Molecules: You'd better learn to live with them.
Yesterday's entry on epoxides may have brought to mind epoxies. The similarity isn't a coincidence. Chloromethylepoxide, or "epichlorohydrin," is the basis for many epoxy adhexives.
One tube contains some epoxide, such as epichlorohydrin, along with some bisphenol A - the very same stuff you find in polycarbonate. This is actually partially polymerized ("oligomers") - the degree of polymerization and ratio of epichlorohydrin to bisphenol A can determine how hard an epoxy you get - this is often the basis for "soft" epoxies.
It's not over yet, though. Tomorrow I'll cover what's in that other tube.
Comments
The image link's broken; change
epichlorohyhdrin.gif to epichlorohydrin.gif.
The full link:
http://scienceblogs.com/moleculeoftheday/images/epichlorohydrin.gif
Posted by: Nick | March 21, 2007 9:53 AM
Epichlorhydrin was also a very minor contaminant in commercial trichloroethylene (TCE), a common degreasing agent that is a prevalent groundwater contaminant. When NIH did animal bioassays of TCE in the seventies they found it was an animal carcinogen but had to redo the results because of the epichlorhydrin contamination (also a carcinogen).
Posted by: revere | March 21, 2007 10:11 AM
Epoxy resins usually initiate failure at the opened epoxide linkage, hence high temp systems with anhydride rather than amine cures, e.g., diglycidylbisphenol-A plus styrene maleic anhydride copolymer or bridged bis(phthalic anhydride)s. Improved properties are also obtained by being more clever than bisphenol-A.
The condensation of phenol plus aldehyde or ketone in dilute aqueous sulfuric acid is general and rapid. It is one of the few facile routes to quaternary carbon centers. Acetone is cheap. Other ketones give much more interesting bisphenols - hexafluoroacetone, cyclopentanone, acetophenone, benzophenone, fluorenone, [dihydro]isophorone... and [N-methyl] 2,2,6,6-tetramethyl-4-piperidone (triacetoneamine) or N-hydroxy-2,2,6,6-tetramethyl-4-piperidone by using hydroxylamine rather than ammonia.
High MW polycarbonate plastics with more hindered quaternary carbons polymerized in situ by opening of low viscosity molten cyclic oligomers have extraordinary high temperature properties.
Posted by: Uncle Al | March 21, 2007 6:04 PM