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1.
将缩聚产物分子量分布(MWD)的MonteCarlo方法和聚合反应动力学的MonteCarlo方法结合起来,可在研究聚合反应动力学的同时获得MWD随时间的变化.将该方法用于研究非等活性的AB—AA型缩聚反应的动力学与实验结果十分一致.通过考察高活性AA单体加入后对其动力学行为和相应的MWD的影响,作者提出了对聚苯撑醚砜的AB型缩聚合成中加快其反应速度和改进MWD的实用方法.  相似文献   

2.
研究了在双十六烷基二甲基溴化铵(DCDAB)形成的微泡溶液中,二苯酮(BP)/三乙胺(TEA)体系的光化学初级反应和引发MMA光聚合反应.动力学实验结果表明,DCDAB微泡对聚合反应有显著的催化作用,使聚合速度提高近4倍左右,其效果和离子型胶束的催化作用结果相近.由DCDAB微泡中光聚合得到的产物PMMA,具有较高的结构规整性,它的间同和全同结构可达70%左右.  相似文献   

3.
研究了新型高活性乙烯气相聚合催化剂TiCl4/MgCl2/ZnCl2/SiCl4/醇/Al(i-Bu)3体系中钛和醇组分含量对聚合反应和产物颗粒形态的影响。测定了乙烯气相聚合反应动力学曲线,确定了聚合动力学方程。用SEM,DSC,WAXD,^1^3CNMR对催化剂及聚合物的形态,结构和性能进行了分析和表征。  相似文献   

4.
MonteCarloSimulationofBandTextureFormationinMacroscopicallyOrientedSemirigidPolymerSystemZhangHong-dong;YANDong;andYANGYu-lia...  相似文献   

5.
运用BOC-MP方法和MonteCarlo模拟方法,讨论了在钾存在的情况下,Cu(100)上WGS反应中各反应物种吸附热性能的变化,以及各表面基元反应步骤动力学参数的变化规律.研究结果表明,当钾处于低覆盖度时(<0.10),WGS反应的反应速率随表面钾浓度的增大而增大;而当钾表面浓度较高时,反应速率却随表面钾覆盖度的增大而减小.这可能是由于反应的速控步骤随表面钾覆盖度的变化而发生了改变  相似文献   

6.
研究了金刚石格点上自避随机行走(SAW)尾形链,采用精确计数和MonteCarlo模拟方法求得该SAW尾形链的构象数C(D)1(N)和均方末端距[h(D)1(N)]2及其分量随链长N的变化关系.发现它们与自由SAW链一样都服从标度律,从这些量的计算机实验数据拟合求出了金刚石格点上SAW尾形链的临界指数和格点指数.计算结果还表明短链SAW在壁的法向与NRW尾形链一样有所伸展,均方末端距的法向分量几乎是平行分量的2倍;但随N→∞,链自回避效应对壁的作用有所屏蔽.这些都与简立方格子模型上得到的结果一致.  相似文献   

7.
运用BOC-MP方法和Monte Carlo模拟方法,讨论了在钾存在的情况下,Cu(100)上WGS反应中各反应物种吸附热性能的变化,以及各表面基元反应步骤动力学参数的变化规律,研究结果表明,当钾处于低覆盖度时(〈0.10),WGS反应的反应速率随表面钾浓度的增大而增大;而当钾表面浓度较高时,反应速率却随表面钾覆盖度的增大而减小。这可能是由于反应的速控步骤随表面钾覆盖度的变化而发生了改变。  相似文献   

8.
李蕾 《分子催化》1998,12(2):90-100
采用以ASED-MO为基础的结构自动优化的EHTOPT法及Monte-Carlo法,对甲醇羰基化制乙酸的催化剂分子结构及共聚物配体的交替结构进行了理论研究。  相似文献   

9.
量子MonteCarlo固定节面法试探函数研究黄宏新曹泽星(湖南师范大学化学系长沙410081)关键词量子MonteCarlo方法试探函数奇点条件固定节面量子MonteCarlo(FNQMC)方法是QMC方法中使用最多的一种,它的试探函数一般是这样组...  相似文献   

10.
通过对偏氯乙烯(VDC)和丙烯酸酯类(ACR)单体共聚物熔点变化的测定,比较其与Flo-ry方程的偏离性,结合Monte-Carlo模拟及1HNMR的结果,推断了不同共聚单体对共聚物结晶性的影响以及共聚物的基本晶体结构。  相似文献   

11.
Compared with other types of polymerization, the molecular weight and its distribution (MWD) of equilibrium ring‐opening polymerization (EROP) are complicated and have not been extensively studied. By using statistic method, a series of equations based on polymerization mechanism is established to describe numbers of rings, chains, and active centers. Using this new model, the predicted results of polydimethylsiloxane synthesized by EROP agree well with experimental results. This model has advantages in molecule number, calculation speed, and stability when compared with the Monte Carlo simulation. It also has the potential to replace Monte Carlo simulation in MWD prediction.  相似文献   

12.
A comprehensive mathematical model for styrene stereoregular polymerization was carried out. This model was generated by coupling the single particle growth model (SPGM) with kinetics model, to predict the effect of intraparticle mass transfer resistance and initial catalyst size on the polymerization kinetics. SPGM was derived based on a modified multigrain model (MMGM) to calculate the spatial-time evolution of styrene concentration under intraparticle mass transfer limitations. Then, the SPGM was solved simultaneously with kinetics model to estimate the polymerization rate and molecular weight distribution (MWD) under the above mentioned limitations. The results show that a significant radial distribution of styrene concentration across polymer growing. Moreover, the diffusion resistance was most intense at the early step of the polymerization and the effects of the polymerization rate are more strongly. Additionally, it is appear that increasing the initial catalyst size leads to a decrease in the rate of polymerization. For MWD, the model simulation show that the diffusion resistance led to have an increase in the molecular weight within a period of time similar to the one needed in the catalyst decay. The validation of the model with experimental data given a agreement results and shows that the model is able to predict monomer profile, polymerization rate, and MWD of syndiotactic polystyrene.  相似文献   

13.
Free‐radical polymerization of styrene was carried out in the presence of chain transfer agents (CTAs) with functionality, f = 1–4. The size exclusion chromatography (SEC) with an ultraviolet absorption detector (UV) was used to measure the molecular weight distribution (MWD). A Monte Carlo simulation method proposed earlier was used to investigate the experimental results. In this simulation method, one can observe the structure of each polymer molecule directly, and very detailed information can be obtained in a straightforward manner, including the elution curve of SEC. It was found that up to the functionality f = 3, the equal reactivity model that assumes the reactivity of all functional groups in a CTA is equal agrees reasonably well with the experimental results. However, with f = 4, the reactivity of the fourth functional group seems to decrease and the substitution effects may need to be accounted for to fine control the formed branched structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1267–1275, 1999  相似文献   

14.
Summary: Simulation models are important tools for the development and optimization of polymerization processes because they can describe catalyst performance and polymer properties as a function of polymerization kinetics and process conditions. As the polyolefin industry moves towards the production of resins with more complex microstructures, these models become essential for process understanding and product design. A simulation model has been developed for the polymerization of ethylene in a process with n reactors working in series. The model can predict raw material conversions and product properties like the molecular weight distribution (MWD) coupled with short chain branching distribution (SCBD), melt index, density and fluff morphology. Model parameters have been obtained from laboratory data. The model predictions are in good agreement with experimental results.  相似文献   

15.
Living radical polymerization has allowed complex polymer architectures to be synthesized in bulk, solution, and water. The most versatile of these techniques is reversible addition–fragmentation chain transfer (RAFT), which allows a wide range of functional and nonfunctional polymers to be made with predictable molecular weight distributions (MWDs), ranging from very narrow to quite broad. The great complexity of the RAFT mechanism and how the kinetic parameters affect the rate of polymerization and MWD are not obvious. Therefore, the aim of this article is to provide useful insights into the important kinetic parameters that control the rate of polymerization and the evolution of the MWD with conversion. We discuss how a change in the chain‐transfer constant can affect the evolution of the MWD. It is shown how we can, in principle, use only one RAFT agent to obtain a polymer with any MWD. Retardation and inhibition are discussed in terms of (1) the leaving R group reactivity and (2) the intermediate radical termination model versus the slow fragmentation model. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3189–3204, 2005  相似文献   

16.
Summary: The deconvolution of molecular weight distributions (MWDs) may be useful for obtaining information about the polymerization kinetics and properties of catalytic systems. However, deconvolution techniques are normally based on steady‐state assumptions and very little has been reported about the use of non‐stationary approaches for the deconvolution of MWDs. In spite of this, polymerization reactions are often performed in batch or semi‐batch modes. For this reason, dynamic solutions are proposed here for simple kinetic models and are then used for deconvolution of actual MWD data. Deconvolution results obtained with dynamic models are compared to deconvolution results obtained with the standard stationary Flory‐Schulz distributions. For coordination polymerizations, results show that dynamic MWD models are able to describe experimental data with fewer catalytic sites, which indicates that the proper interpretation of the reaction dynamics may be of fundamental importance for kinetic characterization. On the other hand, reaction dynamics induced by modification of chain transfer agent concentration seem to play a minor role in the shape of the MWD in free‐radical polymerizations.

This Figure illustrates that MWDs obtained at unsteady conditions should not be deconvoluted with standard steady‐state Flory‐Schulz distributions.  相似文献   


17.
测定了络合Ⅱ型TiCl3-Al(C2H5)3催化1-辛烯聚合中不同时间的产物分子量分布,用4个Schulz-Flory“最可几”分布函数叠加,较好地拟合了实测分布,从而确定此体系有4种活性中心。从拟合及动力学测定结果确定了4种活性中心的聚合速率、浓度及链增长速率常数、链转移速率常数等,讨论了各活性中心的结构及聚合机理。  相似文献   

18.
何学浩 《高分子科学》2013,31(3):371-376
The AB2 type bulk polymerization of 3,5-bis(trimethylsiloxy)benzoyl chloride is studied by the reactive 3d bond fluctuation lattice model (3d-BFLM). Through tuning the reactivity parameters, the experimental data are fitted well via an iterative dichotomy method. By using the optimized reactivity parameters, the number-average degree of polymerization and degree of branching obtained in simulation are very close to experimental data. Meanwhile, the information about the weightaverage degree of polymerization and the polydispersity index is provided, and the internal structural properties of hyperbranched polyesters are investigated. Simulation results demonstrate that the 3d-BFLM can be used to study specific hyperbranched polymerizations semi-quantitatively which is helpful to deep understand the kinetics of reactions and make predictions for specific polymerization systems.  相似文献   

19.
The kinetics of ethene polymerization catalyzed by Cp2ZrCl2‐methylaluminoxane (MAO) is studied by applying a new kinetic model. Important kinetic parameters of polymerization were estimated. In addition a method of calculating the molecular‐weight distribution (MWD) of the resultant polyethene was established by developing this new model. The final product is expected to comprise three components, which are produced by different active‐site types, and the MWD of one of the components is less than 2. Good agreement between the estimated value and the variation of polydispersity was achieved.  相似文献   

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