Bulk styrene polymerization, thermally

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... 

Figure 3 shows a stabihty diagram for a bulk styrene polymerization. Performance is governed by foin- variables the monomer inlet temperature, the tube diameter, the wall temperatin-e, and the mean residence time in the tube. Figure 3 shows the effects of wall temperature and tube diameter for plausible values of the other variables. Very small tubes are stable for any wall temperature. Intermediate size tubes are subject to hydrodynamic instabihty and large tubes are subject to thermal nmaway. The maximum conversion for a tube larger than 0.95 cm is 20% and is achieved in a 5-cm tube. 

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. 

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... 

However, the probability for the reaction progression greatly depends on the monomer conversion. Because the viscosity of the dispersed phase, in the first stage, is fairly low and the quantity of styrene is sufficiently high, the decomposition process (Figure 9.4) occurs only up to the benzoyloxy radical, which can directly start the kinetic chain. The purely thermal start of chains with reactive dimers of styrene, as a result of Diels-Alder reaction, can be ignored at fairly low temperatures of suspension polymerization, in contrast to the conditions for the bulk styrene process [4-7]. 

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. 

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. 

Anionic-Radical Combinations. Radical grafting of one monomer on the backbone of another polymer is well known and is the basis of an important commercial process for making high impact polystyrene. Styrene is thermally bulk polymerized in the presence of 5 to 10% (by weight) polybutadiene, the polymerization proceeding by a free-radical grafting path (70). 

The thermal polymerization of -MeOSt has already been mentioned by Staudinger and Dreher [239]. Heating a bulk sample to 90 °C for several days yielded a polymer with a DP = 390 (by viscosity measurements). Later, Russian authors [269] polymerized thermally all three isomers at 100 to 125 °C and found the p and m isomers to polymerize less rapidly than styrene, but the o isomer more rapidly. The stereoregularity of poly(/ -MeOSt) prepared by thermal polymerization in bulk at 60 °C was examined by Yuki et al. [270]. 100-MHz H-NMR spectra showed a rather split signal for the methoxy group and was interpreted in terms of pentad sequences. The analysis of the thermally polymerized sample showed a rather low content of syndiotactic triads. Kawamura et al. [244] studied the C-NMR spectra of o- and -MeOSt polymers prepared with BPO in toluene at 80 °C. They found both polymers to be rich in syndiotactic sequences [o derivative,, = 0.80 p derivative, P = 0.1 (P, = probability of racemic addition of monomer to the growing chain)]. 

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. 

Poli has reported the controlled polymerization of styrene at 100 °C in bulk initiated by thermal decomposition of AIBN for the half-sandwich complexes CpMo Cl2L2 (XXI-XXIII) shown in Figure 18. An ATRP/OMRP-RT/CCT interplay, which was observed when using organic halide initiators, will be addressed later in Section 3.11.7. Under OMRP-RT conditions, controlled polymerization was observed for all systems with linear growth of A4n as a function of conversion, without any indication of CCT, although the values are relatively... 

Bead Polymerization Bulk reaction proceeds in independent droplets of 10 to 1,000 [Lm diameter suspended in water or other medium and insulated from each other by some colloid. A typical suspending agent is polyvinyl alcohol dissolved in water. The polymerization can be done to high conversion. Temperature control is easy because of the moderating thermal effect of the water and its low viscosity. The suspensions sometimes are unstable and agitation may be critical. Only batch reaciors appear to be in industrial use polyvinyl acetate in methanol, copolymers of acrylates and methacrylates, polyacrylonitrile in aqueous ZnCh solution, and others. Bead polymerization of styrene takes 8 to 12 h. 

Polyaddition reactions based on isocyanate-terminated poly(ethylene glycol)s and subsequent block copolymerization with styrene monomer were utilized for the impregnation of wood [54]. Hazer [55] prepared block copolymers containing poly(ethylene adipate) and po-ly(peroxy carbamate) by an addition of the respective isocyanate-terminated prepolymers to polyazoesters. By both bulk and solution polymerization and subsequent thermal polymerization in the presence of a vinyl monomer, multiblock copolymers could be formed. 

Thermal Polymerization of Styrene in Bulk (Effect of Temperature)... 

Materials. Styrene (BDH Chemicals Ltd.) was stabilized with 0.002 % t-butyl catechol. The stabilizer was removed by washing successively with 10 % potassium hydroxide solution and water, drying over calcium chloride for 24 hr, and vacuum distilling. The monomer was kept in a refrigerator until required. Effective removal of inhibitor was checked by gas chromatography and by dilatometric measurement of the rate of bulk thermal polymerization at 60 °C this was 0.080 % hr which compares with a literature value (17) of 0.089 % hr . ... 

As a sequel to the simple reactor model described above, two-zone cases for the bulk polymerization of styrene were also studied. Polymerizations in straight, empty tubes give rise to unfavorable temperature and velocity profiles which can lead to hydrodynamic or thermal instabilities. These instabilities may be avoided or postponed by manipulating the wall temperature. 

Various methacrylic-styrene copolymers were prepared in which the reactivity of methacrylate monomers used in the first step decreases in the order MM A > BuMA > benzyl methacrylate. For instance, the bulk polymerization of MMA with such an aromatic azo compound proceeds via a living radical mechanism and the sterically crowded C-C(C6H5)3 terminal bond of polymethacrylate 37 can be cleaved thermally to produce a,co-diaromatic PMMA-h-PS block copolymers in 48-72% yield. 

In evaluating this approach, the question of how and when to introduce the catalyst to the polymerization mixture arose. The simplest method would be to put the catalyst in the styrene monomer being fed to a continuous bulk polymerization system. Then the polymer would be produced with the catalyst molecularly dispersed in it. Priddy et al. evaluated both a sulfonic acid catalyst and also thermally labile acid esters that generate acids during high-temperature devolatilization [38],... 

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. 

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. 

Continuous Bulk Thermal Polymerization of Styrene-Comparison of Computer Prediction With Experimental Data... 

In the study113) an attempt was made to model the whole process of thermal bulk copolymerization of styrene with polybutadiene up to high degrees of conversion. The calculations were based on the previously developed model of thermal bulk polymerization of styrene and supplemented with the reactions of chain transfer to rubber. 

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. 

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... 

---