Home  About us  Contact
 

Silicate Galleries (silicate + gallery)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Poly(styrene- b -tetrahydrofuran)/clay nanocomposites by mechanistic transformation

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2009
Zuleyha Yenice
Abstract Synthesis of poly(styrene- block -tetrahydrofuran) (PSt- b -PTHF) block copolymer on the surfaces of intercalated and exfoliated silicate (clay) layers by mechanistic transformation was described. First, the polystyrene/montmorillonite (PSt/MMT) nanocomposite was synthesized by in situ atom transfer radical polymerization (ATRP) from initiator moieties immobilized within the silicate galleries of the clay particles. Transmission electron microscopy (TEM) analysis showed the existence of both intercalated and exfoliated structures in the nanocomposite. Then, the PSt- b -PTHF/MMT nanocomposite was prepared by mechanistic transformation from ATRP to cationic ring opening polymerization (CROP). The TGA thermogram of the PSt- b -PTHF/MMT nanocomposite has two decomposition stages corresponding to PTHF and PSt segments. All nanocomposites exhibit enhanced thermal stabilities compared with the virgin polymer segments. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2190,2197, 2009 [source]

Long-lived layered silicates-immobilized 2,6-bis(imino)pyridyl iron (II) catalysts for hybrid polyethylene nanocomposites by in situ polymerization: Effect of aryl ligand and silicate modification

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009
Giuseppe Leone
Abstract Heterogeneous-layered silicate-immobilized 2,6-bis(imino)pyridyl iron (II) dichloride/MMAO catalysts, in which the active polymerization species are intercalated within sodium- and organomodified-layered silicate galleries, were prepared for producing hybrid exfoliated polyethylene (PE) nanocomposites by means of in situ polymerization. The inorganic filler was first treated with modified-methylaluminoxane (MMAO) to produce a supported cocatalyst: MMAO reacts with silicates replacing most of the organic surfactant, thus modifying the original crystallographic clay order. MMAO anchored to the nanoclay was able to activate polymerization iron complexes initiating the polymer growth directly from the filler lamellae interlayer. The polymerization mechanism taking place in between the montmorillonite lamellae separates the layers, thus promoting deagglomeration and effective clay dispersion. Transmission electron microscopy revealed that in situ polymerization by catalytically active iron complexes intercalated within the lower organomodified clay led to fine dispersion and high exfoliation extent. The intercalated clay catalysts displayed a longer polymerization life-time and brought about ethylene polymerization more efficiently than analogous homogeneous systems. PEs having higher molecular masses were obtained. These benefits resulted to be dependent more on the filler nature than on the ligand environment around the iron metal center and the experimental synthetic route. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 548,564, 2009 [source]

Synthesis of Polybutadiene Nanocomposites: In situ Polymerization of 1,3-Butadiene Catalyzed by Phyllosilicate Interlayer Spacing-Confined Cobalt(II) Phosphine Complexes

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 3-4 2009
Giuseppe Leone
Abstract Heterogeneous phyllosilicate interlayer spacing-confined cobalt catalysts were prepared by reaction of cobalt phosphine complexes with methylaluminoxane-modified clay. The catalytic systems obtained were used for the in situ polymerization of 1,3-butadiene. The polymerization taking place within the silicate galleries separates the pristine layer aggregates, allowing for the design of polybutadiene-based nanocomposites through the intercalation of the active polymerization centers. Depending on the type of cobalt complex used (i.e., type of phosphine bond to the metal) it is possible to control the microstructure (1,2 content) and the tacticity (percentage of rr, mr and mm triads) of the polymer growing directly in between the inorganic silicate host lamellae. [source]

Less-ordered lamellar structure of intercalated poly(L -lactide)/organo-modified montmorillonite hybrids

POLYMER ENGINEERING & SCIENCE, Issue 6 2006
Pham Hoai Nam
Hybrids of poly(L -lactide)/organophilic clay (PLACHs) have been prepared via a melt-compounding process using poly(L -lactide) (PLLA) and different contents of surface-treated montmorillonite modified with dimethyl dioctadecyl ammonium-salt. The crystalline structures of PLLA and dispersion states of clay particles in those PLACHs were investigated by use of wide-angle X-ray diffraction, small-angle X-ray scattering, transmission electron microscopy (both cross section and replication modes), and polarized optical microscopy. Those structures are viewed from the conformational changes of PLLA chains in the space of a few nanometer widths between silicate galleries to crystalline lamellae of several nanometer thicknesses, and spherulitic textures more than micrometer sizes. After annealing treatments at 115°C for 1 hr, the PLACHs formed coarse-grained spherulitic textures with 40 ,m diameter composed of less-ordered and fragmented lamellae, caused by the reduced mobility of the PLLA chain due to the dispersed clay particles in the PLLA matrix and the intercalation of the PLLA chains in the silicate galleries. The formation of the interfibril structure accompanied by the fragmented lamellae among the dispersed clay particles was examined. POLYM. ENG. SCI., 46:703,711, 2006. © 2006 Society of Plastics Engineers [source]