Levels of Residual Monomer(s) in Acrylic Polymers
All acrylic polymers will contain some level of residual, unpolymerized monomer whether intentional, or as a byproduct of the polymerization process. The level of residual monomer(s) in the polymer will depend upon the polymerization process employed, the monomers involved, and the conditions of polymerization. Acrylic polymers that are used in sensitive product applications such as medical or dental products
or highly technical applications are usually subject to stringent compositional standards that include limiting levels of residual monomers that ensure safety in use, and compliance with industry and regulatory standards.
Emulsion polymerized polymers have the lowest residual monomer levels of any industrial produced acrylic polymer with levels in the range of 0.01% to 0.05%. These low levels are achieved as the hydrophobic monomer tends to partition preferentially into the latex particle where it is incorporated extremely efficiently into the polymer.
Typically bulk polymerized polymers that are used for molding processes including injection molding, compression molding and extrusion, will have residual unreacted monomers present in the final polymer in a range of 0.1% to 0.9%, although some of this residual monomer may be evolved during thermal processing.
Since cast sheet produced PMMA has a lengthy polymerization phase it tends to have the highest molecular mass and the lowest levels of residual monomer of any bulk polymerized polymer and is typically in the range 0.05% to 0.3%, although shortened polymerization cycles can lead to higher residual monomer levels.
Continuous cast produced acrylic sheet in contract has residual monomer levels in the polymer closer to that of bulk polymerized polymers.
Solution polymerized polymers provided in a hard pellet form will typically contain residual monomer levels similar to bulk polymerized polymers. Solution polymerized polymers provided in solvent will contain relatively high levels of residual monomer but since they are in solution in organic solvent these levels are insignificant compared to the high solvent content.
In all cases, questions about issues related to residual monomer content of a specific product should be directed to the supplier of the product.
1 FDA Good Manufacturing Practices (GMP). International Standard ISO 13485:2003 for medical device manufacturing, the design standard EN ISO 9001:2008 and the EU Implantable Medical Device Directives EN 46002
