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![SCHEME 1. — Proposed reaction path for high cis-1,4-PB (Co[I] is the...](profile/Prasanta-Behera-3/publication/303891071/figure/fig1/AS:389143902343170@1469790544839/SCHEME-1-Proposed-reaction-path-for-high-cis-1-4-PB-CoI-is-the-active-catalyst-in_Q320.jpg)
Elastomers with pendant alkenyl functionality can be easily modified using different types of postpolymerization reactions that lead to improved properties. This investigation reports the preparation of polybutadiene (PB) with control vinyl content by Co-based catalyst followed by modification of vinyl functionality via thiol-ene reaction. In this...
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... trans, and vinyl contents were determined by 1 H NMR analysis. Figure 6 represents the 1 H NMR spectrum of PB (B). Different protons have been designated in Figure 6. ...
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... 6 represents the 1 H NMR spectrum of PB (B). Different protons have been designated in Figure 6. The resonances at d value of 5.0 ppm correspond to the terminal vinyl protons, and the resonances at 5.5 ppm are due to the protons of cis, trans microstructure as well as the secondary proton (ÀCH¼CH 2 ) of vinylic double bond (designated as ''e''). ...
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... at 5.0 ppm due to vinylic units compared with the 1 H NMR of PB (B) in Figure 8 indicates the successful thiol-ene modification. The extent of thiol-ene reaction in vinyl PB was determined by comparing the integral areas of the resonances at 5.0 ppm of the residual vinylic double bond and of the same at 5 ppm in pristine vinyl PB ( Figure 6). Figure 9 shows the GPC traces of vinyl PB and thiol-modified vinyl PB. ...
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... trans, and vinyl contents were determined by 1 H NMR analysis. Figure 6 represents the 1 H NMR spectrum of PB (B). Different protons have been designated in Figure 6. The resonances at d value of 5.0 ppm correspond to the terminal vinyl protons, and the resonances at 5.5 ppm are due to the protons of cis, trans microstructure as well as the secondary proton (ÀCH¼CH 2 ) of vinylic double bond (designated as ''e''). The resonances at 1.0 to 2.2 ppm are due to differentÀCH 2 Àand .CHÀprotons in PB designated as b, d, and c. The vinyl content was calculated by comparing the integral area at 5.0 ppm and at 5.3 to 5.7 ppm, which are due to vinyl content (1,2-content) and 1,4 content, respectively, in ...
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... trans, and vinyl contents were determined by 1 H NMR analysis. Figure 6 represents the 1 H NMR spectrum of PB (B). Different protons have been designated in Figure 6. The resonances at d value of 5.0 ppm correspond to the terminal vinyl protons, and the resonances at 5.5 ppm are due to the protons of cis, trans microstructure as well as the secondary proton (ÀCH¼CH 2 ) of vinylic double bond (designated as ''e''). The resonances at 1.0 to 2.2 ppm are due to differentÀCH 2 Àand .CHÀprotons in PB designated as b, d, and c. The vinyl content was calculated by comparing the integral area at 5.0 ppm and at 5.3 to 5.7 ppm, which are due to vinyl content (1,2-content) and 1,4 content, respectively, in ...
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... thiol-ene modification of vinyl PB was carried out using benzyl mercaptan as thiolating agent in the presence of AIBN, a thermal initiator. Figure 8 shows the 1 H NMR spectrum of thiol modified vinyl PB. The resonances at 7.3 ppm are due to the aromatic protons of benzylic moiety (Ph-CH 2 À), designated as ''l.'' The resonances at about 2.5 ppm and 3.7 ppm are due to the ÀCH 2 -SÀ and ÀS-CH 2 -Ph protons, designated as ''j'' and ''k,'' respectively. The decrease in Table I). resonances at 5.0 ppm due to vinylic units compared with the 1 H NMR of PB (B) in Figure 8 indicates the successful thiol-ene modification. The extent of thiol-ene reaction in vinyl PB was determined by comparing the integral areas of the resonances at 5.0 ppm of the residual vinylic double bond and of the same at 5 ppm in pristine vinyl PB ( Figure 6). Figure 9 shows the GPC traces of vinyl PB and thiol-modified vinyl PB. The multimodal molar mass distribution is due to the nonequivalence of the kinetic activity of the active sites of polymerization. 53 Schröder et al. 54 found the bimodal distribution of PB prepared by the nickel-based catalyst and trialkylaluminium-based cocatalyst system. They reported that the bimodal curve is due to the presence of two different types of active catalyst species, which give a polymer with very broad molar mass distribution. Nickel in a different oxidation state bonds differently to the cocatalyst and generates a different type of active species. In our case, cobalt can polymerize the butadiene in two oxidation states (i.e., Co[0] and Co [I]), which can generate two different types of active species. Thus, a bimodal distribution was found in the GPC traces. Again, GPC traces indicate that there is an increase in molecular weight after thiol-ene modification. The increase in molecular weight is due to the attachment of benzyl mercaptan units on to the polymer chain. Further, the possibility of coupling the macromolecular chain during the thiol-ene reaction also leads to an increase in the molecular weight. Importantly, there is no shift of elution volume in the right-hand side in the GPC traces ( Figure 9), indicating there is no degradation of the polymer chains during the thiol-ene ...
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... The stretch vibration of hydroxide (O-H) bond, that signals adsorption water on ferrite, is responsible for the peak at 3441.01 cm À1 [23]. The position of spinel ferrite discovered by (Ni-O) and (Fe-O) in the 400-600 cm À1 range is stretching vibration [24]. ...
The magnetic structure of NiFe2O4 particles has been obtained by using a sol-gel auto combustion technique with limejuice as a surface-active agent as well as a fuel agent. The above process is classified as sustainable chemistry, which is a procedure that is both environmentally friendly and less expensive than other methods. Some of the physical and chemical techniques used to diagnose nanomaterials include energy-dispersive X-ray spectroscopy, XRD, FTIR, TEM, FESEM, and Brunauer-Emmett-Teller. The phase purity and particle size of 24.27 nm were revealed by XRD patterns. Pb⁺², as well as Cd⁺² absorption characteristics, have been investigated in relation to adsorbent concentration, pH, temperature, and contact time. When the pH ranges from three to nine, the best time to contact is 60 min for Pb⁺² and 90 min for Cd⁺². When compared to the Langmuir adsorption model, the adsorption studies revealed a strong relationship with a Freundlich adsorption isotherm. The thermophysical properties have been described, showing an endothermic reaction for ΔH, a spontaneous process for ΔG, as well as a positive value for ΔS, which was characterized by an increase in process disorder.
... rubber via reaction with the pendant as well as the main chain double bond. [63][64][65][66] The grafting of suitable functional groups onto PB may help in showing its self-healing property. ...
The formation of microcracks is a common problem in elastomeric materials. The propagation of microcracks to bigger cracks results in the failure of the elastomeric material, which needs to be replaced by a new material, thus creating a huge elastomer waste. The introduction of self-healing property into the elastomeric material is an important way to repair microcracks and to stop the crack propagation process. This review summarizes the progress in self-healing elastomers (polybutadiene rubber, styrene-butadiene rubber, polyisoprene rubber, butyl rubber, nitrile butadiene rubber, chloroprene rubber, and silicon rubber) based on conjugated diolefins. The use of various self-healing mechanisms and their effect on the self-healing property as well as reprocessability has been discussed. The challenges and future research opportunities are highlighted. This journal is
This report presents an evaluation of thiyl radical-induced cis/trans isomerism in double bond-containing elastomers, such as natural, polychloroprene, and polybutadiene rubbers. The study aims to extensively investigate structural changes in polymers after functionalisation using thiol-ene chemistry, a useful click reaction for modifying polymers and developing materials with new functionalities. The paper reports on the use of different thiols, and cis/trans isomerism was detected through 1H NMR analysis, even at very low alkene/thiol mole ratios. The study finds that the configurational arrangements between non-functionalised elastomer units and thiolated units followed a trans-functionalised-cis units arrangement up to an alkene/thiol mole feed ratio of 0.3, while from 0.4 onward, a combination of trans-functionalised-cis and cis-functionalised-trans configurations are found. Additionally, it is observed that by increasing the level of functionalisation, the glass transition temperature of the resulting modified elastomer also increases. Overall, this study provides valuable insights into the effects of thiol-ene chemistry on the structure and properties of elastomers and could have important implications for the development of new materials with enhanced functionality.
Polybutadiene (PBR) occupies the second position among synthetic rubber after styrene‐butadiene rubber with a global production capacity of ∼2.8 million metric tons per year. It is produced by solution polymerization process using the Ziegler‐Natta catalyst system. PBR with varied microstructure feature is produced using different types of transition metal in combination with alkyl aluminum. The presence of different microstructures in the product impact properties and performances of the rubber. This article focuses on PBR polymerization processes with different types of catalyst systems and their effect on microstructure of products.
Butadiene rubber (BR) is one of the most useful and second most produced rubber worldwide. Polymerization of 1,3-butadiene (BD) is a highly stereospecific reaction that offers a wide variety of BR with different microstructures and influences the fundamental properties of the rubber. Since the first successful polymerization of conjugated diene using the Ziegler–Natta–based catalyst (TiCl4 or TiCl3 with aluminum alkyls) in 1954, the research on producing synthetic rubber with an appropriate catalyst system has been accelerated. Subsequently, various research groups are actively engaged in designing active catalyst systems based on a suitable combination of transition metal complexes with alkyl-aluminum and successfully using them in BD polymerization. Although various scientific inventions have proven their significance for the production of high-quality BR, with the rising demands in improving the quality of the product, research on developing new catalyst systems with enhanced catalytic activity and high stereoselectivity is still in progress. The present review focuses on the synthesis of BR using various transition metal catalysts and discusses their microstructures. The catalysts based on new-generation metal complexes with phosphorus, nitrogen, and oxygen donor ligands (e.g., phosphines, imines, 1,10-phenanthroline, and imino-pyridines) have been introduced. The role that catalysts play in the production of BR with different microstructures (i.e., high-cis, high-trans or low-cis, low-trans polybutadiene) has also been described. The combination of catalyst (transition metal complex) and suitable co-catalyst (alkyl-aluminum) is the major factor influencing the reaction and microstructure of the resulting polymer. This report focuses on the effect of transition metal catalysts (i.e., lithium [Li], titanium [Ti], zirconium [Zr], iron [Fe], cobalt [Co], nickel [Ni], and neodymium [Nd]) on the activity and stereoselectivity of polymers such as 1,4-cis-, 1,4-trans-, and 1,2-vinyl-polybutadiene.
Iron Salen complexes varied with steric effect were designed and examined in polymerization of butadiene coupled with triphenylphosphate as electron donor. The results demonstrate they are able to serve as unique catalysts, yielding a family of crystalline 1,2 syndiotactic polybutadienes as thermoplastic resin materials. The incorporation of sterically hindered group into the iron catalyst provides a high degree of control over the stereospecificity with certain adverse effect on activity. The necessity of donor during the stereopolymerization of butadiene is also highlighted by concomitant increase in activity and selectivity at higher temperature. The formed stereo active sites are very uniform in nature irrelative to the alkylaluminum and monomer feeding, resulting in polymers having constant microstructures and stable properties. The highly stable catalytic performances by the catalyst formed by accessible catalyst component could be industrially favored for production of syndiotactic 1,2 polybutadiene.
Coordination polymerization of butadiene was initiated by a catalyst system consisting of tributyl phosphate (TBP) as ligand, molybdenum pentachloride as primary catalyst and triethyl aluminum substituted by m-cresol as co-catalyst. The effects of the substitution of m-cresol on the activity of the catalyst system, molecular weight and molecular weight distribution, intrinsic viscosity and microstructures of the resulting polymers were investigated in details. The molecular weight and molecular weight distribution of the polymerization products were determined by GPC. The microstructure of the polymerization products was characterized by FTIR, ¹³C NMR and DSC techniques. The experimental results indicated that the polymerization activity of the reaction system and the molecular weight of the polymerization products gradually increased with the increase of the substitution content of m-cresol, namely, Al(OPhCH3)2Et > Al(OPhCH3)Et2 > Al(OPhCH3)0.5Et2.5>AlEt3. The 1,2-structure contents of the polymerization products could be adjusted between 89 and 91% through the control of the substitution of m-cresol, and there was minute quantities of crystalline structures in the resulting polymers due to the increasing content of the syndiotactic 1,2-polybutadiene. In a word, the existence and increase of steric hindrance of m-cresol made it easier for polymerization products to form interdisciplinary 1,2-structure.
Organic supporter poly(styrene-co-divinylbenzene) (PS-DVB) was synthesized, and gas-phase polymerization of 1,3-butadiene was performed with PS-DVB-supported Nd(vers)3/Al2Et3Cl3/Al(i-Bu)3 catalysts. Millimeter-sized granules of high cis-1,4 content (>98%) polybutadiene with an Mn of 5.3-5.5× 105 were obtained. Dispersants used in gas-phase polymerization of 1,3-butadiene have a significant influence on apparent activities of catalysts and appearance of products. The morphology of polybutadiene granules was also investigated by scanning electron microscopy.
