Copolymer composition drift

The major unresolved questions for these systems are the coalescence and flocculation of particles under mechanical agitation and the parameters which influence copolymer composition drift. 

The precipitation polymerization literature is reviewed with particular attention to the influence of particle formation and growth, autoaccelerating polymerization rates, and copolymer composition drift on polymer reactor design. 

FIGURE 6-21 Simple method for determining copolymer composition drift... 

The production of copolymers leads to some additional constraints to reactor design beyond what is required for homopolymer. The most important of these is composition drift. The reactivity ratios of a monomer mixture define the composition of a copolymer that is instantaneously produced from a given monomer mixture. This is true in a plug flow reactor or a backmixed reactor. However, in the plug flow reactor, the copolymer composition drifts from that produced from the initial monomer composition to that produced by the monomer composition at the end of the polymerization. In contrast, in the backmixed reactor, all copolymer produced is of the same composition, which... 

A second motivation for using a monomer-feed semibatch procedure is to control copolymer composition and/or particle morphology. Delayed feed of part of the more reactive monomer can be used to eliminate or reduce the composition drift of the copolymer. The delayed feed of a comonomer mixture when the reactor is operated in the monomer-starved regime can also be used to prevent copolymer composition drift. Such operations will produce polymer particles with more uniform morphology. Different monomer addition schemes can be employed to control nonuniform particle morphology (see papers by Bassett et al. in General References 7 and 9). 

These observations on copolymerization of vinyl acetate with n-butyl aaylate are typical of batch emulsi( i copolymerizations. Such reactions invariably suffer from uncontrolled copolymer composition drift and yield copolymers which are heterogeneous in composition to an extoit which is determined by the particular monomers, formulation and reaction conditions onployed. 

Carson WW, Dwyer JL, Boumajny B (2008) Copolymer compositional drift across molecular weight measured by LC-FTIR. Int J Polym Anal 13 463-470... 

In the case of styrene-acrylonitrile copolymers, the method of choice for batch suspension polymerization is normally that involving the azeotropic monomer/comonomer composition to minimize copolymer compositional drift. Nevertheless, complications often arise because considerably more acrylonitrile than styrene dissolves in the continuous aqueous phase. As conversion proceeds, acrylonitrile diffuses into the polymer particles and the monomer ratio in the bead changes, causing the composition of the copolymer to change as well [4]. 

Ni H, Hunkeler D. Prediction of copolymer composition drift using artificial neural networks copolymerization of acrylamide with quaternary ammonium cationic monomers. Polymer 1997 38 667-675. 

For many applications the tolerance for copolymer composition drift is small and its control is essential. The two strategies most commonly used for this purpose are ... 

If a batch polymerisation is performed to high conversion under non-azeotropic conditions, then the monomer feed composition changes and the composition of the copolymer (composition drift) also changes. It is then possible that the copolymer formed initially is no longer miscible in the copolymer formed in a later part of the reaction. Phase separation then occurs and one speaks of heterogeneous copolymers. Such a heterogeneous copolymer has the properties of the different polymers it is composed of (e.g. may have two glass... 

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