Experimental Criteria for Living Polymerizations

Seven experimental criteria for living polymerizations are critically reviewed. The limitations of the use of linear plots of M?_n (or X?;_n) versus conversion and linear plots of the number of polymer chains versus conversion are illustrated by an example of alkyllithium-initiated polymerization of styrene by incremental additions of styrene with deliberate termination (5% per incremental monomer addition). The experimental criteria of using narrow molecular weight distribution and the formation of block copolymers are illustrated with practical examples and size exclusion chromatography data. The use of the terms ‘living polymerization with reversible termination’ and ‘living polymerization with reversible chain transfer’ are proposed.     

Kinetic model for short-cycle bulk styrene polymerization through bifunctional initiators

A model describing the kinetics of bulk styrene polymerization through bifunctional initiators has been developed. The diffusion-controlled propagation and termination reactions at high monomer conversions are modeled with the free volume theory for polymer solutions. Three different commercially available bifunctional initiators were experimentally evaluated for a wide range of polymerization conditions to study the effect of the reaction rate on the molecular weight and molecular weight distribution. The model predictions for the same polymerization conditions show excellent agreement with the experimental data, for the whole range of conversions, for both reaction rate and molecular weight distribution development, under all the conditions tested. It is demonstrated throughout this study that high molecular weights, very high reaction rates, and narrow molecular weight distributions can be achieved simultaneously by using bifunctional initiators. A comparison between monofunctionally initiated systems with the bifunctionally initiated ones shows that short-cycle reactions with reductions in polymerization time of up to 75% may be achieved with the bifunctional initiators for a wider range of conditions without significantly affecting the molecular weight and molecular weight distribution of the final product.     

The role of diffusion in the Ziegler polymerization of ethylene

A theoretical and experimental study has been made of the polymerization of ethylene in a slurry reactor using a highly active Ziegler catalyst in the presence of hydrogen. A model of the polymerization system has been set up in which polymerization is assumed to proceed with encapsulation of catalyst subparticles. Allowance is made for an experimentally observed first-order decay in intrinsic catalyst activity. The theoretical prediction of the model for the monomer absorption rate behavior and the molecular weight characteristics of the polymers formed are in agreement with experimental findings. Experimental evidence is presented that in the earliest moments of a polymerization significant amounts of polymer are formed with molecular weights 100 times those in the balance of the polymerization. It is concluded that in this system the polymerization is diffusion controlled throughout the major part of the catalyst lifetime. This diffusion phenomenon, together with the gradual loss of active sites, is of vital importance in determining the molecular weight and molecular weight distribution of the polyethylene product.     

Amphiphilic styrene–acrylic acid copolymers from the free‐radical retrograde‐precipitation polymerization (FRRPP) process

The free‐radical retrograde‐precipitation polymerization (or FRRPP) process, a free‐radical polymerization that occurs above the lower critical solution temperature (LCST), was extended to copolymer formation. Control over the rate of polymerization and entrapment of polymer radicals in the FRRPP process was used to generate tapered styrene–acrylic acid block copolymers. To show the effectiveness of the FRRPP process, the same procedure was used with solvents that are not LCST‐based precipitants for the polymer. Kinetic data show substantial chain termination in non‐FRRPP copolymerization systems. Molecular weight information also shows propagation control in the FRRPP system. Solubilization and emulsification studies also indicate the capability of the FRRPP system in generating a much higher proportion of amphiphilic tapered block copolymers in the solid product. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 426–431, 2003     

Population balance modeling for a continuous gas phase olefin polymerization reactor

Steady-state population balance models have been developed for a continuous flow gas phase olefin polymerization process with both uniform sized and log-normally size distributed high activity catalyst feeds. For the calculation of polymer properties such as molecular weight averages and weight fraction of comonomers in the copolymer, a multigrain solid core model was used with an assumption that intraparticle monomer mass transfer resistance is negligibly small. The multigrain solid core model was incorporated into the population balance model and the effects of feed catalyst particle size distribution and catalyst deactivation parameters on the polymer production rate, polymer particle size distribution, and polymer properties were investigated. It is observed for deactivating catalyst that the polymer particle size distribution tends to be narrower with a reduced amount of large polymer particles. For the catalyst with nonuniform site deactivation, polymer particles of different sizes exhibit different molecular weight and copolymer composition. © 1994 John Wiley & Sons, Inc.     

两亲性苯乙烯嵌段共聚物的合成及结构表征

以α,α'-二甲基-α-乙酸-三硫代碳酸酯(BDATC)为链转移剂,采用可逆-加成-断裂链转移(RAFT)自由基聚合方法合成了末端带有—COOH官能团的两亲性嵌段共聚物聚苯乙烯-b-聚甲基丙烯酸聚乙二醇单甲醚-b-聚苯乙烯(PSt-b-POEOMA-b-PSt),这种含有亲水性端基的嵌段共聚物可以自组装成核-壳结构的纳米微粒,用于载药高分子的模板研究。利用FTIR、1HNMR、GPC对产物结构进行表征,用热失重(TG)和差示扫描量热(DSC)的方法研究了3种不同比例的嵌段共聚物的热性能。实验结果表明,通过RAFT聚合方法得到了所设计的嵌段共聚物,相对分子质量(简称分子量,下同)分布1.35左右;嵌段共聚物的热稳定性较好,通过玻璃化转变温度(Tg)的变化推测出嵌段共聚物中两种嵌段比例对两嵌段相容性的影响。     

Controlling the phase behavior of block copolymers via sequential block growth

Block copolymers remain one of the most extensively investigated classes of polymers due to their abilities to self-organize into various nanostructures and modify polymer/polymer interfaces. Despite fundamental and technological interest in these materials, only a handful of experimental phase diagrams exist due to the laborious task of preparing such diagrams. In this work, two copolymer series are each synthesized from a single macromolecule via sequential living anionic polymerization to yield molecularly asymmetric diblock and triblock copolymers systematically varying in composition. The phase behavior and morphology of these copolymers are experimentally interrogated and quantitatively compared with predictions from mean-field theories, which probe copolymer phase behavior beyond current experimental conditions.     

可逆加成-断裂链转移聚合制备聚氯乙烯-b-聚乙二醇-b-聚氯乙烯共聚物

合成了含黄原酸酯端基的聚乙二醇（X-PEG-X）大分子链转移剂,并以其为可逆加成-断裂链转移试剂调控氯乙烯（VC）溶液和悬浮聚合,合成聚氯乙烯-b-聚乙二醇-b-聚氯乙烯（PVC-b-PEG-b-PVC）三嵌段共聚物。X-PEG-X调控VC溶液聚合得到的共聚物的分子量随聚合时间增加而增大,分子量分布指数小于1.65。X-PEG-X具有水/油两相分配和可显著降低水/油界面张力的特性,以X-PEG-X为链转移剂和分散剂,通过自稳定悬浮聚合也可合成PVC-b-PEG-b-PVC共聚物,共聚物颗粒无皮膜结构,分子量随聚合时间增加而增大;由于VC悬浮聚合具有聚合物富相和单体富相两相聚合特性,共聚物分子量分布指数略大于溶液聚合共聚物。通过乙酸乙烯酯（VAc）扩链反应进一步证实了PVC-b-PEG-b-PVC的“活性”,并合成PVAc-b-PVC-b-PEG-b-PVC-b-PVAc共聚物。水接触角测试表明PVC-b-PEG-b-PVC的亲水性优于PVC。     

Bulk copolymerization of styrene and acrylonitrile: Experimental kinetics and mathematical modelling

The kinetics of styrene-acrylonitrile bulk copolymerization have been experimentally investigated over a wide range of conditions. The effects of temperature, and initiator and of comonomer concentrations on rate of polymerization and on copolymer properties including chain microstructure and molecular weight averages are reported. A mathematical model which uses the free volume theory to account for diffusion controlled termination and propagation reactions is developed. The model is capable of predicting the conversion, composition and sequence length development up to limiting conversions.     

Synthesis of hydroxyl‐terminated copolymer of styrene and 4‐vinylpyridine via nitroxide‐mediated living radical polymerization

The random copolymers of styrene (St) and 4‐vinylpyridine (4‐VP) with hydroxyl end group and low polydispersities were synthesized by nitroxide‐mediated living radical polymerization initiated by azobisisobutyronitrile (AIBN) and 4‐hydroxyl‐2,2,6,6–tetramethylpiperidine‐oxyl (TEMPO‐OH). The experimental results have shown that all synthesized copolymers have narrow molecular weight distribution. The conversion of monomers and the molecular weight of copolymer increased with polymerization time. The copolymerization rate is affected by molar ratios of HTEMPO to AIBN. ¹H‐Nuclear magnetic resonance spectra shows that one end of copolymers was capped by TEMPO‐OH moiety. The use of this method permits the copolymer with hydroxyl chain end and controllable molecular weight and molecular weight distribution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1842–1847, 2004     

Progress in the catalyst for ethylene/α-olefin copolymerization at high temperature

Ethylene/α-olefin copolymers are one of the most widely-used polyolefin materials. With the continuous improvement of polyolefin catalysts, high-performance polyolefin materials were synthesized by adjusting the chain microstructure, changing the comonomer type and comonomer insertion amount, among which the ethylene/α-olefin random copolymer elastomer (POE) and olefin block copolymer elastomer (OBC) are the most famous and well accepted by the market. The excellent properties of POE and OBC first depend on their polymer chain microstructure. The chain microstructure of polyolefins is fundamentally determined by the catalysts, polymerization conditions, comonomer feed policies, and reaction engineering. High-performance ethylene/α-olefin copolymer elastomers are currently prepared by high-temperature solution polymerization process, which needs to be carried out at a temperature above the melting point of the polymer and is beneficial to speed up the polymerization reaction rate and control the polyolefin chain microstructure. However, the high-temperature solution polymerization process launched more stringent requirements for the olefin coordination polymerization catalyst. Systematic reports on catalysts for high-temperature solution copolymerization of ethylene and α-olefins are lacking. In this review, we screened some catalysts suitable for the controllable copolymerization and high-temperature solution copolymerization of ethylene/α-olefin based on the catalyst's heat resistance, copolymerization activity, comonomer insertion ability, molecular weight, and distribution of the copolymer, including traditional Z–N catalysts, metallocene catalysts, and post-metallocene catalysts. And the future development of catalysts for high-temperature solution copolymerization of olefins, catalysts for precise control of polyolefin chain microstructures, and catalysts for olefin copolymerization with polar monomers at high temperature are envisaged.     

Phase separation in polymer blends comprising copolymers: 7. Statistical theory of block copolymer-homopolymer systems

The miscibility of a homopolymer in corresponding domains of a copolymer predicted by Meier's theory is far less than found experimentally. In this paper, a density gradient model is suggested for describing the segment distribution of the bound and free chains in block copolymer-homopolymer systems. Using this model, Helfand's theory, which has been successful in explaining microphase separation of block copolymers, is extended to polymer blends of homopolymer and corresponding block copolymer with lamellar structure. The calculated free energy of mixing of the system shows that the predicted miscibility is much larger than that obtained by Meier's theory and is in good agreement with the main known experimental results. In particular, on the basis of the present theory, homopolymer can be expected to be solubilized by corresponding blocks in the whole composition range provided that the molecular weight of the former is less than that of the latter.     

Dynamic prediction of the bivariate molecular weight-copolymer composition distribution using sectional-grid and stochastic numerical methods

In the present study, a two-dimensional fixed pivot technique (2-D FPT) and an efficient Monte Carlo (MC) algorithm are described for the calculation of the bivariate molecular weight-copolymer composition (MW-CC) distribution in batch free-radical copolymerization reactors. A comprehensive free-volume model is employed to describe the variation of termination and propagation rate constants as well as the variation of the initiator efficiency with respect to the monomer conversion. Simulations are carried out, under different reactor conditions, to calculate the individual monomer conversions, the leading moments of the ‘live’ and ‘dead’ polymer chain length distributions as well as the dynamic evolution of the distributed molecular properties (i.e., molecular weight distribution (MWD), copolymer composition distribution (CCD) and joint MW-CC distribution). The validity of the numerical calculations is examined via a direct comparison of the simulation results, obtained by the two numerical methods, with experimental data on the styrene-methyl methacrylate batch free-radical copolymerization. Additional comparisons between the 2-D FPT and the MC methods are carried out for different polymerization conditions. It is clearly shown that both numerical methods are capable of predicting the distributed molecular and copolymer properties, with high accuracy, up to very high monomer conversions. It is also shown that the proposed dynamic MC algorithm is less computationally demanding than the 2-D FPT.     

水溶性偶氮引发剂AIBA引发AN-MA-IA水相沉淀共聚合的研究

以含有亲水基团的偶氮二异丁脒盐酸盐（AIBA）为引发剂,以丙烯腈（AN）、丙烯酸甲酯（MA）和衣康酸（IA）为单体,β-巯基乙醇（β-ME）为分子量调节剂,采用水相沉淀聚合法制备了不同分子量的AN-MA-IA共聚物,研究了AIBA浓度、单体浓度和β-ME浓度对聚合过程的影响。根据AIBA分解半衰期和单体竞聚规律确定了聚合温度70℃和pH=4.7为较优反应条件。结果表明,AIBA浓度是影响聚合转化率的决定因素,通过调整AIBA浓度可以得到分子量60000~500000的PAN共聚物,较高的AIBA浓度会由于聚合场所的改变而造成分子量分散度小幅上升;浓度在0.2%（质量）以内时,分子量调节剂β-ME可以调控PAN共聚物的分子量,并使其分布变窄。     

Styrene-butadiene branched star-shaped asphalt modifiers: Synthesis and mechanical characterization

Abstract

The synthesis and the corresponding characterization of styrene-butadiene (SB), branched, star-shaped copolymers was investigated as part of a research project on asphalt modification using polymers with precise molecular structures. The method of anionic polymerization was followed to prepare samples of block copolymers of SB, a synthesis method that controls chain-architecture, molecular weight distribution, monomer distribution, and the average molecular weight. The research studies are the synthesis of block copolymers including linear, three- and four-arms constructs, depending on the coupling agent used. The techniques of nuclear magnetic resonance (1NMR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and rheology were carried out to characterize the copolymers. From the results of the 1NMR, DSC, and GPC analyses, all star-shaped copolymers investigated showed a similar block copolymer composition. Furthermore, the rheological behavior of one of the synthesized star-shaped copolymers was nearly the same as a four-branched commercial copolymer. Rheologically, the four-arm block copolymer sample had the largest storage modulus (G′) among the branched copolymers synthetized, indicating that such architecture produces a highly structured material. In regard to polymer-modified asphalt formulations, the three-branched copolymer architecture yielded better elastic behavior than the four-branch version. In summary, the findings of this investigation provide new insight about a polymer system that may offer advantages in industrial asphalt paving applications.     

Prediction of molar mass distribution,number and weight average degree of polymerization and branching of low density polyethylene

An extended mathematical model of an autoclave reactor for the high pressure polymerization of ethylene is presented. It allows one to predict not only the conversion but also the molar mass distribution, short and long chain branching, number and weight average degree of polymerization as a function of the synthesis conditions. The model includes the initiation step, chain growth, chain termination by disproportionation and combination, chain transfer to the monomer, polymer and modifier, and intramolecular chain transfer in the polymer radical. Number and weight average degrees of polymerization were computed by means of generating functions. For the calculation of the molar mass distribution recursion formulae are given. The performance of the model is shown by the good agreement of the predicted values with the experimental data.     

Simulation of kinetic analysis on terpolymerization of styrene/butyl methacrylate/methacrylic acid system

The simultaneous differential equations which connected the copolymerization kinetics of the component reaction in the multi-copolymerization system with the changing rate of the concentration of each monomer and radical, the concentration and the molecular weight of the polymer obtained are analysed in a number of ways. The distribution of the components and the degree of polymerization are also simulated. The styrene/butyl methacrylate/methacrylic acid terpolymerization system, using carbon tetrachloride as solvent and benzoyl peroxide as initiator, was chosen. The simulation model which satisfied the experimental values of the concentration of the multiple components in the system, the composition and molecular weight distribution and the number of chlorine atoms introduced into the copolymer ends is established. When the time interval changed, the effects on the distribution of the composition in copolymers and the distribution of the degree of polymerization were also calculated.     

苯乙烯可逆加成-断裂链转移聚合动力学

为了实现可逆加成-断裂链转移(RAFT)聚合过程中,苯乙烯均聚、高分子量聚苯乙烯的合成及苯乙烯与其他单体共聚时,对苯乙烯转化率、共聚时组成和分子量大小的控制,进行了二硫代苯乙酸-1-苯基乙酯(PEPDTA)调控苯乙烯本体和细乳液聚合动力学分析。在本体聚合中,反应速率慢,链增长自由基与"中间态"自由基的终止反应对聚合速率影响较小,很难合成窄分布、高转化率、高分子量的聚苯乙烯;在细乳液聚合中,反应速率快、转化率高,随着PEPDTA含量增加,乳胶粒数量减少、粒径分布变宽,诱导期和缓聚现象明显;聚合物的数均分子量随转化率线性增长,RAFT试剂浓度越高,分子量分布越窄,反应时间越长,分布越宽。以Smith-Ewart方程为基础,建立了苯乙烯RAFT细乳液聚合动力学模型,模型动力学曲线与实验数据相符合,能较好地预测实验过程。     

Disparate polymerization facilitates the synthesis of versatile block copolymers from poly(trimethylene carbonate)

A disparate polymerization technique is utilized for preparing versatile block copolymers from poly(trimethylene carbonate) (poly(TMC)). In this study, 4-(chloromethyl)benzyl alcohol (CBA) is used for the disparate polymerization. The hydroxyl group of CBA is involved in ring-opening polymerization and the benzyl chloride group is involved in incorporating dithiocarbamate for pseudo-living radical polymerization. First, TMC is polymerized from the hydroxyl group of CBA by using an organocatalyst. The benzyl chloride group in CBA is modified using a dithiocarbamate, and then vinyl and methacrylate monomers are polymerized by photo-driven pseudo-living radical polymerization. The resulting block copolymers are versatile and the molecular weight distribution is reasonably narrow. In the present study, N-isopropylacrylamide, acrylamide glycolic acid, and 2-hydroxyethyl methacrylate are used for the disparate polymerization. The resulting block copolymers could be well dissolved in water by incorporation of hydrophilic segment into hydrophobic poly(TMC). The solution property is characterized in terms of hydrophobic domain formation and phase transition under ambient conditions. Moreover, enzymatic degradation is evaluated by using a copolymer-coated substrate. The block copolymer synthesis technique is considerably versatile, and the resulting polymer function can be freely designed. The disparate polymerization technique is a promising approach that provides universal materials for integrating biodegradable polyesters and functional polymers.     

Synthesis and Characterization of Glycidyl Azide‐r‐(3,3‐bis(azidomethyl)oxetane) Copolymers

Glycidyl azide‐r‐(3,3‐bis(azidomethyl)oxetane) copolymers were synthesized by cationic copolymerization of epichlorohydrin and 3,3‐bis(bromomethyl)oxetane, using butane‐1,4‐diol as an initiator and boron trifluoride etherate as a catalyst, followed by azidation of the halogenated copolymer. The main objective of this work is the preparation of an OH‐terminated amorphous polymer with energetic content higher than that of the well‐known glycidyl azide homopolymer. The effect of experimental conditions, i.e., the rate of monomer feeding, on the final molecular weight and functionality of the copolymer has also been investigated. The obtained copolymers were extensively characterized to determine their composition and thermal stability. The heat of reaction for the polymerization of the halogenated key precursors has also been measured. It was found that even though both the operating conditions and the catalytic system were chosen in order to favor a living character of the polymerization, the final product seems to be the result of a combined living and active chain end mechanism. In particular, the latter is responsible for the formation of oligomers and not hydroxyl‐terminated chains. Nevertheless, the average number of OH groups is high enough to allow a cross‐linking of the polymeric chains, by addition of polyisocyanates and subsequent formation of inter‐chain urethanic bonds.