迭代学习控制在氯乙烯聚合反应中的应用

由于氯乙烯聚合反应釜是一个具有纯滞后时间长、时间常数大的,且很难建立精确数学模型的被控对象,因此本文提出一种新的控制方案,即采用控制输入和系统初态同时进行学习的闭环PD型迭代学习控制,给出了该算法谱半径形式的收敛条件,并利用算子理论证明了系统在任意初态条件下经过逐次迭代后,其输出能够完全跟踪期望轨迹。仿真结果表明了该算法的有效性。

苯乙烯聚合反应过程的灰箱建模

针对结构部分已知且参数未知的一类工业反应过程的建模问题,以苯乙烯聚合反应过程为背景展开研究。在该反应过程中,反应机理已知,包含链引发反应、链增长反应、链转移反应以及链终止反应等,而其中各基元反应中的反应速率方程的结构及参数不甚明了。针对此类问题,提出将已知的机理部分构建白箱模型,将未知的反应速率部分构建神经网络黑箱模型,并将黑箱模型与白箱模型连接构成整个反应过程的灰箱模型。该方法通过实验的验证,证明了其实用性及有效性。

加核自缩合乙烯基聚合反应体系的热力学特征

从统计力学角度出发,对加核二元自缩合乙烯基聚合反应体系的热力学特征进行了研究.给出了引发核与引发单体间的配料比、反应物的体积分数及引发核的官能度等因素与反应体系热力学统计特征之间的定量关系,重点讨论了内能、比热、多分散性指数和均方回转半径等物理量随反应条件的变化规律.结果表明,通过调控反应温度、改变反应物的浓度(体积分数)和配料比以及选取合适的引发核等方法可制备出具有预期结构和性能的超支化高分子.

插层聚合法制备MMT/聚乙烯纳米塑料

本研究以2,6-二乙酰基吡啶、2,4,6-三甲基苯胺和FeCl2.4H2O为原料,制备了后过渡金属铁的二亚胺配合物。将其负载在改性蒙脱土上,以己烷为溶剂、AlEt3为助催化剂进行聚合反应。通过红外光谱、X射线分析、热分析等,系统地研究了蒙脱土的改性条件对蒙脱土结构、蒙脱土载体铁系催化剂的聚合行为及聚合物结构与热性能的影响。研究表明最佳插层条件是:1831为插层剂、80℃、反应2 h、蒙脱土/1831(质量比)为3/1,此时层间距为2.72 nm,催化剂活性达1.073×106(g PE/mol Fe.h),聚乙烯堆密度为0.351g/cm3,形成MMT/PE纳米塑料。

自缩合乙烯基聚合体系中的环化效应

基于超支化高分子的生长代数模型,利用Monte Carlo模拟方法研究了不同溶剂条件下自缩合乙烯基聚合(SCVP)体系的环化效应.根据SCVP体系的反应机理给出含环反应的微分动力学方程,并通过环化反应的内在特征确定了分子间反应和内环化反应的速率常数.在此基础上,利用Monte Carlo模拟方法得到了高分子的数量分布函数、重均分子量、环数以及含环分子的链段分数等相关物理量,分析了环化效应对于体系平均物理量的影响.进一步根据模拟结果对单体浓度和溶剂效应等对内环化反应的影响予以分析.结果表明,环化效应取决于单体浓度和溶剂效应之间的协同作用,其中单体浓度在环化反应中起着主导作用.

非等速率自缩合乙烯基聚合反应产物的支化度

分析了一般的非等速率自缩合乙烯基聚合反应(SCVP)所生成的超支化聚合物体系的结构单元和支化度.详细计算了支化度随反应进程(A基团转化率x)、活性的A*和B*基团反应速率比(r)和活化剂/单体物质的量比(α)的变化关系.对任何指定的r和α组合,DB随x的增加而单调增加,对确定的x,当α<x/(1+x^(1/2))时,DB随r的增加而单调减少,当α>x/(1+x^(1/2))时,DB随r的变化不再是单调的,有极大值,但无论怎样的r和α组合,最大的支化度都只有0.5.要想进一步提高产物的支化度,可以在反应终了时,在体系中再加入适当的其它单体,使活化基团全部反应掉,从而可使支化度达到2α/(1+α).

二元自缩合乙烯基聚合反应体系的统计热力学

应用统计力学原理对二元自缩合乙烯基聚合反应体系(由单体和引发单体组成)的统计热力学特征予以研究.首先从两种不同的角度给出与聚合反应相应的配分函数,据此得到反应体系的平衡自由能、质量作用定律以及超支化高分子的数量分布函数,进而计算了体系的比热和等温压缩系数等热力学量.进一步研究了超支化高分子的空间尺度,给出反应体系k次均方回转半径的递推公式,计算了各种不同溶剂条件下的均方回转半径,指出引发单体分数、反应程度和溶剂效应对超支化高分子空间尺度的影响.

An Investigation on the Polymerization of Styrene by Fluorescence Probe Technique

The polymerization of styrene is monitored by pyrene excimer formation. The ratio of monomer to excimer intensities ( I m/ I e) of pyrene increases as polymerization proceeds. The increase of I m/ I e is ascribed to the increase of microviscosity surrounding the probes forming excimer during polymerization. The linear relationship between the changing rate of I m/ I e and the polymerization rate of styrene is obtained. Therefore, I m/ I e may be used to monitor the progress of the polymerization of styrene.

Ethylene Polymerization with Palygorskite Supported Nickel-Diimine Catalyst

A nickel-diimine catalyst [N, N'-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1, 3-butadiene nickel dibromide, DMN] was supported on palygorskite clay for ethylene slurry polymerization. The effect of supporting methods on the catalyst impregnation was studied and compared. Pretreatment of the support with methylalumi-noxane (MAO) followed by DMN impregnation gave higher catalyst loading and catalytic activity than the direct impregnation of DMN. Catalyst activity as high as 5.42×105g PE·molNi-1·h-1 was achieved at ethylene pressure of 6.87×105 Pa and polymerization temperature of 20℃. In particular, the morphological change of the support during MAO treatment was characterized and analyzed. It was found that nano-fiber clusters formed during the support pretreatment, which increased the surface area of the support and favored the impregnation of the catalyst. The investigation of polymerization behavior of supported catalyst revealed that the polymerization rate could be kept at a relatively high level for a long time, different from the homogeneous catalyst. By analyzing the SEM photographs of the polymer produced by the supported catalyst, the morphological evolution of polymer particles was preliminarily studied.

Molecular Imprinted Membrane with High Flux by Surface Photo-grafting Copolymerization

Molecular imprinted polymer membranes (MIM) combine the merits of molecular imprint and membrane technology. In this work, a very thin of imprinted polymer that can specifically and selectively absorb the basic template (adenine) was grafted on the surface of polyvinylidene fluoride membrane by photo-grafting copolymerization. Because the molecular imprinted polymer is grafted on the surface of the matrix membrane without blocking the membrane pores, the resultant MIMs have high flux as microfiltration membrane (0.26 mol·m^-2·h^-1 of template and flux for distilled water was 3.6 ml·mim^-1·cm^-2 at 0.8 MPa). Moreover, the MIMs can absorb/desorb template molecules rapidly. Usually, it only takes several minutes for MIMs to absorb more than 75% of the template (adenine) in aqueous solution. And the influences of the type and amount of the functional monomers, the amount of the cross-linker on the absorption capability are discussed to determine the optimal preparation conditions。

Modeling and Simulation of Ethylene Polymerization in Industrial Slurry Reactor Series

A five-site comprehensive mathematical model was developed to simulate the steady-state behavior of industrial slurry polymerization of ethylene in multistage continuous stirred tank reactors. More specifically, the effects of various operating conditions (i.e., inflow rates of catalyst, hydrogen and comonomer) on the molecular structure and properties of polyethylene (i.e.,Mw,Mn, polydispersity index (IPD), melt index, density, etc.) are fully assessed. It is shown that the proposed comprehensive model is capable of simulating the steady-state operation of an industrial slurry stirred tank reactor series. It is demonstrated that changing the catalyst flow rate, changes simultaneously the mean residence-time in both reactors, which plays a significant role on the establishment of polyethylene architecture properties such as molecular mass and IPD. The melt index and density of polyethylene are mainly controlled by hydrogen and comonomer concentration, respectively.

Study on Catalytic Properties of Cyclopentadienyl Bisphenoxyl Titanium Chloride for Ethylene Polymerization via Molecular Simulation

Three mono-cyclopentadienyl metal complexes, [C_6H_4O_2]CpTiCl (Ⅰ),[C_(12)H_8O_2]CpTiCl (Ⅱ), and [C_(20)H_(12)O_2] CpTiCl (Ⅲ), were prepared via the reactions ofcyclopentadienyl titanium trichloride with catechol, 2,2i-bisphenol, and 2,2'-bisnaphthol,respectively. In the presence of a moderate amount of methylaluminoxane (MAO), the complexesexhibited catalytic activities for ethylene polymerization. Complex Ⅰ showed the highest activityat Al/Ti molar ratio of 500 at the temperature of 30℃. With increasing of polymerizationtemperature, catalytic activities and molecular weight of the obtained polyethylene tended todecrease, and molecular weight distribution of polyethylene became narrower. With the molecularsimulation method, the charges on titanium atoms of complexes Ⅰ, Ⅱ, and Ⅲ, and the bond anglesformed by Ti and bisphenoxy ligands were calculated. It was concluded that the smaller the netcharge on Ti and the smaller the angle of O1―Ti―O2, the higher the activity of the complex.

Synthesis of poly (vinyl acetate) oligomersand their phase behavior in supercritical carbon dioxide

Three poly(vinyl acetate)(PVAc)oligomers with controlled molecular weight and narrow molecular distribution are synthesized by reversible addition-fragmentation chain transfer(RAFT)polymerization.The effects of the reaction temperature and the added amount of initiator of the PVAc polymerization are discussed.In addition,the phase behavior of the prepared PVAc in pressured CO2 is determined via the cloud point method.The results indicate that the cloud point of PVAc increases with the increase in the molecular weight,the PVAc concentration,and the temperature.The cloud point pressures for the PVAc mass concentration of 0.12%with the molecular weight of 1 550,2 120,and 2 960 g/mol are 13.48,13.83 and 15.43 MPa,respectively,at the temperature of 35℃.It reveals that the solubility of PVAc in ScCO2 at relatively low pressure is remarkably limited.

Studies on the Polymerization of Styrene in the MCM-41 Phase

The polymerization of styrene in the media of MCM-41 is carried out by means of host-guest polymerization of styrene in MCM-41 mesoporous material with the aim to investigate the effects of interface and confinement of MCM-41 on host-guest interactions. Detailed physical properties of the mesoporous MCM-41 material containing polystyrene is characterized by XRD(X-ray diffraction), FT-IR(Fourier transform infrared), TGA(thermal gravimetric analysis), and nitrogen adsorption-desorption isotherms. We also find a great increase in the glass transition temperature of guest polystyrene influenced by the confined geometry of the host by differential scanning calorimetry(DSC).

HYDROLYSIS TRANSFORMATION OF A POLYSTYRENE-b-POLY(tert-BUTYL ACRYLATE) COPOLYMER AND MICELLIZATION PROPERTIES OF THE HYDROLYZED COPOLYMER

A very mild and extremely efficient hydrolysis method for transformation of polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA) to polystyrene-b-poly(acrylic acid) (PS-b-PAA) was designed and carried out using more convenient and inexpensive chlorotrimethylsilane/sodium iodide as reagents. The hydrolysis product can self-assemble in aqueous media to give regular micelles with PS block forming the core and PAA block forming the corona, or in tetrahydrofuran (THF) to give reverse micelles with the hydrophilic block in the core.

Simulation of Rate Retardation in RAFT Polymerization of Styrene with Low RAFT-Initiator Ratio

Bulk polymerizations of styrene (St) were carried out in the presence of three reversible addition fragmentation chain transfer (RAFT) agents benzyl dithiobenzoate (BDB), cumyl dithiobenzoate(CDB), and 1-phenylethyl dithiobenzoate (PEDB) under low ratio of RAFT agent to initiator. The kinetic model was developed to predict polymerization rate, which indicates that the RAFT polymerization of St is a first-order reaction. In the range of experimental conversions, the plots of -ln(1-x) against time t are approximately linear (x is monomer conversion). The kinetic study reveals the existence of strong rate retardation in RAFT polymerization of styrene. A coefficient K_r is defined to estimate the rate retardation in the RAFT system considering the assumption that the retardation in polymerization rate is mainly attributed to slow fragmentation of the intermediate radicals. K_r relates to the structure of RAFT agents as well as the concentrations of RAFT agent and azobis isobutyronitrile (AIBN). For a certain RAFT agent, the value of K_r is enhanced by the increase in the initial concentration of RAFT agent and the higher ratio of RAFT to AIBN. With the same recipe for different RAFT agents, the increasing trend for the values of K_r is BDB<PEDB<CDB.

CONTROLLED SEQUENTIAL AND RANDOMRADICAL COPOLYMERIZATION OF STYRENE AND BUTYL METHACRYLATE BY ATOM TRANSFER RADICAL POLYMERIZATION

Diblock copolymers containing polystyrene (PSt) andpolybutyl methacrylate (PBMA)segnents and random coplymer of styrene (St) and butyl methacrylate (BMA) havebeen prepared by atom transfer radical polymerizanon (ATRP). Diblock copolymers ofBAN and St with predetermined molecular weight (1× 104ed.5 × 104)and narrowermolecular weight distribution(1.25～1.5) were obained The random copolymercompositions were determined by 1HNMR spectroscopy and the reactivity ratios wereevaluated by the extended Kelen-Tudos method to be γst=0.91, γBMA=0.32.

Synthesis, structure and ethylene polymerization behavior of titanium complexes [C_3H_6(N = CH-Ar-O)_2]TiCl_2

The reaction of C3H6(N=CH-Ar-OH)2 (Ar = 5-tert-butyl-C6H3 (2a), 3-tert-butyl-C6H3 (2b), 3-methyl-C6H3 (2c)) with 2 equiv. of BuLi followed by 1 equiv TiCl4 yields the dichloride complexes [C3H6(N=CH-Ar-O)2]TiCl2[Ar = 5-tert-butyl-C6H3 (3a), 3-tert-butyl-C6H3 (3b), 3-methyl-C6H3 (3c)]. The structure of compound 3a has been confirmed by X-ray crystallographic analysis. These Ti (IV) dichloride complexes are active catalysts for the polymerization of eth- ylene with methylaluminoxane (MAO) as a cocatalyst. Ac- tivities up to 4.14×105 g (mol Ti h)?1 were obtained in dried toluene. And the molecular weights of polyethylene are in the range 1.53×104—16.4×104. Catalyst activity, polymer yield, and polymer molecular weight can be controlled over a wide range by changing the ligand structure and variation of reac- tion parameters such as Al-Ti ratio and polymerization reac- tion temperature.

Novel acid initiators for the rapid cationic polymerization of styrene in room temperature ionic liquids

Cationic polymerization of styrene has been achieved using several novel acidic initiators in room temperature ionic liquids (ILs) under mild reaction conditions to obtain polymers of low molecular weight with narrow polydispersity. Both strong protic acids such as bis(trifluoromethanesulfonyl) amide acid (HTFSA) and a moderately weak acid such as bisoxalato phosphorous acid (HBOP) have been studied as initiators. It has been observed that HTFSA initiates the polymerization rapidly even at room temperature and below, as compared to HBOP which produces a slower polymerization requiring elevated temperatures to complete. The relative difference in reactivity of the initiators as compared to the previously described HBOB initiator is discussed in terms of the difference in their proton acidity and the consequential basicity of the anions. The efficiency of different ILs as the reaction solvent is also presented.

Ethylene (co-)polymerization by long-lifetime half-sandwich zirconium catalyst bearing a [SSO]-carborane ligand

Half-sandwich zirconium complex 3 containing tridentate carborane [S,S,O] ligand 2 [(HOC6H2R2-4,6)(CH2)SC(B10H10) C(Ph)2P=S, R=tBu] was synthesized by the reaction of CpZrCl3(Cp=η5-C5H5) with sodium salt of ligand 2. Zirconium complex 3 was characterized by elemental and NMR analyses. DFT calculations were also performed on complex 3 to analyze the stereochemistry. The results from DFT calculations indicate that structure S1, in which no sulfur atom bonds to the zirconium atom, exists at the lowest energy level. In the presence of methylaluminoxane(MAO), complex 3 exhibited good catalytic activities for ethylene polymerization and long life-time up to 10 h. Moreover, the complex 3/MAO system displayed excellent catalytic activities toword ethylene copolymerization with 1-hexene or polar olefins.