Free radical chain polymerisation limitation

The major limitations of the feed forward control strategy presented here are that (i) it is only as good as the fundamental data which are used in the models and (ii) it can only be used for systems which conform to the conventionally accepted mode of behaviour of free radical chain polymerisation in solution. However, the same approach can be used with the appropriate models for any copolymerisation process. The range of application can be increased by making an arbitary assessment of the parameters necessary for the control models and/or by introducing a feedback loop which incorporates some state measurement device, e.g., an in-line gas chromatograph for measurement of residual monomers concentrations. Such a scheme is shown in Figure 21. 

The linkage between two chains can also be ionic. Thus the copolymer between ethylene and methacrylic acid (MA) (up to 15% MA), made by free radical polymerisation, yields a polymer with pendant carboxyl groups. Neutralisation with zinc ions gives a crosslinked, thermo-reversible polymer (Surlyn ). The resulting polymer (ionomer) has limited properties, although it is the favoured material for the outer covering of golf balls. 

In this limit, termination within the particle is rate determining. An important implication of termination being diffusion controlled (and hence chain-length dependent) is that, in conventional free-radical polymerisation, termination events are dominated by termination between a mobile short chain (formed in an emulsion polymerisation by entry of a z-mer, by re-entry of an exited radical or by transfer to monomer) and a long, relatively immobile one. This is known as short-long termination . 

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