Parylene is green polymer chemistry. Parylene is the trade name for a variety of chemical vapor deposited poly(p-xylylene) polymers used as moisture and dielectric barriers. Among them, Parylene C is the most popular due to its combination of barrier properties, cost, and other processing advantages.
The man who unlocked Parylene — Michael Mojzesz Szwarc
By 1947, Michael Mojzesz Szwarc had escaped the ravages of Eastern Europe and was launching an academic career in Physical Chemistry at the University of Manchester, England. His interest in the strength of individual chemical bonds had developed to the point of investigating a class of aliphatic carbon-hydrogen bonds in which the carbon was directly attached to a benzene ring. Experimentally, he heated the simplest compounds having these groups, toluene and the xylenes, ortho-, meta- and para-, as gases to very high temperature. Michael followed their degradation products and the rates at which they decomposed, both as a function of temperature.
Para-xylene stands out for the first time.
In the para-xylene case only, downstream from the pyrolysis zone in the cooler reaches of the glass equipment, a tan colored deposit formed, which on disassembly of the apparatus could be removed as a thin, flimsy, tube-shaped mass, "the skin of a small snake". Michael Mojzesz Szwarc correctly deduced that it had been formed by the polymerization of a specific reaction product of p-xylene, called p-xylylene.
Looking beyond the results. Seeing performance characteristics.
Taking his observations one step beyond the immediate requirements of his project (a model investigator), Michael noted the new polymer's exceptional physical and chemical inertness and wondered whether this "Szwarcite" might have some utility. Michael's 'snakeskin' was the world's first vapor deposited poly (p-xylylene or para-xylylene) (PPX). Today, its purer colorless form is what we know call Parylene N.
Para-xylene application research begins as plastics grow.
At the time of Michael Mojzesz Szwarc's discovery in the late 1940s, the young and growing plastics industry was in search of better thermal stability in prospective new polymers. Michael's observations inspired vigorous research in many industrial laboratories, including I.C.I. in the U.K. and DuPont, Kellogg and Polaroid in the U.S.
A few years later, William Franklin Gorham at Union Carbide proposed using the very stable dimer of the reactive p-xylylene, di-p-xylylene (DPX), or [2.2] paracyclophane, as the feedstock for an industrial Vapor Deposition Polymerization (VDP) process to produce PPX. Gorham demonstrated that the necessary reactive intermediate could be produced quantitatively in pure form from DPX under milder conditions than those required for its production from p-xylene. A further advantage of the Gorham proposal was the absence of gaseous by-products, a feature of the production of p-xylylene by all other means presently known.
The trouble with the Gorham proposal was that DPX was only a chemical curiosity at the time. It had been isolated as an impurity in the Szwarc snakeskin, and only tiny amounts were available for its characterization in 1949. Its peculiar strained structure intrigued the academic community, and soon the problem of its synthesis by more conventional means was reported solved in 1951 at the U.C.L.A. Laboratory of Donald Cram (Nobel Laureate, 1988). However, much work remained to be done at Union Carbide before the Gorham proposal could be considered a commercially viable process.
Parylene is commercialized in 1965.
February 17, 1965, all work by Gorham and Union Carbide reached a turning point with an announcement of the availability of a new polymeric coating system. 'Parylenes' was the term used to describe both a new family of polymers plus a unique vacuum method for applying them. Truth be known, Union Carbide developed over 20 types of Parylene, but for numerous reasons, only 3 were deemed commercially viable.