Xufeng Ni

Monte Carlo simulation of gas phase polymerization of 1,3-butadiene Part I. Modeling and programming

Monte Carlo method has been firstly applied to gas phase polymerization system. The kinetics of gas phase polymerization of 1,3butadiene catalyzed by rare earth complex with trialkyl aluminum is discussed. Both absorption and diffusion of monomer in polymer particles are considered. A model and a computer program to simulate gas phase polymerization system are established. The reaction rate constants are obtained by simulating all the five elemental reactions of the polymerization including propagation. According to the results of Monte Carlo simulation, three reasonable polymerization rate versus time curves coincide with experiments with errors between 0.91 and 5.78%. Two kinds of chain transfer reaction contain similar possibilities but play different roles in polymerization. q 2000 Published by Elsevier Science Ltd.

HETEROCYCLIC SCHIFF BASE NEODYMIUM COMPLEX AS CATALYST FOR RING-OPENING POLYMERIZATION OF ε-CAPROLACTONE *

An aromatic heterocyclic Schiff base neodymium complex bearing thiazole was synthesized and its activity in the ring-opening polymerization of e-caprolactone (CL) was examined. The conditions of the CL/Nd molar ratio, monomer concentration, polymerization time and temperature were investigated. Activities of ca.171 kg/Nd·h were obtained under the optimum condition (CL/Nd = 1600 (molar ratio), [CL] = 2.26 mol L-1, 1 h at 50°C), giving a poly(e-caprolactone) (PCL) of number-average molecular weight Mn= 5.4 × 104 and molecular weight distribution MWD = 1.96. The conversion of CL monomer as high as 94% was observed after polymerized for one hour. The mechanism of coordination polymerization has also been illustrated.

High transparent alternate copolymer of norbornene with isoprene catalyzed by bis(phenoxy–imine) titanium complex

A novel highly transparent alternate copolymer of norbornene with isoprene was prepared using a coordination catalytic system composed of bis(phenoxy–imine) titanium complexes and triisobutylaluminum. Distortionless enhancement by polarization transfer 13C NMR microstructure analysis of the copolymer reveals the vinyl-type addition nature of norbornene in the copolymer. The content of norbornene in the copolymer stayed constant at approximately 53%, varying the monomer feed ratio and conversion, which implied an alternating nature in the copolymer backbone. The copolymer obtained with a relatively high molecular weight (Mn = 1.05 to 2.27 × 105 g mol−1) shows good thermal stability and a moderate glass transition temperature (Tg = 75–79.5 °C). The copolymer also exhibits admirable transparency in the visible wavelengths (maximal transmittance ≈ 98%).

Bis(phenolate) N-Heterocyclic Carbene Rare Earth Metal Complexes: Synthesis, characterization and Applications in the Polymerization of n-Hexyl Isocyanate

The rare earth complexes [Ln(L)2K(thf)] bearing a bis(phenolate) N-heterocyclic carbene (NHC) ligand (L = 1,3-bis[O-4,6-di-tBu-C6H2-2-CH2][C(NCH2CH2CH2N)], Ln = Nd (1), Y (2)) were synthesized in situ by the reaction of L1 with KN(SiMe3)2 and Ln[N(SiMe3)2]. The bis(phenolate) NHC precursor L1 also coordinated with rare earth metal forming bis(phenolate) pyrimidinium-bridged rare earth metal complexes [ Ln2(L1)3] (L1 = 1,3-bis[O-4,6-di-tBu-C6H2-2-CH2][CH(NCH2CH2CH2N)]+Cl−, Ln = Sm (3), Y (4)). Very high molecular weight (up to 106) and narrow molecular weight distribution (Mw/Mn = 1.7–2.3) polyhexyl isocyanate could be obtained by using the pyrimidinium based NHC rare earth metal complexes 1, 2 as well as imidazolinium based NHC rare earth complexes 5–7. The NHC complexes were found to be highly active towards the polymerization of n-hexyl isocyanate whereas non-NHC rare earth metal complexes 3, 4, 8 were inactive. The radius of rare earth metal, solvent, polymerization temperature and the structure of the ligand greatly affected the catalytic activity of polymerization. The mechanism of the initiation of the polymerization was studied and the NHC moiety played an important role in the initiation step which was evidenced via NMR analysis.

Polymerization of conjugated dienes with a homogeneous Ziegler–Natta catalytic system based on a carbon-bridged bis(phenolate) yttrium alkyl complex

A novel carbon-bridged bis(phenolate) yttrium alkyl complex [(EDBP)Y(CH2SiMe3)(THF)3] (1) was synthesized by a reaction of 2,2′-ethylidene-bis(4,6-di-tert-butyl-phenol) (EDBPH2) and Y(CH2SiMe3)3. The structure of complex 1 was determined by X-ray crystallography. Homo- and copolymerization of isoprene and 1,3-butadiene was carried out and catalyzed by the 1/MAO/triisobutylaluminum (TIBA) system. The effects of TIBA/MAO and the total [Al]/[1] molar ratio on the activity and regioselectivity of polymerization, kinetics and controllable characteristics of the polymerization system were also investigated.

n-Octyloxyallene homopolymerization and random copolymerization with styrene using catalyst system composed of lanthanide Schiff-base complexes and Al(i-Bu)(3)

The catalyst system composed of lanthanide Schiff-base complexes with [3,5-tBu2-2-(O)C6H2CH=NC6H5]3Ln(THF)(Ln(Salen)3, Ln = Sc, Y, La, Nd, Sm, Gd, Yb) and triisobutyl aluminum shows high activity for n-octyloxyallene (A) homopolymerization with narrow molecular weight distribution (MWD). The influences of reaction conditions on polymerization behavior are investigated, and poly(n-octyloxyallene) has a weight average molecular weight (Mw) of 20.6 × 103 with MWD of 1.39 and 100% yield is obtained under the optimum conditions: [Al]/[Y] = 50 mol/mol, [A]/[Y] = 100 mol/mol, with polymerization at 80 °C for 16 h in bulk. The kinetic studies of n-octyloxyallene homopolymerization indicate that the polymerization rate is first-order with respect to the monomer concentration and shows some controlled polymerization characteristics. Random copolymer of n-octyloxyallene with styrene is obtained by using the same binary catalyst system; the reactivity ratios of the comonomer determined by Kelen-Tüdös method are rA = 1.20 and rSt = 0.35, respectively, the ratio of each segment and Mw of the resulting copolymer could be controlled by varying the feed ratio of each monomer. Determined by differential scanning calorimetry, the copolymers obtained show only one glass transition temperature, which increases gradually with the increase of styrene content in the copolymer.