Carbon-13 nuclear magnetic resonance studies of poly(N-vinylcarbazole)

The ¹³C NMR spectra of poly(N-vinylcarbazole), [poly(1-(N-carbazolyl)ethylene)], prepared under various polymerization conditions were measured at 25,03 MHz in 1,4-dioxane solution. The spectra were assigned by the chemical shifts and T₁ measurements of the polymers and N-ethylcarbazole as a model compound. The absorption of methylene and methine carbons varied by the polymerization methods. It was tentatively presumed that the polymers obtained by radical polymerization had syndiotactic-rich structures and the polymers prepared with BF₃O(C₂H₅)₂ isotactic-rich structures. The hindered internal rotation of the bulky carbazolyl group at the main chain of poly(N-vinylcarbazole) was also observed. The ¹³C NMR spectra indicated that the polymerization of N-vinylcarbazole with nitroethane proceeded by a radical mechanism while that with chloranil, (2,3,5,6-tetrachloro-1,4-benzoquinone), proceeded by a cationic mechanism.     

Stereoregularity of polystyrene derivatives, 2. Poly(methoxystyrene)s Obtained by Anionic Catalysts.

The stereoregularity of poly(methoxystyrene)s was determined from the absorption of the aromatic C¹ carbon assuming a first-order Markov statistics holds for the polymerization as well as polystyrenes. The stereoregularity of poly(p-methoxystyrene)s prepared by sodium, potassium, or rubidium cations as catalysts in THF hardly varied and syndiotactic-rich polymers were obtained, whereas a random polymer was formed with cesium-naphthalene. In the polymerization of p-methoxystyrene in toluene, syndiotactic-rich polymers were obtained with butyllithium and random polymers were prepared by sodium or potassium cations as catalysts. The stereoregularity of poly(o-methoxystyrene)s prepared by sodium or potassium cations in tetrahydrofuran changed with the polymerization temperatures, and highly syndiotactic polymers were formed at?78°C. The structure of poly(o-methoxystyrene)s obtained in toluene, markedly depended on the initiators; that is, with increasing the size of the ionic radius of the counterions, the isotacticity of the polymers decreased. The mechanism of the polymerization and the substituent effect of the stereoregularity are discussed.     

Stereoregularity of polystyrene and mechanism of polymerization

The Stereoregularity of polystyrenes prepared with radical, anionic, and cationic initiators was determined by means of ¹³C-NMR spectroscopy. Aromatic C₁ carbon spectra measured on o-dichlorobenzene solutions consisted of about six peaks and the peak at the highest magnetic field (at 146,3 ppm) was assigned to an rrrr pentad. The proportion of racemic dyads P_r, was directly calculated from the proportion of the rrrr pentad peak assuming that the Bernoullian statistics holds for the polymerization of styrene. The P_r values of polystyrenes prepared with radical initiators at temperatures from 80° to 0°C were 0,72–0,73, while the cationic polymerizations gave P_r values ranging from 0,54 to 0,68. The P_r values of the same polystyrenes were also calculated by use of a p-xylene/chloroform mixture as solvent for the ¹³C-NMR measurements. For anionically obtained polystyrenes, considerably different P_r values were found using both solvent systems. From this, it was considered that the anionic polymerization of styrene with butyllithium as catalyst does not obey the Bernoullian statistics.     

The structure of poly(N-vinylcarbazole) obtained with cationic initiators and electron acceptors as catalysts

Poly(N-vinylcarbazole)s, [poly(l-(N-carbazolyl)ethylene)s], (PVCz's) were prepared under various polymerization conditions. The stereoregularities were estimated by means of ¹³C NMR spectroscopy. Although the stereoregularity of the polymers obtained by BF₃O(C₂H₅)₂ was hardly changed by the polymerization temperature, it changed with the solvent polarity from an isotactic-rich configuration in toluene and CH₂Cl₂ to a syndiotactic-rich configuration in nitrobenzene. The ¹³C NMR spectra of the polymers obtained by organic electron acceptors, support the conclusion that the polymerization by tetracyanoethylene, p-bromanil, 2,3-dichloro-5,6-dicyano-p-benzoquinone, and tetrachlorophthalic anhydride proceed by a cationic mechanism. In the polymerization of N-vinylcarbazole (VCz) with maleic anhydride as an electron acceptor, a small amount of copolymer was obtained together with the homopolymer of VCz. Although the structure of the homopolymers is the same as that of the radically obtained polymer, it is considered that the polymer is formed by a cationic mechanism. The polymerizations of VCz by inorganic compounds, such as ferric nitrate, cupric nitrate, cupric bromide, etc., as catalysts are cationic.     

Solution polymerization of selected polyphosphazenes

Several alkoxy/aryloxy-substituted phosphazene polymers [P(OR)₂ ? N]_n, where R = C₆H₅, CH₂CF₃, C₈H₁₀, were prepared by the reaction of polydichlorophosphazene with their corresponding sodium salts. The polydichlorophosphazene was obtained by the solution polymerization of hexachlorocyclotriphosphazene in 1,2,4-trichlorobenzene. Sulfamic acid and ammonium sulfamate were used as catalysts. Apparently, sulfamic acid functions as a catalyst through its acid group in some decomposed form. New catalysts, p-toluenesulfonic acid and sulfobenzoic aicd, have been developed for this solution polymerization. The polymerization favors a cationic mechanism. A promoter, CaSO₄·2H₂O, was found to speed up the polymerization reaction. Effect of several parameters such as dilution, catalyst concentration, and promoter concentration on the properties of the final polymer were investigated. The polymers were characterized by differential scanning calorimetry, gel permeation chromatography, and ³¹P solution NMR spectroscopy.     

Living polymerization of phenylacetylene by rhodium‐based ternary catalysts, (diene)Rh(I) complex/vinyllithium/phosphorus ligand. Effects of catalyst components

It was proved that a Rh‐based ternary catalyst composed of [(nbd)RhCl]₂ (nbd: bicyclo[2.2.1]hepta‐2,5‐diene), (triphenylvinyl)lithium, and triphenylphosphine induces living polymerization of phenylacetylene. [(nbd)RhCl]₂ was effective as the main catalyst, whereas neither [(cod)RhCl]₂ (cod: 1,5‐cyclooctadiene) nor [(coe)₂RhCl]₂ (coe: cyclooctene) induced living polymerization. The anionic ligands such as chlorine, methoxy, and acetoxy groups in the Rh complex hardly affected the living polymerization. When vinyllithium as second catalyst component possessed a bulky substituent such as phenyl or t‐butyl group on its α‐carbon, stable vinylrhodium species were generated, which led to living polymerization. At least one substituent was necessary on the β‐carbon of the vinyllithium for the living polymerization. Tris(4‐substituted phenyl)phosphines worked well as third components among various phosphorus ligands. The polymerization was decelerated as the basicity of the phosphine ligand increased.     

Stereoregularity of polystyrene derivatives, 3. Poly(methylstyrene)s Obtained by Anionic Catalysts

The stereoregularity of the polymers of ortho-, meta-, and para-methylstyrenes prepared with various anionic catalysts was determined by means of ¹³C NMR spectroscopy. The substituent effect on the stereoregularity was discussed comparing with that of polystyrenes obtained under the same polymerization conditions. Syndiotactic-rich poly(methylstyrene)s were prepared with butyllithium in toluene and the syndiotacticity increased in the order of para-, meta-, and ortho-derivatives. Although the structure of the polymers prepared with sodium-naphthalene (Na-naph.) in THF did not change with the position of the substituent, in toluene, however, the methyl group at ortho-position influences the stereoregularity. The trend of the stereoregularity of the polymers produced by potassium-naphthalene was almost the same as that of poly(methylstyrene)s prepared by Na-naph. Nearly random polymers were obtained with the cesium ion as catalyst.     

A new catalyst for the polymerisation of tetrahydrofuran

The study of molecular weight distribution and the degree of branching on cis-poly-butadienes obtained by using complex catalysts Til₄ + (i C₄H₉)₆Al (I) and (i C₄H₉)₂AlCl + CoCl₂ (II) has established that the structural characteristics of these polymers do not depend exclusively on the type of catalyst used. The polymers obtained in the presence of catalyst II having a narrow molecular weight distribution at the beginning of the polymerization process become highly polydisperse towards the end of the reaction. This result as well as the increase in chain branching of the type II polymers at high degrees of conversion suggest interchain reactions to occur readily in the course of polymerization. In the case of type I polymers a narrow molecular weight distribution is observed; the polymerization having a stationary character during all its stages at 25°C. At lower temperatures, however, this character is disturbed, the polymer molecular weight increasing with the increase in conversion degree. Type I polymers are practically linear upto 100% conversion. Thus, both branching and molecular weight distribution of these polymers depend on polymerization conditions, affecting them differently for the two catalysts used.     

Stereoregularity of polystyrene derivatives, 4. Poly(α-methylstyrene) obtained by anionic catalysts

The stereoregularity of poly(α-methylstyrene)s prepared by anionic initiators was determined from the peak area of α-methyl proton absorptions and aromatic C¹ carbon absorptions. Highly syndiotactic polymers were obtained at 0°C in both toluene and tetrahydrofuran (THF). Sodium, potassium, and cesium naphthalenes gave polymers with the same syndiotacticity in THF. The syndiotacticity of polymers prepared by sodium and potassium naphthalenes as catalyst in both toluene and THF decreased at low temperatures. This behavior is similar to that of o-methylstyrene and m-methylstyrene in THF. The stereoregulation mechanism in the anionic polymerization of α-methylstyrene is discussed and compared with that of polystyrene and ring substituted polystyrenes.     

Polymerization of tert-butyl methacrylate with Ni(acac)2-methylaluminoxane catalyst

The polymerization of tert-butyl methacrylate (tBMA) with nickel(II) acetylacetonate [Ni-(acac)₂] in combination with methylaluminoxane (MAO) was investigated. The binary catalyst is necessary to initiate the polymerization, however, high MAO/Ni mole ratios are not necessary to obtain high catalytic activity. A linear dependence of the molecular weight of the resulting polymers on polymer yield was observed, and the polydispersities of the polymers were relative narrow. The triad tacticity for the polymer obtained was determined to be mm = 3%, mr = 43%, rr = 54%.     

Cationic polymerization of methoxyallene with Lewis acids

The cationic polymerization of methoxyallene ( 1 ) was carried out with some Lewis acids at ?50°C in dichloromethane. BF₃OEt₂ was found to be an effective catalyst for the cationic polymerization of 1 . From analyses of ¹H and ¹³C NMR spectra, the obtained polymers consist of units with the 1,2-double bond of 1 being opened, although the 2,3-double bond is consumed also to an amount of 24 to 43 mol-%. This decrease in 2,3-double bond content in the polymer may be attributed to intramolecular cyclization of the propagating cation and/or the intermolecular reaction of the propagating cation with polymer to produce a graft polymer. Moderately polar solvents such as dichloromethane proved to be best suited for obtaining polymers with high double bond content.     

1H and 13C NMR spectra of poly(propyl α-bromoacrylate) and poly(methyl α-bromoacrylate)

The ¹³C NMR spectra measured at 25 MHz of the methyl and propyl esters of isotactic and syndiotactic poly(α-bromoacrylate) were sufficiently resolved to be analysed for pentad tacticity sequences. The pentad tacticity of the syndiotactic polymers prepared with free radical initiators at ?40°C agreed with those calculated for Bernoullian sequence distributions based on P_r values of 0,83–0,87. The tacticities of the isotactic polymers prepared with heterogeneous catalysts were determined on the basis of these assignments. Good internal consistency was obtained between the calculated and observed pentad proportions from the quaternary and carbonyl carbon peaks in the spectra of these polymers. The order of chemical shifts for the meso and racemic dyads and tetrads in these polymers were opposite to those found in the equivalent methacrylate polymers, but as with the latter, the ¹³C-T₁ values were longer in the isotactic than in the syndiotactic polymers.     

Propene polymerization with a magnesium chloride-supported ziegler catalyst, 1. Principal kinetics

The main kinetic behavior of the slurry polymerization of propene with a MgCl₂-supported TiCl₄/C₆H₅COOC₂H₅ catalyst, activated by Al(C₂H₅)₃, was studied, Examination of the dependence of the polymerization rate on temperature and concentrations of Al(C₂H₅)₃ and of propene resulted in a Langmuir-Hinshelwood rate law with the number of polymerization centers dependent on time. The Polymerization rate as function of the polymerization temperature shows a maximum, which is compatible with the rate law. The analysis of the phenomenon of an optimum temperature gave 15 KJ. mol^?1 and 36 KJ. Mol ^?1 for the activation energy of the rate determining step and the adsorption energy of Al(C₂H₅)₃, respectively. Examination of the rapid decay of the polymerization rate showed that the main part of the decay is represented by a second order decay independent of the amount of polymer produced, which can be understood by a second order decay of surface sites by Al(C₂H₅)₃. The number of active centers of the catalyst in gas phase polymerization was estimated applying the inhibition method with carbon monoxide. The results show a constant value for the propagation rate constant, K_p, during the second order rate decay. The observed polymerization kinetics strongly suggest the existence of two kinds of polymerization centers (isotactic and atactic).     

Studies of atom transfer radical polymerization (ATRP) of acrylates by MALDI TOF mass spectrometry

Atom transfer radical polymerization (ATRP) of methyl, butyl and tert‐butyl acrylates was studied at conditions when low molecular weight polymers (M_n ≅ 2·10³) are formed, i. e., at relatively high concentration of initiator (ethyl 2‐bromopropionate) and catalyst (CuBr/amine). MALDI TOF analysis of the polymer samples isolated at different stages of polymerization revealed that in the course of polymerization potentially active macromolecules terminated with bromine are gradually converted into inactive macromolecules devoid of terminal bromine. A possible transfer mechanism, involving amine is a component of the catalytic system, is proposed. It was shown that quantitative analysis of the MALDI TOF spectra allows one to estimate the ratio of apparent rate constants of propagation and degradative transfer, providing quantitative information to what extent the system conforms to the contolled polymerization scheme.     

Polymerization of aromatic aldehydes, 11. Polymerization of 3-(o-formylphenyl)propionaldehyde and o-phenylenediacetaldehyde

Polymerization of 3-(o-formylphenyl)propionaldehyde ( 4 ) and o-phenylenediacetaldehyde ( 5 ) were performed with several ionic catalysts. The cationic polymerization of 4 yielded polyacetals which contained a seven-membered cyclic unit ( 7 ) in mole fractions of 0,3–0,5. The uncyclized unit ( 6 ) contained the pendant aromatic aldehyde. Apparently, the aromatic aldehyde group reacted during the course of the intramolecular cyclization. Polymerizations of 5 with BF₃·O(C₂H₅)₂, lithium tert-butoxide, or Al(C₂H₅)₃-TiCl₄ as catalysts, similarly gave polyacetals containing a seven-membered cyclic unit ( 10 ) in mole fractions of 0,5–0,8. The extent of cyclization decreased with increase in temperature in the cationic polymerization, resulting in a difference of ?7,5 kJ mol^?1 (?1,8 kcal mol^?1) between the activation energy of intramolecular cyclization and that of intermolecular propagation. The polymerization with Al(C₂H₅)₃ as catalyst gave a polyester via propagation involving a hydride shift.     

Poly(vinylsaccharide)s, 4. Synthesis and polymerization of 6-o-methylallylgalactose derivatives

Methylallyl ethers of 1,2:3,4-di-O-isopropylidene-D-galactopyranose and 1,2:3,4-di-O-cyclohexylidene-D-galactopyranose were synthesized as new monomers containing saccharide moieties and copolymerized with maleic anhydride. The hitherto unknown 6-O-(2-alkoxycarbonylallyl)-1,2:3,4-di-O-isopropylidene-D-galactopyranoses ( 8a and 8b; alkyl: methyl and ethyl, respectively) were prepared and polymerized under free radical conditions. The substances were characterized by ¹³C NMR, elemental analyses and molecular weight determinations. Water solubility of these polymers was obtained by removing the isopropylidene protecting groups. The inherent viscosities of these polymers, measured in 0,1 M Na₂SO₄ aqueous solution, were of the same order of magnitude as those of polyacrylamides of the corresponding degrees of polymerization.     

The microtacticity of poly(acrylic esters)

Several acrylic esters were polymerized with radical and anionic initiators and the stereoregularity of the polymers was determined. The radical polymerization of tert-butyl acrylate gave syndiotactic-rich polymers at low temperatures as did isopropyl and trimethylsilyl acrylates. A radically obtained polymer of triphenylmethyl acrylate was atactic in contrast to poly(triphenylmethyl methacrylate). In the anionic polymerization with phenylmagnesium bromide or butyllithium as catalyst, the stereoregularity of the polymers was governed by the coordination of the catalyst which depends on the polarity and bulkiness of ester groups, the polarity of solvents, and the temperature in the polymerization.     

External alkoxysilane donors in Ziegler-Natta catalysis. Effects on poly(propylene) microstructure

Correlations were sought between the structure of an external alkoxysilane donor and the microstructure of the polymer chain obtained by the polymerization of propene with a heterogeneous, high-activity Ziegler-Natta catalyst. Fourteen different alkoxysilanes of structure R_nSi(OR′)_4-n, where n = 1–3, R = n-alkyl or phenyl and R′ = C_1–3-alkyl, were used as external donors. The polymers were fractionated by boiling heptane extraction. The microstructures of the polymers were studied by means of ¹³C NMR spectroscopy. The structure of the donor had a marked effect on the catalyst activity and isotacticity of the polymer. However, all of the alkoxysilanes tested produced qualitatively similar differences in the microstructure of poly(propylene): the size of the isotactic mmmm pentad peak varied with the donor efficiency, but the sizes of the non-isotactic pentad peaks were more or less constant relative to each other. In the boiling heptane soluble fraction, isotacticity and syndiotacticity increased and the viscosity-average molecular weight M?_v decreased when a good external donor was used in the polymerization. Results indicate that all external alkoxysilane donors tested have the same qualitative effect on active centers, and only isotacticity, i.e., the number of mmmm sequences, can be controlled by an external alkoxysilane donor. The effectiveness and selectivity of deactivation strongly depend on the structure of the donor.     

Pressure-induced cis to trans isomerization of poly(ortho- and para-methoxyphenylacetylene)s prepared by [Rh(norbornadiene)Cl]2 catalyst. A Raman,UV, and ESR study

The stereospecific polymerization of o- and p-methoxyphenylacetylenes (MOPAs) with [Rh(norbornadiene)Cl]₂ as a catalyst in the presence of an organic base (triethylamine) at 30°C is reported, together with the detailed characterization using resonance Raman, diffuse reflection UV, and ESR spectroscopic methods. The resulting polymers were shown to selectively have a cis-transoid form. It was found, interestingly, that the resultant aromatic polyacetylenes in the cis form are easily isomerized to those in the trans form when a pressure of ca. 100∼200 kg/cm² was exerted on the solid polymers at room temperature.     

13C NMR spectra of poly(alkyl α-chloroacrylate)s

¹³C NMR spectra of isotactic and syndiotactic poly(ethyl α-chloroacrylate)s and poly(isopropyl α-chloroacrylate)s were measured in toluene-d₈ at 25 MHz. The spectra were analyzed for triad, tetrad and pentad tacticities comparing the spectra with the results previously obtained by ¹H NMR spectroscopy. Tetrad tacticities of the polymers were measured from the resonance of the backbone methylene carbon and favorably compared with tetrad values obtained by ¹H NMR. The resonance of the carbonyl carbon showed the peaks corresponding to the tactic triad with a pentad splitting in mm resonance. The triad values obtained from the carbonyl carbon resonance were in good agreement with those calculated from the tetrad values as well as the triad tacticities obtained by ¹H NMR. The quaternary carbon reconances were very complicated because the chemical shift differences for the different tactic triads were of the comparable magnitude with those for the pentads, and a tentative peak assignment was made with the aid of the statistical calculation of pentad values assuming first-order Markovian statistics for the isotactic polymer and Bernoullian statistics for the syndiotactic polymer.