Copolymer during batch polymerization

Figure 1. Changes in copolymer composition (PMMA/PMAA ratio) during batch polymerization of MMA-MAA copolymer system comparison between theoretical and experimental values ((O) experimental point (1) = 0.60, r2 = 1.50 (2)...

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. 

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... 

Block copolymer synthesis from living polymerization is typically carried out in batch or semi-batch processes. In the simplest case, one monomer is added, and polymerization is carried out to complete conversion, then the process is repeated with a second monomer. In batch copolymerizations, simultaneous polymerization of two or more monomers is often complicated by the different reactivities of the two monomers. This preferential monomer consumption can create a composition drift during chain growth and therefore a tapered copolymer composition. 

Likewise, for the semibatch operation, the influence of monomer was seen in the differences between macro- and miniemulsion feeds. For extremely water-insoluble monomers, the miniemulsion-feed mode lessens the departure of the copolymer composition from the feed composition during semi-starved semibatch polymerization. However, this is accomplished by simultaneously broadening the PSD. Results from the GPC analysis indicated that the polymers with lower molecular weight and broader distribution were formed in the semibatch process, in contrast to the batch run. 

Because of facile cross-propagation, statistical (or nearly random) copolymerization is very easily achieved in free-radical systems, in contrast to ionic reactions. The reactivity of many comonomers are relatively similar. For example, in RP, methacrylates have similar reactivity to styrene and are 3 times more reactive than acrylates. However, in anionic polymerization acrylates are 100 times more reactive than methacrylates and the latter much more reactive than styrene. In cationic polymerization the opposite reactivity order is observed. The copolymerization of monomers with similar reactivity should result in statistical copolymers with no compositional variation during the pol5unerization. This has been observed for copolymerization of the same type of monomers such as various styrenes, various methacrylates, and various acrylates. This is the case for both CRP and conventional RP. However, in batch copol5unerizations of different classes of comonomers there is a continuous change of residual monomer composition in the reaction because one comonomer reacts faster than the other one. 

The open-loop observer formed by Equations 7.23,7.27, and 7.28 has been successfully used to estimate the unreacted amounts of monomers in different monomer systems under different conditions [25-29]. Once the unreacted amounts of the monomers (Al and A ) are estimated during the course of the polymerization, the conversion and copolymer compositions can be readily estimated for batch and semibatch reactors. The accuracy of the estimation depends on the reactivity ratios and enthalpies of polymerization for each monomer that can be obtained experimentally or are available in the literature. 

Suspension polymerization is carried out using a single reactor or two parallel reactors. A mixture of monomers, monomer-soluble initiator (peroxides and azo compounds), and any additives (e.g., chain transfer agents) is dispersed in water by mechanical agitation in the presence of a suspension stabilizer. The suspension polymerization temperatures ranges from 70°C to 125 C. The reactor temperature is increased gradually during the batch. SAN copolymer particles of 10-3(K)0 p,m are obtained. To keep the copolymer composition constant, a mixture of monomers is added into the reactor as in emulsion processes. 

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