Batch Polymerization Process (06-Oct-2009)

Batch Polymerization Process

This article relates to a polymerization process for preparing polymers.  In particular, a process for preparing condensation and step growth polymers using a batch process that utilizes the unique mixing capabilities of the SC mixer produced by Design Integrated Technologies Inc.

Polyesters, polyamides, and polyurethanes are families of step growth or condensation polymers of commercial importance.  These materials are used to produce products that range from adhesives, sealants and coatings; to capsules in the pharmaceutical industry.  The production of these materials in the absence of solvent is desired, especially in the case where the final application of the material is desired to be solvent free.  Bulk processing of these polymers can produce materials with viscosities as high as 3*10⁶ cps, which makes them very difficult to process.  Also, the continuous production of these materials often requires the production of large quantities thereby making the production of small qualities commercially undesirable.

A method of producing small, solvent free quantities of material involving mixing all of the raw materials in a batch reactor and allowing enough residence time to allow the polymer to fully react will be presented in this article.  The mixing may also be manipulated to control the molecular weight distribution of the polymer.  As stated earlier this process could result in a polymer with a viscosity as high as 3*10⁶ cps.  Most conventional mixers are incapable of mixing liquids this viscous particularly when the mixing involves two materials of very different volumes or viscosities.  The conventional mixers are defined as a cylindrical tank with a pitch blade or radial impeller; or a cylindrical tank with a helical ribbon or screw type impeller.  Further, a highly viscous product produced in a cylindrical tank would be difficult to remove resulting in long batch cycle times.

All of these issues can be resolved by producing the polymer in a conical vessel with close clearance helical impellers to remove the material from the vessel walls.  Mixing can be further enhanced by the presence of a central screw in the vessel.  This central screw can assist the helical impeller in the mixing process and can then be used to discharge the highly viscous final polymer.  Another advantageous feature of a bulk polymer batch reactor is that it provides the operator with increased flexibility with regards to raw material additions and th...