Synthesis of highly isotactic (mm > 0.70) polyacrylonitrile by anionic polymerization using diethylberyllium as a main initiator

An attempt was made to synthesize steroregular polyacrylonitrile (PAN) with a high triad isotacticity (i.e. the content of mm (m, meso)) exceeding 0.70 by the anionic polymerization method. In the stereospecific polymerization of acrylonitrile (AN) initiated by diethylberyllium (Et₂Be) in xylene at 130°C, the (mm) content as well as the viscosity-average molecular weight (MÞ_v) of PAN increased by addition of diisobutylaluminum hydride (i-C₄H₉)₂AlH) as an additive to the polymerization system. Maximum (mm) content, attained in the molar ratio region of (i-C₄H₉)₂AlH/Et₂Be > 1.0, was about 0.73. The stereospecific polymerization of AN was also initiated using a mixture of Et₂Be and di-n-hexylamagnesium ((Et₂Be/(n-C₆H₁₃)₂ Mg system), where both Et₂Be and (n-C₆H₁₃)₂ Mg can induce the stereospecific polymerization of AN at 130°C. The (mm) content of the PAN sample prepared using the Et₂Be/(n-C₆H₁₃)₂ Mg system ((mm) = 0.64) was higher than that of PAN samples synthesized using Et₂Be alone ((mm) = 0.56) and (n-C₆H₁₃)₂Mg alone ((mm) = 0.51) under the same conditions except initiator. A significant difference in ¹³C chemical shifts of α-carbons between Et₂Be (1.35 ppm) and (n-C₆H₁₃)₂Mg (10.72 ppm) dissolved in hydrocarbon solvent at 110°C leads us to the conclusion that when Et₂Be induces the stereospecific polymerization in the Et₂Be/(n-C₆H₁₃)₂Mg system as initiator, the main role of (n-C₆H₁₃)₂Mg is considered to be the suppression of the association of Et₂Be (active site) itself.     

Anionic polymerization of dienes using oligobutadienyl-lithium as initiator

The aim of this work is to combine the microstructure of a radical-polymerized diene (butadiene and isoprene) with the functionality of an anionically prepared one, which could be used for polyurethane preparation after functionalization. A two-step anionic procedure was used in order to obtain a hydrocarbon-soluble lithium-based initiator. When compared with the related anionic polymers obtained under classical conditions, the vinyl content of the polydienes was three times greater. These findings are discussed on a mechanistic basis. © 1998 Society of Chemical Industry     

甲基铝氧烷对稀土催化体系催化异戊二烯聚合的影响

考察了甲基铝氧烷(MAO)作为助催化剂对稀土催化体系催化异戊二烯聚合的影响,结果表明MAO可极大地提高体系的催化活性,获得顺-1,4结构含量95%(质量分数)以上的聚异戊二烯,并且调节n(MAO)/n(Nd)和n(Al)/n(Nd)的值可有效地提高聚合产物的相对分子质量.     

Synthesis and kinetic behavior of stereotriblock polybutadiene using dilithium as initiator

Anionic polymerization of butadiene was conducted in cyclohexane using 1,1,4,4‐tetraphenyl‐1,4‐dilithium butane (TPB–DiLi) as initiator and dipiperidinoethane (DPE) as modifier. The polymer design effects of DPE/TPB–DiLi (simplified as DPE/Li) and polymerization temperature on the 1,2 content of polybutadiene (PB) were examined and 1,2‐polybutadiene (1,2‐PB) with a nearly 100% 1,2 content was obtained. 1,2–1,4–1,2‐Stereotriblock polybutadiene (STPB) can be synthesized easily by means of one feed reaction. DSC and DMA analyses showed that STPB with the designed molecular structure (molecular weight, block ratio, and 1,2 content in 1,2 blocks) has two T_g's and two loss moduli and exhibits microphase separation. Studies on reaction kinetics established the polymerization kinetics equation of 1,4‐PB as ?d[M]/dt = 0.356[C]^0.5[M], indicating the first‐order relationship between polymerization rate and monomer concentration. At 50°C, the addition of the strong polar modifier DPE into the system increased the reaction rate. The apparent propagating activating energies before and after DPE addition were also determined in this study. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1049–1054, 2003     

Controlled and stereospecific polymerization of rac‐lactide with a single‐site ethyl aluminum and alcohol initiating system

A single‐site ethyl aluminum complex, [2,2‐ diethyl‐1,3‐propylenebis(3,5‐di‐tert‐butyl‐salicylideneiminato)] ethyl aluminum (2), with a geminal diethyl substitutent on the diamino bridge was synthesized by the reaction of AlEt₃ with 1 equiv of N,N′‐(2,2‐diethyl‐1,3‐propylene)bis(3,5‐di‐tert‐butylsalicylideneimine). X‐ray diffraction showed that complex 2 contained a five‐coordinate aluminum atom with a distorted trigonal bipyramidal geometry in the solid state. ¹H‐NMR and ¹³C‐NMR spectra indicated that the two conformational enantiomers of 2 tautomerized quickly on the NMR timescale in solution. In the presence of isopropyl alcohol, the ring‐opening polymerization (ROP) of rac‐lactide with complex 2 produced a crystalline stereoblock polylactide (PLA). The stereoblocks contained an average of 12 units (L? = 12) of enantiomerically pure lactic acid. There was a linear relationship between the monomer conversion and number‐average molecular weights of the polymer. An induction period was observed for the polymerization. The induction period increased with decreasing concentration of catalyst 2 and isopropyl alcohol. In the presence of poly(ethylene glycol) (PEG), a PLA/PEG/PLA stereocomplex was prepared directly by the ROP of rac‐lactide with complex 2, which was confirmed by NMR, gel permeation chromatography, wide‐angle X‐ray diffraction, and differential scanning calorimetry. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 102–108, 2005     

Synthesis and characterization of poly(acrylonitrile)/montmorillonite nanocomposites from surface‐initiated redox polymerization

We have developed a facile method to prepare polyacrylonitrile/montmorillonite (PAN/MMT) nanocomposites using the surface‐initiated redox polymerization of acrylonitrile (AN) in the aqueous phase. The MMT silicate surfaces were first treated with diethanolamine, and the modified MMT (DEA‐MMT) was subsequently used together with the Ce(IV) salt to serve as a redox system. The PAN chains growing on a surface‐tethered DEA expand the interlayer space, and thus lead to intercalated/exfoliated nanocomposites. The nano‐morphology of the prepared nanocomposites depends on the AN/OH molar ratio in feed. An exfoliated PAN/MMT nanocomposite was obtained when the feeding AN/OH molar ratio = 300 was used. The molecular weight of PAN in the nanocomposites prepared by the present method is also dependent on the AN/OH molar ratio in feed and can be up to ca. 160,000 g/mol. The differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) analyses show that the increasing fraction of exfoliated silicate structures should enhance the contact interface between the silicate and polymer, resulting in the higher glass transition temperature and thermal stability. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of amines on the polymerization of isoprene with sec-butyllithium catalyst

Polymerization of isoprene (IP) with alkyllithium (RLi) catalysts in the presence of amines such as triethylamine (TEA), 1,2-dipiperidinoethane (DPPE) and N,N,N′,N′-tetramethyldiaminoalkanes [(CH₃)₂N(CH₂)_nN(CH₃)₂ where n=1, 2, 3, 4 and 6 (TMDAA)] has been studied. By adding the amines, the polymerization rate of IP was accelerated, and the contents of 3,4- and 1,2-units in the resulting polymers increased. The effects of methylene chain length of the TMDAA on the polymerization were examined. It was found that both the polymerization rates and the microstructure of the polymers depend on the methylene length of the TMDAA. The amines having 2 and 3 methylenes in (CH₃)₂N(CH₂)_nN(CH₃)₂ favoured production of the polymer consisting of predominantly 1,2- and 3,4-units. It was proposed that two types of active sites for the polymerization of IP were produced depending on the number n of the TMDAA. Two types of active species were confirmed to be produced with sec-BuLi in the presence of N,N,N′,N′-tetramethylethylenediamine (TMEDA) depending on the TMEDA/sec-BuLi mole ratios. © 1998 SCI.     

Studies of the stereospecific polymerization mechanism of propylene by a modified Ziegler-Natta catalyst based on 125 MHz 13C n.m.r. spectra

The mechanism of stereospecific polymerization of propylene (catalysed by a modified Ziegler-Natta system, TiCl₄/MgCl₂/C₆H₅COOC₂H₅/Al(C₂H₅)₃), has been analysed using the values of triad and pentad tacticity determined using 125 MHz ¹³C n.m.r. spectroscopy. The well-known single active-site models, such as the Bernoullian, first- and second-Markovian, and enantiomorphic models, were found to be inadequate to describe the observed tacticity. A two-sites model, in which at one site the stereospecific polymerization proceeds in obedience to the Bernoullian model and at the other proceeds under the control of enantiomorphic-site model, is proposed. It was found that the pentad tacticities of both soluble and insoluble (in boiling heptane) fractions of polypropylene agreed well with the two-sites model.     

Electroinduced dispersion polymerization of acrylonitrile in the presence of poly(acrylic acid) and catalytic amount of CE(IV)

Electroinduced dispersion polymerization of acrylonitrile initiated by Ce(IV) was performed in an electrolytic cell in the presence of poly(acrylic acid) (PAA). Micron‐size polyacrylonitrile (PAN) particles were stabilized with PAA by electrostatic interaction or by a PAA–Ce(III)–PAN ternary complex formation. A PAA–PAN stable polymer was formed in the cathodic compartment, and the reduced initiator was reoxidized in the anode, thus allowing for the continuation of the process. A possible mechanism of polymerization is suggested. © 2002 John Wiley & Sons, Inc. J Appl Polym Sci 84: 723–728, 2002; DOI 10.1002/app.10076     

Effect of electron donors on 1,3‐butadiene polymerization by a Ziegler–Natta catalyst based on neodymium

High‐cis polybutadiene produced by catalyst systems based on a rare earth is an elastomer used to produce green tires. This type of tire presents lower rolling resistance, which allows higher fuel economy, and thus fewer chemical compounds are discharged into the atmosphere. In this work, the influence of electron donors [tetrahydrofuran (THF) and tetramethylethylenediamine (TMEDA)] present in the polymerization solvent on the microstructure and molecular weight characteristics of the polybutadiene produced by neodymium catalysts was studied. The catalyst synthesis was carried out in glass bottles for 1 h at a temperature between 5 and 10°C. The catalyst components were diisobutylaluminum hydride, neodymium versatate, and tert‐butyl chloride. The polymerization reaction was carried out for 2 h. The reaction temperature was kept at 70± 3°C. The addition of TMEDA or THF above a determined concentration reduced the catalytic activity, molecular weight, and concentration of cis‐1,4 units (<96%), whereas the polydispersity increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2539–2543, 2005     

烷基铝对齐格勒-纳塔催化剂催化1-丁烯聚合性能的影响

采用5种烷基铝,在2 L不锈钢高压反应釜中对齐格勒-纳塔催化剂催化1-丁烯液相本体聚合反应进行研究。结果表明,与单一烷基铝相比,复配烷基铝使1-丁烯聚合活性明显提高,当n(三乙基铝)∶n（三异丁基铝）=100∶100时,活性最高,为13.5 kg·g^-1,且以复配烷基铝为助催化剂,高氢气量时,催化剂的氢调敏感性较强。     

异戊二烯／THF负离子聚合产物的微观结构

研究了２０～５０℃下,以ｎ－ＢｕＬｉ为引发剂,环己烷为溶剂,ＴＨＦ为极性调节剂的异戊二烯负离子聚合产物的微观结构。结果表明：随聚合温度升高,聚异戊二烯的３,４－结构含量降低;在同一温度下,随ＴＨＦ用量的增加,３,４－结构含量增加。［ＴＨＦ］／［ｎ－ＢｕＬｉ］（Ｒ,摩尔比）大于１２时,才会出现１,２－结构,且聚合温度越高,出现１,２－结构时的Ｒ值越高,并随Ｒ值的继续升高,１,２－结构含量也不断增加。此外,还建立了４个微观结构含量与ＴＨＦ用量的定量关系式。     

异戊二烯—环己烷—乙醚体系负离子聚合产物的微观结构

研究了在１５－３０℃下,以正丁基锂为引发剂,环己烷为溶剂,乙醚为极性调节剂的异戊在负离子聚合产物的微观结构。结果表明：在同一乙醚／正丁基锂摩尔比值下,随聚合温度升高,试样的３,４－结构摩尔分数降低;在同一温度下,随乙醚用量的增加,３,４－结构摩尔分数增加;以乙醚为极性添加剂时,聚合物分子链上含有３,４－和１,４－结构,不含１,２－结构;以乙醚为溶剂时,聚合物分子 含有３,４－,１,４－及１,２－结     

Block copolymers of acrylonitrile and poly(dimethylsiloxane)s

The chemical redox system of ceric ammonium nitrate(Ce⁴⁺) and poly(dimethylsiloxane)s (PDMS) with monohydroxy (MH), dihydroxy (DH), and diamine(DA) chain ends was used to polymerize acrylonitrile (AN) to produce monohydroxy poly(dimethylsiloxane)s‐b‐polyacrylonitrile (MH.PDMS‐b‐PAN), dihydroxy poly(dimethylsiloxane)s‐b‐polyacrylonitrile (DH.PDMS‐b‐PAN), and α, ω‐diamine poly(dimethylsiloxane)s‐b‐polyacrylonitrile (DA.PDMS‐b‐PAN) block copolymers. The concentration, reaction time, and the type of poly(dimethylsiloxane) affect the yield and the molecular weight of the copolymers. The ratio of AN/ceric salt/PDMS has remarkably affects the properties of formed copolymers. DH.PDMS‐b‐PAN copolymers were also prepared by electroinduced polymerization in the presence of catalytic amount of Ce⁴⁺ in a divided electrochemical cell where Ce³⁺ is readily oxidized into Ce⁴⁺ at the anode. The products were characterized by Fourier transform infrared spectroscopy, ¹H‐NMR spectroscopy, DSC, and their surface properties were investigated through contact‐angle measurements. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Heterophase polymerization of different methacrylates: Effect of alkyl ester group on kinetics and colloidal behavior

In this article, methyl‐ (MMA), ethyl‐ (EMA), n‐butyl‐ (BMA), n‐hexyl (HMA), and 2‐ethyl hexyl (2‐EHMA) methacrylates were homopolymerized in heterophase at 60°C using sodium dodecyl sulfate as surfactant and potassium persulfate as initiator. The effects of monomer content in the reaction mixture (2.5 and 3.5 wt %) and the alkyl ester groups of the methacrylates on the kinetics, average particle diameter (Dp), molar masses, tacticity, and glass transition temperature (T_g) were studied. The final weight average molecular weights were in the range of 4.53 × 10⁵ to 2.78 × 10⁶ g/mol with polydispersities between 1.7 and 3.1 for different methacrylates. For 2.5 wt % of monomer concentration, the order of increase in polymerization rate was Rp_HMA > Rp_BMA > Rp_2‐EHMA > Rp_EMA > Rp_MMA, whereas for 3.5 wt % of monomer concentration was Rp_BMA > Rp_HMA > Rp_2‐EHMA > Rp_EMA > Rp_MMA. This behavior was ascribed to the differences in the water solubility, monomer partitioning between the different phases, and monomers reactivity. The Dp values varied between 42 and 65 nm, increasing according to the hydrophobicity of each monomer. ¹³C‐NMR (nuclear magnetic resonance) and differential scanning calorimetry analysis demonstrated that 79–87% of syndiotactic configuration was obtained for the different polymers. The steric effect of the alkyl ester length in the methacrylates contributed directly to promote the syndiotactic configuration. Nevertheless, T_g values (between ?7 and 120°C) for these polymers decreased when the alkyl ester length increased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40191.     

Butadiene polymerization in the presence of VOCl3–dialkylmagnesium catalytic system

The butadiene polymerization in toluene at 25°C on VOCl₃? (n‐C₄H₉)Mg(iso‐C₈H₁₇) catalytic system was investigated. The kinetic parameters of polymerization and molecular characteristics of polybutadiene were determined. It was shown that substitution of traditional organoaluminum cocatalysts in trans‐regulating vanadium systems does not have an effect on its stereospecificity, but significantly influences on the active centers reaction ability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 596–600, 2003     

Effect of substituted groups on the living anionic polymerization of 2-vinylcarbazole derivatives

To study the effect of the substituents in the N-position of the carbazole on anionic polymerization, 2-vinylcarbazole derivatives of 9-butyl-2-vinylcarbazole (NBu2VCz), 9-phenyl-2-vinylcarbazole (NPh2VCz), and 9-(pyridin-2-yl)-2-vinylcarbazole (NPy2VCz) were synthesized. The anionic polymerization of NBu2VCz and NPh2VCz using s-BuLi was performed at −78 °C with a 100% yield, but the polymerization of NBu2VCz showed a broader molecular weight distribution (M_w/M_n = 1.23) than NPh2VCz (M_w/M_n = 1.11). The anionic polymerization of NPy2VCz using s-BuLi and DPM-K had a yield below 5%. In particular, the living anionic polymerization of NPh2VCz with s-BuLi/styrene ([s-BuLi/St]₀ = 0.33) shows a narrower M_w/M_n. The block copolymerization of NPh2VCz with styrene, α-methylstyrene (α-MeSt), and 2-vinylpyridine (2VP) was achieved successfully. The resulting block copolymers of PNPh2VCz-b-P2VP with f_PNPh2VCz = 17.7, 34.6, 48.1, 62.4, and 82.9 were synthesized for investigation of living characteristics.     

Synthesis of asymmetric H-shaped block copolymer by the combination of atom transfer radical polymerization and living anionic polymerization

A new asymmetric H-shaped block copolymer (PS)₂-PEO-(PMMA)₂ has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)₂-CHCOOCH₂CH₂OH with an active hydroxyl group. The chlorine was removed to yield the (PS)₂-CHCOOCH₂CH₂OH ((PS)₂-OH). The hydroxyl group of the (PS)₂-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)₂-PEO-OH. The (PS)₂-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)₂-PEO-OCCHCl₂ ((PS)₂-PEO-DCA). The asymmetric H-shaped block polymer (PS)₂-PEO-(PMMA)₂ was prepared via ATRP of MMA at 130 °C using (PS)₂-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)₂-PEO-(PMMA)₂, were confirmed by ¹H NMR, GPC and FT-IR.     

极性添加剂存在下铝-镍催化体系的苯乙烯-异戊二烯-丁二烯共聚物的氢化反应

采用负离子聚合法合成苯乙烯-异戊二烯-丁二烯三元共聚物( SIBR),并对其结构进行了表征;研究了结构调节剂N,N,N＇,N＇-四甲基乙二胺(TMEDA)、二乙二醇二甲醚(2 G)和四氢呋喃(THF)作外加添加剂时,对三异丁基铝(简称Al)/环烷酸镍(简称Ni)体系(A1与Ni的摩尔比为5)催化SIBR氢化反应的影响....