Bulk Polymerization Method

Bulk polymerization method is the most widely used method of polymerization due to its ease and adaptability [Kan et al., 2008). MIP synthesis using bulk polymerization method often is carried out in a single reaction vessel where, a functional monomer, template, cross-linker, and initiator are dissolved in an appropriate porogen. 

The polymerization mixture is thoroughly degassed with an inert gas [generally N2) in order to remove oxygen dissolved in this mixture as oxygen can inhibit the polymerization process. The degassing step is normally carried out in an ice bath in order to minimize the possible evaporation of any of the components present, especially those at the lowest concentrations. 

After degassing, the flask is closed quickly and tightly and the mixture is ready to polymerize. Thermally initiated polymerization 

UV radiation for polymerization is normally used when any of the compounds involved in the polymerization process is thermally unstable or low temperatures are required for whatever reason. 

During polymerization, a minimum amount of porogen is used. Thus, the growing polymer chains precipitate in bulk forming a single monolith solid. The resulting polymer monolith is ground and sieved in order to obtain the desired particle size fraction for the intended application once the polymerization reaction is complete. 

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We rarely use bulk polymerization methods to produce chain growth polymers. Bulk polymerization finds little use for these materials, because the process generates relatively few... 

Table 18.1 MIPs prepared by bulk polymerization method for the pharmaceutical templates...

As stated above, columns packed with irregular materials are less than ideal in terms of chromatographic performance. Thus, in recent years much effort has been dedicated to develop alternative methods to prepare imprinted stationary phases that are superior in terms of efficiency, mass transfer characteristics, and sample load capacity. Micrometer-sized spherical-imprinted polymers with narrow size distribution have been prepared through several techniques reported in Table 2. It should be considered that all these procedures show serious limitations. These are high sensitivity to small changes in polymerization conditions, a polymerization medium that is not compatible with weak noncovalent interactions between functional monomers and their template, high costs or procedure complexity (which can hinder a wide application of these techniques as valid substitutes to bulk polymerization method). 

Since poly(vinyl chloride) is insoluble in its own monomer, the bulk polymerization is a precipitation polymerization. It is carried out in a 12,000 dm cylindrical rotating autoclave to prevent the coagulation of precipitated polymer, which can occur if the heat of the polymerization is not dissipated. A modern process uses two polymerization stages. In the first stage, polymer is produced in relatively low yields. The polymer, which precipitates in the form of a low-density granular material, is then transferred to a second kettle, where further polymerization to high yields occurs on addition of more monomer. This process produces the polymer in particulate form, a form particularly suitable for the assimilation of plasticizers. In addition, this type of plasticizer takeup produces a more homogeneous system than is possible with the older, bulk polymerization method. 

The polymer can be made by suspension, emulsion, solution, or bulk polymerization methods. Most of the PVC used in calendering, extrusion, and molding is prepared by suspension polymerization. Emulsion polymerized vinyl resins are used in plastisols and organisols. ° Only a small amount of commercial PVC is prepared by solution polymerization. The microstructure of PVC is mostly atactic, but a sufficient quantity of syndio-tactic portions of the chain allow for a low fraction of crystallinity (about 5 percent). The polymers are essentially linear, but a low number of short-chain branches may exist. The monomers are predominantly arranged head to tail along the backbone of the chain. Due to the presence of the chlorine group, PVC polymers are more polar than polyethylene. The molecular weights of commercial polymers are M = 100,000 to 200,000 ... 

Pattanayak, A. and Jana, S.C. (2005) Synthesis of thermoplastic polyurethane nanocomposites of reactive nanoclay by bulk polymerization methods. Polymer, 46, 3275. 

On the industrial scale known are also the semicontinuous or continuous bulk polymerization methods. 

Some experiments on the polymerization of BCMO with the chelate catalyst are recorded in the patent literature( ). In this work, high molecular weight polymer (ninh up 4.3) was obtained at very high temperatures (200-250 C.) in a continuous, bulk polymerization method. These data indicate that the chelate catalyst polymerizes BCMO by a coordination mechanism. Presumably the very high temperature works well because of the relatively low basicity of BCMO. ... 

In this paper, we present results on shape memory behavior of polyurethane (PU)/clay nanocomposites. These nanocomposites were prepared via bulk polymerization method and contained exfoliated clay particles as revealed by transmission electron microscopy and wide angle X-ray diffraction method. The PU matrix contained a crystalline soft segment, which was responsible for shape fixity. The presence of clay decreased the crystallinity of soft segments and consequently shape fixity, but the magnitude of shape recovery stress increased, e.g., by 20% with only 1 wt% clay. The mechanism of reinforcement was studied by monitoring stress relaxation and phase separation. 

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