Styrene, conversion polystyrene

Conversion of styrene to polystyrene is an example of such molecular structure, which is repetitive and simple. Relatively little opportunity is offered to precisely control critical molecular design parameters. Although nanostructure dimensions can be attained, virtually no control over atom positions, covalent connectivity or shapes is possible. 

The grafting is accomplished in the commercial mass polymerization process by polymerizing styrene in the presence of a dissolved rubber. Dissolving the elastomer in the styrene monomer before polymerization produces HIPS grades. Since the two polymer solutions are incompatible, the styrene-rubber system phase separates very early in conversion. Polystyrene forms the continuous phase, with the rubber phase existing as discrete particles having occlusions of polystyrene. Different production techniques and formulations allow the rubber phase to be tailored to a wide range of properties. Typically ... 

The experimental data on the Pn of homopolystyrene, the efficiency of polystyrene grafting to rubber, and the dependence of styrene polymerization on rubber concentration were compared with the calculated data, with up to 8% of styrene conversion at T = 100 °C. 

Poly (butadiene- -styrene) was synthesized by grafting polystyrene onto polybuta diene. Styrene conversions up to 80% corresponding to G. E. of 50% were obtained. The graft copolymers were soluble over the styrene conversion range of 0 to 80%. Temperature, medium polarity, polybutadiene concentration and microstructure affect G. E. 

In contrast to the grafting reactions (22), the crosslinking reaction during preparation of high impact polystyrene becomes effective only at very high styrene conversions (> 95%) at which the rubber double bond concentration in the total reaction mixture approaches the monomer concentration. In rubber lamellae, this shift in concentration in favor of the rubber double bonds is even more pronounced because of the incompatibility of polybutadiene and polystyrene. 

Figure 6. Simulated variation of the ratio rubber phase volume/styrene + polystyrene phase volume vs. styrene conversion EPDM elastomer, type C and polystyrene, [tj] toluene/30°C = 0.8 dl/g...

The dependence of styrene conversion on polymerization time in the presence of BP and NLM shows that increase in the amount of regulator with constant primary initiator concentration results essentially in decrease of the polymerization rate. Decrease of polystyrene MW is observed only at the initial stage of process. 

With the increase of monomer conversion the polystyrene MW is increasing. The higher the initial NLM concentration, the faster it achieves the MW obtained under the same conditions but without the regulator at a styrene conversion equal to 10-30%. These trends are characteristic for styrene polymerization in the presence of BP and TBPB with the other aliphatic mercaptans as well. Figure 1 shows that decrease in the length of the t-mercaptan results in lowering of the reaction rate. 

Figure 3 also shows the dependences of the styrene conversion on time and polystyrene MW on styrene conversion in the presence of BP and NLM. Their analysis allows us to conclude that the reaction between BP and NLM doesn t take place to completion in reality. In the polymerization system there is a regulator, although the initiator was introduced with a considerable excess as compared to the supposed stoichimetric ratio of their interaction. 

Ethylene from cracking of the alkane gas mixtures or the naphtha fraction can be directly polymerized or converted into useful monomers. (Alternatively, the ethane fraction in natural gas can also be converted to ethylene for that purpose). These include ethylene oxide (which in turn can be used to make ethylene glycol), vinyl acetate, and vinyl chloride. The same is true of the propylene fi action, which can be converted into vinyl chloride and to ethyl benzene (used to make styrene). The catalytic reformate has a high aromatic fi action, usually referred to as BTX because it is rich in benzene, toluene, and xylene, that provides key raw materials for the synthesis of aromatic polymers. These include p-xylene for polyesters, o-xylene for phthalic anhydride, and benzene for the manufacture of styrene and polystyrene. When coal is used as the feedstock, it can be converted into water gas (carbon monoxide and hydrogen), which can in turn be used as a raw material in monomer synthesis. Alternatively, acetylene derived from the coal via the carbide route can also be used to synthesize the monomers. Commonly used feedstock and a simplified diagram of the possible conversion routes to the common plastics are shown in Figure 2.1. 

As shown in Fig. 4.4.2, it takes a relatively small amount (at least 10%) of ionic component in a molecule for it to exhibit surfactancy. This is achievable with the FRRPP process, because one can always add an acid monomer to react with a hydrophobic polymer radical even in the presence of unreacted hydrophobic monomer. The example is when methacrylic acid was added to polystyrene radicals even at 30% styrene conversion to produce an amphiphilic S-block-(S-stat-MAA) amphiphilic material (see Section 4.2). Methacrylic and acrylic acid monomers are normally reactive to polymer radicals in general, as it can be seen from their reactivity ratios. When amine-PDMS was reacted with the acid groups of the... 

The systems poly(methyl methacrylate)-styrene and polystyrene-methyl methacrylate were studied by Watson and co-workers [111]. The composition of these interpolymers is shown in Fig. 5.25 [111]. In the polystyrene-methyl methacrylate system, 53% of the original polymer remained as homopolymer at the end of the reaction. Homopoly(methyl methacrylate) was formed during the early stages of reaction (40 and 91% of the polymerized monomer after 80 and 95% conversion, respectively). The amount of block polymer reached a maximum of only 42% of the product. 

At high conversions, the solvation of the rubber and the gel effect (Trommsdorf effect) cause an increase in the molecular weight of the grafted polystyrene. The viscosity change with styrene conversion in the manufacture of HIPS is shown in Fig. 10 with typical rubber particle morphology [34]. 

Fig. 15. Oxygen permeability versus 1/specific free volume at 25 °C (30). 1. Polybutadiene 2. polyethylene (density 0.922) 3. polycarbonate 4. polystyrene 5. styrene-acrylonitrile 6. poly(ethylene terephthalate) 7. acrylonitrile barrier polymer 8. poly(methyl methacrylate) 9. poly(vinyl chloride) 10. acrylonitrile barrier polymer 11. vinyUdene chloride copolymer 12. polymethacrylonitrile and 13. polyacrylonitrile. See Table 1 for unit conversions.

A well-known high conversion reactor is the so-called polymerization press, a modified plate-and-frame filter press where polystyrene is polymerized in frames alternating between cooling platens through which water (or steam) can be circulated. Other versions of the high conversion reactor have been utilized, e.g., the early "can process of Dow, where styrene monomer was placed in sealed cans in water baths and the metal stripped off at the end of the polymerization 2). 

Process flow for a typical batch-mass polystyrene process(1) is shown in Figure 1. Styrene monomer is charged to the low conversion prepolymerization reactor with catalyst and other additives, and the temperature is increased stepwise until the desired conversion is reached. It is then transferred into the press. Polycycles are 6 to 14 hours in the low conversion reactor, and 16 to 24 hours in the press. At completion, the cakes are then cooled with water and removed from the press to be ground and then (usually) extruded into pellets. 

Low Conversion Reactors. The major problem in temperature control in low conversion reactors is the orders cf magnitude increase in viscosity as the conversion increases. Fig.8 shows the viscosity of a polystyrene solution as the function of percent PS. The data are for polystyrene with a Staudinger molecular weight of 60,000 at 100 C and 150 C in a cumene solution, a satisfactory analog for styrene monomer solutions. As the polymer concentration increases from 0 to 60%, viscosity increases from about 1 cp to 10 cp. 

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