Effect of alkyl substituents on initiator activity in cationic polymerization of styrene with p-methoxybenzyldialkylsulfonium salts as initiators

The effect of alkyl substituents on cationic polymerization of styrene with p-methoxybenzyldialkysulfonium salts was studied. p-Methoxybenzyl tetramethylene ( 1 ), dimethyl ( 2 ), diethyl ( 3 ), dibuty ( 4 ), and diisopropylsulfonium salts ( 5 ) were synthesized by the reaction of p-methoxybenzyl bromide with the corresponding sulfides, followed by exchange of the counter anion Br^? with SbF^?₆. These sulfonium salts served as potent cationic thermal initiators of which activity was estimated by the bulk and solution polymerizations of styrene. The bulk polymerizations with 1–4 (0.1 mol %) for 30 min gradually proceeded at 30–50°C, but the exothermic polymerization occurred vigorously at 40–60°C. The Polymerization with 5 took place exothermically even at room temperature. Temperature-conversion curves of the polymerizations for 30 and 5 min revealed that the activity of the sulfonium salts was in the following order: 5 > 4 > 3 > 2 ≈ 1 . This order was explained by the order of the bulkiness of the alkyl substituents on the sulfur atom. Number-average molecular weight (M?_n) of polystyrene obtained by the polymerization undergoing no exothermic process was in a range of 6600–16000, which depended on the structure of the alkyl substituents: the more bulky the substituent was, the higher M?_n was.     

Synthesis and properties of polythienylenes

Although polymerization of 2,5-dibromothiophene via coupling of the Grignard reagent with organonickel salts was reported in two earlier communications, a detailed examination of reaction variables was not done. This report provides results from variation in the following: time, amount of magnesium, amount of iodine, dilution, and variation in the halide of the monomer. The highest yield was obtained for reactions with 1:1 molar ratio of monomer to magnesium in more concentrated solutions of tetrahydrofuran for a reaction time of 4 h. For variation in the halogen of the monomer the following yield sequence was obtained: I > Br > Cl. The results are compared with the corresponding benzenoid system investigated by Yamamoto. In addition, polymerization studies were carried out with other brominated thiophene monomers. Use of an organic promoter (cis-1,4-dichloro-2-butene) in place of a nickel salt proved successful in the generation of poly(2,5-thienylene).     

Effects of metal salts on polymerization. Part III. Radical polymerizabilities and infrared spectra of vinylpyridines complexed with zinc and cadmium salts

Radical polymerization of 4-vinylpyridine (4-VP), 2-vinylpyridine (2-VP), and 2-methyl-5-vinylpyridine (MVP) was studied in concentrated DMF solutions of ZnCl₂, ZnBr₂, ZnI₂, Zn(CH₃COO)₂, and Cd(CH₂COO)₂ at 50°C. Polymerization of 4-VP and MVP was accelerated by the addition of the metal salts, while the polymerization of 2-VP was greatly retarded. The sequence of the accelerating effect of metal salts for 4-VP was in the following order: Cd(CH₃COO)₂ > ZnCl₂ > Zn(CH₃COO)₂ > ZnBr₂ > ZnI₂. This sequence is almost the same as that reported in a previous report for MVP. However, the order was reversed for the retarding effect on the polymerization of 2-VP. At the intermediate concentration of metal salts, polymerization of 4-VP proceeded heterogeneously, which was explained by considering crosslinking of poly-4-VP by the metal ion. Since a linear correlation between the rate R_p and the degree of polymerization was observed for the 4-VP–Zn(CH₃COO)₂ system, the accelerating effect was postulated to be due to the enhancement in k_p. Results of copolymerization of VP with styrene as M₂ in a concentrated solution of Zn(CH₃COO)₂ indicated the strong activation of 4-VP by complex formation (r₁ = 2.7 ± 0.5, r₂ = 0.08 ± 0.03), whereas the change in the monomer reactivity of MVP is smaller (r₁ = 2.0 ± 0.2, r₂ = 0.35 ± 0.05). The behavior of 2-VP was abnormal (r₁ = 3.35 ± 0.3, r₂ = 0.55 ± 0.15, then r₁r₂ > 1), which was attributed to the steric effect by complex formation. Solid complexes formed between pyridine, 4-VP, 2-VP, or MVP and zinc salts were prepared as samples for infrared spectroscopy. The shifts in infrared absorption bands of these amines were studied by comparing the infrared spectra of the amines before and after the complex formation, and the results were interpreted in terms of electronic as well as steric interactions of metal salts with ligands. Conjugation of the metal salt with the ligand π-orbitals was necessary to explain both infrared spectra and polymerization results.     

Low-temperature polymerization of lactams by using as catalyst the salt derived from NaAlEt4 and monomer and with several compounds as initiator

Low-temperature polymerization of α-pyrrolidone, α-piperidone, and ?-caprolactam was examined by using the salts derived from NaAlEt₄ and monomer, sodium lactamates, or the salt derived from AlEt₃ and monomer as catalyst and with N-acetyl lactams, ethyl acetate, or lactones as initiator. Sodium lactamate catalyst gave unsatisfactory results in the cases of ethyl acetate or lactones initiators, and gave the following order for the relative efficiency of initiators: N-acetyl lactam > ?-caprolactone ≥ ethyl acetate > β-propiolactone. The polymerization results obtained by the salt from NaAlEt₄ catalyst–ethyl acetate initiator system were nearly the same as those with N-acetyl lactam. The increases in the degree of polymerization and in the yield of polymer were observed in case of the salt from NaAlEt₄ catalyst-lactone initiator system, particularly in the cases of α-piperidone and ?-caprolactam. Also an incorporation of initiator into polymer chain was observed.     

Kinetics of Condensation Reactions between Ethanolamine (Amino‐Alcohol) and Dicarboxylic Acids at 413 K

The kinetics of condensation polymerization reactions between amino‐alcohol and various dibasic acids ranging from oxalic acid (n = 0 number of –CH₂ groups) to sebacic acid (n = 8) is studied at 413 K in an inert atmosphere, with a catalyst and ensuring removal of product water. All of the studied reactions are chemically identical, and their rates may differ only in so far as reactivity affected by molecular weight. Our analysis of the kinetic data reveals that all reactions obey third‐order kinetics, and the degree of polymerization increases even upto 20 h, if same stoichiometry for both the reactants is maintained. The velocity constants for the reactions were found to be in the order for the acids as succinic > oxalic > sebacic > adipic. The rates are also comparable to similar reactions of diols and diacids. The analysis further reveals that the chain length as well the structural characteristics of the reactant molecules govern the speed of the reaction. It seems that the proper conformations and structural geometry do play an important role in the collisional process of formation of products in a desired time. The probable implications of the results and analysis of these observations are discussed.     

Photoinitiation. II. Kinetics of the acrylonitrile polymerization photoinitiated by aromatic hydrocarbons

The kinetics of acrylonitrile polymerization photoinitiated by aromatic hydrocarbons have been studied. For the acrylonitrile polymerization photoinitiated by naphthalene the rate of polymerization depends on the square root of incident light intensity, on the square root of naphthalene concentration, and on the 1.5 power of acrylonitrile concentration. In the system acrylonitrile-1-methoxynaphthalene the rate of acrylonitrile polymerization depends on the first power of acrylonitrile concentration. The monoradical character of this polymerization process has been established. For the interpretation of experimental results a reaction mechanism involving the formation of the exciplex between the first singlet or triplet of aromatic hydrocarbon and acrylonitrile in the ground state as a precursor of polymerization reactions is suggested. The photoinitiating efficiency of various aromatic hydrocarbons in acrylonitrile polymerization increases in the order: fluoranthene (zero efficiency) ? pyrene < phenanthrene, fluorene ≈ 2-methoxynaphthalene ≈ biphenyl < anthracene < 2-methylnaphthalene < 1-methoxynaphthalene < 2,3,6-trimethylnaphthalene < 2,3-dimethylnaphthalene ≈ naphthalene < 1-methylnaphthalene < 2,6-dimethylnaphthalene < p-terphenyl < acenaphthene, provided that the systems absorb the same amount of the incident light. The explanation of this result ensues from the study of the effect of concentration on the rate of polymerization and from the quenching of hydrocarbon fluorescence by acrylonitrile. The photoinitiating efficiency of a given aromatic hydrocarbon is mainly determined by the value of the rate constant k_q for the formation of exciplex as well as the self-quenching efficiency of aromatic hydrocarbon. By using the literature data for the lifetime of fluorescence τ the values of k_q were calculated from the Stern-Volmer equation expressing the quenching of hydrocarbon fluorescence by acrylonitrile. The order of aromatic hydrocarbons according to increasing values of k_q is as follows: pyrene < phenanthrene < anthracene ≈ naphthalene < 2-methylnaphthalene ≈ 1-methylnaphthalene ≈ 2,3-dimethylnaphthalene < 2,6-dimethylnaphthalene < acenaphthene < p-terphenyl < 1-methoxynaphthalene. The study of the concentration effect reflecting the self-quenching of aromatic hydrocarbons during polymerization has given the following sequence for decreasing self-quenching efficiency of aromatic hydrocarbons: 2-methoxynaphthalene ≈ pyrene > anthracene > 1-methoxynaphthalene > fluorene > 2,6-dimethylnaphthalene, phenanthrene, acenaphthene > 2,3,6-trimethylnaphthalene > 2,3-dimethylnaphthalene > 1-methylnaphthalene > naphthalene. It has been shown that the photoinitiating efficiency of a given aromatic hydrocarbon in the polymerization of acrylonitrile can be roughly predicted from the position of that aromatic hydrocarbon in the above-mentioned sequences.     

Chain-transfer constant of fluoroalcohols

Chain transfer constants of some fluoroalcohols [HCF₂(CF₂)_n?1CH₂OH, n = 2, 4, 6] in the catalyzed polymerization of vinyl acetate, styrene, acrylonitrile, and methyl methacrylate at 60°C have been evaluated by a method based on degree of polymerization. Since fluoroalcohols are normally nonsolvents for polymers, a homogeneous reaction phase is maintained by carrying out the polymerization in benzene (except in case of acrylonitrile, where no solvent was used). The transfer constants vary, depending on the reactivity as well as the polarity of the radicals, in the following order: vinyl acetate > styrene > methyl methacrylate > acrylonitrile. Of the three fluoroalcohols studied, the transfer constants increase with the increasing value of n. The results have been interpreted in terms of polar structure contribution in the transition state of the transfer reactions.     

Synthesis and activity of aryl benzyl methyl sulfonium salts as cationic initiators: Effect of substituent on aryl group

Benzyl o-, m-, and p-substituted phenyl methyl sulfonium salts ( 2b – 2g ) were synthesized and their activities as cationic initiators were evaluated in the bulk polymerization of phenyl glycidyl ether (PGE). Especially, their activities were estimated with respect to the effect of substituents on the aryl groups. In the polymerizations of PGE with a series of benzyl p-substituted phenyl methyl sulfonium salts, the order of their activities was found to be 2c (CH₃OCOO) > 2b (CH₃COO) > 2d (CH₃O) ～ 2a (HO). In particular, 2c was the most active initiator of all, capable of initiating the polymerization of PGE even at room temperature. In the polymerizations with 2a, 2e (m-Cl), 2f (o-CH₃), and 2g (m-CH₃), the activity of 2e was the highest of all while those of 2a, 2f , and 2g were almost the same. These results strongly suggested that the electron-withdrawing group placed on the aryl group undoubtedly enhanced the activity of the sulfonium salts as the cationic initiators.     

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     

Application of S‐alkylsulfonium salts of aromatic sulfides as new thermal latent cationic initiators

The cationic initiation activity of derivatives of S‐methylsulfonium salts of dibenzothiophene ( 3a ), diphenyl sulfide ( 4a ), thioanisole ( 4d ), and tetrahydrothiophene ( 5 ) was evaluated in the polymerization of glycidyl phenyl ether ( 1 ). These initiators were soluble in 1 and capable of initiating the cationic polymerization of 1 on heating, with the exception of methyltetrahydrothiophenium tetrafluoroborate ( 5 ; in the range of room temperature to 160 °C). Among them, methyldiphenylsulfonium tetrafluoroborate ( 4a ) showed a moderate thermal latency that brought about the polymerization of 1 efficiently at 160 °C but not below 80 °C. S‐Alkylsulfonium salts of aromatic sulfides such as phenoxathiin ( 6a ) and thianthrene ( 6b ) also were evaluated for their activity in the cationic polymerization of 1 , from which the thermal latent behavior of these salts also was confirmed (i.e., there was no reaction at 60 °C for 3 h, but there was a high enough conversion at 140 °C). Furthermore, the catalytic activity of S‐alkylsulfonium derivatives was controllable by both the property of the substituents on the aromatic rings and the character of the alkyl groups on the sulfur atom. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 18–27, 2000     

Cationic ring-opening polymerization of carbazolyl-containing epoxy monomers by triphenyl carbenium salts as thermal- and photolatent initiators

Abstract  

Photoinitiated cationic polymerizations of various epoxy monomers bearing a carbazole moiety, 9-[3-(allyloxy)-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[3-methoxy-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[2-(oxiran-2-ylmethoxy)ethyl]-9H-carbazole, as well as a composition of 3,6-dibromo-9-(oxiran-2-ylmethyl)-9H-carbazole with 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate were investigated in bulk using triphenyl carbenium salts having anions such as BF₄ ⁻, SnCl₅ ⁻, and SbCl₆ ⁻. Dark polymerizations of the carbazolyl monomers in the presence of the initiators are studied. These photoinduced polymerization reactions give oligomers of degree of polymerization 4-22. The effect of the anion of the photoinitiator and polymerization time on the polymerization reaction is discussed.     

Nitrogen‐Rich Amino‐triazolium Salts Based on Binary 4,5‐Dicyano‐1,2,3‐triazolate (C4N5–) Anion

A series of amino‐triazolium salts based on 4,5‐dicyano‐1,2,3‐triazolate (C₄N₅^–) anion were synthesized for first time by means of facile deprotonation reactions. The ionic compounds were characterized by single‐crystal X‐ray diffraction, vibrational spectroscopy, and elemental analysis. The thermal stability of the salts was assessed by differential scanning calorimetry, which showed good thermal stabilities up to above 180 °C. The heats of formation of these salts were computed using the methods of isodesmic reactions. In addition, the sensitivities of the studied salts toward impact and friction were determined, and all salts were found to be neither impact (> 40 J) nor friction sensitive (> 360 N).     

Catalytic action of metallic salts in autoxidation and polymerization. IV. Polymerization of methyl methacrylate by cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide or dioxane hydroperoxide

Polymerization of methyl methacrylate was carried out by four initiating systems, namely, cobalt(II) or (III) acetylacetonate–tert-butyl hydroperoxide (t-Bu HPO) or dioxane hydroperoxide (DOX HPO). Dioxane hydroperoxide systems were much more effective for the polymerization of methyl methacrylate than tert-butyl hydroperoxide systems, and cobaltous acetylacetonate was more effective than cobaltic acetylacetonate in both hydroperoxides. The initiating activity order and activation energy for the polymerization were as follows: Co(acac)₂–DOX HPO (E_a-9.3 kcal/mole) > Co (acac)₃–DOX HPO (E_a = 12.4 kcal/mole) > Co(acac)₂–t-Bu HPO (E_a = 15.1 kcal/mole) > Co(acac)₃–t-Bu HPO (E_a-18.5 kcal/mole). The effects of conversion and hydroperoxide concentration on the degree of polymerization were also examined. The kinetic data on the decomposition of hydroperoxides catalyzed by cobalt salts gave a little information for the interpretation of polymerization process.     

Highly Dense Nitranilates‐Containing Nitrogen‐Rich Cations

High density energetic salts containing nitrogen‐rich cations and the nitranilic anion were readily synthesized in high yield by metathesis reactions of sodium nitranilate 2 and an appropriate halide. All of the new compounds were fully characterized by elemental, spectral (IR, ¹H, ¹³C NMR), and thermal (DSC) analyses. The structure of hydrazinium nitranilate ( 4 ) was also determined by single‐crystal X‐ray analysis. The high symmetry and oxygen content of the anion give these salts extensive hydrogen bonding capability which further results in the high densities, low water solubilities, and high thermal stabilities (T_d> 200 °C) of these compounds. Theoretical performance calculations were carried out by using Gaussian 03 and Cheetah 5.0. The calculated detonation pressures (P) for these new salts fall between 17.5 GPa ( 10 ) and 31.7 GPa ( 4 ), and the detonation velocities (νD) range between 7022 m s^?1 ( 13 ) and 8638 m s^?1 ( 4 ).     

Cationic ring-opening polymerization of carbazolyl-containing epoxy monomers by triphenyl carbenium salts as thermal- and photolatent initiators

Abstract  Photoinitiated cationic polymerizations of various epoxy monomers bearing a carbazole moiety, 9-[3-(allyloxy)-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[3-methoxy-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[2-(oxiran-2-ylmethoxy)ethyl]-9H-carbazole, as well as a composition of 3,6-dibromo-9-(oxiran-2-ylmethyl)-9H-carbazole with 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate were investigated in bulk using triphenyl carbenium salts having anions such as BF₄ ⁻, SnCl₅ ⁻, and SbCl₆ ⁻. Dark polymerizations of the carbazolyl monomers in the presence of the initiators are studied. These photoinduced polymerization reactions give oligomers of degree of polymerization 4-22. The effect of the anion of the photoinitiator and polymerization time on the polymerization reaction is discussed. Graphical abstract        

Synthetic and mechanistic aspects of anionic polymerization of methyl methacrylate using tetrabutyl ammonium thioimidate

The tetrabutylammonium salts of ionic organo-initiator containing N,N'-diisopropylthiourea (TUA-1) or N,N'-diethylthiourea (TUA-2) serve as inexpensive initiators for the anionic polymerization of methyl methacrylate (MMA) at room temperature. The molecular weights of obtained polymers are in the range of 1500–22,700 g mol⁻¹ and the molecular weight distributions are fairly broad (Đ = 1.9–2.5) in optimized cases. The molar ratio of monomer to initiator can be achieved up to 800. Side-reactions, for example, backbiting, transfer reactions result in the polymerization being a non-living manner, thus leading to broad molecular weight distributions of the resulting polymers. The effects of counterion nature were also studied from the polymerization of MMA using TUA-1 anion with sodium or potassium salts as counterions under identical conditions. Detailed investigation indicates that the polymerization proceeds via a sulfur anion initiated repeated 1,4-Machael addition. In general, thioimidate initiators induced MMA polymerization feature certain induction periods, which is ascribed to slow addition thioimidate to CC double bond of MMA as a result of low initiator efficiency.     

Effects of initiators and photo-acid generators on nitroxide-mediated photo-living radical polymerization of methyl methacrylate

The effects of the structure of initiators and photo-acid generators on the nitroxide-mediated photo-living radical polymerization of methyl methacrylate were explored. The bulk polymerization was performed at room temperature using nine different initiators in the presence of (4-tert-butylphenyl)diphenylsulfonium triflate as the photo-acid generator. 2,2′-Azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile), dimethyl 2,2′-azobis(2-methylpropionate), and 2,2′-azobis(N-butyl-2-methylpropionamide) produced the polymers with a molecular weight distribution (MWD) around 1.6, while the racemic- and meso-(2RS,2′RS)-azobis(4-methoxy-2,4-dimethylvaleronitrile) provided a 1.4 MWD. 2,2′-Azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane-1-carbonitrile), and 1-(cyano-1-methylethoxy)-4-methoxy-2,2,6,6-tetramethylpiperidine produced a broad MWD over 4.0. The structure of the photo-acid generator also had an influence on the molecular weight control. The photo-acid generator of sulfonium salts supporting the alkyl, methoxy, phenoxy, methylthio, and tert-butoxycarbonylmethoxy groups, coupled with halogens with the exception of the iodide had no effect on the MWD. On the other hand, the salts containing the iodide, phenylthio, and naphthyl groups produced polymers with broad MWDs and with uncontrolled high molecular weights.     

Alkali metal salts of acrylamide C3H4NOM (M = Li,Na, and K): Synthesis and vibrational spectra

Alkali metal salts of acrylamide C₃H₄NOM (M = Li, Na, and K) were synthesized for the first time by metallation of acrylamide with alkali metals, their alkyl derivatives, or hydrides. The structures of the compounds synthesized were studied by Raman and IR spectroscopy. Based on the results obtained, an ionic structure was proposed for the salts. The salts were tested as initiators of the anionic polymerization of acrylamide. The catalytic activity of C₃H₄NOM in the polymerization of acrylamide is not lower than that of the well known catalyst, KOBu¹.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2316–2319, September, 1996.     

Cationic polymerization with p-substituted benzyl p-hydroxyphenyl methyl sulfonium salts: Effect of substituents and mechanistic aspects of initiation reaction

Various p-substituted benzyl p-hydroxyphenyl methyl sulfonium salts ( 2 ) were synthesized and their initiator activities were evaluated in bulk polymerization of glycidyl phenyl ether (PGE). The order of the activity was found to be 2b (X = CH₃) > 2a (X = H) ≈ 2c (X = Cl) > 2d (X = NO₂), indicating that the introduction of an electron-donating group enhanced the activity. In Hammett's plots, the logarithm of the ratio of the polymerization rates (log k_x/k_H) was correlated with σ⁺_ρ better than with σ_p and a negative ρ⁺ value (-1.18) was obtained. Reaction of 2a with benzyl mercaptan mainly gave dibenzyl sulfide and p-hydroxyphenyl methyl sulfide. The obtained results seemed to demonstrate that the OH group of the aryl group yielded no proton as initiator for the polymerization, whereas the benzyl group caused the polymerization, which was initiated by the corresponding benzyl cation formed by C? S bond cleavage. © 1993 John Wiley & Sons, Inc.     

Photoinitiated cationic oligomerization of aryl 1-propenyl ethers

A series of aryl 1-propenyl ethers (ArPE) were prepared by the isomerization of the corresponding allyl aryl ethers (AArE) and used for photoinduced cationic polymerization studies. Attempted polymerization reactions using diaryliodonium salts as photoinitiators generally resulted in low yields of oligomers. Further studies revealed that these compounds have much lower reactivity in cationic vinyl polymerization as compared to their alkyl analogues. Moreover, side reactions resulting from chain transfer due to Friedel–Crafts alkylations take place and compete with vinyl polymerization. These side reactions are responsible for the low molecular weights observed in the cationic photopolymerization of aryl 1-propenyl ether monomers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3017–3025, 1999