Tetraalkylammonium salts as additives in anionic polymerization of methyl methacrylate

The anionic polymerization of methyl methacrylate was carried out in the presence of t-BuOK/Quaternary ammonium salt (QAS) and α-lithio-ethylisobutyrate/QAS in toluene and THF. Seven QAS and one quaternary phosphonium salt of different size and shape were used as modifiers. With the aid of the model system alkali picrate/QAS, it was found that the interaction between the picrate salt and QAS in toluene does not proceed as a pure cation exchange reaction. Two types of adducts were distinguished: Initiator/QAS with a very long hydrocarbon chain (>C₁₂) promote isotactic placement, while the adducts t-BuOK/QAS with two or more bulky substituents produce a highly syndiotactic polymer with high conversion and comparatively low polydispersity in pure toluene.     

Poly(ethylene oxide) gel as a novel polymerization medium anionic polymerization of methyl methacrylate

Crosslinked poly(ethylene oxide)-(PEO-N) is used as a novel medium for the anionic polymerization of methyl methacrylate (MMA) initiated by t-BuOK and ethyl-α-lithioisobutyrate (α-LiEtIB) in toluene. Comparative studies with linear poly(ethylene oxide)-(PEO-L) are performed as well. It is found that PEO-N effectively binds both initiators, and the polymerization process takes place mainly in the gel phase. PEO-N accelerates the polymerization process initiated by t-BuOK enabling the formation of high-molecular-weight polymers with high yields. Part of poly(methyl methacrylate)-(PMMA) remains in the gel particles yielding semi-interpenetrating networks with amphiphilic properties. PEO additives do not influence profoundly the course of the polymerization, initiated by α-LiEtIB. The influence of PEO-N on the proceeding of the polymerization is discussed in some detail.     

Effect of tetraalkylammonium salts on the tacticity of poly(methyl methacrylate), 2.. Initiation by potassium tert-butoxide

The anionic polymerization of methyl methacrylate was carried out in the presence of potassium tert-butoxide (t-BuOK)/quaternary ammonium salts (QAS) in toluene and tetrahydrofuran at −60°C. It was found that in toluene some QAS additives substantially increase the syndiotacticity of poly(methyl methacrylate). Two types of QAS were distinguished, quite different in their action. The addition of QAS with one or two longchain alkyl groups (>C₁₂), does not change significantly the mode of the monomer addition, whereas the polymerization in the presence of tetraalkylammonium salts with four equal substituents and dimethyldidodecylammonium bromide yields predominantly a syndiotactic polymer with high conversion and comparatively low polydispersity (M̄_w/M̄_w = 1.3−1.5). In some cases QAS additives are more effective modifiers than cryptand [2.2.2].     

Stereospecific polymerization of benzyl α-(alkoxymethyl) acrylates

α-(Alkoxymethyl) acrylates, such as methyl α-(phenoxymethyl) acrylate, benzyl α-(methoxymethyl)acrylate (BMMA), benzyl α-(benzyloxymethyl)acrylate, and benzyl α-(tert-butoxymethyl)acrylate, were synthesized, and their polymerizability and the stereoregularity of the polymers obtained by radical and anionic methods were investigated. The radically obtained polymers were found to be atactic by ¹³C- and ¹H-NMR analyses, but the polymers obtained with lithium reagents in toluene at −78°C were highly isotactic. Further, it is noteworthy that isotactic polymers were also produced with lithium reagents even in tetrahydrofuran. Effects of polymerization temperature and counter cation on stereoregularity were clearly observed in the polymerization of BMMA, and a potassium reagent afforded an almost atactic polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 721–726, 1997     

PMMA/MMT nanocomposites prepared by one-step in situ intercalative solution polymerization

Poly(methylmetacrylate)/montmorillonite (PMMA)/(MMT) nanocomposites were prepared by one-step in situ intercalative solution polymerization involving simultaneous modification of MMT with quaternary ammonium salts (QAS), polymerization and polymer intercalation. Polymerization proceeded at 70 °C in a mixture of ethanol and water, whereas the nanocomposite was precipitated with only water. Four QAS’s with different alkyl chain lengths, as well as a QAS with an additional acrylic group, were used to study the influence of the type of quaternary ammonium salt on intercalation. The largest extent of intercalation was achieved in nanocomposites with the QAS having one long alkyl (C16) chain. The obtained PMMA/MMT intercalated nanocomposites exhibited a higher glass transition temperature, better thermal stability, and improved solvent resistance than the pure PMMA.     

离子液体/季铵盐辅助氯过氧化物酶促氧化合成聚酚

基于氯过氧化物酶(CPO)催化氧化苯酚衍生物单体,建立了一个聚酚的绿色合成体系.以对苯基苯酚、对甲基苯酚、4-乙基苯酚、对羟基肉桂酸、对异丙基苯酚和邻甲基苯酚等6种底物为考察对象,以聚合物的产率、聚合度及热稳定性为评价指标,研究了体系中引入离子液体(ILs)或季铵盐(QAS)以及底物结构和反应微环境等对聚合反应和聚合物性质的影响.结果表明,引入少量咪唑类ILs或QAS可有效提高产物收率,其中ILs/QAS的阳离子基团越大和疏水链越短,越有利于酶催化聚合反应的进行;而ILs/QAS添加量的影响则呈现"钟罩"型规律.同时,苯酚对位取代远比邻位取代有利于聚合反应进行;而对位取代基中烷基类给电子基团比芳香基取代更有优势,所得聚合物的聚合度和热稳定性相对增大,但随着取代基团的增大,其空间位阻不利于聚合物产率的提高;反应体系的p H应控制在弱酸性至近中性,以避免竞争性的副反应的发生;而氧化剂H_2O_2则需要采用间歇式加入以抑制瞬时过浓导致CPO活性中心卟啉环的氧化损伤.基于CPO的活性中心结构分析了聚合机理.     

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.     

Ring-opening polymerization of α,β-disubstituted oxiranes by α-methoxyphenylmethylium hexachloroantimonate

α-Methoxyphenylmethylium hexachloroantimonate was used as a novel initiator for the polymerization of α,β-disubstituted oxiranes such as cyclohexene oxide (CHO) and 2-butene oxide (trans and cis) (2-BO) at ?78°C with dichloromethane or dichloromethane-toluene mixtures as solvents. The CHO polymerization mixture became turbid and the polymer precipitated in dichloromethane. The CHO polymerization proceed quantitatively in dichloromethane–toluene mixtures. The molecular weight distribution of polyCHO obtained was bimodal regardless of the solvent used. The polymerization of trans-2-BO was heterogeneous in both dichloromethane and dichloromethane–toluene mixture. The polymerization mixtures of cis-2-BO were transparent but reached a limit yield which was less than the polymer yield of trans-2-BO. Furthermore, the microstructure of the poly2-BOs were analyzed by Vandenberg's method and the results confirmed Vandenberg's finding that inversion of configuration occurs in the propagation step.     

Kinetics of anionic polymerization of α-methylstyrene in tetrahydrofuran and toluene mixed solvents

The kinetics of anionic polymerization of α-methylstyrene with Na⁺ as counterion have been studied in mixed solvents of tetrahydrofuran (THF) and toluene in various compositions at ?25 to 5°C. The ion-pair rate constant k(_±) increases by about a factor of 50 at ?10°C, whereas the activation energy decreases from 5.1 to ?2.2 kcal/mole, when THF in the mixed solvent increases from 30 to 100 vol-%. The plot of log k(_±) against (D ? 1)/(2D + 1) is a curve, where D is the dielectric constant of the medium. This deviation from linearity is explained in terms of propagation by two types of ion-pairs.     

Living cationic polymerization of vinyl ethers with a naphthyl group: Decisive effect of the substituted position on naphthalene ring

Living cationic polymerization of a vinyl ether with a naphthyl group [2‐(2‐naphthoxy)ethyl vinyl ether, βNpOVE] was achieved using base‐assisting initiating systems with a Lewis acid. The Et_1.5AlCl_1.5/1,4‐dioxane or ethyl acetate system induced the living cationic polymerization of βNpOVE in toluene at 0 °C. The living nature of this reaction was confirmed by a monomer addition experiment, followed by ¹H NMR and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) analyses. In contrast, the polymerization of αNpOVE was not fully controlled; under similar conditions, it produced polymers with broad molecular weight distributions. The ¹H NMR and MALDI‐TOF‐MS spectra of the resultant poly(αNpOVE) revealed that the products had undesirable structures derived from Friedel–Crafts alkylation. The higher reactivity of αNpOVE in electrophilic substitution reactions, such as the Friedel–Crafts reaction, was attributable to the greater electron density of the naphthyl ring, which was calculated based on frontier orbital theory. The naphthyl groups significantly affected the properties of the resultant polymer. For example, the glass transition temperatures (T_g) of poly(NpOVE)s are higher by approximately 40 °C than that of poly(2‐phenoxyethyl vinyl ether). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

n-Butyllithium/α-methylstyrene/benzene/diethyl ether: A suitable initiation system for anionic syntheses of model co- and homopolymers of styrene and isoprene

An initiation system of the anionic polymerization, intended for the syntheses of homopolymers and block copolymers with narrow molar mass distribution, was tested with styrene and isoprene. The actual initiating species, viz., the oligomeric α-methylstyryl anion, originates by the reaction of n-butyllithium with α-methylstyrene in a benzene/diethyl ether 1:1 (v:v) solvent mixture at room temperature. The homopolymers and two-block copolymers of styrene and isoprene, prepared by using this system, were characterized by light scattering, membrance osmometry, GPC, and ¹H NMR spectroscopy. By using the suggested initiation system, it is possible to synthesize well-defined homopolymers and block copolymers with low polydispersity (as judged by the shape of the GPC peaks and by the values of the polydispersity index), especially in a molar mass region between 4 × 10⁴ and 1.5 × 10⁵ g/mol. Above the upper limit of this interval, an appropriate decrease of the diethyl ether/benzene volume ratio is recommended, though the polymerization time must then be prolonged.     

Stereoregulation in the polymerization of methyl α-ethylacrylate by n-BuLi in toluene

The polymerization of methyl α-ethylacrylate was carried out in toluene by n-BuLi at various temperatures. The yield of the polymer decreased with increase in the polymerization temperature and at 30°C and above no polymer was obtained, indicating that the ceiling temperature of this monomer lay between 0 and 30°C. The isotacticity increased with an increase in the polymerization temperature and at 0°C a highly isotactic polymer was obtained. The fractionation of the polymer obtained at ?78°C showed that the polymer was a mixture of isotactic and syndiotactic ones. Upon the addition of a small amount of methanol or water in the polymerization mixture the isotacticity of the polymer increased while the yield decreased. Syndiotactic polymer was obtained in the polymerization by n-BuLi in tetrahydrofuran as well as by diisobutyl aluminum diphenylamide in toluene.     

Reverse Atom‐Transfer Radical Polymerization at Room Temperature

This paper aims at reporting on the “living”/controlled radical polymerization of methyl methacrylate initiated with the benzoyl peroxide (BPO)/Cu^IX (X=Br,Cl)/2,2'‐bipyridine (bpy) redox system at room temperature. No control is observed for the polymerization conducted in bulk and in toluene, whereas a polymer with predetermined molecular weight and rather narrow molecular weight distribution is formed in butanone. The solvent has thus a decisive effect on the reverse atom‐transfer radical polymerization of methyl methacrylate initiated with the BPO/Cu^IX (X = Br,Cl)/bpy ternary system at 25°C.     

Stereospecific polymerization of α-methylstyrene by friedel-crafts catalysts

The relationship between stereoregularity and polymerization conditions of α-methylstyrene has been studied by means of NMR spectra. The effects of solvents and various Freidel-Crafts catalysts have been investigated. The stereoregularity of poly-α-methylstyrene increased with increased polymer solubility in the solvent used and with decreasing polymerization temperature. This behavior is completely different from the stereospecific polymerization of vinyl ethers and methyl methacrylate in homogeneous systems. This may be due to the strong steric repulsion exerted by the two substituents in the α-position of α-methylstyrene. For example, with BF₃ · O(C₂H₅)₂ as catalyst at ?78°C., atactic polymer is obtained in n-hexane, a nonsolvent for α-methylstyrene, whereas highly stereoregular polymer is produced in toluene or methylene chloride, good solvents for the polymer. However, the polarity of the solvent and the nature of the catalyst hardly affect the stereoregularity of the polymer.     

Atom transfer radical polymerization of styrene in toluene/water mixtures

The atom transfer radical polymerization (ATRP) of styrene in water/toluene mixtures was studied. A linear dependence of the molecular weight on conversion was observed, but the initiation efficiency decreased when the catalyst concentration increased. The variation of the amount of water in the system affected the control of the ATRP, indicating that the presence of the aqueous phase influenced the concentration of copper halides in the organic phase. The partitioning of copper halides resulted in almost complete migration of Cu^II into the aqueous phase, which assisted with catalyst removal after polymerization. For example, the amount of residual copper in the organic phase determined by inductively coupled plasma was less than 1 ppm when the polymerization mixture was exposed to air for 30 min. The ATRP of styrene in water/toluene mixtures occurred with the preservation of Br at the polymer chain end, as confirmed by successful block copolymerization. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3153–3160, 2002     

Towards more controlled poly(n-butyl methacrylate) by atom transfer radical polymerization

The homogeneous controlled/‘living’ free radical polymerization of n-butyl methacrylate in toluene or o-xylene at 90 °C, in bulk and in solution, using the novel combination of the catalyst bis-triphenylphosphine iron(II)chloride tetrahydrate (FeCl₂ · 4H₂O(PPh₃)₂) with ethyl 2-bromoisobutyrate ((CH₃)₂CBrCO₂Et)) and α,α-dichloroacetophenone (CHCl₂COPh) as initiators has been investigated. The rate of polymerization initiated by the two initiators exhibited first-order kinetic with respect to the monomer. A linear increase of the number-average molecular weight (M_n) versus monomer conversion was observed for these systems. Among the two initiation systems, ethyl 2-bromoisobutyrate gave the fastest polymerization rate. A system with Fe³⁺ added at the beginning of the polymerization was examined and the lowest polydispersity (M_w/M_n∼1.2) was found when 10% Fe³⁺, relative to Fe²⁺ was added.     

Ionic organic/inorganic materials. I. Novel cationic siloxane copolymers containing quaternary ammonium salt groups in the backbone

The synthesis and characterization of some novel cationic siloxanes copolymers containing quaternary ammonium salt (QAS) groups in the backbone is reported in this article. One cationic oligomer having QAS in the backbone and reactive groups like 2,3‐epoxypropyl and 2‐hydroxy‐3‐chloropropyl (RCO) as well as 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane or α,ω‐bis(3‐aminopropyl)oligodimethylsiloxane (AP) were used as precursors for this goal. Elemental analysis, IR and ¹H NMR spectroscopy, thermogravimetric analysis, and X‐ray photoelectron spectroscopy were used to characterize the obtained copolymers. The thermal stability of the cationic siloxane copolymer increased when the siloxane oligomer having a high number of siloxane units in the chain (AP) was used as a precursor. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3570–3578, 2002     

Macromolecular engineering of polylactones and polylactides. XV. Poly(D,L)-lactide macromonomers as precursors of biocompatible graft copolymers and bioerodible gels

The functional aluminum alkoxide, Et₂Al? O? (CH₂)₂? O-C(O)? C(CH₃)?CH₂, is a very effective initiator for the (D ,L )-lactide (LA) polymerization in toluene at 707deg;C. The coordination-insertion type of polymerization is living and exclusively yields linear P (D ,L )-lactide macromonomers of a predictable molecular weight and a narrow molecular weight distribution. IR and ¹H-NMR studies show that the methacryloyl group of the initiator is selectively and quantitatively attached to one chain end, whereas the second extremity is systematically a hydroxyl function resulting from the hydrolysis of the living growing site. α,ω-Dimethacryloyl-P(D ,L )-lactides, i.e., α,ω-macromonomers, have also been successfully synthesized by the additional control of the termination step, i.e., by reaction of Al alkoxide end groups with methacryloyl chloride. α-Macromonomer and α,ω-macromonomer P(D ,L )-lactides are easily free-radical copolymerized with 2-hydroxyethyl methacrylate (HEMA), resulting in a hydrophilic poly (HEMA) backbone grafted with hydrophobic P(D ,L )-lactide subchains and a biodegradable amphiphilic network, respectively. © 1994 John Wiley & Sons, Inc.     

Atom transfer radical polymerization of 2-methoxy ethyl acrylate and its block copolymerization with acrylonitrile

2-Methoxy ethyl acrylate (MEA), a functional monomer was homopolymerized using atom transfer radical polymerization (ATRP) technique with methyl 2-bromopropionate (MBP) as initiator and CuBr/N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA) as catalyst system; polymerization was conducted in bulk at 60 °C and livingness was established by chain extension reaction. The kinetics as well as molecular weight distribution data indicated towards the controlled nature of polymerization. The initiator efficiency and the effect of initiator concentration on the rate of polymerization were investigated. The polymerization remained well-controlled even at low catalyst concentration of 10% relative to initiator. The influence of different solvents, viz. ethylene carbonate and toluene on the polymerization was investigated. End-group analysis for the determination of high degree of functionality of PMEA was determined with the help of ¹³C{¹H} NMR spectra. Chain extension experiment was conducted with PMEA macroinitiator for ATRP of acrylonitrile (AN) in ethylene carbonate at 70 °C using CuCl/bpy as catalyst system. The composition of individual blocks in PMEA-b-PAN copolymers was determined using ¹H NMR spectra.