Stereospecific polymerization of α-methylstyrene by friedel-crafts catalysts

The relationship between stereoregularity and polymerization conditions of α-methylstyrene has been studied by means of NMR spectra. The effects of solvents and various Freidel-Crafts catalysts have been investigated. The stereoregularity of poly-α-methylstyrene increased with increased polymer solubility in the solvent used and with decreasing polymerization temperature. This behavior is completely different from the stereospecific polymerization of vinyl ethers and methyl methacrylate in homogeneous systems. This may be due to the strong steric repulsion exerted by the two substituents in the α-position of α-methylstyrene. For example, with BF₃ · O(C₂H₅)₂ as catalyst at ?78°C., atactic polymer is obtained in n-hexane, a nonsolvent for α-methylstyrene, whereas highly stereoregular polymer is produced in toluene or methylene chloride, good solvents for the polymer. However, the polarity of the solvent and the nature of the catalyst hardly affect the stereoregularity of the polymer.     

Photoinduced ionic polymerization. III. Cationic polymerization and copolymerization of cyclohexene oxide and α-methylstyrene in the presence of pyromellitic dianhydride

The photoinduced ionic polymerization of cyclohexene oxide was studied in the presence of pyromellitic dianhydride. The polymerization is initiated by the excited chargetransfer complex between cyclohexene oxide and the electron-acceptor and proceeds by a cationic mechanism. Photoinduced cationic polymerization of α-methylstyrene was also observed in the presence of pyromellitic dianhydride. The initiation mechanism of the polymerization was elucidated by means of electron spin resonance measurements. The concentration of pyromellitic dianhydride anion-radicals measured in this way was found to be proportional to the rate of polymerization. This result shows clearly that the photopolymerization is initiated by cation-radicals formed from photoexcited donoracceptor complexes. The attempted photocopolymerization of cyclohexene oxide and α-methylstyrene gave a mixture of homopolymers. The composition of the product depends on the wavelength of the light used.     

Radiation-induced polymerization at high dose rate. II. α-Methylstyrene in bulk

Bulk polymerization of α-methylstyrene was carried out in a wide dose rate range, 7.6–256 rad/sec by γ rays and 8.5 × 10³–2.1 × 10⁵ rad/sec by electron beams. At high dose rate by electron beams, cationic polymerization took place along with formation of oligomeric product of DP _n = ～4. At low dose rate by γ rays, radical polymerization was found to occur in water-saturated monomer. The cationic polymerization at high dose rate proceeds with essentially the same mechanism as was already known in γ-ray polymerization of dry monomers. Relatively low reaction rate of the cationic polymerization compared with that of styrene is explained with the fact that the propagation of α-methylstyrene is much more easily inhibited by a slight amount of water.     

Recent Progress of Photo- and Radiation-Induced Ionic Polymerizations

Photoinduced ionic polymerizations of the monomers α-methylstyrene, cyclohexeneoxide, nitroethylene, and acrylonitrile were carried out in the presence of electron acceptor or donor molecules. These polymerizations are proved to be initiated by ions formed through the dissociation of the photoexcited electron donor-acceptor complex and to proceed by ionic mechanism.

The molecular weight distribution of the polymer and the light intensity dependency on the rate of polymerization indicate that free ionic and ion-pair propagations coexist in the cationic polymerization of α-methylstyrene.

Anionic polymerizations were observed for the nitroethylenetetrahydrofuran and acrylonitrile-dimethylformamide systems.

Radiation-induced cationic polymerizations of styrene and α-methylstyrene were found to proceed by free cationic propagation. The effect of added electron acceptors in these polymerizations was investigated.     

Polymerization of Styrene Initiated by Photoexcited Charge-Transfer Complex

Photopolymerization of styrene in the presence of pyromellitic dianhydride, an electron acceptor which forms a charge-transfer complex with the monomer, was studied. Polymerization was initiated by illumination with a light of wavelength longer than 350 nm, where only the charge-transfer absorption band exists. It was found that the reaction involves cationic and radical polymerizations and that the reaction course strongly depends on polarity of the system. It was also suggested by the dependence of the rate of polymerization on light intensity and temperature that the cationic polymerization consists of free ion and ion-pair polymerizations. These results were compared with those of the photoinduced cationic polymerization of α-methylstyrene, which has previously been studied.     

Molecular weight distribution studies. I. Radiation-induced polymerization of liquid α-methylstyrene

The concentration of water in purified and BaO-dried α-methylstyrene was found to be 1.1 × 10^?4M. The radiation-induced bulk polymerization of the α-methylstyrene thus prepared was studied in the temperature range of ?20°C to 35°C. The polymerization rate varied as the 0.55 power of the dose rate. The theoretical molecular weights and molecular weight distribution were calculated from a proposed kinetic scheme and these values were then compared with those found experimentally. The agreement between these two was reasonably close, and therefore it was concluded that, from the molecular weight distribution point of view, the proposed kinetic scheme for the cationic polymerization of α-methylstyrene is an acceptable one. The rate constant for chain transfer to monomer k_f changed with temperature and was found to be responsible for the decrease in the molecular weight of the polymer with increase in temperature. k_f and k_p at 20°C were found to be 0.95 × 10⁴ l./mole-sec and 0.99 × 10⁶ l./mole-sec, respectively.     

The formation of radical cations of styrene and α-methylstyrene in the irradiation of mixtures of these monomers with TiCl4 and SnCl4 in a semicrystalline heptane matrix

The formation of paramagnetic intermediates following the irradiation of styrene, α-methylstyrene, and their mixtures at ?90°C in the presence of TiCl⁴ and SnCl⁴ in the polycrystalline heptane matrix was investigated. The effect of light on vinyl aromatic monomers leads to the formation of radical cations of styrene and α-methylstyrene, which subsequently initiate the polymerization. The polymerization of styrene and α-methylstyrene supposedly proceeds via the cationic mechanism.     

Photo and thermal polymerization sensitized by donor–acceptor interaction. I. N-vinyl-carbazole–acrylonitrile and related systems

Spontaneous photo and thermal polymerization of N-vinylcarbazole (VCZ)–acrylonitrile (AN), VCZ–acetonitrile, AN-N-ethylcarbazole, and AN-ferrocene were studied. These combinations of electron donor with acceptor were thermally rather stable but showed prominent photopolymerizability when the systems were irradiated by near ultraviolet light. The VCZ–AN system showed multireactivity producing VCZ polymer and a copolymer of VCZ with AN. The composition of copolymer was approximately the same as that of polymer produced in radical copolymerization. The effects of additives (DPPH, NH₃, H₂O, air) indicated simultaneous occurrence of cationic and radical polymerization in the AN–VCZ and acetonitrile–VCZ systems. The results were interpreted on the assumption of initial formation of a cation radical–anion radical pair. The ratio of cationic to radical polymerization differed for photo and thermal polymerization. In no case was anionic polymerization detected.     

Polymerization of β-cyanopropionaldehyde. V. Anionic polymerization initiated by benzophenone–alkali metal complexes

Anionic polymerization of β-cyanopropionaldehyde was studied with use of benzophenone-monosodium, -disodium, and -dilithium complexes as initiators. The resulting poly(cyanoethyl)oxymethylene was compared with that obtained by cationic and coordinated initiators previously reported. Polymer of higher stereoregularity but lower molecular weight was formed in the present system. The marked influence of the initiator concentration on the polymer yield and stereoregularity is explained on the basis of the difference in the degree of association of the alcoholate ion pair, i.e., the associated ion pair may form stereoregular polymer and the nonassociated or less-associated ion pair may form a large amount of amorphous atactic polymer. The initiation with benzophenone-dialkali metal complex was found to be bond-formation type. Chain transfer with active hydrogen of β-cyanopropionaldehyde frequently occurs.     

Ionic polymerization under an electric field. III. Cationic polymerizations of α-methylstyrene and styrene

Cationic polymerizations of α-methylstyrene and styrene were carried out in an electric field with iodine as a catalyst and ethylene dichloride as the solvent. The effects of the field on the rate of polymerization and the degree of polymerization were studied. It was found that the field increased the rate of polymerization of α-methylstyrene and, also slightly increased the degree of polymerization, whereas the field had no influence on these quantities in the case of styrene. The expressions for the rate of polymerization and the degree of polymerization, which were derived in a previous paper and refined in the present paper, show that these quantities are generally a function of the degree of dissociation of ion pairs at growing chain ends. For a comparatively large degree of dissociation, these expressions can account for the field effect as was observed on α-methylstyrene, if one assumes that the degree of dissociation in the presence of an electric field is larger than that in its absence, and that the free-ion propagation proceeds much faster than the ion-pair propagation. For a small degree of dissociation, however, these expressions become practically independent of the degree of dissociation so that a possible increase due to the presence of an electric field gives rise to no observable effect on the polymerization. This situation may be interpreted as corresponding to the case of styrene. In other words, the polymerization of α-methylstyrene has more free ionic character than that of styrene.     

The cationic polymerization and copolymerization of isopropenylmetallocene monomers

Three types of isopropenylmetallocene monomers were synthesized and subjected to polymerization and copolymerization by cationic initiators; (1) isopropenylferrocene (IF); (2) (η⁵-isopropenylcyclopentadienyl)dicarbonylnitrosylmolybdenum (IDM); and (3) 1,1′-diisopropenylcyclopentadienylstannocene (DIS), and related derivatives of each. IF was synthesized by a three-step procedure involving the acetylation of ferrocene, conversion of the latter to 2-ferrocenyl-2-propanol, and dehydration of the carbinol. IF was homopolymerized under various cationic initiation conditions, but only low molecular weight homopolymers were obtained. Copolymerization of IF with styrene and with p-methoxy-α-methylstyrene also gave only low molecular weight products. The formation of only low molecular weight polymers in all polymerization reactions is believed to result from the effect of the unusually high stability of ferrocenyl carbenium ions on its propagation reaction. The observed polymerization behavior of α-trifluoromethylvinylferrocene is in accord with this conclusion. IDM and DIS did not form polymeric products under cationic conditions, although copolymers could be obtained for each of these monomers and styrene with a free radical polymerization initiator (AIBN).     

Cationic polymerization of α-methylstyrene in dichloromethane initiated with system 2,5-dichloro-2,5-dimethylhexene-BCl3. II. Continuous addition of monomer into initiator,quasiliving polymerization

A slow continuous addition of dichloromethana solutions of α-methylstyrene (α-MeSt) into a dichloromethane solution of 2,5-dichloro-2,5-dimethylhexane (DDH) with BCI₃ (initiating system II) prepared in advance resulted, in the temperature range between ?20 and ?40°, in a quasilving polymerization of α-MeSt. At ?20°C and a 100% conversion a polymer with a very narrow molecular weight distribution is formed, M?_w/M?_n - 1.1. Quasiliving polymerization of α-MeSt has not been achieved with freshly prepared dischloromethane solutions of DDH with BC₃ (initiating sytem I), or with solutions of BCI₃ alone (initiating system III). Polarity of the polymerization medium affected molecular weight distribution (MWD) of the polymer, and the polydispersity index decreased with decreasing polarity. MWD of the polymer samples were studied by the GPC method, the structure of poly (α-methylstyrene) (Pα-MeSt) was investigated by the ₁H-NMR analysis     

Stereospecific polymerization of benzyl α-(alkoxymethyl) acrylates

α-(Alkoxymethyl) acrylates, such as methyl α-(phenoxymethyl) acrylate, benzyl α-(methoxymethyl)acrylate (BMMA), benzyl α-(benzyloxymethyl)acrylate, and benzyl α-(tert-butoxymethyl)acrylate, were synthesized, and their polymerizability and the stereoregularity of the polymers obtained by radical and anionic methods were investigated. The radically obtained polymers were found to be atactic by ¹³C- and ¹H-NMR analyses, but the polymers obtained with lithium reagents in toluene at −78°C were highly isotactic. Further, it is noteworthy that isotactic polymers were also produced with lithium reagents even in tetrahydrofuran. Effects of polymerization temperature and counter cation on stereoregularity were clearly observed in the polymerization of BMMA, and a potassium reagent afforded an almost atactic polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 721–726, 1997     

Polymerization of α-methyleneindane: A cyclic analog of α-methylstyrene

α-Methyleniedane (MI), a cyclic analog of α-methylstyrene which does not undergo radical homopolymerization under standard conditions, was synthesized and subjected to radical, cationic, and anionic polymerizations. MI undergoes radical polymerization with α,α′-azobis(isobutyronitrile) in contrast to α-methylstyrene, owing to its reduced steric hindrance, though the polymerization is slow even in bulk. Cationic and anionic polymerization of MI with BF₃OEt₂ and n-butyllithium, respectively, proceed rapidly. The thermal degradation behavior of the polymer depends on the polymerization conditions. The anionic and radical polymers are heteortactic-rich. Reactivity ratios in bulk radical copolymerization on MI (M₂) with methacrylate (MMA, M₁) were determined at 60°C (r₁ = 0.129 and r₂ = 1.07). In order to clarify the copolymerization mechanism, radical copolymerization of MI with MMA was investigated in bulk at temperatures ranging from 50 to 80°C. The Mayo–Lewis equation has been found to be inadequate to describe the result due to depolymerization of MI sequences above 70°C.     

Stereospecific polymerization of methacrylonitrile. II. Influence of polymerization conditions on polymerization and on properties of polymers

Stereospecific polymerization of methacrylonitrile with diethylmagnesium has been studied. Polymerization temperature has an important effect on polymerization. The conversion, stereoregularity, and intrinsic viscosity of the polymer increased significantly with increasing polymerization temperature. Stereoregularity of the polymer improved with increasing the polymerization time and the monomer concentration, but it is independent of the catalyst concentration. Intrinsic viscosity of the crystalline polymer increased with increasing monomer concentration but is independent of the polymerization time and the catalyst concentration. It is suggested that two mechanisms are involved in this polymerization: coordinated anionic polymerization to from the crystalline polymer, and probably conventional anionic polymerization to form the amorphous polymer. It is found that crystalline polymer can also be obtained in homogeneous phase such as in tetrahydrofuran solvent.     

The effect of additives on the polymerization of methyl methacrylate. tris(1,2-dibromo-propyl)phosphate

The effect of the additive, Tris(1,2-dibromopropyl)phosphate, on the kinetics of free radical polymerization of methyl methacrylate is studied. No marked differences were observed in the homopolymerization despite the reported effect of this additive on the mechanical properties of the resulting polymer. It was concluded that the additive was a multifunctional transfer agent producing linear and branched polymer molecules. Several model transfer agents have been studied to confirm these conclusions. H-NMR spectra of the polymer confirm that there is no change in the stereoregularity of the polymer prepared in the presence of this additive, and no copolymerization of the phosphate unit.     

Cationic Copolymerization with Depropagation. The Copolymerization of α-Methylstyrene and Styrene

ABSTRACT

To evaluate the existence of the depropagation reaction in the copolymerization of vinyl monomers, the cationic copolymerization of α-methylstyrene with styrene was studied. The copolymer composition exhibited an extensive dependency on the temperature of polymerization and the monomer concentration, this fact not being explained by the Mayo-Lewis equation. Treatment of the copolymerization in terms of the depropagation reaction led to an estimate of the monomer reactivity ratio and the equilibrium constant between the polymer and the monomer of α-methylstyrene. A comparison of the equilibrium constants thus obtained with those reported in the literature indicates that the magnitude of the equilibrium constants depends on the sequence length of α-methylstyrene units. By extrapolation to long sequence length, the equilibrium constants approach the values which are reported for high molecular weight poly(α-methylstyrene).     

Equilibrium anionic polymerization of α-methylstyrene in p-dioxane

The equilibrium anionic polymerization of α-methylstyrene in p-dioxane, with potassium as initiator, has been investigated at 5, 15, 25, and 40°C by using high-vacuum techniques. The comparison of these results with those obtained previously for the equilibrium polymerization of α-methylstyrene in tetrahydrofuran revealed that, although the values of ΔG_1c, the free-energy change upon the polymerization of 1 mole of liquid monomer to 1 bases-mole of liquid amorphous polymer of infinite chain length, are the same for both systems, there is a distinct effect of the solvent. This effect is reflected in the value of monomer equilibrium concentration and its variation with polymer concentration and is explained in terms of a solvent–monomer and solvent–polymer interaction parameter.     

Synthetic applications of non-polymerizable monomers in living carbocationic polymerization

The foundation and methodology of using highly reactive but non-polymerizable monomers in living cationic polymerizations is introduced. The chemistry and kinetics of 1,1-diphenylethylene (DPE) addition to living polyisobutylene (PIB) in methyl chloride/n-hexanes 40/60 v/v at −80°C is reported. Monoaddition occurred even when large excess of 1,1-diphenylethylene was used. The methanol quenched polymer of the DPE capped PIB carried -OCH₃ functionality exclusively, suggesting that the diphenyl alkyl chain-ends are completely ionized, which was confirmed by conductivity studies. By in-situ functionalization using soft nucleophiles a variety of functional groups were obtained, most notably ester upon reaction with silyl ketene acetal. It was found that the diphenyl carbenium ion is an efficient initiating species for the polymerization of reactive monomers such as vinyl ethers and α-methylstyrene. The synthesis of PIB based block copolymers was accomplished by sequential monomer addition, using para-methylstyrene, α-methylstyrene or isobutyl vinyl ether as the second monomer. It involved capping with DPE, followed by tailoring the Lewis acidity to the reactivity of the second monomer by the addition of titanium(IV) alkoxide, by replacing the Lewis acid with a weaker one or by the use of a common ion salt. PIB-b-PMMA was obtained by the combination of living cationic and group transfer (GTP) polymerizations.     

Laser-initiated polymerization of epoxies in the presence of maleic anhydride

Laser-initiated polymerization of cyclohexene oxide in the presence of maleic anhydride was investigated. The influences of solvents laser irradiation time and the monomer feed ratio on the polymer yield and composition were evaluated. The rate of polymerization increased with an increase in the molar concentration of maleic anhydride in the monomer feed. Short irradiation times of 1–3 min duration gave very high yield of epoxy polymer (>80% conversion). Infrared spectral studies of the polymer product indicated the formation of polyether linkage at lower levels of conversion and an adduct of polyether and maleic anhydride at higher polymer conversions. The quantitative chemical analyses results also showed similar results. The results indicated that the polymerization was initiated by the excited charge transfer complex between the electron donor, cyclohexane oxide, and the electron acceptor–maleic anhydride. In the initial stages of polymerization, cyclohexene oxide undergoes a cationic polymerization in the presence of the radical anion of maleic anhydride. Laser-initiated polymerization of cyclohexene oxide/maleic anhydride is several hundred times more efficient than UV-initiated polymerization, as measured by the energy absorbed by the polymer system.