Polymerization continued composition during

The variation of copolymer composition during the course of a batch polymerization can be reduced by conducting the reaction as a so-called semibatch process. This is a starved feed operation in which part of the charge is fed to the reaction vessel and polymerization is started. The remainder of the monomer feed is pumped in continuously or intermittently at a rate sufficient to keep the... 

Samples taken during three different AN/S polymerizations were analyzed chromatographically. Target composition was 70/30 AN/S for all three polymerizations. It is difficult to prepare high nitrile copolymers of styrene because reactivity ratios of the two monomers are very different. This study used continuous addition of monomers to achieve the desired polymer composition. Addition rates were those needed to maintain an excess of acrylonitrile. 

It is in the technique of solidifying the mass that plastisol propellants differ so markedly from composite propellants. In composite propellants, the nonvolatile liquid is comprised of monomers or low molecular weight prepolymers. Solidification is accomplished by completion of the polymerization reactions. Much attention must be given to the degree of completion of these reactions during manufacture so as to minimize changes in physical properties as a consequence of continued slow polymerization, or so-called post-cure, following manufacture. 

Procedure 3. Addition of DPP to Polymerizing DMP. The method of Procedure 1 was followed, with only the DMP initially present. After 30 minutes the reaction mixture was a thick gel, with much of the polymer out of solution. The DPP was added at this point, and oxidation was continued for four hours, during which the viscosity decreased gradually and the polymer returned to solution. Precipitation in methanol yielded 13.5 grams (92.5% ) of polymer having an intrinsic viscosity of 0.56 dl/gram and a composition of 49 mole % DMP and 51% DPP. 

This model is based on the particle formation during polymerization where the polymer particles are sterically stabilized by graft-copolymerized PEO chains on the particle surface. In the later stage the polymer particles were supposed to grow in size mainly by copolymerization of monomers occluded in the particles which may favor the substrate monomer (styrene) over the macromonomer as compared to the composition in the continuous phase. 

During the semi-continuous polymerization, 4-5 small samples were withdrawn from the polymerization for the determination of the comonomer and copolymer composition. A few drops of the sample latex were mixed with hydroquinone, cooled in ice, and subjected to GC analysis to determine the amounts of unreacted monomer. The rest of the sample (5-8 ml) was poured into mixed solvent of ispropanol/hexane (45/55) containing hydroquinone, and the precipitated polymer, after it was washed with hexane, was dried in a vacuum oven at 45°C for more than 5 hours. A certain amount of the dried polymer was dissolved in dimethyl formamide (DMF), and titrated for the carboxyl content with NaOH solution using phenolphthalein as the indicator. 

Although MAA monomer possesses a larger reactivity ratio than MMA monomer, more MAA was found to exist in the outer side of the particle in the batch latex, as shown in Figures 5 and 6. This behavior could be explained if one can accept the fact that the MAA-rich polymers, which are formed early on during the polymerization, can migrate to the surface of the particle due to their higher hydrophilicity and plasticization of the polymer with the monomer. In the semi-continuous process, it could be expected that copolymer with the same composition as the comonomer feed is formed, and the particle contains a uniform distribution of carboxyl groups. 

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