Narrow molecular weight distribution butyl rubber synthesis method

The invention belongs to the technical field of rubber synthesis and provides a narrow molecular weight distribution butyl rubber synthesis method. The method utilizes a haloalkane-C4-10 saturated alkane mixed solvent, the content of haloalkane is in a range of 1-55% by volume, a used main catalyst comprises R-Al-Cl2, R2-Al-Cl1 and vanadium trihalide oxide, water is added into the catalyst according to a certain ratio, benzopyrene and/or nitrosamine compound is added into the main catalyst so that an initiator aid is formed and a main initiator comprises R-Al-Cl2 and R2-Al-Cl1. The catalysis system is a homogeneous system and is convenient for charging. Through use of a trace amount of water, a stable complex initiation system is formed. The method solves the problem that butyl rubber molecular weight is reduced along with temperature increasing. The butyl rubber has number-average absolute molecular weight of 2000-550000 and molecular weight distribution of 1.1-2.0.