Solution Polymerization

Solution polymerization is a method of industrial polymerization. In this procedure, a monomer is dissolved in a non-reactive solvent that contains a catalyst.

The reaction results in a polymer which is also soluble in the chosen solvent. Heat released by the reaction is absorbed by the solvent, and so the reaction rate is reduced. Moreover the viscosity of the reaction mixture is reduced, not allowing auto acceleration at high monomer concentrations. Once the maximum or desired conversion is reached, excess solvent has to be removed in order to obtain the pure polymer. Hence, solution polymerization is mainly used for applications where the presence of a solvent is desired anyway, as is the case for varnish and adhesives. It is not useful for the production of dry polymers because of the difficulty of complete solvent removal.

This process is one of two used in the production of sodium polyacrylate, a super absorbent polymer used in disposable diapers.

Notable polymers produced using this method are polyacrylonitrile (PAN) and polyacrylic acid (PAA).

Solution polymerization is used to create polymers and copolymers by dissolving a monomer and a catalyst in a non-reactive solvent. During this process, the solvent liquid absorbs the heat generated by the chemical reaction which controls the reaction rate. The liquid solvent used in the solution polymerization procedure usually remains a solvent for the resulting polymer or copolymer. This process is only suitable for the creation of wet polymer types, as the removal of excess solvent is difficult. While removal of excess solvent is possible using distillation, it is usually not considered economically possible in an industrial situation.

The process of solution polymerization offers a few advantages as well as one major disadvantage. The advantages include precise control of the chemical reaction, control of the resulting heat and viscosity, and control over auto acceleration of the process. The disadvantage of the process is the difficulty involved in the removal of excess solvent from the finished polymer.

The solvents used in the solution polymerization procedure must be chosen carefully. A solvent that is non-reactive to the monomer is essential to the process. If a reactive solvent is used, dangerous chain reaction processes or other undesirable effects can occur as a result of auto acceleration. Auto acceleration is a reaction that occurs when the heat produced by polymerization does not dissipated quickly enough by the solvent. As the heat builds up, the viscosity of the solution increases, causing the polymerization process to accelerate beyond safe control.

Industrial solution polymerization processes are commonly used to produce polymers with special characteristics. The chemical reaction that takes place between the monomer and catalyst can lend unique properties to the end product. One example of this type of polymer is sodium polyacrylate, the exceptionally absorbent polymer used in disposable diapers.

While this process is not generally feasible for dry polymers, it works well for wet polymer types. The process of industrial solution polymerization is used to create polymers and copolymers that can be used in their solution form. Examples of this usage include industrial glues and surface coatings.

Synthetic elastomers can also be produced using the solution polymerization process. This method produces a more precise polymer than emulsion polymerization methods. By controlling the addition of refined monomers to the catalyst-solvent solution, the resulting polymers can be carefully designed for specific properties. These synthetic elastomers are commonly found in products such as latex gloves, neoprene wetsuits and floor covering materials

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