The Experts below are selected from a list of 228 Experts worldwide ranked by ideXlab platform
Erhard W Fischer - One of the best experts on this subject based on the ideXlab platform.
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structure of Polybutadienes synthesized with a new catalyst system 2 blends of trans and cis 1 4 polybutadiene
Macromolecular Chemistry and Physics, 2001Co-Authors: E M Antipov, Evguenia A Mushina, Manfred Stamm, Erhard W FischerAbstract:The structure, composition and temperature behaviour of Polybutadienes prepared with binuclear metal complex catalysts immobilized on a solid carrier are investigated by differential scanning calorimetry, infra-red spectroscopy and X-ray scattering. Polybutadienes of nascent structure are blends of trans-1,4- and cis-1,4-homopolymers, whereas 1,2-units are randomly distributed in both macromolecules. The blends exhibit two-step melting characteristics for the crystalline trans-1,4-polybutadiene: the low-temperature transition from the monoclinic crystal form to the pseudohexagonal mesophase and the high-temperature transition from mesophase to the melt. A bimodal character of the endothermic maximum in DSC traces was observed for the former transition. In addition, it was shown that the nascent blend treated by hot toluene posseses a three-phase structure and contains, besides the well-known trans-1,4-polybutadiene crystalline and amorphous phases, an additional phase component of unknown structure.
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structure of Polybutadienes synthesised with a new catalyst system 3 random copolymers of trans 1 4 and 1 2 polybutadiene
Macromolecular Chemistry and Physics, 2001Co-Authors: E M Antipov, Manfred Stamm, Boris F Schklyaruk, Erhard W FischerAbstract:The structure and phase composition of random copolymers based on mesomorphic trans-1,4-polybutadiene containing a different amount of vinyl units (2-41 mol-%) were studied at various temperatures by X-ray analysis and differential scanning calorimetry. As the amount of 1,2-units in the polymer increases, temperatures of the phase transitions crystal-mesophase and mesophase-melt decrease, thus leading to a more narrow temperature range corresponding to an existence of the mesomorphic state. At a concentration of alien units of about 30 mol-%, the copolymer loses the ability to form a mesophase. Upon a further increase of 1,2-unit content (35-40 mol-%), the copolymer no longer crystallizes. The phase diagram of the copolymer is discussed in relation of temperature of phase transitions versus composition. It was shown that the destruction of the regular structure of the mesophase polymer by incorporation of alien units in its main chain leads to substantial decrease of the tendency of the material to mesomorphism, even more strongly than its ability to crystallize.
Dirong Gong - One of the best experts on this subject based on the ideXlab platform.
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controlling external diphenylcyclohexylphosphine feeding to achieve cis 1 4 syn 1 2 sequence controlled Polybutadienes via cobalt catalyzed 1 3 butadiene polymerization
Journal of Catalysis, 2019Co-Authors: Dirong Gong, Weilun Ying, Junyi Zhao, Wenxin Li, Yuechao Xu, Xuequan Zhang, Carmine Capacchione, Alfonso GrassiAbstract:Abstract Microstructure and unit sequence are critical parameters that determine the properties of polybutadiene materials. In this contribution, we have reported the syntheses, characterization of 6-(di-tert-butyl-phosphine) amine fused 2-R-pyridine compounds (R = 1′H-oxazoline (L1); 4′,4′-dimethyl oxazoline (L2); 4′-isopropyl oxazoline (L3) supported cobalt dichloride complexes and their performances in regio-selectivity, sequence and molecular weight controlled polymerization of butadiene. In combination with MMAO, the cobalt-mediated polymerization displays many characteristics of a living and cis-1,4 polymerization system over a wide temperature window of 0–80 °C. We show it is possible to tune the number average molecular weight in the range of 152–164 kg/mol with narrow MWD values of 1.04–1.34. The steric bulkiness on the catalysts has detrimental effect on the polymerization rate, (kobs(Co1, substituent free) of 0.037 L/mol·min. >Kobs(Co3, isopropyl) of 0.030 L/mol·min. >Kobs(Co2, dimethyl) to 0.024 L/mol·min.). With diphenylcyclohexylphosphine (Ph2CyP) as in-situ additive, the cobalt catalyst is highly active in cis-1,4 and 1,2-syndiotactic tunable butadiene polymerization to produce various cis-1,4-block-syn-1,2 Polybutadienes differing in block length. By continuous Ph2CyP feeding, this cobalt catalyst has been applied for the first synthesis of a regiogradient polybutadiene which starts with a cis-1,4 rich polybutadiene block and ends with an syn-1,2 rich block where the 1,2 specificity controlled between 28.7 and 88.5 mol%, moderate syndiotacticity (rr) of 49.8–64.5% and controlled molecular weight. The processing and mechanical properties were also evaluated. The phosphine dependent regio-selectivity and sequence controlled polymerization provide an simple and efficient strategy for various cis-1,4-syn-1,2 multi-block and cis-1,4-syn-1,2 regiogradient polybutadiene with tunable physical and mechanical properties.
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preparation and property investigation of chain end functionalized cis 1 4 Polybutadienes via de polymerization and cross metathesis of cis 1 4 Polybutadienes
Polymer Chemistry, 2019Co-Authors: Weilun Ying, Alfonso Grassi, Dirong GongAbstract:The transformation of cis-1,4-polybutadiene (PBD) to chain end functionalized propyltriethoxysilane (PBD-Si(OEt)3), trimethylsilane (PBD-SiMe3), phosphate (PBD-Phosphate), di-tert-butylphenol (PBD-Phenol) and propane epoxide (PBD-PO) cis-1,4-Polybutadienes via depolymerization by the Grubbs (II) catalyst and tandem cross metathesis employment of the corresponding chain transfer reagents (CTAs) has been developed. The formation of difunctionalized cis-1,4 polybutadiene (DF) with controlled molecular weight takes place, along with minor amounts of a mono-functionalized polymer (MF) and a non-functionalized polymer (NF) as evidenced by NMR, IR, GPC and MALDI-TOF. The precise cis-1,4 regiocontrol of functionalized rubber leads to further investigation of thermal-mechanical properties of elastomers. The PBD-Phosphate and PBD-Phenol exhibit enhanced thermal properties when the decomposition onset temperature was increased and the decomposition rate was also decreased compared to those of pure cis-1,4 polybutadiene. PBD-Si(OEt)3 was hydrolyzed on SiO2 and the resultant product was utilized as a compatibilizer for improving the interfacial interaction between filler SiO2 and matrix cis-1,4 polybutadiene. As a result, improvements of the resultant vulcanizate properties regarding elongation at break, tensile strength and loss factor are observed. The established knowledge of the correlation of functional groups in the chain end with thermal-physical properties could provide guidelines to develop high performance rubber materials from various conjugated diene elastomers.
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synthesis of high crystalline syndiotactic 1 2 Polybutadienes and study on their reinforcing effect on cis 1 4 polybutadiene
Polymer, 2017Co-Authors: Huafeng Chen, Dirong Gong, Jingshan Mu, Wei Li, Feng Jiang, Gengsheng Weng, Yanming Hu, Xuequan ZhangAbstract:Abstract A novel compound diethyl acetylphosphonate has been explored as efficient additive in iron based catalyst for stereo-polymerization of 1,3-butadiene to afford high crystalline 1,2-syndiotactic polybutadiene. Excellent 1,2 selectivity in range of 91.0–98.4% with controllable crystallinity has been achieved at high catalytic efficiency in wide ranges of cocatalyst and additive feeding as well as at large temperature scope. As reinforcing agent, two crystalline polymers differing in crystallinity 4.4% and 51.9% are blended and co-cured with cis-1,4 polybutadiene (PB) with 10 wt-%, providing samples PB1 and PB2, respectively. SEM from the sample fracturesurface shows the s-PBD particles are intimately mixed and homogeneously dispersed in PB matrix due to the strong interfacial interaction. The analysis of the mechanical properties of sample PB2 finds the tensile strength of increases by one-fold and the elongation at break increases by two-fold when head to head comparison to those of the CB filled PB, while the shear modulus G′ and loss factor (tan δ) are as good as those charged with CB. These results highlight the role of s-PBD as reinforcing agent of PB rubber, yielding high performance rubber materials with improved mechanical properties.
E M Antipov - One of the best experts on this subject based on the ideXlab platform.
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Modification of polybutadiene with caprolacton during polymerization
Polymer Science Series B, 2009Co-Authors: L. A. Nekhaeva, V. M. Frolov, N. A. Konovalenko, O. A. Khokhlova, V. L. Khodzhaeva, M. P. Filatova, B. F. Shklyaruk, E M AntipovAbstract:Polybutadiene has been modified with ɛ-caprolacton during butadiene polymerization carried out in the presence of catalytic systems based on neodymium and organoaluminum compounds at a butadiene conversion of 90–96%. The structure, phase state, and temperature behavior of Polybutadienes modified with ɛ-caprolacton have been studied by IR and 13C NMR spectroscopy, DSC, and X-ray diffraction analysis. The above approach shows promise for the synthesis of new-generation elastomers which do not rank below conventional rubbers in terms of their characteristics but possess biodegradability.
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structure of Polybutadienes synthesized with a new catalyst system 2 blends of trans and cis 1 4 polybutadiene
Macromolecular Chemistry and Physics, 2001Co-Authors: E M Antipov, Evguenia A Mushina, Manfred Stamm, Erhard W FischerAbstract:The structure, composition and temperature behaviour of Polybutadienes prepared with binuclear metal complex catalysts immobilized on a solid carrier are investigated by differential scanning calorimetry, infra-red spectroscopy and X-ray scattering. Polybutadienes of nascent structure are blends of trans-1,4- and cis-1,4-homopolymers, whereas 1,2-units are randomly distributed in both macromolecules. The blends exhibit two-step melting characteristics for the crystalline trans-1,4-polybutadiene: the low-temperature transition from the monoclinic crystal form to the pseudohexagonal mesophase and the high-temperature transition from mesophase to the melt. A bimodal character of the endothermic maximum in DSC traces was observed for the former transition. In addition, it was shown that the nascent blend treated by hot toluene posseses a three-phase structure and contains, besides the well-known trans-1,4-polybutadiene crystalline and amorphous phases, an additional phase component of unknown structure.
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structure of Polybutadienes synthesised with a new catalyst system 3 random copolymers of trans 1 4 and 1 2 polybutadiene
Macromolecular Chemistry and Physics, 2001Co-Authors: E M Antipov, Manfred Stamm, Boris F Schklyaruk, Erhard W FischerAbstract:The structure and phase composition of random copolymers based on mesomorphic trans-1,4-polybutadiene containing a different amount of vinyl units (2-41 mol-%) were studied at various temperatures by X-ray analysis and differential scanning calorimetry. As the amount of 1,2-units in the polymer increases, temperatures of the phase transitions crystal-mesophase and mesophase-melt decrease, thus leading to a more narrow temperature range corresponding to an existence of the mesomorphic state. At a concentration of alien units of about 30 mol-%, the copolymer loses the ability to form a mesophase. Upon a further increase of 1,2-unit content (35-40 mol-%), the copolymer no longer crystallizes. The phase diagram of the copolymer is discussed in relation of temperature of phase transitions versus composition. It was shown that the destruction of the regular structure of the mesophase polymer by incorporation of alien units in its main chain leads to substantial decrease of the tendency of the material to mesomorphism, even more strongly than its ability to crystallize.
Franco Ferrero - One of the best experts on this subject based on the ideXlab platform.
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calorimetric analysis of the cross linking reaction of epoxidized Polybutadienes
Journal of Thermal Analysis and Calorimetry, 2006Co-Authors: Franco FerreroAbstract:Liquid Polybutadienes were epoxidized with hydrogen peroxide-acetic acid confirming the influence of the microstructure on the epoxy content. Thermal cross-linking of the epoxidized products was studied by DSC and a different behaviour due to epoxy content as well as to microstructure was found. A correlation between enthalpy/epoxy ratio and vinyl content was also observed. The addition of a radical initiator as dicumyl peroxide (DCP) yielded exothermal effects of cross-linking in the original Polybutadienes, confirming the higher reactivity of the vinyl groups. In the epoxidized products, the introduction of DCP gave a peak split, which was explained by the overlap of two cross-linking mechanisms, due to residual double bonds and epoxy groups. From the DSC data, the isothermal curves of cross-linking conversion were calculated as a function of time, for a better comparison of the performances and properties of the epoxidized Polybutadienes.
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calorimetric analysis of the graft polymerization of maleic anhydride onto liquid Polybutadienes
Journal of Thermal Analysis and Calorimetry, 2004Co-Authors: Franco FerreroAbstract:The kinetics of the reaction of maleic anhydride with liquid Polybutadienes of various microstructures was studied by using differential scanning calorimetry (DSC). The kinetic results of thermal maleinization show a dependence from m.w. and polybutadiene microstructure. The introduction of a gel inhibitor as copper naphthenate has proved that crosslinking reactions also occur during the maleinization. On the other hand, the maleinization in the presence of a radical initiator as dicumyl peroxide (DCP) shows thermal effects higher than pure thermal reaction with a partial overlap of the calorimetric peaks due to maleinization and crosslinking.
Manfred Stamm - One of the best experts on this subject based on the ideXlab platform.
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structure of Polybutadienes synthesized with a new catalyst system 2 blends of trans and cis 1 4 polybutadiene
Macromolecular Chemistry and Physics, 2001Co-Authors: E M Antipov, Evguenia A Mushina, Manfred Stamm, Erhard W FischerAbstract:The structure, composition and temperature behaviour of Polybutadienes prepared with binuclear metal complex catalysts immobilized on a solid carrier are investigated by differential scanning calorimetry, infra-red spectroscopy and X-ray scattering. Polybutadienes of nascent structure are blends of trans-1,4- and cis-1,4-homopolymers, whereas 1,2-units are randomly distributed in both macromolecules. The blends exhibit two-step melting characteristics for the crystalline trans-1,4-polybutadiene: the low-temperature transition from the monoclinic crystal form to the pseudohexagonal mesophase and the high-temperature transition from mesophase to the melt. A bimodal character of the endothermic maximum in DSC traces was observed for the former transition. In addition, it was shown that the nascent blend treated by hot toluene posseses a three-phase structure and contains, besides the well-known trans-1,4-polybutadiene crystalline and amorphous phases, an additional phase component of unknown structure.
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structure of Polybutadienes synthesised with a new catalyst system 3 random copolymers of trans 1 4 and 1 2 polybutadiene
Macromolecular Chemistry and Physics, 2001Co-Authors: E M Antipov, Manfred Stamm, Boris F Schklyaruk, Erhard W FischerAbstract:The structure and phase composition of random copolymers based on mesomorphic trans-1,4-polybutadiene containing a different amount of vinyl units (2-41 mol-%) were studied at various temperatures by X-ray analysis and differential scanning calorimetry. As the amount of 1,2-units in the polymer increases, temperatures of the phase transitions crystal-mesophase and mesophase-melt decrease, thus leading to a more narrow temperature range corresponding to an existence of the mesomorphic state. At a concentration of alien units of about 30 mol-%, the copolymer loses the ability to form a mesophase. Upon a further increase of 1,2-unit content (35-40 mol-%), the copolymer no longer crystallizes. The phase diagram of the copolymer is discussed in relation of temperature of phase transitions versus composition. It was shown that the destruction of the regular structure of the mesophase polymer by incorporation of alien units in its main chain leads to substantial decrease of the tendency of the material to mesomorphism, even more strongly than its ability to crystallize.