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Methods & Processes
Free vs. Controlled Radical Polymerization
Posted: March 13, 2007
Industry expert Tony O’Lenick asks: What is the difference between free radical polymerization and controlled radical polymerization (CRP)? Thomas O’Lenick, a graduate student at the University of Tennessee specializing in CRP, explains.
Radical polymerization is the reaction of vinyl monomers (CH2=CH-R) in the presence of catalyst to make high molecular weight polymers -(CH2CH(R))x-. The process is relatively easy to perform and vinyl monomers are easily polymerized. These properties account for their commercial utilization, both in industrial and in personal care applications.
There are, however, a few problems with conventional radical polymerizations, including free monomer levels and uniformity of the polymer chain. Both of these factors can be very important to the cosmetic formulator.
Recently, new methods have been developed that allow for controlling the radical polymerization to minimize monomer content and produce very uniform molecules. These processes are so-called CRPs. The control comes by a variety of techniques including the use of so-called stable free radical mediated polymerization (SFRP), atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization.
The commonality among these methods is that they all limit and control the number of radicals reacting at any one time. This means that the monomer is added to the active chain end and not to another monomer. Monomer will continue to add to the chain until the polymerization concentration is exhausted.