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2019 Volume 37 Issue 10
2019, 37(10): 943-950
doi: 10.1007/s10118-019-2298-9
Abstract:
(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(ORʹ)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3; Rʹ = 2,6-Me2C6H3, 2,6-iPr2C6H3, 2,6-F2C6H3, C6F5, C6Cl5] exhibited from moderate to remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene (NBE). The catalytic activities were affected by the ligand substituents, and V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6X5)(PMe3)2 (X ＝ F, Cl) demonstrated the exceptionally high catalytic activities for ROMP of NBE. The complexes polymerized cycloheptene (CHPE) and cis-cyclooctene (COE), and ROMP of COE by the OC6Cl5 analogue proceeded in a living manner even at 80 °C, and the activity increased with increasing the temperature up to 120 °C. Highly active catalysts for ROMP of cyclic olefins (NBE, cyclopentene, and CHPE) can be generated in situ by premixing isolated V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 with 1.0 equiv. of C6F5OH or C6Cl5OH via immediate phenoxy exchange; the activity was affected by the kind of phenol added [TOF in the ROMPs of NBE: 4.62 × 104 min–1 (upon addition of C6F5OH) versus 37.3 min–1 (none)].
(Imido)vanadium(V)-alkylidene complexes of type V(CHSiMe3)(NR)(ORʹ)(PMe3)2 [R = Ad, C6H5, 2,6-Me2C6H3, 2,6-Cl2C6H3; Rʹ = 2,6-Me2C6H3, 2,6-iPr2C6H3, 2,6-F2C6H3, C6F5, C6Cl5] exhibited from moderate to remarkable catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene (NBE). The catalytic activities were affected by the ligand substituents, and V(CHSiMe3)(N-2,6-Cl2C6H3)(OC6X5)(PMe3)2 (X ＝ F, Cl) demonstrated the exceptionally high catalytic activities for ROMP of NBE. The complexes polymerized cycloheptene (CHPE) and cis-cyclooctene (COE), and ROMP of COE by the OC6Cl5 analogue proceeded in a living manner even at 80 °C, and the activity increased with increasing the temperature up to 120 °C. Highly active catalysts for ROMP of cyclic olefins (NBE, cyclopentene, and CHPE) can be generated in situ by premixing isolated V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 with 1.0 equiv. of C6F5OH or C6Cl5OH via immediate phenoxy exchange; the activity was affected by the kind of phenol added [TOF in the ROMPs of NBE: 4.62 × 104 min–1 (upon addition of C6F5OH) versus 37.3 min–1 (none)].
2019, 37(10): 951-958
doi: 10.1007/s10118-019-2288-y
Abstract:
The synthesis of sulfur-containing polymer, a very promising functional material, has made a great progress in the past several years. This review is focused on the very recent advances in poly(monothiocarbonate)s derived from carbonyl sulfide (COS) and epoxides including biomass-derived epoxides. Of significance, metal-free catalyst systems, including triethyl borane/Lewis base pair and thiourea/Lewis base pair are developed for the alternating copolymerization of COS with epoxides. Thereof, the thiourea/Lewis base pair is highly active to the copolymerization of COS with epoxide in a living manner. Moreover, a series of crystalline poly(monothiocarbonate)s are presented, including the copolymers derived from COS with oxetane, ethylene oxide, enantiopure epichlorohydrin, and achiral meso-epoxides via enantioselective copolymerization. Based on these COS/epoxide copolymerization process, a variety of COS-based block copolymers with well-defined structure are presented.
The synthesis of sulfur-containing polymer, a very promising functional material, has made a great progress in the past several years. This review is focused on the very recent advances in poly(monothiocarbonate)s derived from carbonyl sulfide (COS) and epoxides including biomass-derived epoxides. Of significance, metal-free catalyst systems, including triethyl borane/Lewis base pair and thiourea/Lewis base pair are developed for the alternating copolymerization of COS with epoxides. Thereof, the thiourea/Lewis base pair is highly active to the copolymerization of COS with epoxide in a living manner. Moreover, a series of crystalline poly(monothiocarbonate)s are presented, including the copolymers derived from COS with oxetane, ethylene oxide, enantiopure epichlorohydrin, and achiral meso-epoxides via enantioselective copolymerization. Based on these COS/epoxide copolymerization process, a variety of COS-based block copolymers with well-defined structure are presented.
2019, 37(10): 959-965
doi: 10.1007/s10118-019-2227-y
Abstract:
Polymerizations of linear α-olefins (CnH2n, CH2＝CH―R, R = Cn−2) catalyzed by early transition metals typically afford amorphous polymers with alkyl chains (Cn−2), while chain-straightening polymerizations of α-olefins with nickel-based catalysts produce semicrystalline polyolefins. Polymerizations of various α-olefins were carried out using an α-diamine nickel catalyst with a significantly distorted chelating ring. The influences of temperature, monomer concentration, and chain length of α-olefins on polyolefin microstructure were examined in detail. The α-diamine nickel catalyst realized highly regioselective 2,1-insertion of α-olefins regardless of reaction temperature and monomer concentration. Increased chain length of α-olefins led to the formation of more linear polyolefin. Semicrystalline polyolefins with high melting temperatures (Tm) were made from α-olefins through highly regioselective 2,1-insertion and precise chain-straightening.
Polymerizations of linear α-olefins (CnH2n, CH2＝CH―R, R = Cn−2) catalyzed by early transition metals typically afford amorphous polymers with alkyl chains (Cn−2), while chain-straightening polymerizations of α-olefins with nickel-based catalysts produce semicrystalline polyolefins. Polymerizations of various α-olefins were carried out using an α-diamine nickel catalyst with a significantly distorted chelating ring. The influences of temperature, monomer concentration, and chain length of α-olefins on polyolefin microstructure were examined in detail. The α-diamine nickel catalyst realized highly regioselective 2,1-insertion of α-olefins regardless of reaction temperature and monomer concentration. Increased chain length of α-olefins led to the formation of more linear polyolefin. Semicrystalline polyolefins with high melting temperatures (Tm) were made from α-olefins through highly regioselective 2,1-insertion and precise chain-straightening.
2019, 37(10): 966-973
doi: 10.1007/s10118-019-2229-9
Abstract:
The molecular weight of a polymer is of prime importance and greatly influences the processing and mechanical properties of the polymer. Trans-1,4-poly(butadiene-co-isoprene) multi-block copolymer rubbers (TBIR) exhibit outstanding fatigue resistance, low heat build-up and good abrasion resistance, and are expected to be desirable candidate for high performance tire. Study on the influence of TBIR with different molecular weights on the structure and properties of TBIR and natural rubber (NR)/TBIR blends is essential to understand its contribution to the greatly improved dynamic properties of the rubber vulcanizates. TBIR with different molecular weights characterized by 1H-NMR, 13C-NMR, GPC, and DSC were highly trans-1,4-copolymers with similar chain sequence distribution and crystalline trans-1,4-polyisoprene (TPI) blocks. The green strength and modulus of TBIR increased with the increasing molecular weight. The NR/TBIR compounds filled with 40 phr carbon black were chemically cured by sulfur for the preparation of NR/TBIR vulcanizates. The compatibility between NR and TBIR, filler distribution, crosslinking bond and density, and properties of NR/TBIR vulcanizates were studied. The NR/TBIR vulcanizates showed increasing tensile strength, hardness, modulus, rebound, abrasion resistance, and flexural fatigue properties with increasing molecular weight of TBIR. Furthermore, they presented significant improvement in flexural fatigue resistance when compared with that of NR vulcanizate. The contribution mechanism of TBIR on the NR/TBIR blends was discussed. The TBIR with a wide range of molecular weight are ideal rubbers for high performance tires.
The molecular weight of a polymer is of prime importance and greatly influences the processing and mechanical properties of the polymer. Trans-1,4-poly(butadiene-co-isoprene) multi-block copolymer rubbers (TBIR) exhibit outstanding fatigue resistance, low heat build-up and good abrasion resistance, and are expected to be desirable candidate for high performance tire. Study on the influence of TBIR with different molecular weights on the structure and properties of TBIR and natural rubber (NR)/TBIR blends is essential to understand its contribution to the greatly improved dynamic properties of the rubber vulcanizates. TBIR with different molecular weights characterized by 1H-NMR, 13C-NMR, GPC, and DSC were highly trans-1,4-copolymers with similar chain sequence distribution and crystalline trans-1,4-polyisoprene (TPI) blocks. The green strength and modulus of TBIR increased with the increasing molecular weight. The NR/TBIR compounds filled with 40 phr carbon black were chemically cured by sulfur for the preparation of NR/TBIR vulcanizates. The compatibility between NR and TBIR, filler distribution, crosslinking bond and density, and properties of NR/TBIR vulcanizates were studied. The NR/TBIR vulcanizates showed increasing tensile strength, hardness, modulus, rebound, abrasion resistance, and flexural fatigue properties with increasing molecular weight of TBIR. Furthermore, they presented significant improvement in flexural fatigue resistance when compared with that of NR vulcanizate. The contribution mechanism of TBIR on the NR/TBIR blends was discussed. The TBIR with a wide range of molecular weight are ideal rubbers for high performance tires.
2019, 37(10): 974-980
doi: 10.1007/s10118-019-2232-1
Abstract:
A phenol-containing dibenzhydryl-based α-diimine ligand bearing hydroxy group on para-position of aniline moiety was designed, synthesized, and investigated in Ni- and Pd-catalyzed ethylene polymerization. The Ni complex bearing hydroxy groups resulted in not only high polyethylene molecular weight (Mn up to 1.5 × 106), but also significantly increased melting temperature (Tm up to 123 °C) and greatly decreased branching density (33/1000C) versus the Ni catalyst bearing OMe group on para-position of aniline moiety. This is consistent with the hypothesis that the deprotonation of the phenol moiety generated a phenoxide bearing strong electron-donating O− substituent by methylaluminoxane (MAO) cocatalyst. The Pd complexes bearing hydroxy groups exhibited similar catalytic properties to those of the Pd catalyst bearing OMe groups did.
A phenol-containing dibenzhydryl-based α-diimine ligand bearing hydroxy group on para-position of aniline moiety was designed, synthesized, and investigated in Ni- and Pd-catalyzed ethylene polymerization. The Ni complex bearing hydroxy groups resulted in not only high polyethylene molecular weight (Mn up to 1.5 × 106), but also significantly increased melting temperature (Tm up to 123 °C) and greatly decreased branching density (33/1000C) versus the Ni catalyst bearing OMe group on para-position of aniline moiety. This is consistent with the hypothesis that the deprotonation of the phenol moiety generated a phenoxide bearing strong electron-donating O− substituent by methylaluminoxane (MAO) cocatalyst. The Pd complexes bearing hydroxy groups exhibited similar catalytic properties to those of the Pd catalyst bearing OMe groups did.
2019, 37(10): 981-989
doi: 10.1007/s10118-019-2281-5
Abstract:
A series of new photodegradable poly(furan-amine)s (PFAs) were synthesized by a one-pot, catalyst-free, multicomponent cyclopolymerization between diisocyanides, dialkylacetylene dicarboxylates, and aromatic dialdehydes. All polymerizations were conducted in toluene at 100 °C for 6 h without inert gas protection and furnished polymers with a satisfactory molecular weight (Mw up to 32200) and yield. The PFA structure was confirmed by spectroscopic techniques, such as GPC, FTIR, and NMR, as well as by comparison with a model compound. The polymers exhibited good solubility in common organic solvents and thermal stability. All the PFAs had high refractive indices in the visible light region (400 nm to 800 nm). Moreover, the PFAs were substantially degraded by UV irradiation due to the presence of furan rings. The film thickness reduction rate could be over 90%.
A series of new photodegradable poly(furan-amine)s (PFAs) were synthesized by a one-pot, catalyst-free, multicomponent cyclopolymerization between diisocyanides, dialkylacetylene dicarboxylates, and aromatic dialdehydes. All polymerizations were conducted in toluene at 100 °C for 6 h without inert gas protection and furnished polymers with a satisfactory molecular weight (Mw up to 32200) and yield. The PFA structure was confirmed by spectroscopic techniques, such as GPC, FTIR, and NMR, as well as by comparison with a model compound. The polymers exhibited good solubility in common organic solvents and thermal stability. All the PFAs had high refractive indices in the visible light region (400 nm to 800 nm). Moreover, the PFAs were substantially degraded by UV irradiation due to the presence of furan rings. The film thickness reduction rate could be over 90%.
2019, 37(10): 990-994
doi: 10.1007/s10118-019-2318-9
Abstract:
Janus polymerization is featured as a combination of cationic and anionic growing ends in one living polymer chain. In the copolymerization of THF and CL catalyzed by lutetium triflates and initiated by propylene oxide, three stages are identified by kinetic study including (1) fast cationic polymerization with slow anionic one, (2) fast anionic polymerization with dormant cationic one, and (3) reactivation of cationic polymerization with coupling of anionic and cationic chain ends. In this work, density functional theory (DFT) calculation is employed to investigate the reaction details of ionic polymerization and dormancy. A " tripedal crow” configuration is proposed to illustrate the unique high-coordinated ligand exchange configuration in anionic polymerization in different stages. The trigger of dormancy is determined as chain structures rather than concentration of triflate anion according to both calculation and experimental results.
Janus polymerization is featured as a combination of cationic and anionic growing ends in one living polymer chain. In the copolymerization of THF and CL catalyzed by lutetium triflates and initiated by propylene oxide, three stages are identified by kinetic study including (1) fast cationic polymerization with slow anionic one, (2) fast anionic polymerization with dormant cationic one, and (3) reactivation of cationic polymerization with coupling of anionic and cationic chain ends. In this work, density functional theory (DFT) calculation is employed to investigate the reaction details of ionic polymerization and dormancy. A " tripedal crow” configuration is proposed to illustrate the unique high-coordinated ligand exchange configuration in anionic polymerization in different stages. The trigger of dormancy is determined as chain structures rather than concentration of triflate anion according to both calculation and experimental results.
2019, 37(10): 995-1004
doi: 10.1007/s10118-019-2295-z
Abstract:
Recently, we reported the first VOx/SiO2 ethylene polymerization catalyst for making Cl-free UHMWPE, and found the dominant promotion effects of Al-/Ti-/Zr-modifications over this catalyst system (Macromol. Chem. Phys. 2017, 218, 1600443). In this work, density functional theory is applied to investigate the underlying mechanism of this remarkable promotion effect of Al-/Ti-/Zr-modifications on a molecular and atomic level. The cluster model with V(III) is found to be the most possible active site due to its lowest overall energy barrier for monomer insertion, though the process of C2H4 coordination and the subsequent formation of transition state are most energy favored for V(II) species. By modifying one of or both V―O―Si in the active model with V―O―M (M ＝ Al, Ti, or Zr), the energy barrier for the binding of the upcoming C2H4 gets lower (particularly for Al- and Zr-modified catalysts), and the transition state also becomes more stable. Generally, the insertion process of C2H4 gets easier after support Al-/Ti-/Zr-modifications. This dominant promotion effect is partially ascribed to the more enriched positive charge distribution on or nearby the V center, and the narrower energy gap between the LUMO of model catalysts and the HOMO of C2H4 for these modified catalysts also contributes much. In addition, the decreased steric hindrance around the V center should be taken into account for the modified models as well. Furthermore, the Brønsted acidity of the catalysts is investigated by introducing a pendent hydroxyl group to the model catalysts, which has a close contact with the V center. Similar promotion effect of support modification by Al, Ti, and Zr could still be observed.
Recently, we reported the first VOx/SiO2 ethylene polymerization catalyst for making Cl-free UHMWPE, and found the dominant promotion effects of Al-/Ti-/Zr-modifications over this catalyst system (Macromol. Chem. Phys. 2017, 218, 1600443). In this work, density functional theory is applied to investigate the underlying mechanism of this remarkable promotion effect of Al-/Ti-/Zr-modifications on a molecular and atomic level. The cluster model with V(III) is found to be the most possible active site due to its lowest overall energy barrier for monomer insertion, though the process of C2H4 coordination and the subsequent formation of transition state are most energy favored for V(II) species. By modifying one of or both V―O―Si in the active model with V―O―M (M ＝ Al, Ti, or Zr), the energy barrier for the binding of the upcoming C2H4 gets lower (particularly for Al- and Zr-modified catalysts), and the transition state also becomes more stable. Generally, the insertion process of C2H4 gets easier after support Al-/Ti-/Zr-modifications. This dominant promotion effect is partially ascribed to the more enriched positive charge distribution on or nearby the V center, and the narrower energy gap between the LUMO of model catalysts and the HOMO of C2H4 for these modified catalysts also contributes much. In addition, the decreased steric hindrance around the V center should be taken into account for the modified models as well. Furthermore, the Brønsted acidity of the catalysts is investigated by introducing a pendent hydroxyl group to the model catalysts, which has a close contact with the V center. Similar promotion effect of support modification by Al, Ti, and Zr could still be observed.
2019, 37(10): 1005-1014
doi: 10.1007/s10118-019-2309-x
Abstract:
To achieve the red-shifted absorptions and appropriate energy levels of A-D-A type non-fullerene acceptors (NFAs), in this work, we design and synthesize two new NFAs, named TPDCIC and TPDCNC, whose electron-donating (D) unit is constructed by a thieno[3,4-c]pyrrole-4,6-dione (TPD) core attached to two cyclopentadithiophene (CPDT) moieties at both sides, and the electron-accepting (A) end-groups are 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) and 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile (NC), respectively. Benefiting from TPD core, which easily forms quinoid structure and O···H or O···S intramolecular noncovalent interactions, TPDCIC and TPDCNC show more delocalization of π-electrons and perfect planar molecular geometries, giving the absorption ranges extended to 822 and 852 nm, respectively. Furthermore, the highest occupied molecular orbital (HOMO) levels of TPDCIC and TPDCNC remain relatively low-lying due to the electronegativity of the carbonyl groups on TPD core. Considering that the absorptions and energy levels of the two NFAs match well with those of a widely used polymer donor, PBDB-T, we fabricate two kinds of organic solar cells (OSCs) based on the PBDB-T:TPDCIC and PBDB-T:TPDCNC blended films, respectively. Through a series of optimizations, the TPDCIC-based devices yield an impressing power conversion efficiency (PCE) of 10.12% with a large short-circuit current density (JSC) of 18.16 mA·cm−2, and the TPDCNC-based ones exhibit a comparable PCE of 9.80% with a JSC of 17.40 mA·cm−2. Our work is the first report of the TPD-core-based A-D-A type NFAs, providing a good reference for the molecular design of high-performance NFAs.
To achieve the red-shifted absorptions and appropriate energy levels of A-D-A type non-fullerene acceptors (NFAs), in this work, we design and synthesize two new NFAs, named TPDCIC and TPDCNC, whose electron-donating (D) unit is constructed by a thieno[3,4-c]pyrrole-4,6-dione (TPD) core attached to two cyclopentadithiophene (CPDT) moieties at both sides, and the electron-accepting (A) end-groups are 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (IC) and 2-(3-oxo-2,3-dihydro-1H-cyclopenta[b]naphthalen-1-ylidene)malononitrile (NC), respectively. Benefiting from TPD core, which easily forms quinoid structure and O···H or O···S intramolecular noncovalent interactions, TPDCIC and TPDCNC show more delocalization of π-electrons and perfect planar molecular geometries, giving the absorption ranges extended to 822 and 852 nm, respectively. Furthermore, the highest occupied molecular orbital (HOMO) levels of TPDCIC and TPDCNC remain relatively low-lying due to the electronegativity of the carbonyl groups on TPD core. Considering that the absorptions and energy levels of the two NFAs match well with those of a widely used polymer donor, PBDB-T, we fabricate two kinds of organic solar cells (OSCs) based on the PBDB-T:TPDCIC and PBDB-T:TPDCNC blended films, respectively. Through a series of optimizations, the TPDCIC-based devices yield an impressing power conversion efficiency (PCE) of 10.12% with a large short-circuit current density (JSC) of 18.16 mA·cm−2, and the TPDCNC-based ones exhibit a comparable PCE of 9.80% with a JSC of 17.40 mA·cm−2. Our work is the first report of the TPD-core-based A-D-A type NFAs, providing a good reference for the molecular design of high-performance NFAs.
2019, 37(10): 1015-1022
doi: 10.1007/s10118-019-2310-4
Abstract:
The performances of lithium-ion batteries (LIBs) are dependent on the wettability and stability of porous separators. Mussel-inspired coatings seem to be useful to improve the surface wettability of commercialized polyolefin separators. However, it is still a challenge to guarantee their stability under polar electrolytes. Herein, we report a facile and versatile way to enhance the wettability and stability of polypropylene separators by constructing robust polydopamine (PDA) coatings triggered with CuSO4/H2O2. These coatings were conveniently deposited on the polypropylene separator surfaces and the PDA-coated separators exhibited the improved surface wettability and thermal stability. The electrolyte uptake increased nearly two folds from the pristine separator to the modified ones. Correspondingly, the ionic conductivity also rose from 0.82 mS·cm–1 to 1.30 mS·cm–1. Most importantly, the CuSO4/H2O2-triggered PDA coatings were very stable under strong polar electrolytes, endowing the cells with excellent cycle performance and enhanced C-rate capacity. Overall, the results unequivocally demonstrate that application of PDA coatings on polyolefin separator triggered by CuSO4/H2O2 is a facile and efficient method for improving the wettability and stability of separators for high LIBs performance.
The performances of lithium-ion batteries (LIBs) are dependent on the wettability and stability of porous separators. Mussel-inspired coatings seem to be useful to improve the surface wettability of commercialized polyolefin separators. However, it is still a challenge to guarantee their stability under polar electrolytes. Herein, we report a facile and versatile way to enhance the wettability and stability of polypropylene separators by constructing robust polydopamine (PDA) coatings triggered with CuSO4/H2O2. These coatings were conveniently deposited on the polypropylene separator surfaces and the PDA-coated separators exhibited the improved surface wettability and thermal stability. The electrolyte uptake increased nearly two folds from the pristine separator to the modified ones. Correspondingly, the ionic conductivity also rose from 0.82 mS·cm–1 to 1.30 mS·cm–1. Most importantly, the CuSO4/H2O2-triggered PDA coatings were very stable under strong polar electrolytes, endowing the cells with excellent cycle performance and enhanced C-rate capacity. Overall, the results unequivocally demonstrate that application of PDA coatings on polyolefin separator triggered by CuSO4/H2O2 is a facile and efficient method for improving the wettability and stability of separators for high LIBs performance.
2019, 37(10): 1023-1030
doi: 10.1007/s10118-019-2319-8
Abstract:
Propylene slurry polymerization with a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was conducted after different durations of pre-contact of the catalyst with triethylaluminum cocatalyst. The number of active centers ([C*]/[Ti]) was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and measuring sulfur content in the polymer. The pre-contact treatment caused selective deactivation of a part of active centers with low stereoselectivity and much lower activity in the initial stage of polymerization as compared with the polymerization run without the pre-contact stage. The active center concentration and polymerization activity decreased with prolonging of the pre-contact stage. The proportion of stereoselective active centers was increased by prolonging the pre-contact stage, so the isotacticity of produced polypropylene was enhanced. Release of active centers through catalyst particle fragmentation was significantly retarded, and the polymerization rate curve changed from decay type to induction type by the pre-contact treatment. In the induction period both non-stereoselective and stereoselective active centers were released and activated, resulting in gradual reduction of the polymer’s isotacticity in the first 5−10 min of polymerization. Selective deactivation of non-stereoselective active centers also took place in propylene polymerization using the catalyst without pre-contacting with the cocatalyst. In this case, the polymerization rate decayed with time after a short induction period of 2−5 min. Over reduction of the active center precursors with low stereoselectivity by triethylaluminum was considered as the reason for their deactivation during the pre-contact or the polymerization processes.
Propylene slurry polymerization with a MgCl2-supported Ziegler-Natta catalyst containing internal electron donor was conducted after different durations of pre-contact of the catalyst with triethylaluminum cocatalyst. The number of active centers ([C*]/[Ti]) was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and measuring sulfur content in the polymer. The pre-contact treatment caused selective deactivation of a part of active centers with low stereoselectivity and much lower activity in the initial stage of polymerization as compared with the polymerization run without the pre-contact stage. The active center concentration and polymerization activity decreased with prolonging of the pre-contact stage. The proportion of stereoselective active centers was increased by prolonging the pre-contact stage, so the isotacticity of produced polypropylene was enhanced. Release of active centers through catalyst particle fragmentation was significantly retarded, and the polymerization rate curve changed from decay type to induction type by the pre-contact treatment. In the induction period both non-stereoselective and stereoselective active centers were released and activated, resulting in gradual reduction of the polymer’s isotacticity in the first 5−10 min of polymerization. Selective deactivation of non-stereoselective active centers also took place in propylene polymerization using the catalyst without pre-contacting with the cocatalyst. In this case, the polymerization rate decayed with time after a short induction period of 2−5 min. Over reduction of the active center precursors with low stereoselectivity by triethylaluminum was considered as the reason for their deactivation during the pre-contact or the polymerization processes.
2019, 37(10): 1031-1038
doi: 10.1007/s10118-019-2335-8
Abstract:
Ziegler-Natta precatalysts were synthetized from Lewis-base-modified-MgCl2 supports and treated by various Lewis acids, prior to activation by triethylaluminum, in order to increase their activity in ethylene polymerization. BCl3 provided the highest increase in activity. Interestingly, polymerization results showed no substantial modification of polymer properties, which is consistent with that Lewis acid only promotes the creation of new active sites, after activation by TEA, possessing very similar features to the original ones achievable with conventional precatalysts (i.e. without Lewis-acid treatment).
Ziegler-Natta precatalysts were synthetized from Lewis-base-modified-MgCl2 supports and treated by various Lewis acids, prior to activation by triethylaluminum, in order to increase their activity in ethylene polymerization. BCl3 provided the highest increase in activity. Interestingly, polymerization results showed no substantial modification of polymer properties, which is consistent with that Lewis acid only promotes the creation of new active sites, after activation by TEA, possessing very similar features to the original ones achievable with conventional precatalysts (i.e. without Lewis-acid treatment).
2019, 37(10): 1039-1044
doi: 10.1007/s10118-019-2334-9
Abstract:
Electric conductivity and rheological responses of colloidal electrolytes consisting of lithium bis(trifluoromethanesulfon) imide, polyethylene glycol (PEG) oligomer, and fumed silica have been investigated. Incorporating silica could improve ionic conductivity of the electrolytes at the same lithium/oxygen ratios. The colloidal electrolytes demonstrate a sol to gel transition with increasing silica content while they exhibit shear thickening behaviors during steady flow at intermediate range of strain rate. The presence of lithium salt, on the one hand, could lower the crystallinity of PEG or forbid the crystallization and on the other hand, interferes the chain adsorption on the surface of silica. Furthermore, lithium salt strongly retards the segmental relaxation of PEG in the colloidal electrolytes.
Electric conductivity and rheological responses of colloidal electrolytes consisting of lithium bis(trifluoromethanesulfon) imide, polyethylene glycol (PEG) oligomer, and fumed silica have been investigated. Incorporating silica could improve ionic conductivity of the electrolytes at the same lithium/oxygen ratios. The colloidal electrolytes demonstrate a sol to gel transition with increasing silica content while they exhibit shear thickening behaviors during steady flow at intermediate range of strain rate. The presence of lithium salt, on the one hand, could lower the crystallinity of PEG or forbid the crystallization and on the other hand, interferes the chain adsorption on the surface of silica. Furthermore, lithium salt strongly retards the segmental relaxation of PEG in the colloidal electrolytes.
