Polymerization continued product, effect

A major drawback of molar mass control by changing ftAl/ Nd rati°s is the simultaneous alteration of polymerization rates. As shown for the system NdV/DIBAH/EASC, an increase in nDiBAH/ Ndvrati°s from 10 to 30 reduces molar mass by 73% but also doubles the rate of polymerization [178,179]. For NdV/TIBA/EASC the variation of ftTiBA/ Ndv from 10 to 30 reduces molar masses by 78% but increases the polymerization rate even 27-fold (Fig. 11) [179]. As shown by these two examples, on one hand, variations of ftAi/ Nd-ratios have a considerable effect on molar mass, and on the other hand, lead to an undesired side effect regarding reaction rates. Because of these interdependencies, in the large-scale continuous production of Nd-BR, adjustments of the ftAl/ Ndv rati°s have to be counteracted by adaptations of residence time in order to keep monomer conversion per reactor and fi-... 

Polymerization reactions require stringent operating conditions for continuous production of quality resins. In this paper the chain-growth polymerization of styrene initiated with n-butyllithium in the presence of a solvent is described. A perfectly mixed isothermal, constant volume reactor is employed. Coupled kinetic relationships descriptive of the initiator, monomer, polystyryl anion and polymer mass concentration are simulated. Trommsdorff effects (1) are incorporated. Controlled variables include number average molecular weight and production rate of total polymer. Manipulated variables are flow rate, input monomer concentration, and input initiator concentration. The... 

Looking at in line continuous production of initiators for the polymerization of acrylics and vinylics, the long-life cations and anions quoted here and the prepolymerization effects observed in many cases make it attractive to consider these intermediates for applicative purposes as well. 

Xylitol is a specialty chemical with the effects of extreme cooling, caries prevention and safety for diabetes, which are beneficial for manufacturing foods and mouth-care products. As a platform chemical, it also can be converted to various compounds for polymer synthesis and directly polymerized for production of unsaturated polyester resin (Werpy and Petersen, 2004). Danisco (currently part of Dupont Co.) is the largest xylitol producer, and many companies in China and South America (Brazil) manufacture xylitol commercially. The global market of xylitol is estimated to be more than 125,000 tons per year, with 4.5-5.5/kg for bulk purchase and 20/kg in supermarket (da Silva and Chandel, 2012). Xylitol has a 12% share of the total polyols market with growth estimated to increase threefold (da Silva and Chandel, 2012). The xylitol market continues to increase worldwide due to an enhancement in health consciousness and chewing gum market, and new application development as a chemical feedstock. 

The copolymerization kinetics are such that nitrile rubbers produced at a polymerization temperature of 5°C have an azeotropic composition of 42.5% acrylonitrile. In other words, the composition of the monomer feed and the copolymer produced will be equal and constant as the polymerization conversion increases. On the other hand, hot polymerization conditions (50 °C) have an azeotropic composition of 37.5% acrylonitrile. In either case, if a batch polymerization is conducted at a composition which differs from the azeotropic mixture, the composition of the nitrile rubber formed will vary as a function of conversion. This effect is especially pronounced for low acrylonitrile levels, which are relatively far from the azeotropic composition. Continuous production methods meter in the faster reacting monomer in order to keep the monomer and... 

Solution Polymerization. Solution polymerization of vinyl acetate is carried out mainly as an intermediate step to the manufacture of poly(vinyl alcohol). A small amount of solution-polymerized vinyl acetate is prepared for the merchant market. When solution polymerization is carried out, the solvent acts as a chain-transfer agent, and depending on its transfer constant, has an effect on the molecular weight of the product. The rate of polymerization is also affected by the solvent but not in the same way as the degree of polymerization. The reactivity of the solvent-derived radical plays an important part. Chain-transfer constants for solvents in vinyl acetate polymerizations have been tabulated (13). Continuous solution polymers of poly(vinyl acetate) in tubular reactors have been prepared at high yield and throughput (73,74). 

The chemical changes that can occur during processing and effect product performances include (1) continued polymerization and cross-linking, which increases viscosity (2) depolymerization or damaging of molecules, which reduces viscosity and (3)... 

This section is divided into three parts. The first is a comparison between the experimental data reported by Wisseroth (].)for semibatch polymerization and the calculations of the kinetic model GASPP. The comparisons are largely graphical, with data shown as point symbols and model calculations as solid curves. The second part is a comparison between some semibatch reactor results and the calculations of the continuous model C0NGAS. Finally, the third part discusses the effects of certain important process variables on catalyst yields and production rates, based on the models. 

Reactor Conditions for Experimental Runs. Operating conditions for the continuous, stirred tank reactor runs were chosen to study the effects of mixing speed on the monomer conversion and molecular weight distribution at different values for the number average degree of polymerization of the product polymer. 

Due to the retractive forces in stretched mbber, the aldehyde and zwitterion fragments are separated at the molecular-relaxation rate. Therefore, the ozonides and peroxides form at sites remote from the initial cleavage, and underlying mbber chains are exposed to ozone. These unstable ozonides and polymeric peroxides cleave to a variety of oxygenated products, such as acids, esters, ketones, and aldehydes, and also expose new mbber chains to the effects of ozone. The net result is that when mbber chains are cleaved, they retract in the direction of the stress and expose underlying unsaturation. Continuation of this process results in the formation of the characteristic ozone cracks. It should be noted that in the case of butadiene mbbers a small amount of cross-linking occurs during ozonation. This is considered to be due to the reaction between the biradical of the carbonyl oxide and the double bonds of the butadiene mbber [47]. 

Several different companies have greened various steps of the process. In VNB production by-products come from competing Diels-Alder reactions and polymerization, largely of cyclopentadiene. The reaction is usually carried out in a continuous tube reactor, but this results in fouling, due to polymerization, at the front end, where the dicyclopentadiene is cracked to cyclopentadiene at temperatures over 175 °C. Whilst fouling does not have a very significant effect on yield, over time it builds up. 

In contrast to the results from previous studies with related monomers, at low temperatures, from —78 to —40°C, no polymerization reaction apparently occurred. However, if the polymerization reactions initiated with either BF3 0Et2 or SnCl were carried out at 0°C and the system was allowed to attain ambient temperature (20°C) over a period of 24 h, or if initiation was done directly at ambient temperature and stirring was continued for 24 h, good yields of low molecular weight polymers, which were insoluble in methanol, were obtained. The latter procedure was found to be the most effective, but at 0°C only viscous residues resulted. However, for shorter polymerization periods, even at 20°C, no products insoluble in methanol were obtained, and the monomer was recovered virtually unreacted. 

Polymer production technology involves a diversity of products produced from even a single monomer. Polymerizations are carried out in a variety of reactor types batch, semi-batch and continuous flow stirred tank or tubular reactors. However, very few commercial or fundamental polymer or latex properties can be measured on-line. Therefore, if one aims to develop and apply control strategies to achieve desired polymer (or latex) property trajectories under such a variety of conditions, it is important to have a valid mechanistic model capable of predicting at least the major effects of the process variables. 

In 1988, Terry and coworkers attempted to homopolymerize ethylene, 1-octene, and 1-decene in supercritical C02 [87], The purpose of their work was to increase the viscosity of supercritical C02 for enhanced oil recovery applications. They utilized the free radical initiators benzoyl peroxide and fert-butyl-peroctoate and conducted polymerization for 24-48 h at 100-130 bar and 71 °C. In these experiments, the resulting polymers were not well studied, but solubility studies on the products confirmed that they were relatively insoluble in the continuous phase and thus were not effective as viscosity enhancing agents. In addition, a-olefins are known not to yield high polymer using free radical methods due to extensive chain transfer to monomer. 

In 1994, we reported the dispersion polymerization of MM A in supercritical C02 [103]. This work represents the first successful dispersion polymerization of a lipophilic monomer in a supercritical fluid continuous phase. In these experiments, we took advantage of the amphiphilic nature of the homopolymer PFOA to effect the polymerization of MMA to high conversions (>90%) and high degrees of polymerization (> 3000) in supercritical C02. These polymerizations were conducted in C02 at 65 °C and 207 bar, and AIBN or a fluorinated derivative of AIBN were employed as the initiators. The results from the AIBN initiated polymerizations are shown in Table 3. The spherical polymer particles which resulted from these dispersion polymerizations were isolated by simply venting the C02 from the reaction mixture. Scanning electron microscopy showed that the product consisted of spheres in the pm size range with a narrow particle size distribution (see Fig. 7). In contrast, reactions which were performed in the absence of PFOA resulted in relatively low conversion and molar masses. Moreover, the polymer which resulted from these precipitation... 

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