Copolymerization batch

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. 

Levels of acrylic acid higher than 1.5% inhibit the batch copolymerization reaction of ethylene and vinyl acetate. 

The copolymer generator calculates a series of "mini-batch" copolymerizations and has been described in more detail by Molau (19) and Meyer and Lowry (20). The sequence distribution generator uses Harwood s (14) run number approach to calculate triad functions. 

Before getting to that, there is something important you should realize about batch copolymerizations, by which we mean a reaction where monomer is not being continuously introduced. The copolymer composition and the parameters that measure the departure from randomness and things like run number can change considerably with conversion. In other words, the type of copolymer that you get at the beginning of the reaction can be very different to what you get near the end, when most of the monomer has been used up. 

Now, if you recall the copolymer equation relating the composition of the copolymer formed at any instant of time (FA, FB), to the monomer feed composition (fA, fB) in a batch copolymerization (Equation 6-5), it should be clear that unless you have rA = rB 1, so that Fa - fA, then one of the monomers is going to be used up faster than the other (unless rA < 1, rB < 1 and you start with a monomer composition corresponding to the azeotrope condition). That means copolymer composition varies with conversion—we say there is compositional drift. 

Miniemulsion copolymerization in a CSTR involves some very interesting features. However, in the interest of clarity, these systems will be discussed along with results for batch copolymerization. 

Reimers [102] carried out batch copolymerizations in both macro- and equivalent miniemulsions. MMA was used as the main monomer. The MMA was copolymerized in macroemulsion- or miniemulsion with p-methylstyrene (pMS), vinyl hexanoate (VH), vinyl 2-ethylhexanoate (VEH), vinyl n-decanoate (VD) or vinyl stearate (VS). The comonomers were copolymerized at 10%wt comonomer, 90%wt MMA. SLS was used as the surfactant and KPS as the initiator. The comonomers (all highly water insoluble) were used as the costabilizer. Miniemulsions were sonicated, while equivalent macroemulsions were only subjected to vigorous mixing. Polymerizations were carried out at 60 °C. 

If the feed composition is an azeotropic mixture or if ri = F2 =, the feed and copolymer compositions will remain constant during the course of a batch copolymerization. More generally, however, both compositions will change with conversion, and it is important to be able to calculate the course of such changes. 

A batch copolymerization mixture initially contains mol monomer M] and Wj mol monomer M2. After a fraction p of the initial monomers have been polymerized, the unreacted monomers are, respectively, and m2. Now, /, and Fi are the mole fractions of monomer 1 in the feed and corresponding copolymer, respectively, and ... 

A thermosetting appliance enamel consists of a terpolymer comprising about 72 parts of vinyl toluene (70/40 meta/para) with about 20 parts of ethyl acrylate (to reduce brittleness of the copolymer) and 8 parts of an acidic vinyl comonomer. The acid is incorporated in the copolymer to provide sites for subsequent cross-linking with a diepoxide. It seems reasonable to expect that grease and slain resistance of the cross-linked enamel will be enhanced if the cross-links are not clustered and almost all initial polymer molecules contain at least one or a few cross-linking sites. To achieve this in a batch copolymerization, what are the best reactivity ratios (approximately) of the major component (vinyl toluene) and the vinyl acid comonomer Show you reasoning. 

Ail microspheres were prepared using soap-free emulsion polymerization. Carboxylated microspheres were prepared by batch copolymerization. Batch copolymerization was performed with main monomer, S, lwt% of co-monomer, MAA, and 0.4wt% of initiator, KPS. All weight fractions were based on the amount of main monomer, S. These microspheres were named CM-1 for low carboxylated PS/PMAA, respectively. 

Nayak, A. and Gupta, S. K. (2004). Multi-objective optimization of semi-batch copolymerization reactors using adaptations of genetic algorithm, Macromol. Theor. SimuL, 13, pp. 73-85. 

During batch copolymerization, composition may drift with conversion because of differences in comonomer reactivity and can result in less valuable... 

More often than not, reactivity differs from monomer to monomer. This is evident when the reactivity ratios differ from a value of one. Thus, if one is operating at concentrations other than the azeotropic composition, batch copolymerization will result in a changing copolymer composition throughout the reaction. For example, a copolymerization with rj > 1 and r2 < 1 would result in the instantaneous copolymer composition decreasing in monomer 1 as monomer conversion increases. The degree of compositional drift that leads to a heterogeneous copolymer composition depends on the ratio of reactivity ratios where heterogeneity increases with the... 

Tip 13 (related to Tip 12) Copolymerization, copolymer composition, composition drift, azeotropy, semibatch reactor, and copolymer composition control. Most batch copolymerizations exhibit considerable drift in monomer composition because of different reactivities (reactivity ratios) of the two monomers (same ideas apply to ter-polymerizations and multicomponent cases). This leads to copolymers with broad chemical composition distribution. The magnirnde of the composition drift can be appreciated by the vertical distance between two items on the plot of the instantaneous copolymer composition (ICC) or Mayo-Lewis (model) equation item 1, the ICC curve (ICC or mole fraction of Mj incorporated in the copolymer chains, F, vs mole fraction of unreacted Mi,/j) and item 2, the 45° line in the plot of versus/j. 

Hint 1. Plot Fj versus /i in a batch copolymerization for different combinations of r and r2 and observe the composition drift. Is the direction of composition drift always the same Are azeotropic points stable or unstable to small perturbations in monomer concentration ... 

As for batch processes, monomer partitioning is a factor which influences individual values of [M]p (and hence reaction kinetics) in all of the aforementioned types of semi-batch copolymerization. The approach to partitioning in the absence of monomer droplets which was put forward by German, Maxwell and co-workers (see Section 7.3.2.2) also is appropriate to monomer-starved semibatch processes. Assuming that thermodynamic equilibrium is established during addition of monomer, then all that is needed is to account for the changing masses of the unreacted monomers and polymer, as monomers are fed to the reaction vessel and removed from it through polymerization. 

In ordinary batch copolymerization there is usually a considerable drift in monomer composition because of different reactivities of the two monomers (based on the values of the reactivity ratios). This leads to a copolymer with a broad chemical composition distribution (CCD). In many cases (depending on the specific final product application) a composition drift as low as 3-5% cannot be tolerated, for example, copolymers for optical applications on the other hand, during production of GRIN (gradient index) lenses, a controlled traj ectory of copolymer composition is required. This is partly circumvented in semibatch operation where the composition drift can be minimized (i.e., copolymer composition can be kept constant ) by feeding a mixture of the monomers to the reactor with the same rate by which each of them is consumed in the reactor. 

In the absence of an azeotrope, and when one monomer is more reactive than the other in a binary batch copolymerization (e.g., rj > 1 and T2 < 1), the instantaneous copolymer composition will decrease in monomer A with increase in conversion. The extent of composition drift, which leads to a copolymer heterogeneous in composition, depends on the ratio of reactivity ratios ri/r2 (increasing with any increase in ri/ra), the initial monomer composition and the monomer conversion. A copolymer which is heterogeneous in composition usually has inferior properties, therefore industrial processes have been developed to reduce composition heterogeneity. These processes are usually semibatch, but sometimes continuous as well. 

Most monomers have different reactivity ratios, which lead to production of copolymers that do not have the same composition of the monomer mixture. In batch copolymerization, the copolymer produced at the beginning of the process is richer in the most reactive monomer, while the copolymer becomes richer in the less reactive monomer at the end of the batch. This composition drift causes the production of heterogeneous polymer mixtures, which may be deleterious for the performance of the polymer material. With the exception of the azeotropic reactions, most copolymerization systems experience composition drifts during batch copolymerizations, which must be corrected if homogeneous copolymer materials are to be produced. For this reason, copolymerizations are usually performed in semibatch (with manipulation of monomer feed flow rates) or continuous mode. 

A random copolymerization of ethylene and propylene is carried out in solution. From previous experiments it was found that the copolymerization is purely random, and that die ratio p = 20 (ethylene is the more active monomer). It is intended to make a copolymer containing 60 mol.% of ethylene and 40 mol.% of propylene, so that the build-in ratio p = 1.5. A semi-batch copolymerization... 

Fig. 7.6. Batch copolymerization of styrene and butadiene with n-butyllithium (1 g) at 20°C in toluene (10 kg) with various styrene feed fractions xs (20 mol monomer overall). Simulation of overall conversion with data from Ref 35.

Fig. 9.12. Average copolymer composition and sequence length as functions of chain length for batch copolymerization. Kinetic data kd - 6.25 X 10 s ki - 3.75 x 10 m (kmol s) kpM — 1000 m (kmol s ) hpAB — 100 m (kmol s)...

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