Radical Cyclopolymerization of Divinyl Ether. The Microstructure of the Polymer and the Cyclopolymerization Mechanism

Abstract

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...

Radical Cyclopolymerization of Divinyl Ethers. The Polymerization Kinetics and the Polymer Structure.

“…5 The complete removal of the pendent group was confirmed by NMR spectroscopy and the NMR data were consistent with the elemental analysis.…”

“…5 The same situation arises for poly(PVE) and poly(CH 3 -PVE). As will be discussed below, the pendent groups were invariably substituted vinyl groups (propenyl and methylpropenyl groups), and single five-membered intermediates were formed stereoselectively which produced the corresponding monocyclic and bicyclic units.…”

“…5 PYE was prepared by the isomerization of allyl vinyl ether obtained by the exchange reaction of nbutyl vinyl ether and allyl alcohol in the presence of Hg (OAc)z according to the procedure of Watanabe et a/. 6 : bp 66-67°C, lit 6 bp 66-67°C.…”

“…The structure of Poly(DVE) was determined in our previous paper 5 by comparing the 13 C-NMR spectrum of the polymer with the chemical shifts calculated using model compounds (methylcyclopentanes and 2,5-dimethylcyclopentane). Recently, there were published 13 C-NMR data of more appropriate model compounds.…”

Radical Cyclocopolymerization of Divinyl Ether Derivatives with Maleic Anhydride. The Structure Determination of the Alternating Copolymers by 13C-NMR Spectroscopy

“…7 • 8 cis-Dipropenyl ether (OPE) was prepared by the base-catalyzed rearrangement of diallyl ether. Diallyl ether (bp 94-95°C, lit 9 94°C) was treated by potassium tert-butoxide in dimethylsulfoxide at 90°C for 90 h. The isomerized product was distilled, washed with alkali and water, and redistilled: bp 90-92°C (lit 10 90-94°C), 0.8016.…”