SynopsisThe structure of the 1:2 copolymer of divinyl ether and maleic anhydride was investigated by W-NMR spectroscopy. The polymer contains the bicyclic unit composed of one molecule of each monomer and the maleic anhydride unit. The carbon chemical shift for these units was calculated on the basis of the chemical shift of many model compounds. The major peaks of the cyclopolymer prepared in chloroform were consistent with the presence of the symmetrical bicyclic unit with cis junction and the trans monocyclic anhydride unit. The carbonyl carbon spectrum for the copolymer obtained in a mixed solvent of acetone and CS2 suggested the predominant formation of the unsymmetrical bicyclic unit. The polymerization process was discussed on the basis of these results.
ABSTRACT:The radical polymerizations of divinyl ether (DVE), cis-propenyl vinyl ether (PVE) and 2-methylpropenyl vinyl ether (CH 3 -PVE) were carried out with AIBN initiator. The polymers were composed of five-membered monocyclic units with pendent unsaturated groups and [3,3,0]bicyclic units. The bicyclization was favored at low monomer concentrations and with methyl-substituted monomers. The microstructures of the polymers were determined by 13 C-NMR spectroscopy, through extensive use of the model compounds. A common cyclopolymerization process has emerged from the data obtained. The monomers react exclusively at the unsubstituted vinyl group, and the trans ring closure produces five-membered monocyclic radicals which then propagate intermolecularly or cyclize to give trans-fused bicyclic units.KEY WORDS 13 C-NMR Spectroscopy I Cyclopolymerization I Poly-(divinyl ether) 1 Poly(cis-propenyl vinyl ether) 1 Poly(2-methylpropenyl vinyl ether)
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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