mehdi salami-kalajahi

In this study, reversible addition-fragmentation chain transfer (RAFT) polymerization was used to synthesize hydrophobic polystyrene (PS), poly(methyl acrylate) (PMA), and poly(methyl acrylate-b-styrene) (PMA-b-PS) block copolymers with three distinct molecular weights. Polyaniline (PANI) was synthesized by electrochemical method. Proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) have both been used to examine the properties of the polymers synthesized. In aqueous media at room temperature, PANI has been co-assembled with PS, PMA, and PMA-b-PS. The size and morphology of the co-assembled structures have been examined using transmission electron microscopy (TEM), dynamic light scattering (DLS), and field emission scanning electron microscopy (FE-SEM). According to the findings, polymers hydrophobicity increased with increasing molecular weight, causing faster precipitation in aqueous solution and a reduction in particle size. The results demonstrated that adding conductive polymer produced core-shell morphologies, while the core morphologies are different. Thermodynamic principles governed morphology, and the most likely morphology to develop was the one that minimized the total surface free energy. The polymers caused the surface tension between the polymers with water and the surface tension between the primary polymer and the secondary polymer to be reduced by overlapping each other and precipitation.

By varying the level of graphene's surface oxidation in this paper, the thickness of the interphase region was altered, and its influence on the conductivity was investigated. Due to the similarity of water-based epoxy chemical groups with graphene oxide oxygen groups, the interphase region was reinforced. Infrared spectroscopy and thermal gravimetry were performed to evaluate the graphene oxide synthesis, and Raman spectroscopy was also performed to investigate the structural defects on graphene sheets. At first glance, based on the interphase region theory, it is expected that by increasing the oxidation rate of graphene nanosheets, the electrical conductivity of polymeric coatings will increase, and the percolation threshold will decrease. On the other hand, due to increased oxidation, the structural defect on graphene nanosheets increases, and the conductivity of the coatings is expected to decrease. Due to the opposite effect of the two factors mentioned above, the effectiveness of nanocomposite samples was studied, and the impressment of each factor was investigated in this project.

Laboratory runs can be minimized via experimental design which yields the optimum and best data regarding the independent parameters. In this research work, response surface methodology (RSM) based on a threelevel central composite design (CCD) was utilized to optimize and evaluate the interactive effects of processing conditions for polymerization of 1,3-butadiene (Bd) diene monomer using Ziegler-Natta catalyst. The polybutadiene rubber (PBR) having different cis content and molecular weight was obtained. The catalyst components included neodymium versatate (NdV3) as catalyst, triethyl aluminum (TEAL) as cocatalyst or activator, and ethylaluminum sesquichloride (EASC) as chloride donor. For the modeling, three independent variables, namely monomer concentration (8-28 wt%), reaction time (1.5-2.5 h), and reaction temperature (45-75ºC) at three levels were selected to optimize the dependent variables or responses including monomer conversion, viscosity-average molecular weight and the cis isomer content of the obtained polymer. The interaction between three crucial parameters was studied and modeled. Quadratic models were obtained to relate process conditions to dependent variables. It was observed that the optimal conditions predicted by RSM were consistent with the experimental data. Statistical analysis demonstrated that concentration of the monomer and the time of reaction significantly affected cis content. Moreover, processing conditions to achieve the desired response variables were predicted and experimentally approved. The optimal reaction conditions derived from RSM are monomer concentration = 19 wt%, polymerization time = 2 hours, and polymerization temperature = 50ºC. Polymerization was carried out at optimum conditions. The appropriate level of dependent variables including 94.2% monomer conversion, 151812 g/mol viscosity-average molecular weight and 98.8% cis content was acquired.

In this study, the effect of 1,2,3-trichloropropane (TCP) as trifunctional monomer on thermophysical properties of synthesized poly(ethylene tetrasulfide) (PETS) is investigated. To this end, different amounts of TCP (0-40 mol. % of halide-containing monomer) were incorporated into the structure of polysulfide polymer via interfacial condensation polymerization. Measurement of gel, fraction showed that by the introduction of only 10 mol. % of TCP, synthesized structure is almost crosslinked. The X-Ray Diffraction (XRD) results revealed that all samples are semi-crystalline whereas the crystallinity of samples strongly depends on the amount of TCP. All samples showed a glass transition temperature (Tg) less than 0 °C followed by melting temperature (Tm). Higher amountof crosslinking monomer resulted in higher Tg while Tm and heat of fusion (ΔHm) were reduced. According to ThermoGravimetric Analysis (TGA) results, all samples exhibited a two-stage degradation process. Although, the introduction of 10 mol. % TCP into the structure of PETS resulted in lower thermal stability of obtained polymer, adding higher amounts of TCP led to the higher thermal stability of polymers.

Hypothesis: Thermally stable nanocomposites were prepared by incorporation of carbon nanotubes (CNT) into the epoxy resin matrix cured by novolac resin. CNT modified with epoxy functional groups is capable of reaction with hydroxyl groups of novolac resin. Therefore, a new and robust method was planned for development of covalent bonding between the filler and matrix. On the other hand, due to slow reaction of epoxy and hydroxyl groups in the absence of catalyst, triphenylphosphine was used as the catalyst to accelerate the curing process.

CNT was modified with nitric acid to obtain oxidized CNT (CNTCOOH). After grafting of butane diol at the surface of CNTCOOH, hydroxyl-containing CNT (CNTOH) was prepared. Afterward, epoxy functional groups were applied at the surface of CNTOH through its modification with (3-glycidyloxypropyl) triethoxysilane in order to prepare epoxy-containing CNT (CNTG). Finally, CNTG and epoxy resin were placed in the hybrid network through the curing process with novolac resin. Finding: The results of FTIR-spectroscopy and X-ray photoelectron spectroscopy showed that modification of CNT was effectively carried out. X-ray diffraction analysis confirmed uniform distribution of CNTG in the matrix of cured epoxy resin. As thermogravimetric analysis exhibited, char yield of the cured epoxy resin (26.6%) was considerably increased to 32.8% and 38.2% through incorporation of 2 and 4 wt% of CNTG into the network, respectively. According to the scanning electron microscopy and transmission electron microscopy images, CNT showed tubular and entangled structure with smooth and uniform surface which even retained its structure after modification reaction. Finally, this approach can be successfully used for production of thermally-resistant thermoset hybrids for thermal protection applications

In current work, halogenated sunflower oil was reacted with Na2S3 to produce sunflower oil-based polysulfide polymer. Cloisite 30B as organomodified nanoclay was used in different contents to investigate its effect on the properties of the synthesized polymer. All nanocomposites were prepared via in situ polymerization method in aqueous media. Fourier Transform-InfraRed (FT-IR) spectroscopy revealed the inclusion of nanoclay in a polymeric matrix.X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) were used to study the degree of intercalation/exfoliation of nanoplatelets in matrices. Proton Nuclear Magnetic Resonance (1H NMR) was utilized to study the molecular weight of synthesized polymers. Thermal stability of nanocomposites was determined by means of Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) was used to investigate thermophysical properties. According to results, nanocomposite with 1 wt. % of Cloisite 30B showed an exfoliated morphology whereas the higher amount of nanoclay resulted in intercalated nanoplatelets with different degrees of intercalation. Also, adding more Cloisite 30B nanoplatelets led to more decrease in molecular weight. After the introduction of nanoclay into nanocomposites structure and increasing its content, the thermal stability of nanocomposites was improved whereas no significant improvement of thermal stability was observed by increasing clay content from 3 to 5 wt. %. Also, all samples showed only the glass transition temperature (Tg) and no distinct peak related to melting was observed. Adding more nanoclay resulted in higher Tg value due to the confinement effect of nanoplatelets.

Although reversible addition-fragmentation chain transfer (RAFT) polymerizationhas attracted great attention of many researchers over recent years,outstanding questions on the mechanism and kinetics of dithioester-mediatedRAFT polymerization (especially dithiobenzoates) still have remained unsolved. In thiswork, based on experimental observations and exact theoretical predictions, thekinetic schemes of RAFT polymerization are extended to a wider range of reactionssuch as irreversible intermediate radical terminations and reversible transfer reactions.The reactions which have been labeled as kinetic schemes are theoretically the mostprobable existing reactions and are used for mathematical modelling. The detailedkinetic scheme is applied to three kinds of RAFT polymerization systems by utilizing themethod of moments. Unknown kinetic rate constants are obtained by curve fitting of themodelling results and theoretical data, and applying the least square method; orestimation by considering the theoretical facts and experimental findings. The origin ofthe rate retardation and induction periods has been understood by studying the mainand pre-equilibrium stages of dithiobenzoate-mediated RAFT homopolymerization. Acopolymerization system in the presence of RAFT agent has also been examined toconfirm the capability of introduced kinetic scheme in different monomer/RAFT agentsystems. Although unknown parameters were obtained theoretically, their consistencywith other researcher's works shows the accuracy of the modelling procedure. Themodelling results are in excellent agreement with experimental data which proves thevalidity and applicability of the detailed kinetic scheme. The results have shown thatsome reactions may not occur in many RAFT polymerization systems and can beeliminated and therefore more kinetic and mechanistic studies are required.