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1.
N. Guarrotxena G. Martínez J. Milln 《Journal of polymer science. Part A, Polymer chemistry》1996,34(12):2387-2397
The nucleophilic substitution in poly(vinyl chloride) (PVC) with sodium benzenethiolate has been studied in two kinds of solvent differing in the molecular structure in the vicinity of the carbonyl group. From the evolution of the content of isotactic ( mm ), heterotactic ( mr ), and syndiotactic ( rr ) triads; and of mmmm, mmmr and rmmr isotactic pentads, in the unmodified parts of the polymer, as followed by 13C-NMR, it is unambiguously inferred that any chlorine but the central one of either the isotactic triad at mmr tetrads or the heterotactic triad at rmrr pentads is unreactive. Only a small fraction of mmr tetrads reacts occasionally by the central chlorine of its mr triad instead of the mm . Of those structures, the mmr , especially when located at the end of long isotactic sequences, proves to be highly reactive compared to the rmrr structure. By comparing quantitatively the microstructural changes with degree of substitution and taking into account that the reaction is of SN2 type, the mechanisms of substitution through the three foregoing reactive chlorines have been stated. They are found to be independent of the type of solvent and to account for all the changes in triad and pentad content as experimentally found. Instead, the solvent dependence of the ratio between the mmr - and rmrr -based processes of substitution is such that the depletion of mmr compared to that of rmrr structure may be controlled. The conformational sensitivity of this behavior is discussed on the basis of side work in our laboratory. As a whole, the results of the present work provide some original concepts as to the role of the tacticity dependent microstructure and the related local conformations in the chemical reactions of PVC. © 1996 John Wiley & Sons, Inc. 相似文献
2.
Fe(III) and PAN form Fe(PAN),OH complex in CHCl3 extract which shows absorption maxima at 550 nm and 775 nm (log ε550,= 4.06, log ε775 = 4.08). In the Fc(III)-PAN-Triton X-100 system, two complex species Fe(PAN)2+ and/or Fe(PAN)2OH may be formed. Fe(PAN)2+ possesses a strongly absorbing peak at 550 nm (log ε550 = 4.36). In this paper the effect of Triton X-100 micelles on the Fe(III)-PAN color reaction has been investigated in detail. We consider that the high density of ether linkages in Triton X-100 micelles concentrate hydrous Fe(III) ions and change their existing state. Moreover, the micelles not only raise the reactivity of Fe(III), but also enhance the rate of the color reaction. 相似文献
3.
George M. Benedikt 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2):85-98
Abstract We synthesized and analyzed by 1H NMR the mixture of meso (m) and racemic (r) 1,2,4,5-tetrachloropentane, as well as the mixture of mm, mr, and rr isomers of 1,2,4,6,7-pentachloroheptane and its precursor 1,2,6,7-tetrachloroheptane-4-ol as models for PVC 1,2-dichloroethyl end group. We were able to correct previous assignments as well as extend the 1H-NMR analysis of this end group in PVC to the triad level. 相似文献
4.
Rui Chen Meiran Xie Qing Wu Shangan Lin 《Journal of polymer science. Part A, Polymer chemistry》2000,38(3):411-415
The half‐titanocene (η5‐pentamethylcyclopentadienyl)tribenzyl titanium (Cp*TiBz3) with methylaluminoxane (MAO) as the cocatalyst was employed to catalyze propene polymerization at ambient pressure. A novel atactic polypropene elastomer with a high molecular weight (M̄w = 2 − 8 × 105) was produced. The effects of the polymerization conditions on the catalytic activity and polymer molecular weight are discussed. 13C NMR analysis confirmed that the catalyst system Cp*TiBz3/MAO produced atactic polypropenes, and the polymerization mechanism was in agreement with the Bernoullian process. The triad sequence distribution of the polymer was measured and found to be as follows: mm = 6.15%, mr = 40.87%, and rr = 52.98% (Bernoullian factor B = 1.03); this indicated that the insertion of propene with the catalyst system followed a chain‐end control model. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 411–415, 2000 相似文献
5.
Weiping Du Huifang Chen Haifeng Xu Ding Pan Ning Pan 《Journal of Polymer Science.Polymer Physics》2009,47(15):1437-1442
The spinnability and polydispersity of polyacrylonitrile/dimethyl sulfoxide (PAN/DMSO)/H2O spinning solutions with conventional PAN molecular weight and comparative high PAN concentration have been investigated using a cone‐plate rheometer. It is observed from the measurements that, the viscosities of the solutions decreased with the rising of shear rate, and then stabilized to almost the same value, regardless of the PAN concentration. The chain orientation in the fiber formed under constant shear rate cannot be changed considerably even after long relaxation of more than 900s. For dynamic experiments, a steady increase of both G′ and G″ with escalating oscillation frequency was seen for all samples. Higher viscous‐elastic modulus at higher H2O content was found, too. It is also concluded from the log G′ ? log G″ plot and the gel point that the PAN/DMSO/H2O system with regular PAN molecular weight behaves very close to a mono‐disperse system, thus very suitable for gel spinning and for preparation of high performance PAN precursor fiber. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1437–1442, 2009 相似文献
6.
R. Marupov I. Ya. Kalontarov Y. Asrorov A. M. Mavlyanov F. F. Niyazi 《Journal of polymer science. Part A, Polymer chemistry》1977,15(12):2835-2842
By the methods of infrared and mass spectroscopy, the structure of grafted copolymer of polycaproamide (PCA) with polyacrylonitrile (PAN) was examined. It is shown on the grounds of analysis of infrared absorption bands and mass spectrum of the volatile products of grafted copolymer thermodestruction that the graft copolymerization in the redox system Fe+3/H2O2 is carried out at the expense of the radicals, formed on COOH groups of PCA. The structure of grafted chains PAN changes owing to formation of cycles containing ? S? and C?N groups at the grafted copolymer treatment with Na2S. By the means of complex thermal analysis, the steadiness of the obtained products to thermooxidizing destruction was investigated. It was found that the presence of sulfur in the grafted copolymer PCA–PAN considerably intensifies the processes of grafted-chain PAN cyclization as compared with the PAN homopolymer. It was shown that Na2S treatment brings to the product with the minimized absorption of oxygen at the isothermal heating that indicates its stability with regard to thermooxidizing destruction 相似文献
7.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):1935-1948
Polyacrylonitrile (PAN) polymers were prepared by inclusion polymerization of the monomer using various molar equivalents of β-cyclodextrin (β-CD). Stereoregular (isotactic, atactic and syndiotactic) distributions of the prepared PAN polymers were determined from terminal model Bernoullian statistics using 13C-NMR data. With an increase in acrylonitrile (AN): β-CD ratios, the proportion of isotactic polymers increased. Also, Tg increased along with degradation temperature at higher AN: β-CD ratios. However, molecular weight of the polymers prepared was lower at an AN: β-CD ratio of 10:1, but was found to be larger than the control at an AN: β-CD ratio of 20:1. 相似文献
8.
Mixed complexes of Pb(II) with some carboxylate ions, viz. tartrate (tart2?), malonate (mal2?) and citrate (citr3?); and imidazole (im) have been studied polarographically at 25°C and at constant ionic strength μ = 2.0 (NaNO3) and at pH 6. The polarographic reduction of the complexes in each case is reversible and diffusion-controlled. Pb(II) forms a single mixed complex with tartrate and imidazole, viz [Pb(tart)(im)] with stability constant log β11 = 4.19; with mal2? and im, three mixed complexes, [Pb(mal)(im)], [Pb(mal)(im)2] and [Pb(mal)2(im)]2? with stability constants log β11 = 4.3, log β12 = 7.3 and log β21 = 5.5 respectively are formed. With citr3? and im a single mixed species, [Pb(citr)(im)]? with stability constant log β11 = 8.0 is formed. Various equilibria involved in the mixed systems have been discussed. 相似文献
9.
Charge decay properties at 90°C have been studied for four poly(propylene) (PP) samples of different content of isotactic (mm), syndiotactic (rr) and heterotactic (mr, rm) triads. Comparing the charge decay properties with the previously measured space charge distribution and taking into account the specific stereochemical sequences which characterize each of the samples, it is apparent that mmrm and rrrm sequences furnish better storage properties. In contrast, mmrr and short heterotactic sequences would both exhibit worse retention power of negative and positive charge. Correlations – although still tentative – justify those specific stereochemical sequences as being well defined factors for determining the electrical properties of PP. 相似文献
10.
Roger Spitz Marie-France Llauro-Darricades Alain Michel Alain Guyot Carmen Mijangos Gerardo Martinez Jose Luis Millan 《Journal of polymer science. Part A, Polymer chemistry》1986,24(8):1753-1777
The nucleophilic substitution of the chlorine atoms of poly(vinyl chloride) with sodium thiophenate is assumed to obey an SN2 mechanism with inversion of configuration and a steric control according to which reactivities R of the triads follow the order Rmm > Rmr ? Rrr. Such a reaction cannot be described by simple differential equations, but a Monte Carlo simulation, first generating a random Bernouillian chain and then simulating random attack of the chain by the reactant according to the triad reactivities, allows a good agreement with the experimental results of both the kinetics of a reaction carried out in cyclohexanone solution at 40°C and the evolution of the 13C and 1H NMR spectra of the tertiary carbon atoms, assuming the following parameters: Bernouillian probability for a meso placement in the initial chain: 0.431; relative reactivities of the mm, mr and rm, rr triads: 1, 0.5, and 0., respectively. The agreement is excellent until the reaction is about three-quarters complete; this shows a limiting level of about 60% substitution. Better agreement can be obtained up to the limit, if a secondary process of steric control by the substituant in a partially substituted mr triad is assumed. Other possibilities for that secondary process are discussed. 相似文献
11.
Madhuri A. Phadke Deepak A. Musale Sudhir S. Kulkarni Sandeep K. Karode 《Journal of Polymer Science.Polymer Physics》2005,43(15):2061-2073
Fourier transform infrared spectroscopy was used to study the interactions among LiCl, ZnCl2, and AlCl3 with N,N‐dimethylformamide (DMF) and poly(acrylonitrile) (PAN). It was observed that all three salts complex with DMF as well as PAN. The strength of the cation interaction with the >C?O oxygen of DMF was found to be higher than that with the ? CN group of PAN. The >C?O stretching frequency of DMF with ZnCl2 was red shifted, indicating stronger complex formation compared with other two cations. With the addition of salt, the salt–DMF pseudo solvent was found to become a θ solvent for PAN compared with neat DMF. This change in PAN solvation power was primarily the result of DMF–salt complexation. As a result of the complexation, Mark‐Houwink constant a, was found to reduce from 0.75 (for pure DMF) to ~0.6 for DMF–salt solvents, indicating decreased PAN chain expansion. Comparison of intrinsic viscosity [η] values indicated that addition of salts to PAN–DMF solutions resulted in: (i) decrease in the DMF solvation power, which causes less expanded polymer coils, and (ii) increased interpolymer chain entanglements via salt‐promoted chain association. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2061–2073, 2005 相似文献
12.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1982,38(8):855-857
The metal isotope technique is applied to the investigation of the metal—ligand bands in the i.r. spectra of complexes of type: Cu(PAN)X and Cu(PAN)2 where X = Cl, Br and PAN symbolizes 1-(2-pyridylazo)-2-naphthol. For the Cu(PAN)Cl complex, bands at 337, 274 and 196 cm−1 were assigned to the CuO, CuNpy and CuNazo stretching vibrations, respectively. Two CuCl stretching vibrations have been found at 298 and 236 cm−1. The spectrum indicates that in the Cu(PAN)2 complex, PAN acts as a bidentate ligand as only CuO and CuNazo bonds are formed. 相似文献
13.
Nanoscale poly(cyclohexyl methacrylate) (PCHMA) particles were prepared by a modified microemulsion polymerization procedure. 13C‐NMR analysis suggested that such PCHMA samples were higher in syndiotactic content (61–72% rr) and lower in isotactic content (1–3% mm). The glass transition temperatures (Tg's) of the products were also higher than that reported in the literature. The polymer properties, such as particle size, molecular weight, tacticity, and Tg were affected by the reaction conditions. The smaller the particle size, the higher the syndiotacticity, the lower the isotacticity and the greater the molecular weight, then the higher the Tg of the PCHMA samples. Possible mechanism of rich‐syndiotacticity was also discussed. 相似文献
14.
The preparation and characterization of stereoregular isotactic polyacrylonitrile (PAN) by electron beam (EB) irradiation
on a urea canal complex are described. The EB method has several advantages over the ordinary γ-ray irradiation method: a
very short polymerization time is needed (within a few seconds) and EB irradiation is carried out intermittently, and so all
the polymer properties can be studied as a function of the EB irradiation dose. The structure–properties relationships of
PAN, such as intrinsic viscosity versus the number-average molecular weight and the viscosity versus the isotacticity range
were clarified. Significant information for the optimization of the tacticity of PAN was extracted.
Received: 23 August 1999 Accepted : 10 January 2000 相似文献
15.
1-(2-Pyridylazo)-2-naphthol (PAN) reacts with either gallium or indium at pH 5–6 giving a red complex in an aqueous medium in the presence of N.N-dimethyl-formamide. The maximum absorption of both PAN complexes of gallium and indium in an aqueous solution is at 545 mμ. The gallium-PAN complex shows a characteristic enhancement of color by addition of small amounts of ethers. Based on this selective enhancement reaction, gallium can be determined in the presence of other metals without separation. The results of determining gallium and indium in the presence of each other are reported. Both gallium and indium form M2(PAN)3; but in the presence of certain organic solvents, a different gallium complex, Ga(PAN)5, and the same indium complex, In2(PAN)3, are formed. The reaction of PAN with cadmium can be masked by iodide; an example of determining indium in the presence of cadmium is given. The PAN method has a sensitivity of 0.003 μg/cm2 for gallium and 0.005μg/cm2 for indium and an absorptivity of 24,900 for the Ga-PAN complex and of 24,500 for the In-PAN complex, respectively. The methods have been successfully applied to the determination of both gallium and indium in germanium thin films. 相似文献
16.
George M. Benedikt Brian L. Goodall Larry F. Rhodes Alan C Kemball 《Macromolecular Symposia》1994,86(1):65-75
We have been able to obtain the 1H NMR subspectra of most of the major saturated end groups in PVC. In order to assign the terminal vinyl (TV) group, CH2CH-CHCl-, we synthesized and analyzed the symmetrical model compound 3,5-dichloro-1,6-heptadiene (4) containing a racemic (r) and a meso (m) isomer. They exhibit distinct NMR signals for the vinyl protons, which allowed us to subsequently assign the r diad and the previously unreported m diad terminal vinyl resonances present in very small amounts in commercial PVC. The study of the solvent induced chemical shifts of the vinyl protons in an experimental PVC sample containing an unusually high level of this end group allowed us to further assign it in terms of the terminal rr, rm, mm and mr triads. 相似文献
17.
Ezio Rizzardo Ming Chen Bill Chong Graeme Moad Melissa Skidmore San H. Thang 《Macromolecular Symposia》2007,248(1):104-116
SUMMARY: Factors affecting the choice of RAFT agent [RSC(Z) = S] for a given polymerization are discussed. For polymerization of methyl methacrylate (MMA), tertiary cyanoalkyl trithiocarbonates provide very good control over molecular weight and distribution and polymerizations show little retardation. The secondary trithiocarbonate RAFT agents with R = CHPh(CN) also gives good control but an inhibition period attributed to slow reinitiation is manifest. Radical induced reduction with hypophosphite salts provides a clean and convenient process for removal of thiocarbonylthio end groups of RAFT-synthesized polymers. Two methods providing simultaneous control over stereochemistry and molecular weight distribution of chains formed by radical polymerization are reported. Polymerization of MMA in the presence of scandium triflate provides a more isotactic PMMA. A similar RAFT polymerization with trithiocarbonate RAFT agents also provides control and avoids issues of RAFT agent instability seen with dithiobenzoate RAFT agents in the presence of Lewis acids. RAFT polymerization of tetramethylammonium methacrylate at 45 °C provides a more syndiotactic PMMA of controlled molecular weight and distribution (after methylation; mm:mr:rr 2:21:77 compared to 3:35:62 when formed by bulk polymerization of MMA). 相似文献
18.
Abstract The characterizations of poly(N-vinylcarbazole) (PVCZ) obtained via asymmetrical polymerization have been studied by using 1H-NMR spectrum, UV spectrum, DSC, and GPC analysis. The tacticities, i.e., the isotactic diad mole fractions, were found to increase when using the initiator AIBN to the catalyst (?)Sp?+(+)CSA??, and the extinction coefficients to decrease. Bimodal molecular weight distribution (MWD)s were caused by two propagating species of the free ions and the ion-pairs during the polymerization process. 相似文献
19.
Makiko Seno 《European Polymer Journal》2004,40(9):2247-2250
Vinyl phenylsulfonylacetate (VPSA) was prepared by the reaction of vinyl chloroacetate with sodium benzenesulfinate in acetone in the presence of a phase-transfer catalyst. VPSA showed a high radical homopolymerizability similar to vinyl acetate in spite of the fact that VPSA carries a phenyl group. The polymerization of VPSA with 2,2′-azobisisobutyrate (MAIB) was kinetically investigated in acetone. The overall activation energy of the polymerization was 27.6 kcal/mol. The polymerization rate (Rp) at 50 °C was expressed by Rp=k[MAIB]0.67[VPSA]1.1. Poly(VPSA) showed exothermic (27 °C) and endothermic (57 °C) peaks in its DCS curve, corresponding to crystallization and melting. The tacticity of poly(VPSA) was estimated to be rr=29, mr=49, and mm=22. 相似文献
20.
A. Burkanudeen G. Santhana Krishnan N. Murali 《Journal of Thermal Analysis and Calorimetry》2013,112(3):1261-1268
The effect of stereoregularity, in terms of isotactic triad content on the thermal behavior of carbon fiber precursor polymers synthesized through different polymerization routes such as solid state and radical solution polymerization techniques, was investigated by the thermogravimetric analysis and differential scanning calorimetric measurements. The isotactic contents of I-PAN and A-PAN were estimated with 13C NMR. The thermal cyclization reactions of atactic polyacrylonitrile (A-PAN) with low isotactic content (26.4–29.7 %) occurred at a lower temperature than that of isotactic polyacrylonitrile (I-PAN) with higher content (48.7–51.6 %). The percentage of mass loss observed in I-PAN was less as compared to A-PAN. The molecular mass characteristics of PAN obtained through solid state and radical solution polymerization were [M n (10.2–14.3 × 104), M v (2.44–3.26 × 105)] and [M n (10.2–14.3 × 104), M v (2.29–2.74 × 105)] Daltons (Da). 相似文献