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Styrene Units (styrene + unit)
Selected AbstractsStyrene,butadiene block copolymer with high cis -1,4 microstructureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Han Zhu Abstract The sequential block copolymerization of styrene (St) and butadiene (Bd) was carried out with an activated rare earth catalyst composed of catalyst neodymium tricarboxylate (Nd), cocatalyst Al(i-Bu)3 (Al), and chlorinating agent (Cl). The microstructure, composition, and morphology of the copolymer were characterized by FTIR, 1H NMR, 13C NMR, and TEM. The results show that styrene,butadiene diblock copolymer with high cis -1,4 microstructure of butadiene units (, 97 mol %) was synthesized. The cis -selectivity for Bd units was almost independent on the content of styrene units in the copolymer ranging from 18.1 mol % to 29.8 mol %. The phase-separated morphology of polystyrene (PS) domains of about 40 nm tethered by the elastomeric polybutadiene (PB) segments is observed. The PS- b - cis -PB copolymer could be used as an effective compatilizer for noncompatilized binary PS/cis -PB blends. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Synthesis of comb polymers via grafting-onto macromolecules bearing pendant diene groups via the hetero-Diels-Alder-RAFT click conceptJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2010Antoine Bousquet Abstract Comb polymers were synthesized by the "grafting-onto" method via a combination of Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization and the hetero-Diels-Alder (HDA) cycloaddition. The HDA reactive monomer trans, trans-hexa-2,4-dienylacrylate (ttHA) was copolymerized with styrene via the RAFT process. Crosslinking was minimized by decreasing the monomer concentration,whilst keeping monomer to polymer conversions low,resulting in reactive backbones with on average one reactive pendant diene groups for 10 styrene units. The HDA cycloaddition was performed between the diene functions of the copolymer and a poly(n -butyl acrylate) (PnBA) prepared via RAFT polymerization with pyridin-2-yldithioformate, which can act as a dienophile. The coupling reactions were performed within 24 h at 50 °C and the grafting yield varies from 75% to 100%, depending on the number average molecular weight of the PnBA (3500 g mol,1 < Mn < 13,000 g mol,1) grafted chain and the reaction stoichiometry. The molecular weights of the grafted block copolymers range from 19,000 g mol,1 to 58,000 g mol,1 with polydispersities close to 1.25. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1773,1781, 2010 [source] Photostabilization of styrene,ethylene,butylene,styrene block copolymer by hindered phenol and phosphite antioxidantsJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2006Cristina Luengo The photostabilization of poly(styrene- b -ethylene- co -butylene- b -styrene) (SEBS), by hindered phenols and their combination with phosphite antioxidants has been studied by using a variety of spectroscopic methods including FTIR, UV, and luminescence spectroscopy coupled with crosslinking and hydroperoxide analysis. The addition of a hindered phenol was found to photostabilize the SEBS in terms of the inhibition of discoloration, and the formation of hydroperoxides, acetophenone, and oxidation products, as well as chain scission and disaggregation of the styrene units. Strong synergism was found with combinations of a hindered phenol and phosphite antioxidant, especially with an increase in the phosphite concentration. Residual titanium traces present as impurities in the material were found to play an important role in the photo-oxidation of SEBS. Molecular weight appeared to be a determining factor in the proportion of chain scission/crosslinking reactions that occured. Nevertheless, the addition of antioxidants and the reduction of titanium content also proved satisfactory in stabilizing the low-molecular-weight material. J. VINYL. ADDIT. TECHNOL. 12:2,7, 2006. © 2006 Society of Plastics Engineers [source] Synergistic profiles of chain-breaking antioxidants with phosphites and hindered amine light stabilizers in styrene,ethylene,butadiene,styrene (SEBS) block copolymerJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 1 2006Cristina Luengo The photostabilization of poly(styrene- b -ethylene- co -butylene- b -styrene) (SEBS) by phosphite/p -hydroxybenzoate antioxidants and hindered phenol/hindered amine light stabilizers (HALS) was studied by using a variety of spectroscopic methods, including FTIR, UV, and luminescence spectroscopy coupled with crosslinking and hydroperoxide analysis. The results were compared with those obtained for hindered phenols and their combinations with phosphite antioxidants. All the stabilizing packages stabilized the SEBS in terms of the inhibition of discoloration and the formation of hydroperoxides, acetophenone, and oxidation products, as well as chain scission and disaggregation of the styrene units. Although phosphite/p -hydroxybenzoate combinations appeared to reduce the formation of oxidation products, they did not show any remarkable enhancement in long-term stabilization with respect to phenolic/phosphite antioxidants. On the other hand, strong synergistic profiles were found with the HALS. Mobility and diffusion impediments in the polymeric material appeared to play an important role in the stabilizing activity of the HALS. J. VINYL. ADDIT. TECHNOL. 12:8,13, 2006. © 2006 Society of Plastics Engineers [source] A New Family of Styrene/Diene RubbersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 9 2007Philippe Zinck Abstract The insertion of single styrene units into polyisoprene is demonstrated using borohydrido rare earth/dialkylmagnesium systems. This yields a new family of styrene/diene copolymers (SBR rubbers). The resulting poly[(1,4- trans -isoprene)- co -styrene] exhibits quite narrow molecular weight distributions, up to 30% inserted styrene, and a 96,98% 1,4- trans -microstructure. The presence of a bulky and electron-rich ligand in the coordination sphere of the metal leads to an increase of the amount of styrene inserted and narrower chemical composition and molecular weight distributions. The presence of significant quantities of styrene in the medium does not alter the selectivity of the reaction, in contrast with cis -specific polymerizations. [source] Styrene/substituted styrene copolymerization by Ph2Zn,metallocene,MAO systems: homo- and copolymerization of p -methoxystyrene with styrene,POLYMER INTERNATIONAL, Issue 5 2008Franco M Rabagliati Abstract BACKGROUND: The present work is part of a general study regarding the homo- and copolymerization of styrene using diphenylzinc,additive initiator systems, with the aim of improving the properties of commercial atactic polystyrene. The study is focused on syndiotactic polystyrene and/or copolymers of styrene (S) with substituted styrene, styrene derivatives or various ,-olefins. This research has been ongoing over the last 15 years. RESULTS: The reported experiments show that binary metallocene,methylaluminoxane (MAO) and ternary Ph2Zn,metallocene,MAO, depending on the metallocene employed, are capable of inducing both homo- and copolymerization of styrene and p -methoxystyrene (p -MeOS). The results indicate that for a styrene/p -MeOS mole ratio with p -MeOS > 25% the product obtained has only a minor incorporation of styrene units. The efficiency of the metallocenes studied follows the order bis(n -butylcyclopentadienyl)titanium dichloride ((n -BuCp)2TiCl2) > indenyltitanium trichloride (IndTiCl3) > Cp2TiCl2. CONCLUSION: Metallocenes (n -BuCp)2TiCl2, Cp2TiCl2 and IndTiCl3 in binary systems combined with MAO, as well as in ternary systems combined with Ph2Zn and MAO, induce the homopolymerization of p -MeOS and its copolymerization with styrene. The styrene/p -MeOS copolymer obtained was enriched in p -MeOS with respect to the initial feed, in agreement with the I+ inductive effect of the methoxy group in the para position of styrene. As already reported, the role of Ph2Zn was nullified by its complexation with the p -MeOS comonomer. Copyright © 2008 Society of Chemical Industry [source] High-Density DNA Functionalization by a Combination of Cu-Catalyzed and Cu-Free Click ChemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2010Katrin Gutsmiedl Dipl.-Chem. Abstract We report the regioselective Cu-free click modification of styrene functionalized DNA with nitrile oxides. A series of modified oligodeoxynucleotides (nine base pairs) was prepared with increasing styrene density. 1,3-Dipolar cycloaddition with nitrile oxides allows the high density functionalization of the styrene modified DNA directly on the DNA solid support and in solution. This click reaction proceeds smoothly even directly in the DNA synthesizer and gives exclusively 3,5-disubstituted isoxazolines. Additionally, PCR products (300 and 900 base pairs) were synthesized with a styrene triphosphate and KOD XL polymerase. The click reaction on the highly modified PCR fragments allows functionalization of hundreds of styrene units on these large DNA fragments simultaneously. Even sequential Cu-free and Cu-catalyzed click reaction of PCR amplicons containing styrene and alkyne carrying nucleobases was achieved. This new approach towards high-density functionalization of DNA is simple, modular, and efficient. [source] | ||||||||||