New advances in the mathematical modeling of the continuous bulk process for the production of high‐impact polystyrene using multifunctional initiators

New advances in the mathematical modeling of the bulk continuous high‐impact polystyrene (HIPS) process are presented. The model consists of three modules that allow the simulation of: (1) a polymerization reactor train, (2) a devolatilization (DV) stage, and (3) structure–properties relationships. The model is based on a kinetic mechanism that includes thermal initiation, chemical initiation by sequential decomposition of a multifunctional initiator, propagation, transfer to monomer, transfer to rubber, termination by combination and re‐initiation, as well as high temperature crosslinking and oligomer generation reactions. The present model is comprehensive from a kinetic perspective, since it can be used to simulate a HIPS process using initiators of any functionality and structure. The model is adjusted and validated using previously unpublished experimental data for bulk continuous HIPS polymerization in a pilot‐scale plant. The experimental work includes a series of polymerizations using three different multifunctional initiators: (1) luperox‐331 M80 (L331), (2) pinacolone diperoxide, and (3) diethyl ketone triperoxide. The pilot plant comprised the main stages of an industrial HIPS process: prepolymerization, finishing and DV. Theoretical results show a good agreement with the experimental measurements. POLYM. ENG. SCI., 59:E231–E246, 2019. © 2018 Society of Plastics Engineers     

Bulk polymerization of styrene in the presence of polybutadiene. The use of bifunctional initiators

This work experimentally and theoretically investigates the use of bifunctional initiators in the synthesis of high-impact polystyrene (HIPS). The experimental design involved a series of nonisothermal bulk polymerizations of styrene (St) in the presence of polybutadiene (PB). The performance of three commercial initiators [2,5-dimethyl −2,5 bis(2-ethylhexanoyl peroxy] hexane or L–256; 2,5 bis(benzoyl peroxy) hexane or L–118; and ethyl 3,3 di(t-butyl peroxide) butirate or L–233] were compared to the performance of a standard monofunctional initiator (terbutylperoctoate or TPBO), and to the blank case (i.e., without initiator). From samples taken along the prepolymerization period, the phase inversion point and the 30% conversion point were estimated. For the final product, the free polystyrene (PS) molecular weights and the St grafting efficiency were measured. A mathematical model was developed that predicts the evolution of the MWDs for the free PS the residual PB, and the graft copolymer, together with the chemical composition distribution for the total graft copolymer. Compared to the monofunctional case, the L–256 initiator induces phase inversion and rubber grafting at low conversions. Also, it shortens the prepolymerization times by around 38%, without affecting the molecular characteristics of the final product. L–118 also shortens prepolymerization time with respect to TBPO; but is not as effective as L–256 or TBPO in promoting rubber grafting. At the polymerization end, the final molecular characteristics are practically independent of the initiator type because most of the polymerization in induced by monomer initiation. Due to its slow decomposition rate, the L–233 initiator is less effective that TBPO for reducing prepolymerization times and for promoting phase inversion. © 1996 John Wiley & Sons, Inc.     

Synthesis of polystyrene with mixtures of mono- and bifunctional initiators

This work studies the bulk and nonisothermic polymerization of styrene (S) using mixtures of mono- and bifunctional initiators. The effects on polymerization rate and on molecular weight averages after changes in the global initiator concentration and in the nature of the initiator mixtures were experimentally and theoretically analyzed. The mathematical model was adapted from the literature to admit initiator mixtures and to simulate the applied temperature profiles. Compared to the standard use of monofunctional initiators, the use of initiator mixtures that include bifunctional initiators presents the advantage of reducing the polymerization time, while not deteriorating the final polymer quality. The simulation program accurately describes the evolution of conversion, but exhibits some deviations with the average molecular weights. © 1996 John Wiley & Sons, Inc.     

Heterogeneous bulk polymerization of styrene in the presence of polybutadiene: Calculation of the macromolecular structure

A mathematical model is presented that simulates the polymerization of styrene in the presence of polybutadiene (PB) for producing high‐impact polystyrene (HIPS) via the heterogeneous bulk process. The model follows the polymerization in two phases; and calculates in each phase the main reaction variables and the molecular structure of the three polymeric components: free polystyrene (PS), unreacted PB, and graft copolymer. Two polymerizations (at 90 and 120°C) were carried out and simulated. The model was validated with measurements of the monomer conversion, the grafting efficiencies, and the average molecular weights. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3023–3039, 2006     

高抗冲聚苯乙烯(HIPS)连续生产的模拟

根据热引发连续本体聚合生产高抗冲聚苯乙烯 (HIPS)的动力学机理 ,建立了苯乙烯 /顺丁二烯橡胶本体聚合过程的多釜串联 (CSTR)数学模型 ,并由两个不同品牌的实际工业生产数据对模型进行了验证。得到了各釜出口苯乙烯单体的转化率、HIPS的接枝效率、接枝率以及自由PS的重均分子量及其分布     

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.     

Kinetics of bulk styrene polymerization catalyzed by symmetrical bifunctional initiators

The kinetics of bulk styrene polymerization catalyzed by symmetrical bifunctional initiators [2,5-dimethyl-2,5-bis(benzoyl peroxy) hexane] is studied. Being characterized by the presence of two peroxide groups of equal thermal stabilities, this bifunctional initiator system shows complex initiation, propagation, and termination reaction pathways. The kinetic model for bulk styrene polymerization with the bifunctional initiator is presented and compared with experimental data. The experimental data indicate that the model is quite satisfactory in describing the polymerization rate and polymer molecular weights for bulk styrene polymerization catalyzed by the symmetrical bifunctional initiator.     

Free-radical polymerization of styrene with a binary mixture of symmetrical bifunctional initiators

The kinetics of bulk styrene polymerization catalyzed by a binary mixture of symmetrical bifunctional initiators has been investigated. When the bifunctional initiators having different thermal stabilities are mixed, an unsymmetry in the initiator functions is formed in situ via propagation, chain transfer, and termination reactions. For the quantification of the polymerization kinetics, a kinetic model has been developed using the molecular species modeling technique. For various polymerization conditions, good agreements between the model predictions and experimental data have been obtained. It is shown that polymerization rate and molecular weight can be easily regulated under isothermal reaction condition by changing the initiator composition. A comparison of the detailed kinetic model with a simple kinetic model for monofunctional initiators has also been made to illustrate the molecular weight increasing effect of the bifunctional initiator system. © 1992 John Wiley & Sons, Inc.     

Bulk polymerization of styrene catalyzed by bi‐ and trifunctional cyclic initiators

A study of the bulk free‐radical polymerization of styrene in the presence of the cyclic bi‐ and trifunctional initiators cyclohexanone triperoxide, diethylketone triperoxide, acetone triperoxide, cyclohexanone diperoxide, and pinacolone diperoxide is reported. When these multifunctional initiators are used for styrene polymerization at high temperatures, it is possible to produce polymers with high molecular weights and narrow polydispersities at a high reaction rate. Additionally, the former initiators are used in a mixture that shows that the molecular parameters are influenced by the initiator concentration in the initiation system, in addition to the system employed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1–11, 2002     

Quantitative analysis of grafting and crosslinking on Thermal Bulk Polymerization of high impact polystyrene

Analytic expressions for grafting of polystyrene (PS) onto polybutadiene (PBD) and crosslinking of PBD during thermal bulk polymerization of high impact polystyrene (HIPS) were derived by using moment distribution function based on Peng’s kinetic scheme [1]. The ratio of chain transfer constant for PBD to that for styrene monomer, k₅/k₃, was determined by the linear correlation between grafting efficiency (GE) and In 1/(1-X) where X was the conversion of styrene. Both the GE and In 1/(1-X) were determined from experiments. According to this correlation, the GE did not depend on the reaction temperature, which seemed that the temperature dependence was offset in the ratio of chain transfer constant for PBD to that for styrene monomer in this analytic expression. The degree of crosslinking drastically increased at high temperature (≥190°C) and at high conversion such as 95%. With minor modification, these analytic formulas could be used for the polymerization using initiators. Furthermore, it will be useful to design the polymerization process.     

Polymerization of styrene in the presence of polybutadiene: determination of the molecular structure

This work experimentally and theoretically determines the molecular macrostructure of the polymer mixture that is developed (at relatively low conversions) in a solution polymerization of styrene (St) in presence of polybutadiene (PB). The reaction was carried out at 70°C in a batch‐stirred tank reactor. From samples taken along the reaction, the three polymeric components of high‐impact polystyrene (HIPS) (i.e., polystyrene  PS , residual PB, and graft copolymer) were first separated from each other by solvent extraction. Then, the graft copolymer was ozonized to isolate the St branches. The molecular weight distributions (MWDs) of the total HIPS, the three HIPS components, and the grafted St branches were determined by the size exclusion chromatography (SEC). For the graft copolymer and the total HIPS, the variation of the St mass fraction with molecular weights was also determined by SEC. All measurements were compared with theoretical estimates, and a reasonable agreement is observed. For the theoretical estimates, the mathematical model of Estenoz, D. A.; Valdez, E.; Oliva, H. M.; Meira, G. R. (J Polym Sci 1996, 59, 861) was extended to compare the MWD of the St branches with the MWD of the free PS. For the sought experimental conditions, these two distributions had very similar results but in a bulk industrial process, larger discrepancies are to be expected. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1950–1961, 1999     

高抗冲聚苯乙烯的合成机理与结构,性能

详细评述了高抗冲聚苯乙烯树脂的合成机理，讨论了聚合动力学、接枝反应与接枝率、分子量及其分布、相转变及相结构的调控规律，介绍了树脂结构与性能的关系。     

Synthesis and characterization of high‐impact polystyrene using a multifunctional cyclic peroxide as the initiator

This work deals with the synthesis of high‐impact polystyrene (HIPS) using a novel cyclic multifunctional initiator, the diethyl ketone triperoxide (DEKTP), analyzing its effect on the prepolymerization step and its influence over the HIPS final properties. DEKTP showed a low selectivity toward grafting reactions at any of the concentrations of initiator and temperatures evaluated, and when it was used under a temperature ramp (120–130°C, heating rate = 2°C/min), the synthesis of HIPS was possible with an adequate development of morphology and impact strength (i.e., 67 J/m) depending on DEKTP concentration. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Analyzing the real advantages of bifunctional initiator over monofunctional initiator in free radical polymerization

Monofunctional initiators are extensively used in free radical polymerization. To enhance productivity, a higher temperature is usually used; however, this leads to lower molecular weights. Bifunctional initiators can increase the polymerization rate without decreasing the average molecular weight and this can be desirable. A bifunctional initiator is an important issue to be investigated, and it is of great interest to industries. The objective of this work is to study polymerization reactions with mono‐ and bi‐functional initiators through comprehensive mathematical models. Polystyrene is considered as case study. This work collects and presents some experimental data available in literature for polymerization using two different types of bifunctional initiators. Model prediction showed good agreement with experimental data. It was observed that the initial initiator concentration has a huge impact on the efficiency of initiators with functionality bigger than one and high concentrations of bifunctional initiator make the system behave as if it were a system operating with monofunctional initiator. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Free‐radical bulk polymerization of styrene with a new trifunctional cyclic peroxide initiator

The bulk free‐radical polymerization of styrene in the presence of a new cyclic trifunctional initiator, 3,6,9‐triethyl‐3,6,9‐trimethyl‐1,4,7‐triperoxonane, was studied. Full‐conversion‐range experiments were carried out to assess the effects of the temperature and initiator concentration on the polymerization kinetics, molecular weight, and polydispersity. Gel permeation chromatography was used to measure the molecular weight and the molecular weight distribution of polystyrene. When this multifunctional initiator was used for styrene polymerization at higher temperatures, it was possible to produce polymers with higher molecular weights and narrower molecular weight polydispersity at a higher rate. This showed that the molecular weight and polydispersity were influenced by the initiator concentration and the polymerization temperature in an unusual manner. Moreover, polystyrene, obtained with trifunctional peroxide, had O? O bonds in the molecular chains and was investigated with differential scanning calorimetry and gel permeation chromatography. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1035–1042, 2004     

双官能团引发剂引发甲基丙烯酸甲酯的聚合速率

研究了双官能团引发剂2,5-双(2-乙基己酰过氧化)-2,5-二甲基己烷（TX-141）引发甲基丙烯酸甲酯（MMA）的自由基聚合动力学,考察了引发剂浓度、聚合温度对聚合动力学的影响.结果表明：该体系的聚合活化能为91 kJ•mol^-1左右,计算得到TX-141引发剂的分解活化能为140 kJ•mol^-1左右,与实验值接近;TX-141引发剂的反应级数约为0.72,说明MMA聚合终止基元反应中单基和双基终止并存.同时与相似半衰期的过氧化二苯甲酰（BPO）比较,发现当TX-141引发剂浓度为BPO的1/2时,两者在各个聚合温度下的聚合动力学曲线几乎相同;但相对分子质量有明显增加,随聚合转化率增加,TX-141与BPO引发的聚合物数均分子量之比从1.2变化到1.33;由TX-141引发的聚合物低转化率时DSC曲线出现放热峰,而高转化率以及BPO引发的聚合物则没有.说明双官能团引发剂TX-141引发聚合时,在低转化率下TX-141引发剂的2个过氧键没有全部断裂,随聚合进行,断裂程度加深.     

聚丁二烯橡胶改性高抗冲聚苯乙烯的性能研究

介绍了聚丁二烯橡胶的用量、种类和结构以及粒径对高抗冲聚苯乙烯性能的影响     

自由基聚合引发剂研究进展

自由基聚合是大规模生产各种烯类聚合物的有效方法，在工业生产中，约70％以上的烯类聚合物都是通过自由基聚合来实现的。自由基聚合引发体系可归纳为过氧化物类引发剂、偶氮引发剂、二硫化物引发剂、氧化还原引发体系、双官能度及多官能度引发剂和大分子引发剂等。本文着重介绍近年来新发展起来的水溶性偶氰引发剂、双官能度及多官能度引发剂、大分子引发剂以及氧化还原引发剂的最新进展。     

Bulk polymerization of styrene in presence of polybutadiene: Calculation of molecular macrostructure

In our previous publication the detailed molecular macrostructure generated in a solution polymerization of styrene (St) in the presence of polybutadiene (PB) at 60°C, was theoretically calculated. In this work, an extended kinetic mechanism that incorporates monomer thermal initiation, chain transfer to the rubber, chain transfer to the monomer, and the gel effect is proposed, with the aim of simulating a bulk high-impact polystyrene (HIPS) process. The mathematical model enables the calculation of the bivariate weight chainlength distributions (WCLDs) for the total copolymer and for each of the generated copolymer topologies and the univariate WCLDs for the free polystyrene (PS), the residual PB, and the crosslinked PB topologies. These last topologies are characterized by the number of initial PB chains per molecule; copolymer topologies are characterized by the number of PS and PB chains per molecule. The model was validated with published literature data and with new pilot plant experiments that emulate an industrial HIPS process. The literature data correspond to a dilute solution polymerization at a constant low temperature with chemical initiation and a bulk polymerization at a constant high temperature with thermal initiation. The new experiments consider different combinations of prepolymerization temperature, initiator concentration, and solvent concentration. One of the main conclusions is that most of the initial PB is transformed into copolymer. For example, for a prepolymerization temperature of 120°C with addition of initiator, the experimental measurements indicate that the final total rubber mass is approximately three times higher than the initial PB. Also, according to the model predictions, the final weight fractions are: free PS, 0.778; graft copolymer, 0.220; initial PB, 0.0015; and purely crosslinked PB, 0.0005. The final graft copolymer exhibits the following characteristics: average molecular weights, M _n,C = 492,000 and M _w,C = 976,000; average weight fraction of St, 0.722; and average number of PS and PB branches per molecule, 5.19 and 1.13, respectively. © 1996 John Wiley & Sons, Inc.     

四官能度过氧化物引发制备高抗冲聚苯乙烯

引言高抗冲聚苯乙烯(HIPS)可通过顺丁橡胶(PB)接枝苯乙烯共聚制备,相比通用聚苯乙烯(GPPS),其抗冲性能高、拉伸形变大,但这些性能受HIPS分子量及分布、接枝效率、橡胶粒子形态及大小的影响很大。制备时可改变剪切速率、橡胶类型及用量、引发剂用量来调节产物分子量及分布、接枝效率、橡胶粒子形态及大小,进而控制