Radical polymerization rearrangement

Experimental conversion-time data, obtained from the literature, on the bulk free radical polymerization of MMA initiated by AIBN at several temperatures and initiator concentrations, were described by the model. However, the expressions for the rate of conversion and gel effect index were first simplified and rearranged. ... 

New seven-membered diazepinone alkoxyamines 394 for nitroxide-mediated radical polymerization were prepared through the Beckmann rearrangement (equation 159). 

Radicals can undergo other reactions such as rearrangements and fragmentations. These are also propagation reactions by definition but they do not concern us here because free-radical polymerizations are not usually performed under conditions in which these processes are significant. 

Some monomers isomerize during cationic polymerization. The net result is that the structure of the polymer repeating unit is not the same as that of the monomer. This occurs if the carbocation which is formed by initial attack on the monomer can isomerize to a more stable form. Isomerization is more prevalent in cationic than in anionic or free radical polymerizations because carbenium or oxonium ions rearrange easily. 

Bergbreiter, D. E., Waichuk, B. Meisenheimer Rearrangement of Aiiyi N-Oxides as a Route to Initiators for Nitroxide-Mediated "Living" Free Radical Polymerizations. Macromolecules 1998, 31, 6380-6382. 

A polymeric pinacol,poly[3-methyl-2-(4-vinylphenyl)-2,3-butanediol],has been prepared by radical polymerization of the styrenic diol monomer and shown to be cleanly and quantitatively converted to a non-conjugated ketone in the solid state by reaction with a photochemically-generated acid [151,348, 350]. The rearrangement reaction can be readily monitored by IR spectroscopy as the disappearance of the hydroxyl OH absorption is accompanied by appearance of a new ketone carbonyl absorption (Fig. 116). Since a polar alcohol (isopropanol) dissolves the polar diol polymer in the unexposed regions but cannot dissolve the less polar ketone polymer produced in the exposed regions, the resist functions as a negative system with alcohol as a developer. The diol polymer is stable thermally to 225 °C in the absence of acid. 

Another route to PHOST synthesis, pioneered at Hoechst-Celanese, is the radical polymerization of 4-acetoxystyrene, followed by base hydrolysis in ammonium hydroxide. The 4-acetoxystyrene is readily prepared via Friess rearrangement of phenyl acetate to form 4-hydroxyacetophenone, followed by protection of the OH group with the acetyl group, and followed by reduction to carbi-nol, and finally, dehydration to yield the monomer. " ... 

Propagation involves the consecutive additions of monomer molecules to the carbonium ion at the growing chain end. Termination in cationic polymerization usually involves rearrangement to produce a polymer with an unsaturated terminal unit and the original complex or chain transfer to a monomer and possibly to the polymer or solvent molecule. Unlike free-radical polymerization, termination by combination of two cationic polymer growing chains does not occur. 

In free radical polymerizations, polymerization equilibria can be observed especially well with diradicals. For diradicals, the combination of two monomer radicals leads to a new diradical. Bicyclo[2.2.1]-heptene-2 and SO2, for example, copolymerize spontaneously. In this case, an adduct compound is first formed, and this then rearranges to give a diradical ... 

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