Anionic polymerization of β-nitrostyrenes

The rate of polymerization of β-nitrostyrene initiated by sodium alkoxide was setudied gravimetrically. The rate was found to be first order with respect to monomer concentration and first order with respect to initiator concentration. Rate constants in the order of 0,25 dm³ · mol^?1 · s^?1 were obtained at 15°C, 20°C, and 25°C for the polymerization of β-nitrostyrene, p-methoxy-β-nitrostyrene, and p-methyl-β-nitrostyrene initiated by sodium methoxide and by sodium ethoxide. The activation energy of polymerizations initiated by sodium methoxide and by sodium ethoxide was ～24 kJ · mol^?1 and ～ 16 kJ · mol^?1, respectively. The number average degree of polymerization of poly(β-nitrostyrene)s was determined by polymerization of the monomer in the pressence of ¹⁴C-alkanol. This is the first time that accurate number average molar masses of poly(β-nitrostyrene)s have been reported since conventional methods of molar mass determination cannot be used owing to the insolubility of these polymers in most common organic solvents.     

Synthesis and ring-opening polymerization of α-chloromethyl-α-methyl-β-propiolactone

α-Chloromethyl-α-methyl-β-propiolactone (CMMPL) was synthesized by dehydrohalogenation of α,α-dichloromethyl-β-propionic acid which was obtained by chlorination of α,α-hydroxymethyl-β-propionic acid (DMPA). Due to high strain of the four-numbered ring, CMMPL can be polymerized by ring-opening with or without an initiator. Both electrophiles like trifluoroacetic acid (TFAA) and nucleophiles like triethylamine (TEA) and pyridine, as well as organometallic compounds such as stannous octoate [Sn(Oct)₂)], aluminium triisopropoxide [Al(OⁱPr)₃] and tetrabutyl orthotitanate [Ti(OC₄H₉)₄], were found to be effective initiators. The polymerization can be conducted by either solution or bulk polymerization. P(CMMPL) is insoluble in almost all organic solvents at room temperature. An endothermic peak (ca. 214 ˜ 250°C) attributed to the melting transition of P(CMMPL) was observed in DSC curves. P(CMMPL) tends to have high crystallinity (40% ˜ 60%) as demonstrated by its X-ray diffraction patterns, and the crystallinity was found to vary with the types of initiator used.     

Structure of active species in the cationic polymerization of β-propiolactone and ε-caprolactone

The study of the structure of the end-groups of poly(β-propiolactone) and poly(ε-caprolactone) by ¹H, ³¹P{¹H} NMR, and IR spectroscopy revealed that the mode of ring scission in the monomer in the first propagation step depends on the initiator used. In the initiation of the β-propiolactone and ε-caprolactone polymerization with halonium salts ((CH₃)₂Br^⊕SbF₆^? or (CH₃)₂I^⊕SbF₆F₆^?) the exocyclic oxygen atoms in the monomer molecules are attacked and oxonium ions are formed. The propagation steps proceed with alkyl-oxygen bond scission in the active center and with attack at the exocyclic oxygen atom in the subsequent monomer molecule. Thus, the tertiary oxonium ions are the exclusive active species from the very beginning of the polymerization. Acylium cations (CH₃CO^⊕ SbF₆^? or CH₃CH₂CO^⊕SbF₆^?) as initiators attack both exo-and endocyclic oxygen atoms in the monomers and the initiation proceeds with almost equal proportions of alkyl-oxygen and acyl-oxygen bond scission. Thus, in the polymerization of β-propiolactone the concentration of the acylium growing species decreases with increasing number of propagation steps and finally the tertiary oxonium ions are becoming the exclusive growing species. In the polymerization of ε-caprolactone the active acylium centers apart from propagation participate also in side reactions leading to the cleavage of a proton.     

Termination kinetics in free-radical bulk terpolymerization — the systems methyl acrylate – butyl acrylate – dodecyl acrylate and methyl methacrylate – butyl methacrylate – dodecyl methacrylate

Termination rate coefficients, k_t , for the terpolymerization of mixtures containing the three acrylates: methyl, butyl, and dodecyl acrylate or the corresponding members of the methacrylate family: methyl, butyl, and dodecyl methacrylate, have been measured via the single pulse (SP)-PLP technique. In the homopolymerization of each of the six monomers an initial plateau region of almost constant k_t is seen which extends at least up to 15% and, for dodecyl acrylate and dodecyl methacrylate, even up to about 50% monomer conversion. Terpolymerization k_t in this region of low and moderate conversion is remarkably well described by a rather simple correlation which exclusively contains homopolymerization k_t and the composition of the monomer mixture. This correlation turns out to be very useful for the modeling of k_t in mixtures of monomers that exhibit such an initial plateau region of k_t . For the systems under investigation, terpolymerization k_t may be estimated within ± 30%. This finding is very remarkable in view of the enormous differences in homopolymerization k_t within each monomer family, e. g., k_t of methyl acrylate exceeds the corresponding dodecyl acrylate value by a factor of 50 (or 5 000%). The entire set of experiments has been carried out at 40°C and 1 000 bar where the signal to noise ratio of the laser-induced single pulse experiments is very satisfactory. No reason is seen why the conclusions about modeling of terpolymerization k_t should not be valid at other reaction conditions including ambient pressure.     

Formation of Macrozwitterions in the polymerization of β-propiolactone initiated by betaine. 4th Communication on Macrozwitterions

The anionic polymerization of β-propiolactone at 25°C in ethanol initiated by the betain \documentclass{article}\pagestyle{empty}\begin{document}${\rm (CH}_3 )_3 \mathop {\rm N}\limits^ \oplus - {\rm CH}_{\rm 2} {\rm COO}^ \ominus $\end{document} was investigated. Macrozwitterions of the structure were produced, n being intentionally as low as ca. 11. The structure of the product was proven by the nitrogen content of the reprecipiated polymer, by IR and NMR spectroscopy and by titration of the carboxylate endgroups. Some carboxylic acid endgroups were formed by chain transfer with the solvent ethanol. The positive charge at the polymer chain was proven by electrophoresis of polymer after esterification of the carboxylate chain end. Furthermore the dielectric constant of dilute solutions of the polymer in CHCl₃ was determined and is discussed. The kinetics of the polymerization process were investigated by IR-spectroscopy. The initiation reaction between monomer and betain is about 5 times slower than the consecutive propagation by addition of monomer to the anionic chain end.     

Formation of the intermediate cyclic six-membered oxonium ion in the cationic polymerization of β-propiolactone initiated with CH3CO⊕SbF

Analysis of the ¹H NMR spectra of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document} /β-propiolactone and of the model systems \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document}/(CH₃)₂O and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} \mathop {\rm C}\limits^ \oplus {\rm OSbF}_{\rm 6}^ \ominus $\end{document}/CH₃COOCH₃ in liquid SO₂ in the temperature region ?70 to ?20°C revealed that the reaction of the acetylium cation with β-propiolactone leads to the cyclic six-membered oxonium ion 4 , participating as an intermediate in the initial stage of polymerization.     

Anionic block polymerization of β-lactones initiated by potassium solutions, 1. Synthesis of poly(4-methyl-2-oxetanone-block-2-oxetanone)

The block polymerization of 4-methyl-2-oxetanone (β-butyrolactone) with 2-oxetanone (β-propiolactone) proceeds fast with a yield of more than 90%, in the presence of potassium solutions in THF containing 18-crown-6. Poly(4-methyl-2-oxetanone-block-2-oxetanone) polymers having the expected molecular weight and composition are formed by this way. Their glass transition and melting temperatures as well as their melting enthalpies, determined by DSC, show a strict correlation with block polymer composition.     

Anionic equilibrium polymerization of α-methylstyrene initiated by butyllithium/dimethoxyethane and glyme-1

The kinetics and mechanism of anionic equilibrium polymerization of α-methaylstyrene in cyclohexane with butyllithium (BuLi) as initiator and dimethoxyethane (DME) and glyme-1 (bis(2-methoxyethyl)) ether; (1G) as polar additives were investigated. The apparent constant of propagation k_ap and of depropagation k_ad were evaluated over a wide concentration range of DME (or 1G). The kinetic equations of the equilibrium polymerization as mole ratios of [DME]/[BuLi] < 1,66, [DME]/[BuLi] > 33,3 and 1,66 < [DME]/[BuLi] < 33,3 were established. The mathematic equations of the equilibrium monomer concentration [M]_e deduced from the kinetic measurements, at the above mentioned ratios [DME]/[BuLi], were used to control the polymerization process. The rate constants of different active species and the equilibrium constants between active species were calculated by the curve fitting method for the DME system. The fact that free ions exist in the polymerization system when the concentration of 1G was about 40 vol.-% was proved by conductance measurements. Finally, the reaction features of the anionic polymerization of α-methylstyrene with various polar additives are compared.     

Kinetic determination of stereoselectivity in the anionic polymerization of α-ethyl-α-phenyl-β-propiolactone

The kinetics of the anionic polymerization of optically active α-ethyl-α-phenyl-β-propiolactone (optical purity 16,8%) initiated with bis(triphenylphosphine)iminium acetate was investigated and the rate constants for the homo-(k_ph) and crosspropagation (k_pc) (considering R and S enantiomers as comonomers) were determined. The knowledge of the values of k_ph and k_pc, equal to 1,53·10^?4 and 9,0·10^?51· mol^?1·s^?1, respectively (25°C, CH₂Cl₂ solvent), allowed us to calculate the distribution of homosequences in the polymer prepared from racemic monomer. The concentration of homosequences was slightly higher than calculated for the process with random enchainment of enantiomers. Thus, the content of homodyads, homotriads, and homotetrads equals 63, 40, and 25%, whereas for the random process it was 50, 25, and 13%, respectively. This difference is, however, too small to create homoblocks which could be responsible for the observed crystallinity of these polymers.     

Polylactones, 2 Copolymerization of glycolide with β-propiolactone, γ-butyrolactone or δ-valerolactone

Numerous copolymerizations of glycolide with β-propiolactone, γ-butyrolactone or δ-valerolactone were conducted either in bulk or in nitrobenzene solution at temperatures in the range of 20 to 150°C. Three classes of catalysts were used, namely acidic catalysts initiating cationic polymerizations, complexing catalysts initiating insertion mechanisms, and anionic catalysts. The molar composition of the copolyesters was determined from ¹H NMR spectra and the sequence distribution of the comonomers from ¹³C NMR spectra. No reasonable copolymerization of glycolide and βhyphen;propiolactone was obtained at 20°C in nitrobenzene, whereas all catalysts yielded copolyesters at 100°C. In the case of glycolide/γ-butyrolactone only bulk copolymerizations at 60°C with acidic initiators were successful. Under other conditions only homopolymerization of glycolide was observed. Copolymerizations of glycolide and γ-valerolactone were performed in bulk and in nitrobenzene with both acidic and complexing initiators, whereas anionic initiators only caused homopolymerization of glycolide. Acidic initiators favored the incorporation of δ-valerolactone, whereas the complexing initiators favored the incorporation of glycolide. The crystallinity of the glycolide/δ-valerolactone copolymers was characterized by means of differential scanning calorimetry, and a good agreement with the expectations from both molar composition and sequence distribution was found.     

Emulsion polymerization of butyl methacrylate initiated by 2,2′-azoisobutyronitrile, 1. Kinetics and mechanism

The effect of 2,2′-azoisobutyronitrile (AIBN) on the kinetics and mechanism of emulsion polymerization of butyl methacrylate was studied in the presence of anionic emulsifier disodium dodecylphenoxybenzene disulfonate (Dowfax® 2A1) at 60°C. The ratio between the proportion of the polymerization in monomer droplets and that of the polymerization in the aqueous phase was determined for the overall initial rate of butyl methacrylate polymerization in the region of the increasing polymerization rate (interval I). Using the model of polymerization in discrete particles, the portion of the polymerization in monomer droplets with a diameter of 100 nm in the overall polymerization rate is 24,4%; the portion of the polymerization in the water phase is only 0,022% for a concentration of Dowfax® 2A1 of 5 · 10^?2 mol · dm^?3, and 60,4% and 0,054% for a Dowfax® 2A1 concentration of 1 · 10^?2 mol · dm^?3. The exponent of the emulsifier concentration in the equation for the polymerization rate is 0,56 for interval I and 0,36 for interval II; the exponent for the concentration of AIBN over the conversion range between 0 and 30% is 0,34. For the proposed reaction mechanism it is assumed that 2-cyanoisopropyl radicals, generated from AIBN in the water phase, are responsible for the initiation of polymerization in micelles swollen by monomer and in polymer/monomer particles. Polymer/monomer particles are formed also by co-precipitation of oligomer radicals, which in turn are formed by polymerization of monomer molecules present in the water phase. Polymerization within monomer droplets has no significant influence on the course of emulsion polymerization.     

Polylactones, 7. The mechanism of cationic polymerization of β-propiolactone and ϵ-caprolactone

Homopolymerisations of β-propiolactone and ?-caprolactone, initiated by means of methyl trifluorosulfonate, triethyloxonium tetrafluoroborate or acetylium perchlorate, were investigated. Both ¹H and ¹³C NMR spectra proved that the alkylating initiators yield polyesters with alkyl ester end groups, indicating a chain growth via alkyl-oxygen cleavage of the lactone. At temperatures below 100°C cationic polymerizations initiated by alkylating reagents were found to proceed via end groups which may cause degradation due to back-biting. When ?-caprolactone was reacted with excess methyl triflate, high concentration of triflate ester end groups were formed, whereas in the case of β-propiolactone active end groups were not detectable by ¹H NMR spectroscopy. Initiation with acetylium perchlorate yielded a polyester with acetate end groups. Acetate end groups were also obtained, when “living” polymers, initiated with methyl triflate, were reacted with acetic anhydride. It could be shown that the formation of acetate end groups does not indicate an electrophilic attack at the endocyclic oxygen. Furthermore, it is discussed that any experimental evidence for a cationic chain growth via acyloxygen bond cleavage is lacking.     

Anionic polymerization of oxiranes and cyclic siloxanes initiated with potassium salt-crown ether systems

Potassium carboxylates and 18-crown-6 form initiator systems for the anionic polymerization of oxiranes to afford polyethers with an acyloxy group at one of the chain ends. Because of the slow initiation as compared to the propagation step, the resulting polymers have wide molecular weight distributions (M _w/M _n ≈ 4,0). The presence of a small amount of water in the catalysts accelerates the initiation to give polymers with narrow molecular weight distributions (M _w/M _n ? 1,2). The polymerization of methyloxirane is accompanied by a significant chain-transfer reaction to the monomer, especially at high temperatures. Hexamethylcyclotrisiloxane is also polymerized by the same initiators. Furthermore, potassium salts of carboxylic acids initiate the polymerizations in the presence of a crown ether.     

Anionic polymerization of carbazolyl-substituted oxiranes initiated by potassium alkalide,potassium tert-butoxide and potassium hydride

The influence of the kind of initiating system and the addition of a crown ether on the anionic polymerization of oxiranes with a carbazoyl substituent is described. Potassium alkalide, potassium tert-butoxide and potassium hydride were used as initiators. Selecting a suitable initiator and crown ether concentration, carbazolyl-containing polymers with polymerization degrees from 4 to 60 can be produced. Using a suspension of potassium hydride in tetrahydrofuran, polymers with relatively high molar masses were obtained.     

Polymerization of β-propiolactone by metal acetylacetonates and carboxylates

Some metal acetylacetonates and carboxylates are effective for the polymerization of β-propiolactone ( 2 ). The activity depends on the metallic ion. Heterochelates containing 2,2′-dipyridyl or 1,10-phenanthroline and acetylacetone as ligands have a large effect due to the tertiary amine groups. Titanocene dichloride is an effective promoter for these polymerizations. The combination of titanocene dichloride and metal acetylacetonates has an activity for the polymerization of 2-chloroethyl vinyl ether, which neither component has separately.     

Emulsion polymerization of butyl methacrylate initiated by 2,2′-azoisobutyronitrile, 3. On the applicability of the modified Smith-Ewart model

The applicability of the modified Smith-Ewart model to the butyl methacrylate emulsion polymerization in interval II, initiated by both 2,2′-azoisobutyronitrile (AIBN) and ammonium persulfate at 60°C, was tested. The equilibrium monomer concentration in the latex particles in interval II was found to be constant and independent of the emulsifier concentration and the initiator type used. The rate of initiation increases with increasing emulsifier concentration for the polymerizations initiated with a water-soluble initiator. In the systems with the oil-soluble initiator, the rate of initiation is independent of the emulsifier concentration. The rate of polymerization increase with increasing emulsifier concentration for both initiator systems. In the system with the oil-soluble initiator lower values of the polymerization rate and higher values of the viscosity-average molecular masses of the polymer were observed. The number of particles, the radical concentration within polymer particles and the calculated rate of polymerization increase, while the mean particle radius decreases with increasing concentration of the emulsifier for both systems. The average-number of radicals per particle and the ratio of the rate constants for propagation and termination was found to be independent of the emulsifier concentration and the initiator type. A good agreement was observed between the estimated and observed particle radii for both initiator systems. The Smith-Ewart model was found to be applicable for the emulsion polymerization of butyl methacrylate initiated by both ammonium persulfate and AIBN.     

Radical polymerization of a trimer of methyl acrylate as polymerizable α-substituted acrylate

The radical polymerization of a trimer of methyl acrylate was investigated in relation to the steric hindrance-assisted polymerization of an α-(substituted methyl)acrylic ester. The trimer can also be regarded as a model of the unsaturated end group formed by the addition-fragmentation chain transfer of methyl α-(bromomethyl)acrylate during methyl acrylate polymerization. The trimer polymerizes slowly to a low-molecular-weight polymer at 30–60°C, and electron spin resonance (ESR) quantification of the propagating radical of the trimer allowed the determination of the absolute rate constants of propagation (k_p) and termination (k_t). The k_p and k_t values for the trimer indicate slow propagation and slow termination of polymerizable acrylates bearing a bulky α-substituent. In conformity with a higher reactivity of the trimer of methyl acrylate than the corresponding trimer of methyl methacrylate, poly(methyl acrylate) bearing an unsaturated end group, which is produced by the polymerization of methyl acrylate in the presence of methyl α-(bromomethyl)acrylate, was confirmed to copolymerize with methyl acrylate to yield a branched homopolymer.