Polymerization stages

Acrylate polymerizations are markedly inhibited by oxygen therefore, considerable care is taken to exclude air during the polymerization stages of manufacturing. This inhibitory effect has been shown to be caused by copolymerization of oxygen with monomer, forming an alternating copolymer (81,82). 

The quahty of the water used in emulsion polymerization has long been known to affect the manufacture of ESBR. Water hardness and other ionic content can direcdy affect the chemical and mechanical stabiUty of the polymer emulsion (latex). Poor latex stabiUty results in the formation of coagulum in the polymerization stage as well as other parts of the latex handling system. 

At moderately high molecular weights, the reaction mass becomes highly viscous, which limits heat transfer and evaporation of the condensation water. This high viscosity limits further melt polymerization in the bulk. In the literature, the melt polymerization stage is sometimes omitted and the prepolymers are condensed to high molecular weights in the solid state.6,28 41 The polymerizations can easily be carried out without a catalyst. 

The use of the CSTR and LFR by this process follows the guidelines discussed in Section 2.3.2. The former is used for the first polymerization stage where viscosity is relatively low. The latter where viscosities are high enough to suppress backmixing and where very high exit conversions are desired. 

The mixing vessels serve as buffers between the polymerization stage operated in batch mode and the separation units operated continuously. The capacity of each mixing vessel is three polymerization batches and the minimal hold-up is 0.1 polymerization batches to ensure a sufficient mixing effect. 

Options for assignment of the equipment The assignment of the units to the processing steps is fixed with respect to the stages of the plant but variable with respect to particular units within the stages (e.g., the reactors of the polymerization stage). 

Batch size The batch sizes in the preparation stage and in the polymerization stage are variable as batches may be split in the preparation stage and mixed in the polymerization stage. However, the concept of batches does not apply in the finishing stage. 

Changeovers No changeovers appear in the preparation stage and in the polymerization stage. The start-ups and shut-downs of the finishing lines are changeovers with certain set-up times which cause costs (see below). 

In the polymerization stage, the number of events, i.e., of the polymerization starts, N, is given and the events are identified by the index n = 1... N. Start times of polymerizations are represented by continuous variables in e [0, H] in with H denoting the given scheduling horizon. As an initial condition, the first polymerization is defined to start at tn= i = t°. 

The aggregated scheduling problem is subject to uncertainties in the following parameters (1) the capacity of the polymerization stage, i.e., a possibly reduced availability of polymerization reactors due to equipment failures, and (2) the demand profiles. 

The capacity of the polymerization stage limits the number of batches that can be produced in each period i. 

The dried mixed feed is now ready for the polymerization step, and catalysts can be added to the solution (solvent plus monomers) just prior to the polymerization stage or in the lead polymerization reactor. 

From an experimental point of view, observations of the initial phase separated morphology via electron microscopy is complicated by the removal of unreacted monomer, except for the fully polymerized stage. 

Fig. 17 Top row. conversion (ln([M]o/[M]t) against time plots for 50mol% copolymerizations (a, c, e). Bottom row. relationship between the monomer feed (/i) and the actual monomer incorporation (Fi) at the initial ( 20% conversion) and final (>50% conversion) polymerization stages (b, d, f). Both conversion and monomer incorporation are shown for EtOx NonOx (a, b), MeOx NonOx (c, d), and MeOx EtOx (e, f) copolymerizations. (Reprinted with permission from [88]. Copyright (2006) American Chemical Society)...

Fig. 11 Visualization of the sequential progress of branching stage by staining with rose bengal. DC-derivatized PST surface (GO) was graft-copolymerized with CMS and dimethylaminoethyl acrylamide (DMAEMA), and subsequent quarternization, while narrowing the irradiation area in each polymerization stage (item, GI item, GI+GII item, GI+GII- -GIII) by the combination of three kinds of masks with linear openings (line widths 2 mm for GI, 1 mm for GII, 0.5 mm for GUI). Bar=0.5 mm...

Free-radical polymerization processes are used to produce virtually all commercial methaerylie polymers. Usually free-radical initiators tqv > such as a/o compounds or ieroxides are used to initiate the polymerisations. Photochemical and radiation-initiated polymerizations are also well known. At it constant temperature, the initial rate of the hulk or solution radical polymerization of methaerylie monomers is first-order with respect to monomer eoneentration. anil one-half order with respect to the initiator concentration. Methacrylate polymerizations are markedly inhibited by-oxygen therefore considerable care is taken to exclude air during the polymerization stages of manufacturing. 

From the process-design perspective the versatility of applications of PVC demands a precise adjustment of material properties to quality requirements, which are for the most part determined during the polymerization stage, namely by molecular-weight distribution (MWD) and the morphology of particles. 

The kinetics of polycondensation hy nucleophilic aromatic substitution in highly polar solvents and solvent mixtures to yield linear, high molecular weight aromatic polyethers were measured. The basic reaction studied was between a di-phenoxide salt and a dihaloaromatic compound. The role of steric and inductive effects was elucidated on the basis of the kinetics determined for model compounds. The polymerization rate of the dipotassium salt of various bis-phenols with 4,4 -dichlorodiphenylsulfone in methyl sulfoxide solvent follows second-order kinetics. The rate constant at the monomer stage was found to be greater than the rate constant at the dimer and subsequent polymerization stages. 

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