Polymerisation Supply chains

Chain transfer to monomer and to other small molecules leads to lower molecular weight products, but when polymerisation occurs ia the relative absence of monomer and other transfer agents, such as solvents, chain transfer to polymer becomes more important. As a result, toward the end of batch-suspension or batch-emulsion polymerisation reactions, branched polymer chains tend to form. In suspension and emulsion processes where monomer is fed continuously, the products tend to be more branched than when polymerisations are carried out ia the presence of a plentiful supply of monomer. 

A commercial guargum supplied by Hindustan Chemicals and Gums, Bhiwani, India, has been used. To remove the protein, fat and fibrous impurities, a method given by Whitcomb et al. 3] has been adopted to purify the guargum. The various amounts of polyacrylamide chains have been grafted onto guargum main chain using redox initiators by solution polymerisation technique. 

Fig. 3.20. Emulsion polymerisation. Reaction diagrams for the beginning of polymerisation. A growing chain radical in the aqueous phase may be involved in any of three processes. Process 1 It may reach the critical size for precipitation and form a primary particle. Process 2 It may penetrate a micelle and nucleate it. Process 3 It may be captured by a growing particle coming from a nucleated micelle (PI) or by a primary particle (P2). Reservoir droplets supply the monomer to reaction sites through the aqueous phase. Non-nucleated micelles disappear rapidly to provide surfactant for the surfaces of growing particles...

The process of emulsion polymerisation begins when the free radicals derived from the, usually water-soluble, polymerisation initiator enter the monomer-saturated micelles where they find a sufficient number of solubilised molecules to start a rapid chain reaction (Elgood and Gilbekian, 1973). Each polymer radical first exhausts the monomer contained in the micelle and then captures additional supplies from 50 or more other micelles before the chain reaction is terminated. Some of the depleted micelles then break up and the released emulsifier molecules are adsorbed at the surface of the newly formed primary polymer particles (Dunn, 1971). The remainder are replenished by diffusion from the emulsified monomer droplets, which act essentially as reservoirs. 

A polymer molecule is composed of a large number of repeating units (each of which is known as a mer) supplied by a molecule known as a monomer in a process called polymerisation. The bonds between adjacent mers are strong covalent bonds but, in the absence of cross-linking, the chains themselves only interact through weak van der Waals forces. 

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