A new class of polymers

For years, polymer chemistry textbooks have stated that 1,2-disubstituted ethylenes could not be transformed into polymers.

However, University of Delaware (UD) polymer chemist Chris Snively and professor of chemical engineering Jochen Lauterbach were determined to prove the textbooks wrong. As a result of their persistence, the researchers have discovered a new class of ultra-thin polymer films with potential applications ranging from coating tiny microelectronic devices to plastic solar cells.

The discovery was reported as a &quotcommunication to the editor" in the Nov 28 edition of Macromolecules, a scientific journal published by the American Chemical Society.

The research, which also involved doctoral student Seth Washburn, focused on formerly nonpolymerisable ethylenes. Among them are several compounds that are derived from natural sources, such as cinnamon, and are FDA approved for use in fragrances and foods. One of the compounds is found in milkshakes, according to the scientists.

&quotThere''s been a rule that these molecules wouldn''t polymerise," Snively, who is a research associate in Lauterbach''s laboratory group, noted. &quotWhen I first saw that in a textbook when I was in graduate school, I said to myself, ''Don''t tell me I can''t do this.''"

And thus, the quest to disprove a widely accepted scientific rule of thumb began.

Since the late 1990s, Lauterbach and Snively have been developing a method to make extremely thin polymer layers on surfaces. These nanofilms - at least 1000 times thinner than a human hair - are becoming increasingly important as coatings for optics, solar cells, electrical insulators, advanced sensors and numerous other applications.

Formerly, to make a pound of polymer, scientists would take a monomer and a solvent and subject them to heat or light. Recently, Lauterbach and Snively developed a new polymer-making technique that eliminates the need for a solvent.

Their deposition-polymerisation (DP) process takes place in a vacuum chamber, where the air is pumped out and the pressure is similar to outer space. The material to be coated, such as a piece of metal, is placed in the chamber, and the metal is cooled below the monomer''s freezing point, which causes the monomer vapour to condense on the metal. Then the resulting film is exposed to ultraviolet light to initiate polymerisation.

The two-step process allows for the formation of uniform, defect-free films with thicknesses that can be controlled to within billionths of a metre.

The process is fairly ''green'' in that not only are no solvents used, but there is very low energy consumption using this method, according to Lauterbach.

&quotYou can also do photolithography with it," he said, meaning that the polymer will appear only where the light hits the monomer film.

While their polymerisation technique was reported a few years ago, the class of materials the UD scientists have applied it to lately is new and unique.

&quotWe can make nanometre-thick films, but we can''t make a gram of the material yet," Snively noted. &quotWe''re working on ways to scale up the process."

The scientists also want to find out if the materials may be stronger, tougher or possess unique properties compared to other polymers.

&quotIt''s exciting because you don''t really know what all their properties are yet," Snively said.

As for all the potential applications, Lauterbach said, &quotWe''re kind of in the discovery phase, looking to see where all these materials could be used."

And until the current polymer textbooks are revised, Lauterbach and Snively will take great relish when they ask their students to make note of a change in the margins.

&quotRight now, the excitement for us is that we''ve proved textbooks wrong," Lauterbach said.