Graphene or graphite monolayer is a 2-D layer with thickness of one atomic layer, where carbon atoms form hexagonal crystalline structure. Graphene is considered to be the thinnest, strongest and hardest known material. Due to its exceptional and unique properties such as large surface area, high tensile strength, thermal and electrical conductivity, graphene has great potential for use in composite engineering. In a polymer composite, even a very low loading level of graphene can significantly improve electrical, physical, mechanical and barrier properties of composite. Traditional methods of graphene functionalization are based on previously modified graphene and involve multistep organic syntheses. These methods are time consuming and have low productivity. A simpler, more environmentally friendly and cost-effective way of functionalizing graphene with polymer chains is possible by using ultrasound, which creates acoustic cavitation. In this study we showed that the phenomenon of cavitation is responsible for successful functionalization. In addition, we also showed that the key parameter influencing the success of functionalization is the intensity or amplitude of ultrasound.