Synthesis and characterization of poly(methyl methacrylate)/graphene‐based thermally expandable microcapsules

Graphene oxide (GO) was prepared via Hummers' method and reduced by hydrazine monohydrate. GO was modified with (3‐methacryloxypropyl)triethoxysilane (MPS) and the obtained GO‐MPS nanosheets were reduced by hydrazine monohydrate. The different modified nanosheets were utilized to fabricate microballoons based on methyl methacrylate‐triethylene glycol dimethacrylate (TEGDMA) copolymer having a core/shell structure which contained pentane as a blowing agent. To investigate the effect of the presence of nanosheets on the properties of microballoons, gel point occurrence, initial pentane content and the remained pentane during expansion, the expansion properties, and the particle morphology were studied. Kinetic studies showed that GO and GO‐MPS accelerated polymerization, whereas the reduced nanosheets exhibited a retardation effect on kinetics. The microballoons containing GO and GO‐MPS encapsulated more pentane and effectively retained it during the expansion process. Also, higher pentane content led to lower density of synthesized nanocomposites whereas improved expansion properties were achieved. According to the scanning electron microscopy images, due to retardation effect of reduced graphene oxide (rGO) and rGO‐MPS nanosheets, the shell surrounding the hydrocarbon in the microballoons contained more defects which could accelerate penetration of pentane through the shell. This resulted in a less expansion for the microballoons having poly(methyl methacrylate) (PMMA)/rGO or PMMA/rGO‐MPS shells compared to those having PMMA/GO or PMMA/GO‐MPS shells. POLYM. COMPOS., 39:950–960, 2018. © 2016 Society of Plastics Engineers