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2017 Volume 35 Issue 12
2017, 35(12):
Abstract:
2017, 35(12): 1447-1456
doi: 10.1007/s10118-017-2003-9
Abstract:
Conjugated block copolymers have gained increasing interests in recent years. Development of a novel method for facile synthesis of conjugated block copolymers with desired structures and functions is greatly desired. In this mini review, we summarized the recent advances in one-pot synthesis of conjugated block copolymers containing π-conjugated polythiophene and helical polyisocyanide segments by using a nickel(Ⅱ) complex as single catalyst. The sequential living polymerization of the two monomers proceeded in a controlled manner, affording expected block copolymers in high yields with controlled molecular weights (Mns) and narrow molecular weight distributions (Mw/Mns). By using this method, a family of block copolymers with expected structure and tunable compositions can be facilely prepared. Introducing functional groups onto the pendant, these block copolymers can exhibit interesting self-assembly property, tunable light emission and multi-responsiveness.
Conjugated block copolymers have gained increasing interests in recent years. Development of a novel method for facile synthesis of conjugated block copolymers with desired structures and functions is greatly desired. In this mini review, we summarized the recent advances in one-pot synthesis of conjugated block copolymers containing π-conjugated polythiophene and helical polyisocyanide segments by using a nickel(Ⅱ) complex as single catalyst. The sequential living polymerization of the two monomers proceeded in a controlled manner, affording expected block copolymers in high yields with controlled molecular weights (Mns) and narrow molecular weight distributions (Mw/Mns). By using this method, a family of block copolymers with expected structure and tunable compositions can be facilely prepared. Introducing functional groups onto the pendant, these block copolymers can exhibit interesting self-assembly property, tunable light emission and multi-responsiveness.
2017, 35(12): 1457-1462
doi: 10.1007/s10118-017-1996-4
Abstract:
A D-A copolymer, P2FBTTPTI, was developed by copolymerizing a pentacyclic acceptor unit, thieno[2', 3':5, 6]pyrido[3, 4-g]thieno[3, 2-c]isoquinoline-5, 11(4H, 10H)-dione (TPTI), with 3, 3'-difluoro-2, 2'-bithiophene (2FBT). P2FBTTPTI possessed a low highest occupied molecular orbital (HOMO) energy level (-5.50 eV) and a good hole mobility (4.14×10-4 cm2·V-1·s-1). P2FBTTPTI:PC71BM solar cells gave a decent power conversion efficiency (PCE) of 7.64% and a high open-circuit voltage (Voc) of 0.95 V.
A D-A copolymer, P2FBTTPTI, was developed by copolymerizing a pentacyclic acceptor unit, thieno[2', 3':5, 6]pyrido[3, 4-g]thieno[3, 2-c]isoquinoline-5, 11(4H, 10H)-dione (TPTI), with 3, 3'-difluoro-2, 2'-bithiophene (2FBT). P2FBTTPTI possessed a low highest occupied molecular orbital (HOMO) energy level (-5.50 eV) and a good hole mobility (4.14×10-4 cm2·V-1·s-1). P2FBTTPTI:PC71BM solar cells gave a decent power conversion efficiency (PCE) of 7.64% and a high open-circuit voltage (Voc) of 0.95 V.
2017, 35(12): 1463-1473
doi: 10.1007/s10118-017-1994-6
Abstract:
o-Carborane-containing poly(hydroxy ethers) (P1, P2 and P3) were synthesized via "advancement reaction" of o-carborane-containing bisphenol (4) and diglycidyl ether of bisphenols (DGEBA and 1). FTIR and 1H-, 13C-, and 11B-NMR were utilized to characterize the obtained polymers. TGA test was conducted under nitrogen and air. It is found that the shielding effect of carborane moiety on its adjacent aromatic structures contributes to high initial decomposition temperatures, while oxygen in air has an adverse effect on the initial decomposition temperature. The oxygen can combine with polymer chain to form peroxide and hydroperoxide groups, which are more reactive during the degradation process. Besides, o-carborane-containing poly(hydroxy ethers) have high char yield at elevated temperatures. The boron atom combines with oxygen from the polymer structure or/and from air, thus to form a three-dimensional network linked with B-O-B and B-C bonds, and retain the polymer weight to a large extent.
o-Carborane-containing poly(hydroxy ethers) (P1, P2 and P3) were synthesized via "advancement reaction" of o-carborane-containing bisphenol (4) and diglycidyl ether of bisphenols (DGEBA and 1). FTIR and 1H-, 13C-, and 11B-NMR were utilized to characterize the obtained polymers. TGA test was conducted under nitrogen and air. It is found that the shielding effect of carborane moiety on its adjacent aromatic structures contributes to high initial decomposition temperatures, while oxygen in air has an adverse effect on the initial decomposition temperature. The oxygen can combine with polymer chain to form peroxide and hydroperoxide groups, which are more reactive during the degradation process. Besides, o-carborane-containing poly(hydroxy ethers) have high char yield at elevated temperatures. The boron atom combines with oxygen from the polymer structure or/and from air, thus to form a three-dimensional network linked with B-O-B and B-C bonds, and retain the polymer weight to a large extent.
2017, 35(12): 1474-1487
doi: 10.1007/s10118-017-1999-1
Abstract:
A series of (SiO2/MgO/ID/MgCl2)·TiClx Ziegler-Natta catalysts for propylene polymerization has been prepared with a new method. These catalysts were synthesized using soluble Mg-compounds as the Mg-source and the preparation progress was relatively simple. The catalyst could copy the spherical shape of the carrier very well. The propylene polymerization results showed that the catalyst revealed the best activity with 9, 9-di(methoxymethyl)fluorene (BMMF) as internal donor at 50 ℃ with the optimal molar ratio Al/Ti=5, which was much lower than what the industrial polypropylene catalyst used (at least molar ratio Al/Ti=100), resulting in great cost saving. Additionally, the polymerization kinetics of the catalyst exhibited very stable property after achieving a relatively high value. These catalysts possessed rather high activity and good hydrogen response. The isotactic index (Ⅱ) value of the PP products could be higher than 98% in the presence of both internal and external electron donors. Moreover, temperature rising elution fractionation method was used to understand the influence of donors and H2 on the properties of the PP products.
A series of (SiO2/MgO/ID/MgCl2)·TiClx Ziegler-Natta catalysts for propylene polymerization has been prepared with a new method. These catalysts were synthesized using soluble Mg-compounds as the Mg-source and the preparation progress was relatively simple. The catalyst could copy the spherical shape of the carrier very well. The propylene polymerization results showed that the catalyst revealed the best activity with 9, 9-di(methoxymethyl)fluorene (BMMF) as internal donor at 50 ℃ with the optimal molar ratio Al/Ti=5, which was much lower than what the industrial polypropylene catalyst used (at least molar ratio Al/Ti=100), resulting in great cost saving. Additionally, the polymerization kinetics of the catalyst exhibited very stable property after achieving a relatively high value. These catalysts possessed rather high activity and good hydrogen response. The isotactic index (Ⅱ) value of the PP products could be higher than 98% in the presence of both internal and external electron donors. Moreover, temperature rising elution fractionation method was used to understand the influence of donors and H2 on the properties of the PP products.
2017, 35(12): 1488-1496
doi: 10.1007/s10118-017-1976-8
Abstract:
Polymer chain ends play an important role in the glassy dynamics of polymeric materials. In this study, a combination of single molecule defocus fluorescence microscopy and well-controlled atom transfer radical polymerization was used to investigate site-dependent segmental mobility of poly(n-butyl methacrylate). As the temperature increased, the rotation of fluorophores, which were selectively labelled in chain end and chain middle, was gradually activated. The power spectra of rotation trajectories, the distribution of angular displacement as well as the population of rotating fluorophores demonstrated that the local dynamics was more activated at the chain ends than the middles, showing the unique contribution of the chain end to the dynamics of the system.
Polymer chain ends play an important role in the glassy dynamics of polymeric materials. In this study, a combination of single molecule defocus fluorescence microscopy and well-controlled atom transfer radical polymerization was used to investigate site-dependent segmental mobility of poly(n-butyl methacrylate). As the temperature increased, the rotation of fluorophores, which were selectively labelled in chain end and chain middle, was gradually activated. The power spectra of rotation trajectories, the distribution of angular displacement as well as the population of rotating fluorophores demonstrated that the local dynamics was more activated at the chain ends than the middles, showing the unique contribution of the chain end to the dynamics of the system.
2017, 35(12): 1497-1507
doi: 10.1007/s10118-017-1985-7
Abstract:
In this article, hybrid fillers with different dimensions, namely, 2-dimensional (2-D) expanded graphite (EG) and 1-dimensional (1-D) multi-walled carbon nanotubes (CNTs), were added to aromatic nylon MXD6 matrix via melt-blending, to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness (EMI SE). For ternary composites of MXD6/EG/CNTs, the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample, which turned the polymer-based composites from an insulator to a conductor, and the thermal conductivity has been enhanced by 477% compared with that of neat MXD6 sample. Meanwhile, the EMI SE of ternary composite reaches~50 dB at the overall filler loading of only 18 wt%. This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.
In this article, hybrid fillers with different dimensions, namely, 2-dimensional (2-D) expanded graphite (EG) and 1-dimensional (1-D) multi-walled carbon nanotubes (CNTs), were added to aromatic nylon MXD6 matrix via melt-blending, to enhance its thermal and electrical conductivity as well as electromagnetic interference shielding effectiveness (EMI SE). For ternary composites of MXD6/EG/CNTs, the electrical conductivity reaches up nine orders of magnitude higher compared to that of the neat MXD6 sample, which turned the polymer-based composites from an insulator to a conductor, and the thermal conductivity has been enhanced by 477% compared with that of neat MXD6 sample. Meanwhile, the EMI SE of ternary composite reaches~50 dB at the overall filler loading of only 18 wt%. This work can provide guidance for the preparation of polymer composites with excellent thermal and electrical conductivity via using hybrid filler.
2017, 35(12): 1508-1516
doi: 10.1007/s10118-017-2000-z
Abstract:
A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.
A setup of blown film machine combined with in situ synchrotron radiation X-ray diffraction measurements and infrared temperature testing is reported to study the structure evolution of polymers during film blowing. Two homemade auto-lifters are constructed and placed under the blown machine at each end of the beamline platform which move up and down with a speed of 0.05 mm/s bearing the 200 kg weight machine. Therefore, structure development and temperature changes as a function of position on the film bubble can be obtained. The blown film machine is customized to be conveniently installed with precise servo motors and can adjust the processing parameters in a wide range. Meanwhile, the air ring has been redesigned in order to track the structure information of the film bubble immediately after the melt being extruded out from the die exit. Polyethylene (PE) is selected as a model system to verify the feasibility of the apparatus and the in situ experimental techniques. Combining structure information provided by the WAXD and SAXS and the actual temperature obtained from the infrared probe, a full roadmap of structure development during film blowing is constructed and it is helpful to explore the molecular mechanism of structure evolution behind the film blowing processing, which is expected to lead to a better understanding of the physics in polymer processing.
2017, 35(12): 1517-1523
doi: 10.1007/s10118-017-1993-7
Abstract:
The influence of cyanuric acid (CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(ε-caprolactone) (PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.
The influence of cyanuric acid (CA) as an efficient nucleating agent on the crystallization behavior and morphology of biodegradable poly(ε-caprolactone) (PCL) was extensively studied in this work with several techniques for the first time. The nonisothermal melt crystallization behavior and overall isothermal melt crystallization rate of PCL were significantly enhanced by only a small amount of CA. The addition of CA apparently improved the nonisothermal melt crystallization peak temperature, overall isothermal melt crystallization rate, and nucleation density of PCL spherulites, but did not modify the crystallization mechanism and crystal structure of PCL, indicating that CA was an efficient nucleating agent for the crystallization of PCL. The possible nucleation mechanism of CA on the crystallization of PCL was also discussed on the basis of their crystal structures.
2017, 35(12): 1524-1539
doi: 10.1007/s10118-017-1980-z
Abstract:
The variation of phase morphology, critical temperature of demixing, and molecular dynamics for polystyrene/poly(vinyl methyl ether) (PS/PVME) blends induced by hydrophilic nanosilica (A200) or hydrophobic nanosilica (R974) was investigated. With the phase separation of blend matrix, A200 migrated into PVME-rich phase due to strong interaction between A200 and PVME, while R974 moved into PS-rich phase. The thermodynamic miscibility and concentration fluctuation during phase separation of blend matrix were remarkably retarded by A200 nanoparticles due to the surface adsorption of PVME on A200, verified by the correlation length ξ near the critical region from rheological measurement and the weakened increment of reversing heat capacity (ΔCp) during glass transition via modulated differential scanning calorimetry (MDSC). The restricted chain diffusion induced by nanosilica still occurred despite no influence of A200 and R974 on the segmental dynamics of homogenous blend matrix. The interactions between nanosilica and polymer components could restrict the terminal relaxation of blend matrix and further manipulate their phase behavior.
The variation of phase morphology, critical temperature of demixing, and molecular dynamics for polystyrene/poly(vinyl methyl ether) (PS/PVME) blends induced by hydrophilic nanosilica (A200) or hydrophobic nanosilica (R974) was investigated. With the phase separation of blend matrix, A200 migrated into PVME-rich phase due to strong interaction between A200 and PVME, while R974 moved into PS-rich phase. The thermodynamic miscibility and concentration fluctuation during phase separation of blend matrix were remarkably retarded by A200 nanoparticles due to the surface adsorption of PVME on A200, verified by the correlation length ξ near the critical region from rheological measurement and the weakened increment of reversing heat capacity (ΔCp) during glass transition via modulated differential scanning calorimetry (MDSC). The restricted chain diffusion induced by nanosilica still occurred despite no influence of A200 and R974 on the segmental dynamics of homogenous blend matrix. The interactions between nanosilica and polymer components could restrict the terminal relaxation of blend matrix and further manipulate their phase behavior.
2017, 35(12): 1540-1551
doi: 10.1007/s10118-017-1990-x
Abstract:
In our current work, the effect of the shear temperature on the growth of β-crystal in isotactic polypropylene (iPP) with β-nucleating agent is investigated by means of in situ two-dimensional wide-angle X-ray diffraction (2D-WAXD). At low shear temperatures, the formed shear-induced oriented precursors are hard to relax back to random coiled state due to the weak mobility of molecular chains. Therefore, plenty of oriented α-crystals are induced by shear-induced oriented precursors, while β-crystal is greatly depressed. As the shear temperature increases, oriented β-crystal gradually increases along with the decrease of α-crystal. It is deduced that the shear temperature at which the content of β-crystal increases to the (maximum) value found in quiescent crystallization is almost the same as that at which the accelerating effect of flow on crystallization kinetics is completely erased. Our work manifests its significance in regulating β-crystal and thus in the structure and property manipulation of iPP.
In our current work, the effect of the shear temperature on the growth of β-crystal in isotactic polypropylene (iPP) with β-nucleating agent is investigated by means of in situ two-dimensional wide-angle X-ray diffraction (2D-WAXD). At low shear temperatures, the formed shear-induced oriented precursors are hard to relax back to random coiled state due to the weak mobility of molecular chains. Therefore, plenty of oriented α-crystals are induced by shear-induced oriented precursors, while β-crystal is greatly depressed. As the shear temperature increases, oriented β-crystal gradually increases along with the decrease of α-crystal. It is deduced that the shear temperature at which the content of β-crystal increases to the (maximum) value found in quiescent crystallization is almost the same as that at which the accelerating effect of flow on crystallization kinetics is completely erased. Our work manifests its significance in regulating β-crystal and thus in the structure and property manipulation of iPP.
2017, 35(12): 1552-1560
doi: 10.1007/s10118-017-1986-6
Abstract:
Differential scanning calorimetry (DSC) has been widely applied to study crystallization and melting of materials. However, for polymeric lamellar crystals, the melting thermogram during heating process usually exhibits a broad endothermic peak or even multiple endotherms, which may result from changes of metastability via recrystallization process. Sometimes, the recrystallization exotherm cannot be observed due to its overlapping with the melting endotherm. In this work, we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly(butylene succinate) (PBS) crystals. With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior. The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature. For instance, PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon. High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not exhibit observable recrystallization behavior. Furthermore, the melting endotherms were fitted via the melting kinetics equations. The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range, which is attributed to the different degrees of stabilization. Finally, the mechanism of melting-recrystallization is briefly discussed. We propose that apparent melt-recrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier.
Differential scanning calorimetry (DSC) has been widely applied to study crystallization and melting of materials. However, for polymeric lamellar crystals, the melting thermogram during heating process usually exhibits a broad endothermic peak or even multiple endotherms, which may result from changes of metastability via recrystallization process. Sometimes, the recrystallization exotherm cannot be observed due to its overlapping with the melting endotherm. In this work, we employed a step heating procedure consisting of successive heating and temperature holding stages to measure the metastability of isothermally crystallized poly(butylene succinate) (PBS) crystals. With this approach we could gain the fraction of crystals melted at different temperature ranges and quantitatively detect the melting-recrystallization behavior. The melting-recrystallization behavior depends on the polymer chain structure and the crystallization temperature. For instance, PBS block copolymer hardly shows recrystallization behavior while PBS oligomer and high molecular weight PBS homopolymer demonstrate remarkable melting-recrystallization phenomenon. High molecular weight PBS isothermally crystallized in the low temperature range shows multiple melting-recrystallization while those isothermally crystallized at elevated temperatures do not exhibit observable recrystallization behavior. Furthermore, the melting endotherms were fitted via the melting kinetics equations. The original isothermally crystallized lamellae demonstrate quite different melting kinetics from the recrystallized lamellar crystals that melt at the highest temperature range, which is attributed to the different degrees of stabilization. Finally, the mechanism of melting-recrystallization is briefly discussed. We propose that apparent melt-recrystallization phenomenon be observed when melting of preformed lamellar crystals and recrystallization of thicker lamellae have similar free energy barrier.
2017, 35(12): 1561-1571
doi: 10.1007/s10118-017-1992-8
Abstract:
A series of polymer blends were prepared from 1, 3-bis(3, 4-dicyanophenoxy)benzene (3BOCN) and epoxy resin with methyl tetrahydrophthalic anhydride as curing agent. The curing behavior and curing kinetics of the blends were studied by differential scanning calorimetry. The apparent activation energy of the blends with various contents of 3BOCN was higher than that of the blends without 3BOCN. A model experiment suggested that there is no obvious reaction between phthalonitrile and epoxy. The thermal and mechanical properties of the polymer blends were evaluated. The polymer blends exhibit high storage modulus and char yield compared with the neat epoxy. The polymer blends show ductile fracture morphology by scanning electron microscopy (SEM) images.
A series of polymer blends were prepared from 1, 3-bis(3, 4-dicyanophenoxy)benzene (3BOCN) and epoxy resin with methyl tetrahydrophthalic anhydride as curing agent. The curing behavior and curing kinetics of the blends were studied by differential scanning calorimetry. The apparent activation energy of the blends with various contents of 3BOCN was higher than that of the blends without 3BOCN. A model experiment suggested that there is no obvious reaction between phthalonitrile and epoxy. The thermal and mechanical properties of the polymer blends were evaluated. The polymer blends exhibit high storage modulus and char yield compared with the neat epoxy. The polymer blends show ductile fracture morphology by scanning electron microscopy (SEM) images.
2017, 35(12): 1572-1586
doi: 10.1007/s10118-017-2001-y
Abstract:
A series of mixed, random cylindrical brush copolymers bearing polystyrene (PS) and poly(ε-caprolactone) (PCL) side chains were synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). These novel cylindrical brush copolymers have been characterized by means of nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). It was found that the mikto-armed cylindrical brush copolymers were microphase-separated in bulks and that the morphologies were dependent on the mass ratios of PS to PCL side chains. One of the cylindrical brush copolymers was employed to incorporate into epoxy thermoset to investigate effect of the mikto-armed cylindrical brush architecture on the reaction-induced microphase separation behavior. Depending on the concentration of the cylindrical brush in epoxy, the thermosets can display the morphologies with the spherical, worm-like and lamellar PS microdomains dispersing in continuous thermosetting matrices.
A series of mixed, random cylindrical brush copolymers bearing polystyrene (PS) and poly(ε-caprolactone) (PCL) side chains were synthesized via the combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). These novel cylindrical brush copolymers have been characterized by means of nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). It was found that the mikto-armed cylindrical brush copolymers were microphase-separated in bulks and that the morphologies were dependent on the mass ratios of PS to PCL side chains. One of the cylindrical brush copolymers was employed to incorporate into epoxy thermoset to investigate effect of the mikto-armed cylindrical brush architecture on the reaction-induced microphase separation behavior. Depending on the concentration of the cylindrical brush in epoxy, the thermosets can display the morphologies with the spherical, worm-like and lamellar PS microdomains dispersing in continuous thermosetting matrices.
