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Author Topic: Is there a monomer that will polymerise in air to form a protective layer?  (Read 4701 times)

Offline rabbit1

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I am interested in learning about how polymer films form when a dissolved monomeric material comes in contact with air. In the same way that an apple produces a protective (brown) skin when cut, I want to know what sort of monomer will polymerise in contact with air to form a similar sort of protective skin that halts the polymerisation process. Can anyone help?  Thanks!
« Last Edit: 22/06/2008 14:27:27 by chris »


 

Offline chris

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A lot of polymerisation reactions rely on free radical initiators. Benzoyl peroxide and styrene is a good example. These are the base of car repair pastes and fillers. You mix a small amount of the initiator - the peroxide - with a large amount of the monomer - the styrene.

The radicals from the peroxide rob odd styrenes of an electron; these "radicalised" monomers then make good their electron deficiency by forming a covalent bond with another styrene molecule, and so on.

But, the hardener isn't actually critical to the process. If you leave the styrene out in the air for long enough there are sufficient sources of radicals in the environment - including ionising sunlight (UV) to trigger the process.

Therefore, all you'd need to make your self-healing surface would be some kind of chemical that would react very nicely with oxygen to produce some radicals, and a monomer. What those chemicals might be though, I am not sure, so I shall have to defer to a professional chemist to tell us...!?

Chris
 

Offline RD

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Quote
1: Nature. 2001 Feb 15;409(6822):794-7. Links
Autonomic healing of polymer composites.
White SR, Sottos NR, Geubelle PH, Moore JS, Kessler MR, Sriram SR, Brown EN, Viswanathan S.
Department of Aeronautical and Astronautical Engineering, University of Illinois at Urbana-Champaign, Urbana 61801, USA.

Structural polymers are susceptible to damage in the form of cracks, which form deep within the structure where detection is difficult and repair is almost impossible. Cracking leads to mechanical degradation of fibre-reinforced polymer composites; in microelectronic polymeric components it can also lead to electrical failure. Microcracking induced by thermal and mechanical fatigue is also a long-standing problem in polymer adhesives. Regardless of the application, once cracks have formed within polymeric materials, the integrity of the structure is significantly compromised. Experiments exploring the concept of self-repair have been previously reported, but the only successful crack-healing methods that have been reported so far require some form of manual intervention. Here we report a structural polymeric material with the ability to autonomically heal cracks. The material incorporates a microencapsulated healing agent that is released upon crack intrusion. Polymerization of the healing agent is then triggered by contact with an embedded catalyst, bonding the crack faces. Our fracture experiments yield as much as 75% recovery in toughness, and we expect that our approach will be applicable to other brittle materials systems (including ceramics and glasses).

PMID: 11236987 [PubMed]
http://www.ncbi.nlm.nih.gov/pubmed/11236987
 

Offline chris

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Thanks RD - but the article you quote doesn't contain much in the way of a recipe for the chemicals required...
 

Offline Bored chemist

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Linseed oil.
 

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