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Catalytic chain transfer polymerization of isobutylene: The role of nucleophilic impurities 下载免费PDF全文
Tota Rajasekhar Ujjal Haldar Jack Emert Philip Dimitrov Rich Severt Rudolf Faust 《Journal of polymer science. Part A, Polymer chemistry》2017,55(22):3697-3704
Fast polymerization of isobutylene (IB) initiated by tert‐butyl chloride using ethylaluminum dichloride·bis(2‐chloroethyl) ether complex (T. Rajasekhar, J. Emert, R. Faust, Polym. Chem. 2017, 8, 2852) was drastically slowed down in the presence of impurities, such as propionic acid, acetone, methanol, and acetonitrile. The effect of impurities on the polymerization rate was neutralized by using two different approaches. First, addition of a small amount of iron trichloride (FeCl3) scavenged the impurity and formed an insoluble · impurity complex in hexanes. The polymerization rate and exo‐olefin content were virtually identical to that obtained in the absence of impurities. Heterogeneous phase scavenger (FeCl3) exhibited better performance than homogenous phase scavengers. In the second approach, conducting the polymerization in wet hexanes, the fast polymerization of IB was retained in the presence of impurities with a slight decrease in exo‐olefin content. 1H NMR studies suggest that nucleophilic impurities are protonated in the presence of water, and thereby neutralized. Mechanistic studies suggest that the rate constant of activation (ka), rate constant of propagation (kp), and rate constant of β‐proton elimination (ktr) are not affected by the presence of impurities. To account for the retardation of polymerization in the presence of impurities, delay of proton transfer to monomer in the chain transfer step is proposed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3697–3704 相似文献
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J. D. Londono A. Habenschuss J. G. Curro J. J. Rajasekaran 《Journal of Polymer Science.Polymer Physics》1996,34(17):3055-3061
Wide-angle X-ray diffraction measurements were performed on polymer melts of isotactic and syndiotactic polypropylene (IPP and SPP), poly(ethylenepropylene) (PEP), polystyrene (PS), polyisobutylene (PIB), and polyethylene (PE), to study the dependence of the short-range structure of polymer liquids on chain architecture. Total structure functions, which comprise intra- and intermolecular contributions, were derived from the scattering data. The trivial Fourier components of the intramolecular structure (C(SINGLE BOND)>C ≃ 1.54 Å and C(SINGLE BOND)C(SINGLE BOND)C ≃ 2.55 Å) were subtracted from the total structure functions. The remaining functions contain only those intramolecular contributions dependent on the chain's conformational degrees of freedom, plus the intramolecular contributions. The structural differences between the polymers in momentum space are discerned only when the trivial components are subtracted. This subtraction also reduces the effects of truncation errors on Fourier transformation to real space. The short-range structure of PIB appears very different compared to all the others, which correlates with anomalies in a number of physical properties for this polymer. © 1996 John Wiley & Sons, Inc. 相似文献
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M. H. Wagner 《Rheologica Acta》1990,29(6):594-603
The nonlinear strain measure of a polyisobutylene (PIB) melt as determined by analysis of uniaxial, planar, ellipsoidal, and equibiaxial extensions is compared to the predictions of the molecular model of Doi and Edwards. It is found that the universal strain function of the Doi-Edwards model is unable to predict the nonlinear behavior of this polymer melt in general extensional flow. The qualitative agreement between predictions and experimental data for the strain dependence of shear stress and first normal stress difference in shear flow that was considered as powerful evidence for the correctness of the Doi-Edwards model seems to be accidental. The exaggerated strain dependence of the model suggests a need to reconsider the assumptions concerning the chain retraction process.Presented at the Golden Jubilee Conference of the British Society of Rheology and Third European Rheology Conference, Edinburgh, 3–7 September, 1990.Dedicated to Professor F.R. Schwarzl on the occasion of his 65th birthday 相似文献
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Mikls Nagy Lszl Orosz Sndor Kki Gyrgy Dek Pl Herczegh Mikls Zsuga 《Macromolecular rapid communications》2004,25(11):1073-1077
Summary: A new, simple, and effective synthetic method for the preparation of glucose‐terminated polyisobutylenes starting from the corresponding hydroxyl‐terminated polymers is reported. Detailed NMR and matrix‐assisted laser desorption/ionization mass spectrometric (MALDI‐TOF MS) investigations showed the exclusive presence of bis(glucopyranosyl) polyisobutylene. Dynamic light scattering (DLS) investigations of this polymer in solution in both tetrahydrofuran and water showed that microphase separation takes place by the formation of micelles and/or vesicles.
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Isomerization of the adduct resulting from the protonation of 5-methylene-2-norbornene by trifluoroacetic acid was studied by UC-NMR spectroscopy. Relative rate constants were determined under various experimental conditions. The influence of temperature, solvent, and relative reactant concentrations was examined. 相似文献
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Jung S. Shim Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》1999,37(6):815-824
Select mechanical, thermal, and rheological properties of star‐blocks consisting of 5–21 polystyrene‐b‐polyisobutylene (PSt‐b‐PIB) arms radiating from cyclosiloxane cores are described. The tensile properties of products containing 23–41 wt % of PSt are substantially higher (9.6–23.8 MPa) than those of linear triblocks of comparable arm molecular weights and compositions over the 25–85°C temperature range. The mechanical properties of star‐blocks seem to be much less sensitive to diblock contamination than linear triblock thermoplastic elastomers of similar hard/soft segment composition. The tensile strength of star‐blocks increases by increasing the number of arms (Nw,arm) and reaches a plateau in the Nw,arm = 5–10 range. Star‐blocks exhibit higher strengths with lower PSt segmental Mn than linear triblocks. Solvent cast triblock copolymers exhibit higher tensile strengths than compression molded products; however, star‐blocks show no significant property differences between cast and molded samples. The dynamic melt viscosities of the star‐blocks are substantially lower than those of linear triblocks with comparable hard/soft segment compositions, which is consistent with the star's unique microarchitecture and should lead to improved overall processibility. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 815–824, 1999 相似文献
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The far-field properties and beam quality of vectorial nonparaxial Hermite–Laguerre–Gaussian (HLG) beams are studied in detail, where, instead of the second-order-moments-based M2 factor, the extended power in the bucket (PIB) and βparameter are used to characterize the beam quality in the far field and the intensity in the formulae is replaced by the z component of the time-averaged Poynting vector Sz. It is found that the Sz PIB and βparameter of vectorial nonparaxial HLG beams depend on the mode indices n, m, αparameter and waist-width-to-wavelength ratio w0/λ and the PIB and βparameter are additionally dependent on the bucket's size taken. 相似文献
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The spatial correlation properties and the spectral intensity distributions of focused Gaussian Schell-model (GSM) array beams are studied in detail. The closed-form expressions for the spectral degree of coherence and the spectral intensity of focused GSM array beams are derived. It is shown that the spectral degree of coherence of focused GSM array beams is the same as that of focused GSM beams in the focal plane. On the other hand, it is found that, in the focal plane the spectral intensity distribution of focused GSM array beams is the fringe pattern when the value of the coherence length is small. However, it becomes one peak located at the center as the value of the coherence length is large enough. In the focal plane, the spectral intensity maximum increases and the width of the normalized spectral intensity distribution decreases as the beam number increases. In general, for GSM array beams, the width of the modulus of the spectral degree of coherence in the focal plane always exceeds that of the normalized spectral intensity distribution, which is different from the behavior of focused GSM beams. In addition, the power in the bucket (PIB) and the beam propagation factor (M2 factor) are also discussed. The main results are explained physically. 相似文献