chains. Similar to the effect of graphene content, a reverse behavior was observed for the attached chains. Efficiency of grafting reactions along with the graft contents was studied by X-ray photoelectron spectroscopy (XPS), elemental analysis, and thermogravimetry analysis. The grafting ratio of MPS modifier was calculated to be 9.7 % via the data of Si contents in the XPS survey scan data. Finally, the morphology of the functionalized graphene was studied by transmission electron microscopy.
Polystyrene nanocomposite with mixed free and anchored chains was synthesized by atom transfer radical polymerization. Attachment of 3-(trimethoxysilyl)propyl methacrylate with a double bond on the nanoporous silica aerogel surface results in a double bond grafted silica aerogel which could be incorporated into the polystyrene chains by a grafting-through process. Conversion and molecular weight evaluation was carried out using gas chromatography and gel permeation chromatography, respectively. Double bond containing silica aerogel has an inconsiderable effect on conversion. There is no considerable discrepancy between the molecular weights of the free and anchored chains. Addition of silica aerogel with pendant C@C bonds leads to increase of apparent rate constant of polymerization and also molecular weights. This is mainly because of initiator trapping in silica aerogel pores. Every percent of double bond containing silica aerogel with respect to styrene results in trapping of about 0.08 mol of ethyl alpha-bromoisobutyrate among the silica pores. POLYM. COMPOS., 34:1648COMPOS., 34: -1654COMPOS., 34: , 2013
Nanoporous silica aerogel particles were synthesized via sol-gel process and modified with a hydrophobic surfactant. Batch polymerizations of styrene in presence of silica aerogel particles were studied via free radical and reversible addition-fragmentation chain transfer (RAFT) polymerizations. Monomer conversion, molecular weight, and polydispersity index of each system were monitored during polymerization to investigate the reaction kinetics. According to results, in both systems, the presence of silica aerogel particles has a sensible influence on polymerization kinetic and adding aerogels results in decreased polymerization rate, conversion, and molecular weight. Moreover, the prepared samples were characterized by Fourier transform infrared spectroscopy. Also, thermal gravimetric analysis (TGA) and differential scanning calorimetric techniques was used to observe the effect of aerogel particles on thermal properties of synthesized nanocomposites. According to TGA depiction, in free radical samples, one-stage degradation, related to random chain scission, is observed while degradation of RAFT-prepared nanocomposites occurred in two steps due to the decomposition of RAFT moieties and random chain scission.
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