Abstract
Functional groups in a monomer molecule usually play an important role during polymerization by enhancing or decreasing the reaction rate due to the possible formation of side bonds. The situation becomes more complicated when polymerization takes place in the presence of graphene oxide since it also includes functional groups in its surface. Aiming to explore the role of functional groups on polymerization rate, the in situ bulk radical polymerization of hydroxyethyl acrylate (HEA) in the presence or not of graphene oxide was investigated. Differential scanning calorimetry was used to continuously record the reaction rate under both isothermal and non-isothermal conditions. Simple kinetic models and isoconversional analysis were used to estimate the variation of the overall activation energy with the monomer conversion. It was found that during isothermal experiments, the formation of both inter- and intra-chain hydrogen bonds between the monomer and polymer molecules results in slower polymerization of neat HEA with higher overall activation energy compared to that estimated in the presence of GO. The presence of GO results in a dissociation of hydrogen bonds between monomer and polymer molecules and, thus, to higher reaction rates. Isoconversional methods employed during non-isothermal experiments revealed that the presence of GO results in higher overall activation energy due to the reaction of more functional groups on the surface of GO with the hydroxyl and carbonyl groups of the monomer and polymer molecules, together with the reaction of primary initiator radicals with the surface hydroxyl groups in GO.
Highlights
Graphene is a single-atomic, two-dimensional layer of sp2 hybridized carbon atoms arranged in a honeycomb lattice
The greatest scientific interest has been found in the synthesis of nanocomposites of graphene or graphene oxide with polyaniline for the production of high performance supercapacitors with enhanced electrical conductivity [3,4,5,6,7,8,9,10]
In order to identify the oxidation of graphite to graphite oxide and its exfoliation to graphene oxide, as well as the presence of GO in the polymer matrix, X-ray diffraction (XRD) measurements were carried out for graphite, GO, neat PHEA, and the nanocomposites of PHEA and GO
Summary
Graphene is a single-atomic, two-dimensional layer of sp hybridized carbon atoms arranged in a honeycomb lattice. It has recently attracted enormous research interest due to its exceptional micromechanical, electrical, thermal, and optical properties [1,2]. Graphene has an extremely high elastic modulus, E ≈ 1 TPa and ultimate strength, σ∼ 130 GPa. Adding highly exfoliated carbon layers can significantly alter the mechanical and electrical properties of polymers at extremely small loadings [3]. Adding highly exfoliated carbon layers can significantly alter the mechanical and electrical properties of polymers at extremely small loadings [3] These properties make graphene a very important additive for the development of functional graphene-reinforced polymer composites with improved properties. The greatest scientific interest has been found in the synthesis of nanocomposites of graphene or graphene oxide with polyaniline for the production of high performance supercapacitors with enhanced electrical conductivity [3,4,5,6,7,8,9,10]
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