Polymerisation pdf

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Zhang, J. Jiao, Z. Jiao, L. Kong, J. Xu, J. Li, J. Zuo, X. Oledzka, K. Sokolowski, M. Catalyst may be ionic or co-ordination catalyst which can either dissolved or suspended. The presence of inert solvents medium helps to control viscosity, increase and promote proper heat transfer. The product obtained is in liquid phase. For most cases water is taken as solvent. Advantages Disadvantages Heat transfer easy due to presence of High mol.

In this type apart from dispersed particles and dispersion media several other components are added. Usually the dispersion media is water. These droplets have the natural tendency to coalesce and gradually become larger and forms immiscible layer.

In order to discourage this tendency emulsifying agents such as soap like materials are added. Apart from that surface tension regulators, buffers, protective colloids are added to prevent pre-mature coalescence and precipitation of droplets of monomer as well as those of partially polymerized polymer by preventing adhesion of sticky drops. The emulsifying agents are substances with very low solubility in medium and therefore as its concentration is increased, the molecularly dispersed substances begins to form molecular aggregates known as micelles which exists either in spherical form or thin layer.

In micelles because of their hydrophilic and hydrophobic characteristics, the molecules orient themselves so as to have the tails towards centre and head towards water phase. The concentration of emulsifying agent at which ion like molecules begin to form micelle is called critical micelle concentration CMC which changes the rate of change of physical properties When monomer is added which is organic in nature prefers the interior of the micelle because of organic environment.

Micelle has the tendency to contract because of surface tension. Hence the migration of monomer from monomer droplets to the interiors of micelle continues till equilibrium is reached between swelling and contracting tendencies.

When initiators are decomposed in water phase it bounces around the solution to create radicals. At this point the surface area presented by monomer-swollen micelle is much greater than monomer droplets so the probability for radicals to enter the monomer-swollen micelle is very high.

When the radicals enter the micelle it initiates the reaction. Both diffuse. Thus the uninitiated monomer swollen micelles gradually disappear losing their monomer content. When a second radical find its way into the micelle, for the conditions prevailing within the micelle the rate of termination is much greater than the rate of propagation.

Hence chain terminates eventually and remains until a third radical enters, initiating the growth of second chain and so on. Advantages Disadvantages No chain transfer problem and heat Because of several additives added to transfer problem.

The products obtained the system the product obtained in less in the form of latex are directly usable pure when compared to bulk polymerization Very high mol. The size of monomer dispersed is greater compared to emulsion polymerization. Here the monomer is insoluble in dispersion medium.

Initiator, suspension stabilizer are dispersed in water or inert organic liquids provided the monomer and polymer is insoluble in it. The mechanism is similar to mass and solution polymerization. Unlike in emulsion polymerization where close, intimate contact between the two phases is established by emulsifying agent, each bead or pearl of the monomer in suspension polymerization acts as minute, discrete mass polymerization system. A protective colloid such as Magnesium carbonate is insoluble is the solution and collects at the droplet-water interface by surface tension and prevents the coalescence of drops upon collision.

Polymer Science - By Gowariker, V. Principles of polymerization - By George Odian 3. Textbook of Polymer technology — I By R. Sinha 4.