Bulk Polymeric Components

These commercial examples provide evidence that inclusion of nanoparticle species can indeed reduce the overall flame retardant additive levels required to achieve a desired fire performance level. To corroborate this, work in our laboratories ° with PA6 and PA6,6 films and selected phosphorus-containing flame retardants suggests this to be the case when selected functionalized nanoclays are also present, and this work is reviewed below. 

TABLE 11.2 UL-94 Test Results for Polystyrene Nanocomposites Containing Either Dibromostyrene Comonomer or Phosphate Additives 

Flame Retardant Comonomer or Additive Clay PHRR at 35 kW/m UL-94 Result 

From these studies, although it is clear that nanoclay-flame retardant interactions are not simple and may be dependent on respective concentrations present, inclusion of nanodispered phases offers the opportunity to reduce overall additive loadings or to improve fire performance at currently acceptable loadings. 

In Chapter 7 the combination of nanocomposites with metal hydroxide flame retardants has generally been discussed. Since the use of metal hydroxide usually requires very high concentrations within the polymer matrix (often higher than 50% w/w), to achieve desired levels of flame retardancy as noted above regarding the work of Beyer, - the influence on rheology and hence processability can be significant. Hornsby and Roflion have discussed this issue and they report that compounded polymer melt viscosities and shear sensitivities, for example. 

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Bulk and solution polymerizations are more or less self-explanatory, since they operate under the conditions we have assumed throughout most of this chapter. A bulk polymerization may be conducted with as few as two components monomer and initiator. Production polymerization reactions are carried out to high conversions which produces several consequences we have mentioned previously ... 

There is an interior optimum. For this particular numerical example, it occurs when 40% of the reactor volume is in the initial CSTR and 60% is in the downstream PFR. The model reaction is chemically unrealistic but illustrates behavior that can arise with real reactions. An excellent process for the bulk polymerization of styrene consists of a CSTR followed by a tubular post-reactor. The model reaction also demonstrates a phenomenon known as washout which is important in continuous cell culture. If kt is too small, a steady-state reaction cannot be sustained even with initial spiking of component B. A continuous fermentation process will have a maximum flow rate beyond which the initial inoculum of cells will be washed out of the system. At lower flow rates, the cells reproduce fast enough to achieve and hold a steady state. 

While there have been several studies on the synthesis of block copolymers and on the molecular weight evolution during solution as well as bulk polymerizations (initiated by iniferters), there have been only a few studies of the rate behavior and kinetic parameters of bulk polymerizations initiated by iniferters. In this paper, the kinetics and rate behavior of a two-component initiation system that produces an in situ living radical polymerization are discussed. Also, a model that incorporates the effect of diffusion limitations on the kinetic constants is proposed and used to enhance understanding of the living radical polymerization mechanism. 

When dimensional stability is achieved due to cell wall bulking, the dimensional stabilization achieved is equal to the volume of the water-saturated sample minus the volume of the modified wood. Another class of modification reaction is due to cross-linking between the cell wall polymeric components. In this case, dimensional stability is imparted to the modified wood because movement of the cell wall is restrained, although the volume of the cell wall occupied by the modifying agent may still have an influence (Figure 2.9c). Ohmae etal. (2002) have suggested a method by which the various mechanisms can be... 

The propylene oxide complex not only dissociated into its components but also transformed to either an oligomer or a polymer of propylene oxide when it was allowed to stand in solution. This transformation could be followed by H-NMR techniques with the use of a-deuterated propylene oxide instead of the non-deuterated one. Its rate depended on the nature of solvent and on the temperature. This experimental result implies that the monomer liberated by dessociation of the complex is polymerized by the catalyst, that only a minute fraction of the organozinc component of the complex actually acts as a catalyst for polymerization, and that the rate of propagation is far faster than that of initiation. These implications together with the evidence that coordination of the monomer to the catalyst is a prerequisite for the stereospecific polymerization led us to the detailed studies of the bulk polymerization, that is, the polymerization of propylene oxide in propylene oxide solution. 

The simplest procedure for grafting copolymerization, in terms of number of components in the reaction medium, is a bulk polymerization of the monomer in mixture with the molten polyamide. This has been claimed in an earlier patent (2), related to improvements in dyeability and hydrophylic properties of the resulting yam, obtained by melt spinning of the product of reaction with monomers such as 2,5-dichloro styrene, lauryl methacrylate, N-vinyl pyrrolidone, and N-vinyl carbazole. 

If an alkyl- or aryltrichlorosilane is treated, in bulk or in solution, with a considerable excess of water, an amorphous, infusible, insoluble product is usually formed with the approximate empirical composition, (RSi01-5)x or (ArSiOi.g). Insolubility has precluded estimation of the molecular weights of these products, and the amorphous appearance has discouraged crystallographic studies. These amorphous polymers are probably randomly cross-linked. Only in recent years have definable, low polymeric components of this composition been isolated and identified. 

This task is a standard part of the manufacturing process with polymer concentrations between 10 and 85%. Depending on the manufacturing process, the solvent (in the case of solution polymerization) or monomer (in the case of bulk polymerization) must be removed from the polymer, which may not contain more than the legally admissible or market-dictated residual components at the end of the process. 

Description Catalyst components are mixed and fed directly to prepolymerization (1) with a light inert hydrocarbon, where a first bulk polymerization occurs under mild controlled conditions. This step exploits the catalyst system potential in terms of morphology, mileage and complete reliability in the following gas-phase reaction sections. 

However, the introduction of the solvent into the polymerization medium poses new problems. The solvents must be pure, without inhibiting and transfer agents. Every solvent takes part in the polymerization process its effect is almost never limited to the mere physical dilution of the monomer. It solvates the active centres it participates in processes connected with energy and impulse transfer often it serves as a transfer agent (so that the degrees of polymerization of solution-polymerized products are usually lower compared with bulk-polymerized polymers) it may form complexes with some component of the system it modifies initiation efficiency by the cage effect etc. 

Free radical polymerization of neat monomer in the absence of solvent and with only initiator present is called bulk or mass polymerization. Monomer in the liquid or vapor state is well mixed with initiator in a heated or cooled reactor as appropriate. The advantages of this method are that it is simple, and because of the few interacting components present, there is less possibility for contamination. However, vinyl-type polymerizations are highly exothermic so that control of the temperature of bulk polymerization may be difficult. Also, in the absence of a solvent viscosities may become very high toward the end of a polymerization, which could make stirring difficult, and add to the difficulty of heat removal from the system. The advantages of this system, however, are sufficiently attractive for this to be used commercially for the free radical polymerization of styrene, methyl methacrylate, vinyl chloride, and also for some of the polymerization processes of ethylene [7]. 

Bulk Macroporous Polymers (DVB-50-B-T, DVB-50-B-A). Comparison of DVB-50-B-T with DVB-50-S-T reveals there is little difference between polymers prepared in bulk and by suspension techniques. Both materials, prepared with toluene as cosolvent, reveal fluorescence quenching traces that are almost superimposable. There is, however, a very dramatic difference between material prepared by bulk polymerization using different cosolvents. Polymer DVB-50-B-T reveals a large fraction of all sites are quenched within 15 sec (Figure 6), a small tail on this curve indicates a component (<5%) of inaccessible sites. In contrast, the material prepared with... 

In the example of bulk polymerizations cited here, the polymer isolation procedure follows that of Lift and Eirich [14] since they maintain that the original procedures of Bartlett and co-workers did not adequately remove volatile, low-molecular-weight components fix>m the polymers. Consequently, the MW determinations by Bartlett and co-workers are thought to be low. 

Asua et al. [121] and Nomura and Fujita [122,123] have analysed the case of oil-soluble initiators theoretically. The latter group [124,125] has verified the conclusions experimentally for styrene with azobis-isobutyronitrile as initiator. Below the cmc of the emulsifier suspension polymerization occurs in the monomer droplets but, in the presence of emulsifier micelles many more much smaller latex particles are produced and emulsion polymerization kinetics becomes dominant. Only the portion of the initiator partitioned into the water phase is significant in the initiation of the emulsion polymerization. The molar mass distribution of the polymer obtained is bimodal initially [125]. The molar mass of the polymer produced by suspension polymerization in the droplets is the same as that produced by bulk polymerization under comparable conditions and only about one-hundredth of that of the emulsion polymer. Wth increase of conversion the contribution of the lower molar mass component to the overall molar mass distribution becomes insignificant. 

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. 

In bulk polymerization, the only components of the formulation are monomers and the catalyst or initiator. When the polymer is soluble in the monomer, the reaction mixture remains homogeneous for the whole process. Examples of homogeneous bulk polymerization are the production of low-density polyethylene (LDPE), general purpose polystyrene and poly(methyl methacrylate) produced by free-radical polymerization, and the manufacture of many polymers produced by step-growth polymerization including poly(ethylene terephthalate), polycarbonate and nylons. In some cases (e.g., in the production of HIPS and acrylonitrile-butadiene-styrene (ABS) resins), the reaction mixture contains a preformed... 

By combining the extruder diagram with the reaction diagram an interaction diagram for steady-state operation with single-component bulk polymerizations can be obtained (Fig. 7.3). The coupling between both diagrams is... 

Metal Carbene Catalysts. The first use of isolated single-component car-bene catalysts showed that the Fischer (4) and Casey carbenes (5) polymerize phenylacetylene, ferf-butylacetylene, and cyclooctyne in low yields (130). For example, the bulk polymerization of tert-butylacetylene with (4) gives a high molecular weight (Mn = 260,000) polymer in 28% yield. Polymer-supported Fischer carbene (4) is also active for the polymerization of phenylacetylene under photoirradiation (145). As a catalyst, the Casey carbene (5) is less stable but more active than the Fischer carbene (130). The Rudler carbene (6) readily releases the in-tramolecularly ligated double bond upon the approach of an acetylenic monomer. Thus, it is more active than the Fischer and Casey carbenes (146-148). These carbene complexes are, however, unable to control the polymerization. 

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