Tuesday, November 29, 2011

A Polymer with Reversible CHEMICAL Crosslinks

One bit of research (Science Magazine, subscription required) that had a lot of discussion (here and here) this past week or so has been the development of a "thermoset" plastic that can be heated and allowed to flow as a thermoplastic does.

I do think the research is interesting and should prove to be quite useful in the future, but what I really dislike is all the hype that these reflow characteristics are so unique and novel - they are not. Styrenic block copolymers and other thermoplastic elastomers show this behavior all the time - they are nondeformable materials at room temperature, but when you heat them up, they become liquids that can be shaped to any form you desire. The materials are made up of blocks of two different polymers along the same chain. At room temperature, the blocks phase separate and form physical crosslinks that prevent deformation. Upon heating, the physical crosslinks soften and allow the material to flow.

What is novel in the latest research is that the crosslinks are chemical, not physical. Heat reversibly breaks up the crosslinks, while cooling restores them. That's a neat trick that I've not seen before and is certainly worth the discussion. It's just that the thermomechanical behavior isn't novel.

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