Monomer flooded conditions

Rm > p , which leads to [M]p = [M] and a build-up of monomer in the reaction vessel with excess monomer forming into droplets. Under these monomer-flooded conditions Rp = and the semi-batch polymerization is essentially indistinguishable from the equivalent batch reaction. 

The simplest way to establish the value of Rm below which monomer-starved conditions can be achieved, is to perform an experiment in which the chosen seed stage is carried out as planned for the semi-batch process, and to then add the remaining monomer over a short period of time to ensure that monomer-flooded conditions are attained. Measurement of the rate of polymerization (which should be i p ) after the initial period required for swelling of the seed particles, gives the limiting value of R ) below which monomer-starved conditions can be expected. 

Equation (7.44) can be used to define the limiting value of Rm (i.e. ) [ I ) above which monomer-flooded conditions will obtain. Since this situation corresponds to = 1 — substitution gives... 

The transition from monomer starved to monomer-flooded conditions during the polymerization reaction was followed online in the work reported in Reference [50] by ACOMP... 

When more hydrophobic monomers are used, the hydro-phobicity of the CCT reagents can be altered and when tetraphenylcobaloxime boron fluoride (COPhBF) is used, it is found to reside predominantly in the organic phase. The best results are often achieved under monomer-flooded conditions that keep the glass transition temperature (Tg) of the monomer-filled particles below the reactor temperature. CCT does actually reduce the rate of polymerization such that the monomer can be fed at a rate that maintains the instantaneous conversion low enough for the particle to be swollen with monomer, allowing diffusion of the catalysts between the aqueous and monomer phases. If the amount of the catalyst is reduced and the rate increases, this can lead to viscous, glassy particles that prevent catalyst mobility, which is observed as a... 

Molar mass and crosslinking can be influenced in addition by the amount of initiator, by the process conditions (e.g. monomer-starved conditions versus monomer-flooded conditions) and by using crosshnking monomers, such as divinyl benzene, butanediol diacrylate or allyl methacrylate. 

The reaction order 0.56 obtained from Rp°c [SDSJ0 56 indicates the emulsifier-flooded condition (the monomer droplet surface not saturated with SDS). However, the increased coverage of the droplet surface by emulsifier is accompanied by the enhanced homogeneous nucleation, i.e., Nw increases significantly with increasing [SDSJ. Monomer droplet nucleation predominates in the particle formation process for the run with the lowest [SDSJ (4 mM). By contrast, mixed modes of particle nucleation are operative in the polymerizations with... 

In copolymerisations (70, 408), the copolymer composition may be controlled by the relative rates of monomer addition. In this way, any large differences in the comonomer reactivity ratios or water solubilities can be overcome to produce a copolymer with uniform composition. In order to maintain control of the monomer concentration in the polymer particles, the polymerisation may have to be performed under monomer-starved conditions. This means that the polymer particles are not saturated with monomer, but are being polymerised at an instantaneous conversion of 90% or greater. If the monomer addition rate is greater than the polymerisation rate, the reactor will be operating under flooded conditions, and control over the copolymer composition is lost. 

Alb AM, Reed WF. Online monitoring of molecular weight and other characteristics during semibatch emulsion polymerization under monomer starved and flooded conditions. Macromolecules 2009 42 8093-8101. 

For instance, this procedure is followed in manypapers dealing with the semi-continuous emulsion copolymerisation of vinyl acetate and butyl acrylate (e.g. El-Aasser et al, 1983). Two main situations can be distinguished with respect to the monomer addition rate, (a) Flooded conditions the addition rate is higher than the polymerisation rate, (b) Starved conditions the monomers are added at a rate lower than the maximum attainable polymerisation rate (if more monomers were to be present). The latter process (starved conditions) is often applied in the preparation of homogeneous copolymers/latex particles. In this case after some time during the reaction, because of the low addition rates, a steady state is attained in which the polymerisation rate of each monomer is equal to its addition rate and a copolymer is made with a chemical composition identical to that of the monomer... 

A first study of reaction kinetics with ACOMP was made for the semibatch emulsion polymerization of MMA at 70 °C [50]. The use of continuous monitoring method described in the previous sections offered a robust means of determining the characteristic features of the starved and flooded monomer conditions and identifying them during the experiments. 

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