Effects of mercaptides on anionic polymerization. II. Polymerization of acrylonitrile initiated by mercaptides

The polymerization of acrylonitrile by the several alkali metal mercaptides was investigated. The initiation reaction was found spectroscopically and by the sodium fusion method to proceed in a Michael-like form similar to a cyanoethylation reaction. From the results of the copolymerization of acrylonitrile and methyl methacrylate by the mercaptides, it was found that the mercaptides behaved as the anionic initiators. The effects of the counterions on the rate of polymerization were found to increase with increasing the electropositivites in the order of Li < Na < K. A negative overall activation energy was obtained, ?2.2 kcal/mole, in the temperature region of ?30°C to +20°C. The catalytic reactivities of the mercaptides were smaller than those of the corresponding oxygen analogs, except in the case of the phenyl substituent. Only in the case of the phenyl substituent, thiophenoxide was found to be much more effective than phenoxide, phenyl-SNa ? phenyl-ONa. The catalytic reactivities of the various sodium mercaptides were also determined to follow not only the basicities of the nucleophiles, but also the polarizabilities as follows: tert-butyl-SNa ≈ n-dodecyl-SNa > phenyl-SNa > n-octyl-SNa > isopropyl-SNa > n-propyl-SNa > ethyl-SNa. The enhanced reactivity of thiphenoxide in spite of the low pK_a value was attributed to the higher polarizability based on the low α effect.     

Polymerization of N-vinylcarbazole by transition metal salts

The polymerization of N-vinylcarbazole (NVC) in the presence of transition metal salts such as WCI₆, MoCI₅, TaCl₅ and NbCl₅ under different reaction conditions was studied. In general, aromatic solvents were found to be superior to aliphatic solvents in the polymerization of NVC, i. e., both conversion and molecular weight were higher in aromatic solvents. It was observed that the polymerization reaction proceeds rapidly and almost quantitatively, even at low monomer concentration (< 5 × 10^?2M) and at low catalyst to monomer mole ratio (10^?5) in aromatic solvents. The copolymerization of NVC with acenaphthylene (ACN) was also investigated in solution at room temperature. The resulting homo- and copolymer were characterized by IR, NMR, x-ray diffraction, and elemental analysis. Thermal and photophysical properties are also reported. From the spectral data, the polymerization solvent was found to have a strong influence upon the polymer stereoregularity.     

Solid-State polymerization of the binary mixture of methacrylate and liquid-crystalline compound by electron beam

Solid-state polymerization of a binary mixture of nonliquid-crystalline monomer and liquidcrystalline compound was carried out using electron beam. The monomers were benzoic acid containing 4-[ω-(meth)acryloyloxyalkyloxy] benzoic acids, in which the alkylene spacer was ethylene, hexamethylene, or undecamethylene. The conversion yield of monomer to polymer to a large extent increased with increasing content of a liquid-crystalline compound with a terminal carboxylic group, such as 4-n-alkyloxybenzoic acid, while the addition of a liquid-crystalline compound without terminal carboxylic group did not affect polymerization of the monomer. Phase diagrams of the mixture of monomer and liquid-crystalline compound were examined using cross-polarizing microscopy and differential scanning calorimetry (DSC). All mixtures of monomer and 4-n-alkyloxybenzoic acid or liquid-crystalline compound without terminal carboxylic group showed liquid-crystallinity in a broad composition range. It was concluded that liquid-crystalline compounds with terminal carboxylic acid may form hydrogen bondings with methacrylate or acrylate monomer having terminal carboxylic acid which enhance polymerizability of the mixture. The stereoregularity of polymers determined by NMR depended on increasing irradiation dose and temperature rather than the content of the added liquid-crystalline 4-n-decanoxybenzoic acid.     

Effects of mercaptides on anionic polymerization. III. Polymerization of methyl methacrylate by thiophenoxides in polar aprotic solvents

Sodium thiophenoxide initiated the polymerization of methyl methacrylate in polar aprotic solvents (DMF, DMSO, HMPA). The active species that initiated the polymerization of the monomer was found by spectrophotometric measurements and by the sodium fusion method to be sodium thiophenoxide itself. The activation energy for the polymerization of the monomer in DMF solvent obtained was E = 3.4 kcal/mole below 30°C, and E = ?3.3 kcal/mole above the temperature. The phenomena were reasoned as the result of the formation of two active species: a solvent-separated ion pair and a contact ion pair. The effects of counterions on the reactivity of thiophenoxide increased with increasing electropositivity of the metals: Li < Na < K. Sodium phenoxide, the oxygen analog of thiophenoxide, was also found to initiate the polymerization of the monomer in the solvents. The relative reactivity of thiophenoxide to phenoxide for the monomer in HMPA at 30°C was thus determined: phenyl-SNa > phenyl-ONa. The relative effect of the polar aprotic solvents on the reactivity of thiophenoxide was also as follows: HMPA > DMF > DMSO. The kinetic studies were made by the graphical evaluation of rate constants. The following results were obtained for the monomer at 20°C in DMF solvent: K_p = 3.5 × 10² 1./mole-hr and K_t = 9.8 × 10^?2/hr.     

Syndiotactic‐ and heterotactic‐specific radical polymerizations of N‐n‐propyl‐α‐fluoroacrylamide and phase‐transition behaviors of aqueous solutions of poly(N‐n‐propyl‐α‐fluoroacrylamide)

Radical polymerization of N‐n‐propyl‐α‐fluoroacrylamide (NNPFAAm) was investigated in several solvents at low temperatures in the presence or absence of Lewis bases, Lewis acids, alkyl alcohols, silyl alcohols, or fluorinated alcohols. Different effects of solvents and additives on stereospecificity were observed in the radical polymerizations of NNPFAAm and its hydrocarbon analogs such as N‐isopropylacrylamide (NIPAAm) and N‐n‐propylacrylamide (NNPAAm); for instance, syndiotactic (and heterotactic) specificities were induced in radical polymerization of NNPFAAm in polar solvents (and in toluene in the presence of alkyl and silyl alcohols), whereas isotactic (and syndiotactic) specificities were induced in radical polymerizations of the hydrocarbon analogs under the corresponding conditions. In contrast, heterotactic specificity induced by fluorinated alcohols was further enhanced in radical polymerization of NNPFAAm. The effects of stereoregularity on the phase‐transition behaviors of aqueous solutions of poly(NNPFAAm) were also investigated. Different tendencies in stereoregularity were observed in aqueous solutions of poly(NNPFAAm)s from those in solutions of the hydrocarbon analogs such as poly(NIPAAm) and poly (NNPAAm). The polymerization behavior of NNPFAAm and the phase‐transition behavior of aqueous poly(NNPFAAm) are discussed based on possible fluorine–fluorine repulsion between the monomer and propagating chain‐end, and neighboring monomeric units. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis of bio-based poly(methacrylates) using SG1-containing amphiphilic macroinitiators by nitroxide mediated miniemulsion polymerization

SG1-based amphiphilic macroinitiators were synthesized from oligoethylene glycol methyl ether methacrylate and 10 mol% acrylonitrile or styrene (as the controlling comonomer) to conduct the nitroxide mediated polymerization of bio-based methacrylic monomers (isobornyl methacrylate (IBOMA) and C13 alkyl methacrylate (C13MA)) in miniemulsion. The effect of the addition of surfactant (DOWFAX 8390), co-stabilizer (n-hexadecane) and different reaction temperatures (80, 90 and 100°C) on polymerization kinetics was studied. We found that the NMP of IBOMA/C13MA using amphiphilic macroalkoxyamines were most effective during miniemulsion polymerization (linear trend of M_n versus conversion and high latex stability) in presence of 2 wt% surfactant and 0.8 wt% co-stabilizer (relative to monomer) at 90°C. The effect of surfactant, co-stabilizer and temperature on particle size during the polymerization was studied and suggested a decrease in initial particle size with the addition of surfactant and co-stabilizer. Finally, the thermal properties of IBOMA/C13MA polymers, prepared by amphiphilic macroinitiators, were examined thoroughly, indicating a T_g in the range of −44°C < T_g < 109°C.     

Effect of monomer hydrophilicity on ARGET–ATRP kinetics in aqueous mini-emulsion polymerization

Activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP)-based aqueous miniemulsion polymerization where the polymerization takes place in the stabilized monomer droplets is described. In this work, we compared styrene, n-butyl methacrylate (nBMA) and tert-butyl methacrylate (tBMA) and investigated the influence of their hydrophobicity on dispersity, molecular weight and particle stability based their partition coefficients (logP) (2.67, 2.23, and 1.86, respectively). Tetrabutylammonium bromide (TBAB) was used as a phase transfer agent for the controlled delivery of Cu²⁺-Br/tris(2-pyridylmethyl)amine (TPMA), a hydrophilic catalyst, into monomer droplets of varying hydrophobicity. The resulting dispersity and particle stability of each polymer is a function of its logP value, with the most hydrophobic monomer (styrene) displaying the narrowest dispersity and most control (Đ < 1.3), and the most hydrophilic polymer poly(tert-butyl methacrylate) (PtBMA) having reduced emulsion stability, determined by the observation of aggregate formation. Selected polymerization parameters, including effects of total ascorbic acid feed concentration and the monomer concentration and their effects on dispersity are reported. The controlled polymerizations of hydrophilic monomers using ARGET-ATRP in miniemulsion conditions and understanding the effect of monomer hydrophilicity on the emulsion stability will broaden the use of ARGET-ATRP in emulsion polymerization for the synthesis of polymer-grafted nanoparticles with hydrophilic corona.     

Polymerization of methyl methacrylate under ultrasonic irradiation. Part IV. Effect of ultrasonic irradiation on Grignard catalyst and stereoregularity of the polymers produced in dioxane–tetrahydrofuran mixed solvent

Two series of polymerization of methyl methacrylate with Grignard reagent in dioxane—tetrahydrofuran mixed solvent was carried out under ultrasonic irradiation. In series A, catalyst was added to the mixture of monomer and solvent, and in series B, catalyst was previously mixed with solvent. The effect of ultrasonic irradiation on Grignard catalyst and the microstructure in reacting sites were discussed on the basis of the stereoregularity of the polymers produced. The stereoregularity of the polymers in series A was higher than that in series B. The effect of ultrasonic irradiation on the stereoregularity was completely reversed in series A and B and it increased in the former and decreased in the latter. It was, therefore, assumed that ultrasonic irradiation affected the microstructure in the reacting sites in series A, while it increased the relative amount of R₂Mg which gave polymers with poor stereoregularity in series B.     

Semicontinuous heterophase polymerization under monomer starved conditions to prepare nanoparticles with narrow size distribution

The semicontinuous polymerization of methyl methacrylate (MMA) in heterogeneous medium under monomer‐starved conditions is reported here. The effect of monomer addition rate on kinetics, particle size, particle number, and PMMA average molar masses are reported. This process permits the synthesis of high‐solid content latexes containing nano‐sized particles (<40 nm) with narrow particle size distributions [(D_w/D_n) < 1.1]. Moreover, the molar masses (M_n ≈ 0.3–1.2 × 10⁶ g/mol) are much lower than those expected by chain transfer to monomer, which is the typical termination mechanism in 0–1 emulsion and microemulsion reactions. Both particle size and average molar masses decrease as the rate of monomer addition is diminished. Possible explanations for this process are provided. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1463–1473, 2007     

Cationic polymerization of α,β-disubstituted olefins. XV. Stereospecific polymerization of butenyl ethers by cationic catalysts

Methyl, ethyl, and isopropyl butenyl ethers, CH₃CH₂CH?CHOR, were polymerized with homogeneous catalysts at ?78°C. Toluene, methylene chloride, and nitroethane were used as solvents, and BF₃O(C₂H₅)₂ and SnCl₄·CCl₃CO₂H were used as catalysts. The stereoregularity of the polymers were compared by x-ray diagrams and infrared absorption ratios. The stereoregularity of polymers increased with increasing content of the trans isomer in the monomer and with increasing polarity of the solvent. In the polymerization of methyl and ethyl butenyl ethers, crystalline polymers were obtained from both the trans and cis isomers. The crystalline polymer prepared from the trans isomer and that from the cis isomer had the same steric structure. This behavior is quite different from that observed in the polymerization of propenyl ethers. It is concluded that the bulkiness of the group on the olefinic β-carbon plays an important role in the stereospecific polymerization of α,β-disubstituted olefins.     

RAFT Miniemulsion Polymerization Kinetics, 1 – Polymerization Rate

The polymerization kinetics of a RAFT‐mediated radical polymerization inside submicron particles (30 < D_p < 300 nm) is considered. When the time fraction of active radical period, ϕ_A, is larger than ca. 1%, the polymerization rate increases with reducing particle size, as for the cases of conventional emulsion polymerization. The rate retardation by the addition of RAFT agent occurs with or without intermediate termination in zero‐one systems. For the particles with D_p < 100 nm, the statistical variation of monomer concentration among particles may not be neglected. It was found that this monomer‐concentration‐variation (MCV) effect may slow down the polymerization rate. An analytical expression describing the MCV effect is proposed, which is valid for both RAFT and conventional miniemulsion polymerizations.

     

Studies of the polymerization of diallyl compounds. XXVI. Enhanced polymerizability by the hydroxyl group in the polymerization of diallyl hydroxydicarboxylates

In order to elucidate the effect of the hydroxyl group on the polymerization of diallyl hydroxydicarboxylates, we investigated in detail the radical polymerizations of diallyl succinate (DASu), diallyl malate (DAMa), and diallyl tartrate (DATa), each of which have similar structure differing only in the number of hydroxyl groups present. The rate of polymerization (R_p) was quite enhanced in the order DASu < DAMa < DATa, in accord with the increase in the number of hydroxyl groups within a monomer unit. The enhanced ability of the allylic monomer radical to reinitiate chain growth was also in the same order, as was clear from the dependence of R_p on the initiator concentration. The dependence of the residual unsaturation of the polymer on the monomer concentration in the polymerizations of DAMa and DATa was abnormal in terms of cyclopolymerization. These results are discussed in connection with the formation of the intermolecular hydrogen bond through the hydroxyl groups.     

乙烯基二联苯单体的螺旋选择性自由基聚合

为了深入理解乙烯基二联苯单体自由基聚合过程中的手性传递,进行了手性单体(+)-2-[(S)-异丁氧羰基-5-(4′-己氧基苯基)苯乙烯、非手性单体2-丁氧羰基-5-(4′-己氧基苯基)苯乙烯的均聚反应及它们二者的共聚反应,探讨了聚合温度和溶剂性质对手性单体均聚物旋光活性、手性单体含量对共聚物旋光活性以及聚合反应溶剂的超分子手性对共聚物旋光活性的影响.研究发现,降低聚合温度、采用液晶性反应介质有利于得到旋光度大的聚合物;少量手性单体的引入即可诱导共聚物形成某一方向占优的螺旋构象,比旋光度随手性单体的含量增加呈线性增长;在胆甾相液晶中制备的非手性单体聚合物不具有光学活性.这些结果表明,该类乙烯基二联苯聚合物具有动态螺旋构象,其光学活性主要依赖于主链的立构规整度和侧基不对称原子的手性.     

Functional Monomers and Polymers. XLV. Activation Parameters for Polymerization of N-[btilde]-Methacryloyloxyethyl Type Monomers Containing Nucleic Acid Bases

In order to determine the effect of functional structure of ester groups on the stereoregularity of polymers, polymerization of N-[btilde]-methacryloyloxyethyl type monomers containing nucleic acid bases was made by using a free-radical initiator. From the NMR spectrometric determination of the stereoregularity of the polymers obtained, it was found that for polymerization of the monomer with adenine as the side group in dimethyl sulfoxide solution, syndiotactic placement appears to be favored by the additional enthalpy of activation required for isotactic placement.     

Preparation of monodisperse hydrophilic polyamide by anionic polymerization of bicyclic oxalactam

The preparation of a monodisperse hydrophilic polyamide was achieved in the anionic polymerization of a bicyclic oxalactam, 8-oxa-6-azabicyclo[3.2.1]octan-7-one (abbreviated BOL) with the use of N-benzoyl BOL and potassium pyrrolidonate (2 and 0.5 mol % to BOL, respectively) in dimethyl sulfoxide at 25°C. The number-average molecular weight of the polyamide increased in direct proportion to the monomer conversion, and was consistent with the value calculated from the amounts of the consumed monomer and activator. The molecular weight distribution (MWD) of the polyamide obtained until the middle stage of polymerization (polymerization time, < 10 min; monomer conversion, < 60%) was found to be narrow (M_w/M_n = 1.1). The MWD was gradually broadened in the later stage of the polymerization, which may result from the redistribution of molecular weight of the resulting polyamide not only by the polymerization–depolymerization equilibrium, but also by transamidation between polymer chains.     

Stereospecific polymerization of benzyl vinyl ether by BF3·OEt2

Polymerization of benzyl vinyl ether was carried out by BF₃·OEt₂, and the effects of polymerization conditions on the stereoregularity of the polymer were studied by NMR analysis. The polymerization at ?78°C in toluene gave a highly isotactic polymer. The isotacticity of the polymer was independent of the catalyst concentration but increased with a decrease in the initial monomer concentration and decreased slightly on raising the reaction temperature. When the polymerizations were carried out in toluene—nitroethane mixtures, a gradual decrease in the isotacticity and a rapid decrease in the molecular weight of the polymer were observed with increasing nitroethane in the solvent. The molecular weight of the polymer was almost constant, regardless of the catalyst concentration, and increased with increasing initial monomer concentration and decreasing polymerization temperature. When the polymerization was performed in toluene at ?78°C with a small amount of water or benzyl alcohol, a linear relationship was found between the reciprocal DP of the polymer and water or benzylalcohol concentration. The mechanisms of the initiation reaction and the stereoregulation in the polymerization were also discussed.     

Influence of preparative conditions on molecular weight and stereoregularity distributions of polypropylene

The influence of preparative conditions on the molecular weight and stereoregularity distributions of polypropylene was investigated. The stereoregularity distribution is narrowed by using a highly stereospecific catalyst, by decreasing the polymerization temperature, and for the three-component catalyst by keeping the mole proportion of the electron-donating third component at 0.5. The molecular weight distribution can be narrowed by using a highly stereospecific catalyst, a high monomer concentration, and a high polymerization temperature, and by having a lower conversion, particularly at low monomer concentration. The possibility of long-chain branching in polypropylene was indicated by data from the fractionation of tritium-labeled polymers.     

Living anionic polymerization of N‐methoxymethyl‐N‐isopropylacrylamide: Synthesis of well‐defined poly(N‐isopropylacrylamide) having various stereoregularity

Anionic polymerization of N‐methoxymethyl‐N‐isopropylacrylamide ( 1 ) was carried out with 1,1‐diphenyl‐3‐methylpentyllithium and diphenylmethyllithium, ‐potassium, and ‐cesium in THF at ?78 °C for 2 h in the presence of Et₂Zn. The poly( 1 )s were quantitatively obtained and possessed the predicted molecular weights based on the feed molar ratios between monomer to initiators and narrow molecular weight distributions (M_w/M_n = 1.1). The living character of propagating carbanion of poly( 1 ) either at 0 or ?78 °C was confirmed by the quantitative efficiency of the sequential block copolymerization using N,N‐diethylacrylamide as a second monomer. The methoxymethyl group of the resulting poly( 1 ) was completely removed to give a well‐defined poly(N‐isopropylacrylamide), poly(NIPAM), via the acidic hydrolysis. The racemo diad contents in the poly(NIPAM)s could be widely changed from 15 to 83% by choosing the initiator systems for 1 . The poly(NIPAM)s obtained with Li⁺/Et₂Zn initiator system possessed syndiotactic‐rich configurations (r = 75–83%), while either atactic (r = 50%) or isotactic poly(NIPAM) (r = 15–22%) was generated with K⁺/Et₂Zn or Li⁺/LiCl initiator system, respectively. Atactic and syndiotactic poly(NIPAM)s (42 < r < 83%) were water‐soluble, whereas isotactic‐rich one (r < 31%) was insoluble in water. The cloud points of the aqueous solution of poly(NIPAM)s increased from 32 to 37 °C with the r‐contents. These indicated the significant effect of stereoregularity of the poly(NIPAM) on the water‐solubility and the cloud point in water © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4832–4845, 2006     

Photopolymerization of water-soluble acrylic monomers induced by colloidal CdS and Cd x Zn1 − x S nanoparticles

Photocatalytic activity of CdS and Cd _x Zn_1−x S nanoparticles in the polymerization of acrylamide and acrylic acid in aqueous solutions has been found. It has been shown that the most probable way of the photogeneration of primary radicals is the reduction of an adsorbed monomer by the conduction band electrons of the semiconductor nanoparticles, a monomer oxidation by the valence band holes and atomic hydrogen addition to a monomer being complementary photoinitiation routes. A correlation between the composition of Cd_xZn_1-xS nanoparticles and their photocatalytic activity in the acrylamide polymerization has been established. It has been shown that an increase in the quantum yield of the photopolymerization in a sequence СdS < Cd_0.75Zn_0.25S < CdS_0.5Zn_0.5S < Cd_0.3Zn_0.7S originates from a concurrent increase of the conduction band potential of the semiconductor nanoparticles. A kinetic equation of the photocatalytic acrylamide polymerization has been derived. Quantum yields of the photoinitiation have been found to be as small as 10⁻⁴ to 10⁻³.     

Living Free Radical Polymerization of Cyclodextrin Host‐Guest Complexes of Styrene via the Reversible Addition Fragmentation Chain Transfer (RAFT) Process in Aqueous Solution

Summary: Host‐guest complexes of styrene and randomly methylated β‐cyclodextrin (m‐β‐CD) were polymerized in aqueous medium via the reversible addition fragmentation chain transfer (RAFT) process. 3‐Benzylsulfanylthiocarbonylsulfanylpropionic acid (TTC) was used as trithiocarbonate‐type RAFT agent. The results indicate a controlled character of the polymerization of the styrene complexes as the number‐average molecular weight, , increases linearly with monomer to polymer conversion; however, the molecular weights of the obtained polystyrenes deviate to higher values than those theoretically predicted. Nevertheless, the molecular weights can be controlled by variation of the initial RAFT agent concentration. The polystyrenes produced in this system exhibited narrower polydispersities (1.23 < < 2.36) than those produced without RAFT agent (5.24 < < 9.21) under similar conditions. The present contribution represents the first example of RAFT polymerization of a m‐β‐CD‐complexed hydrophobic vinylmonomer (styrene) from homogenous aqueous solution.

Schematic presentation of complexation and RAFT polymerization of m‐β‐CD‐complexed styrene with TTC as RAFT agent and evolution of the full molecular weight distributions in the CD‐mediated styrene free radical RAFT polymerization.