Polymerization speeding

Very recently, Bordiga et al. [99] designed and performed new experiments allowing the collection of FTIR spectra at low temperature and in the presence of CO, which is known to reduce the polymerization speed. Under these conditions, the reduced rate allowed the observation of shorter olygomeric chains [99]. hi Fig. 5 it is evident that, at the lowest reaction times, the v(CH2) peaks were located at 2931 and 2860 cm , i.e., at values distinctly different from those observed in the normal experiments (2920 and 2851 cm ), see Fig. 4. Only after prolonged contact time these new components were overshadowed by the usual bands of the long polymeric chains. In conclusion, these results demonstrate that the study of the reaction in the presence of the... 

An interesting property of nitric esters, namely their ability to catalyse certain reactions of addition polymerization has been reported recently. Initially this observation was made by Rogovin and Tsaplina [66] while polymerizing styrene and methyl methacrylate in the presence of nitroglycerine. The latter amounted to 5-20 parts by weight corresponding to about 10% of the polymerized substance. As a result of the increased polymerization speed, the molecular weight of the polymer is smaller than if polymerization is carried out slowly. 

This unusual behavior was accounted for by O Driscoll and Kuntz411), who postulated an extremely fast addition of butadiene to lithium polystyryl but slow addition of styrene to lithium polybutadienyl. Such a relation prevents the formation of any significant proportion of lithium polystyryl in the polymerizing system as long as butadiene monomer is available. Since the homopolymerization of butadiene is relatively slow, whereas that of polystyrene is rather fast, the polymerization speeds up as butadiene disappears. 

An interesting feature is that the plateau in the ethanol level is the same for all three temperatures. When the plateau is reached, the polymerization process appears to dominate the hydrolyzation process. Another interesting feature is that the water level does not go to zero. There is a minimum indicating polymerization has begun before complete hydrolysis of all alkoxy groups. Beyond the minimum, the water level increases logarithmically with time. The rate of increase of the water level increases with increased temperature indicating that polymerization speeds up with temperature. The data for water level extends to the gel point, so increases in temperature shorten the time to gel. 

Lastly, the process and polymers produced by onium salt photoinitiated cationic polymerizations are eminently useful. Like the corresponding photoinitiated radical polymerizations which they complement, these cationic systems will find a wide range of applications where polymerization speed and economy of energy utilization are of prime concern. 

Styrene can be polymerized radically up to high conversions. Van der Goot et al. (3) described this process in a 40 mm counterrotating twin-screw extruder with an LjD ratio of 15. A major problem in the styrene process was the low polymerization speed, leading to a low throughput (6g/min) when high conversions have to be obtained. However, styrene could be polymerized up to a conversion of almost 99% (98.6%) (the conversions were measured gravimetrically). However, the conversion of some styrene... 

Within the acrylate-functional resins many distinctions can be made, for instance for functionality, polymerization speed, polarity, and so on. However, these distinctions generally do not result in different methods of production. The production can be divided into three main classes, from each of which a characteristic example will be given. 

N-Vinyl amides such as N-vinyl caprolactam are sometimes used as reactive diluents as well, especially in those cases in which a high demand is put on the polymerization speed. An example of this is the fiber optic industry, in which the cure process is performed at draw speeds around 30 m s (irradiation times are in the order of milliseconds). 

It is assumed that the overall polymerization speed V is equal to the speed of chain growth V. By substitution of [Mn] in formula for one obtains the following equation for V ... 

The criterion of maintaining equal power per unit volume has been commonly used for dupHcating dispersion qualities on the two scales of mixing. However, this criterion would be conservative if only dispersion homogeneity is desired. The scale-up criterion based on laminar shear mechanism (9) consists of constant > typical for suspension polymerization. The turbulence model gives constant tip speed %ND for scale-up. 

A continuing trend has been to polymeric retainers. Laminated phenoHc cages have often been used for high speeds at temperatures up to 130°C. Heat stabili2ed nylon-6,6 has come iato broad use ia small ball beariags, both with and without glass reinforcement (39). Polyimide and PTFE are used up to 250°C. 

The added electron is delocalized on the monovalent radical ion to which it is reduced (3). There is no general agreement on the molecular representation of the reduced stmcture. Various other viologen compounds have been mentioned (9,12). Even a polymeric electrochromic device (15) has been made, though the penalty for polymerization is a loss in device speed. Methylviologen dichloride [1910-42-5] was dissolved in hydrated... 

An example of liquid/liquid mixing is emulsion polymerization, where droplet size can be the most important parameter influencing product quality. Particle size is determined by impeller tip speed. If coalescence is prevented and the system stability is satisfactory, this will determine the ultimate particle size. However, if the dispersion being produced in the mixer is used as an intermediate step to carry out a liquid/liquid extraction and the emulsion must be settled out again, a dynamic dispersion is produced. Maximum shear stress by the impeller then determines the average shear rate and the overall average particle size in the mixer. 

For thermoset-matrix materials, heat is usually added as a catalyst to speed the natural chemical reaction of polymerization. Two-part epoxies, such as found in your local hardware store, consist of a tube of epoxy and a tube of chemical hardener that react when mixed. Heat... 

The most important feature of o/w suspension polymerization is the formation of an oil droplet suspension of the monomer in the water and the maintenance of the individual droplets throughout the polymerization process. Droplet formation in an oil-in-water mixture is accomplished and controlled by two major factors mechanical stirring and the volume ratio of the monomer phase to water. The stirring speed is a key factor in controlling the size of oil droplets and the final size of the polymers. The stirring speed usually needs to be over... 

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