D. Braun, Thomas Skrzek
Feb 1, 1995
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0
Influential Citations
15
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Journal
Macromolecular Chemistry and Physics
Abstract
Tetraarylsuccinonitriles 2 were synthesized via oxidative dimerization of diarylacetonitriles 1 in basic media. The thermal decomposition of 2 results in two identical diarylcyanomethyl semi-radicals 3. The dissociation energy (Ea) measured using the thiophenol radical scavenging technique was found to amount to 94,3 ± 9,2 kJ/mol in the case of tetraphenylsuccinonitrile 2a. Tetraarylsuccinonitriles 2 show an atypical “stepwise” initiation mechanism in free-radical polymerization, particularly in the case of methyl methacrylate (MMA) as monomer. In the initial phase of the polymerization reaction a very high concentration of diarylcyanomethyl primary radicals 3 leads to the formation of short-chain telechelics with both end groups originating from the initiator. In the further course of the polymerization these MMA telechelics are able to re-form radicals by the scission of thermolabile carbon-carbon bonds and by the release of initiator end groups, and so the MMA telechelics ‘re-initiate’ the free-radical polymerization (“resuscitable free-radical polymerization”). In styrene polymerization, tetraarylsuccinonitriles 2 indeed cause a pronounced primary radical termination effect, but the styrene telechelics formed in contrast to MMA telechelics are thermostable, and therefore no “re-initiation” effect occurs. The X-ray structure determination of the styrene telechelic 2,2,3,5,5-pentaphenyladiponitrile 4a exhibits a bond length of the thermolabile carbon-carbon bond of 158,7 pm as compared to 162,8 pm of the corresponding MMA telechelic 2,2,5,5-tetraphenyl-3-methoxycarbonyl-3-methyladiponitrile and emphasizes the higher thermal stability of 4.