Reactions of cationic living poly(tert-butyl aziridine)

The cationic polymerization of N-tert-butyl aziridine (TBA) can be conducted in such a way that the rate of termination is much slower than the rate of propagation, thus permitting preparation of a corresponding polymer which is “temporarily living”. Reactions of N-methyl-N-tert-butyl aziridinium triflate (which is the model for the active species of the living polymer) with different nucleophiles show that, at room temperature, the aziridinium ring reacts almost instantaneously with nucleophiles to form the corresponding ring-opened product. Analogous reactions with the aziridinium end group of living poly-TBA lead to polymers with varying end groups such as hydroxy, ester, primary, secondary or tertiary amino, halogen, and others. End group analysis by means of 360-MHz ¹H-NMR nuclear magnetic resonance spectroscopy showed that the concentration of the end groups was in all cases equal to the concentration of the methyl head group, originating form the initiation reaction, if the terminating nucleophile was added five minutes after initiation (at 15°C). Under these conditions the polymerization is quantitative for initiator concentrations down to 0.01 mol L^?1.     

Cationic polymerization of aliphatic cyclocarbonates

Numerous polymerizations of trimethylene carbonate (TMC) and neo-pentylene carbonate (NPC) were conducted in solution using methyl triflate as initiator. The polymerization mechanism was elucidated and rapid backbiting degradation along with the formation of ether groups was detected. When strong Lewis acids such as BF₃, SnCl₄ or SnBn₄ were used as initiators, much higher molecular weights were obtained, but the resulting polycarbonates still contained ether groups. BuSnCl₃ was found to be the most useful initiator yielding high molecular weight polycarbonates free of ether groups. However, in this case it is not clear, if a cationic mechanism or a coordination-insertion mechanism is involved.     

Carbazole substituted N-acylated linear polyethylenimines (PEI). synthesis and characterization of poly[N-(9-carbazolyl)acetylethylenimine] and poly[N-(2-(9-carbazolyl))propanoylethylenimine]

The synthesis of carbazola substituted N-acylated polyethylenimines, namely, poly[N-(9-carbazolyl)acetylethylenimine] 20 and poly[N-(2-(9-carbazolyl))propanoylethylenimine] 21 by a grafting reaction onto PEI and isomerization polymerization of the carbazole substituted 2-oxazolines is reported. A complete acylation of amino groups in PEI by the 9-carbazolylacetyl groups was achieved by the p-nitrophenyl active ester method but PEI was only partially N-acylated by the 2-(9-carbazolyl)propanoyl groups under similar reaction conditions. The carbazole substituted 2-oxazolines, namely, 2-(9-carbazolyl)methyl-2-oxazoline 18 and (R,S)-2-[1-(9-carbazolyl)]ethyl-2-oxazoline 19 , were prepared by a base induced cyclization of ß-chloroamides. The ring-opening isomerization polymerization of 18 and 19 in the molten state with a cationic initiator (dimethyl sulfate, methyl triflate, or ethylene glycol ditosylate) gave 20 and 21. Gel permeation chromatography of 20 and 21 obtained with different monomerto-initiator ratios gave evidence of a chain transfer reaction with the monomer. The polymers were characterized by elemental analyses, IR, and ¹H-NMR spectroscopy.     

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.     

Synthesis and characterization of graft copolymers based on polyepichlorohydrin via reversible addition-fragmentation chain transfer polymerization

In this study, synthesis of poly(epichlorohydrin-g-methyl methacrylate) graft copolymers by reversible addition-fragmentation chain transfer (RAFT) polymerization was reported. For this purpose, epichlorohydrin was polymerized by using HNO₃ via cationic ring-opening mechanism. A RAFT macroinitiator (macro-RAFT agent) was obtained by the reaction of potassium ethyl xanthogenate and polyepichlorohydrin. The graft copolymers were synthesized using macro-RAFT agent as initiator and methyl methacrylate as monomer. The synthesis of graft copolymers was conducted by changing the time of polymerization and the amount of monomer-initiator concentration that affect the RAFT polymerization. The effects of these parameters on polymerization were evaluated via various analyses. The characterization of the products was determined using ¹H-nuclear magnetic resonance (¹H-NMR), Fourier-transform infrared spectroscopy, gel-permeation chromatography, thermogravimetric analysis, elemental analysis, and fractional precipitation techniques. The block lengths of the graft copolymers were calculated by using ¹H-NMR spectrum. It was observed that the block length could be altered by varying the monomer and initiator concentrations.     

Cationic polymerizations of 2‐alkyloxazolines catalyzed by bismuth salts

Acidic bismuth salts, such as BiCl₃, BiBr₃, BiJ₃, and Bi‐triflate catalyzed the ring‐opening polymerization of 2‐methoxazoline (MOZ) in bulk at 100 °C, whereas less acidic salts such as Bi₂O₃ or Bi(III)acetate did not. Bi‐triflate‐catalyzed polymerizations of 2‐ethyloxazoline (EtOZ) were performed with variation of the monomer–catalyst ratio (M/C). It was found that the molecular weights were independent of the M/C ratio. The formation of cationic chain ends and the absence of cycles was proven by reactions of virgin polymerization products with N,N‐dimethyl‐4‐aminopyridine or triphenylphosphine. The resulting polymers having modified cationic chain ends were characterized by ¹H NMR spectroscopy and MALDI‐TOF mass spectrometry. The polymerization mechanism including chain‐transfer reactions is discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4777–4784, 2008     

Enzymatic polyesterification in organic media. Enzyme-catalyzed synthesis of linear polyesters. I. Condensation polymerization of linear hydroxyesters. II. Ring-opening polymerization of ϵ-caprolactone

With the object to synthesize polyesters by enzymatic catalysis in organic media, two directions have been investigated: (1) the condensation polymerization of linear ω-hydroxyesters and (2) the ring-opening polymerization of lactones. The commercially-available crude porcine pancreatic lipase (PPL), suspended in organic solvents, was the preferred enzyme for the reactions. In order to determine the optimal conditions for the condensation polymerization, the bifunctional methyl 6-hydroxyhexanoate was used as a model compound to study the influence of the following parameters: type of the enzymecatalyst, kind of solvent, concentration, temperature, duration, size of the reaction mixture, and stirring. Film-forming polyesters with a degree of polymerization (DP) up to about 100 were obtained from linear aliphatic hydroxyesters in n-hexane at reflux temperature (69°C). Yet concurrently with the intermolecular condensation polymerization, macrolactones were also formed by intramolecular reaction. Two aromatic hydroxyesters did not react under these conditions. For the ring-opening polymerization of lactones the reaction of ?-caprolactone with methanol as the preferred nucleophile, was studied. Polyesters with a DP of up to 35 were obtained in n-hexane at temperatures between 25 and 40°C. The degrees of polymerization of the polyesters were determined by comparative analyses of the end groups in the ¹H-NMR spectra and by determination of molecular weights either by vapor phase osmometry, gel permeation chromatography, or intrinsic viscosity. © 1993 John Wiley & Sons, Inc.     

Synthesis and characterization of poly(ethylene oxide‐co‐ethylene carbonate) macromonomers and their use in the preparation of crosslinked polymer electrolytes

Methacrylate‐functionalized poly(ethylene oxide‐co‐ethylene carbonate) macromonomers were prepared in two steps by the anionic ring‐opening polymerization of ethylene carbonate at 180 °C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number‐average molecular weight of 2650 g mol^?1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self‐supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 × 10^?6 S cm^?1 at 20 °C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195–2205, 2006     

Polymers of carbonic acid. XVII. Polymerization of cyclobis(tetramethylene carbonate) by means of BuSnCl3 and Sn(II) 2-ethylhexanoate

Dimeric cyclotetramethylene carbonate (TeMC)₂ was polymerized in bulk at 185°C. Either nBuSnCl₃ or Sn(II)2-ethylhexanoate (SnOct₂) were used as catalysts. SnOct₂ proved to be somewhat less reactive, but high yields (up to 93%) and high viscosities (ν_inh up to 0.85 dL/g) were obtained with both catalysts. Viscosity-average molecular weights (M_v) in the range of 50–75 × 10³ were determined. The isolated crystalline poly(tetramethylene carbonate)s were characterized by IR, ¹H- and ¹³C-NMR spectra, DSC measurements and WAXD powder pattern. CH₂OH and octoate end groups were detected by means of ¹H-NMR spectroscopy when SnOct₂ was used as initiator, but ether groups were absent. DSC measurements revealed that poly(tetramethylene carbonate) is a slowly crystallizing polymer with a degree of crystallinity below 50% and a melting temperature in the range of 64–69°C depending on the molecular weight. Thermogravimetric analyses proved that polyTeMC decomposes completely between 240 and 340°C without leaving a residue. CO₂ and tetrahydrofuran were the main degradation products. © 1996 John Wiley & Sons, Inc.     

Organosilicon‐Assisted Transformation of Living Anionic into Living Cationic Polymerization

A novel method is described for transforming an anionic polymerization process into a cationic polymerization process assisted by organosilyl groups. The reaction of the p‐tolyldimethylsilyl end group of polystyrene and trifluoromethanesulfonic acid produced a silyl triflate end group that served as a macroinitiator for the living cationic polymerization of isobutyl vinyl ether. The Si O linkage in the block copolymers underwent specific cleavage by reaction with tetrabutylammonium fluoride.

     

Lifetime of living polymers in cationic polymerization. III. Living polymerization of isobutyl vinyl ether initiated by a cationogen/etalcl2 system in the presence of 1,4-dioxane as an added base

The concentration ([P^*]) and lifetime (half-life) of the propagating species were measured in the living cationic polymerization of isobutyl vinyl either initiated by the 1-(isobutoxy) ethyl acetate [CH₃COOCH (OiBu) CH₃]/ethylaluminum dichloride (EtAlCl₂) system in the presence of excess 1,4-dioxane in n-hexane at 0 to +70°C; the acetate serves as a cationogen that forms an initiating vinyl ether-type carbocation. The measurements were based on the end-capping reaction with sodiomalonic ester [Na^⊕?CH (COOEt)₂], which was shown to react rapidly and quantitatively with the living growing end. From the terminal malonate group of the quenched polymers, [P^*] was determined by ¹H-NMR spectroscopy. In contrast to its constancy during the polymerization, [P^*] progressively decreased with time after the complete consumption of monomer. The postpolymerization decay was first order in [P^*], and the lifetime (half-life) of the living end was determined from the decay rate constant. The lifetime increased on lowering polymerization temperature, decreasing EtAlCl₂ concentration, and increasing dioxane concentration. In particular, the “base-stabilized” living ends, generated by the CH₃COOCH (OiBu) CH₃/EtAlCl₂/dioxane system, turned out extremely stable at 0°C (half-life > 5 days in the absence of monomer).     

Poly(3-hydroxyoxetane)—an analog of poly(vinyl alcohol): Synthesis,characterization, and properties

The spontaneous polymer formed from 3-hydroxyoxetane (HO), as first reported by Wojtowicz and Polak, is linear, low molecular weight, water-soluble, atactic, poly(3-hydroxyoxetane) (PHO) of high crystallinity with ? OCH₂CH(OH)CH₂OH end units. The highly crystalline nature of this atactic polymer may be related to the crystalline nature of atactic poly(vinyl alcohol) since PHO can be considered a copolymer of vinyl alcohol and formaldehyde. Spontaneous PHO apparently is formed in a cationic polymerization by the carboxylic acids produced by the air oxidation of HO on standing at room temperature for several months. The polymerization can be duplicated by the addition of 2% hydroxyacetic acid to HO. The rate of this unusual cationic polymerization increases greatly with acid strength, e.g., trifluoromethanesulfonic acid reacts explosively with pure HO. A mechanism is proposed for this cationic polymerization. High molecular weight, water-soluble, linear atactic, and highly crystalline PHO (mp = 155°C) was made by polymerizing the trimethylsilyl ether of HO with the i-Bu₃Al–0.7 H₂O cationic catalyst followed by hydrolysis. Two ¹H-NMR methods for measuring the tacticity of PHO were developed based on finding two different types of methylene units at 400 MHz with the methine protons decoupled. Also, an ¹H-NMR method was developed for measuring branching in HO polymers. High molecular weight, linear PHO with enhanced isotacticity (80%) has been obtained in low yield as a water-insoluble fraction with T_m = 223°C. The low molecular weight PHO prepared previously by the base-catalyzed, rearrangement polymerization of glycidol is highly branched.     

New polymer syntheses. LXI. Synthesis and alkylation of aromatic poly(pyrazine-ether)s

Three poly(pyrazine-ether)s were prepared from 2,6-dichloropyrazine, silylated bisphenol-A and, in two cases, 4,4′-dichlorodiphenylsulfone. The alkylation of these poly(pyrazine-ether) with methyl triflate, dimethyl sulfate, methyl 4-nitrobenzenesulfonate, or γ-propanesultone was studied by ¹H-NMR spectroscopy in nitrobenzene. Several N-methylated poly(pyrazine-ether)s were also isolated and characterized by elemental analyses, inherent viscosities, ¹H-NMR spectra, ¹⁵N-NMR spectra, and DSC measurements. Furthermore, their solubilities in six different solvents were determined. Complete methylation raises the glass transition temperatures, reduces the solubility in aprotic solvents, and favors dissolution in methanol or ethanol.     

Kinetics and thermodynamics of anionic polymerization of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane

Kinetic activation parameters and thermodynamic functions describing the reversible anionic polymerization of 2-methoxy-2-oxo-1,3,2-dioxaphosphorinane (1,3-propylene methyl phosphate) were determined. Enthalpy and entropy of the anionic propagation ? depropagation equilibrium were found to be close to those found previously by the present authors for the cationic polymerization, while the activation parameters of propagation and depropagation differ substantially for both processes and reflect the differences in the involved mechanisms. Thus, data for anionic polymerization (and cationic polymerization in parentheses) are: ΔH_1s° = ?0.7 kcal/mole (?1.1); ΔS_1s° = ?2.8 cal/mole-deg (?5.4); ΔH_p^? = 26.7 kcal/mole, and ΔS_p^? = ?6.1 cal/mole-deg. The polymers obtained have low degrees of polymerization (DP _n ≤ 10) because of the extensive chain transfer, leaving cyclic end groups in macromolecules. The presence, structure and concentration of the end groups have been determined by ¹H-, ³¹P-, and ¹³C-NMR spectra.     

Synthesis and properties of α-substituted benzylpyridinium salts as cationic initiators

α-Methylbenzylpyridinium SbF₆ (1a) and α,α-dimethylbenzylpyridinium SbF₆ (1b) were prepared and the effect of α-methyl groups on the active species and the activity of 1a, 1b during the cationic polymerization of glycidyl phenyl ether (GPE) was evaluated. 1b was prepared by the reaction of α,α-dimethylbenzyl alcohol with pyridinium hexafluoroantimonate (2) in several solvents, and the yield depended on the dipole moment of the solvents, although it was poor for the reaction of α,α-dimethylbenzyl chloride with pyridine for the steric hindrance of the α-methyl groups followed by exchange with NaSbF₆. Both 1a and 1b acted as a latent thermal initiator during the cationic polymerization of GPE and 1b showed higher activity during cationic polymerization with the higher steric effect of the α-methyl groups than 1a. The ¹H-NMR analysis of the obtained poly GPE indicated that the active species of 1b changed from the benzyl cation to H⁺, depending on the reaction temperature, although 1a released benzyl cations as active species in the cationic polymerization of GPE. © 1996 John Wiley & Sons, Inc.     

Lifetime of living polymers in cationic polymerization. II. Living polymerization of isobutyl vinyl ether initiated by the hydrogen iodide/zinc halide systems

In the living cationic polymerization of isobutyl vinyl ether (IBVE) initiated by the hydrogen iodide/zinc halide (HI/ZnX₂; X = I, Br, Cl) systems, the concentration ([P^*]) of the living propagating species was determined by quenching with sodiomalonic ester ( 1 ). The quenching reaction was shown to be clean, instantaneous, and quantitative to give poly (IBVE) with a terminal malonate group from which [P^*] was obtained by ¹H-NMR spectroscopy. In the polymerizations in toluene below +25°C, [P^*] was constant and equal to the initial concentration ([HI]₀) of hydrogen iodide, independent of the type and concentrations of ZnX₂ as well as monomer conversion. At 0 and +25°C, however, the living species started decaying immediately after the complete consumption of monomer. In contrast, such a decay process was absent at ?15°C even in the absence of monomer until about an hour (depending on the conditions) after the end of polymerization. The deactivation reaction was first order in [P^*], and the lifetime (half-life) of the living species was longer at lower temperature and at lower ZnX₂ concentration. On the basis of these [P^*] and lifetime measurements, the HI/ZnX₂ systems were also compared with the HI/I₂ counterpart.     

New Transformation of 1,3‐Oxathiolane‐2‐thione into 1,3‐Dithiolan‐2‐one via Polymerization and Depolymerization

This article deals with the cationic and anionic depolymerization of polydithiocarbonate, which was synthesized by cationic polymerization of 5‐phenoxymethyl‐1,3‐oxathiolane‐2‐thione ( 1 ) using methyl triflate as the initiator. The cationic depolymerization of the obtained polymer was carried out in the presence of 5–20 mol‐% of methyl triflate or triflic acid catalyst in chlorobenzene at 60 °C for 96 h to afford 4‐phenoxymethyl‐1,3‐dithiolan‐2‐one ( 2 ) in 35–83% yield. The anionic depolymerization of the polymer was carried out in the presence of 5 mol‐% of triethylamine or potassium tert‐butoxide at 20 °C for 24 h to afford 2 in 85–100% yield.     

The propagating species in living cationic polymerization: Living nature and steric structure of polymers

This paper discusses the nature of the living growing species in cationic polymerization from the viewpoint of the steric structure of poly(isobutyl vinyl ether) [poly(IBVE)]. At −78 °C, living polymerization was induced with the HCl-IBVE adduct (1)/ZnCl₂ system in a EtNO₂/CH₂Cl₂ mixture, whereas similar systems with EtAlCl₂ led to conventional cationic polymerization. In this polar medium, both systems gave polymers with very similar and low isotacticity (meso ≈ 56%), indicating that the propagating reaction is mediated by free ions. Thus, regardless of solvent polarity, or involvement of free ions or ion pairs, living cationic polymerization requires a suitably nucleophilic counteranion. As model reactions of the growing species, 1/ZnCl₂ and 1/EtAlCl₂ were directly analyzed by ¹H NMR spectroscopy.     

Studies in the formation of poly(oxazolidone)s. III. Catalysis and kinetics of the model oxazolidone formation from cyclohexyl isocyanate and phenylglycidyl ether

The reaction of cyclohexyl isocyanate with phenylglycidyl ether was selected as model reaction for the synthesis of cycloaliphatic isocyanate-based poly(2-oxazolidone)s. The selectivity of AlCl₃ and AlCl₃-triphenylphosphine oxide (AlCl₃–TPPO) and AlCl₃-hexamethylphosphoric triamide (AlCl₃–HMPA) complexes was studied for 2-oxazolidone formation. The reaction products were identified by means of the melting point, ¹H-NMR, and IR spectroscopy. The kinetics of the model reaction was studied using AlCl₃-TPPO in o-dichlorobenzene at 120 and 140°C.     

Polymerization of coordinated monomers. XIX. Kinetic study of the alternating copolymerization of methyl methacrylate with styrene by boron trichloride

Alternating copolymerizations of methyl methacrylate with styrene in the presence of boron trichloride at 0°C in 1,2-dichloroethane were carried out by using benzoyl peroxide as an initiator. Conversion increased proportionally with polymerization time, whereas the degree of polymerization was constant irrespective of time. The rate depended linearly on the square root of the concentration of benzoyl peroxide. The equilibrium constants for the formation of the ternary molecular complex composed of methyl methacrylate, styrene, and boron trichloride in 1,2-dichloroethane at ?20, ?10, and +4°C were determined by ¹H-NMR spectroscopy. The concentrations of the ternary molecular complex in the polymerization mixtures were evaluated from the equilibrium constant of the formation. The rate of the alternating copolymerization was proportional to the first order of the concentration of the ternary molecular complex. The distribution of methyl methacrylate-centered triads in the alternating copolymer was different from that of styrene-centered triads. These results can be explained by a mechanism involving the homopolymerization of a ternary molecular complex.