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.     

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     

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     

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     

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。     

Bulk polymerization of styrene in plate and frame batch reactors

Thermal bulk polymerization of styrene in the plate and frame batch reactor i.s simulated with a mathematical model which accounts for chain transfer to monomer and gel effect. The design parameters are: the frame thickness, the temperature policy, and the level of prepolymerization in the feed. The recommended frame thickness with 27% prepolymerization is 5 in. The resulting polydispersities and number average chain lengths range from 2.2–2.3 and 2000–2100 respectively. The implementation of temperature policy, particularly the timing of the application of the coolant, is critical to obtain satisfactory polymer quality. When pure styrene feed is used the reactor displays thermal ignition unless the frame thickness is less then 2 in. For a 5 in. frame prepolymerization should be at least 25 percent to permit adequate temperature control.     

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.     

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.     

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.     

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.     

Microemulsion polymerization of styrene in the presence of macroinimer

The kinetics of o/w electrostatically and sterically-stabilized microemulsion polymerization of styrene with and without macromonomeric azoinitiator (macroinimer; MIM) have been investigated. The microemulsion polymerization stabilized by the ionic emulsifier sodium dodecyl sulfate (SDS) or the non-ionic emulsifier Tween 20 (Tw 20) was initiated by ammonium peroxodisulfate (APS)/sodium thiosulfate (STS) redox system. The rate of polymerization vs. conversion curve shows the two non-stationary rate intervals. This behavior is a result of two opposing effects, the continuous particle nucleation and the decrease of monomer concentration at the reaction loci. The addition of MIM favors the additional particle nucleation. The sterically (Tw 20)-stabilized microemulsion polymerization is much faster than that of the electrostatically (SDS)-stabilized microemulsion polymerization. This was attributed to the higher Tw 20 concentration and increased solubilization of MIM and comonomer concentration in the polymer particles. The formation of initial large polymer particles is attributed to the intensive agglomeration polymer particles with monomer droplets. The continuous decrease in the average size is mainly attributed to the additional particle nucleation.     

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.     

Emulsion polymerization of styrene in the presence of carbohydrate-based amphiphiles

Summary Novel amphiphilic N-alkyl-, N-decenyl-, and N-alkyl-N'-methyl-semicarbazones of maltose and maltotriose with C_nH_2n+1 alkyl chains and n=8,9,10,11,12,16 were applied as emulsifiers in styrene emulsion polymerization. Surfactant properties, emulsion polymerization, and rheology were examined as a function of amphiphile molecular architectures. Both critical micelle concentration and average polystyrene particle size increased with decreasing alkyl chain length. Using N-methyl-N-[11-(acryloylamino)-undecanoyl]-glucamine comonomer in a starved feed emulsion polymerization process, it was possible to prepare uniform polystyrene latex with glucamide surface.     

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.     

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.     

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.     

Emulsion polymerization of styrene with ionic comonomer in the presence of methanol

Soap-free emulsion polymerization of styrene with sodium vinylbenzyl sulfonate (NaVBS) was studied in the presence of water–methanol mixtures. In the presence of both methanol and NaVBS, the particle size and uniformity increased with methanol content. Increasing the concentration of NaVBS decreased the particle size. Initiator and electrolyte level had similar effects on particle size as in recipes prepared in aqueous medium.