Radical ring-opening

The chemistry of polymerization of the oxetanes is much the same as for THE polymerization. The ring-opening polymerization of oxetanes is primarily accompHshed by cationic polymerization methods (283,313—318), but because of the added ring strain, other polymerization techniques, eg, iasertion polymerization (319), anionic polymerization (320), and free-radical ring-opening polymerization (321), have been successful with certain special oxetanes. 

Reviews on radical ring-opening polymerization include those by Sanda and Endo,172 Klemm and Schultz,173 Cho,1 4 Moszner et at.,175 Endo and Yokozawa176... 

Quinone methides 156 and 157 were generated on irradiation of the cis and trans forms of 155, respectively (Eqs. 1.42 and 1.43).99 100 The mechanism is believed to involve a radical ring opening of the cyclopropane ring, followed by hydrogen or methyl migration. 

Scheme 3.44. General scheme of domino radical ring-opening reactions of cyclopropyl ketones...

Scheme 3.45. Domino radical ring-opening/cyclization procedure for the synthesis of spiroketone 3-171.

As discussed previously, radical ring-opening reactions of three-membered systems via cyclopropylmethyl and oxiranylmethyl radicals represent a fruitful method in organic synthesis [111]. De Kimpe and coworkers have now shown that azirid-ines can also be used, featuring a radical one-step synthesis of pyrrolizidines 3-280... 

Ionic and Radical Ring Opening with Loss of Nitrogen... 

Since it was shown that free radical ring-opening polymerization (2) made it possible to introduce functional groups, such as esters C3j, carbonates (4), thioesters (5), and amides (6), into the backbone of an addition polymer, it was reasoned that simple hydrolysis would produce the desired oligomers that could be terminated with various combinations of hydroxyl, amino, thiol, and carboxylic acid groups. 

BAILEY ET AL. Free-Radical Ring-Opening Polymerization... 

Treatment of this monomer with benzoyl peroxide gave a high molecular weight polyester by a free radical ring-opening polymerization which can be rationalized by the accompanying scheme. The structure of the polyester IV was established by analysis and hydrolysis as well as infrared and NMR spectroscopy. 

Biodegradable Pofymers Produced by Free-Radical Ring-Opening Pofymerization... 

This indicates the possibility of making addition polymers biodegradable by the introduction of ester linkages in to the backbone. Since the free radical ring-opening polymerization of cyclic ketene acetals, such as 2-methylene-1,3-dioxepane (1, Scheme I), made possible the introduction of ester groups into the backbone of addition polymers, this appeared to be an attractive method for the synthesis of biodegradable addition polymers. 

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