Ambient Polymerization of Acrylic Pressure Sensitive Adhesives

Traditional solution acrylic polymers for pressure sensitive adhesives (PSA) are synthesized using conventional free radical initiation systems based upon organic peroxide or azo compounds 1 . Such syntheses are heat activated and employ solvent reflux temperatures during the polymerization process. The resulting acrylic polymers are formed with a relatively broad molecular weight distribution which can diminish both the processing and adhesive performance of the final product. To overcome this limitation, a variety of controlled radical polymerization (CRP) methods have been developed to synthesize acrylic polymers with controlled architectures including nitroxide-mediated CRP (NM-CRP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT) 2-3 . These techniques provide control of molecular weight and can produce polymers with narrow molecular weight distributions. However, these techniques can be expensive, require long preparation times, use heavy metal catalysts and/or have significant odor. For applications such as PSAs where high structural precision is helpful not essential, the additional processing costs render CRP difficult to justify over conventional polymerization schemes. Using a novel polymerization initiator system, it is now possible to synthesize acrylic polymers with controlled molecular weights of unexpectedly narrow distributions in facile ambient atmospheric conditions. These novel acrylic PSAs exhibit improved control of adhesive performance over conventional free radical initiation systems without the processing complications of CRP methods 4 .