Semicontinuous polymerization

Effects of starvation feeding in semicontinuous or continuous polymerization systems. 

New Telechelic Polymers and Sequential Copolymers by Polyfunctional Initiator-Transfer Agents (Inifers) End Reactive Polyisobutylenes by Semicontinuous Polymerization... 

Semicontinuous polymerization experiments were carried out in a stainless steel enclosure (dry box) under a dry nitrogen atmosphere in three neck flasks (11) equipped with overhead stirrer and an inlet for the continuous introduction of precooled inifer/isobutylene/ solvent feeds to stirred, dilute BCI3/solvent charges. Experiments with binifer were performed at -80°C by the use of CH3Cl/n-hexane solvent mixtures (80/20 v/v), with trinifer at -40°C using CH3CI... 

Conventional polymerizations were carried out by rapidly adding the BCI3 coinitiator to stirred inifer/isobutylene/solvent charges. The composition of the final charges was identical to the final composition of the corresponding semicontinuous runs. Heat evolution could often be observed in conventional batch polymerization upon BCI3 addition. 

Kinetics of the Idealized Semicontinuous Polymerization Technique. Based on the kinetic scheme outlined by Equations 1 through 5 the following set of differential equations describe the changes in the concentrations during polymerization ... 

In semicontinuous polymerization under stationary conditions the concentration of monomer and inifer are constant ... 

Table I. Comparison of Semicontinuous and Conventional Polymerization Techniques for the Preparation of Telechelic Polyisobutylenes by Binifer and Trinifer...

Conclusions. Table II compares some characteristics of the semicontinuous and batch techniques. According to 1H NMR and GPC data the semicontinuous technique produces polymers with well defined symmetrical end groups, while the batchy polymerization may yield once-fired and unfired chain ends. The M Mn values of polymers obtained in semicontinuous runs are close to theoretical, whereas those harvested in conventional batch polymerization exhibit broader molecular weight distributions due to changing [I] and [M], presence of once-fired and/or unfired chain ends, and insufficient reactor control. The latter circumstance may even result in bimodal distributions. 

The molecular weights of polymers formed in semicontinuous experiments are controlled by the concentration ratio [M]/[I] in the feed, while in batch polymerizations the molecular weights are controlled mostly by the reactivity of the inifer (i.e., the value of the chain transfer constant Cj rendering too reactive or unreactive inifers unsuitable). In batch polymerizations complete depletion of... 

The semicontinuous polymerization was carried out in a 500-ml four-neck flask immersed in a constant temperature bath at 60° C, and equipped with a reflux condenser, a two-bladed stainless steel stirrer and a graduated dropping funnel. The water and surfactant were introduced into the flask, then nitrogen gas was bubbled with agitation for at least 20 minutes. The initiator solution was added, and after 5 minutes the mixture of monomer addition started and continued for a total of three hours. The polymerization was continued for at least one hour past this point. Under these conditions the rate of monomers addition was less than 1/10 of their maximum rate of polymerization (Rpmax). 

Figure 2. Changes in conversion ratio CMma/CMaa during semicontinuous polymerization of MMA-MAA comonomer system (CMma) instantaneous conversion of MM A (C mm a) instantaneous conversion of MAA ((A) SP-28 (90/10) (d) SP-26 (85/15) (O) SP-27 (80/20))...

Figure 5. Distribution of carboxyl groups in MMA-MAA copolymer latexes as weight percent based on the MAA content used in the polymerization (1) carboxyl groups in the serum (2) surface carboxyl groups (3) carboxyl groups next to the surface (4) carboxyl groups buried deeply (5) unneutralized carboxyl groups (A) batch-type latexes (B) semicontinuous-type latexes...

Figure 1. Conversion representation of MMA semicontinuous emulsion polymerization. Curve A results from neglecting lag in sampling while curve B is corrected for 2.7 min of lag.

Figure 2. Rate representation for MMA semicontinuous emulsion polymerization ((-----) the monomer feed rate (right or-...

Figure 7. Conversion representation for a multicomponent acrylic, semicontinuous solution polymerization...

Synthesis. A series of latexes was prepared by semicontinuous emulsion polymerization of methyl methacrylate. A dialkyl ester of sodium sulfosuccinic acid surfactant yielded the narrow particle size distribution required. An ammonium persulfate/sodium metabisulfate/ferrous sulfate initiator system was used. The initiator was fed over the polymerization time, allowing better control of the polymerization rate. For the smaller size latexes (200 to 450 nm), a seed latex was prepared in situ by polymerizing 10% of the monomer in the presence of the ammonium persulfate. Particle size was adjusted by varying the level of surfactant during the heel reaction. As the exotherm of this reaction subsided, the monomer and the sodium metabisulfate/ferrous sulfate feeds were started and continued over approximately one hour. The... 

Batch and Semibatch Polymerization. The reactor is normally operated in a semicontinuous mode by delaying vinyl acetate, solvent, and initiator. The same reactor can be used for stripping the poly(vinyl acetate) solution, provided that careful addition of methanol is used in order to prevent the viscosity in the reactor from becoming excessive (249). The disadvantages of batch polymerization are lack of product consistency and unsatisfactory economics in large scale production (250,251). The true batch reaction, where all the reactants are added to the reactor at time zero, yields a product having a very broad molecular weight distribution of limited commercial value. 

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