Abstract
The two-dimensional material graphene has many excellent physicochemical properties such as large specific surface area, high electron migration rate, good chemical properties, good thermal conductivity, high elastic modulus and mechanical strength that make it very valuable for theoretical research and application in the preparation of graphene/polymer composites. In this paper, the effects of ultrasonic intensity and reaction time on the molecular weight and yield of PMMA under supercritical CO2 conditions were investigated. It was found that there are threshold and optimal values of ultrasonic intensity for initiating the reaction in supercritical CO2 system. The threshold value is 150 W/cm2 and the optimal ultrasonic intensity value is 225 W/cm2. There is also an optimal value of ultrasonic initiation time for ultrasonic initiation polymerization. Combining the reaction yield and the molecular weight of the product, 2 h of ultrasonic initiation is a suitable initiation reaction time. Based on the synthesis of PMMA by ultrasonic excitation, the preparation of Graphene/PMMA composites by ultrasound assistance was also investigated. The TG and DTG characterization of PMMA and complex materials prepared by ultrasonic excitation showed that the radicals generated by ultrasonic excitation were uniformly distributed and did not generate unsaturated double bonded polymers. The electrical conductivity of the Graphene/PMMA composites prepared by ultrasonic excitation at a graphene content of 1 wt% increased to 1.13 × 10-1 S/cm, which is better than that of the Graphene/PMMA prepared by in situ polymerization. This may be attributed to the ultrasound-assisted supercritical CO2 fluid action that resulted in a more uniform distribution of Graphene mixed with PMMA in the prepared composites. Therefore, it is of important practical significance for the preparation of Graphene/PMMA composites by ultrasound-induced polymerization.