Polymerization of α-methylstyrene by n-butyllithium in tetrahydrofuran

The kinetics of polymerization of α-methylstyrene by n-BuLi (labeled with C¹⁴ and unlabeled) has been studied in tetrahydrofuran at ?78°C. The catalyst n-BuLi was used as a complex of n-BuLi in THF and a hexane solution of n-BuLi. Contrary to expectations, the relative polymerization rate and the catalyst consumption were higher when a hexane solution of n-BuLi was used. Experimental molecular weights of the polymers greatly exceeded those calculated for the case of complete catalyst consumption. The polymers exhibited low polydispersity, and when a hexane solution of n-BuLi was used, the molecular weight distribution was bimodal. The rate of initiation for the case of polymerization α-methylstyrene with a hexane solution of n-BuLi as a catalyst was much higher than in the polymerization of α-methylstyrene with the use of the complex of n-BuLi in THF as in situ catalyst. Experimental data confirm the preferable interaction of α-methylstyrene with associated n-BuLi in the presence of THF. The complex which was formed as a result of such interaction is an active centers of polymerization.     

Anionic copolymerization of optically active α-methylbenzyl methacrylate and trityl methacrylate. I. Reactivity of monomers

The monomer reactivity ratios were determined in the anionic copolymerization of (S)- or (RS)-α-methylbenzyl methacrylate (MBMA) and trityl methacrylate (TrMA) with butyllithium at ?78°C, and the stereoregularity of the yielded copolymer was investigated. In the copolymerization of (S)-MBMA (M₁) and TrMA (M₂) in toluene the monomer reactivity ratios were r₁ = 8.55 and r₂ = 0.005. On the other hand, those in the copolymerization of (RS)-MBMA with TrMA were r₁ = 4.30 and r₂ = 0.03. The copolymer of (S)-MBMA and TrMA prepared in toluene was a mixture of two types of copolymer: one consisted mainly of the (S)-MBMA unit and was highly isotactic and the other contained both monomers copiously. The same monomer reactivity ratios, r₁ = 0.39 and r₂ = 0.33, were obtained in the copolymerizations of the (S)-MBMA–TrMA and (RS)-MBMA–TrMA systems in tetrahydrofuran (THF). The microstructures of poly[(S)-MBMA-co-TrMA] and poly-[(RS)-MBMA-co-TrMA] produced in THF were similar where the isotacticity increased with an increase in the content of the TrMA unit.     

Polymerization of α-methylstyrene by living polymer in tetrahydrofuran

Kinetics of polymerization of α-methylstyrene by poly-α-methylstyrylsodium (a “living” polymer) has been studied in tetrahydrofuran at ?78°C. Complex dependences were established: that of the conversion X on reduced time φ and that of the apparent rate constant for the polymer chain propagation on conversion X and on the concentration of living polymers and monomer. The experimental data obtained were explained by assuming a coordination mechanism of anionic polymerization including the following elementary reaction: (a) generation of active polymerization centers (K₁) by interaction of the living polymer with the monomer; (b) propagation of the polymer chains (K₂); (c) monomolecular (K₃₁) and bimolecular (K₃₂) reactions of isomerization of active centers resulting in the formation of high molecular weight living polymers capable of again becoming active centers of polymerization. Approximate derivation of kinetic equation was carried out and the constants of elementary reactions were determined (K₁ = 0.15, K₂ = 24, K₃₂ = 14.1./mole-min and K₃₁ = 0.05 min^?1). The coincidence of the expected dependencies X = F(τ; φ) K_p = F(X; n₀^?1/2); dx/dτ = F(n₀) with the experimental ones was followed with the aid of computers. The expected change in the values of X and K_p depending on the contribution of each elementary reaction to the overall polymerization process was analyzed.     

Effect of tetraalkylammonium salts on the tacticity of poly(methyl methacrylate), 1. Initiation by ethyl α-lithioisobutyrate

The anionic polymerization of methyl methacrylate (MMA) was carried out in the presence of ethyl α-lithioisobutyrate (α-LiEtIB)/quaternary ammonium salts (QAS) in toluene and tetrahydrofuran/toluene (vol. ratio 75/25) at −60°C. It was found that the tacticity of PMMA strongly depends on size and shape of QAS. A highly isotactic polymerization in toluene was observed, when using the system α-LiEtIB/trimethylhexadecylammonium bromide. The initiator system α-LiEtIB/tetrahexylammonium chloride produces polymers with a high (>50%) syndiotactic content and relatively low polydispersity. The influence of QAS on the mode of polymerization is due to specific salt effect resulting from the cation exchange reaction, from the participation of the bulky substituent in the primary solvation shell, and ionic aggregation between the growing anion, Q⁺ and LiX.     

Polymerization of 1-chloro-2-β-naphthylacetylene by Mo catalysts and polymer properties

1-Chloro-2-β-naphthylacetylene (ClβNA) polymerized in good yields in the presence of MoCl₅-based catalysts. The highest weight-average molecular weight of poly(ClβNA) reached about 3 × 10⁵. The polymer was a yellow solid (absorption cutoff in CHCl₃ 450 nm). It was soluble in toluene, chloroform, etc., and provided a tough film by the solvent casting method. The polymer retained its weight up to 300°C in air; it was thermally less stable than poly(1-chloro-2-phenylacetylene) but more stable than poly(β-naphthylacetylene). The oxygen permeability coefficient (P_O2) of this polymer was 19 barrers (25°C), which is fairly small for a substituted polyacetylene. © 1996 John Wiley & Sons, Inc.     

Anionic polymerization of biomass‐derived furfuryl methacrylate: Controlling polymer tacticity and thermoreversibility

Biomass‐derived furfuryl methacrylate (FMA) has been successfully polymerized for the first time by anionic polymerization to produce atactic (at‐), isotactic (it‐), or syndiotactic (st‐) poly(furfuryl methacrylate) (PFMA), depending on initiator structure and reaction conditions. Thermal properties of the PFMA materials are strongly affected by the polymer tacticity. Most notably, while both isotactic and syndiotactic polymers can undergo inter‐ or intrachain crosslinking reactions when heated to 290 °C, there is no evidence for the atactic polymer to perform the same reaction. Furthermore, the PFMA tacticity also greatly affects the amount of stable carbonaceous materials it produces when heated to 650 °C, with st‐PFMA forming the largest amount of such materials (26.9%), as compared to only 5.6% by at‐PFMA. Using the Diels–Alder (DA) “click reaction” between the reactive furfuryl group within the PFMA polymers as the diene equivalent and a bismaleimide as the dienophile, thermoreversible smart polymers have been successfully prepared. Thermoreversibility of the preformed crosslinked polymers has been demonstrated, thanks to the facile retro‐DA reaction upon heating and the DA reaction upon cooling of such self‐healing materials. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2793–2803     

Polymerization of α-methylene-N-methylpyrrolidone

α-Methylene-N-methylpyrrolidone (α-MMP) was synthesized and homopolymerized by bulk and solution methods. The poly(α-MMP) is readily soluble in water, methanol, methylene chloride, and dipolar aprotic solvents at room temperature. Thermogravimetric analysis of poly(α-MMP) showed a 10% weight loss at 330°C in air. The kinetics of α-MMP homopolymerization and copolymerization were investigated in acetonitrile, using azobisisobutyronitrile (AIBN) as an initiator. The rate of polymerization R_p could be expresed by R_p = k[AIBN]^0.49[α-MMP]^1.3. The overall activation energy was calculated to be 84.1 kj/mol. The relative reactivity ratios of α-MMP (M₂) copolymerization with methyl methacrylate (r₁ = 0.59, r₂ = 0.26) in acetonitrile were obtained. Applying the Q-e scheme led to Q = 2.18 and e = 1.77. These Q and e values are larger than those for acrylamide derivatives.     

Polymerization and copolymerization of α-methacrylophenone

Under a variety of conditions it has not been possible to induce the free-radical-initiated homopolymerization of α-methacrylophenone (α-MAP). The only product isolated from such efforts was the Diels-Alder dimer of the monomer. A Mayo-Lewis plot of the free-radical copolymerization of α-MAP and styrene shows considerable scatter but the copolymer composition indicates that an α-MAP unit can add to itself. These results have been ascribed to a penultimate effect. α-MAP is homopolymerized by dimsylsodium or n-butyllithium. Attempted copolymerization of α-map and styrene with n-butyllithium produces >95% α-MAP. Unexpectedly, α-MAP does not homopolymerize with lithium dispersion, but does react in the presence of styrene to give product containing a relatively small amount of α-MAP.     

Stereoselective synthesis of D-α-glucopyranosides,di-and tri-saccharides via 6-O-acetyl-glucopyranosyl bromides

Acetyl bromide cleaved 2,3,4-tri-O-benzyl-l,6-anhydro-B-D-glucopyranose (la) or 2,3,4-tri-O-benzyl-1,6-anhydro-B-Z)-galactopyranose (1a') to give the corresponding a-D-pyranosyl bromides (2). Reaction of 2 with ROH/diisopropylethylamine gave the corresponding a-glucopyra-nosides, di- and tri-saccharides with good yield. It was available to use 13C NMR to monitor the glycosidation reaction.     

Polymerization photoinitiated by carbonyl compounds. IV. α-diketones and α-substituted alkanones

The photoinitiation efficiency of the free-radical polymerization of methyl methacrylate and styrene by several carbonly compounds has been determined. The compounds considered were α-substituted ketones and α-dicarbonyl compounds. For the ketones, the initiation efficiency employing methyl methacrylate depends on the α substitution; the values obtained change from less than 10^?3 (acetone) to 0.65 (3-hydroxy-3-methyl-2-butanone). All ketones are more efficient towards methyl methacrylate than styrene. This result can be explained in terms of triplet quenching by the last monomer. The results obtained employing α-dicarbonyl compounds do not conform to a simple pattern. In particular, benzil shows a considerably larger efficiency towards styrene than for methyl methacrylate. Since benzil is efficiently quenched by styrene, the initiation must involve the interaction of an excited benzil molecule and the monomer.     

Polymerization of 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose and 1,2-O-isopropylidene-α-D-glucofuranose

A new method for preparing D -glucose polymers is described. Isopropylidene derivatives of D -glucofuranose, particularly the 1,2-mono-O-derivative, are treated with Lewis acids, such as boron trifluoride, to eliminate acetone and produce a highly branched polymer with a molecular weight of 12,700. Approximately one isopropylidene unit remains, possibly on the potential reducing end of the glucan. Up to 95% of the polymer units are D-glucopyranoside units indicating that ring expansion occurs during the condensation.     

Effect of temperature and solvent on polymer tacticity in the free‐radical polymerization of styrene and methyl methacrylate

The effect of temperature and solvent on polymer tacticity in free‐radical polymerization of styrene and methyl methacrylate was studied by ¹³C and ¹H NMR, respectively. Polystyrene shows a mild syndiotactic tendency (P_m = 0.36 ± 0.02) that is independent of temperature over a wide range (?10 to 120 °C), while poly(methyl methacrylate) shows a stronger syndiotactic tendency (P_m = 0.17 ± 0.01 at 30 °C) that decreases as temperature is increased (P_m = 0.22 ± 0.02 at 80 °C). None of the polymerization solvents studied (bulk, THF, DMF, DMSO, acetonitrile, and acetone) had a significant effect on polymer tacticity in either system. The triad fractions of both polymers showed deviations from the Bernoulli model, implying that the antepenultimate unit affects the propagation reaction. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3351–3358     

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.     

Polymerization of α-halogenated p-xylenes with base

Various α-halo-p-xylenes have been polymerized with base yielding p-xylylene polymers. The reaction involves a 1,6-dehydrohalogenation to give a xylylene which then polymerizes. α,α′-Dichloro-p-xylene forms poly-α-chloro-p-xylylene and polymers containing stilbene units; α,α,α′,α′-tetrachloro-p-xylene gives poly-α,α,α′-trichloro-p-xylylene; alkyl, aryl, and halogen ring-substituted α-chloro-p-xylenes give the corresponding ring-substituted poly-p-xylylenes. The more halogens in the α positions (up to five), the weaker the base necessary for dehydrohalogenation. Sodium hydroxide in methanol will polymerize tetrachloro-p-xylene, while potassium tert-butoxide in refluxing p-xylene is necessary to polymerize α-chloro-p-xylenes. Stilbenes are formed when α-halo-p-xylenes are reacted with potassium tert-butoxide in polar solvents such as dimethyl sulfoxide.     

Polymerization of β-cyanopropionaldehyde. IV. Polymerization by the adducts of β-cyanopropionaldehyde with triethylaluminum

Adducts (X, Y, and Z) between triethylaluminum and β-cyanopropionaldehyde (CPA) have been prepared and characterized. It was found that an equimolar amount of triethylaluminum undergoes Grignard type addition reaction with aldehyde group of CPA to give aluminum alkoxide and that another equimolar quantity of triethylaluminum undergoes coordination with the nitrile group of CPA (adduct X, in which the molar ratio of CPA to aluminum is 1:2). The coordinated triethylaluminum in adduct X may be changed to aluminum alkoxide by the addition of further equimolar amount of CPA (adduct Y, molar ratio = 1:1); on the other hand, heating at 130°C affords mixtures of aluminum aldimine and aluminum ketenimine structures (adduct Z, molar ratio = 1:2). From the cryoscopic measurement, adduct Z may be regarded as a coordinated polymer joined through bridged structures I and II. In the polymerization of CPA at ?78°C, the stereoregularity of the resulting poly-(cyanoethyl)oxymethylene was found to increase in the order: X < triethylaluminum < Y < Z. The polymerizations with triethylaluminum, X, and Y are considered to be initiated by NCCH₂CH₂CH(C₂H₅)? O? Al(C₂H₅)₂. The degree of association of the species may influence the stereoregularity of the polymer.