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.     

Molecular weight distributions in styrene polymerization with asymmetric bifunctional initiators

We model the molecular weight distribution (MWD) of polystyrene obtained using asymmetric bifunctional initiators. We do that by extending an existing model able to predict conversions and average molecular weights. By applying probability generating functions to the mass balances, a finite set of differential equations is obtained. This set must be solved and numerically inverted in order to obtain the MWD. Validation was performed using available experimental data on average molecular weights. Those calculated from the predicted MWD agree well with the reported experimental data. In order to show the potential of the model as a tool to tailor MWD, we use it to evaluate operating conditions in a batch reactor that would result in bimodal MWD.     

Miniemulsion polymerization of styrene in the presence of macromonomeric initiators

Macromonomeric azo initiators (macroinimers, MIM) which have the properties of macromonomers, macrocrosslinkers and macroinitiators in a macrostructure were used in miniemulsion polymerization of styrene in the presence or absence of any other stabilizer and initiator. MIMs were prepared from the reaction of 4,4′-dicyano-4,4′-azovaleryl chloride, with poly(ethylene glycol) (PEG) of different molecular weights (400 and 2000 g/mol) and with 4-vinylbenzyl chloride. The stabilizing and initiator efficiency of MIMs and the effect of the chain length of PEG units were evaluated.     

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.     

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.     

Bulk and suspension polymerization of styrene in the presence of n-pentane. An evaluation of monofunctional and bifunctional initiation

The plasticizing effect of n-pentane on the rate of bulk free radical polymerization of styrene and molecular weight distribution development has been modeled on the basis of the free volume theory for both monofunctional and bifunctional initiation. A strong decrease in the reaction rate in the late stages of the polymerization, due to the displacement of the onset of the gel effect, has been observed for both types of initiation. This decrease in the polymerization rate limited the terminal conversion to values well below 100% for mono-functional initiation. However, in bifunctionally initiated polymerization, terminal conversions close to 100% were obtained in spite of the decrease in reaction rate. Contrary to what was expected, the molecular weight distribution obtained at terminal conversion was almost completely insensitive to these changes in polymerization rate. This phenomenon is explained in terms of limited transfer to monomer reactions when n-pentane is present in the system. In suspension polymerization, the limiting conversion and plasticizing effects of n-pentane in monofunctionally initiated systems, caused enhanced coalescence leading to suspension set-up. In bifunctionally initiated systems this enhanced coalescence was completely overcome by the short duration of the particle growth stage, owing to high polymerization rates, and stable suspensions were achieved. For these systems the particle size distributions obtained were similar to that of suspension polystyrene without n-pentane. © 1993 John Wiley & Sons, Inc.     

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 in the presence of organomodified montmorillonite

The effect of montmorillonite (Cloisite 6A) on the bulk polymerization of styrene initiated by benzoyl peroxide (BPO) was studied by the dilatometric determination of the polymerization rates. The bulk polymerization rates increased as the montmorillonite input quantity increased. The effect became greater when the BPO concentration decreased. Under the assumption that clay participated in the radical initiation reaction of the chains, the reaction orders for clay and BPO were determined to be approximately 1.0 and 0.5, respectively. X‐ray diffraction and thermogravimetric analysis studies showed that the structure and properties of the obtained polystyrene (PS)/montmorillonite nanocomposites were greatly affected by the BPO concentration. With lower BPO concentrations, a larger interlayer distance and a higher extent of delamination for the clay were observed in the obtained PS/montmorillonite nanocomposites. The nanocomposites prepared with lower BPO concentrations also showed higher heat‐decomposition‐resistance temperatures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1146–1152, 2005     

Instability of styrene/polystyrene/polybutadiene/polystyrene‐b‐polybutadiene emulsions that emulate styrene polymerization in the presence of polybutadiene

This article investigates the room temperature demixing of oil‐in‐oil emulsions containing styrene (St), polybutadiene (PB), a St‐butadiene star block copolymer (BC), and two polystyrene (PS) samples of different molecular weights and is a contribution toward a better understanding of the stability/instability of the reaction mixture in a bulk high‐impact polystyrene (HIPS) process close to the phase inversion. Twelve bulk prepolymerizations of St in the presence of PB were emulated, at 10%, 15%, and 20% conversion; and with constant grafting efficiencies. All the blends contained 6% in weight of butadiene units. After stirring the blends for 24 h, the decantation demixing process was monitored along 30 days, with daily measurement of the interface levels after appearance of a clear interface. For some of the isolated phases, their unswollen morphologies were observed by transmission electron microscopy. All the isolated phases exhibited macrophase separation into homopolymer‐ and copolymer‐rich macrodomains with lamellar microdomains. The BC showed a greater affinity toward the PS‐rich phase. The separation of an independent BC‐rich phase in the blends containing the high molar mass PS and at high grafting efficiencies, modifies the idea of the graft‐ or BC molecules located at the interface of large PS‐rich and PB‐rich phases. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

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     

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     

Atom transfer radical polymerization (ATRP) of styrene and acrylonitrile with monofunctional and bifunctional initiators

A bifunctional initiator (benzal bromide) was used to initiate the bulk atom transfer radical polymerization of styrene and acrylonitrile at 90 °C with CuBr/2,2-bipyridyl. We compared these results with those of a monofunctional initiator of similar structure (1-bromoethyl benzene) under the same polymerization conditions. The monofunctional initiator worked better than the bifunctional initiator when both comonomers were added simultaneously at the beginning of the copolymerization; the bifunctional initiator was only effective when acrylonitrile was added after 20 min of polymerization with styrene. The styrene-acrylonitrile copolymers were characterized by gel permeation chromatography, ¹³C nuclear magnetic resonance spectroscopy, Fourier-transform infrared spectroscopy, and refractometry. Copolymer composition was monitored by both ¹³C NMR and by the change in the specific refractive index increment.     

The component miscibility evolution during polymerization of the polybutadiene containing styrene solutions

In situ graft copolymerization of polystyrene (PS) on polybutadiene (PB) during polymerization of PB solution in styrene monomer was investigated to determine the performance of grafting process, chain structure of generated copolymers, and their effectiveness as compatibilizing agents for incompatible PS-rich and PB-rich phases. The amount of copolymers and their chain structures at different stages of polymerization were determined by gel permeation chromatography (GPC) curves of the reactive blends (taken directly from the reaction) and physical blends (physically prepared based on total composition of reactive blends). It was demonstrated that copolymer formation started from the early stage of polymerization and continued up to the phase inversion stage. In addition, PS grafting on PB occurred initially via single-chain attachment and then converted to a double-chain scenario later on. Compatibilizing efficiency of the copolymers was evaluated by Huggins coefficient (k _H) obtained by performing dilute solution viscometry (DSV) on samples taken at different stages of conversions. The effect of molecular weight of PB on the grafting process and the effectiveness of copolymers generated were also studied. It was found that while compatibilizing role of the copolymers produced from high molecular weight PB (HPB) increases as conversion goes further, the compatibilizing efficiency of the copolymers produced from low molecular weight PB (LPB) shows a very sharp variation in a small range of conversion. Plotting k _H of physical blends against weight fraction of PB molecules in solid content of the solutions (w _PB) showed negative deviation from mixture law with a W-like pattern containing two minima with a maximum in between. While a negative deviation was assumed as indication of immiscibility of the components, upward deviation at middle values of w _PB was attributed to molecular segregations that reduce the interface between the incompatible PS-rich and PB-rich phases.     

On the graft polymerization of styrene and acrylonitrile onto polybutadiene in the presence of vinyl acetate. II. Properties of graft polymers

The properties of the graft polymers of styrene, acrylonitrile, and vinyl acetate onto polybutadiene rubber that were prepared for the modification of graft polymers of styrene and acrylonitrile onto polybutadiene (ABS polymers) by emulsion polymerization up to a high degree of conversion have been studied and discussed. Both the impact strength and notched impact strength of the graft polymers have been found to remarkably increase with a rising quantity of vinyl acetate, in particular, in the case of styrene substitution, whereas in the case of acrylonitrile substitution by vinyl acetate, the two characteristics become noticeably poorer. The effects of the vinyl acetate amount and the type of substituted monomers on bending strength, tensile strength, Vicat softening point, and glass transition temperature of the graft polymers are also clearly different. Furthermore, the properties of the above graft polymers blended with styrene/acrylonitrile copolymers have been studied.     

L-menthol-based initiators for atom transfer radical polymerization of styrene

Two new atom transfer radical polymerization (ATRP) initiators, 2-isopropyl-5-methylcyclohexyl 2-bromopropanoate ( 1 ) and 2-Isopropyl-5-methylcyclohexyl 2-bromo-2-methylpropanoate ( 2 ), have been synthesized by the reaction of 2-bromopropanoyl bromide and 2-bromo-2-methylpropanoyl bromide, respectively, with L-menthol and characterized by ¹H and ¹³C NMR and FTIR spectroscopic studies. ATRP of styrene has successfully been carried out in a control manner using these initiators along with catalyst/ligand system consisting of Cu(I)Br/N,N,N ^/,N ^/,N ^//-pentamethyldiethylenetriamine. Polymerizations have yielded polystyrenes (PSts) of controlled molecular weight with low polydispersity index having a menthyl end group, as confirmed by ¹H NMR and gel permeation chromatography [GPC]. The controlled nature of the polymerization has also been confirmed by kinetic study of the polymerization process monitored via ¹H NMR and GPC. Initiator 2 has evolved as most efficient among the two. The obtained end-functional PSt has also been used as a macroinitiator for homochain extension with styrene and heterochain extension with methyl methacrylate to produce PSt-b-PMMA, showing the living nature of the polymerization process. In comparison with the PSt sample prepared using widely used initiator ethyl-2-bromo-isobutyrate with almost the same molecular weight and polydispersity, initiator 2 -made L-menthyl-capped PSt has shown higher light transmission properties of its dichloromethane solution at ~259 nm, higher thermal stability, lower glass transition temperature, a broad melting temperature, and higher surface roughness over its film. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47964.     

The cobalt chelates of polyaminocarboxylic acids as initiators in the emulsion polymerization of styrene

The use of Cobalt(II) complexed with various polyaminocarboxylic acids and hydrogen peroxide has been shown to be an effective initiator for the emulsion polymerization of styrene. The polyaminocarboxylic acids used were ethylenediaminetetraacetic acid (EDTA), ammonia diacetic acid (ADA), N,N′-bis(2-aminoethyl)ethylenediaminehexaacetic acid (TTHA), ammonia triacetic acid (ATA), and N′-hydroxyethylethylenediamine-N,N,N′-triacetic acid (HEEDTA). In the case of the HEEDTA system, the effect of varying the concentrations of the initiator components was examined and found to be broadly similar to that observed in other metal ion chelate-hydrogen peroxide initiators. All the systems were effective over a wide pH range (generally 3–9), and zero-order rates in the range of 30–90%/hr were observed, although there was considerable variation in detail in the manner in which the zero-order rate depended on pH. The behavior of these systems is commented upon in the light of earlier results on similar systems and of previously published redox potentials of the related cobalt(II)–cobalt(III) chelate systems.     

On the graft polymerization of styrene and acrylonitrile onto polybutadiene in the presence of vinyl acetate. I. Preparation of graft polymers

In order to modify the graft polymers of styrene and acrylonitrile onto polybutadiene (ABS polymers), the preparation of the graft products of styrene, acrylonitrile, and vinyl acetate onto polybutadiene rubber by emulsion polymerization was described and theoretically studied up to a high degree of conversion. Depending on the residual monomer content of the products, the polymer composition obtained in the experiment was compared with the theoretical one for the substitution of certain quantities of styrene, acrylonitrile, or styrene and acrylonitrile by vinyl acetate in the mass ratio of 3 : 1. Deviations were discussed. The specific viscosity of the polymers of styrene, acrylonitrile, and vinyl acetate separated from the elastomer phase, considerably decreases during the substitution of acrylonitrile by increased vinyl acetate quantities.     

聚丁二烯橡胶接枝苯乙烯本体自由基聚合机理

采用傅里叶变换红外光谱法和碘值法分析了在热引发和化学引发方式下,低顺式和高顺式聚丁二烯橡胶接枝苯乙烯聚合物的双键结构和含量,确定了橡胶接枝苯乙烯本体自由基聚合机理。结果表明,热引发时,接枝机理主要是自由基夺取橡胶链上α氢原子;而化学引发时,同时存在自由基与橡胶双键加成的机理。橡胶的结构不同导致接枝点的位置差异,在低顺式聚丁二烯橡胶体系中,自由基以夺取反式-1,4-结构和1,2-乙烯基结构为主,而在高顺式聚丁二烯橡胶体系中。自由基以夺取顺式-1,4-结构为主。     

Chain transfer in vinyl chloride polymerization in the presence of polybutadiene

Vinyl chloride (M) was polymerized in the presence of a low molecular weight polybutadiene (S) at 60°C in the presence of x,x′-azobisdiisobutyronitrile as initiator, which does not affect the transfer reaction. The raw material was fractionated for the purpose of separating the pure PVC homopolymer. The number-average molecular weight of PVC homopolymer, determined by size exclusion chromatography (SEC), was used in Mayo's equation to obtain the value of the transfer constant Cs, which was found to be 11. A simplified reaction scheme is given according to which it is possible to explain why the reaction yield decreases and the crosslinking density increases by increasing the [S]/[M] ratio.     

Thermal polymerization of styrene in the presence of TEMPO

To investigate aspects of the contribution of (thermal) self-initiation in nitroxide-mediated radical polymerization (NMRP) of styrene, selective styrene polymerizations with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in the absence of initiator were carried out at 120 and 130 °C. The results of these experiments (including conversion data, molecular weight averages, polydispersity and molecular weight distribution information) were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of a bimolecular initiator (benzoyl peroxide; BPO). It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide polystyrene with low polydispersity, the polymerization was never as controlled as that obtained by a BPO-initiated NMRP.