 2 devices.