The influence of the nature of organoaluminum compound on kinetic heterogeneity of active sites in lanthanide‐based diene polymerization

The influence of organoaluminum compound on kinetic heterogeneity of active sites in lanthanide‐based diene polymerization was investigated. It was shown that heterogeneity of investigated catalytic systems was displayed in the existence of four types of active centers. They are formed at the beginning of the polymerization process and produce macromolecules with lengths that are definite for each type of active centers. The organoaluminum compound's nature greatly influences the kinetic activity of polymerization centers. The method of analysis of the curves' maximum distribution on kinetic activity and the change of kinetic activity of every active centers' type were proposed, which permits the calculation of values of concentration for each type of active center separately. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 358–368, 2003     

Multiple active site Monte Carlo model for heterogeneous Ziegler‐Natta propylene polymerization

In this study, the kinetics of propylene polymerization catalyzed with the fourth heterogeneous Ziegler‐Natta catalyst is studied. More than one type of active site is present in the propylene polymerization based on an analysis of the GPC curves. A multiple active site kinetic model (MSmodel) is proposed by using Monte Carlo technique. Good agreements in the polymerization kinetics are achieved for fitting the kinetic profiles with the MSmodel. In addition, the MSmodel is used to describe the dynamic evolutions of the active sites and their effects on the propylene polymerization. The simulated results indicate that different types of active sites have different polymerization kinetics and the site type can affect the propylene polymerization kinetics. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Modeling of the propylene polymerization catalyzed by single‐/multi‐active site catalyst: A Monte Carlo study

In the present study, a model is established to describe the propylene polymerization kinetics catalyzed by the typical catalysts with single‐/multi‐active site type in a liquid phase stirred‐tank reactor using the Monte Carlo simulation method, regardless of the mass and heat diffusion effects within the polymer particles. Many kinetic data, including polypropylene yield, concentration transformation of catalyst active sites, number–average molecular weight, etc., are obtained by the model. The simulated kinetic results are found to be in agreement with the reference ones obtained in a population balance model. Furthermore, the comparisons of the kinetic data between the polymerization catalyzed by the catalyst with single‐active site type (typically silica‐supported metallocene) and the catalyst with multi‐active site type (typically MgCl₂‐supported Ziegler‐Natta catalyst) have been studied using the model. Especially, the effects of hydrogen on the polymerization are studied using the model. The studied results show that the theory of catalyst active site can be used to explain the different propylene polymerization kinetics catalyzed by the typical catalyst with single‐/multi‐active site type. In addition, the role of hydrogen in the propylene polymerization needs to be emphasized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The first report on the atom transfer radical polymerization of an optically active acidic monomer based on L‐phenylalanine

For the first time, acidic monomer chiral N‐acryloyl‐L ‐phenylalanine was polymerized directly by atom transfer radical polymerization under mild conditions. Controlled polymerization was carried out in pure water, methanol/water mixture, or pure methanol using water‐soluble initiators, such as 2‐hydroxyethyl‐2′‐methyl‐2′‐bromopropionate and sodium‐4‐(bromomethyl)benzoate at room temperature. The corresponding optically active biocompatible amino acid‐based homopolymers were obtained in good yields with narrow molecular weight distributions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of imine‐carbon substituent in 6‐bromo‐2‐iminopyridine‐based cobalt(II) complexes on 1,3‐butadiene polymerization

6‐Bromo‐2‐iminopyridine cobalt(II) complexes bearing different imine‐carbon substituents ( Co1 – Co7 ) were synthesized and subsequently employed for 1,3‐butadiene polymerization. All the complexes were identified using Fourier transform infrared spectra and elemental analysis, and complexes Co1 and Co3 were further characterized using single‐crystal X‐ray diffraction analysis, demonstrating they adopted distorted trigonal bipyramidal and tetrahedral geometries, respectively. Activated by methylaluminoxane, these complexes exhibited high cis‐1,4 selectivity, and the activity was highly dependent on the substituent at the imine‐carbon position of the ligand. Addition of PPh₃ to the polymerization systems could enhance the catalytic activity and simultaneously switched the selectivity from cis‐1,4 to cis‐1,2 manner. On the basis of the obtained results, a plausible mechanism involving the regulation of selectivity and activity is proposed. © 2019 Society of Chemical Industry     

Gas phase polymerization of 1,3‐butadiene with supported neodymium‐based catalyst: Investigation of molecular weight

The gas phase polymerization of 1,3‐butadiene (Bd), with supported catalyst Nd(naph)₃/Al₂Et₃Cl₃/Al(i‐Bu)₃ or/and Al(i‐Bu)₂H, was investigated. The polymerization of Bd with neodymium‐based catalysts yielded cis‐1,4 (97.2–98.9%) polybutadiene with controllable molecular weight (MW varying from 40 to 80 × 10⁴ g mol^?1). The effects of reaction temperature, reaction time, Nd(naph)₃/Al(i‐Bu)₃ molar ratio, and cocatalyst component on the catalytic activity and molecular weight of polymers were examined. It was found that there are two kinds of active sites in the catalyst system, which mainly influenced the MW and molecular weight distribution of polybutadiene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1945–1949, 2004     

Perfectly AB‐alternating copolymers via alternating diene metathesis polymerization: one‐step synthesis,characterization and properties

Perfectly alternating copolymers with functional phosphate groups were synthesized via reacting diacrylates with terminal dienes using alternating diene metathesis polymerization, showing a controllable polymerization characteristic which was evidenced by changing the relative stoichiometry of the two monomers. The compositional analysis and the sequence structural information of the polymers obtained from ¹H NMR spectra demonstrated that the resulting copolymers possessed strictly alternating structure. In addition, the thermal and flame‐retardant properties of the alternating copolymers were investigated, indicating favorable thermal degradation and flame retardancy which is an important feature for future applications. This special combination of the benefits of metathesis polymerization and phosphorus chemistry is a highly versatile system for materials in many applications. © 2013 Society of Chemical Industry     

The determination of active filter aid adsorption sites by temperature-programmed desorption

Temperature programmed desorption (TPD) was used to evaluate the active sites of several filter aids that have been promoted for use by the deep-frying industry: activated carbon, aluminas, bleaching earths, diatomaceous earth, silica and synthetic magnesium silicate. TPD analysis determines both the total surface concentration of the active sites and the details of their intensity distribution. A correlation analysis was made between the adsorbents' oil treatment performance and the observed acidic/basic sites. For some of the adsorbents, the adsorption of free fatty acids and the percent change in the color of the oil was shown to relate to the total basic sites and acid sites, respectively. The study also showed that other factors might affect these adsorptivities.     

Acyclic diene metathesis polymerization: The synthesis of unsaturated polyketones

The first acyclic diene metathesis (ADMET) polymerization of unsaturated ketone containing monomers using the molybdenum catalyst, Mo(CHCMe₂Ph)(N-2,6-C₆H₃-i-Pr₂)[OCCH₃(CF₃)₂]₂ is reported. 6,6,8,8-Tetramethyl-1,12-tridecadiene-7-one undergoes homopolymerization; copoly-merizations are carried out with 1,9-decadiene and 2,12-dimethyl-2,12-dipentenylcyclododecan-1-one, 2,12-diallylcyclododecan-1-one, and trans-2,12-diallyl-2,12-dimethylcyclododecan-1-one These polymerizations are initiated under bulk conditions and are continued in solution. No evidence of Wittig chemistry is observed between the carbonyl functional group and the catalyst when a high degree of steric hindrance exists around the carbonyl moiety. Polymer structures were characterized by IR, ¹H NMR, and ¹³C NMR spectroscopy. Molecular weights were determined by endgroup analysis and gel permeation chromatography.     

Monte Carlo simulation of gas phase polymerization of 1,3‐butadiene. Part II: Kinetics optimization and confirmation

Studies on the deactivations and initiations of gas phase polymerizations of 1,3‐butadiene have been achieved by Monte Carlo simulation. Initiation and deactivation control the reaction before and after the peak of the polymerization rate, respectively. The influence of polymerization temperature has been studied. Monte Carlo modeling of polymerization kinetics and mechanism was confirmed by the agreement of experimental data and simulation results of polymerizations run with a temporary evacuation of monomer. The balance of catalysts and active chains is established by both initiation and chain transfer reactions with cocatalyst, which causes a ‘pseudo‐stability’ stage. © 2003 Society of Chemical Industry     

Propylene polymerization over MgCl2‐supported TiCl4 catalysts bearing different amounts of a diether internal electron donor: Extrapolation to the role of internal electron donor on active site

In this work, the composition of MgCl₂‐supported Ziegler‐Natta (ZN) catalysts bearing different amounts of 9,9‐bis(methoxymethyl)fluorine (BMMF) and the propylene polymerization over these catalysts are investigated. Based on the experimental results, the models of active sites suitable for ZN catalysts with/without internal donor BMMF are established, and they can be described as follows: atactic site (I)—isolated TiCl₄ monomeric species on the (110) lateral cut (around which there is no complexes), weakly isospecific site (II)—semi‐isolated and surrounded TiCl₄ monomeric species on the (110) lateral cut (in the vicinity of which BMMF or other TiCl₄ is adsorbed), and highly isospecific site (III)—dimeric TiCl₄ species (Ti₂Cl₈) on the (104) lateral cut. Meanwhile, the mechanism underlying the role of BMMF on active sites is revealed (i) convert atactic sites (I) to weakly isospecific site (II) by occupying either or both of L₁ or/and L₂ vacancies around site; (ii) improve the isotacticity of weakly isospecific site (II) in donor‐free ZN catalyst by adsorbing at L₂ vacancy or/and replacing the Cl for TiCl₄ at L₁; and (iii) replace highly isospecific site (III). In addition, these roles of BMMF are successively achieved according to the amount of BMMF added. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fe‐mediated ARGET atom transfer radical polymerization of methyl methacrylate in ionic liquid‐based microemulsion

Poly(methyl methacrylate) (PMMA) was synthesized by activator regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) of MMA in ionic liquid‐based microemulsion with polyoxyethylene sorbitan monooleate (Tween 80) as surfactant. The polymerization was carried out at 25°C with CCl₄ as initiator, FeCl₃·6H₂O/N,N,N′,N′‐tetramethyl‐1,2‐ethanediamine (TMEDA) as catalyst complex in the presence of reducing agent ascorbic acid (VC). The polymerization kinetics showed the feature of controlled/″living″ process as evidenced by a linear first‐order plot. The well‐controlled polymers were obtained with narrow polydispersity indices and the ionic liquid‐based microemulsions were transparent with a particle size less than 30 nm. The obtained polymer was characterized by ¹H NMR and gel permeation chromatography. The chain extension was successfully achieved by the obtained PMMA macroinitiator/FeCl₃·6H₂O/TMEDA/VC initiator system based on ARGET ATRP method. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Inhibition of radical polymerization in solvent‐based systems (security of solvent‐based radical polymerization of PSA‐acrylic in a plant reactor)

This article shows the influence of some chain‐transfer agents as inhibitors for acrylic solvent‐based polymerization. These chain‐transfer agents can offer significant advantages, as outlined below. The following chain‐transfer agents were studied to stop or slow down the polymerization process in the case of a runaway: n‐dodecyl mercaptan, trimethylolpropane‐trimercaptoacetate, phenothiazine, diphenylphenylen diamine, cuprum oxide, isopropanol, toluene, and carbon tetrachloride. Synthesized pressure‐sensitive adhesive based on acrylic polymers and containing 2‐ethylhexyl acrylate, methyl acrylate, and acrylic acid were used for the production of self‐adhesives with high cohesion. The polymerization was accomplished in ethyl acetate. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1354–1357, 2003     

Cure‐on‐demand wood adhesive based on the frontal polymerization of acrylates

We demonstrated for the first time a cure‐on‐demand wood adhesive using thermal frontal polymerization with Southern Pine wood. Monomer structure, initiator loading, and filler loading all had an impact on the strength of the adhesive and the cure‐on‐demand ability. More flexible, ethoxylated monomers produced stronger adhesives; though, the ethoxylate groups reduce the ability of the system to be polymerized frontally. Addition of a highly reactive comonomer (acrylic acid) to increase molecular weight between crosslinks along with the ethoxylated triacrylate increased the propensity for frontal polymerization and made a tougher polymer. Increasing initiator loading could help ensure front propagation, but a maximum initiator loading was reached where the gaseous byproducts of the peroxide initiator made the network highly porous and thus lacking strength. Fillers such as kaolin and sawdust helped overcome decreases in strength at high initiator loadings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44064.     

Zinc‐based catalyst for the ring‐opening polymerization of cyclic esters

A zinc‐based catalyst zinc bis[bis(trimethylsilyl)amide] was used for the polymerization of cyclic esters including L ‐lactide (L ‐LA) and 2‐methyl‐2‐carboxyl‐propylene carbonate (MBC). The polymerization of L ‐lactide in THF could be carried out successfully under mild conditions in very short time by using the zinc catalyst and alcohols as the initiators. Kinetic study in solution polymerization prooved the polymerization has high monomer conversion degree close to 100% and the molecular weight of the resulting polyester has linear increase with the increase of [M]₀ /[I] (molar ratio of monomer to initiator). Sequential polymerization of L ‐LA and MBC in THF also showed high MBC conversion of 94% with a narrow molecualr weight maintained, indicating a living nature of this polymerization. The zinc catalyst system has also been used for the L ‐LA bulk polymerization with a high monomer conversion. ¹³C NMR indicated the polymer possesses high regioregularity and the minor regioirregular component was owing to the D ‐LA in the monomer inserted into the polymer mainchain during the transesterifcation. Interaction between monomer and zinc catalyst has been found to be a key factor to sustain a homogenous solution during the initiating procedure. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

丁二烯气相聚合研究进展

介绍了目前国外丁二烯气相聚合的研究情况,包括丁二烯气相聚合用催化剂,聚合颗粒增长及模型化,聚合动力学等方面的最新进展。     

The architecture of hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE via one‐pot strategy combining living free radical polymerization with coordination polymerization

The copolymerization of styrene with ethylene was promoted by CpTiCl₃/BDGE/Zn/MAO catalyst system combining free radical polymerization with coordination polymerization via sequential monomer addition strategy in one‐pot. The effect of polymerization conditions such as temperature, time, ethylene pressure, and Al/Ti molar ratio on the polymerization performance was investigated. The hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE triblock copolymer was obtained by solvent extraction and determined by GPC, DSC, WAXD, and ¹³C‐NMR. The DSC result indicated that the aPS‐b‐random copolymer‐b‐PE had a T_g at 87°C and a T_m at 119°C which attributed to the T_g of aPS segment and the T_m of PE segment, respectively. The microstructure of the hydroxy‐functionalized aPS‐b‐random copolymer‐b‐PE was further confirmed by WAXD, ¹³C‐NMR, and ¹H‐NMR analysis; and these results demonstrated that the obtained block copolymer consisted of aPS segment, S‐E random copolymer segment, and crystalline PE segment. The connection polymerization of the hydroxy‐functionalized aPS with random copolymer‐b‐PE was revealed by GPC results. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

酶活性部位柔性的分形分析

引言蛋白质三维结构的研究一直是生物学上一个重要而复杂的问题。通过X晶体衍射和核磁共振技术,人们已经积累了大量的蛋白质结构数据,但进一步解析蛋白质结构与功能间的关系,尚存在一定难度。作为非线性科学分支的分形理论(fractaltheory),以其独特的研究方法揭示了自然界中非线性过程内在的随机性及其所具有的特殊规律性。虽然分形理论在20世纪70年代才首次提出[1],但     

Study of optically active methacrylates containing 1,1′‐binaphthyl side‐groups polymerized by anionic,group transfer and free radical methods

Optically active and racemic poly(meth)acrylates with pendant 1,1′‐binaphthalene moiety of 2‐methacryloyloxy‐ and 2‐acryloyloxy‐2′‐methoxy‐1,1′‐binaphthalene (MAMBN and AMBN) were synthesized by anionic, group transfer and free radical polymerization methods. Their polymerizability and chiroptical properties are somewhat different, depending on the three types of polymerization methods used. The yields for poly(MAMBN)s are lower than for poly(AMBN)s. The optical rotation of the optically active polymers is identical to that of the corresponding monomers. The values of specific rotation of optically active poly(AMBN)s are much larger than those of optically active poly(MAMBN)s. © 2002 Society of Chemical Industry     

Effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile using dialkylmagnesium as catalyst

An attempt was made to clarify the effect of addition of organoaluminum and organoboron compounds in the stereospecific polymerization of acrylonitrile (AN) initiated by dialkylmagnesium (R₂Mg) above 100°C. The triad isotacticity (i.e. the content of mm (m: meso)) as well as the viscosity-average molecular weight (M?_v) of polyacrylonitrile (PAN) increased when trialkylaluminum (R₃Al) and trialkylboron (R₃B) were used as additives. Diisobutylaluminum hydride [(i-C₄H₉)₂AlH] was found to be the best additive. in the stereospecific polymerization of AN, giving PAN with higher (mm) content (0.63), higher M?_v value (5.2 × 10⁴), and a yield approximately double that obtained using (n-C₆H₁₃)₂Mg alone. When the (n-C₆H₁₃)₂Mg/(i-C₄H₉)₂AlH system was used, the yield, (mm), and M?_v of PAN increased with polymerization temperature (T_p); maximum values of yield, (mm), and M?_v were obtained at c. 130°C. The optimum amount of additives was approximately equimolar to R₂Mg as initiator. The ¹³C chemical shift of α-carbon in R₂Mg at 90°C shifted by mixing with R₃Al and R₃B, respectively, indicating the existence of interaction between R₂Mg and the additives. The main role of the additives is considered to be suppression of the self-association of R₂Mg by strong interaction with R₂Mg.