Radical polymerization (AIBN initiator) of divinyl ether yielded partially cyclized, soluble polymers. The pendent vinyloxy group could be completely removed by treating the polymers with 2% hydrochloric acid in methanol. Based on 13C-NMR spectra of these polymers, the original polymer was concluded to contain a five-membered monocyclic unit with the pendent vinyloxy group and a bicyclic unit (dioxobicyclo[3.3.0]octane system) in the 1:l ratio. The carbon chemical shifts expected for all the possible stereoisomers of these structural units were estimated using a number of model compounds. Apparently a single stereoisomer was formed for both the monocyclic unit (trans ring closure) and the bicyclic unit (with the trans junction). Finally, the steric course of the cyclopolymerization was compared with those of the related systems.Divinyl ether undergoes radical polymerization t o produce soluble polymers with highly cyclized structures.2 Aso et al.3 proposed that t h e polymer contained bicyclic s t r u c t u r e s and uncyclized units, and G u a i t a e t al.* suggested t h e presence of the monocyclic and bicyclic s t r u c t u r e s on t h e basis of kinetic and stereochemical considerations. Recently, we reported briefly that among m a n y conceivable structural units shown in Figure 1, the polymer coqtained an unsaturated unit S, o and a bicyclic unit SS5 in the 1:l ratio.5 In this paper, we describe t h e s t r u c t u r e d e t e r m i n a t i o n of the polymer in detail. T h e stereochemistry of t h e cyclic unit is also described, and the cyclopolymerization process is discussed based on these s t r u c t u r a l data. Experimental SectionMaterials. Divinyl ether (Japan Oil Seal Co.) was washed with aqueous alkali and water, dried over KOH, and distilled from CaH,, bp 27-28 "C. Azobis(isobutyronitri1e) (AIBN) was recrystallized from ethanol. Bicyclo[3. 3.O]octane (Chemical SampleCo.) was confirmed to be sufficiently pure by gas chromatography (impurity peak less than 1%): mp -52 to -50 "C (lit.6 mp below -80 "C (cis isomer), -30 "C (trans isomer)); d'84 0.8703, d'64 0.8721 (lit.6 dLS4 0.8716 (cis isomer), d16, 0.8648 (trans isomer)). The bicyclooctane was concluded to be in the cis configuration from these data. Solvents were purified in the usual procedure.Polymerization. Given amounts of monomer, AIBN, and solvent were placed in ampules and subjected to the freezepump-thaw cycle several times. The ampules were then sealed in vacuo and immersed in a polymerization bath. The polymer was recovered by precipitation in methanol, purified by reprecipitation from benzene and methanol, and freeze-dried. The polymers were white powders and soluble in many common solvents when not cross-linked. The polymerization results are summarized in Table I. Gelation occurred frequently at higher polymerization temperatures or a t greater conversions. The amount of the residual double bond was determined by 'H-NMR spectroscopy (CC14 solvent, Varian A60 instrument) from the relative peak area of the vinyl methine proton (6.0...
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