Bulk styrene polymerization, thermally initiated

For the bulk polymerization of styrene using thermal initiation, the kinetic model of Hui and Hamielec (13) was used. The flow model (Harkness (1)) takes radial variations in temperature and concentration into account and the velocity profile was calculated at every axial point based on the radial viscosity at that point. The system equations were solved using the method of lines with a Gear routine for solving the resulting set of ordinary differential equations. 

Another approach to anisotropic materials is to measure the bulk expansion of material using dilatometry (Fig. 6). The technique was used extensively to study initial rates of reaction for bulk styrene polymerization in the 1940s, an experiment which the author has used in his thermal analysis class on TMA. By immersing the sample in a fluid (normally silicon oil) or... 

Description The process involves continuous, bulk-phase polymerization of styrene using a combination of thermal and chemical initiation. A typical unit design consists of separate reaction trains for GPPS and HIPS grades, which have been optimized for each resin... 

When bulk styrene is heated to 120°C, polymerization occurs because of thermal initiation in the absence of an added initiator. It is observed that polystyrene with M = 200,000 is produced under these conditions at a rateofO.Ol 1 gpolymer/liter/min. Using this information calculate the total initial rate of polymerization expected if an initiator with concentration 0.1 M,ki = 10 sec , and / 0.8 is added to this system at 120°C. 

Crystal polystyrene is produced by thermally initiated (Section 6.5.4) bulk polymerization of styrene at temperature of I20°C or more. (The term crystal refers to the optical clarity of products made from this polymer, which is not crystalline.) The rate of polymerization would decrease with increasing conversion and decreasing monomer concentration if the reaction were carried out at constant temperature. For this reason, the polymerization is performed at progressively increasing temperatures as the reaction mixture moves through a series of reactors. The exothermic heat of polymerization is useful here in raising the reaction temperature to about 250°C as the process nears completion. 

From the discussion above, it is clear that there is no evidence for catalysis of persulfate initiation in emulsion polymerization systems. However, many ionic reactions have been shown to be subject to large catalytic effects in the presence of emulsifier micelles (Fendler and Fendler, 1975) so that the question arises as to whether there are any radical reactions that are subject to micellar catalysis and whether this phenomenon plays any part in any emulsion polymerization systems, Prima fade evidence that uiicellar catalysis may be important when emulsified monomer is allowed to polymerize thermally is provided by the work of Asahara et al. (1970, 1973) who find that several emulsifiers decrease the energy of activation for thermal initiation of alkyl methacrylate and styrene, [n particular, the energy of activation for thermal initiation of styrene emulsified with sodium tetrapropylene benzene solfonate was reported as S3 kl mol. much lower than any value determined in bulk. Hui and Hamielec s value of ] IS kj tnol (1972) seems to be representative of the data available on thermal initiation in bulk. The ctmclusions of Asahara et al. are based on observations of the temperature dependence of the degree of polymerization and are open to several objections. 

A mathematical model for styrene polymerization, based on free-radical kinetics, accounts for changes in termination coefficient with increasing conversion by an empirical function of viscosity at the polymerization temperature. Solution of the differential equations results in an expression that calculates the weight fraction of polymer of selected chain lengths. Conversions, and number, weight, and Z molecular-weight averages are also predicted as a function of time. The model was tested on peroxide-initiated suspension polymerizations and also on batch and continuous thermally initiated bulk polymerizations. 

The samples were synthesized by the same techniques as those used for the styrene ionomers (12). The protonated styrene-methacrylic acid copolymers were prepared by thermal initiation. The polymerization took place in sealed glass tubes in the bulk at 80 °C after several freeze-thaw cycles. A conversion of 10% was obtained after 19 hr. The polymer was precipitated in methanol and neutralized in a benzene-methanol solution. A similar procedure was used for the deuterated samples except that the unreacted deuterated styrene monomer was evaporated prior to the precipitation. The mixing of the deuterated and protonated styrene copolymers was performed in a benzene solution by stirring for 1 hr. The benzene used as the solvent contained a minimum amount of methanol necessary to dissolve the ionomer (approximately 5-10% for the samples of high ion content). The samples were freeze-dried, then dried further at 60°-80°C under vacuum, and finally compression-molded at Tg - - 30°C. 

In the thermally initiated bulk polymerization of styrene (density = 0.906 g cm" ) in the presence of dithiocarbamate chain transfer agent (CTA), the following data were obtained ... 

In the case of thermal initiation of styrene [79,80], the polymerization rate was found to be proportional to [AIBN] and [KPS] , in good agreement with other data for three- or four-component microemulsions [66,81]. The dependence on AIBN concentration is consistent with the prediction of 0.40 based on the micellar nucleation theory in emulsion polymerization (Smith-Ewart case 2) (see, e.g.. Ref 129). The dependence on KPS concentration lies between this case and the value of 0.5 for solution or bulk polymerization. 

Postma et al. (2006) reported the synthesis of well-de ned polystyrene (PSt) with primary amine end groups through the use of phthalimide-functional RAFT agents. Styrene (St) polymerization with the RAFT agent, butyl phthalimidomethyl trithiocarbonate (P25-I), as shown in Scheme PI 1.25.1, was conducted at 110°C with thermal initiation in bulk and the following reaction conditions [RAFT]o = 0.0288 M and [St]o/[RAFT]o = 303, achieving 70% monomer conversion in 24 h to obtain RAFT PSt (P2S-II) with M = 22,400 g mol i and = 1.12. The polymerization was also successfully conducted at 60°C with AIBN... 

The predictive capabilities of the new kinetic model were demonstrated by a direct comparison of model predictions with experimental measurements on monomer conversion, number and weight average molecular weights and molecular weight distribution. The polymerization was carried at different temperatures in a batch, bulk polymerization system. In the temperature range of 100 - 150 °C, a chemical initiator (e.g., Dicumyl Peroxide, DCP) was employed in combination with the thermal initiation of styrene. On the other hand, at higher temperatures (150 - 180 °C), the polymerization was initiated exclusively by the thermal initiation mechanism. 

Rubens [284] describes the radical polymerization of o- and p-ClSt with BPO, y-irradiation, and thermally without initiator. Thermal polymerization at 70 to 90 °C in bulk showed that the initial rates of polymerization for styrene, p-ClSt, and o-ClSt are in the ratio 1 4 10.7. Both initiation with BPO and y-irradiation yielded polymers with respectable molecular weight (DPn= 1000 to 6000), which was similar to the values obtained by thermal polymerization. Breitenbach et al. [285] pubUshed a short note on the emulsion polymerization of o-ClSt with and without K2S20g initiator at 50 °C. 

A wide variety of polystyrene-like polymers and copolymers (crystal. Impact modified, ABPMS, PMS-AN, PMS-BR, PMS-MA and PMS-MMA)(28) have been prepared from PMS using bulk, solvent and suspension polymerization techniques in our laboratories and pilot plants using thermal, anionic and chemical initiation. From a resin manufacturing point of view, PMS monomer can be processed in existing styrene polymerization equipment to produce poly-PMS analogues. However, process development must be done to optimize conditions for each resin type. 

Bulk polymerization of styrene with the organomontmorillonites occurred with a freshly distilled monomer (all of the inhibitor is removed). Azobisiosobutylnitrile (AIBN) was employed as the initiator. Thermal initiation occurred at 60°C for 72 h. 

The Cavicchi group reported the synthesis of tributyl- and triphenylphosphonium functionalised RAFT agents and their use in the bulk, thermally initiated polymerization of styrene (Fig. 3)." ... 

This problem was first treated in detail by Haward (1949). He considered the case of a bulk polymerization that has been compartmentalized by subdividing the reaction system into a large number of separate droplets, each of volume v. Radicals are generated exclusively within the droplets and always in pairs. An example would be the polymerizatiim of styrene in emulsified droplets dispersed in water initiated the thermal decomposition of an oil-soluble initiator which partitions almost exclusively within the monomer droplets. In the model considered by Haward, radicals are unable to exit from the droplets into the external phase. The only radical-loss process is in fact bimolecular mutual termination. It therefore follows that all the droplets must always contain an even number (including zero) of propagating radicals, and that the state of radical occupancy will change in increments of 2. The conclusion reached by Haward is that in this case the effect of compartmentalization is to reduce the overall rate of polymerization per unit volume of disperse phase. The f ysical reason for this is that, as the volume of the droplets is reduced, so are the opportunities for a radical to escape from the others—and hence to avoid mutual... 

The computer program simulates the batch polymerization of styrene and has been applied to the relatively low temperature peroxide-initiated polymerization typical of suspension processes and to higher temperature bulk, thermal conditions. It has been useful in the design of new suspension processes and for more general process analysis. 

High Impact Polystyrene (HIPS) HIPS is a heterogeneous material produced by continuous bulk or bulk-suspension processes, in which a butadiene-based elastomer (polybutadiene (PB), or a block copolymer of styrene-butadiene) is first dissolved in styrene monomer (St) and the resulting mixture is then heated so that the polymerization proceeds either thermally or with the aid of a chemical initiator. At the molecular level, the product is a mixture of free polystyrene (PSt) chains and elastomer chains grafted with PSt side chains. The process yields a continuous (free) PSt matrix containing... 

Most studies have dealt either with the free radical polymerization of hydrophobic monomers—e.g., styrene [56-89], methyl methacrylate (MMA) [68,73,74,84,86,90-93] or derivatives [2,94,97], and butyl acrylate (BA) [98-100]—within the oily core of O/W microemulsions or with the polymerization of water-soluble monomers such as acrylamide (AM) within the aqueous core of W/O microemulsions [101-123]. In the latter case, the monomer is a powder that has to first be dissolved in water (1 1 mass ratio) so that the resulting polymer particles are swollen by water, in contrast with O/W latex particles, where the polymer is in the bulk state. The polymerization can be initiated thermally, photochemically, or under )>-radiolysis. The possibility of using a coulometric initiation for acrylamide polymerization in AOT systems was also reported [120]. Besides the conventional dilatometric and gravimetric techniques, the polymerization kinetics was monitored by Raman spectroscopy [73,74], pulsed UV laser source [72,78], the rotating sector technique [105,106], calorimetry, and internal reflectance spectroscopy [95]. 

The suspension polymerization of styrene is mostly carried out with dibenzoyl peroxide. Bulk polymerization is often no longer carried out purely thermally high-temperature initiators such as 1,2-dimethyl-1,2-diethyl-1,2-diphenyl ethane or vinyl silane triacetate, CH2=CH—Si(OOCCH3)3, are added. 

Bulk polymerizations lead to very pure polymer since only monomer and polymer, and, sometimes, initiator also, are present. Examples are the thermal polymerization of styrene to crystal poly(styrene) and the free-radical-initiated polymerization of methyl methacrylate. 

Alkanolamines are used as cross-linking and hardener accelerators in epoxy resins applications. Improved thermal and oxidative stability of polyvinyl alcohol, poly(phenylene ether), polystyrene, polypropylene, and polyethylene polymers are achieved by the addition of small amounts of the alkanolamines. Diethanolamine and morpholine act as initiators for the preparation of poly (alkyl methacrylate) in bulk or solution polymerization. The ethanolamines are efficient initiators for the preparation of polyvinyl chloride. Alkanolamines promote cross-linking of styrene copolymers with polystyrene or polyvinyl alcohol. Addition of alkanolamines to phenolic formaldehyde or urea formaldehyde resins affords improved electrical properties and increased water solubility. 

Both systems yielded polymers with molecular weights of about 35000g/mol, with the initiated polymerization being three to four times faster than the thermal one. Olaj [286] reports on the kinetics of thermally and AIBN-started radical polymerization of u-ClSt in bulk at 30 °C. He found the rate of polymerization to be about 15 times higher than that of styrene. Propagation kinetics of para substituted styrenes have been investigated by Coote and Davis [246] (see also Section II.C on ur-methylstyrenes). 

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