Practical Methods of Chain Polymerisation

Chain reactions are used to prepare a variety of high molar mass polymers of commericial importance and in practice may take one of four forms, namely bulk, solution, suspension, and emulsion methods. These four methods are described in the sections that follow, together with the loop modification which has become of commercial importance recently in producing latexes by emulsion polymerisation for the paint industry. 

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The properties of a polymer network depend not only on the molar masses, functionalities, chain structures, and proportions of reactants used to prepare the network but also on the conditions (concentration and temperature) of preparation. In the Gaussian sense, the perfect network can never be obtained in practice, but, through random or condensation polymerisations(T) of polyfunctional monomers and prepolymers, networks with imperfections which are to some extent quantifiable can be prepared, and the importance of such imperfections on network properties can be ascertained. In this context, the use of well-characterised random polymerisations for network preparation may be contrasted with the more traditional method of cross-linking polymer chains. With the latter, uncertainties can exist with regard to the... 

Practically, the polymerisation can be carried out in two different ways (Figure 5.3). The first method is to simply add the deactivator into the polymerisation medium containing monomer and radical initiator and then adapt the experimental conditions so that the trapped radical can be reactivated. The second method consists of using a pre-made dormant species of small size (where R-T is considered as a unimolecular initiator) to start the polymerisation without the need of a radical initiator. In both cases, initiation must be fast, so that all growing chains are created within a short time span. It should, however, be noted that the second method leads to a better control over molar mass as the initiator efficiency is usually close to 1, which might not always be the case when a classical radical initiator is used. 

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