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High Cis (high + cis)

Distribution by Scientific Domains
Polymers and Materials Science100%

Selected Abstracts

Preparation of high cis -1,4 polyisoprene with narrow molecular weight distribution via coordinative chain transfer polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2010
Changliang Fan
Abstract High cis -1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)3), dimethyldichlorosilane (Me2SiCl2), and diisobutylaluminum hydride (Al(i -Bu)2H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual-catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of high cis -1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i -Bu)2H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i -Bu)3), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i -Bu)2H. Finally, CCTP polymerization mechanism is validated by continuously decreased Mw/Mn value of polymer when increasing concentration of Al(i -Bu)2H extra added in the Nd(ver)3/Me2SiCl2/Al(i -Bu)3 catalyst system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source]

Styrene,butadiene block copolymer with high cis -1,4 microstructure

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007
Han 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]

Preparation of high cis -1,4 polyisoprene with narrow molecular weight distribution via coordinative chain transfer polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 21 2010
Changliang Fan
Abstract High cis -1,4 polyisoprene with narrow molecular weight distribution has been prepared via coordinative chain transfer polymerization (CCTP) using a homogeneous rare earth catalyst composed of neodymium versatate (Nd(vers)3), dimethyldichlorosilane (Me2SiCl2), and diisobutylaluminum hydride (Al(i -Bu)2H) which has strong chain transfer affinity is used as both cocatalyst and chain transfer agent (CTA). Differentiating from the typical chain shuttling polymerization where dual-catalysts/CSA system has been used, one catalyst/CTA system is used in this work, and the growing chain swapping between the identical active sites leads to the formation of high cis -1,4 polyisoprene with narrowly distributed molecular weight. Sequential polymerization proves that irreversible chain termination reactions are negligible. Much smaller molecular weight of polymer obtained than that of stoichiometrically calculated illuminates that, differentiating from the typical living polymerization, several polymer chains can be produced by one neodymium atom. The effectiveness of Al(i -Bu)2H as a CTA is further testified by much broad molecular weight distribution of polymer when triisobutylaluminum (Al(i -Bu)3), a much weaker chain transfer agent, is used as cocatalyst instead of Al(i -Bu)2H. Finally, CCTP polymerization mechanism is validated by continuously decreased Mw/Mn value of polymer when increasing concentration of Al(i -Bu)2H extra added in the Nd(ver)3/Me2SiCl2/Al(i -Bu)3 catalyst system. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 [source]