Unit16Styrene-ButadieneCopolymer

1、Unit 16 Styrene-Butadiene Copolymer第十四单元丁二烯-苯乙烯共聚物The synthetic rubber industry, based on the free-radical emulsion process, was created almost overnight during World War II. Styrene-butadiene (GR-S) rubber crated at that time gives such good tire treads that natural rubber has never regained this m

2、arket.合成橡胶工业，以自由基乳液过程为基础，在第二次世界大战期间几乎很快地形成。 那时，丁苯橡胶制造的轮胎性能相当优越，使天然橡胶在市场黯然失色。The GR-S standard recipe is丁苯橡胶的标准制法是ComponentParts by weightCom叩眦thParts by weightbutadiene75poiaAsimn peroxydisulfatestyrene255,0fi-dodMy mercaptan0,5wateriBO，一组分重量分数组分重量分数丁二烯72过硫酸钾苯乙烯25肥皂片十二烷基硫醇0.5水0.35.0180This mixture i

3、s heated with stirring and at 50 C gives conversions of 5%6% per hour. Polymerization is terminated at 70%75% conversion by addition of a-stop ” , suchashorthydroquinone (approximately 0.1 part), to quench radicals and prevent excessive branching and microgel formation. Unreacted butadiene is remove

4、d by flash distillation, and syrene by steam-stripping in a column. After addition of an antioxidant, such as N-phenyl-伊naphthylamine (PBNA) (1.25 parts), the latex is coagulated by the addition of brine, followed by dilute sulfuric acid or aluminum sulfate. The coagulated crumb is washed, dried, an

5、d baled for shipment.混合物在搅拌下50c加热，每小时转化5%6%,在转化率达70%75%时通过加 入终止剂”聚合反应终止，例如对苯二酚(大约 0.1的重量百分含量)，抑制自由基并 避免过量支化和微凝胶形成。未反应的丁二烯通过闪蒸去除，苯乙烯在萃取塔中通过蒸 汽萃取(剥离)。在加入抗氧剂后，例如 N-甲基-S蔡胺(1.25的重量百分含量)，加入 盐水，其次加入稀释的硫酸或硫酸铝后乳液凝胶。凝胶碎片被洗涤、干燥并包装装运。Fig.14.1 SBR plant flow diagram Courtesy of Hydrocarbon Processing and Petrole

6、um Refiner.图14.1 丁苯橡胶厂流程图取自燃类加工和石油产品精制This procedure is still the basis for emulsion polymerization today. An important improvement is continuous processing 川ustrated in Fig. 14.1; computer modeling has also been described.今天这种生产过程仍是胶体聚合反应的基础。如图14.1所示一个重要的进步是连续操作；也采用计算机模型描述。In the continuous process

7、, styrene, butadiene, soap, initiator, and activator (an auxiliary initiating agent) are pumped continuously form storage tanks through a series of agitated reactors at such a rate that the desired degree of conversion is reached at the last reactor. Shortstop is added, the latex warmed with steam,

8、and the unreacted butadiene flashed off. Excess styrene is steam-stripped, and the latex finished as shown in Fig. 14.1.在连续操作中，苯乙烯、丁二烯、肥皂、引发剂和活化剂(一种助引发剂)用泵从 储罐通过一系列的混合反应器，泵送流率根据末釜的转化率控制。加入终止剂，乳液用 蒸气加热，未反应的丁二烯被闪蒸。剩余的苯乙烯被蒸气剥离，如图14.1表示乳液完成。Table 14- t Typiral formHlations for cold SURCcunponentFormulat

9、ion 1Form ujM ion 2butadiene7271一styrene2829/dodecyl mcrcdptMi0.2o. ibdiisopropylbfaiEcne monohydrope roxide尔盟/?-menthane hydroperoxideQ. 08ferrous sulfate huptahydTHte0.14a03potissjum pyrophosphate0.1Ktrisoditim phosphate dccahydrate5 5t e t rasodium ethylfnediammeletraaretate0. 035sodium formaldeh

10、yde0. OSrosin acid soap4.0t，5waitr130200表14.1冷苯胶的典型配方组分配方1配方2丁二烯7271苯乙烯2829特叶二烷基硫醇0.20.18过氧化一异丙苯0.08过氧化薄荷烷0.08硫酸亚铁七水合物0.140.03焦磷酸钾0.18磷酸钠十水合物0.5乙二胺四乙酸钠0.035甲醛次硫酸钠0.08松香酸4.04.5水180200SBR prepared from the original GR-S recipe is often called hot rubber; cold rubber is made at 5 c by using a more acti

11、ve initiator system. Typical recipes are given in Table 14.1 At 5 C ,60% conversion to polymer occurs in 1215h.由常规丁苯制法制备的丁苯胶常称作热胶；冷胶通过使用一种更高活性的引发体系在5c制成。典型的配方在表14.1中给出。5、60%转化率、1215 h聚合物形成。Cold SBR tire treads are superior to those of hot SBR. Polymers with abnormally high molecular weight (and cons

12、equently too tough to process by ordinary factory equipment) can be processed after the addition of up to 50 parts of petroleum-base oils per hundred parts of rubber (phr). These oil extenders make the rubbers more processible at lower cost and with little sacrifice in properties; they are usually e

13、mulsified and blended with the latex before coagulation.冷丁苯橡胶轮胎优于那些热丁苯胶。具有异常高的分子量的聚合物(因此采用常规 的工厂设备由于太粘稠而难以加工)在每一百份的橡胶中加入大于50份的石油基础油后能够加工。这些油添加剂使橡胶更易加工体现在低成本和性能方面低损耗；他们在凝 胶之前通常乳化并与胶乳混合。Recent trends have been toward products designed for specific uses. The color of SBR, which is important in many non

14、tire uses, has been improved by the use of lighter-colored soaps, shortstops, antioxidants, and extending oils. For example, dithiocarbamates are substituted for hydroquinone as shortstop; the latter is used on hot SBR where dark color is not objectionable. A shortstop such as sodium dimethyldithioc

15、arbamate is more effective in terminating radicals and destroying peroxides at the lower temperatures employed for the cold rubbers.最近倾向于设计特殊用途的产品。丁苯橡胶的颜色，在许多非轮胎使用中十分重 要，通过使用浅色的肥皂、终止剂、抗氧剂和扩展油加以改进。例如，二硫化氨基甲酸 盐替代对苯二酚作为终止剂；后者适用于不被人反对的黑色丁苯橡胶。在冷胶的制备中如二硫化氨基甲酸钠的终止剂在低温情况下对终止自由基和消灭过氧化物更有效。Free-radical dissoc

16、iative initiators that function by dissociation of a molecule or ion into two radical species are normally limited to inorganic persulfates in the case of butadiene polymerization.在丁二烯聚合反应过程中自由基分解的引发剂即一分子分解或离子成两个自由基 物种的引发剂通常限制于过硫酸盐。The other important class of free-radical initiators, redox systems,

17、 contain two or more components that react to produce free radicals. Dodecyl mercaptan added to control molecular weight also appears to aid free-radical formation by reaction with persulfate. The commercial importance of such chain-transfer agents or modifiers cannot be overemphasized. Without mole

18、cular weight control the rubbers would be too tough to process.其他重要的自由基引发剂类别，氧化还原体系，包含反应产生自由基的两种或多 种组分。加入控制分子量的十二烷基硫醇与过硫酸盐反应也出现了助自由基的形成。这 种链转移剂或调节剂具有极其重要的商业价值。不控制分子量橡胶将过于粘稠难以加 工OTate D p , Bechea T W. Encyclopedia of Polymer Science and Engineering, 2nd ed. Vol. 2. Editor-in-chilf Kroschwitz JI. New

19、 York: John wiley & Sons, 1985. 553555UNIT 14 Styrene-Butadiene CopolymerThe synthetic rubber industry, based on the free-radical emulsion process, was created almost overnight during World War I . Styrene-butadiene (GR-S) rubber created at that time gives such good tire treads that natural rubb

20、er has never regained this market. ?The GR-S Standard recipe isThis mixture is heated with stirring and at 50C gives conversions of 5% 6% per hour.Polymerization is terminated at 70%75% conversion by addition of a "short-stop", such as hydroquinone (approximately 0. 1 part), to quench radi

21、cals and prevent excessive branching and microgel formation. Unreacted butadiene is removed by flash distillation, and styrene by steam-stripping in a column. After addition of an antioxidant, such as iV-phenyl- anaphthylamine (PBNA) (1.25 parts), the latex is coagulated by the addition of brine, fo

22、llowed by dilute sulfuric acid or aluminum sulfate. The coagulated crumb is washed, dried, and baled for shipment.This procedure is still the basis for emulsion polymerization today. An important improvement is continuous processing illustrated in Fig. 14.1; computer modeling has also been described

23、.In the continuous process, styrene, butadiene, soap, initiator, and activator (an auxiliary initiating agent) are pumped continuously from storage tanks through a series of agitated reactors at such a rate that the desired degree of conversion is reached at the last reactor.? Shortstop is added, th

24、e latex warmed with steam, and the unreacted butadiene flashed off. Excess styrene is steam-stripped, and the latex finished as shown in Fig. 14.1.SBR prepared from the original GR-S recipe is often called hot rubber, cold rubber is made at 5'C by using a more active initiator system. Typical re

25、cipes are given in Table 14.1. At 5*C , 60% conversion to polymer occurs in 1215h.Cold SBR tire treads are superior to those of hot SBR. Polymers with abnormally high molecular weight (and consequently too tough to process by ordinary factory equipment) can be processed after the addition of up to 5

26、0 parts of petroleum-base oils per hundred parts of rubber (phr) . These oil extenders make the rubbers more processible at lower cost and with little sacrifice in properties; they are usually emulsified and blended with the latex before coagulation.Recent trends have been toward products designed f

27、or specific uses. The color of SBR, which is important in many nontire uses, has been improved by the use of lighter-colored soaps, shortstops, antioxidants, and extending oils. For example, dithiocarbamates are substituted for hydroquinone as shortstop ; the latter is used on hot SBR where dark col

28、or is not objectionable. A shortstop such as sodium dimethyldithiocarbamate is more effective in terminating radicals and destroying peroxides at the lower temperatures employed for the cold rubbers.Free-radical dissociative initiators that function by dissociation of a molecule or ion into two radi

29、cal species are normally limited to inorganic persulfates in the case of butadiene polymerization.The other important class of free-radical initiators, redox systems, contain two or more components that react to produce free radicals. Dodecyl mercaptan added to control molecular weight also appears

30、to aid free-radical formation by reaction with persulfate. The commercial importance of such chain-transfer agents or modifiers cannot be overemphasized. ? Without molecular weight control the rubbers would be too tough to process.Reading MaterialsSteady-State Multilicity in Continuous Emulsion Poly

31、merizationThe phenomenon of multiple steady states is seen in emulsion polymerization. Fig. 14. 2 is a plot of steady-state monomer conversion as a function of reactor residence time for methyl methacrylate emulsion polymerization in a CSTR. A region of multiplicity is indicated by the fact that the

32、 upper and lower branches of the curve overlap between residence times of 30 and 50 minutes. The dotted line is an estimate of the shape of the unstable middle branch which is experimentally unobservable. The dashed lines indicate experimental instances of ignition and extinction. At 50 minutes resi

33、dence time the system has been observed to move from the lower steady state of 54% conversion to the upper steady state at approximately 80% with no discernible change in operating conditions (ignition). Extinction has been observed when the residence time is changed from 30 minutes to 20 minutes on

34、 the upper branch, resulting in a drop in conversion from the upper to the lower steady-state values. The phenomenon of multiple steady states arises in emulsion polymerization for much the same reason as itappears insolutionpolymerization:the autocatalytic nature of the polymerization(due to the ge

35、l effect),combined with the mass balance, results in the possibility of steady-state multiplicity.Steady-state multiplicity can be an operational problem for a number of reasons. If one wishes to operate at an intermediate level of monomer conversion (perhaps to minimize viscosity or prevent excessi

36、ve chain branching), one may be forced to operate in the unstable region, relying on closed-loop control to stabilize the operating point. This is tricky at best. Additionally, the steady state (upper or lower) to which the system goes on start-up will depend on how the start-up is effected. A caref

37、ul start-up policy may be needed to assure that the system arrives at the desired steady state. In general, a conservative start-up, with the temperature and initiator concentration brought to steady-state values slowly will result in operation on the lower branch, while aggressive start-up (high te

38、mperature and/or high initiator concentration during start-up) will result in steady-state operation on the upper branch. Finally, large upsets in the process may cause ignition or extinction. This may lead to loss of temperature control in the case of ignition, or loss of reactor productivity in th

39、e case of extinction. A system designed to operate at the upper steady state will be operating way below design product yield at the lower steady state. Additionally, the product quality (MWD, CCD, etc. ) will be different for the two operating points. The polymerisation reactor designer should be a

40、ware of the potential for multiplicity, and, if possible, design the system to operate outside this region.CSTR polymerization reactors can also be subject to oscillatory behavior. A nonisothermal CSTR free radical solution polymerisation can exhibit damped oscillatory approach to a steady state, un

41、stable (growing) oscillations upon disturbance, and stable (limit cycle) oscillations in which the system never reaches steady state,and never goes unstable, but continues to oscillate with a fixed period and amplitude. However, these Phenomena are more commonly observed in emulsion polymemation.Hig

42、h-volume products such as styrene-butadiene rubber (SBR) often are produced by continuous emulsion polymerization. This is most often done in a train of 515 CSTRs in series. Sustained oscillations (limit cycles) in conversion, particle number, and free emulsifier concentration gave been reported, un

43、der isothermal conditions in continuous emulsion polymerization systems. This limit cycle behavior leaves its mark on the product in the form of disturbances in the molecular weight distribution and particle size distribution which cannot be blended away. Fig. 14. 3 shows evidence of a sustained osc

44、illation (limit cycle) during emulsion polymerization of methyl methacrylate in a single CSTR. Com parison of the monomer conversion and surface tension data graphically illustrates the mechanism of oscillation. It will be noted that the surface tension oscillates with the same period as the convers

45、ion (67 residence times). This can be explained with the classical micellar initiation mechanism (or with homogeneous nucleation) . Beginning at a time of about 300 minutes, the conversion rises rapidly as new particles form and old particles grow. As the particle surface area increases , additional

46、 surfactant is adsorbed on the particles. Meanwhile micelles dissociate to keep the aqueous phase saturated. Once all of the micelles have dissociated, it is no longer possible to maintain the aqueous phase at saturation, and the surface tension begins to rise. This is observed at about 320 minutes.

47、 At the point at which micelles are no longer present, micellar initiation stops and the rate of polymerization slows. Eventually, since particles are washing out while no new particles are being formed, the conversion begins to fall. Since the total particle surface area is decreasing at this point

48、, and since surfactant is continually being introduced with the feed, the surface tension falls as the aqueous phase reapproaches saturation. As the aqueous phase becomes saturted initiation begins again. Saturation of aqueous phase may be observed by noting the point at which the surface tension re

49、aches its CMC value. As new micelles are formed they adsorb free radicals, become polymer particles, and begin to grow and adsorb surfactant. The cycle then repeats.Modeling studies show that while the instability arises above the CMC (and is promoted by large values of initiator concentration and r

50、esidence time, and low surfactant concentration), it is the on/off nature of the nucleation mechanism which governs the nature of oscillations in monomer conversion. The surface tension oscillation leads the conversion oscillation by approximately one residence time. This is consistent with the abov

51、e explanation since changes in surfactant concentration are quite rapid while changes in the number of particles and rate of reaction require a finite growth time to appear as changes in the monomer conversion. Damped oscillations at start-up have been noted for a large number of monomer systems.Damped oscillat