Cationic polymerization of α,β-disubstituted olefins. V. Reactivity of propenyl alkyl ethers in cationic polymerization

To elucidate the effect of the introduction of a methyl group in the β-position of a vinyl monomer, propenyl alkyl ethers were copolymerized with vinyl ethers having the same alkoxy group. Propenyl alkyl ethers with an unbranched alkoxy group (ethyl or n-butyl propenyl ether) were more reactive than the corresponding vinyl ethers. This behavior is quite different from that of β-methylstyrene derivatives. However, propenyl alkyl ethers with branched alkoxy groups at the α carbon atom (isopropyl or tert-butyl propenyl ether) were less reactive than the corresponding vinyl ethers. Also, cis- isomers were more reactive than the trans isomers, regardless of the kind of alkoxy group and the polarity of the solvent.     

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.     

Cationic polymerization of vinyl monomers initiated by 10-methylphenothiazine cation radicals

A small quantity of 10-methylphenothiazine cation radical (MPT^.+), electrochemically prepared and stocked in acetonitrile solution, initiated cationic polymerizations of n-butyl, t-butyl, and 2-methoxyethyl vinyl ethers and p-methoxystyrene, while no initiation occurred for phenyl vinyl ether, styrene, methyl methacrylate, and phenyl glycidyl ether. ¹H-NMR studies of oligomers and low molecular weight compounds isolated from the reaction mixture for the polymerization of t-butyl vinyl ether in the presence of a small amount of D₂O indicated that electron transfer from the monomer to MPT^.+ was involved in the initiation step. ¹H- and ¹³C-NMR and MO calculation implied that monomers with higher electron densities on the vinyl groups and with lower ionization potentials were more susceptible to the initiation of MPT^.+. © 1994 John Wiley & Sons, Inc.     

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 of γ-methyl- and α-methylphenylallene

The cationic polymerizations of γ-methylphenylallene ( 1 ) and α-methylphenylallene ( 2 ) were carried out with some Lewis acids at 25 and 0°C in dichloromethane to obtain the corresponding polymers through allyl cations, respectively. Tin (IV) chloride was found to be an effective catalyst for the cationic polymerization of both allenes 1 and 2 compared with other Lewis acids. Thus, in the polymerization of 1 , methanol-insoluble polymer was only obtained using Tin (IV) chloride, and M?_n of methanol-insoluble polymer obtained by Tin (IV) chloride was the highest in the polymerization of 2 . From the analysis of ¹H- and ¹³C-NMR spectra of the obtained polymers, the polymer from 1 consisted of two kinds of units polymerized by each double bonds of allene 1 , whereas the polymer from 2 consisted of only one unit polymerized by terminal double bond of allene 2 . Moreover, effect of solvent on the cationic polymerizations of 1 and 2 were discussed.     

The morphology of polyethylene prepared by γ-ray-induced polymerization in various solvents

Polyethylenes were prepared by γ-ray-induced polymerization in ethyl and n-butyl alcohols, tert-butyl alcohol containing 5 vol-% of water, 2,2,5-trimethylhexane, 2,2,4-trimethylpentane, and cyclohexane in the temperature range 25–90°C. The morphology of the polymers as-polymerized and studied by electron microscopy depends on three factors through the degree of undercooling: the affinity of the solvent, polymerization temperature, and the polymer molecular weight. Large lamellar crystals are formed even in the alcohols when at least two of them are chosen properly.     

Cationic polymerization by aromatic initiating systems. IV. Synthesis and characterization of α-ω-diphenylpolyisobutylene

The polymerization of isobutylene using ø₃Al coinitiator and the tertiary chlorides tert.-butyl chloride (t-BuCl) and 2,6-dichloro-2,6-dimethylheptane (Cl^t-R-Cl^t) initiators has been studied. Polymerization rates with the t-BuCl/ø₃Al and Cl^t-R-Cl^t/ø₃Al initiating systems were high in the ?20 to ?70°C range. Yields and molecular weights increased with decreasing temperature. As predicted by model experiments the extent of phenylation increases with decreasing temperatures. According to spectroscopic evidence the polyisobutylenes carry phenyl end groups.     

Living cationic polymerization of isobutyl propenyl ether as β-substituted vinyl ether

Isobutyl propenyl ether [IBPE; CH₃CH=CH? OCH₂CH(CH₃)₂] was polymerized with a mixture of hydrogen iodide and iodine (HI/I₂ initiator) in n-hexane at ?40°C to yield living polymers with a nearly monodisperse molecular weight distribution (MWD) (M?_w/M?_n ≈ 1.1). The number-average molecular weight (M?_n) of the polymers increased proportionally to IBPE conversion and further increased when a new monomer feed was added to a completely polymerized solution. The M?_n was controlled by the initial concentration of hydrogen iodide if the acid was charged in excess over iodine. In polymerization by iodine alone the M?_n of the polymers obtained in nonpolar solvents (n-hexane and toluene) also increased with conversion, but their MWD was broader (M?_w/M?_n = 1.3–1.4) than in the HI/I₂-initiated systems under similar conditions. The iodine-initiated polymerization in polar CH₂Cl₂ solvent, in contrast, led to nonliving polymers with a broad MWD (M?_n/M?_n = 1.6–1.8) and M?_n, independent of conversion. The living polymerization of IBPE was also compared with that of the corresponding isobutyl vinyl ether, to determine the effect of the β-methyl group in IBPE.     

Cationic polymerization of β-pinene,styrene and α-methylstyrene

Molecular weight distributions determined by gel permeation chromatography demonstrate that α-methylstyrene copolymerizes with both β-pinene and styrene, forming both bi- and terpolymers. The composition of precipitated polymer versus crude polymer, as determined by nuclear magnetic resonance, suggests that β-pinene and styrene also copolymerize. Extraction of the latter bipolymer of β-pinene and styrene with acetone gives only a small amount of insoluble β-pinene homopolymer, confirming that β-pinene and styrene copolymerize in m-xylene. GPC analysis shows that each copolymer contains some homopolymer. A comparison of M _n with molecular weight calculated from NMR analysis, assuming chain transfer to solvent, indicates that chain transfer is the predominant method of forming dead polymer. The carbonium ions of the growing chain tend to transfer to solvent with increasing ease in the order β-pinene, styrene, and α-methylstyrene.     

Synthesis and polymerization of vinyl esters and vinyl ethers having bulky substituents

In order to clarify the effect of bulky substituents on the stereoregulation of vinyl monomers, vinyl-1-adamantanecarboxylate and vinyl 1-adamantyl ether were synthesized and polymerized by radical and cationic mechanisms, respectively. As open-chain models of the adamantyl group, vinyl trialkylacetate (alkyl = ethyl, n-propyl, and n-butyl) and vinyl tri-n-propylcarbinyl ether were also synthesized and polymerized. The adamantly group in the vinyl ester favored syndiotactic propagation in a manner similar to the trimethylcarbinyl group. Higher homologs of tri-n-alkylcarbinyl group showed higher syndiotacticity but this effect was saturated in higher members of the series. The effect of the adamantyl group in vinyl ether was similar to that of the tert-butyl group, leading to high isotacticity on cationic polymerizations in nonpolar solvents and to atactic polymers in polar solvents, but the tri-n-propylcarbinyl group was found unique in leading to what was assumed to be a heterotactic polymer. Polymers with the adamantyl group showed much higher softening points than polymers of the corresponding open-chain groups.     

Polymerization of optically active β-substituted β-propiolactones. IV. β-1,1-dichloroalkyl β-propiolactones polymerized with aluminum triisopropoxide

The polymerization of three optically active β-1,1-dichloroalkyl β-propiolactones has been investigated in toluene, at 55°C, using aluminum triisopropoxide (Al(OiPr)₃) as initiator in a range of monomer/initiator molar ratios smaller than 150. β-1,1-dichloroethyl β-propiolactone polymerizes according to a living mechanism. However, the ability to polymerize decreases with an increase in the length of the alkyl substituent. For instance, β-1,1-dichloro-n-propyl β-propiolactone is obtained only in low yields, whereas β-1,1-dichloro-n-butyl β-propiolactone does not polymerize at all. Actually, each of the lactones investigated reacts with Al(OiPr)₃ in an initiation step that obeys a coordination-insertion mechanism. However, the size of the chloroalkyl substituent has a critical effect on the propagation: when the alkyl group contains more than two methylene units, the insertion of a second monomer becomes exceedingly slow.     

Poly(γ-alkyl glutamates). I

Good yields of some crystalline γ-alkyl esters of L -glutamic acid were obtained by carrying out the esterfication with a small (20–50 mole-%) excess of alcohol in aqueous hydrochloric acid or 60–80% sulfuric acid followed by neutralization with an alkaline solution. This new method made it possible to synthesize various γ-alkyl L -glutamates, including those higher than ethyl, and consequently, various poly(γ-alkyl L -glutamates) such as methyl, ethyl, n-propyl, n-butyl, isobutyl, and isoamyl. The conformation of these poly-L -glutamates in the solid state was determined by the infrared absorption method. The molecular motions of the polymers of γ-methyl, -ethyl, -n-propyl, -n-butyl, and-isoamyl L -glutamates and poly(γ-methyl-D -glutamate) in the solid state were studied by NMR, and dielectric and mechanical measurements. At temperatures up to 400°K., the NMR spectra of poly(γ-methyl D -glutamate) can be explained only by rotational motion of the side chain. Also, from NMR results, rotational motion of C?O groups in the side chain of poly(γ-methyl D -glutamate) is expected near room temperature, and such a motion was examined by dielectric measurements. Rotation of C?O groups in the side chains of polymers of γ-methyl, γ-ethyl, γ-n-propyl, γ-n-butyl, and γ-isoamyl L -glutamate was also observed near room temperature by dielectric measurements in the frequency range from 10² to 10⁶ cps. Activation energies obtained by dielectric and mechanical measurements were similar to those for the side chain motions of the corresponding esters of poly(methacrylic acid). Although it has been noted that the molecular motion of poly(γ-benzyl L -glutamate) in the solid state at room temperature may be related to the motion of its back bone, the molecular motion in these poly-L -glutamates at these temperatures can be explained only in terms of side-chain rotation.     

Effect of temperature and solvents on stereospecific polymerization of vinyl alkyl ethers catalyzed by aluminum sulfate–sulfuric acid complex

The effect of polymerization temperature and solvents was determined on the crystallinity of polymers of vinyl isobutyl ether and of vinyl n-butyl ether prepared with aluminum sulfate–sulfuric acid complex catalyst. Principally, the methyl ethyl ketone (MEK)-insoluble fractions of these polymers were used for characterization. Density, per cent crystallinity by x-ray diffraction, infrared ratio, and dilatometric volume contraction of these polymer fractions were used as criteria of crystallinity. The MEK-insoluble fractions of poly(vinyl n-butyl ethers) prepared in carbon disulfide in the temperature range of ?30 to +25°C did not show any significant difference in the values of the above crystallinity parameters. The polymer obtained at 50°C. was less crystalline than the rest of the polymers. The MEK-insoluble fractions of poly(vinyl isobutyl ethers) prepared at 0–50°C. in carbon disulfide and n-heptane solvents also did not significantly differ in their degree of crystallinity. They were, however, decidedly less crystalline than the MEK-insoluble fractions of the corresponding polymers obtained at ?20°C. These data a indicate that on increasing the temperature of polymerization the crystallinity of the polymers was either unchanged or decreased slightly. The polymerizations of vinyl n-butyl ether and vinyl isobutyl ethers were also carried out in binary mixtures of carbon disulfide with n-heptane, chlorobenzene, and MEK. Generally, increasing the concentration of carbon disulfide increased the inherent viscosities of polymers as well as the weight percentage of their MEK-insoluble fractions. The MEK-insoluble fraction of poly(vinyl isobutyl ether) prepared in carbon disulfide-MEK mixture (volume ratio 2:1) was isotactic and highly crystalline. Likewise, the MEK-insoluble fractions of two polymers of vinyl n-butyl ether prepared in MEK itself were also isotactic and highly crystalline. Compared to poly(tetramethylene oxide), these latter fractions exhibited less dependence of rate of crystallization upon temperature. Consequently, at low degrees of supercooling they crystallize much more rapidly than does poly(tetramethylene oxide).     

Structure and reactivity α,β-unsaturated ethers. II. Cationic copolymerizations of propenyl isobutyl ether

cis- and trans-Propenyl isobutyl ethers were copolymerized with each other and each with vinyl isobutyl ether separately under various conditions. In homogeneous polymerizations a cis-β-methyl substitution on vinyl isobutyl ether apparently enhanced the reactivity, whereas the trans substitution tended to reduce it slightly. In heterogeneous catalysis, on the other hand, a β-methyl group on the vinyl ether, whether cis or trans, greatly reduced the reactivity, probably because of the steric hindrance toward the adsorption of monomers on the catalyst surface. The relative reactivities of cis- and trans-propenyl isobutyl ethers ranged from 2 to 20, depending on the polymerization conditions. The polymer end formed from the cis monomer exhibited special steric effects. It was concluded that even in homogeneous media the rotation of the polymer end around the terminal carbon–carbon bond is restricted.     

Living cationic polymerization of α‐methyl vinyl ethers using SnCl4

Cationic polymerization of α‐methyl vinyl ethers was examined using an IBEA‐Et_1.5AlCl_1.5/SnCl₄ initiating system in toluene in the presence of ethyl acetate at 0 ～ ?78 °C. 2‐Ethylhexyl 2‐propenyl ether (EHPE) had a higher reactivity, compared to corresponding vinyl ethers. But the resulting polymers had low molecular weights at 0 or ?50 °C. In contrast, the polymerization of EHPE at ?78 °C almost quantitatively proceeded, and the number‐average molecular weight (M_n) of the obtained polymers increased in direct proportion to the EHPE conversion with quite narrow molecular weight distributions (weight‐average molecular weight/number‐average molecular weight ≤ 1.05). In monomer‐addition experiments, the M_n of the polymers shifted higher with low polydispersity as the polymerization proceeded, indicative of living polymerization. In the polymerization of methyl 2‐propenyl ether (MPE), the living‐like propagation also occurred under the reaction conditions similar to those for EHPE, but the elimination of the pendant methoxy groups was observed. The introduction of a more stable terminal group, quenched with sodium diethyl malonate, suppressed this decomposition, and the living polymerization proceeded. The glass transition temperature of the obtained poly(MPE) was 34 °C, which is much higher than that of the corresponding poly(vinyl ether). This poly(MPE) had solubility characteristics that differed from those of poly(vinyl ethers). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2202–2211, 2008     

Structure and reactivity of α,β-unsaturated ethers. III. Cationic copolymerizations of alkenyl alkyl ethers

The relative cationic polymerizabilities of the geometrical isomers of various alkenyl alkyl ethers were studied both in copolymerizations with each other and in their respective copolymerizations with vinyl isobutyl ether as standard. Copolymerizations were carried out in methylene dichloride at ?78°C. with boron trifluoride etherate as catalyst. The cis isomers have been found to be more reactive than the corresponding trans isomers. A primary alkyl substituent on the β-cis position of vinyl ethyl ether enhances the reactivity. Yet the steric effect is noticeable when the substituents are bulky. Compounds substituted with cis-β-isobutyl and with β-dimethyl showed little tendency to homopolymerization. It was proved that the polymer ends derived from cis and from trans monomers are respectively different in character because of the restricted rotation of the end unit around the terminal carbon–carbon bond. The alternation tendency, remarkable in the copolymerization of cis monomers with vinyl ether, was explained in terms of the cis-opening mechanism.     

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.     

γ-radiation-initiated emulsion polymerization of n-butyl acrylate and of methyl methacrylate

We have investigated the γ-radiation-initiated polymerization of n-butyl acrylate (BA) and of methyl methacrylate (MMA) in aqueous emulsions stabilized with sodium lauryl sulfate (SLS). The reaction rate, as measured by a nonabsolute thermocouple technique, varies as the square root of emulsifier concentration for both monomers. In the case of BA, the dose rate exponent of the reaction rate is 0.7 ± 0.3, whereas the corresponding value for MMA is approximately 0.4. The overall activation energy of the BA polymerization is close to zero, whereas for MMA a value of 4.8 ± 2.1 kcal/mole has been found. The poly(butyl acrylate) molecular weight is effectively independent of soap concentration and of dose rate but decreases as the reaction temperature is increased in the range 30–70°C. The general conclusion drawn from this work is that these radiation-induced emulsion polymerizations differ little from conventionally initiated systems insofar as the reaction kinetics are concerned. Poly(butyl acrylate-g-methyl methacrylate) copolymers have been prepared by a direct irradiation method involving a poly(butyl acrylate) prepolymer seed latex. Some physical properties of this material have been examined.     

Cationic polymerization of cyclocarbonates

Trimethylenecarbonate (TMC) and neopentane diol carbonate (NPC) were polymerized with two groups of initiators, proton and carbenium ion donors or Lewis acids. Initiation with methyltriflate, triflic acid or triethyloxonium tetrafluoroborate in solution gave satisfactory yields (up to 90%) but only low molecular weights (M_n < 5000), due to rapid back-biting degradation. IR- and NMR-spectroscopy demonstrate that the propagation steps involve alkylation of the carbonyl oxygen and cleavage of the alkyl-0 bond by analogy with lactones. Whereas borontribromide and trichloride form solid complexes with NPC or TMC, but do not initiate a polymerization, boron trifluoride is a good initiator. High yields (up to 99,5%) and high molecular weights (M_w > 10⁵) were obtained. However, in analogy to triflic acid initiated polymerizations all polycarbonates contain ether groups. The molar fraction of the ether groups increases with the reaction temperature. High molecular-weight polycarbonates containing ether groups were also obtained with other strong Lewis acids such as SnCl₄, SnBr₄ and TiCl₄. In contrast, weak Lewis acids such as Bu₂SnBr₂ Bu₃SnOMe and Sn(II)2-ethylhexanoate yield polycarbonates free of ether groups. This finding and the NMR-spectroscopically identified endgroups suggest that these weak Lewis acids initiate an insertion mechanism.     

Specifically π→π* Induced Photoreactions of α,β-Unsaturated Ketones: Hydrogen Abstraction by the α-carbon. (Preliminary Communication)

Irradiations at 254 nm of the α,β-unsaturated γ-dimethoxy-methyl ketone 7 in iso-octane and t-butyl alcohol afforded in a specifically π→π*induced process and in high chemical yield the epimeric products 9 and 10 . These products were not formed on n→π* excitation of 7 at > 340 nm, but triplet energy transfer to 1,3-cyclohexadiene could be observed. Photolyses of the hexadeuterio analog 7-d₆ at 254 nm led to the fully deuteriated products (cf. 9-d₆ ) in both solvents, with stereospecific incorporation of a deuterium atom in position C(1α). The structures of 9 and 10 were determined by an X-ray diffraction analysis of 9 and chemical correlations of the two products. The structural constraints in 7 demand a hitherto unprecedented direct transfer of a methoxyl hydrogen to the α-carbon of the excited enone and formation of intermediate 8 .