Initiation of polymerization with substituted ethanes, 13. Free radical polymerization of methyl methacrylate and styrene with substituted succinonitriles

Abstract

AbstractTetraarylsuccinonitriles 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.