Micro-reactors polymerization

Table 1.2 Key data for production of polymers in the compact reactor/mixer/heat exchanger, termed micro reactor, by cationic polymerization yielding propylene, piperylene, butylenes, etc. [50].

In [53], segregated catalyst and polymer particles act as micro reactors where the polymerization process takes place. Each particle is an individual reactor with its own energy and material balance. During polymerization, the catalyst particles undergo a change in volume by a factor of 10 -10, thereby generating the corresponding polymer particles. The particle size distributions of catalyst and polymer are the same. 

For toluene fluorination, the impact of micro-reactor processing on the ratio of ortho-, meta- and para-isomers for monofluorinated toluene could be deduced and explained by a change in the type of reaction mechanism. The ortho-, meta- and para-isomer ratio was 5 1 3 for fluorination in a falling film micro reactor and a micro bubble column at a temperature of-16 °C [164,167]. This ratio is in accordance with an electrophilic substitution pathway. In contrast, radical mechanisms are strongly favored for conventional laboratory-scale processing, resulting in much more meta-substitution accompanied by imcontroUed multi-fluorination, addition and polymerization reactions. 

Figure 4.1 Flow scheme of a plant comprising an electrothermal tubing-based micro reactor configured for ethylene polymerization [1],...

Polyacrylate Formation Investigated in Micro Reactors Organic synthesis 61 [OS 61] Radical polymerization of acrylates... 

Fluorescence spectroscopy as a means of judging process conditions in a polymerization reaction has been reported [48]. The authors optimized parameters such as the reactant ratio and catalyst amount to reach the smallest variability of material properties. The samples were deposited on a 96-micro reactor array and examined with a spectro-fluorometer during the reaction. 

Akay, G. Dogru, M. Calkan, B. Calkan, O.F. Flow induced phase inversion phenomenon in process intensification and micro-reactor technology. Process intensification in water-in-crude oil emulsion separation by simultaneous application of electric field and polymeric demulsifiers. In Microreact Technology and Process Intensification Wang, Y., Halladay, J., Eds. Oxford University Press Oxford, 2005 Chapter, 18. 

Role of Surfactants in Emulsion Polymerization Technology Formation of aggregates as micro-reactors... 

The emulsifier in emulsion polymerization has three key functions, namely stabilizing the monomer droplets during the first stage of the emulsion polymerization, supplying surfactant micelles as the site of the polymerization reaction (literally the micelles can be regarded as some kind of micro-reactors) and stabilizing the latex particles at the end of the emulsion polymerization process pending transportation,... 

In this study, after a brief introduction to PI we provide the bases of a technique for the preparation of polymeric micro-porous materials, known as polyHIPE polymers (PHPs) which are now used extensively in PIM, and micro-reactor technology. These polymers are prepared through the high internal phase emulsion (HIPE) polymerization route. In order to control the pore size, the flow-induced phase inversion phenomenon is applied to the emulsification technique. The metalization of these polymers and formation of nano-structured micro-porous metals for intensified catalysis are also discussed. Finally, we illustrate the applications of these materials in chemical- and bioprocess intensifications and tissue engineering while examining the existence of several size-dependent phenomena. 

Song, Y, C.S.S.R. Kumar, and J. Hormes, Synthesis of palladium nanoparticles using a continuous-flow polymeric micro reactor. Journal of Nanoscience and Nanotechnology, 2004,4 788-793. 

Micro-reactors, in principle, are simple constructs that can be created by employing fine-scale mechanics and/or modern lithographic techniques. One clear requirement is, of course, that the materials used do not interfere with the chemistry involved in the reactions being carried out other important requirements relate to the flow patterns and heat exchange with the surroundings. Both of these conditions can determine the success of a micro-reactor for a particular reaction. Here, attention is focused on polymerization reactions, some examples of which wiU be provided to demonstrate the possible uses and the effects of a micro-reactor on polymerization mechanisms. 

Typically, a polymerization reaction wiU lead to a highly viscous solution or a highly concentrated suspension this may cause clogging of the system that would, in turn, create problems if these reactions were to be conducted on the industrial scale. However, if a micro-reactor system is used first to prepare dispersed mono-sized droplets, and these are then polymerized in the bulk state to produce uniform particles, then this new technology would possess favorable features that would make its industrial application feasible. It is for this reason that micro-reactor systems have attracted so much attention during recent years. 

In general, it is clear that the thermodynamics controls the polymerization reactions and, in most cases, that polymerization will lead intrinsically to a decrease in the entropy of the system. To compensate for this, and in order to maintain a negative free energy, the enthalpy also should be negative this means that the monomers represent molecules that produce heat upon polymerization, and is especially evident in the case of chain-growth monomers. It follows that heat production during the propagation steps represents one of the most important features in a polymerization process. Indeed, it is the ability to control such heat production -both locally and totally - that has led to the success of the micro-reactors. 

To date, only one example has been reported of condensation polymerization in a micro-reactor. In a very elegant study, Kessler etal. [8] showed that the... 

Table 14.1 Results for the anionic polymerization in a micro-reactor showing the retained stoichiometry and monodisperse character of the polymerization. The different concentrations were simply obtained by variation of the flow rates in the reactor [9],...

The group of Yoshida [12] investigated the effect of using a micro-reactor for the anionic polymerization of methacrylates. Compared to a corresponding batch... 

The performance of cationic polymerizations in micro-reactors was first reported in 2004 [13]. Although such jxtlymerizations suffer from the fact that very few monomers are available, under appropriate conditions they can be used to produce low-dispersity polymers. In addition, the dynamic control of the growing chain ends means that the chains experience the same growing conditions and consequently achieve equal length. 

Currently, radical polymerization is the most important type of polymerization employed in polymer chemistry. Based on current developments, it is possible to subdivide the topic into free radical polymerization and controlled radical polymerization which, because of their major difference in terms of mechanism and heat production, exhibit their own peculiar behaviors in micro-reactor processes. 

The free radical polymerization of vinyl monomers should benefit from the excellent heat transfer and mixing speed of micro-reactors. When Hessel et al. [15] investigated, for the first time, the use of a micro-reactor in a free radical polymerization, they modeled the outcome of a solution polymerization of styrene as a monomer and azobisisobutylonitrile (AIBN) as an initiator for three different micro-reactor types [16], the aim being to compare the effects of micro-reactor... 

In the same year, Iwasaki etol. [17] described the effect of a micro-reactor on the free radical polymerization of butyl acrylate, benzyl methacrylate, methyl methacrylate, vinyl benzoate, and styrene. In this case, the reactor system was a simple T-shaped mixing unit, followed by a polymerization section (the latter was responsible for an extended residence time). The total residence times were on the order of 0.5-10 min. In the T-shaped mixing section, the two liquids - one a neat monomer, the other toluene containing 0.03-0.05 mol 1 AIBN as initiator - were combined with the same flow rate. The decay of AIBN in the system was monitored initially at different temperatures, to verify that sufficient initiator was present for complete conversion under all reaction conditions. 

Since the first report on controlled radical polymerization by Matyjaszewski et al. [18], efforts in the area have increased dramatically, with many attempts having been made to perform these types of reaction in micro-reactors. It should be noted, however, that some of the problems associated with free radical polymerizations using micro-reactors would also apply to controlled polymerization reactions. In particular, slow reaction rates, low molar masses, and homogeneous systems would be limiting factors. The one aspect that might be of interest to investigate in micro-reactors would be the rapid mixing of the initiator complex with the monomer, as this would cause the initiation step to occur more rapidly. 

Recently, the group of Beers [19] has been actively involved in demonstrating the applicability of micro-reactors for controlled radical polymerization, notably for high-throughput experiments. In 2004, the group first reported a successful polymerization, using the atom transfer radical polymerization (ATRP) concept, in a micro-reactor when poly(2-hydroxypropyl methacrylate) was obtained, following a residence time of 2 h, with a conversion of 92% and a molar mass of... 

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