Gamma ray-induced liquid-state polymerization of hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane

The radiation-induced bulk polymerization of liquid hexamethylcyclotrisiloxane has been achieved. Appreciable yields of polymer from octamethylcyclotetrasiloxane liquid have also been obtained. These results were achieved on “ultra-dry” monomers and are interpreted in terms of an ionic polymerization mechanism.     

Mechanism of hexamethylcyclotrisiloxane polymerization in the presence of siloxanediols

Polymerization of hexamethylcyclotrisiloxane (D₃ ) in CH₂Cl₂ at 30°C, initiated by triflic acid (TfOH) was studied in the presence of siloxanediols (HD₂OH or HD_xOH) which polycondense giving water, or in the presence of water alone for comparison. D represents a siloxane unit OSiMe₂. In the second case, the relative amounts of cyclic oligomers (D₆, D₉) and of linear high polymer (HP) vary strongly with the molar ratio r =[H₂O]/[TfOH]. When r increases from 1 to 100 (in homogeneous phase), D₉ /D₆ increases from 0.2 to 2 and D₆ /HP decreases from 1 to 0.3. The large decrease of D₆ amount and the increase in D₉/D₆ are attributed to the suppression of their formation through oxonium ions and to their exclusive formation, for r>100, by cyclization of silanol-esters, which is more rapid for HD₉OTf than for HD₆OTf. For polymerization of D₃ in the presence of HD₂ OH, there is a fast and limited ring-opening of D₃ (about 10% conversion over 6 min) at the beginning, without formation of cyclics (D₆, D₉ , etc). Then reaction with D₃ stops. Polymerization of HD₂OH takes place simultaneously, at the same rate as in the absence of D₃, with slow formation of high polymer. At the end of the polycondensation (after, eg, 4 h) D₃ polymerization starts again, giving D₆ , D₉, etc, and HP. The inhibition period for D ₃ is attributed to the complexation of triflic acid hydrates by silanol groups. These activated silanol groups do not react with D₃. A comparison of D₃ polymerization with the addition of water, HD₂OH or HD₁₅OH leads to the conclusion that when r is not too large, propagation involves silylester end-groups, but that for large r ratios (100 or higher), it probably occurs mainly on silanol groups reacting with an activated monomer. © 1999 Society of Chemical Industry     

A new bifunctional initiator for the living polymerization of hexamethylcyclotrisiloxane

Summary A bifunctional living poly(dimethylsiloxane), poly(DMS), was synthesized through the anionic ring-opening polymerization of hexamethylcyclotrisiloxane(D₃) (3) with an initiator system consisting of dilithium salt(2) of bis (p-hydroxydimethylsilyl)phenyl ether(1) and N-methylpyrrolidine in THF solution. The subsequent end-capping reaction of the bifunctional living poly(DMS) with dimethylvinylchlorosilane(4) provided the uniform size poly(DMS) having vinylsilane group at the both chain ends(5).     

固态聚合研究进展

综述了近几年来国内外固态聚合方面的研究进展.介绍了实现固态聚合的3种方式--热引发,高能辐射,紫外光引发和电极激发及其在塑料,医疗卫生、分子烙印.缩微成像设计等领域的广泛应用.并对该技术在今后的发展前景进行了预测.     

超声引发聚合反应的研究

综述了超声波在一些聚合方法中的应用。     

Kinetic studies on anaerobic initiated polymerization

Using a model reaction system consisting of cumene hydroperoxide, N,N-dimethyl-p-to-luidine and O-benzoic sulfimide in toluene solvent (without reactive acrylic monomer), attempts have been made to understand the initiation mechanism operating during anaerobic polymerization. In these studies, the instrumental techniques of visible spectroccopy (VS), high performance liquid chromatography (HPLC) and infrared spectroscopy (IR) were employed. Valuable kinetic data have been obtained using these three instrumental techniques. HPLC studies have shown conclusively that the N,N-dimethyl-p-toluidine (N,N-DMpT) component is significantly depleted during the initiation step of the anaerobic process. By way of contrast, the benzoic sulfimide (BS) concentration was found to be essentially unchanged during initiation. Visible spectral changes with the model anaerobic solutions indicate that the initiation mechanism may involve radical-ionic species derived from N,N-DMpT rather than free radical reactive intermediates. Increasing the acidity of the reaction solution, with addition of acetic acid, appears to accelerate the initiation rate under anaerobic conditions.     

原位合成引发剂引发原子转移自由基及衰减链转移同步聚合

在甲基丙烯酸甲酯(MMA)单体中,以偶氮二异丁腈(AIBN)与I2反应原位合成α-碘代异丁腈(IIBN),进一步作为原子转移自由基聚合引发剂分别与CuCl、FeCl2.4H2O等催化剂,MA5-DETA、PMDETA等络合剂相匹配引发MMA的ATRP,同时又作为衰减链转移聚合(DT)的可逆链转移剂同步进行DT聚合。实验结果表明:所得聚合物分子量可控,分子量分布(PDI)很窄(1.05～1.25),引发剂效率较高。动力学的研究结果显示:分子量随转化率而增长;由Ln[M]0/[M]t对时间作图,呈现良好的线形关系,表明聚合过程中增长自由基浓度是一个恒定值,证明由IIBN引发的聚合是典型的活性自由基聚合;这种方法克服了极不稳定的在α-位带有吸电子基团的碘化物的购运和储存的困难。不失是一种简单,快捷,方便的方法。     

Effect of ultrasound on electrochemically initiated acrylamide polymerization

Acrylamide was polymerized under different voltages with ammonium persulfate as the initiator at room temperature. The polymerization reactions were performed in two different ways. In one case, the reaction was performed in a classical, three‐electrode electrochemistry cell, and in the other, the cell was placed in an ultrasonic bath, and ultrasound was applied during the reaction. Both reactions were performed at room temperature. The conversion was rapid; even in the normal electrochemical case, the composite rate constant was comparable to the case with free‐radical polymerization of acrylamide at 50–70°C. When ultrasound was applied, the conversion values increased more. The heterogeneity index and molecular weights of the polymers produced with and without ultrasound were measured with size exclusion chromatography. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 83–89, 2002; DOI 10.1002/app.10233     

Effective promotion of tetrahydrofuran polymerization initiated with heteropolyacid

Tetrahydrofuran was polymerized using the heteropolyacid H₃PW₁₂O₄₀ as the initiator and ethylene oxide as the promoter, which effectively increased the rate and conversion of the polymerization. Water and butylene glycol were used to control the molecular weight of the product in the range of 1000–3000. The polymer was found to be polyether glycol containing 10–22 mol % oxyethylene moieties with hydroxyl groups at both chain ends. The melting point was ∼ 10°C lower compared to polytetramethylene ether glycol having the same molecular weight. The concentration of active species remained unchanged in the main period of the polymerization, indicating the absence of chain termination. The values of the chain propagation rate constant of tetrahydrofuran polymerization at 0 and 20°C were found to be 3.78 × 10⁻³ and 1.98 × 10⁻² L mol⁻¹ s⁻¹, respectively, which are close to the rate constant of chain propagation of tetrahydrofuran on ionic active species. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2303–2308, 1999     

Anionic polymerization of methyl methacrylate initiated by thiophenol

Methyl methacrylate (MMA) was polymerized by thiophenol without oxidants. Hydroquinone had no effect on the polymerization, indicating that the polymerization proceeded via a non-radical process. Since other monomers with an x,β-unsaturated carbonyl group polymerized similarly, the initiation and propagation were explained by the Michael addition. Radical scavengers such as 1,1-diphenyl-2-picrylhydrazyl(DPPH) and galvinoxyl enhanced the polymerization because of an accompanying radical polymerization initiated by radical species formed by the reaction of them with thiophenol. Aluminium acetylacetonate, which has no effect on radical polymerization, accelerated the thiophenol-initiated polymerization supporting the postulated mechanism.     

Thermally induced solid-state polymerization in nylon 66

The thermally induced solid-state polymerization of 66 nylon was investigated. It was found that the rate-controlling step in the process is chemical reaction. A mechanism of the form, rate = ktⁿ was shown to hold. The reaction rate constant was found to be k = 1.53 × 10¹⁰ exp [ ? 12,960/RT]. Units of k are (hours)^?0.51. Activation energy determined in this work compared closely to that determined for nylon 6 solid-state polymerization.     

六亚甲基亚氨基锂引发的丁二烯负离子聚合动力学

研究了以六亚甲基亚氨基锂(LHMI)为引发剂、环己烷为溶剂、TMEDA为极性调节剂的丁二烯自聚。其中LHMI可以预先制备,也可以在聚合体系中原位合成。当TMEDA/LHMI质量比小于2时,速率常数(Kp')随着TMEDA/LHMI的增大而升高。与正丁基锂引发体系的Kp'相比,相同条件下LHMI引发体系的Kp'变化不大,说明LHMI不起调节剂的作用。     

Free-radical polymerization of methyl methacrylate initiated by thiol alone

Three different alkyl thiols, i.e., n-propylthiol, isopropylthiol, and 2-methyl-2-undecanethio1, were proved efficient to initiate the polymerization of methyl methacrylate at 40°C. The initial polymerization rate, R_p, increases with increasing thiol concentration but cannot be described by a single-power law. However, R_p is proportional to 1.3th power of the monomer concentration, indicating the participation of monomer in the initiation reaction. With increase of the polarity of solvents, R_p decreases, demonstrating the polar property of the initiating intermediate. The apparent activation energy of overall polymerization was calculated to be 9.3 kcal/mol. Molecular weight measurements indicated the twofold function of the thiol as both an initiator and a regulator.     

Cationic polymerization initiated by intercalation compounds of Lewis acids

The results of initial studies showing the high activity of intercalation compounds of Lewis acids (C₃₀SbCl₅, C₇₇FeCl₃, C₆₄AlBr₃) as initiators of the cationic polymerization of cyclosiloxanes are presented. The influence of some reaction conditions on the yield and the molecular mass of the polymers formed is described.     

Anionic polymerization and copolymerization of cyclosiloxanes initiated by trimethylsilylmethyllithium

Summary A novel initiator, i.e. trimethylsilylmethyllithium has been successfully used for the ring opening polymerization of cyclosiloxanes, in toluene or in the bulk, in the presence of the cryptand [211] or DMSO. Suitable conditions have been found in which monomodal distributions of molecular weights are observed for homopolymers of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (V₄) as well as for copolymers of V₄ with D₃ or D₄. Laboratoire de Chimie Macromoléculaire associé au CNRS, URA 24     

氧化还原体系引发苯乙烯乳液聚合

以不同的过氧化物引发剂分别与硫酸亚铁组成氧化还原引发体系,引发苯乙烯的乳液聚合,研究反应温度和还原剂用量等对聚合的影响.采用气相色谱、三检测体积排除色谱、动态光散射对单体转化率、聚苯乙烯的相对分子质量及其分布和乳胶粒径进行了分析.结果表明:升高温度或增加还原剂用量均会使聚合物的相对分子质量增大,聚合反应速率加快,与常规...     

Photoinduced charge-transfer polymerization of acrylonitrile initiated by N-substituted phenothiazines

The polymerization of acrylonitrile (AN) initiated with phenothiazine (PTZ) and its derivatives has been studied. It is found that N-alkyl- substituted phenothiazines possess greater ability to initiate the polymerization of AN under UV irradiation. The initiation mechanism proposed is that the exciplex formed between N-substituted PTZ and AN plays a key role in the initiation process. The kinetic equation for N-methyl phenothiazine (NMP) was determined to be rate of polymerization, R_p = K[NMP]^0.46[AN]^1.44     

Modeling of solid-state combustion in thermally and chemically heterogeneous media

A thermally and chemically heterogeneous medium is modeled by a set of cylinders pressed from a mixture of solid reagents with coaxially aligned cylindrical rods made from an inert material. The change in velocity of combustion waves propagating over one cylinder is studied by numerical methods under the assumption that there is no heat release from the cylinder surface. The mean velocity of the combustion front in the specimen is shown first to decrease and then to increase with increasing thermal conductivity of the inert rod. Spinning waves are obtained in the range of low velocities of the combustion front. The laws of variations of the maximum temperature in the combustion front are determined. It is shown that the inert rod may serve as a heat sink from the hot charge mixture, may be manifested as dilution by an inert component, enhance heat recuperation, and increase the combustion-wave velocity. Introduction of the inert rod may either destabilize combustion-wave propagation in the region of a stable plane front or stabilize the combustion wave in the range of parameters where the plane front is unstable. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 6, pp. 21–30, November–December, 2007.     

Potassium persulphate-malonic acid redox pair initiated polymerization of methacrylamide

Summary The kinetics of aqueous polymerization of methacrylamide initiated by potassium persulphate-malonic acid redox pair has been investigated at 50±1°C under nitrogen atmosphere. The initial rate of polymerization has been found to be square root dependence to the initial concentration of potassium persulphate and malonic acid. The order of reaction with respect to monomer has been found to be unity. The overall energy of activation has been found to be 66±1 KJ/mol. The effect of addition of manganous sulphate and sulphuric acid has been investigated. On the basis of experimental results a suitable mechanism has been proposed.     

The polymerization mechanism of lactide initiated with zinc (II) acetylacetonate monohydrate

The paper presents the mechanism of lactide polymerization initiated with zinc (II) acetylacetonate monohydrate. However, the actual initiator of this reaction is the complex containing a metal-oxygen bond, formed by the exchange reaction of acetylacetonate ligand with deprotonated lactide derivative. The described reaction results in the release of free acetylacetonate and formation of transitional zinc complex with metal-oxygen bond connecting the zinc atom with derivative of lactide, incorporated - as a new, active in polymerization ligand. Polylactide chain propagation process, which constitutes the following stage of the reaction, is caused by a typical, well known, coordination-insertion ring opening polymerization. The proceeding polymerization maximum yield at the applied conditions does not exceed about 70% in benzene solution and 90% at bulk.