Dynamics of a CSTR for styrene polymerization initiated by a binary initiator system

The steady state and dynamic behavior of a continuous stirred tank reactor has been analyzed for free radical solution polymerization of styrene initiated by a mixture of two initiators having different thermal stabilities. From the steady state analysis of the reactor model with a mean residence time as a bifurcation parameter, four unique regions of steady state solutions are identified in an operating parameter space for a given initiator feed composition. A variety of complex bifurcation behavior such as multiple steady states, Hopf bifurcation and limit cycles have been observed and their stability characteristics have been analyzed. The effects of feed initiator composition and the concentration of the initiator in the feed stream on the reactor dynamics are also presented.     

树状分子引发苯乙烯的原子转移自由基聚合

从第2代端羟基树状聚芳醚出发,合成了2－溴异丁酸聚芳醚酯（G2－Br),并用红外,核磁,MALDI－TOF质谱和元素分析对其进行了表征,以C2-Br为大分子引发剂,在CuBr/2,2′－联吡啶催化作用下引发苯乙烯的原子转移自由基聚合。考察了聚合时间,单体和引发剂配比,聚合温度等因素对聚合的影响,合成了结构规整,分子量分布较窄的树状－线型嵌段共聚物。     

The soluble and insoluble product of diphenylzinc-water systems as initiator in styrene polymerization

The solution resulting from reaction between Ph₂Zn and H₂O in benzene was used by itself and separated in soluble and insoluble fractions to initiate styrene polymerization. The soluble fraction produced the largest polymer conversion while the insoluble was reponsible of the highest molecular weights. Resulting polystyrenes were atactic but up to 80 – 85% syndiotactic triads were detected by ¹H-NMR analysis. Polystyrene obtained using benzene as solvent showed a low crystalline content while the polymer obtained using dichloromethane did not produce any crystalline fraction. Received: 10 December 1996/Revised: 15 April 1997/Accepted: 18 April 1997     

The ferric hydroxide/hydrazine system as an initiator of vinyl polymerization

The reaction between ferric hydroxide and hydrazine was used to initiate the solution polymerization of methyl methacrylate. Polymerization occurs readily at pH > 6, over a wide range of iron concentration and of temperature. The initiation reaction appears to be of heterogeneous nature, like those in similar metal hydroxide/hydrazine systems.     

Graphene as initiator/catalyst in polymerization chemistry

One of the most important applications of graphene-based materials is the formation of nanocomposite materials, where graphene in the bulk-polymer matrix transfers its properties onto the polymeric material. Control of the polymer/graphene interface by attached polymeric interlayers is essential to generate nanocomposites, thus avoiding the aggregation of graphene nanoparticles. Among all graphene materials graphene oxide (GO) and reduced graphene oxide (r-GO) can be prepared on large scales useful for mass production graphene/polymer composites. The direct use of graphene materials as both, the polymerization initiator or catalyst and additive not only diminishes the agglomeration of particles in composites but also reduces the process of composite production to one facile step, which in turn avoids further purification regarding to strong acid initiators and metal particles catalysts. Here, literature activities within the past ∼10 years using graphene-based materials either as initiator or catalyst in different polymerization reactions are reviewed.     

Calculation of molecular weight distribution in styrene polymerization initiated by a binary initiator system

A computational scheme is presented for the calculation of molecular weight distribution in styrene polymerization initiated by a binary initiator system. In this paper, the method of finite molecular weight moment is presented by calculation of the polymer chain length distribution. This method is compared with the method of integrating an infinite number of polymer population balance equations. The results of the two methods show a reasonably good agreement. It is possible to produce polymer having the same molecular weight distribution.     

Anomalous particle through soap-free emulsion polymerization of styrene using oil-soluble initiator

One of oil-soluble initiators, VF-096, might work as cross-linker. This initiator would enable to synthesize the particle with cross-linking, which was involved with the particle morphology. Soap-free emulsion polymerization of styrene using this initiator was carried out to develop the method to control the particle morphology in one batch system. As a result, it was found that anomalous particle was generated without stirring and the particle morphology changed to be spherical by increasing shear stress through the stirring. One of the origins of the anomalous particle was the phase separation of the water in the particle and release of it from inside of the particle to the bulk.     

Synthesis of a difunctional organolithium compound as initiator for the polymerization of styrene‐butadiene/isoprene‐styrene triblock copolymer

A difunctional organolithium compound was prepared by the addition of butyllithium (BuLi) to 1,4‐bis(4‐methyl‐1‐phenylethenyl)benzene (MPEB). The effects of the solvent, polar modifier (THF), butyl lithium structure, and reaction time on the formation of the difunctional organolithium compound were studied. Results showed that toluene as solvent was in favor of the addition reaction over cycohexane, in the absence of the polar modifier. However, cycohexane was a better option as solvent for the addition reaction, when polar modifier was employed. A small amount of polar modifier could efficiently accelerate the reaction rate and have no significant effect on the structure of the polydiene, which was initiated by the polar modifier containing organolithium compound. Results also showed that isobutyl lithium was more active in the addition reaction than n‐butyl lithium, because of inductive effect. The optimum molar ratio of THF/Li+ was determined as 4. The THF containing difunctional organolithium cyclohexane solution was sequentially used in the step‐wise polymerization of triblock thermoplastic copolymer SIBS. The so‐prepared SIBS shared the similar phase separation structure with SBS and exhibited excellent mechanic properties. As the content of the central polyisoprene block increases, the tensile strength of the copolymer is decreased, and the elongation at break is increased. The glass transition temperature T_g of the central block was correlated with its content as T_g = 0.33 × ?62.81, where × is the wt % of the central block, based on the triblock copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1395–1402, 2006     

Emulsifier‐free miniemulsion polymerization of styrene using a cationic initiator

Polystyrene latex particles were synthesized using a method based on emulsifier‐free miniemulsion polymerization under ultrasonic irradiation in the presence of 2,2′ azobis (2‐amidinopropane) dihydrochloride (V‐50) as a cationic ionizable water‐soluble initiator and cetyl alcohol as costabilizer. The optimized conditions were obtained by using various parameters, such as the amounts of monomer and initiator, and the time and power of ultrasonic irradiation. In optimal conditions, the latex particles appeared to be about 250 nm in diameter through scanning electron microscopy (SEM). The SEM and gel permeation chromatography (GPC) analyses and monomer conversions of emulsifier‐free miniemulsion polymerization were compared with those of conventional emulsifier‐free emulsion polymerization using V‐50 as initiator in both cases. The results showed that in the miniemulsion polymerization, the rate of polymerization (Rp) was significantly higher, and latex particles were significantly smaller than those in the conventional emulsion polymerization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

The cupric sulphate-hydrazine hydrate system as an initiator for vinyl graft polymerization onto wool

The ability of the cupric sulphate-hydrazine hydrate redox system to induce vinyl graft polymerization onto wool fibres was studied under different conditions. The magnitude of grafting is governed by concentrations of cupric ions, hydrazine hydrate and monomer as well as pH and temperature of the polymerization medium. Detailed studies were carried out on grafting of wool with methyl methacrylate though ethyl acrylate and styrene were also used. Cupric ions were also replaced by ferric ions in some experiments. Main conclusions arrived at from these studies are: (a) there are optimal concentrations of cupric ion and hydrazine hydrate, (b) the grafting reaction is more favoured at higher (pH higher than 7) than that at lower pH's (pH less than 5), (c) 70°C constitutes the optimal temperature for grafting, (d) the graft yield increases by increasing methyl methacrylate concentration, (e) replacement of cupric ion by ferric ion lowers the rate of grafting and (f) the highest graft yield is obtained with methyl methacrylate and the lowest with styrene.     

Winsor I-like (micro)emulsion polymerization of styrene initiated by oil-soluble initiator

Batch emulsion polymerization of styrene initiated by an oil-soluble initiator and stabilized by non-ionic emulsifier (Tween 20) has been investigated. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals typical for the non-stationary-state polymerization. This behavior is a result of the continuous particle nucleation and the decrease of monomer concentration at the reaction loci with increasing conversion. The initial increase of the polymerization rate is attributed to the increase of particle number and the polymerization proceeding under the monomer-saturated condition—the Winsor I-like (micro)emulsion polymerization. The decrease of the polymerization rate is the result of the depressed transfer of monomer from the monomer reservoir to the reaction loci. Above 50 °C the monomer emulsion separates into two phases: the upper transparent monomer phase and the lower blue colored (microemulsion) phase. The polymerization mixture consists of the microdroplets (act as the reaction loci) and large degradable monomer droplets (act as the reservoir monomer and emulsifier). The continuous release of emulsifier from the monomer phase and the microdroplets induce the continuous particle nucleation up to high conversion. The initial formation of large particles results from the agglomeration of unstable growing particles and monomer droplets. The size of large (highly monomer-swollen) particles decreases with conversion and they merge with the growing particles at ca. 40-50% conversion. The coarse initial emulsion transformed during polymerization to the fine (semitransparent) polymer emulsion as a result of the continuous particle nucleation, the shrinking of highly monomer-swollen polymer particles and the depletion of monomer droplets. The low overall activation energy of polymerization is mainly ascribed to the decreased barrier for entering radicals into the latex particles with increasing temperature.     

Anionic polymerization of dienes using oligobutadienyl-lithium as initiator

The aim of this work is to combine the microstructure of a radical-polymerized diene (butadiene and isoprene) with the functionality of an anionically prepared one, which could be used for polyurethane preparation after functionalization. A two-step anionic procedure was used in order to obtain a hydrocarbon-soluble lithium-based initiator. When compared with the related anionic polymers obtained under classical conditions, the vinyl content of the polydienes was three times greater. These findings are discussed on a mechanistic basis. © 1998 Society of Chemical Industry     

溴化苯乙烯/苯乙烯/丙烯腈乳液聚合试验条件探索

以过硫酸钾为引发剂,十二烷基硫酸钠为乳化剂,叔十二烷基硫醇为链转移剂,通过乳液法对溴化苯乙烯、苯乙烯、丙烯腈进行共聚得到溴化苯乙烯-丙烯腈共聚物.考察了引发剂、乳化剂、链转移剂的添加量,反应温度,反应时间,水和单体比例等对聚合反应收率的影响.研究表明：较适宜的反应条件为反应温度80℃,反应时间6h,水与单体质量比4∶1,引发剂质量为单体总质量的0.4％,乳化剂质量为单体总质量的4％,叔十二烷基硫醇为单体总物质的量的2％;上述条件下的产物收率高,相对分子质量4万左右,热分解温度高于350℃.     

Modelling of free radical polymerization of styrene and methyl methacrylate by a tetrafunctional initiator

A mathematical model for free radical polymerizations initiated by tetrafunctional initiators is described in detail with comparisons to experimental results. Reactions involving the fate/efficiency of functional groups are properly accounted for, while in the past, kinetic models for difunctional initiators found in the literature have ignored this. Free volume theory is used to describe the diffusion-controlled regime. Based on model predictions, multi-radical concentrations were estimated to be several orders of magnitude smaller than mono-radical concentrations. Through various case studies, the model was able to demonstrate that the concentration and chain length of various polymer structures (i.e., linear, star or coupled stars) depend upon monomer type and reaction conditions. The model was found to be useful in explaining experimentally observed differences in the behaviour of a tetrafunctional initiator with styrene compared to methyl methacrylate (MMA). In both cases, higher reaction rates could be obtained when switching from a mono- to a tetrafunctional initiator; however, the influence on molecular weight was found to vary between the two systems. Work with styrene showed similar trends as with difunctional initiators, where the tetrafunctional initiator maintained similar molecular weights compared to a monofunctional initiator. Yet, for MMA, replacing the monofunctional initiator with its tetrafunctional counterpart decreased the molecular weight.     

Atom transfer radical polymerization of styrene with FeCl2/acetic acid as the catalyst system

Summary Atom transfer radical polymerization with FeCl₂/CH₃COOH as the catalyst has been successfully implemented for styrene. Various initiators have been used, among which carbon tetrachloride is the most effective one. High molecular weight products were obtained when CCl₄ was used as the initiator, and the measured molecular weight was close to the calculated one. Block copolymerization (PS-b-PMMA) was performed to confirm the living/controlled nature of the polymerization. ¹H NMR was used to characterize the structure of the macromolecular initiator and the block copolymer. If other initiators, such as benzyl bromide, ethyl 2-bromopropionate and α-bromoethyl benzene, were used, the polymerization occurred at ambient temperature resulting in oligomer. The molecular weight of the oligomer approaches to 4600 (M_n,th= 10000). Thus acetic acid, which is cheaper and less toxicity, can be used as coordinative ligand in ATRP initiated by CCl₄ mediated by iron. Received: 13 March 2000/Revised version: 13 November 2000/Accepted: 20 November 2000     

Copolymerization of methylmethacrylate with styrene using triphenylbismuthoniumylide as radical initiator

Bismuthoniumylide‐initiated radical copolymerization of methylmethacrylate with styrene at 60 ± 0.2°C using dioxane as an inert solvent, follows ideal kinetics (R_p ∝ [ylide]^0.5 [MMA]^1.0 [sty]^1.0), and yields alternating copolymer as evident from NMR spectroscopy. The values of reactivity ratios r₁ and r₂, calculated from Finemann–Ross method are 0.48 and 0.45, respectively. The system follows ternary molecular complex mechanism. The radical mode of polymerization has been confirmed by ESR spectroscopy and the effect of hydroquinone. The value of activation energy and k/k_t are 65.0 KJ mol^?1 and 2.5 × 10^?5 l mole^?1 s^?1, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2774–2781, 2001     

PVC树脂聚合用有机过氧化物引发剂

介绍了目前国内外引发剂的使用及开发方向,并对引发剂的选择及其对树脂质量的影响进行了讨论。