Monday, June 16, 2014

When does the "chemistry" disappear in a polymerization?

Polymer chemistry is unique amongst all synthetic fields in that the final product is seldom considered a "chemical".

Anyone attempting to argue with this statement is not going to get too far. Consider the Big 6 polymers - the polyethylenes (both high and low density), polypropylene, polyester, vinyl, and polystyrene. These make up 76% of all polymer production, and yet not a single one is used as a chemical reagent. And most other polymers beyond the Big 6 also fit this description, such as ABS, nylon, PEEK, polycarbonate...They are all produced from chemicals and yet the end product is desired entirely on the basis of physical properties.

Polymerization chemists have long recognized this, and every textbook on the matter has sections describing how different chemical structures within the monomer affect the final mechanical properties. For instance, ethylene oxide in the backbone adds flexibility. And alkyl side chains lower the glass transition temperature as the side chain increases - but only to about C8, afterwhich the side chains start to crystallize. And so on.

And while some may praise chemists such as George Whitesides for challenging chemists to "move beyond the molecule", polymer chemists have been doing this since polymer chemistry began some 3500 years ago.

This is not to say that "polymers-as-reagents" don't exist. They do and are commonly known as reactive polymers, but they are such a tiny fraction of commercial polymers as to be a mere outlier rather than a serious contender for "polymers-as-chemicals".

So when does the "chemistry" disappear?

P.S., I have some more thoughts about this subject, some that will completely invert the subject, but they have to wait until tomorrow.

Previous Years
June 16, 2011 - UV Abosrption and Sun Protection Factors

June 16, 2009 - A sign of economic turnaround?

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