1,721,008 research outputs found
Aqueous emulsion polymerization of styrene and substituted styrenes using titanocene compounds
No full textAqueous emulsion polymerization of styrene in the presence of half-titanocenes which CpTiCl3, (CpCH2CH2OCH3)TiCl3, and of the titanocene (Ph)(2)C[(Cp)(Flu)Ti]Cl-2 is effected. The polymer features are compared with those of polystyrene obtained in the same reaction conditions, by using Cp2TiCl2 as initiator.Titanocene (Ph)(2)C[(Cp)(Flu)Ti]Cl-2 does not show any activity in styrene polymerization. On the contrary, by using both half-titanocenes CpTiCl3 and (CpCH2CH2OCH3)TiCl3, stereoirregular polystyrene is produced. Aqueous emulsion polymerization of substituted styrenes (3-methyl-styrene, 4-methyl-styrene, 3-chloro-styrene, 4-chloro-styrene) is also performed in the presence of Cp2TiCl2. From all monomers, stereoirregular polymers are obtained. Monomer reactivity results dependent on the substituent on the aromatic ring. Aqueous emulsion styrene - 4-chloro-styrene copolymerizations are performed by using Cp2TiCl2, too. Copolymer composition totally reflects that of comonomers used in the feeding. According to a statistical distribution of comonomers, the product of the reactivity ratios is 1.1. (C) 2013 Elsevier Ltd. All rights reserved
Synthesis of di-block copolymers poly (Propylene oxide)block-poly (9-(2,3-epoxypropyl) carbazole) via sequential addition of monomers in one pot
No full textPolypropylene oxide (PPO) and poly(9-(2,3-epoxypropyl) carbazole) (PEPK) di-block copolymers are prepared in one pot via sequential monomer addition by using i-PrONa/i-Bu3Al as an anionic catalytic system. An almost 100% monomer conversion is obtained, and the length of each block is controlled through the monomer/catalyst ratio used. Copolymer molecular weights are quite close to theoretical values calculated assuming the formation of one polymer chain per catalyst; therefore, it is hypothesized that the polymerization reaction proceeds with a living character. The synthesis appears to be particularly efficient and versatile. The calorimetric properties of copolymers obtained in this work are remarkable, since they show two distinct Tg values, corresponding to the PPO and PEPK blocks. The optical measurements of di-block copolymers show more analogous features than those of PEPK homopolymer. Copolymer solution emission spectra just exhibit isolated carbazole fluorescence, whereas in the solid state, film spectra show excimer fluorescence
Stereoselective cyclopropanation by cyclocopolymerization of butadiene
No full text: An unprecedented cyclopropanation by cyclopolymerization reaction is presented. In particular, catalytic copolymerization processes of ethene and butadiene lead with high trans selectivity to a complete cyclocopolymerization of butadiene units. Ethene-based copolymers including cyclopropane and cyclopentane rings, which can be relevant to polyolefin applications, are obtained with high yields. Several aspects relative to the mechanism of this cyclocopolymerization reaction, including the high stereoselectivity, are discussed
Liquid crystalline behavior of polymer networks based on segmented chain mesogenic polymers.
No full textRigid-rod liquid crystalline polyesters based on n-alkoxyterephthalic acid and 4,4'-dihydroxybiphenyl.
No full text
Non-rigid liquid-crystalline networks based on linear, segmented-chain mesogenic polymers.
No full textStereoregular polymers with pendant carbazolyl groups: Synthesis, properties and optoelectronic applications
No full textThe most recent results concerning the stereospecific synthesis and the microstructural, chemico-physical and optical characterization of polymers containing pendant carbazolyl groups are reviewed for the first time. Stereoregular poly(N-alkenyl-carbazole)s, poly(-(Ncarbazolyl) methyl styrene), poly(omega)-(N-carbazolyl)alkyl acrylate)s and poly(omega)-(N-carbazoly)alkyl metacrylate)s are considered in this review, with a particular focus on the influence of polymer stereochemistry on photophysical behavior. Potential applications of these materials in light-emitting diodes (LEDs), electrochromic devices, electrophotography and holographic memories are also discussed. Among these, we show the appealing results of our experiments, concerning the color tuning in organic LEDs based on poly(N-pentenyl-carbazole) by means of the polymer chain stereoregularity
Phase Behavior and Molecular Structure of Liquid-Crystalline Polyesters with Flexible Lateral Substituents.
No full textLiquid crystalline behavior of polymer networks based on segmented chain mesogenic polymers
No full text- …
