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Syndiotactic Poly (syndiotactic + poly)

Distribution by Scientific Domains

Polymers and Materials Science	100%

Selected Abstracts

Time-Resolved Synchrotron SAXS Observations on Sheared Syndiotactic Poly(propylene) Crystallization Process

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 16 2008
Huiying Wen
Abstract The in situ crystallization kinetics of syndiotactic poly(propylene) (sPP) has been investigated by synchrotron small-angle X-ray scattering (SAXS). The structure evolutions during the isothermal crystallization of sPP with different shear rates have been observed. The results show that shear accelerates the process of crystallization kinetics. Even under low shear rate, the lamellae can be distinctly oriented. In contrast, the lamellar parameters such as the long period, lamellar thickness, and the scattering invariant Q can change obviously only under high shear rate. A mesomorphic structure proposed by Strobl is adopted to elucidate the differences of shear effects with low and high shear rates. Based on all the analysis we are convinced that a relatively stable mesomorphic structure forms before shear is composed and the shear effects on the mesophase will be retained to a certain extent until crystallization is finished. [source]

A Study of the Use of Oscillatory Flow to Characterize Isotactic and Syndiotactic Poly(propylene)s

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 19 2006
Elena Rojo
Abstract Summary: A rheological characterization of poly(propylene)s (PP) of different tacticity, monomodal and bimodal molecular distribution and long chain branching (LCB), is presented. Loss factor , plotted as a function of the complex modulus G* allows to discriminate syndiotactic from isotactic PPs, as well as syndiotactic monomodal from bimodal samples. However, using such rheological plots is not effective to investigate the broadness of the molecular weight distribution and other rheological techniques are proposed. Isotactic and syndiotactic PPs submitted to electro beam irradiation give rise to thermorheological complexity, associated to LCB. The degree of LCB is estimated using complex viscosity results. Syndiotactic poly(propylene)s are more prone to give long branches than isotactic samples. A symptom of long chain branching is detected in irradiated syndiotactic PPs. [source]

Syndiotactic poly(propylene)/organoclay nanocomposite fibers: influence of the nano-filler and the compatibilizer on the fiber properties

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 5 2005
Zita Mlynar, íková
Abstract Melt spinning of nanocomposites prepared from syndiotactic poly(propylene) (sPP) and organolayered silicate (M-ODA), containing bound octadecyl ammonium chains, was investigated. The influence of the nano-filler reinforcement and the role of the addition of maleic anhydride grafted isotactic poly(propylene) (iPP-g-MA) as compatibilizer with respect to the fiber proportion was examined. The presence of nano-filler, the drawing ratio, and the compatibilizer addition afforded increased tenacity of the fibers. Only in the presence of the compatibilizer high drawing ratio of the sPP nanocomposite fibers was achieved. Transmission electron microscopy (TEM) was applied to monitor morphology development during nanocomposite fiber spinning in the presence and the absence of the compatibilizer. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Functional syndiotactic poly(,-hydroxyalkanoate)s via stereoselective ring-opening copolymerization of rac -,-butyrolactone and rac -allyl-,-butyrolactone

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2009
Noureddine Ajellal
Abstract The copolymerization of racemic ,-butyrolactone (rac -BLMe) with racemic "allyl-,-butyrolactone" (rac -BLallyl) in toluene, catalyzed by the discrete amino-alkoxy-bis(phenolate) yttrium-amido complex 1, gave new poly(,-hydroxyalkanoate)s with unsaturated side chains. The poly(BLMe - co -BLallyl) copolymers produced have a highly syndiotactic backbone structure (Pr = 0.80,0.84) with a random enchainment of monomer units, as evidenced by 13C NMR, and high molecular weight (Mn up to 58,000 g mol,1) with a narrow polydispersity (Mw/Mn = 1.07,1.37), as determined by GPC. The comonomer incorporation (5,50 mol % rac -BLallyl) was a linear function of the feed ratio. The pendant vinyl bond of the side-chains in those poly(BLMe - co -BLallyl) copolymers allowed the effective introduction of hydroxy or epoxy groups via dihydroxylation, hydroboration-oxidation or epoxidation reactions. NMR studies indicated that all of these transformations proceed in an essentially quantitative conversion and do not affect the macromolecular architecture. Some thermal properties (Tm, ,Hm, Tg) of the prepared polymers have been also evaluated. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3177,3189, 2009 [source]

Time-Resolved Synchrotron SAXS Observations on Sheared Syndiotactic Poly(propylene) Crystallization Process

A Novel Synthetic Procedure for Stereoblock Poly(propylene) with a Living Polymerization System,

MACROMOLECULAR RAPID COMMUNICATIONS, Issue 10 2004
Kei Nishii
Abstract Summary: Propylene polymerization was conducted at 0,°C in heptane or chlorobenzene (CB) by an ansa -fluorenylamidodimethyltitanium complex combined with dried, modified methylaluminoxane that had been treated by dilution with heptane and successively repeatedly vacuum dried to remove any free trialkylaluminiums. The post-polymerizations testified that the living polymerization proceeded irrespective of the solvent used. The heptane system gave the syndiotactic poly(propylene)s (PPs), whereas the CB system gave almost atactic PPs. After the first polymerization in heptane had been completed, the same amounts of propylene and CB were added for the second polymerization. This procedure gave the syndiotactic-atactic stereoblock PP with narrow molecular-weight distributions. Structure of the ansa -fluorenylamidodimethyltitanium complex and its application to the synthesis of syndiotactic-atactic stereoblock poly(propylene)s reported here. [source]

Activity of samarocene catalysts adsorbed on mesoporous silicates for the polymerization of methyl methacrylate

POLYMER INTERNATIONAL, Issue 11 2004
Dr Hajime Yasuda
Abstract A samarocene complex, (C5Me5)2SmMe(thf), was adsorbed on a series of mesoporous silicates of various pore sizes. Pre-treatment of the latter with AlMe3 before adding the complex was effective in deactivating the surface silanol functionalities. The silicates having relatively larger pore size tended to adsorb a larger amount of the complex. The polymerization of methyl methacrylate (MMA) by the complex adsorbed on the silicates with large pore sizes (>29 Å) quantitatively afforded highly syndiotactic poly(MMA)s with higher molecular weights compared with those obtained by the corresponding homogeneous system. Similar catalyst systems of smaller pore size were much less active. Copyright © 2004 Society of Chemical Industry [source]