Microwave-Irradiated Ring-Opening Polymerization of Octamethylcyclotetrasiloxane in the Presence of Water

α, ω-dihydroxyl polydimethylsiloxane (DHPDMS) was prepared via anionic ring-opening polymerization of octamethyl cyclotetrasiloxane (D₄) under microwave irradiation (MI) in the presence of water. The conversion and polymerization rate were calculated by the gravimetric method. The effect of microwave power on the polymerization was investigated. FTIR was used to verify the DHPDMS prepared at different irradiation times. The results show that the conversion is the highest when the initial microwave power is preset at 700 W. Compared with conventional heating (CH), the polymerization rate and equilibrium conversion are both enhanced by the introduction of microwave irradiation. The species and concentration of the cyclosiloxane mixture caused by backbiting reaction were determined by gas chromatography/mass spectrometry (GC/MS). The lower concentration of cyclosiloxane in the polymer prepared under MI indicates that side reactions have been reduced and a pure polymer obtained. The molecular weight and polydispersity index (PDI) measured by GPC show that under MI, the molecular weight of DHPDMS is lower and PDI is narrower than those under CH.     

环氧化物阳离子开环聚合机理

介绍了环氧化物阳离子开环聚合的机理,主要包括活性链端机理和活性单体机理等。活性链端机理认为聚合的活性中心位于聚合增长链的链端,聚合单体与活性链端接触发生聚合反应实现链增长;活性单体机理认为聚合的活性中心位于单体分子,在活性单体向聚合链端羟基增加的过程中实现链增长。两者相结合可较成功地解释环氧化物开环聚合的实验现象。     

DNA Ring-Opening Polymerization Driven by Base Stacking

Supramolecular polymers, relying on reversible intermolecular interactions, promise a wide range of applications, including optoelectronic materials, self-healing materials, and biomedical delivery materials. Among potential molecular candidates, DNA strands act as an excellent platform. DNA has a well-established secondary structure (double helix), and its intermolecular interactions can be readily thermodynamically engineered and kinetically controlled. Extensive studies have demonstrated that various DNA motifs can polymerize/assemble into large polymers with different topology, geometry, and dimensionalities. Most of the reported polymerization is driven by hybridization of DNA strands. Herein, we report a novel system of DNA supramolecular polymerization that is driven by DNA base stacking. The polymerization has been confirmed by native polyacrylamide gel electrophoresis (PAGE) and atomic force microscopy (AFM). We believe that this work will expand the toolbox for DNA supramolecular polymerization and would, with further development, increase further control of DNA supramolecular polymerization.     

Ring-Opening Metathesis Polymerization and Related Olefin Metathesis Reactions in Benzotrifluoride as an Environmentally Advantageous Medium

A tremendous number of solvents, either as liquids or vapors, contaminate the environment on a daily basis worldwide. Olefin metathesis, which has been widely used as high-yielding protocols for ring-opening metathesis polymerization (ROMP), ring-closing metathesis (RCM), and isomerization reactions, is typically performed in toxic and volatile solvents such as dichloromethane. In this study, the results of our systematic experiments with the Grubbs G1, G2, and Hoveyda-Grubbs HG2 catalysts proved that benzotrifluoride (BTF) can replace dichloromethane (DCM) in these reactions, providing high yields and similar or even higher reaction rates in certain cases. The ROMP of norbornene resulted not only in high yields but also in polynorbornenes with a high molecular weight at low catalyst loadings. Ring-closing metathesis (RCM) experiments proved that, with the exception of the G1 catalyst, RCM occurs with similar high efficiencies in BTF as in DCM. It was found that isomerization of (Z)-but-2-ene-1,4-diyl diacetate with the G2 and HG2 catalysts proceeds at significantly higher initial rates in BTF than in DCM, leading to rapid isomerization with high yields in a short time. Overall, BTF is a suitable solvent for olefin metathesis, such as polymer syntheses by ROMP and the ring-closing and isomerization reactions.     

Ring-Opening Polymerization of Siloxanes Using Phosphazene Base Catalysts

Phosphazene bases such as {(NMe₂)₃P=N–)₃P=NBu^t} have been reported in the literature to be strongly basic materials with basicities up to 1×10¹⁸ times stronger than that of diazabicycloundecene (DBU) a strong hindered amine base used in organic reactions. A study of these phosphazene bases as catalysts revealed that they can be activated by small amounts of water, which all silicone feed stocks contain, to form an active ionic base catalyst [(NMe₂)₃P=N–)₃P–NHBu^t]⁺[OH]^–. This paper discusses the use of these types of base catalysts, and their analogues, as ring-opening polymerization catalysts for cyclosiloxanes. Phosphazene base catalysts can be used at low concentrations to make high molecular weight polydimethylsiloxanes with short reaction times over a wide temperature range. Molecular weight can easily be controlled in the presence of suitably functionalized endblockers. Water and carbon dioxide have been shown to have a significant impact on the polymerization rates. Polymers prepared show excellent thermal stability by thermogravimetric analysis (TGA), following neutralization of the catalyst, with decomposition onset temperatures >500°C in some cases. As a result of the extremely low levels of catalyst used, the polymers often do not require filtration.     

氮杂四元环化合物开环反应的研究进展

氮杂环化合物具有良好的生物活性、抗茵性能,还可以用作多种化合物的有机合成模块,近年来一直是医药化学家们在合成中的研究热点之一。氮杂四元环化合物由于结构的特殊性,极易发生开环反应。本文综述了氮杂四元环在不同条件下的开环反应,为以后进一步研究其开环及关环反应提供依据。     

Ring-Opening Reaction of Hexamethylcyclotrisiloxane with Tetrachlorosilane and Isomerization of the Product

A molecular complex of triphenylphosphine oxide and tetrachlorosilane (II) in a solvent mixture that contains 90% toluene and 10% acetonitrile acts as a catalyst to open the cyclic siloxane oligomer, hexamethylcyclotrisiloxane (I). The primary product is the linear oligomer 1,1,1,7-tetrachlorohexamethyltetrasiloxane (III). III can be converted quantitatively to the structural isomer, 1,3,3,7-tetrachlorohexamethyltetrasiloxane (IV), in the same catalyst–solvent mixture either by stirring at room temperature for 12 h or by heating at 90°C for about 1 h. In both reactions, the disappearance of the reactants and the formation of the products can be followed by glc. Products III and IV are characterized by elemental analysis, molecular mass, infrared spectra, and ¹H- and ²⁹Si-NMR spectra. III and IV can be transformed into their fluorinated derivatives, VI and VII, respectively, by stirring for several days in a toluene slurry of KSiF₆. The ¹⁹F-NMR spectra of VI and VII are consistent with the proposed isomeric structures.     

Living Anionic Ring-Opening Polymerization of Unsymmetrically Substituted Silicon-Bridged [1]Ferrocenophanes; A Route to Organometallic Block Copolymers with Amorphous Poly(ferrocenylsilane) Blocks

Living anionic ring-opening polymerization methodology for silicon-bridged [1]ferrocenophanes has been extended to unsymmetrically substituted monomers. This permits access to well-defined amorphous poly(ferrocene) homopolymers and organometallic block copolymers, such as polystyrene-b-poly(ferrocenylmethylphenylsilane), with an amorphous poly(ferrocenylsilane) block. This allows phase separation to occur at lower temperatures, which should facilitate applications in which organometallic nanodomains are desirable.     

Effect of Substitution of [Pd(PPh3)4] by Related Compounds as Catalysts in Reactions of Organic Syntheses

The effect of substitution of [Pd(PPh₃)₄], which is unstable in air, by complexes of the type [MCl₂L₂] (M = Pd, Pt; L = AsPh₃, SbPh₃), [PdL₄](L = PPh₃, AsPh₃, SbPh₃) and [NiX₂(PPh₃)₂] on the syntheses of thioethers, acetylenes and ketones is described.     

苄基化甘露糖原酸酯的开环研究

以甘露糖为原料合成了苄基化甘露糖原酸酯,并对其在酸催化下的开环反应进行了研究,采用1HNMR对各阶段产物进行了表征.结果表明,冰乙酸的催化效果最好,产率可迭90%,同时对冰乙酸催化苄基化甘露糖原酸酯的开环机理进行了探讨,合理地解释了用80%或50%乙酸代替冰乙酸时产率下降的原因,主要是水与亲核试剂乙酸根形成了竞争,生成...     

Preparation and degradation of polysilylenes

Mechanistic aspects of preparation and degradation of polysilylenes (polysilanes) are discussed. Reductive coupling of disubstituted dichlorosilanes at ambient temperatures in the presence of ultrasound leads to monomodal polymers with relatively narrow molecular weight distributions (M _w/M _n from 1.2 to 1.5) and relatively high molecular weights (M _n from 50,000 to 100,000). Ring-opening polymerization of 1,2,3,4,-tetramethyl-1,2,3,4-tetraphenylcyclotetrasilane initiated with carbanions and silyl anions provides polymers with molecular weights from 10,000 to 100,000 and gives potential possibility of the microstructure control. The dearylation of phenyl containing polysilylenes with triflic acid provides polymers with strong electrophilic silyl triflate moieties. They can react with any nucleophiles such as alcohols, amines, carbanions, organometallics, etc., and produce various functional polysilylenes. Synthesis and solid-state transitions in random copolysilylenes are discussed. Thermal, mechanical, and chemical degradation of polysilylenes is described.This review was presented at the Second International Topical Workshop, Advances in Silicon-Based Science.     

Ring-opening polymerization of norbornene and six of its methyl derivatives by well-defined tungsten-carbene complex catalysts

Eight tungsten-carbene complex catalysts of the type W(CHCMe₃)L¹L²L³L⁴, where the ligands L are various combinations of OCH₂CMe₃, SO₃CF₃, OSiPh₃, Br and I, have been used, in the presence and absence of GaBr₃, to polymerize norbornene and six of its methyl derivatives by ring opening. The microstructure of the polymers was determined from their ¹³C NMR spectra; values of cis content, cis-trans blockiness, ring-dyad tacticity and head-tail bias were derived as appropriate to each system. The results are discussed in terms of electronic and steric effects in the propagating carbene complexes.     

Ring-Opening Reactions of Propylene Oxide (Methyloxirane) over Au/MgO and Unsupported Au Catalysts

The ring-opening reactions of propylene oxide (methyloxirane) were studied over an Au/MgO catalyst and Au powder at various temperatures in a pulse microreactor. The supported catalyst was significantly more active, and its activity was dramatically influenced by the method of pretreatment. When it was finished with hydrogen, conversion values were always above 70%, but often it was in the 90%+ range. The major reaction pathways were deoxygenation and isomerization. The comparison in the behavior of Au/MgO and Au powder pointed to the crucial importance of the support–metal interface in oxygen traffic and as a landing place for hydrogen-rich residues being the hydrogen source for water and alcohol formation (hydrogenation).     

β-二酮钛、锆配合物催化丙交酯本体开环聚合

合成了β-二酮钛、锆配合物：乙酰丙酮钛(Catl)、苯甲酰丙酮钛(Cat2)、二苯甲酰甲烷钛(Cat3)、乙酰丙酮锆(Cat4),并分别成功地催化丙交酯本体开环聚合。结果表明,β-二酮钛、锆配合物催化合成聚乳酸均可达到较高的转化率(高于95%),且Cat4的活性大于Car1。着重研究了催化剂用量(即单体与催化剂物质的量比[LA]/[Cat])、聚合时间及聚合温度对Cat1催化丙交酯本体开环聚合反应的转化率及所得聚乳酸相对分子质量的影响。在以Car1为催化剂,单体与催化剂物质的量比为400,聚合温度130℃,聚合时间30h时,可得到黏均相对分子质量M_η=6．79×10~4的聚乳酸。     

Spontaneous Ring-Opening Copolymerization of 1,1,2,2-Tetramethyl-1,2-Disilacyclobutane with Styrene

l,l,2,2-Tetramethyl-l,2-disilacyclobutane (TMDSCB), obtained by alkali metal vapor dehalogenation of l,2-bis(chlorodimethylsilyl(ethane, undergoes room-temperature spontaneous ring-opening Copolymerization with styrene (St) and results in a rubbery copolymer (M_w = 1.6 × 10⁵, M_w/M_n = 4.4). In contrast to a thermoplastic homopolymer of TMDSCB (m.p. 110°C) that is obtained by the same procedure in the absence of styrene, the copolymer exhibits two-phase behavior (Tg = – 37°C, m.p. 106°C), with the heat of melting being considerably lower in the case of the copolymer (cf. 49.0 and 4.8 J g^–1). Spectral and analytical data are consistent with a copolymer structure, [(Me₂SiCH₂CH₂SiMe₂)_k (CH₂CHPh)_l]_n, where k = 3, l = 1 (36%), and k = 6, l = 2 (64%).     

Synthesis of amphiphilic macrocyclic graft copolymer consisting of a poly(ethylene oxide) ring and multi-poly(?-caprolactone) lateral chains

A series of amphiphilic macrocyclic graft copolymers composed of a hydrophilic poly(ethylene oxide) as ring and hydrophobic poly(?-caprolactone) as lateral chains with different grafting lengths and densities of side chains were prepared by a combination of anionic ring-opening polymerization and coordination-insertion ring-opening polymerization. The anionic ring-opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using triethylene glycol and diphenylmethyl potassium (DPMK) as co-initiators, and a linear α,ω-dihydroxyl poly(ethylene oxide) with pendant protected hydroxymethyls (l-poly(EO-co-EEGE)) was obtained. The monomer reactivity ratios of these compounds are r_1(EO) = 1.20 ± 0.01 and r_2(EEGE) = 0.76 ± 0.02, respectively. Then the ring closure of l-poly(EO-co-EEGE) was achieved via an ether linkage by reaction with tosyl chloride (TsCl) in the presence of solid KOH. The crude cyclized product containing the linear chain-extended polymer was hydrolyzed in acidic conditions first and then purified by treating with α-CD. The pure cyclic copolymer of EO and glycidol (Gly) with multipendant hydroxymethyls [c-poly(EO-co-Gly)] as the macroinitiator was used further to initiate the ring-opening polymerization of ?-caprolactone (CL), and a series of amphiphilic macrocyclic graft copolymers c-PEO-g-PCL were obtained. The final products and intermediates were characterized by GPC, NMR and MALDI-TOF in detail.     

Asymmetric Ring-Opening Reactions of Donor-Acceptor Cyclopropanes and Cyclobutanes

Donor-acceptor (DA) cyclopropanes are particularly useful synthetic building blocks, which have been widely applied in the total synthesis of natural products and important chiral molecules in organic synthesis. The asymmetric ring-opening reactions of racemic DA cyclopropanes and cyclobutanes, for example, aryl-substituted 1,1-cyclopropane diesters and aryl-substituted 1,1-cyclobutane diesters, with nucleophiles provides versatile access to optically active γ- and δ-functionalized carbon skeletons, as well as the kinetic resolution of racemic DA cyclopropanes, which are useful chiral skeletons in organic synthesis. Recently, we have developed a series of highly enantioselective ring-opening and annulation reactions of DA cyclopropanes and cyclobutanes with various nucleophiles, such as amines, alcohols, nitrones, azomethine imines, enol silyl ethers, and indoles, by employing nickel and copper catalysts with TOX and SaBOX as ligands. The reactions worked smoothly with excellent diastereoselectivities and enantioselectivities (up to >99/1 dr and up to 99 % ee) over broad substrate scopes.     

生物可吸收材料PDLLA的聚合条件研究

通过乳酸脱水合成出高纯度的D,L 丙交酯。以辛酸亚锡为引发剂,进行丙交酯开环聚合为聚乳酸(PDL LA)的实验研究。讨论了D,L 丙交酯开环聚合的影响因素和PDLLA聚合条件。     

Ring-Opening Amino Esterification of Cyclic Ketones to Access Distal Amino Acid Derivatives

This study developed a method of synthesizing distal amino acid derivatives by the ring-opening reaction of cyclic ketones, following the amino esterification functionalization of both terminals. To achieve this goal, we performed the ring-opening reaction of cyclic ketones with an aminating reagent and alcohol under metal- and photocatalysis-free conditions in a single step. The method directly afforded distal amino acid derivatives bearing C4−C6, C8, and C12 carbon main chains, such as γ, δ, and ϵ-amino esters. The obtained amino esters were simply transformed into amino acids by hydrolysis.     

Radical ring-opening emulsion polymerization of vinylcyclopropanes

Radical emulsion polymerizations of vinylcyclopropanes, 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane (ECVCP) and 1,1-dichloro-2-vinylcyclopropane (CVCP) were examined. ECVCP underwent soap-free and soap-in emulsion polymerizations satisfactorily to afford the ring-opened polymer in good yields. Polymer emulsions were obtained in a spherical shape with single particle size distribution. Meanwhile, emulsion polymerization of CVCP proceeded in only a low conversion. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 497–501, 1998