Cationic polymerization of α,β-disubstituted olefins. Part 17. Effect of polymerization conditions on the reactivity of alkenyl ethers relative to vinyl ethers

In order to clarify the propagation reaction, vinyl ether was copolymerized with the corresponding alkenyl ether under various conditions. cis-Propenyl ether (cis-PE) was several times more reactive than trans-PE and the corresponding vinyl ether in the copolymerization catalyzed by BF₃ · O(C₂H₅)₂ in toluene. However, the reactivity of cis-PE relative to trans-PE and the vinyl ether was found to be greatly decreased with increasing polarity of the solvent and to be very close to unity in such polar solvents as nitroethane. On the other hand, the reactivity of trans-IBPE relative to IBVE was scarcely changed by polymerization conditions. Also, the nature of the initiator and polymerization temperature affect the reactivity of cis-PE relative to the vinyl ether. These phenomena were explained by the relative stability of the bridged and open car bonium ions based on the polarity of the solvent and steric hindrance due to substituents in the trans isomer.     

Cationic polymerization behavior of seven-membered cyclic sulfite

Cationic ring-opening polymerization behavior of a seven-membered cyclic sulfite ( 1 ) was examined. 1 was prepared by the reaction of 1,4-butanediol with SOCl₂ in 58% yield. The cationic polymerization of 1 was carried out at 0, 25, 60, or 100°C with trifluoromethanesulfonic acid (TfOH), methyl trifluoromethanesulfonate (TfOMe), BF₃ · OEt₂, SnCl₄, methyl p-toluenesulfonate (TsOMe), or MeI as an initiator in bulk under a nitrogen atmosphere to afford the polymer with M̄_n 1000–10,400. The order of activities of the initiators for 1 was as follows, TfOH ≅ TfOMe > SnCl₄ > BF₃ · OEt₂ > TsOMe ≅ MeI. The polymerization of 1 with TfOMe afforded a poly(sulfite) below 25°C, but afforded a polymer containing an ether unit at 60°C, which was formed by a desulfoxylation. The higher the activity of the initiator was, the more easily the desulfoxylation occurred. We expected volume expansion on polymerization because cyclic sulfites have large dipole moment values, but it turned out that 1 showed 4.34% shrinkage on polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3673–3682, 1997     

Cationic polymerization of dimethyl-1,3-butadienes

The cationic polymerizations of dimethyl-1,3-butadienes with various catalysts in methylene chloride and toluene have been investigated. The activity of catalysts decreased in the order WCl₆ > AcClO₄ > SnCl₄·TCA > BF₃OEt₂. The homopolymerization rate of dimethyl-1,3-butadienes with WCl₆, AcClO₄, and SnCl₄·TCA decreased in the order 1,3-dimethyl-1,3-butadiene > 2,3-dimethyl-1,3-butadiene > 1,2-dimethyl-1,3-butadiene > 2,4-hexadiene. The polymers prepared with WCl₆, SnCl₄.TCA, and BF₃OEt₂ were rubberlike polymers or white powders, whereas those prepared with AcClO₄ were oily oligomers. The 1,4-propagation increased in the order 1,2-dimethyl-1,3-butadiene < 1,3-dimethyl-1,3-butadiene < 2,3-dimethyl-1,3-butadiene < 2,4-hexadiene. This order may indicate that the steric effect of methyl group determine primarily the microstructure of the polymer. The relative reactivity of dimethyl-1,3-butadienes toward a styryl cation decreased in the order 1,3-dimethyl-1,3-butadiene > 1,2-dimethyl-1,3-butadiene > 2,3-dimethyl-1,3-butadiene > 2,4-hexadiene. This order may be explained in terms of the stability of the resulting allylic cation.     

Studies on the polymerization of bifunctional monomers. XVI. Cyclopolymerization of o-divinylbenzene with triphenylmethyl fluoroborate and presumption of the presence of the free growing cation in this system

Cyclopolymerization of o-divinylbenzene was studied by using triphenylmethyl fluoroborate as initiator. The cyclization constant r_c (ratio of the rate constant for intramolecular cyclization to that for intermolecular propagation) decreased with increase in polarity of the solvent. This solvent effect as well as the effect of catalysts reported previously could be accounted for by a revised model of the propagating species, where both the counter anion and the o-vinyl group were coordinated to the carbonium ion. The difference in activation energy between intramolecular cyclization and intermolecular propagation was 6.2 kcal/mole. This value was close to that obtained previously with BF₃·OEt₂ catalyst but greater than those for anionic and radical polymerizations. When tetraalkylammonium flouroborates were added to the polymerization system in methylene chloride, r_c and the molecular weight of the polymer decreased. These results were ascribed to the decrease in the amount of the free propagating cation by the common ion effect.     

Stereoelective cationic polymerization of propenyl ether by asymmetric catalysts

In order to elucidate the possibility of stereoelective cationic polymerization (asymmetric selective polymerization) of olefinic monomers, racemic cis- and trans-1-methylpropyl propenyl ether and racemic 1-methylpropyl vinyl ether were polymerized by asymmetric alkoxyaluminum dichlorides. In the polymerization of racemic cis-1-methylpropyl propenyl ether with (?)-menthoxyaluminum dichloride in toluene at ?78°C, the polymer obtained showed a positive optical activity, and the residual monomers were converted by BF₃OEt₂ into a polymer having a negative optical activity. Thus, the stereoelective polymerization of racemic cis-1-methylpropyl propenyl ether was beyond any doubt attained in homogeneous cationic polymerization. In the polymerization of the trans isomer by the same catalyst, an optically active polymer was hardly formed. In the polymerization of racemic 1-methylpropyl vinyl ether which has no β-methyl group, stereoelectivity was not observed at all. The cis-1-methylpropyl propenyl ether did not produce an optical active polymer in the polymerization catalyzed by (S)-1-methylpropoxyaluminum dichloride or (S)-2-methylbutoxyaluminum dichloride under the same polymerization conditions.     

Cationic copolymerization of anethole: Reactivity of geometric isomers of α,β-disubstituted ethylenes

Cationic copolymerizations of anethole were carried out under various conditions in order to confirm the relative reactivities of its geometric isomers. trans-Anethole was more reactive than cis-anethole in copolymerizations with p-methoxystyrene or styrene, but less reactive in the mutual copolymerization of cis- and trans-anethole; i.e., the trans isomer was more reactive to a growing chain end with little steric hindrance. Thus the intrinsic reactivity of an olefinic double bond to carbonium ion is greater for the trans isomer than for the cis isomer. This idea is supported by ¹³C NMR spectra, since the signal of the olefinic β-carbon of the trans isomer is at higher field than that of the cis isomer. The behavior of anethole was compared with the results observed in vinyl ethers, where the cis isomer was always more reactive irrrspective of the structure of the growing chain end. In addition, the dependence of monomer reactivity ratios on polymerization conditions is discussed.     

Cationic polymerization of 1-ethoxy-1,3-butadiene

cis- and trans-1-Ethoxy-1,3-butadienes were polymerized by a variety of cationic agents in various solvents at ?78°C. The trans ether, which is the more stable isomer, was found to have greater polymerizability than the cis ether. The trans monomer gave polymers predominantly of the trans-1,4 type, whereas the cis monomer showed a tendency toward the formation of polymers having the microstructure of the 1,2 type. It was concluded that, in the cis ether, the carbon atom which is the most vulnerable to the attack of carbonium ions is the one at the 2-position, whereas, in the case of the trans isomer, the terminal 4-carbon is the most reactive center. The conclusion was confirmed from the results of acetal addition reaction catalyzed by boron trifluoride etherate. The marked contrast in the mode of reaction of the two isomeric ethers toward carbonium ions was interpreted in terms of the difference in the degree of bonding in the transition state.     

Cationic polymerization of α,β-disubstituted olefins. XV. Stereospecific polymerization of butenyl ethers by cationic catalysts

Methyl, ethyl, and isopropyl butenyl ethers, CH₃CH₂CH?CHOR, were polymerized with homogeneous catalysts at ?78°C. Toluene, methylene chloride, and nitroethane were used as solvents, and BF₃O(C₂H₅)₂ and SnCl₄·CCl₃CO₂H were used as catalysts. The stereoregularity of the polymers were compared by x-ray diagrams and infrared absorption ratios. The stereoregularity of polymers increased with increasing content of the trans isomer in the monomer and with increasing polarity of the solvent. In the polymerization of methyl and ethyl butenyl ethers, crystalline polymers were obtained from both the trans and cis isomers. The crystalline polymer prepared from the trans isomer and that from the cis isomer had the same steric structure. This behavior is quite different from that observed in the polymerization of propenyl ethers. It is concluded that the bulkiness of the group on the olefinic β-carbon plays an important role in the stereospecific polymerization of α,β-disubstituted olefins.     

Cationic ring-opening polymerization of 3,3-bis（chloromethyl）oxacyclobutane in ionic liquids

Cationic ring-opening polymerization of 3,3-bis(chloromethyl)oxacyclobutane catalyzed by BF_3·OEt_2 was carried out in ionic liquids [bmim]BF_4 and [bmim]PF_6.The influences of BCMO concentration and molar ratio of BCMO/BF_3·OEt_2 on the molecular weights and yield of PBCMO were investigated.The polymerization in ionic liquids proceed to high conversions,although molecular weights are limited,similar to polymerization in organic solvent such as CH_2Cl_2.Follow a viewpoint of green chemistry, we feel ionic liquid [bmim]BF_4 is superior to [bmim]PF_6.Extracting [bmim]PF_6 from the product using organic solvent as extractant limits its advantage as a green reaction media.     

Living cationic polymerization of cis- and trans-ethyl propenyl ethers and synthesis of block copolymers with isobutyl vinyl ether

The cationic polymerization of cis- and trans-ethyl propenyl ethers (EPE, CH₃? CH?CH? O? C₂H₅), initiated by a mixture of hydrogen iodide and iodine (HI/I₂ initiator) at ?40°C in nonpolar media (toluene and n-hexane), led to living polymers of controlled molecular weights and a narrow molecular weight distribution (MWD) (M?_w/M?_n = 1.2–1.3). The geometrical isomerism of the monomer did not affect the living character of the polymerization. ¹³C NMR stereochemical analysis of the polymers showed that the living propagating end is sterically less crowded than nonliving counterparts generated by conventional Lewis acids (e.g., BF₃OEt₂). New block copolymers between EPE (cis or trans) and isobutyl vinyl ether were also prepared by sequential living polymerization of the two monomers.     

Structure and reactivity of α,β-unsaturated ethers. VIII. Cationic copolymerizations and acetal additions of propenyl and isobutenyl ethyl ethers

Cationic copolymerizations of cis- and trans-propenyl ethyl ethers (PEE) with isobutenyl ethyl ether (IBEE) were carried out in methylene chloride at ?78°C with the use of boron trifluoride etherate as catalyst. Monomer reactivity ratios were r₁ = 24.0 ± 2.4 and r₂ = 0.02 ± 0.02 for the cis-PEE (M₁)–IBEE (M₂) system and r₁ = 19.1 ± 1.8 and r₂ = 0.04 ± 0.02 for the trans-PEE (M₁)–IBEE (M₂) system, indicative of the reactivity order: cis-PEE > trans-PEE ? IBEE. In separate experiments, these β-methyl-substituted vinyl ethers were allowed to react with various acetals in the presence of boron trifluoride etherate. The relative reactivities of these ethers were generally found to decrease in the order: cis-β-monomethylvinyl > vinyl > trans-β-monomethylvinyl > β,β-dimethylvinyl. Comparisons of these results with previously published copolymerization data have permitted the conclusion that, in both the copolymerizations and acetal additions, the single β-methyl substitution on vinyl ethers exerts little steric effect against their additions toward any alkoxycarbonium ion, whereas the β,β-dimethyl substitution results in a large adverse steric effect toward both β-monomethyl- and β,β-dimethyl-substituted alkoxycarbonium ions.     

Cationic Polymerization of 1,5-Dioxepan-2-one with Lewis Acids in Bulk and Solution

Abstract

1,5-Dioxepane-2-one (DXO) was coordinatively ring-opening polymerized with different Lewis acids in bulk and solution. The reactivities of a series of initiators (SnCl₄, FeCl₃, AlCl₃, BCl₃, and BF₃OEt₂) at different temperatures and reaction times were analyzed. Polymerization of DXO in bulk with SnCl₄, FeCl₃, AlCl₃, and BCl₃ gave only oligomers or low molecular weight polymers irrespective of temperature and/or reaction time. Polymerization of DXO with BF₃OEt₂ at 70°C gave yields of nearly 100% and molecular weights up to M _w = 10,000. The polymerization temperature was increased to 100°C and the reaction time prolonged, which resulted in nearly equal molecular weights as at 70°C but with lower yields, higher polydispersity, and generally not full conversion. In addition, side reactions, such as backbiting, transesterification and thermal degradation, occurred to a larger extent at higher reaction temperatures. Solution polymerization using the same initiators and THF, dioxane, or nitrobenzene as the solvent gave polymers of low molecular weights and of low yields, except with FeCl₃ and BF₃OEt₂. The rates of polymerization were significantly higher in nitrobenzene than in dioxane and THF due to polarity and coordination of these solvents to the growing chain. Comparison of the initiators BF₃OEt₂ and SnCl₄ in solution polymerization showed equal reactivity in nitrobenzene for both of them. The BF₃OEt₂-initiated systems give polymers with lower molecular weights than SnCl₄-initiated systems, but with narrower polydispersity.     

Cationic polymerization of α,β-disubstituted olefins. IV. Stereospecific polymerization of propenyl alkyl ethers catalyzed by BF3·O(C2H5)2 and Al2(SO4)3–H2SO4 complex

The cis- and trans-propenyl alkyl ethers were polymerized by a homogeneous catalyst [BF₃·O(C₂H₅)₂] and a heterogeneous catalyst [Al₂(SO₄)₃–H₂SO₄ complex]. Methyl, ethyl, isopropyl, n-butyl and tert-butyl propenyl ethers were used as monomers. The steric structure of the polymers formed depended on the geometric structures of monomer and the polymerization conditions. In polymerizations with BF₃·O(C₂H₅)₂ at ?78°C., trans isomers produced crystalline polymers, but cis isomers formed amorphous ones except for tert-butyl propenyl ether. On the other hand, highly crystalline polymers were formed from cis isomers, but not from the trans isomers in the polymerization by Al₂(SO₄)₃–H₂SO₄ complex at 0°C. The x-ray diffraction patterns of the crystalline polymers obtained from the trans isomers were different from those produced from the cis isomers, except for poly(methyl propenyl ether). The reaction mechanism was discussed briefly on these basis of these results.     

Isomerization of alkenes in the presence of Pd(acac)2-BF3OEt2 catalytic system

Positional isomerization of alkenes was studied in the presence of Pd(acac)₂ + 20BF₃OEt₂ catalytic system. The reactivity of alkenes decreases in the following order: 1-hexene > 1-heptene > 2-methyl-1-pentene > 4-methyl-2-pentene (cis + trans).     

Cationic photopolymerization of cis‐2,3‐tetramethylene‐1,4,6‐trioxaspiro[4,4]nonane

The spiro‐orthoester, cis‐2,3‐tetramethylene‐1,4,6‐trioxaspiro[4,4]nonane (cis‐TTN) ( I ), underwent rapid cationic photopolymerization when exposed to UV light using diphenyliodonium salts as a photoinitiator. The polymer, poly[(trans‐OCB)_x′‐(cis‐OCB)_x″‐(CHO)_y] thus formed consisted of poly(trans‐2‐oxycyclohexyl butanoate) (trans‐OCB)_x′ ( II ), poly(cis‐2‐oxycyclohexyl butanoate) (cis‐OCB)_x″ ( III ), and poly‐ (1,2‐cyclohexene oxide) (CHO)_y segments, and no expected pure poly(ether‐ester), that is, poly(2‐oxycyclohexyl butanoate), was isolated. The structure of the polymer was identified, and the mechanism of the reaction was deduced. The polymer thus formed exhibited expansion in volume during cationic photopolymerization when compared to that obtained by conventional cationic polymerization using a Lewis acid (e.g., BF₃OEt₂, CH₃OSO₂CF₃, or SnCl₄) as an initiator, which demonstrated volume shrinkage during polymerization. The volume expansion of the polymer during polymerization was due to (1) the lower content of the higher density (CHO)_y segment in the polymer chain and, more importantly, (2) the higher and optimal mole ratio of (trans‐OCB)_x′ and (cis‐OCB)_x″ segments that led the polymer in a more disordered, less dense, and higher volumetric state. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3680–3690, 2009     

Transformations of chloroethylenes in the presence of aprotonic acids

The cationic polymerization of vinyl chloride, vinylidene chloride, and cis- and trans- 1,2-dichloroethylenes with the use of Lewis acid-type catalysts has been studied. Vinylidene chloride is smoothly polymerized in the presence of ZnCl₂ at 40°C to form the dimer, 1,1,3,3-tetrachlorobutene-1, and poly(vinylidene chloride) having somewhat increased crystallinity (45%). Vinyl chloride is polymerized very slowly in the presence of AlCl₃ and TiCl₄ to give dimeric, trimeric, tetrameric, and low molecular weight polymer products. The polymerization is followed by carbonium ion isomerization that leads to reaction products of branched structure. The cis- and trans-1,2-dichloroethylenes react in the presence of AlCl₃ only at 50–60°C, and their polymerization is terminated at the stage of dimer and cyclic trimer formation. A mechanism of carbonium ion-initiated polymerization of chloroethylenes is proposed, and the causes which lead to early termination of polymerization are discussed.     

Cationic polymerization with boron halides. VI. Polymerization of styrene with BF3, BCl3, and BBr3

The polymerization of styrene with BF₃, BCI₃, and BBr₃ coinitiators and CH₂Cl₂ solvent has been investigated. The effects of temperature, monomer concentration, and the nature of the boron halide on molecular weights, molecular weight distribution, and conversion were determined. Molecular weights were found to decrease in the order BCl₃ >BF₃ >BBr₃. This sequence was discussed in terms of system ionicity and counterion stability. The overall energies of activation for polymerization (ΔE) were ?1.6 ± 0.3, ?1.9 ± 0.8, and ?0.9 ± 0.5 kcal/mole for BF₃, BCI₃, and BBr₃, respectively, which indicated similar overall polymerization mechanisms in the range of ?20 to ?80°C. The predominant molecular-weight-governing event in polymerizations with BCl₃, and BBr₃ was chain transfer to monomer, whereas with BF₃ chain transfer and termination were nearly equal. Chain termination in BCl₃-coinitiated polymerizations involves chlorination of the growing polystyryl cation by BCl₃OH^? and leads to benzylic chlorine termini.     

Step-growth cationic polymerization of α-hydroxyisopropylferrocene

α-Hydroxyisopropylferrocene, HPF, was synthesized in good yield and polymerized at 20°C with either SnCl₄ or BF₃OEt₂. The polymerization proceeds by self-alkylation of the stable intermediate ferrocenylcarbenium ion on the cyclopentadienyl ring to form oligomers that contain both homoannular and heteroannular links. The unusually high stability of the α-isopropylferrocenylcarbenium ion was demonstrated by synthesizing and isolating α-isopropylferrocenylcarbenium tetrafluoborate from HPF and using it to initiate the polymerization of styrene. Initiation was successful at 20° and at 0°C, but no polymerization occurred ?78°C. The condensation of ferrocene and acetone in the presence of AlCl₃ gave oligomers having structures very similar to those obtained from the cationic polymerization of isopropenylferrocene.     

Cationic ring‐opening polymerization of monothiocarbonate with a norbornene group

This work deals with the cationic ring‐opening polymerization of cyclic thiocarbonates with a norbornene or norbornane moiety, that is, 5,5‐(bicyclo[2.2.1]hept‐2‐ene‐5,5‐ylidene)‐1,3‐dioxane‐2‐thione ( TC1 ) or 5,5‐(bicyclo[2.2.1]heptane‐5,5‐ylidene)‐1,3‐dioxane‐2‐thione ( TC2 ), respectively. The reaction of TC1 initiated by trifluoromethanesulfonic acid (TfOH), methyl trifluoromethanesulfonate (TfOMe), boron trifluoride etherate (BF₃OEt₂), or triethyloxonium tetrafluoroborate (Et₃OBF₄) afforded unidentified products; however, TC1 underwent cationic ring‐opening polymerization with methyl iodide as an initiator to afford polythiocarbonate because the propagating end was stabilized by the covalent‐bonding property. The polymerization of TC2 initiated by TfOH, TfOMe, BF₃OEt₂, or Et₃OBF₄ afforded polythiocarbonate with good solubility in common organic solvents and a narrow molecular weight distribution because of the absence of a double‐bond moiety. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1698–1705, 2002     

Sulfur-containing vinyl monomers. XIII. Cationic copolymerizations of vinyl sulfides with some vinyl monomers

Cationic copolymerizations of vinyl sulfides (VS) with some vinyl monomers with boron tri-fluoride-diethyl etherate catalyst were investigated to evaluate their monomer reactivities. The effects of VS on the copolymer yield and viscosity of the resulting copolymers revealed the inhibition or retardation mechanism which was explained in terms of the formation of a stable vinylsulfonium salt by the reaction between a propagating carbonium ion and VS monomer. From the results of copolymerizations of phenyl vinyl sulfide (PVS) with isobutyl vinyl ether (IBVE), β-chloroethyl vinyl ether (CEVE), α-methylstyrene (α-MeSt), and styrene (St), the relative reactivities of these monomers were found to be in the following order: IBVE > CEVE > PVS > α-MeSt > St. The relatively higher reactivity of PVS than St derivatives was explained on the basis of the conjugative and electron-donating nature of the VS monomer. The effects of alkyl and para-substituted phenyl groups in vinyl sulfides on their reactivities toward the propagating carbonium ion were correlated with polar factors and compared with those of the hydrolysis of α-mercaptomethyl chlorides. The transition state for the propagation reaction in cationic polymerization of VS was proposed to be a π-complex type structure.