Kinetics of the Anionic Ring Opening Polymerization of Cyclosiloxanes Initiated with a Superbase

Kinetics of the anionic ring opening polymerization of octamethylcyclotetrasiloxane, D₄, and hexamethylcyclotrisiloxane, D₃, in toluene solution initiated by hexapyrrolidinediphosphazenium hydroxide, P₂Pyr₆ ⁺OH^– were studied. Reactions are first order both in monomer and in initiator. The specific rate of the D₃ polymerization is higher than that of D₄ by about 2–3 orders of magnitudes. Activation energies are 18.1 kcal mol^–1 for D₄ and 11 kcal mol^–1 for D₃. The back-biting reaction leading to decamethylcyclopentasiloxane, D₅, was followed in the polymerization of D₄. This reaction is retarded by the presence of monomer. The kinetics is interpreted in terms of a mechanism in which the active propagation center appears mostly as a monomer separated ion pair, which is also the intermediate in the propagation step.     

八甲基环四硅氧烷聚合动力学

以四甲基氢氧化铵为催化剂,用蒸汽压法研究了八甲基环四硅氧烷的聚合动力学,获得了７７～１１０℃间的聚合速率常数,并计算出反应活化能为１０３０ｋＪ／ｍｏｌ。     

Cationic Ring Opening Polymerization of Glycolide Catalysed by a Montmorillonite Clay Catalyst

The ring opening bulk polymerization of glycolide catalyzed by Maghnite-H⁺ was reported. Maghnite-H⁺ is a montmorillonite sheet silicate clay, exchanged with protons. The effect of the amount of Maghnite-H⁺ and the temperature on polymerisation was studied. Increasing Maghnite-H⁺ proportion and temperature produced the increase in glycolide conversion. The kinetics indicated that the polymerization rate is first order with respect to monomer concentration. Mechanism studies showed that monomer inserted into the growing chains with the acyl–oxygen bond scission rather than the break of alkyl–oxygen bond.     

Bio‐Based Rubbers by Concurrent Cationic and Ring‐Opening Metathesis Polymerization of a Modified Linseed Oil

Bio‐based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl‐modified linseed oil, Dilulin?, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio‐based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio‐based rubbers have maximum decomposition temperatures of over 450 °C with their thermal stability decreasing with increasing loadings of NBDC.

     

八甲基环四硅氧烷本体聚合动力学研究

The kinetics of bulk polymerization of octamethylcyclotetrasiloxane under acid circumstance is studied.A kinetic model is put forward and kinetic parameters are obtained through optimization.     

八甲基环四硅氧烷本体聚合动力学研究

The kinetics of bulk polymerization of octamethylcyclotetrasiloxane under acid circumstance is studied. A kinetic model is put forward and kinetic parameters are obtained through optimization.     

酸白土催化体系开环八甲基环四硅氧烷的研究及机理探讨

Cationic ring opening polymerization of octamethylcyclotetrasiloxane （Da） initiated by acid treated bentonite was investigated. The experimental conditions were chosen on the basis of preliminary experiments.Higher temperature was found beneficial for the reaction process while stirring intensity beyond a certain level showed no obvious effect on the reaction rate. Polymers were characterized by Fourier transform infrared, proton nuclear magnetic resonance （IH-NMR） and gel perneation chromotography. The width of molecular mass distribution was found ranging between 1.2 and 1.4, which is extraordinarlly narrow compared with that of cationic polymerizations reported elsewhere （〉 1.9）. The results were believed due to the absence of free proton and counter ion which simplifies the polymerization process and the huge steric hindrance provided by bentonite particles which keeps the propagation of polysiloxane onto the surface of bentonite particles in a much more regular way. A feasible mechanism is proposed and seems to be supported well by experiments. Additionally, from the results of α, ω-dihydrogen terminated polysiloxanes prepared, the possibility of applying this potential environmentally friendly heterogeneous catalyst in industrial polymerization of cyclosiloxanes is anticipated.     

二苯基碘鎓氟硼酸盐引发AGE阳离子光聚合与光交联的研究

用合成的二苯基碘钅翁氟硼酸盐作为光敏引发剂 ,研究了含乙烯基和环氧基两种不同官能基的烯丙基缩水甘油醚 ( AGE)的阳离子光聚合和聚合前后微观结构的变化 ,讨论了其阳离子光聚合的特征和机理 ,测定了光聚合引起光交联的凝胶转化率曲线     

Polymerizations of hexamethylcyclosiloxane catalyzed by metal sulfonate/acid chloride combinations

Hexamethylcyclotrisiloxane (D₃) was polymerized in bulk at 100°C, and the conversion was monitored by ¹H‐NMR spectroscopy. Various metal triflates, which were inactive as neat salts, were combined with chlorosilanes, chlorostannanes, phenyl phosphonyl chloride, and carboxylic acid chlorides, which were also inactive when added alone. Most 1 : 1 combinations proved to produce active catalysts for the ring‐opening polymerization of D₃. When the anions of sodium salts were varied alkylsulfonates and the sulfates were more reactive than the triflate. The samarium triflate/diphenyldichlorosilane combination was found to be the most reactive catalyst on the basis of the triflate ions. Regardless of the catalyst combination, the main reaction products in the early stages of all polymerizations were octamethylcyclotetrasiloxane (D₄) and decamethylcyclopentasiloxane (D₅). The polymerization mechanism is discussed. The reactive catalyst combinations also polymerized D₄ at 100°C. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

一种新型用于原子转移自由基聚合过程的Cu（Ⅰ）络合物的研究

将以三齿2,6 双(苯并咪唑)吡啶为配体的Cu(I)离子络合物用作A TRP引发体系的组分之一,并成功地实现了对烯类单体的自由基聚合.聚合过程具有明显的ATRP聚合特征.和几种具不同结构胺配体构成的Cu(I)络合物的聚合速度结果相比较,本工作的结果基本符合烷基胺≈吡啶>亚胺>芳基胺的序列关系.     

Cationic copolymerization behavior of a bicyclic orthoester having hydroxy group with glycidyl phenyl ether and volume change on their copolymerization

This article describes cationic ring‐opening copolymerization of a bicyclic orthoester having hydroxy group (BOE‐OH) and glycidyl phenyl ether (GPE), and the volume shrinkage behavior during the copolymerization. THF soluble polyethers [poly(BOE‐OH‐co‐GPE)] were obtained by the copolymerizations at 80–180°C, while crosslinked poly(BOE‐OH‐co‐GPE) was obtained by the copolymerizations at 220–250°C. This crosslinking reaction may originate from the dehydration of methylol groups in the side chain of poly(BOE‐OH‐co‐GPE). The volume shrinkage during the cationic copolymerization reduced as the increase of the BOE‐OH feed ratio. By contrast, the volume shrinkage on the crosslinking polymerization was almost independent on the BOE‐OH feed ratio. Poly(BOE‐OH‐co‐GPE)s with higher BOE‐OH composition showed lower thermal weight loss temperature owing to the release of H₂O by dehydration of methylol groups. The BOE‐OH component in the THF soluble poly(BOE‐OH‐co‐GPE)s lowered the glass transition temperature (T_g), while that in the crosslinked poly(BOE‐OH‐co‐GPE) increased the T_g probably because of the higher crosslinking density. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1356–1361, 2006     

过硫酸铵/脂肪胺引发丙烯酸钠的聚合动力学

选择过硫酸铵(APS)／脂肪胺类氧化还原型引发体系,研究合成高分子量的水溶性聚丙烯酸钠(PNaAA)的聚合动力学。考察在50℃,55℃及60℃下APS／脂肪胺(包括甲基丙烯酸N,N-二甲胺基乙脂(DMA),尿素／氨,三乙醇胺(TEA))引发体系对丙烯酸钠聚合速率的影响,得到上述引发体系的表观活化能分别为44．54,48．11,40．18kJ／mol。并研究了不同引发体系对PNaAA分子量的影响。综合聚合速率与分子量两方面因素,提出APS／DMA是合成高分子量水溶性PNaAA的良好引发体系。     

Synthesis of vinyl end‐capped polydimethylsiloxane by ring opening polymerization of octamethylcyclotetrasiloxane (D4) catalyzed by rare earth solid super acid SO42‐/TiO2/Ln3+

Rare earth solid super acids SO₄^2?/TiO₂/Ln³⁺ have been successfully developed to synthesize vinyl end‐capped polydimethylsiloxane by ring opening polymerization of octamethylcyclotetrasiloxane (D4) end‐capped with 1,1,3,3‐tetramethyl‐1,3‐divinyldisiloxane. The features of ring opening polymerization reactions have been investigated in detail. The preferable conditions for the ring opening polymerization of D4 are as follows: [Nd³⁺] = 0.07 mol L^?1 and [SO₄^2?] = 1.85 mol L^?1 in the immersing solution; the amount of SO₄^2?/TiO₂/Nd³⁺ calcined at 500 °C was 5 wt% of the amount of D4; polymerization at 80 °C for 1 h. The average molecular weights of the products obtained using various rare earth catalysts were in order Nd > La > Sm > Gd, which shows that the light rare earths were more favorable for higher molecular weight products than the heavy ones. According to the polymerization features, a cationic equilibrium reaction mechanism is proposed. © 2013 Society of Chemical Industry     

Polymerization of Cyclic Monomers, 12

Summary: The radical polymerization of different substituted methyl 2‐(bicyclo[3.1.0]hex‐1‐yl) acrylates, 1a – f , was initiated by 2,2′‐azoisobutyronitrile (AIBN) at 65 °C in chlorobenzene. The radical homopolymerization of 1a – f occurred through the opening of the cyclopropane ring, and lead to polymers with number‐average molecular weights of 13 000 to 434 400 g · mol^?1 and glass transition temperatures between 77 and 121 °C. The monomers 1a – f showed a similar reactivity to MMA (in the copolymerization with MMA). Selected monomers were determined to be diluent monomers for dental filling composites and enable the preparation of composites that show a significantly reduced polymerization shrinkage, compared to composites based on dimethacrylate diluents.

     

Elaboration of Poly(ε‐caprolactone)‐g‐TiNbO5 Nanocomposites via in situ Metal Complex Initiated Intercalative Polymerization

Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO₅ nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO₅ mineral pre‐treated by AlMe₃, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.

SEM image of the fractured surface of a PCL‐TiNbO₅ nanocomposite film.     

Kinetics of the anionic ring‐opening polymerization of octamethylcyclotetrasiloxane initiated by potassium isopropoxide

Kinetics of the anionic ring‐opening polymerization of octamethylcyclotetrasiloxane (D₄) in bulk initiated by potassium isopropoxide was studied. Several promoters including N‐methyl‐2‐pyrrolidinone (NMP), N,N‐dimethylformamide (DMF), and diglyme were used. It is indicated that the reactions are first‐order in D₄ during the initial stage of polymerization. The polymerization rate of D₄ is influenced by a number of factors, such as the nature of promoters, the molar ratio of promoter to initiator (C_p/C_i ratio), and the reaction temperatures. With the use of NMP as promoter, the polymerization rate constant at 30°C is 10.482 h^?1 with the C_p/C_i ratio equal to 3.0. As the C_p/C_i ratio increases, the polymerization rate constant increases sharply and the cyclic oligomers content in polymer decreases evidently. The back‐biting reaction that leads to the formation of decamethylcyclopentasiloxane (D₅) occurred in the polymerization of D₄. The rate of the D₅ formation relatively to the rate of D₄ conversion increases with the conversion of D₄. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3510–3516, 2006     

Kinetics and Mechanism of Potassium Persulphate/L-Serine Initiated Polymerization of Methylmethacrylate

The polymerization kinetics of methyl methacrylate with K₂S₂O₈/L-serine redox system has been investigated volumetrically at 35±0.1°C under nitrogen atmosphere acidic aqueous medium in DMF/H₂O mixture (50% v/v). The rates of polymerization were measured varying concentrations of the monomer, initiator, L-serine as well as temperature; and it was found to increase with increasing of both temperature and concentrations of monomer, initiator, and L-serine. The overall energy of activation (E _a ) has been calculated to be 29.48 kJ/mol from the Arrhenius plot in temperature range 25–50°C. The molecular weight of the polymer was determined by gel permeation chromatography (GPC). Based on kinetic studies and depending on the results obtained, a suitable reaction mechanism has been suggested and the rates of polymerization found to obey the following equation: V _p [methyl methacrylate]^1.09[L-serine]^1.03[K₂S₂O₈]^0.96.     

Copolymerization and terpolymerization of glycolide with lactones by dimethyl(salicylaldiminato)aluminum compounds

The aliphatic poly(esters) are the most common biodegradable and biocompatible synthetic materials used by far for diverse biomedical applications. Co‐polymers and ter‐polymers of glycolide with ε‐caprolactone and lactide are produced in the presence of dimethyl aluminum compounds, bearing salicylaldiminato bidentate ligands differing for the steric hindrance on the ortho position of the phenolato ring. The formation of random poly[glycolide‐co‐(ε‐caprolactone)] samples is favored with more encumbered catalyst. Transesterification reactions of the second mode also contribute to randomize the structure. Copolymers from semi‐crystalline to amorphous are produced by decreasing the glycolide/ε‐caprolactone feed ratio. The terpolymerization of glycolide with ε‐caprolactone and rac‐lactide with the same catalysts affords amorphous and random poly[(glycolide‐co‐lactide‐co‐(ε‐caprolactone)] samples. The incorporation of the monomers is in this case determined by the bulkiness of the catalysts and by the higher coordination ability of the cyclic diesters. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42567.     

Anionic ring‐opening polymerization of adipic anhydride initiated by potassium poly(ethylene glycol)ate

Poly(adipic anhydride) (PAA) was prepared by the ring‐opening polymerization of adipic anhydride (AA) initiated by potassium poly(ethylene glycol)ate. The effects of various factors, such as the amount of initiator, concentration of the monomer, reaction time and temperature, and polarity of the solvent on the polymerization were investigated. The crude polymerized product was a mixture of PAA homopolymer and poly(ethylene glycol)–poly(adipic anhydride) block copolymer, as confirmed by ¹H‐NMR and gel permeation chromatography. Chain‐transfer reactions occurred intensively for the AA polymerization in both the nonpolar solvent toluene and the polar solvents CHCl₃ and tetrahydrofuran, which predominantly determined the molecular weight and the monomer conversion for the polymerized product. The lower monomer conversion in toluene was ascribed to a lower livingness for the initiator in the nonpolar solvent when compared with other two, polar solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2194–2201, 2003     

Kinetics and Mechanism of the Cationic Polymerization of Trioxane. III. Copolymerization with Cyclic Formals

Kinetics and mechanism of three cationic copolymerization systems of trioxane (TO) and 1,3-dioxolane (DO) and/or 1,3,5-trioxepane (TOP) including TO/DO 2.0/0.1, TO/DO/TOP 2.0/0.1/0.055, and TO/TOP 2.0/0.1 in a unit of mol/L in 1,2-ethylene dichloride at 30°C were investigated via evaluations of yields of copolymers and conversions of monomer and comonomer(s) using a gravimetric method and gas chromatography, respectively. The reactivity of DO or TOP was higher than that of TO toward the copolymerizations. Two byproducts, namely, TOP (or DO) and tetroxocane (TOC), were formed during the copolymerization of TO and DO (or TOP). The equilibrium concentrations of TO, DO, TOP, and TOC were ca 0.40, 0.02, 0.02, and 0.02 mol/L, respectively, for the TO/DO and TO/TOP systems whereas relatively high equilibrium concentrations of DO and TOP at ca 0.035 mol/L were for the TO/DO/TOP system. As compared with TO homopolymer, the thermal stability of the copolymers was increased with increasing conversion. The finding that the TO/DO/TOP system having a relatively high amount of cyclic formals consumed in the copolymerization exhibited a relatively low thermal stability suggested that the transacetalization reactions proceeded mainly via oxocarbenium species other than cyclic oxonium species, as compared with the TO/DO and TO/TOP systems.