An aromatic vinyl thermoplastic resin composition includes about 10 to about 99% by weight of a thermoplastic resin including an aromatic vinyl copolymer resin, a rubber-modified vinyl graft copolymer, or a combination of and ; and about 1 to about 90% by weight of a branched aromatic vinyl copolymer resin including a silicon based compound. A method for preparing graphene comprises the following steps: selecting a proper material as a substrate; directly depositing a catalyst and CBr4 on a surface of the substrate; and performing annealing treatment on the sample obtained through deposition. The nut-idling device arranged between the hubs and the outer nut body constitutes a coupling which by means of actuators permits disengagement for each hub.