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A newly developed initiation technique, activators regenerated by electron transfer, was successfully employed to synthesize MCM-41/ polystyrene nanocomposites by in situ atom transfer radical polymerization. Hexagonal structure, surface area, and morphological study of the synthesized MCM-41 nanoparticles were performed by using powder X-ray diffraction, nitrogen adsorption/desorption isotherm, scanning electron microscopy, and transmission electron microscopy respectively. Conversion and molecular weight evaluation was carried out using gas chromatography and size exclusion chromatography respectively. Remarkable decrease of conversion from 69% to 43% was observed by the addition of only 3 wt% MCM-41 nanoparticles. However, polydispersity index increases from 1.14 to 1.41. Increasing of thermal stabilities and also reduction of Tg by increasing MCM-41 nanoparticles loading were comprehended according to the results of thermogravimetric analysis and differential scanning calorimetry, respectively. [ABSTRACT FROM PUBLISHER]

Activator generated by electron transfer for atom transfer radical polymerization was employed to synthesize well-defined mesoporous silica nanoparticles/polystyrene composites. Inherent features of spherical mesoporous silica nanoparticles were evaluated by nitrogen adsorption/desorption isotherm, X-ray diffraction and scanning electron microscopy analysis techniques. Conversion and molecular weight evaluations were carried out using gas and size exclusion chromatography respectively. By the addition of only 3 wt% mesoporous silica nanoparticles, conversion decreases from 81 to 58%. Similarly, number average molecular weight decreases from 17,116 to 12,798 g mol −1 . However, polydispersity index (PDI) values increases from 1.24 to 1.58. A peak around 4.1–4.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric analysis shows that thermal stability of the nanocomposites increases by adding nanoparticles content. Decrease of glass transition temperature is also demonstrated by the addition of 3 wt% of silica nanoparticles according to the differential scanning calorimetry results. [ABSTRACT FROM AUTHOR]

Nanoporous silica aerogel particles were synthesizedviasol–gel process and modified with a hydrophobic surfactant. Batch polymerizations of styrene in presence of silica aerogel particles were studiedviafree 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. [ABSTRACT FROM PUBLISHER]

Graphene oxide (GO) was prepared from the oxidation of graphite and then it was functionalized with (3-aminopropyl)triethoxysilane (APTES) from hydroxyl groups by a coupling reaction. Subsequently, alpha-bromoisobutyryl bromide (BiBB) was attached to the APTES groups to yield initiator anchored graphene nanolayers (GOHBr). Then, GOHBr was used in different amounts as the precursor for atom transfer radical polymerization of styrene to evaluate the effect of graphene loading along with the graft density on the properties of final product. Successful in-plain attachment of APTES, BiBB, and polystyrene to GO was evaluated by Fourier transform infrared spectroscopy. Graphene interlayers expansion by oxidation and functionalization processes was evaluated using X-ray diffraction. The ordered and disordered crystal structures of carbon were evaluated by Raman spectroscopy. Morphology of graphene nanolayers was studied by scanning electron microscopy and also transmission electron microscopy. POLYM. COMPOS., 35:386-395, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Mesoporous silica nanoparticles (MCM-41) surface was functionalized with 3-(trimethoxysilyl)propyl methacrylate (MPS). Then, the resultant double bond containing nanoparticles were used in grafting through simultaneous reverse and normal initiation technique for atom transfer radical polymerization (SR&NI ATRP) of styrene to synthesize well-defined polystyrene nanocomposites with twofold chains. Nitrogen adsorption/desorption isotherm and X-ray diffraction analysis were used to evaluate characteristics of spherical MCM-41 nanoparticles. Morphological studies were also performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography respectively. Addition of MCM-41 nanoparticles by 3 wt.% results in a decrease of conversion from 93% to 82%. Molecular weight of the free and attached polystyrene chains decreases by adding 3 wt.% MCM-41 nanoparticles; however, PDI values increases from 1.27 to 1.78 for free chains and 1.87 to 2.48 for attached chains. A peak around 4.1 ppm which originates from hydrogen atom of terminal units of polystyrene chains in proton nuclear magnetic resonance spectra in combination with low PDI values can appropriately demonstrate the living nature of the polymerization. Increasing thermal stability of the nanocomposites is demonstrated by Thermogravimetric analysis. Differential scanning calorimetry also shows a decrease in glass transition temperature by increasing MCM-41 nanoparticles. MPS-functionalized MCM-41 mesoporous particles was used in grafting through SR&NI ATRP of styrene to synthesize well-defined polystyrene nanocomposites with two-fold chains. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) was modified with two different amounts of 3-(trimethoxysilyl)propyl methacrylate (MPS) by a silane coupling reaction. Atom transfer radical polymerization of styrene in the presence of different amounts of MPS-modified graphene was carried out to evaluate the effect of graphene loading along with the graft density on the properties of the products. Successful attachment of MPS on the surface of GO was evaluated using Fourier transform infrared spectroscopy. Expansion of graphene interlayers by oxidation and functionalization processes was evaluated using X-ray diffraction. The ordered and disordered crystal structure of carbon in pristine and surface modified graphenes was evaluated by Raman spectroscopy. Relaxation behavior of polystyrene chains in the presence of graphene layers and also effect of graft content on the chain confinement was studied using differential scanning calorimetry. High-density nanocomposites show much increase of T by addition of graphene content. Morphology of graphene nanolayers after modification processes was studied by scanning electron microscopy and also transmission electron microscopy. Flat and smooth morphology of graphene nanosheets was disturbed during the oxidation and functionalization processes and consequently wrinkled sheets with curvature were obtained. [ABSTRACT FROM AUTHOR]

Effect of pristine and modified MCM-41 on the kinetics of styrene atom transfer radical polymerization (ATRP) was studied using a double bound containing modifier at 110°C. Conversion, molecular weight and PDI were obtained during the polymerization reactions to study the polymerization kinetics. Addition of the both types of MCM-41 has resulted in inconsiderable variations on the kinetics of polymerization. A similar trend is observed for the molecular weight of the free chains; however, increasing MCM-41 content results in higher PDI values. Also, surface modification of MCM-41 results in lower polymerization rates. In the case of grafted chains, molecular weight and PDI values increase by increasing MCM-41 content. Polystyrene-coated MCM-41 nanoparticles were synthesized by ATRP. Effect of surface modification on the kinetics of ATRP was also investigated. [ABSTRACT FROM AUTHOR]

The effect of clay nanolayers and catalyst concentration on the kinetics of atom transfer radical copolymerization of styrene and butyl acrylate initiated by activators generated by electron transfer (AGET initiation system) or an alkyl halide (normal initiation system) was studied. Monomer conversion was studied by attenuated total reflection-Fourier transform infrared spectroscopy, and also proton nuclear magnetic resonance (1H NMR) spectroscopy was utilized to evaluate the heterogeneity in the composition of poly(styrene- co-butyl acrylate) chains. A decrease in the copolymerization rate of styrene and butyl acrylate in the presence of clay platelets was observed since clay layers confine the accessibility of monomer and growing radical chains. Considering the linear first-order kinetics of the polymerization, successful AGET and normal atom transfer radical polymerization (ATRP) in the presence of clay nanolayers were carried out. Consequently, poly(styrene- co-butyl acrylate) chains with narrow molecular weight distribution and low polydispersity indices (1.13-1.15) were obtained. The linearity of ln([M]0/[M]) versus time and molecular weight distribution against conversion plots indicates that the proportion of propagating radicals is almost constant during the polymerization, which is the result of insignificant contribution of termination and transfer reactions. Controlled synthesis of poly(styrene- co-butyl acrylate)/clay is implemented with the diminishing catalyst concentration of copper(I) bromide/ N, N, N′, N′′, N′′-pentamethyl diethylene triamine without affecting the copolymerization rate of normal ATRP. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 789-799, 2012 [ABSTRACT FROM AUTHOR]

Polymer-clay nanocomposites have been prepared by free radical and RAFT polymerizations. To investigate the effects of nanoclay content and its modification system on the kinetics of polymerization, two different commercial grades of clay including Na-MMT and Cloisite 30B have been used and a method has been developed for further modification of Na-MMT with two commercial modifiers containing either a long organic chain or a vinyl group. Also, kinetics of free radical and RAFT polymerizations of both styrene and methyl methacrylate in the presence of these nanoclays was studied. Morphology of the nanocomposites has been studied by XRD and the results have been assessed with TEM observations. Exfoliated structure was obtained for the nanocomposites with 1 wt.% of vinyl-containing clays. Thermogravimetric behavior of the nanocomposites has been studied by TGA. Incorporation of clays has resulted in an evident increase in thermal stability of both polymers. [ABSTRACT FROM AUTHOR]

The grafting through method was employed to study the effect of nanoclay confinement on the atom transfer radical polymerization (ATRP) of styrene. An ammonium salt containing a double bond on its structure was used as a clay modifier. Employing ATRP to polymerize styrene in the presence of modified montmorillonite resulted in a finely well-defined polystyrene nanocomposite. The gas chromatography (GC) results showed the linear increase of ln( M 0/ M) versus time, which indicated the controlled behavior of the polymerization. Another confirmation of the living nature of the polymerization was the linear increase of molecular weight against monomer conversion concluded from the gel permeation chromatography (GPC) data. Nanoclay exerted acceleration on the polymerization of free polystyrene chains. The polydispersity indexes of polymer chains increased by the addition of nanoclay. In the case of clay-attached polystyrene chains, number and weight-average molecular weights were lower than that of freely dispersed polystyrene chains. The polydispersity index of the clay-attached chains was higher in respect to the freely dispersed polystyrene chains. The living nature of polymer chains was more elucidated by Fourier transform infrared spectroscopy (FTIR). Exfoliation of the clay layers in the polymer matrix of polystyrene nanocomposite containing the lowest amount of nanoclay has proven by Transmission Electron Microscopy (TEM). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

A finely tuned-up and high-performance Monte Carlo simulation, which takes diffusion-controlled and chain-length-dependent bimolecular termination reactions into account, is developed to thoroughly simulate and compare free radical (FRP) and atom transfer radical polymerization (ATRP) of styrene. It is found out that the termination rate constant falls and eventually plateaus upon the increase of the chain length of radicals. In addition, average termination rate constant greatly decreases during ATRP; nonetheless, it remains almost unchanged and smaller in FRP. Moreover, there is an accumulation of CuBr in the reactor as the ATRP proceeds, while the concentration of CuBr decreases and finally plateaus. Polymer chains are entirely initiated at the beginning of the ATRP, whereas initiation of chains continues throughout the free radical polymerization up to the end of the reaction. Also, the dead polymers are much lower in concentration (only 20%) in ATRP as compared to FRP (about 50%). In addition, a shift (toward higher molecular weight) in the location of the peaks of molecular weight distributions can easily be seen for the ATRP system, whilst the chain length distribution of free-radically generated polymers remains the same throughout the free radical polymerization. The molecular weight distributions narrow as the atom transfer radical polymerization progresses. Finally, the simulation results correspond closely to the experimental data. [ABSTRACT FROM AUTHOR]

n optimized and high-performance Monte Carlo simulation is developed to take thorough account of four different cases of termination in styrene ATRP. According to the simulation results, the bimolecular termination rate constant sharply drops throughout the polymerization when either chain-length dependency of termination rate constant, gel effect, or both together is applied to the simulation. In addition, as expected, the initiator is quickly decomposed at the early stages of the polymerization. The concentration of the catalyst in lower oxidation state decreases at first and then plateaus at higher conversion; furthermore, the steady concentration of MY/L in the polymerization is the highest when the chain-lengthdependent diffusion-controlled termination rate constant is employed in the simulation. The rates of deactivation and chain end degradation reactions are also smaller in this case. Therefore, the fraction of dormant chains is higher throughout the reaction and consequently the portion of dead polymers decreases. Besides, molecular weight increases linearly with conversion; however, when neither gel effect nor chain-length dependency of termination rate constant is considered, the molecular weight deviates from linearity at the end of the reaction. The peak of chain length distribution shifts toward higher molecular weight too during the reaction. Finally, the molecular weight distribution broadens at higher conversion; however, the chain length distribution of polymers produced under conditions of applying chain-length-dependent diffusion-controlled termination rate constant is narrower. [ABSTRACT FROM AUTHOR]