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In this work, we report a new synthetic scheme for synthesis of graft copolymers. At first, poly(styrene‐co‐acrylonitrile) copolymers with different molecular weights were synthesized via atom transfer radical polymerization (ATRP). Then, lithium aluminum hydride was used as reducing catalyst of nitrile groups to obtain poly(styrene‐co‐allylamine) copolymers. Amine groups of poly(styrene‐co‐allylamine) copolymers were reacted to 2‐bromo‐2‐methylpropionyl bromide (BiBB) to yield poly(styrene‐co‐N‐allyl‐2‐bromo‐2‐methylpropanamide) (poly(styrene‐co‐NABMPA)) as macroinitiator for "grafting from" ATRP. Then, ATRP of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) was performed to graft PDMAEMA side chains. Finally, self‐assembly behavior of synthesized graft copolymers was investigated in aqueous media with different pH values and morphology of obtained supramolecular structures was studied. Synthesized copolymers were well‐characterized by 1H NMR, 13C NMR, and gel permeation chromatography. Also, morphology of self‐assembled structures was studied by FE‐SEM images whereas dynamic light scattering was utilized to measure particle size and particle size distribution. Results showed that morphology of self‐assembled supramolecular structures depended on molecular weight of backbone and pH value of media. By changing the self‐assembly conditions, different morphologies including spherical, Janus, and interconnected Janus were obtained. [ABSTRACT FROM AUTHOR]

Among molecular structures, colloidal molecules have attracted the attention of the scientific community because of their distinct geometry (topology, size on a nanometer scale). In this field, dendrimers are an example of colloidal polymeric molecules which have a specific size and are identified and regulated by repeating units as generations. The dendrimers are very similar to the colloidal particles in geometric form and size, which is more evident in the higher generations of the colloidal dendrimers. On the other hand, the unique structural features of these macromolecules resemble them as macromolecular colloids. These properties including the high degree of freedom, the controllable molecular size and weight, the need for no initiator, the presence of end groups, the high drug transfer capacity, etc., have made dendrimers applicable to a variety of fields such as medicine, biomedical, pharmaceutical, catalyst, and so on. [ABSTRACT FROM AUTHOR]

Response surface methodology (RSM) with central composite design was used to optimize and analyze the molar ratio of catalyst components for polymerization of 1,3-butadiene (Bd) using Ziegler–Natta catalyst. In this research work, the catalyst component includes neodymium versatate (NdV3) as catalyst, triethylaluminum as cocatalyst or activator and ethylaluminum sesquichloride as chloride donor. The symbols [Nd], [Al], [Cl] and [Bd] were used for catalyst, cocatalyst, donor and monomer concentration, respectively. The interaction between three important and critical variables was studied and modeled. For this purpose, independent variables are [Bd]/[Nd], [Al]/[Nd] and [Cl]/[Nd] molar ratios at three levels to optimize the dependent or response ones which are monomer conversion, molecular weight and cis content of resulting polymer. Quadratic models were achieved and developed to correlate the catalyst components' molar ratio with dependent variables. The optimum conditions predicted via RSM were in good agreement with experimental data obtained from the experimental runs. The statistical analysis of the results showed that [Cl]/[Nd] molar ratio had a significant effect on monomer conversion and cis content. Furthermore, the catalyst components' molar ratio to reach the desirable response parameters is forecasted and experimentally verified. The optimum catalyst components' molar ratio derived via RSM is as follows: [Bd]/[Nd] = 5363.0, [Al]/[Nd] = 27.2 and [Cl]/[Nd] = 2.2. [ABSTRACT FROM AUTHOR]

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) samples were synthesizedviaaqueous atom transfer radical polymerization with DPnof 35, 151, 390, and 546 and dispersity of 1.13, 1.17, 1.20, and 1.18, respectively. All samples were exposed to temperature and pH variations at different concentration of polymer and salt (NaCl). Results indicated that cloud point (Tcl) can be controlled by changing DPn, polymer concentration, and ionic strength of solution. According to results,Tclof the PDMAEMA chains shifted to lower temperatures with increasing solution pH at all molecular weight ranges due to deprotonation of tertiary amine groups in polymer structure. However, higher molecular weight polymers were more sensitive to pH variation especially in alkaline media. Also, higher polymer concentration acted as driving force to decrease cloud point of samples and formation of aggregates that was more predominant for higher molecular weights at alkaline media.Tclof PDMAEMA chains decreased with increasing ionic strength even at low pH values for low molecular weight polymers. [ABSTRACT FROM PUBLISHER]

ABSTRACT The preparation of polystyrene/MCM-41 nanocomposites was carried out by 'grafting from' and 'grafting through' approaches and in the presence of unmodified MCM-41, using reversible addition-fragmentation chain transfer (RAFT) polymerization. The MCM-41 was modified by attaching S-dodecyl- S′-(α,α′-dimethyl-α′′-acetic acid)trithiocarbonate (DDMAT) as the RAFT agent and methacrylate group using 3-methacryloxypropyldimethylchlorosilane. The kinetics of styrene RAFT polymerization by different approaches was compared with the model polymerization mediated by free DDMAT. The quantity of the grafted chain grown from the surface and inside of the pores of MCM-41 and free polymer chains in bulk was determined by thermogravimetric analysis. The molecular weight of the produced polymer chains increased linearly with the monomer conversion for three methods. The gel permeation chromatography showed that the molecular weight of grafted and free polymer chains in the 'grafting from' approach is higher than other methods, and molecular weight distributions were relatively narrower whereas the rate of polymerization for 'grafting from' was higher. © 2013 Wiley Periodicals, Inc. Adv Polym Technol 2013, 32, 21372; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21372 [ABSTRACT FROM AUTHOR]

Reversible addition-fragmentation chain transfer (RAFT) polymerization of 1,3-butadiene using a trithiocarbonate chain transfer agent, S-1-dodecyl- S′-( r, r′-dimethyl- r″-acetic acid)trithiocarbonate (DDMAT), was investigated. For the first time, comprehensive kinetic study of solution RAFT polymerization of 1,3-butadiene is reported. Effect of some factors such as RAFT agent and initiator concentration and initial molar ratio of monomer to both RAFT agent and initiator on the rate of polymerization and molecular weight distribution (MWD) were examined experimentally and discussed quantitatively. The validity of quasi-steady state approximation (QSSA) was shown and the rate of polymerization's equation was obtained. Good compatibility with the experimental and theoretical values of molecular weights was obtained. Also, polybutadiene samples with narrow molecular weight distribution were synthesized. [ABSTRACT FROM AUTHOR]

A number of batch polymerizations were performed to study the effect of pristine nanoparticle loading on the properties of PMMA/silica nanocomposites. In order to improve the dispersion of silica nanoparticles in the PMMA matrix, the silanol groups of the silica are functionalized with methacrylate groups and modified nanoparticles were used to synthesize PMMA/modified silica nanocomposites. Prepared samples were characterized by thermogravimetric analysis (TGA), dynamic light scattering (DLS), dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). According to the results, introduction of modified nanoparticles results in better thermal and mechanical properties than those of pristine nanoparticles. Also, surface modification and increasing silica nanoparticles result in variation of thermal degradation behavior of nanocomposites. The best improvement of the mechanical and thermophysical properties is achieved for nanocomposites containing 7 wt.% silica nanoparticles. [ABSTRACT FROM PUBLISHER]

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]

Poly(styrene- co-methyl methacrylate) nanocomposites were synthesized using reverse atom transfer radical polymerization (RATRP) in miniemulsion. Cetyltrimethylammonium bromide (CTAB) as a cationic surfactant applicable at higher temperatures was used for miniemulsion stabilization. Successful RATRP was carried out by using 4,4′-dinonyl-2,2′-bipyridine (dNbPy) as ligand. Monodispersed droplets and particles with sizes in the range of 200 nm were revealed by dynamic light scattering (DLS). Conversion and molecular weight study was carried out using gravimetry and size exclusion chromatography (SEC) respectively. By adding clay content, a decrease in the conversion and molecular weight and an increase in the PDI value of the nanocomposites are observed. Thermal stability of the nanocomposites in comparison with the neat copolymer is revealed by thermogravimetric analysis (TGA). Increased T g values by adding clay content was also obtained using differential scanning calorimetry (DSC). Scanning electron microscopy (SEM) images of the nanoconposite with 1 wt % of nanoclay loading, display monodispersed spherical particles with sizes in the range of ∼ 200 nm. SEM findings are more compiled with dynamic light scattering (DLS) results. Well-dispersed exfoliated clay layers in the polymer matrix of the nanocomposite with 1 wt % nanoclay loading is confirmed by transmission electron microscopy (TEM) images and X-ray diffraction (XRD) data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Monte Carlo kinetic simulation method was performed to study the reversible chain transfer catalyzed polymerization (RTCP) of styrene in 80°C. The effect of different iodide based catalysts (AI) was investigated on RTCP systems by simulating the chain length distribution, the depletion rate of polymerization ingredients, average molecular weights and the monomer conversion. In RTCP systems a narrow distribution was obtained compared to iodide-mediated polymerization. Superior reversible chain transfer reaction constants (k and k) led to a more uniform chain length distribution and a faster PDI decrement. In each RTCP system k/k ratio, designates the concentration of A* by dictating the dominant side of exchange equilibriums which specifies the number of cross-termination reactions. Addition of cross-termination reactions to the iodide-mediated polymerization system decreases the number of combination reactions leading to lower average molecular weights. Higher k/k ratios also consequences in faster catalyst depletions and lessen monomer conversions. On the other hand, PhE-I was found to deplete rapidly in RTCP systems, changing the nonlinear increase of the number average molecular weight to a linear pattern. The Monte Carlo simulation results were in a fine agreement with experimental data which were obtained from different RTCP systems. [ABSTRACT FROM AUTHOR]

The effect of carbon nanotubes on the kinetics of free radical polymerization of methyl methacrylate (MMA) was investigated. To do this, pristine, acid treated, alcoholic and methacrylate-modified carbon nanotubes with different loadings were used and Conversion, molecular weight and polydispersity index (PDI) of all samples were monitored during polymerization. The results show that carbon nanotubes induce an induction time to polymerization system which is independent of modification system while decrease in monomer conversion can be improved by developing organic moieties on surface. Molecular weight and polydispersity index for free and attached-on-surface chains were studied separately and different kinetics behaviors were observed for them. Molecular weight of free chains was increased by adding carbon nanotubes while more modified nanotubes resulted in much increased molecular weight. On the other hand, more system stability of more modified nanotubes, which was tested using UV-Visible spectra, resulted in higher molecular weights. Adding more nanotubes in the case of MMA-modified nanotubes caused to determine an optimum loading value to reach maximum molecular weight of free chains which was ascribed to system stability according to UV-Visible results. In this optimum loading value, free chains had minimum PDI value. However, increasing carbon nanotubes content led to decreased molecular weight of attached chains while PDI values increased because of shielding effect as physical phenomenon. [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]

Abstract: To study the effect of silica nanoparticles on the kinetics of methyl methacrylate free radical polymerization, a number of batch polymerizations were performed using pristine and methacrylate-modified silica nanoparticles at 75°C. In addition, effect of temperature was investigated on the kinetics of polymerization with 1wt% loading of pristine nanoparticles. Monomer conversion, reaction rate, molecular weight and polydispersity index (PDI) of each polymerization were monitored during polymerization. According to results, no considerable change was obtained on the polymerization kinetics by introduction of any type of nanoparticles, while there is an optimum loading value in which the polymerization rate reaches its maximum level. A similar trend is observed for molecular weight of free chains; however, increasing silica content results in increased PDI values. Also, polymerizations rate is slower for batches containing modified nanoparticles. For chains which are grafted on the surface of modified nanoparticles, molecular weight and PDI values increase by increasing nanoparticle content. [Copyright &y& Elsevier]

In the current work, the Monte Carlo simulation method was applied to ethylene polymerization over Ziegler–Natta catalysts. As expected, polymerization over each center of a Ziegler–Natta catalyst leads to a polymer having a Schultz–Flory molecular weight distribution. Notwithstanding, the total molecular weight distribution obtained by all catalyst centers together is at least twice as broad as that of each center. As another interesting finding, the introduction of hydrogen to the reaction deactivates the catalyst active centers and thereby reduces the catalyst activity. Nevertheless, it does not mainly affect the polymerization kinetics. In addition, the polymer molecular weight falls as hydrogen is added to the reaction since it acts as a strong transfer agent. The same effect is seen when cocatalyst concentration increases. Hydrogen also widens the polymer molecular weight distribution. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 45–56, 2009 [ABSTRACT FROM AUTHOR]

In the present work, ethylene polymerization kinetics was modeled using moment equations. According to the results obtained, the molecular weight distribution of each active center follows a Schultz-Flory distribution. However, the molecular weight distribution of polymer produced is much broader than a Schultz-Flory distribution. Besides, the order of polymerization with regard to monomer concentration is higher than unity. Moreover, the catalyst active centers deteriorate in the presence of hydrogen and consequently catalyst yield drops; nevertheless, polymerization kinetics is not mainly affected by hydrogen. Hydrogen also reduces polymer molecular weight since it is a strong transfer agent in olefin polymerizations. Notwithstanding, it does not affect polydispersity index. Last of all, although increasing cocatalyst concentration does not influence the activity of active centers, it lessens the molecular weight as a transfer agent. [ABSTRACT FROM AUTHOR]

In situ controlled radical polymerization (CRP) is considered as an important approach to graft polymer brushes with controlled grafting density, functionality, and thickness on graphene layers. Polymers are tethered with chain end or through its backbone to the surface or edge of graphene layers with two in situ polymerization methods of "grafting from" and "grafting through" and also a method based on coupling reactions known as "grafting to". The "grafting from" method relies on the propagation of polymer chains from the surface- or edge-attached initiators. The "grafting through" method is based on incorporation of double bond-modified graphene layers into polymer chains through the propagation reaction. The "grafting to" technique involves attachment of pre-fabricated polymer chains to the graphene substrate. Here, physical and chemical attachment approaches are also considered in polymer-modification of graphene layers. Combination of CRP mechanisms of reversible activation, degenerative (exchange) chain transfer, atom transfer, and reversible chain transfer with various kinds of grafting reactions makes it possible to selectively functionalize graphene layers. The main aim of this review is assessment of the recent advances in the field of preparation of polymer-grafted graphene substrates with well-defined polymers of controlled molecular weight, thickness, and polydispersity index. Study of the opportunities and challenges for the future works in controlling of grafting density, site-selectivity in grafting, and various topologies of the brushes with potential applications in stimuli-responsive surfaces, polymer composites, Pickering emulsions, coating technologies, and sensors is also considered. Unlabelled Image • Polymer-grafting on graphene layers was reported by in situ controlled radical polymerization or coupling reactions, • In situ polymerization consists of "grafting from" and "grafting through" methods, • Coupling reactions is commonly known as "grafting to" method. • The "grafting from" method results in higher grafting densities, • Controlling grafting density, site-selectivity in grafting, and various topologies of the brushes are the targets, • Applications in smart surfaces, polymer composites, Pickering emulsions, colloidal systems, coatings, and sensors are considered. [ABSTRACT FROM AUTHOR]