Supernonnucleophilic

I have a B.S. in Biochemistry and it's coming in use on a freelance article for a European patent award. Some dudes patented a way to make "living" polymers, as in always growing, never stopping until you want them to.

A lot to do in a short while.

Just finished the article. It was great to get back into the meat of science again: mechanisms of reaction, carbocations, olefins, tert-butyls, polyisobutylene, etc. Got to speak with Dr. Joseph Kennedy, of the University of Akron, Ohio, about his ground-breaking 1986-ish invention of a "living" cationic polymer process. That's just fancy talk for building molecules with a reactive end that is a cation, has a positive charge. You ask: Just what is "living" polymerization? When I first got the assignment that question jumped out at me, too - and there weren't quotes around "living" in many of the documents I was reading, i.e. original European Patent Documents - pages and pages of technical, in-depth descriptions of reaction processes/structures/possible outcomes. The patent documents are riddled with ridiculous language, numerous noncommittal, all-encompassing quotes, repeated over and over "It is preferred, though not requisite," "not particularly restricted but is preferably ... ." I guess the idea is to establish as wide-ranging a sphere to your patent as possible, so that any other patents might infringe on your territory and get you P A I D. See the European Patent document associated with the invention here.

The "living" aspect of the polymerization process is quite interesting, and Kennedy and Rudolf Faust's breakthrough with the carbocationic version of it is a good story, recounted by Kennedy here in 1999, volume 37 of the Journal of Polymer Science: Part A: Polymer Chemistry. The living aspect of living polymerization allows polymer scientists to have complete control over the polymer they are building; they are able to terminate the growth at any moment, cap the polymer with specific functional groups and or add one or more repeating groups of monomers to form what are called block copolymers (or terpoloymers (three monomers)), etc. The control results in precisely structured, and sized, polymers: an extremely useful tool for synthetic polymer chemists, as you can imagine. Living anionic polymerization had been around since the 1950s, but living cationic polymerization was very difficult because carbocations are extremely reactive. Dr. Kennedy and Dr. Faust found out how to prevent the growing end of the polymer from reacting with the polymer's body in what's called a chain transfer. Also, nonliving polymerizations terminate randomly, resulting in a bunch of polymers of different sizes (molecular weights). The cation process opened up the living polymerization world to olefins (typical carbon-hydrogen molecules with a double bond of the form CnH2n) like isobutylene, the basis of elastomeric polymers like widely-used butyl rubber. The olefins are cheap and readily available, so the wide applicability of the process is promising, cause money makes the world go round.

The notable extension of living cationic polymerization has been Boston Scientific's Taxus® drug-eluting cardiovascular stent. The invention was used to make a complex block copolymer that coats the stent (a device placed in portions of the heart to unblock it/facilitate its working) that gave it both the valuable property of biocompatibility, but also a finely-tuned drug-eluting mechanism. The block copolymer, made by mixing monomers of thermoplastic and elastomeric properties in an exact proportion provided the biocompatibility and also its specific, timely release of important drugs that aid a patient's recovery. Over five million of these Taxus® cardiovascular stents have been used worldwide.

One of Dr. Kennedy and Dr. Faust's key discoveries was a supernonnucleophilic counteranion complex that would stabilize the charge on the reactive carbocation of the growing polymer chain, but resist the extreme temptation, as its anionic nature would dictate, to nab the carbocation's proton and thus kill the polymerization. Supernonnucleophilic anion is basically an oxymoron, but Kennedy and Faust figured it out, and thus "living" cationic polymerization was born.