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Simultaneous reverse and normal initiation technique for atom transfer radical copolymerization (SR&NI ATRP) of styrene and methyl methacrylate in the presence of hexamethyldisilazane (HMDS)-modified silica aerogel nanoparticles (H-SAN) and investigating the effect of addition of H-SAN on the copolymerization and thermal properties of the products are discussed. Some unique features of the H-SAN are evaluated using nitrogen adsorption/desorption isotherm, SEM and TEM. Conversion and molecular weight determinations were carried out using GC and SEC respectively. Adding of H-SAN by 3 wt% results in decrement of conversion from 94 to 73%. In addition, molecular weight of copolymer chains decreases from 19500 to 16000 g.mol-1. However, polydispersity index values increases from 1.29 to 1.65. Linear increase of ln(M0/M) with time for all the samples shows that copolymerization proceeds in a living manner. Increasing thermal stability of the nanocomposites is demonstrated by TGA. DSC results show a decrease in glass transition temperature from 70.3 to 63.5 °C by addition of 3 wt% H-SAN.

Hydrophilic silica aerogel nanoparticles' surface was functionalized with 3-(trimethoxysilyl)propyl methacrylate (MPS). Then, the resultant functionalized nanoparticles were used in grafting through copolymerization of styrene and butyl acrylate by simultaneous reverse and normal initiation technique for atom transfer radical copolymerization (SR&NI ATRP) to synthesize tailor-made random poly (styrene-co-butyl acrylate) nanocomposites with twofold chains. Successful surface modification of hydrophilic silica aerogel nanoparticles with MPS is demonstrated by Fourier transform infrared spectroscopy and thermogravimetric analysis (TG). Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the synthesized silica aerogel nanoparticles. Evaluation of size distribution and 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 MPS-functionalized nanoparticles by 3 mass% results in a decrease in conversion from 71 to 46 %. Molecular weight ( M ) of the free poly (styrene-co-butyl acrylate) chains decreases by adding 3 mass% MPS-functionalized silica aerogel nanoparticles; however, polydispersity index (PDI) value increases from 1.17 to 1.48. Although PDI values of the attached poly (styrene-co-butyl acrylate) chains are increased from 1.54 to 1.76, M values reveal an increment by adding silica aerogel nanoparticles. H NMR spectroscopy results indicate that the molar ration of each monomer in the copolymer chains is approximately similar to the initial selected mole ratio of the monomers. Increasing thermal stability of the nanocomposites is demonstrated by TG. Differential scanning calorimetry also shows a decrease in glass transition temperature by increasing modified silica aerogel nanoparticles. [ABSTRACT FROM AUTHOR]

Hexamethyldisilazane (HMDS) was employed to surface modification of hydrophilic silica aerogel nanoparticles. Then, the resultant modified nanoparticles were used for in situ polymerization of styrene by simultaneous reverse and normal initiation technique for atom transfer radical polymerization (SR&NI ATRP) to synthesize tailor-made polystyrene nanocomposites. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) were employed for demonstrating success surface modification of hydrophilic silica aerogel nanoparticles with HMDS. Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the synthesized hydrophobic silica aerogel nanoparticles. Evaluation of size distribution and morphological studies were also performed by SEM and TEM. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography respectively. Addition of 3 wt% hydrophobic silica aerogel nanoparticles results in a decrease of conversion from 97 to 77%. Molecular weight of polystyrene chains decreases from 11095 to 8755 g.mol-1 by addition of 3 wt% hydrophobic silica aerogel nanoparticles; however, polydispersity index (PDI) values increases from 1.15 to 1.46. Appropriate agreement between theoretical and experimental molecular weight in combination with low PDI values demonstrate the living nature of the polymerization. Thermal stability of the neat polystyrene and its different nanocomposites are studied by TGA. Differential scanning calorimetry shows a decrease in glass transition temperature from 94.8 to 83.5 °C by adding 3 wt% of hydrophobic silica aerogel nanoparticles. [ABSTRACT FROM AUTHOR]

An organic modifier with vinyl moiety, 3-(trimethoxysilyl)propyl methacrylate (MPS), was employed to surface modification of hydrophilic silica aerogel nanoparticles. After that, double bond moieties on the surface were incorporated in grafting through polymerization of methyl methacrylate (MMA) via in situ simultaneous reverse and normal initiation technique for atom transfer radical polymerization (SR&NI ATRP). Grafting through polymerization of MMA results in tailor-made poly(methyl methacrylate) (PMMA) with twofold chains. Successful surface modification of hydrophilic silica aerogel nanoparticles with MPS is demonstrated by Furrier transform infrared spectroscopy and thermogravimetric analysis (TGA). Nitrogen adsorption/desorption isotherm is applied to examine surface area and structural characteristics of the synthesized silica aerogel nanoparticles. Evaluation of size distribution and morphological studies were performed by scanning and transmission electron microscopy. Conversion and molecular weight determinations were carried out using gas and size exclusion chromatography respectively. Addition of MPS-functionalized silica aerogel nanoparticles by 3 wt% results in decrement of conversion from 87 to 66%. By adding 3 wt% MPS-functionalized silica aerogel nanoparticles, molecular weight (M n ) of free MMA chains decreases from 13,563 to 9365; however, polydispersity index (PDI) value increases from 1.19 to 1.56. Although PDI values of attached MMA chains are increased from 1.48 to 2.08, M n values reveal an increment by adding MPS-functionalized silica aerogel nanoparticles content. Low PDI values of the products can appropriately demonstrate the living nature of polymerization. An increment of thermal stability of the nanocomposites by increasing MPS-functionalized silica aerogel nanoparticles is demonstrated by TGA results. Differential scanning calorimetry also shows a decrement in glass transition temperature by increasing MPS-functionalized silica aerogel nanoparticles loading. [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]

Encapsulation of organomodified montmorillonite within poly (methyl methacrylate) via in situ atom transfer radical polymerization with simultaneous reverse and normal initiation system (SR&NI ATRP) was successfully performed. Miniemulsion polymerization technique has been employed for its abundant advantages to encapsulate inorganic materials. Successful SR&NI ATRP was carried out using 4,4′-dinonyl-2,2′-bipyridine (dNbPy) as a hydrophobic ligand and cetyltrimethylammonium bromide (CTAB) as an effective cationic surfactant at high temperatures. Homogeneous distribution of droplets and particles with sizes in the range of around 170 nm was evaluated by dynamic light scattering (DLS) analysis. Final monomer conversion and molecular weight were determined by gravimetry and size exclusion chromatography (SEC) respectively. By increasing nanoclay content, conversion and molecular weight of nanocomposites decreased. Meanwhile, an increase in PDI values was also observed. X-ray diffraction (XRD) analysis results display organoclay layers disordered and delaminated in the polymer matrix. Thermal stability improvement of all the nanocomposites in comparison with the neat polymer was revealed by thermogravimetric analysis (TGA). Homogeneous distribution of spherical particles with sizes in the range of 170 nm was demonstrated by scanning electron microscopy (SEM) images. These results are complied with the DLS results. Transmission electron microscopy (TEM) image display a dispersion of partially exfoliated clay stacks in the matrix of PMNM 2. [ABSTRACT FROM AUTHOR]

Atom transfer radical polymerization (ATRP) of styrene in presence of mesoporous silica nanoparticles was carried out at 110 °C. Reverse atom transfer radical polymerization (RATRP) and simultaneous reverse and normal initiation for atom transfer radical polymerization (SR&NI ATRP) techniques were used as two appropriate introduced techniques for circumventing oxidation problems. Usage of metal catalyst in its higher oxidation state was the main feature of these initiation techniques in which deficiencies of normal ATRP were circumvented. Structure, surface area and pore diameter of synthesized mesoporous silica nanoparticles were evaluated using X–ray diffraction and nitrogen adsorption/desorption isotherm analysis. Average particle size was estimated around 600 nm by electron microscopy images. In addition, according to these images, nanoparticles revealed an appropriate size distribution. Particles size and their distribution were examined using scanning. Final monomer conversion was determined by using gas chromatography. The number and weight average molecular weights (Mn and Mw) and polydispersity indexes (PDI) were also evaluated by gel permeation chromatography. According to the results obtained, addition of mesoporous silica nanoparticles in both RATRP and SR&NI ATRP systems revealed similar effects: decrement of conversion and Mn and also increment of PDI values observed by increasing of mesoporous silica nanoparticles content. Improvement in thermal stability of the nanocomposites in comparison with neat polystyrene was demonstrated by thermogravimetric analysis (TGA). Moreover, in case of nanocomposites, thermal stability was obtained by higher loading of nanoparticles. A decrease in glass transition temperature by higher content of mesoporous silica nanoparticles has been demonstrated by differential scanning calorimetry analysis.