Organoaluminum catalyst for polymerization reaction. Synthesis of isotactic polyacetaldehyde by AIR3–alkali metal hydroxide catalysts in situ

The catalytic behavior of binary systems derived from AIR₃ and alkali metal hydroxide in a molar ratio of 1 to 0.5 in situ for stereospecific polymerization of acetaldehyde was studied for the purpose of preparation of isotactic polyacetal. The polymer obtained can be readily stretched to a film. The polymerization proceeds slowly (in ～20 hr). The polymer yield and stereospecificity of the polymerization by AlEt₃–LiOH (1:0.5) catalyst were not significantly changed by the nature of solvent or dilution as far as studied. AlEt₃–NaOH, AlEt₃–KOH, AlEt₃–CsOH, AliBu₃–LiOH and AlMe₃–LiOH in molar ratios of 1 to 0.5 behaved similarly. AlMe₃–NaOH, AlMe₃–KOH and AliBu₃–NaOH also gave isotactic polymer of high stereoregularity but in lower yields.     

Ring-opening polymerization of cyclic esters and trimethylene carbonate catalyzed by aluminum half-salen complexes

A series of ONO-tridentate Schiff base ligands derived from chiral and achiral amino alcohols and amino acids were synthesized and reacted with AlEt(3) to provide dimeric aluminum complexes. These complexes were tested for the ring-opening polymerization (ROP) of rac-lactide at 70 °C in toluene, producing poly(lactide) with up to 82% isotacticity. The most active of these aluminum complexes was chosen to perform ring-opening homopolymerizations of rac-lactide, trimethylene carbonate (TMC), rac-β-butyrolactone (rac-β-BL), δ-valerolactone (δ-VL), and ε-caprolactone (ε-CL). Kinetic parameters were investigated, and each polymerization was found to be first order with respect to monomer concentration. Fractional orders were observed with respect to catalyst concentration, indicating catalyst aggregation during the polymerization processes. Activation parameters were determined for all monomers, with their ΔG(?) values at 90 °C being in the order rac-lactide ≈ rac-β-BL > δ-VL > TMC ≈ ε-CL. Fineman-Ross and kinetic studies of the copolymerization of rac-lactide and δ-VL both indicate that the rate of rac-lactide enchainment is higher than that of δ-VL, resulting in a tapered copolymer. In addition, single crystals of one of these aluminum complexes were grown in the presence of rac-lactide and characterized using X-ray crystallography. The unit cell contains two lactide monomers, one D- and one L-lactide, adding further proof that polymerization takes place via an enantiomorphic site control mechanism.     

Effect of microwave energy on chain propagation of poly(ε-caprolactone) in benzoic acid-initiated ring opening polymerization of ε-caprolactone

Microwave-assisted ring opening polymerization of ε-caprolactone (ε-CL) initiated by benzoic acid was investigated. The molar ratio of ε-CL to benzoic acid was 5, 15 and 25. The mixtures of ε-CL/benzoic acid were heated under microwave irradiation and the temperatures were self-regulated to equilibrium from 204 to 240 °C with microwave power ranging from 340 to 680 W. The polymer chain propagated fast between 160 and 230 °C, within which the higher the temperature, the faster the propagation. However, when the temperature was over 230 °C, the resultant poly-(ε-caprolactone) (PCL) degraded. The advantage of microwave-assisted polymerization was that the propagation of PCL chain was significantly enhanced but the formation of growing center at the beginning stage of the polymerization was greatly inhibited. With this metal-free method, PCL with weight-average molar mass (M_w) over 4×10⁴ g/mol was prepared.     

Heavier alkali metal complexes of 2-phenylamidopyridine: an X-ray crystallographic and theoretical study of a structurally diverse series of crown ether adducts

Complexes of the anion of the secondary amine 2-phenylaminopyridine (LH) with the heavier alkali metals Na-Cs have been prepared in the presence of various macrocyclic polyether crowns [12-crown-4 (12C4), 15-crown-5 (15C5), and 18-crown-6 (18C6)], which coordinate to the metal ions in all cases. Depending on the combination of alkali metal and crown, the products include separated ion pairs [(crown)(2)M](+)L(-)(12C4/Na, 15C5/K, 15C5/Rb, 15C5/Cs) and contact-ion-pair neutral molecules [(crown)ML](15C5/Na, 18C6/Na, 18C6/K, 18C6/Rb) in which L(-) acts as a bidentate ligand. [((12C4)KL)(2)] is a dimer in which the amido and pyridine N atoms of two ligands bridge the metal ions, while [((18C6)KL(2)K)([infinity])] is a chain polymer with crown O and pyridyl N atoms acting as bridges in corner-sharing KOKN four-membered rings and may be regarded as a potassium potassate complex. [((18C6)Cs(2)L(2))([infinity])] is also polymeric, with a basic arrangement like that of [((12C4)KL)(2)], but with each 18C6 ligand mu-kappa6:kappa6 to two metal centres, generating the polymer. Although most of the [(crown)(2)M](+) sandwich cations have essentially parallel crown ligands, [(12C4)(2)Rb](+) is markedly bent, both in the complex incorporating THF as an additional ligand and in the THF-free complex, where two of these cations form a centrosymmetric dimer through two bridging oxygen atoms; DFT calculations indicate that the bending is inherent, thus enabling the coordination by an extra oxygen atom rather than being a consequence of this coordination. Attempts to isolate the caesium 12C4 derivative were unsuccessful. The compounds have been characterized by NMR spectroscopy, CHN microanalysis and, in most cases, X-ray crystallography.     

Neutron Total Scattering Investigation of the Dissolution Mechanism of Trehalose in Alkali/Urea Aqueous Solution

The atomic picture of cellulose dissolution in alkali/urea aqueous solution is still not clear. To reveal it, we use trehalose as the model molecule and total scattering as the main tool. Three kinds of alkali solution, i.e., LiOH, NaOH and KOH are compared. The most probable all-atom structures of the solution are thus obtained. The hydration shell of trehalose has a layered structure. The smaller alkali ions can penetrate into the glucose rings around oxygen atoms to form the first hydration layer. The larger urea molecules interact with hydroxide groups to form complexations. Then, the electronegative complexation can form the second hydration layer around alkali ions via electrostatic interaction. Therefore, the solubility of alkali aqueous solution for cellulose decreases with the alkali cation radius, i.e., LiOH > NaOH > KOH. Our findings are helpful for designing better green solvents for cellulose.     

Anionic polymerization of lactones initiated by alkali graphitides. IV. Copolymerization of ε-caprolactone initiated by KC24

The copolymerization of ε-caprolactone (ε-CL) with octamethylcyclotetrasiloxane (D₄) and styrene (St) under the action of the second-stage potassium graphitide KC₂₄ was investigated. The copolymerizations were carried out in bulk or in xylene at 20°C. The content of the block copolymer ε-CL/D₄ in the polymerization mixture was 60–95%, the molecular weight ranging between 150,000 and 300,000. The data for the copolymers' composition obtained by ¹H-NMR and GPC showed 14–20% of D₄-units in the copolymer. The amount of the block copolymer ε-CL/St in the polymerization products was 0–87%, and the molecular weights in the case of copolymer formation were between 100,000 and 500,000. The content of St-units in the copolymers was from 10 to 75% as shown by GPC and ¹H-NMR. The mechanism of action of the initiator is discussed.     

Recent development of alkali metal complex promoted iso-selective ring-opening polymerization of rac-Lactide

This article reports the synthesis of a series of alkali metal complexes with diverse multi-dentate ligands. The sodium and potassium complexes show excellent activity in the ring-opening polymerization of ε-CL and δ-VL and rac-Lactide.

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Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions

Rapid dissolution of cellulose in LiOH/urea and NaOH/urea aqueous solutions was studied systematically. The dissolution behavior and solubility of cellulose were evaluated by using (13)C NMR, optical microscopy, wide-angle X-ray diffraction (WAXD), FT-IR spectroscopy, DSC, and viscometry. The experiment results revealed that cellulose having viscosity-average molecular weight ((overline) M eta) of 11.4 x 104 and 37.2 x 104 could be dissolved, respectively, in 7% NaOH/12% urea and 4.2% LiOH/12% urea aqueous solutions pre-cooled to -10 degrees C within 2 min, whereas all of them could not be dissolved in KOH/urea aqueous solution. The dissolution power of the solvent systems was in the order of LiOH/urea > NaOH/urea > KOH/urea aqueous solution. The results from DSC and (13)C NMR indicated that LiOH/urea and NaOH/urea aqueous solutions as non-derivatizing solvents broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form an actual solution.     

Copolymer of lactide and ε-caprolactone catalyzed by bimetallic Schiff base aluminum complexes

A series of copolymers of lactide(LA) and e-caprolactone(ε-CL) with different monomer feed ratios were achieved using three kinds of bimetallic Schiff aluminum complexes as catalysts. The ratios of LA and ε-CL units in different copolymers and the average segments length were determined by NMR analysis. The comparative kinetic study of L-LA/ε-CL and rac-LA/ε-CL copolymerization systems showed that the polymerization rate of LA was faster than ε-CL, and L-LA showed polymerization rate slightly faster than rac-LA. It was inferred that the copolymers achieved by these complexes were gradient copolymers with gradual change in distribution of LA and e-CL units. The thermal properties of these copolymers were characterized by DSC analysis, which showed that the glass transition temperature(Tg) of these copolymers changed regularly according to the pro-portion change of two structural units.     

Crown Ether Phase Transfer Catalysts for An Ionic Polymerization of Bisphenol A / 4,4′‐Dichlorodiphenyl Sulfone

Various crown ethers were prepared and applied as phase transfer catalysts for the an ionic copolymerization of bisphenol A and 4,4′‐dichlorodiphenyl sulfone monomers with alkali salts, e.g., NaNH₂, NaOH and KOH, as initiators. The catalytic abilities of various crown ethers for the an ionic polymerization of bisphenol A / 4,4′‐dichlorodiphenyl sulfone were found to be in the order: 15‐crown‐5 ? monobenzo‐15‐crown‐5 > 18‐crown‐6 > Dicyclohexano‐18‐crown‐6 > Dibenzo‐18‐crown‐6 > 12‐crown‐4 with sodium amide (NaNH₂) as initiator. Sodium amide was shown to be a better initiator than NaOH or KOH with monobenzo‐ 15‐crown‐5 as a catalyst. Effects of solvents and temperature on the crown ether catalytic polymerization were also investigated. Dimethyl sulfoxide (DMSO) exhibited much better for the polymerization than other organic solvents, e.g., toluene, p‐xylene, dimethyl formamide and dioxane. Higher polymerization was found at higher temperatures and about 100% yield of poly(bisphenol A / sulfone) was obtained at 125 °C in 3 hr. The molecular weight of poly(bisphenol A / sulfone) as a function of reaction time was determined with gel permeation chromatography. Concentration effects of crown ether on % yield and molecular weight of poly(bisphenol A / sulfone) were also investigated and discussed.     

Densities and partial molar volumes of aqueous solutions of lithium,sodium, and potassium hydroxides up to 250°C

The densities of aqueous solutions of lithium, sodium and potassium hydroxides were measured up to 3m (mol-kg^–1) with a vibrating tube densimeter from 55 to 250°C an at pressures close to saturation. The apparent molar volumes of the solutions were calculated and the infinite dilution values at each temperature and saturation pressure were obtained by extrapolation. The present data are compared with literature values (for LiOH and KOH below 75°C and over the entire temperature range for NaOH) and with the predictions of a semiempirical model. It is concluded that the high temperature data for NaOH reported here improves the available experimental information on the volumetric properties of this system. The influence of ion association on the volumetric properties of LiOH solutions is also discussed.     

Controlled ring-opening polymerization of cyclic esters with phosphoric acid as catalysts

(R)-(?)-1,1′-Binaphthyl-2,2′-diyl hydrogen phosphate (BPA) has been demonstrated as an efficient organocatalyst for controlled ring-opening homopolymerization of ε-caprolactone (ε-CL) and copolymerization of ε-CL with glycolide and lactide. High molar mass PCL with narrow molar mass distribution has also been synthesized from the bulk ring-opening polymerization (ROP) of ε-CL with BPA as catalysts; the highest molar mass of PCL is 4.35?×?10⁴ g/mol with polydispersity index of 1.20. The successful synthesis of high molar mass PCL is attributed to the bifunctional activation mechanism for the ROP of ε-CL catalyzed by BPA. More interestingly, ppm level of BPA is sufficient to catalyze controlled ROP of ε-CL.     

Dissolution of chitin in aqueous KOH

Our NMR experiments show that chitin can dissolve well in aqueous KOH through a freeze-thawing process, and the dissolution power of the alkali solvent systems is in the order of KOH > NaOH > LiOH aqueous solution, which is totally contrary to that of cellulose in the alkali aqueous solution (i.e., LiOH > NaOH ? KOH). In this work, we systematically study the dissolution process in KOH and KOH/urea aqueous solutions. Chitin has good solubility (solubility ~80 %) in 8.4–25 wt% KOH aqueous solution at ?30 °C. The role of urea also has been investigated: unlike aqueous chitin-NaOH solutions, urea indeed enhances the solubility of chitin in KOH aqueous solutions, but the increased degree becomes unobtrusive with decreasing temperature and increasing dissolution time; the DA decline curves of chitin-KOH and chitin-KOH/urea aqueous solutions are nearly overlapping, indicating that the effect of the urea on the degree of acetylation of chitin in KOH aqueous solutions is small, similar to the NaOH/urea solvent.     

Raman spectra from very concentrated aqueous NaOH and from wet and dry, solid, and anhydrous molten, LiOH, NaOH, and KOH

High-temperature, high-pressure Raman spectra were obtained from aqueous NaOH solutions up to 2NaOHH2O, with X(NaOH)=0.667 at 480 K. The spectra corresponding to the highest compositions, X(NaOH)> or =0.5, are dominated by H3O2-. An IR xi-function dispersion curve for aqueous NaOH, at 473 K and 1 kbar, calculated from the data of Franck and Charuel indicates that the OH- ion forms H3O2- by preferential H bonding with nonhydrogen-bonded OH groups. Raman spectra from wet to anhydrous, solid LiOH, NaOH, and KOH yield sharp, symmetric OH- stretching peaks at 3664, 3633, and 3596 cm(-1), respectively, plus water-related, i.e., H3O2-, peaks near LiOH, 3562 cm(-1), NaOH, 3596 cm(-1), and, KOH, 3500 cm(-1). Absence of H3O2- peaks from the solid assures that the corresponding melt is anhydrous. Raman spectra from the anhydrous melts yield OH- stretching peak frequencies: LiOH, 3614+/-4 cm(-1), 873 K; NaOH, 3610+/-2 cm(-1), 975 K; and, KOH, 3607+/-2 cm(-1), 773 K, but low-frequency asymmetry due to ion-pair interactions is present which is centered near 3550 cm(-1). The ion-pair-related asymmetry corresponds to the sole IR maximum near 3550 cm(-1) from anhydrous molten NaOH, at 623 K. Bose-Einstein correction of published low-frequency Raman data from molten LiOH revealed an acoustic phonon, near 205 cm(-1), related to restricted translation of OH- versus Li+, and an optical phonon, at 625 cm(-1) and tau approximately 0.05 ps, due to protonic precession and/or pendular motion. Strong H bonding between water and the O atom of OH- forms H3O2-, but the proton of OH- does not bond with H significantly. Large Raman bandwidths (aqueous solutions) are explained in terms of inhomogeneous broadening due to proton transfer in a double well. Vibrational assignments are presented for H3O2-.     

Application of Dipotassium Glycoxides–Activated 18-Crown-6 for the Synthesis of Poly(propylene oxide) with Increased Molar Mass

Mono- and dipotassium salts of dipropylene glycol were applied for the polymerization of propylene oxide in mild conditions, i.e., tetrahydrofuran solution at ambient temperature. The structure of polymers was investigated by use of ¹³C NMR and MALDI-TOF techniques. The structure depends strongly on the kind of initiator and additives that are used such as coronand 18-crown-6 and dipropylene glycol. The lowest unsaturation, represented by allyloxy starting groups, has the polymer obtained by use of monopotassium salt without the ligand. The highest unsaturation degree is for the polymer synthesized in the presence of dipotassium salt–activated 18-crown-6. This polymer, obtained at high initial monomer concentration and low initial concentration of initiator, consists of two fractions, i.e., a low molar mass fraction (M_n = 9400) containing mainly macromolecules with alkoxide starting and end groups and a much higher molar mass fraction (M_n = 29500 g/mol) containing macromolecules with allyloxy starting groups and alkoxide or hydroxyl end groups. Addition of free glycol to this system decreases the molar mass of polymers. Similar results were obtained by use of dipotassium salts of other glycols. The mechanisms of the studied processes are discussed.     

Aerobic oxidation of benzylic alcohols with solid alkaline metal hydroxides

Solid alkaline metal hydroxides displayed high catalytic activity and full selectivity in the aerobic oxidation of benzylic alcohols in a non-polar medium. The activity of the solid bases, in decreasing order of reactivity, was KOH > NaOH ≫ LiOH. Water, which is the only by-product of the reaction, plays a crucial role in KOH deactivation by converting the crystal phase of KOH to KOH · H₂O, as confirmed by XRD measurements.     

辛酸镁催化L-丙交酯与ε-己内酯共聚及其共聚物结构与性能研究

以无毒性的辛酸镁为催化剂催化L-丙交酯和ε-己内酯本体开环共聚合,制备了一系列不同单体配比的共聚物.首先用1H-NMR跟踪了共聚合单体转化率,显示L-LA聚合速率显著快于ε-CL.用13C-NMR分析共聚物微观结构和计算单体单元平均序列长度(LLLe和LCe),表明聚合过程中酯交换反应导致单元序列结构重新分布.随着反应进行,LLLe急剧下降而LCe逐渐增加后稍有降低,游程数逐渐增大,共聚物无规度提高.反应初期主要是一级酯交换反应,二级酯交换反应导致的CLC序列结构在反应后期才观察到.由Fineman-Ross法计算出L-丙交酯和ε-己内酯的竞聚率分别为rLA=23和rCL=0.22,表明在聚合反应初期L-LA单体优先插入聚合物增长链端,形成LL单元长嵌段结构.共聚物组成显著影响单元序列长度,各序列长度随相应单体加入量增加而增长.二级酯交换系数(TII[CLC])随ε-CL含量增加而增大.对于整个组成范围内,根据竞聚率计算的LLLr值始终要大于聚合产物的LLLe,而LCr计算值小于或接近LCe实验值.因此,共聚物单元序列分布随共聚物投料比和反应时间而改变,趋向于无规分布.以DSC和XRD分析了共聚物热性能和结晶性,表明共聚物结晶性与单元序列长度密切相关.所有共聚物只有一个玻璃化转变温度Tg,符合无规共聚物的Fox方程,说明所得共聚物为无规共聚物,或者说包含有相容性嵌段成分的共聚物.     

Microwave-assisted Polymerization of ε-Caprolactone with Maleic Acid as Initiator and Drug Release Behavior of Ibuprofen-Poly(ε-caprolaetone) System

Poly(ε-caprolactone) (PCL) with weight-average molar mass over 10000 g/mol was synthesized by microwave-assisted ring-opening polymerization of ε-caprolactonc (ε-CL) with malcic acid (MA) as initiator (2.45 GHz, 360 W, 85 min). Ibuprofen-PCL controlled release system was prepared directly by the ROP of ε-CL in its mixture with ibuprofen. The release of ibuprofen from the system was sustained and steady.     

Head-to-head vinyl polymers. VII. Hydrolysis of head-to-head poly(methyl acrylate)

Head-to-head (H–H) and head-to-tail (H–T) poly(methyl acrylate)s (PMAs) were hydrolyzed in a mixture of acetone and water (4:1 by volume) at 30°C by using various alkali hydroxides as catalysts. For comparison, the H–T copolymer with 26% H–H units, dimethyl succinate (DMS), dimethyl glutarate (DMG), and dimethyl adipate (DMA) as model compounds were also hydrolyzed. It was found that the hydrolyses of all PMAs proceeded autocatalytically; i.e., the rates increased as a function of the reaction time. Both the initial rate constant k₀ and the autoaccelerating effect observed markedly depended on the structures of polymer chains and they decreased with increasing of the H–H sequences. The molecular weights of either H—H or H—T PMA did not show remarkable changes in either k₀ value or accelerating effect. The k₀ values were almost independent of the kinds of bases and were calculated to be 0.06 and 0.18 L mol^?1 min^?1 for H–H and H–T PMA, respectively. On the other hand, the autoaccelerating effect decreased in the order NaOH ? KOH > LiOH > CsOH for H–H PMA and NaOH > LiOH > KOH > CsOH for H–T polymer. When the ratio of acetone to water increased, the k₀ value was found to decrease, whereas the accelerating effect increased. The results obtained are described and discussed.     

Ring-opening polymerization of ε-caprolactone by lithium piperazinyl-aminephenolate complexes: synthesis, characterization and kinetic studies

A series of lithium complexes were prepared from 2(N-piperazinyl-N'-methyl)-2-methylene-4-R'-6-R-phenols ([ONN](RR')) and characterized through elemental analysis, (1)H and (13)C{(1)H} NMR spectroscopy, and X-ray crystallography. Treatment of the ligands with n-butyllithium afforded {Li[ONN](RR')}(3) [R = Me, R' = (t)Bu, (1); R = R' = (t)Bu (2); R = R' = (t)Am, (3), (t)Am = C(CH(3))(2)CH(2)CH(3)], with trimetallic structures in the solid-state as shown by single-crystal X-ray diffraction. The reactivity of these complexes in the ring-opening polymerization of ε-caprolactone (ε-CL), as well as the influences of monomer concentration, monomer/Li molar ratio, polymerization temperature and time, was studied. Rates of polymerization were first order with respect to both monomer and lithium concentrations, and activation energies for the reactions were determined. MALDI-TOF MS analysis revealed that transesterification had occurred during the polymerization.