Polymer Journal, Vol. 13, No. 7, pp 657-669 (1981) Radical Cyclopolymerization of Divinyl Ethers. The Polymerization Kinetics and the Polymer Structure.* Mitsuo TSUKlNO and Toyoki KUNITAKE** Department of Chemical Engineering, Kitakyushu Technical College, Kokura-minami, Kitakyushu 803 and Department of Organic Synthesis, Faculty of" Engineering, Kyushu University, Fukuoka 812, Japan. (Received November 29, 1980) ABSTRACT: The radical polymerizations of divinyl ether (DVE), cis-propenyl vinyl ether (PVE) and 2-methylpropenyl vinyl ether (CH3 -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 13C-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 13C-NMR Spectroscopy I Cyclopolymerization I Poly- (divinyl ether) 1 Poly(cis-propenyl vinyl ether) 1 Poly(2-methylpropenyl vinyl ether) I Divinyl ether (DYE) has been known to give CH3-PYE. Some kinetic studies were also carried soluble polymers with highly cyclized structures by out. radical polymerization, and the structure of the H H cyclized unit has been inferred from the model CHz=Cft CH=CH2 CHz=Cft )>C( 0 0 CH experiments and from the kinetic data. 1 - 3 We 3 DVE PVE recently examined the polymer structure by means H, CH3 of 13C-NMR spectroscopy and concluded that the CH-CH C=C/ T 'cf 'cH cyclopolymerization process involved a five­ 3 CHrPVE membered ring intermediate which would either propagate intermolecularly or cyclize to a bicyclic unit,4 •5 as shown in Scheme l. Interestingly, the cyclization process was highly stereoselective. EXPERIMENTAL In the present study, we carried out a structural Materials study on the cyclopolymers of cis-propenyl vinyl The purification of DYE has been described. 5 ether (PYE) and 2-methylpropenyl vinyl ether PYE was prepared by the isomerization of allyl (CH3-PYE), and compared the effect of the poly­ vinyl ether obtained by the exchange reaction of n­ merization condition on the polymer structure for butyl vinyl ether and allyl alcohol in the presence of each of three related monomers: DYE, PYE, and Hg (OAc)z according to the procedure of Watanabe et 6 : 6 * Contribution No. 611 from Department of Organic a/. bp 66-67°C, lit bp 66-67°C. The isomer­ Synthesis. ization to PYE (cis-isomer) was performed with ** Correspondence should be sent to this author at the reference to the preparation of cis,cis-dipropenyl Fukuoka address. ether7 in the presence of potassium tert-butoxide in 657 M. TSUKINO and T. KUNITAKE stereoselective O-CH=CH CH cyclization I • 2 II 2 M-CH,-CI-:!._ _...CH /CH . Z CH2 '0 kp lntermolecular propagation stereoselective cyclization Scheme 1. dimethylsulfoxide at room temperature for 10 days. Gelation occurred at conversions of ca. 3% in the PVE was separated by distillation under reduced bulk polymerization of DYE, but no gelation occur­ pressure, washed with alkali and water, and re­ red for bulk PVE and CH3-PVE up to conversions distilled: bp 61.5-62.SOC (lit6 61-62°C), of 30--40%. 0. 7899. The isomerization was virtually quanti­ Poly(PVE) tative, but the trans isomer (5%) was also formed. Anal. Calcd for C5 H80: C, 71.33%; H, 9.51 %. Methallyl vinyl ether was similarly prepared by Found: C, 70.93%; H, 9.52%. the exchange reaction of methallyl alcohol and Poly(CH3-PVE) methyl vinyl ether at 30°C in the presence of Anal. Calcd for C6 H100: C, 73.47%; H, 10.20%. molecular sieve 4A and a catalytic amount of Hg Found: C, 73.06%; H, 10.19%. (OAc)z, according to the procedure of Yuki et al. 8 : bp 89.0-89.SOC (lit. 87-88°C,6 90°C8). The iso­ Hydrolysis merization was carried out quantitatively in a way The pendent propenyloxy groups of poly(PVE) similar to that mentioned above for 90 h at 90°C, to and poly(CH3-PVE) were converted to hydroxy give pure CH3-PVE, bp 85.6-87.SOC, 0.7940. groups by hydrolysis of the polymers in mixtures of The structure and purity of this monomer were methanol and hydrochloric acid, as already done confirmed by gas chromatography, 1 H-NMR spec­ for poly(DVE). 5 The complete removal of the pen­ troscopy and elemental analysis. dent group was confirmed by NMR spectroscopy Anal. Calcd for C6 H100: C, 73.47%; H, 10.20%. and the NMR data were consistent with the elemen­ Found: C, 73.01 %; H, 10.42%. tal analysis. Azobisisobutyronitrile (AIBN) was recrystallized Poly(PVE) (hydrolyzed) from ethanol. Solvents were purified by the usual Anal. Calcd for (C5 H8 0)0 .74(C2 H4 0)0 .26: C, procedure. 68. 75%; H, 9.46%. Found: C, 67.91 %; H, 9.52%. Poly(CH3-PVE) (hydrolyzed) Polymerization Anal. Calcd for (C6 H 100)0 .7iC2 H4 0)0 .26: C, Given amounts of monomer, AIBN, and ben­ 70.88%; H, 10.05%. Found: C, 69.49%; H, 9.95%. zene, when necessary, were placed in ampoules and subjected to the freeze-pump-thaw cycle several M icellaneous times. The ampoules were then sealed in vacuo and The amount of the unsaturated pendent group in immersed in a constant temperature bath. The polymer was determined by 1 H-NMR spectroscopy polymer was recovered by precipitation in meth­ (Hitachi R-24B, 60 MHz) using the peak area of the anol, purified by reprecipitation from benzene vinyl methine proton or the propenyl methine pro­ and methanol, and freeze-dried. The polymers were ton (5.4-6.6ppm). 13C-NMR spectroscopy was white powders, soluble in CHC13 , CC14 , etc. obtained under noise decoupling with a Bruker 658 Polymer J., Vol. 13, No. 7, 1981 Cyclopolymerization of Divinyl Ethers 4 "6c 0 3 .0 30 :iS"' ::J 0 2 20 -DVE PVE ---•--- CHfPVE 2 0 2 4 6 8 10 12 1JL--l..__l..__..L__..L__.L.J [M) mol/1 3 Figure L Content of the pendent double bond (PDB) in poly(divinyl ether)s. Polymerization conditions: C6 H6 solvent, 60°C. PDB is 100% provided that each mo­ 2 nomer unit contains one pendent unsaturation. 2 4 6 8 10 WH-90 (22.63 MHz) instrument and a JEOL FX- [M] mol/1 100 (25 MHz) instrument. The molecular weights of Figure 2. Plots of 1/f; against the initial monomer the polymer were determined by gel-permeation concentration: (I) DYE; (2) PVE; (3) CH3-PVE. chromatography: Toyo Soda Co., Model 802 UR. Three columns of different molecular-weight ranges of variation in PDB. This means that the unit were connected in series. Tetrahydrofuran was used structures remain the same and that the PDB as the eluent, and molecular weight was calculated variation is caused by change in the extent of bi­ using a calibration curve of monodisperse poly­ cyclization. The extent of bicyclization is greater styrenes. for poly(PVE) and poly(CH_1-PVE) than for poly­ (DVE). The rates of the intermolecular propagation and RESULTS AND DISCUSSION the intramolecular cyclization from the monocyclic Polymerization Kinetics intermediate (RP and Rc, respectively) are given for The monocyclic and bicyclic units in poly(DVE) DVE by, are formed through a common intermediate.5 The RP = 2kp[M][M ·] (1) same situation arises for poly(PVE) and (2) poly(CH3-PVE). As will be discussed below, the Rc=kc[M·] pendent groups were invariably substituted vinyl were kP and kc are the respective rate constants, and groups (propenyl and methylpropenyl groups), and [M] and [M ·] are the concentrations of the mono­ single five-membered intermediates were formed mer and the monocyclic radical intermediate, stereoselectively which produced the corresponding respectively. monocyclic and bicyclic units. The propagation Then, occurred preferentially from the vinyl side. Figure 1 shows the relationship between pendent (3) unsaturation in polymer and monomer concen­ tration. In all cases, the content of the pendent The extent of bicyclization is given by, double bond (PDB) (i.e., the fraction of the mono­ J- Rc (4) cyclic unit) increased with increasing monomer c- Rp+Rc concentrations, reaching constant values at initial Therefore, monomer concentrations from 3-5 moll- 1 . The 1 kp conversions were kept below 10%. The peak pat­ -=1+2-[M] (5) tern of 13C-NMR spectra did not change, in spite fc kc Polymer J., Vol. 13, No. 7, 1981 659 M. TSUKINO and T. KUNITAKE 6 4 (1) (1) 4 2 8 (2) 3 6 L (2) ("') I 0 Q_ ::4 0: 0 c 0 ::E 2 0 0 (3) (3) 'I' 4 >< c 2 00 2 4 6 8 10 12 ::E [M] mol/1 Figure 3. Rate of polymerization of divinyl ethers 2 4 6 8 10 plotted against the initial monomer concentration: [M] mol/1 Polymerization conditions: C6 H6 solvent, 60' C; AIBN Figure 4. Molecular weight vs. initial monomer con­ 2.5x for DYE (1), 2.5x for centration: (1), DYE; (2), PVE; (3), CH3-PVE. PVE (2), 4.0x for CH3-PVE (3). Polymerization conditions are the same as those of Figure 3. In the case of PVE and CH3-PVE monomers, high monomer concentrations may be also attri­ (6) buted to the solvent effect of the monomer. The since only the vinyl group is involved in the molecular weight of the polymers increased linearly propagation.