Polyolefin production with preformed solid catalysts

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Abstract
A broad range of plastic and elastomeric materials can be made from olefins by solid catalysts, either precipitated in situ or preformed with high surface area. Solid catalysts have been applied to polymer production in two basic processes: suspension and solution. In the suspension process, polymer is made below its softening point in a medium that dissolves neither catalyst nor polymer. In the solution process, polymer is made in solution with a solid catalyst dispersed in the solvent. The literature implies that suspension polymerization is always used with precipitated catalysts, and solution polymerization with preformed catalysts. However, the processes are independent of the catalysts. For example, a single family of promoted preformed catalysts can produce linear polyethylene of low melt index or polypropylene by a suspension process below 150°C., and linear polyethylene of normal melt index or copolymers of ethylene and α‐olefins by a solution process above 150°C. All these routes produce useful polymers with desirable properties. Suspension polymerization is used when the catalyst requires operation at low temperatures, when the product with desired properties can only be obtained at low temperatures, or when the molecular weight of the polymer is too high to give solutions of reasonable viscosity. Solution polymerization is used when the catalyst permits or requires higher temperatures of operation, when the desired product can be made at these temperatures, or when the molecular weight of the product is low enough to form solutions of viscosities that can be readily handled.

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