Junquan Sun

Ring-opening polymerization of d,l-lactide with bis(trimethyl triazacyclohexane) praseodymium triflate

Abstract Ring-opening polymerization of d , l -lactide (LA) was catalyzed by the well-defined bis(trimethyl triazacyclohexane) praseodymium triflate [(Me3TAC)2Pr(OTf)3] (Cat) for the first time. The effect of the [LA]/[Cat] molar ratio, solvents, temperature, and reaction time were investigated in detail. The results show that the praseodymium catalyst is very efficient in the melt polymerization, giving d , l -PLA with molecular weights of 104 in good conversion. The importance of the triazacyclohexane was shown by comparison to the poor catalytic activity of Pr(OTf)3.

Polymerization of methyl methacrylate with a homogeneous neodymium catalyst: Nd(naph)3-BuLi

Abstract Nd(naph)3-BuLi system was used to polymerize methyl methacrylate (MMA) at low temperature (−22 °C). Poly(methyl methacrylate) (PMMA) with a very high molecular weight (2 × 106) was obtained. The effects of ligand, Li Nd molar ratio, catalyst concentration, solvent, temperature and polymerization time were studied. The results showed that both low temperature (−22 °C) and neodymium naphthenate were indispensable to prepare high molecular weight PMMA to high conversion.

Synthesis, characterization and application of a novel carbon bridged half-metallocene chromium catalyst for methyl methacrylate polymerization

A new carbon bridged cyclopentadienyl chromium complex of the type [(C5H4)C(CH3)2 CH2(C5H4N)]CrCl2 was prepared by treatment of CrCl3·(THF)3 in THF solution with the lithium salt of ligand containing cyclopentadienyl and pyridyl groups. The chromium complex was characterized by 1H NMR and elemental analysis(EA), and the crystal structure was determined by X-ray diffraction analysis. Activated by Al(i-Bu)3, the chromium complex displayed a very high activity for methyl methacrylate (MMA) polymerization. After 24 hours,more than 95.5% MMA was converted to polymethyl methacrylate (PMMA) with a viscosity average molecular weight (Wη) of 416000 g·mol−1 at 60 °C for MMA/Al(i-Bu)3/chromium catalyst molar ratio of up to 2000:20:1. Effects of temperature, molar ratios of MMA/catalyst and catalyst/cocatalyst on the polymerization have been studied. The high conversion of MMA and high molecular weight of PMMA with narrow molecular weight distribution is caused by the unique stable active site formed by the new chromium complex and aluminum cocatalyst.

A novel lanthanocene catalyst system for the polymerization of methyl methacrylate Me2Si(CpSiMe3)2NdCl–n-BuMgCl †

Me2Si(CpSiMe3)2NdCl activated by n-BuMgCl at low molar ratio (1 : 1.2) was successfully used to polymerize methyl methacrylate (MMA) for the first time. Grignard reagent indicated better co-catalytic properties than alkyl aluminum. Effects of the catalyst concentration, polymerization time, temperature, and solvents were studied in bulk and solution polymerization respectively. The results showed that this catalyst system was very active for MMA polymerization in toluene at 40°C, producing PMMA with high molecular weight (53.5 × 104) and high conversion (100%).

Ethylene polymerization with novel silicon bridged homo-dinuclear cyanoethyl cyclopentadienyl complexes of titanium and zirconium

Novel homo-dinuclear silicon bridged cyanoethyl cyclopentadienyl complexes of titanium and zirconium (CH3)2Si((η5 − C5H3CH2CH2CN)(C5H5)MCl2)2(M = Ti(1), Zr(2)) were synthesized and developed for the polymerization of ethylene. Compared with their corresponding mononuclear complexes (η5 − C5H4CH2CH2CN)(C5H5)MCl2(M = Ti(3), Zr(4)), the dinuclear complexes had higher catalytic activity. And the polyethylene produced had a higher molecular weight than that obtained with mononuclear catalysts. Effects of conditions on the ethylene polymerization catalyzed by (2)/MAO (methylaluminoxane) were studied in detail. The catalyst showed a very high activity (> 106 g PE/mol Zr·h) under low catalyst concentration and high molar ratio of Al/Zr.