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2018 Volume Issue 9
2018, 0(9): 1141-1143
doi: 10.11777/j.issn1000-3304.2018.18181
Abstract:
Tandem cell is an effective strategy to obtain high efficiency organic solar cells (OSCs), which could address the issues of the absorption limitation and thermalization loss of single junction OSCs. Recently, a tandem cell with a breakthrough power conversion efficiency of 17.3% was reported, in which two subcells with efficient, complementary absorptions were used. The results demonstrate that OSC would achieve comparable efficiency in contrast to other photovoltaic cells through suitable materials design and device optimization in future.
Tandem cell is an effective strategy to obtain high efficiency organic solar cells (OSCs), which could address the issues of the absorption limitation and thermalization loss of single junction OSCs. Recently, a tandem cell with a breakthrough power conversion efficiency of 17.3% was reported, in which two subcells with efficient, complementary absorptions were used. The results demonstrate that OSC would achieve comparable efficiency in contrast to other photovoltaic cells through suitable materials design and device optimization in future.
2018, 0(9): 1144-1154
doi: 10.11777/j.issn1000-3304.2018.18101
Abstract:
Sequence-controlled polymers are those with ordered units along their chains. The precision sequence of biological polymers, such as nucleic acid and peptides, plays a crucial role on physiological and sophisticated functions. Inspired by this, the synthesis of sequence-controlled polymers, that is, the placement of specific functional groups at desired positions on the polymer chain, has become one of the ultimate goals of polymer chemists, and received increasing attention in recent years. Up to date, there are a variety of methods to synthesize sequence-controlled polymers based on the step-growth and chain-growth polymerization mechanisms. Compared to the step-growth polymerization, the chain-growth polymerization is much more challenging to achieve sequence-controlled polymers because of the high activity and low propagating selectivity of the growing active center. Therefore, sequence-controlled polymerization is also considered as the " Holy Grail” in the field of polymer synthesis. Although a variety of methods have been developed to regulate polymer sequences, the pursuit of simple and efficient methods toward sequence-controlled polymerization has never stopped. This feature article summarizes the recent progresses on the synthesis of sequence-controlled polymers, and highlights our group’s research in this area. Firstly, we built " supramolecular monomer” by exploiting the weak intermolecular hydrogen-bond interactions to create sequences with alternating feature. We also developed a " latent monomer” strategy based on the temperature-dependent furan/maleimide Diels-Alder reaction, and diverse sequence-controlled polymers were thus readily created. Moreover, a novel chemical route, based on orthogonal chain end deprotection and thiol-maleimide Michael addition, was developed in our group toward the monodisperse and sequence-defined polymers. Finally, the potential applications of the sequence-controlled polymers are also summarized and prospected.
Sequence-controlled polymers are those with ordered units along their chains. The precision sequence of biological polymers, such as nucleic acid and peptides, plays a crucial role on physiological and sophisticated functions. Inspired by this, the synthesis of sequence-controlled polymers, that is, the placement of specific functional groups at desired positions on the polymer chain, has become one of the ultimate goals of polymer chemists, and received increasing attention in recent years. Up to date, there are a variety of methods to synthesize sequence-controlled polymers based on the step-growth and chain-growth polymerization mechanisms. Compared to the step-growth polymerization, the chain-growth polymerization is much more challenging to achieve sequence-controlled polymers because of the high activity and low propagating selectivity of the growing active center. Therefore, sequence-controlled polymerization is also considered as the " Holy Grail” in the field of polymer synthesis. Although a variety of methods have been developed to regulate polymer sequences, the pursuit of simple and efficient methods toward sequence-controlled polymerization has never stopped. This feature article summarizes the recent progresses on the synthesis of sequence-controlled polymers, and highlights our group’s research in this area. Firstly, we built " supramolecular monomer” by exploiting the weak intermolecular hydrogen-bond interactions to create sequences with alternating feature. We also developed a " latent monomer” strategy based on the temperature-dependent furan/maleimide Diels-Alder reaction, and diverse sequence-controlled polymers were thus readily created. Moreover, a novel chemical route, based on orthogonal chain end deprotection and thiol-maleimide Michael addition, was developed in our group toward the monodisperse and sequence-defined polymers. Finally, the potential applications of the sequence-controlled polymers are also summarized and prospected.
2018, 0(9): 1155-1174
doi: 10.11777/j.issn1000-3304.2018.18108
Abstract:
Hydrogels are three-dimensional polymeric networks with large amount of water as the dispersion medium. The hydrogen bonds between polymer networks and water bind water in the networks, thus making the system lose its fluidity and transform quasi-solid substances. Hydrogel materials can greatly change their shape and volume in response to diverse stimuli, and thus have attracted considerable attention due to their promising applications in soft robots, flexible electronics and sensors. In biological soft tissues, the existence of multi-scale structures, for example, surface micro/nano structures and ordered three-dimensional network structures is crucial to provide biological materials with functionalities, including self-cleaning, freezing tolerance, adaptivity and excellent mechanical performance. Taking inspiration from nature, researchers have increasingly developed a series of bioinspired multiscale hydrogels with high adaptability to various mechanical and environmental conditions. In this review, we first introduce the history of hydrogel. Secondly, the relationship between natural gel materials and their excellent function are summarized. Then the recent researches of bioinspired multi-scale hydrogels focusing on hydrogel ’s surfaces and three-dimensional network designing are discussed. As we mentioned, surface chemical/physical modification and micro/nano structure construction are typical strategies, which can adjust the wettability and adhesion behaviors of hydrogel surface, thus expanding the application of hydrogel in the fields of biomedicine and marine antifouling. In addition, the strategies of three-dimensional networks’ designing, such as introducing non-covalent cross-linking, designing ordered network structure and fabricating heterogeneous networks, are introduced respectively. These strategies can give hydrogels excellent properties including self-healing, anisotropy, high strength, shape memory and freezing tolerance. The development of these biomimetic multiscale hydrogels has expanded the application of hydrogel materials in the fields of wearable devices, software robots, and complex environments. Finally, the current challenges about design of hydrogels’ network, the dispersion of heterogeneous networks, the non-destructive characterization of hydrogels and future perspectives in this field will also be discussed.
Hydrogels are three-dimensional polymeric networks with large amount of water as the dispersion medium. The hydrogen bonds between polymer networks and water bind water in the networks, thus making the system lose its fluidity and transform quasi-solid substances. Hydrogel materials can greatly change their shape and volume in response to diverse stimuli, and thus have attracted considerable attention due to their promising applications in soft robots, flexible electronics and sensors. In biological soft tissues, the existence of multi-scale structures, for example, surface micro/nano structures and ordered three-dimensional network structures is crucial to provide biological materials with functionalities, including self-cleaning, freezing tolerance, adaptivity and excellent mechanical performance. Taking inspiration from nature, researchers have increasingly developed a series of bioinspired multiscale hydrogels with high adaptability to various mechanical and environmental conditions. In this review, we first introduce the history of hydrogel. Secondly, the relationship between natural gel materials and their excellent function are summarized. Then the recent researches of bioinspired multi-scale hydrogels focusing on hydrogel ’s surfaces and three-dimensional network designing are discussed. As we mentioned, surface chemical/physical modification and micro/nano structure construction are typical strategies, which can adjust the wettability and adhesion behaviors of hydrogel surface, thus expanding the application of hydrogel in the fields of biomedicine and marine antifouling. In addition, the strategies of three-dimensional networks’ designing, such as introducing non-covalent cross-linking, designing ordered network structure and fabricating heterogeneous networks, are introduced respectively. These strategies can give hydrogels excellent properties including self-healing, anisotropy, high strength, shape memory and freezing tolerance. The development of these biomimetic multiscale hydrogels has expanded the application of hydrogel materials in the fields of wearable devices, software robots, and complex environments. Finally, the current challenges about design of hydrogels’ network, the dispersion of heterogeneous networks, the non-destructive characterization of hydrogels and future perspectives in this field will also be discussed.
2018, 0(9): 1175-1183
doi: 10.11777/j.issn1000-3304.2018.18002
Abstract:
A novel azopyridine monomer was prepared by diazo coupling: 4-(4-pyridylazo) phenyl methacrylate (PAZO). PAZO was randomly copolymerized with N-isopropylacrylamide (NIPAM) and ethylene glycol methyl ether methacrylate (EGMA) to obtain a multi-response terpolymer (P(NIPAM-co-PAZO-co-EGMA)). The structure of the polymer was characterized by 1H-NMR and gel permeation chromatography (GPC), and the responsiveness of the polymer to UV spectroscopy was studied. Under the acidic conditions, the trans absorption peak of azo pyridine is stable and the weakness is inhibited. Under alkaline conditions, the trans absorption peak is weak, and the cis absorption peak is enhanced and stable. The lowest phase transition temperature (LCST) of the polymer was 49 °C. The trans structure of azopyridine was changed to the cis structure by ultraviolet light irradiation. Before UV irradiation, the hydrodynamic radius of the polymer was 9.82 nm. After the UV illumination, the value became 11.07 nm, and increased by 1.25 nm, indicating that the polymer size was increased after UV illumination. The size of the polymer increased with the increased size of the azo pyridine structure, making the PNIPAM segment more sensitive to temperature and LCST decreased 2 °C to 47 °C. The LCST of polymer sites before introduction of CO2 was 49 °C, and that was changed to 62 °C after passing through CO2. Argon is bubbled through the polymer solution or the solution is left open at 60 °C for a period of time to evacuate the CO2. The LCST of the solution changes to 49 °C again. Before and after the introduction of CO2, there was no obvious change in the LCST point of the aqueous solution of PNIPAM, indicating that the carbonic acid did not affect the amine group on the PNIPAM group, but instead was protonated with the azopyridine group. The CO2 and argon gasses were repeatedly introduced. The LCST of the polymer solution changed reversibly between 49 and 62 °C.
A novel azopyridine monomer was prepared by diazo coupling: 4-(4-pyridylazo) phenyl methacrylate (PAZO). PAZO was randomly copolymerized with N-isopropylacrylamide (NIPAM) and ethylene glycol methyl ether methacrylate (EGMA) to obtain a multi-response terpolymer (P(NIPAM-co-PAZO-co-EGMA)). The structure of the polymer was characterized by 1H-NMR and gel permeation chromatography (GPC), and the responsiveness of the polymer to UV spectroscopy was studied. Under the acidic conditions, the trans absorption peak of azo pyridine is stable and the weakness is inhibited. Under alkaline conditions, the trans absorption peak is weak, and the cis absorption peak is enhanced and stable. The lowest phase transition temperature (LCST) of the polymer was 49 °C. The trans structure of azopyridine was changed to the cis structure by ultraviolet light irradiation. Before UV irradiation, the hydrodynamic radius of the polymer was 9.82 nm. After the UV illumination, the value became 11.07 nm, and increased by 1.25 nm, indicating that the polymer size was increased after UV illumination. The size of the polymer increased with the increased size of the azo pyridine structure, making the PNIPAM segment more sensitive to temperature and LCST decreased 2 °C to 47 °C. The LCST of polymer sites before introduction of CO2 was 49 °C, and that was changed to 62 °C after passing through CO2. Argon is bubbled through the polymer solution or the solution is left open at 60 °C for a period of time to evacuate the CO2. The LCST of the solution changes to 49 °C again. Before and after the introduction of CO2, there was no obvious change in the LCST point of the aqueous solution of PNIPAM, indicating that the carbonic acid did not affect the amine group on the PNIPAM group, but instead was protonated with the azopyridine group. The CO2 and argon gasses were repeatedly introduced. The LCST of the polymer solution changed reversibly between 49 and 62 °C.
2018, 0(9): 1184-1193
doi: 10.11777/j.issn1000-3304.2018.18014
Abstract:
A series of KF/Al2O3 solid base catalysts were prepared by a wet impregnation method and applied to the synthesis of poly(ethylene terephthalate) (PET) from 1,4-dicarboxybenzene and ethylene glycol. The effect of KF content and calcination temperature on the structure, active components and properties of the catalysts were investigated. The structure of KF/Al2O3 catalysts was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET. The basic strength and basicity of KF/Al2O3 catalysts were measured by Hammett indicator. The relationship between KF content, calcination temperature and the structure, basic strength and basicity of KF/Al2O3 catalyst was investigated. The relationship between the structure, basic strength and basicity of KF/Al2O3 catalysts and the catalytic activity in PET synthesis was also studied. The results showed that KF/Al2O3 catalysts could be used to synthesize high-molecular-weight PET. It was found that several types of basic centers such as K3AlF6, KAlO2, K2O and K2CO3 existed in the catalyst. The specific surface area of KF/Al2O3 was reduced with increasing KF content. The particle size of KF/Al2O3 increased with increasing KF content. The basic strength and basicity of KF/Al2O3 increased with increasing KF content and calcination temperature. The activity of KF/Al2O3 was related to the basic strength and basicity and was not really influenced by the specific surface area and particle size. Medium strength basic sites were responsible for the higher intrinsic viscosity, and strong basic sites could cause decomposition of the obtained polymer. Strong basic sites were mainly due to potassium carbonate, potassium aluminate and potassium oxide. The catalytic effect of 25-KF/Al2O3-400 was better than that of Sb2O3. It contained γ-Al2O3, K3AlF6 and a small amount of K2CO3. It had moderate basic strength, basicity and high activity. Based on the obtained results, the possible active site was K3AlF6. The intrinsic viscosity of 1.07 dL/g, with carboxyl end group content of 20.29 mol/t, DEG content of 2.85%, L value of 86.6 and b value of 4.6, was obtained with 0.1 wt% of catalyst concentration.
A series of KF/Al2O3 solid base catalysts were prepared by a wet impregnation method and applied to the synthesis of poly(ethylene terephthalate) (PET) from 1,4-dicarboxybenzene and ethylene glycol. The effect of KF content and calcination temperature on the structure, active components and properties of the catalysts were investigated. The structure of KF/Al2O3 catalysts was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET. The basic strength and basicity of KF/Al2O3 catalysts were measured by Hammett indicator. The relationship between KF content, calcination temperature and the structure, basic strength and basicity of KF/Al2O3 catalyst was investigated. The relationship between the structure, basic strength and basicity of KF/Al2O3 catalysts and the catalytic activity in PET synthesis was also studied. The results showed that KF/Al2O3 catalysts could be used to synthesize high-molecular-weight PET. It was found that several types of basic centers such as K3AlF6, KAlO2, K2O and K2CO3 existed in the catalyst. The specific surface area of KF/Al2O3 was reduced with increasing KF content. The particle size of KF/Al2O3 increased with increasing KF content. The basic strength and basicity of KF/Al2O3 increased with increasing KF content and calcination temperature. The activity of KF/Al2O3 was related to the basic strength and basicity and was not really influenced by the specific surface area and particle size. Medium strength basic sites were responsible for the higher intrinsic viscosity, and strong basic sites could cause decomposition of the obtained polymer. Strong basic sites were mainly due to potassium carbonate, potassium aluminate and potassium oxide. The catalytic effect of 25-KF/Al2O3-400 was better than that of Sb2O3. It contained γ-Al2O3, K3AlF6 and a small amount of K2CO3. It had moderate basic strength, basicity and high activity. Based on the obtained results, the possible active site was K3AlF6. The intrinsic viscosity of 1.07 dL/g, with carboxyl end group content of 20.29 mol/t, DEG content of 2.85%, L value of 86.6 and b value of 4.6, was obtained with 0.1 wt% of catalyst concentration.
2018, 0(9): 1194-1201
doi: 10.11777/j.issn1000-3304.2018.18010
Abstract:
Aromatic sulfonated polymers are one class of very important functional polymers and can be used as proton exchange membranes (PEMs) for fuel cells. As one of the key components in fuel cells, they can provide ionic pathway for proton transport and act as a separator for the reactants. In order to improve their ionic conductivity and dimensional and chemical oxidation stabilities, this study reports a series of sulfonated poly(aryl ether ketone)s proton exchange membrane materials from their design of macromolecular structures. A series of novel poly(arylene ether ketone)s containing fluorene and pendant phenyl groups (4-PAEK-xx) were first synthesized through nucleophilic polycondensation reaction using 9,9-bis(3-phenyl-4-hydroxy) phenyl fluorene, 4,4′-(hexafluoroisopropylidene)diphenol and 1,4-bis(4-fluorobenzoyl)benzene as starting materials. They were then used to prepare a series of side-chain type poly(arylene ether ketone)s proton exchange membranes with multiple sulfonic groups (4-SPAEK-xx) by mild post-sulfonation reaction and solution casting. The structures and properties of these membranes were investigated. The results indicated that 4-SPAEK-xx membranes displayed moderate water absorption and low swelling ratio with the values in the range of 21% − 51.2% and 7.4% − 17.2% at 80 °C, respectively. These proton exchange membranes also exhibited good ionic conductivity with the values in the range of 115 − 171 mS/cm at 80 °C. The ionic conductivity of 4-PAEK-45 membrane (the ion exchange capacity of 2.12 mequiv/g) was even higher than that of the commercialized Nafion membrane. Moreover, these membranes had good thermal and mechanical property and chemical oxidative stability. Excellent comprehensive properties of 4-SPAEK- xx membranes were mainly ascribed to the incorporation of multiple pendant sulfonic groups and long fluorinated hydrophobic structures. The incorporation of multiple pendant sulfonic groups can not only effectively reduce the content of sulfonated units in the polymers, but also separate the ionic groups from the polymer backbones. Meanwhile, the incorporation of long fluorinated hydrophobic structures could further improve the dimensional and chemical oxidation stability of the obtained membranes. It is believed that this research would provide a valuable insight for the design and preparation of proton exchange polymer membranes of high-performance with aromatic sulfonated groups.
Aromatic sulfonated polymers are one class of very important functional polymers and can be used as proton exchange membranes (PEMs) for fuel cells. As one of the key components in fuel cells, they can provide ionic pathway for proton transport and act as a separator for the reactants. In order to improve their ionic conductivity and dimensional and chemical oxidation stabilities, this study reports a series of sulfonated poly(aryl ether ketone)s proton exchange membrane materials from their design of macromolecular structures. A series of novel poly(arylene ether ketone)s containing fluorene and pendant phenyl groups (4-PAEK-xx) were first synthesized through nucleophilic polycondensation reaction using 9,9-bis(3-phenyl-4-hydroxy) phenyl fluorene, 4,4′-(hexafluoroisopropylidene)diphenol and 1,4-bis(4-fluorobenzoyl)benzene as starting materials. They were then used to prepare a series of side-chain type poly(arylene ether ketone)s proton exchange membranes with multiple sulfonic groups (4-SPAEK-xx) by mild post-sulfonation reaction and solution casting. The structures and properties of these membranes were investigated. The results indicated that 4-SPAEK-xx membranes displayed moderate water absorption and low swelling ratio with the values in the range of 21% − 51.2% and 7.4% − 17.2% at 80 °C, respectively. These proton exchange membranes also exhibited good ionic conductivity with the values in the range of 115 − 171 mS/cm at 80 °C. The ionic conductivity of 4-PAEK-45 membrane (the ion exchange capacity of 2.12 mequiv/g) was even higher than that of the commercialized Nafion membrane. Moreover, these membranes had good thermal and mechanical property and chemical oxidative stability. Excellent comprehensive properties of 4-SPAEK- xx membranes were mainly ascribed to the incorporation of multiple pendant sulfonic groups and long fluorinated hydrophobic structures. The incorporation of multiple pendant sulfonic groups can not only effectively reduce the content of sulfonated units in the polymers, but also separate the ionic groups from the polymer backbones. Meanwhile, the incorporation of long fluorinated hydrophobic structures could further improve the dimensional and chemical oxidation stability of the obtained membranes. It is believed that this research would provide a valuable insight for the design and preparation of proton exchange polymer membranes of high-performance with aromatic sulfonated groups.
2018, 0(9): 1202-1211
doi: 10.11777/j.issn1000-3304.2018.18032
Abstract:
A series of polytetrahydrofuran (PTHF) and polydimethylsilane (PDMS) triblock copolymers (PTHF-b-PDMS-b-PTHF) have been synthesized via the combination of controlled termination of living PTHF chains (PTHF+) and ― NH2 functional groups along PDMS macromolecular backbone with the copolymerization efficiency of near 100%. PTHF living chains and PTHF+ were in situ prepared through living cationic opening polymerization of tetrahydrofuran (THF) with AllylBr/AgClO4 initiating system at 0 °C. The molecular weights of the PTHF chains were adjusted by mediating the molar ratio of the monomer to initiator. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR) were used to characterize the microstructure of as-prepared triblock copolymers. Thermal properties of the triblock copolymers PTHF-b-PDMS-b-PTHF were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Additionally, polarization microscopy (POM) was employed to investigate the effect of number-average molecular weight (Mn,PTHF) of PTHF segments on the crystallization of the triblock copolymers. To have a further insight of the structures of the triblock copolymers, transmission electron microscopy (TEM) was also used to study their micromorphology. The antimicrobial activity of the material was characterized by determination of the E. coli inhibition zone. All characterization results aforementioned demonstrate that the well-defined triblock copolymers of PTHF-b-PDMS-b-PTHF with silver nanocomposites could be successfully prepared in situ with very high efficiency of ca. 95%. The crystallization of the triblock copolymers increased with increasing molecular weight of PTHF segments. Compared to the corresponding homopolymers of PTHF and PDMS, the thermal stability of the triblock copolymers was obviously improved. Moreover, the existence of amino groups (＞N―H) in the macromolecular chains and a large number of ether bonds (―O―) from PTHF segments resulted in the formation of hydrogen bonds between the macro molecular chains of the triblock polymer, leading to the formation of physically cross-linked copolymer networks with more flexibility and better mechanical properties. Based on the strong hydrogen bonds, the obtained polymer networks show a pretty good self-healing performance at room temperature. The triblock copolymers were cut off at room temperature, then the cut section was self-healed for 24 h at room temperature, and the self-healed copolymers could be stretched to 1.5 times of the original length, which proved that the materials behaved good self-healing performance. Furthermore, the antimicrobial activity of the triblock copolymers was characterized by the inhibition zone method, and the diameter of inhibition zone of antibacterial was determined to be 13 mm, indicating a good antibacterial property. A novel nanocomposite, consisting of the triblock copolymer/silver, was synthesized in situ via controlled/living cationic ring-opening polymerization, and showed excellent properties resulted from PTHF, PDMS and Ag nano-particles, suggesting their potential applications in biological and medical fields.
A series of polytetrahydrofuran (PTHF) and polydimethylsilane (PDMS) triblock copolymers (PTHF-b-PDMS-b-PTHF) have been synthesized via the combination of controlled termination of living PTHF chains (PTHF+) and ― NH2 functional groups along PDMS macromolecular backbone with the copolymerization efficiency of near 100%. PTHF living chains and PTHF+ were in situ prepared through living cationic opening polymerization of tetrahydrofuran (THF) with AllylBr/AgClO4 initiating system at 0 °C. The molecular weights of the PTHF chains were adjusted by mediating the molar ratio of the monomer to initiator. Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR) were used to characterize the microstructure of as-prepared triblock copolymers. Thermal properties of the triblock copolymers PTHF-b-PDMS-b-PTHF were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Additionally, polarization microscopy (POM) was employed to investigate the effect of number-average molecular weight (Mn,PTHF) of PTHF segments on the crystallization of the triblock copolymers. To have a further insight of the structures of the triblock copolymers, transmission electron microscopy (TEM) was also used to study their micromorphology. The antimicrobial activity of the material was characterized by determination of the E. coli inhibition zone. All characterization results aforementioned demonstrate that the well-defined triblock copolymers of PTHF-b-PDMS-b-PTHF with silver nanocomposites could be successfully prepared in situ with very high efficiency of ca. 95%. The crystallization of the triblock copolymers increased with increasing molecular weight of PTHF segments. Compared to the corresponding homopolymers of PTHF and PDMS, the thermal stability of the triblock copolymers was obviously improved. Moreover, the existence of amino groups (＞N―H) in the macromolecular chains and a large number of ether bonds (―O―) from PTHF segments resulted in the formation of hydrogen bonds between the macro molecular chains of the triblock polymer, leading to the formation of physically cross-linked copolymer networks with more flexibility and better mechanical properties. Based on the strong hydrogen bonds, the obtained polymer networks show a pretty good self-healing performance at room temperature. The triblock copolymers were cut off at room temperature, then the cut section was self-healed for 24 h at room temperature, and the self-healed copolymers could be stretched to 1.5 times of the original length, which proved that the materials behaved good self-healing performance. Furthermore, the antimicrobial activity of the triblock copolymers was characterized by the inhibition zone method, and the diameter of inhibition zone of antibacterial was determined to be 13 mm, indicating a good antibacterial property. A novel nanocomposite, consisting of the triblock copolymer/silver, was synthesized in situ via controlled/living cationic ring-opening polymerization, and showed excellent properties resulted from PTHF, PDMS and Ag nano-particles, suggesting their potential applications in biological and medical fields.
2018, 0(9): 1212-1220
doi: 10.11777/j.issn1000-3304.2017.17333
Abstract:
The thickening of monolayer crystals of low molecular weight poly(ethylene oxide) (PEO) fractions on mica surface are in situ monitored by an atomic force microscopy (AFM) coupled with a hot stage. Two PEO fractions, with different molecular weights (HPEO2K, Mn = 2000; HPEO3K, Mn = 3000), have been examined. It is found that thickening domains continuously emerge when smooth once-folded-chain crystals are annealed isothermally below their melting temperature. A single thickening domain can grow in thickness and lateral size simutaneously. The growth of the thickness of the thickening domain follows a sigmoidal curve and depends significantly on the annealing temperature. It is found that the thickness of the thickening domain grows linearly with the logarithm of time. Such linear relation implies that its underlying mechanism should be nucleation and growth, as confirmed by a theoretical derivation of the thickness of the thickening domain as a function of time based on this mechanism. For each annealing temperature, a linear regression between the thickness of the thickening domain and the logarithm of time is performed and the obtained reciprocal of the slope linearly depends on the reciprocal of the annealing temperature. Then the surface free energy of the lateral surface of the folded-chain crystals can be inferred from the relation between the reciprocal of the slope and the annealing temperature. In this study, the value of the lateral surface free energy is found to be 1.25 and 1.22 kJ/mol for HPEO2K and HPEO3K, respectively. These values agree well with each other and also with reported values, which further validates our proposed mechanism. The lateral size of the thickening domain grows linearly with time as long as its thickeness approaches the extended-chain crystal. Such type of growth resembles the direct growth of the polymer crystals from the melt. However, its reltation between the growth rate and the annealing temperature is quite different from that of the growth of polymer crystals: the growth rate increases with the annealing temperature in the thickening case while it decreases with the crystallization temperature in the crystallization case. It indicates that there is an activation process rather than a nucleation process during thickening, which has been attributed to the chain sliding diffusion within the folded-chain crystals.
The thickening of monolayer crystals of low molecular weight poly(ethylene oxide) (PEO) fractions on mica surface are in situ monitored by an atomic force microscopy (AFM) coupled with a hot stage. Two PEO fractions, with different molecular weights (HPEO2K, Mn = 2000; HPEO3K, Mn = 3000), have been examined. It is found that thickening domains continuously emerge when smooth once-folded-chain crystals are annealed isothermally below their melting temperature. A single thickening domain can grow in thickness and lateral size simutaneously. The growth of the thickness of the thickening domain follows a sigmoidal curve and depends significantly on the annealing temperature. It is found that the thickness of the thickening domain grows linearly with the logarithm of time. Such linear relation implies that its underlying mechanism should be nucleation and growth, as confirmed by a theoretical derivation of the thickness of the thickening domain as a function of time based on this mechanism. For each annealing temperature, a linear regression between the thickness of the thickening domain and the logarithm of time is performed and the obtained reciprocal of the slope linearly depends on the reciprocal of the annealing temperature. Then the surface free energy of the lateral surface of the folded-chain crystals can be inferred from the relation between the reciprocal of the slope and the annealing temperature. In this study, the value of the lateral surface free energy is found to be 1.25 and 1.22 kJ/mol for HPEO2K and HPEO3K, respectively. These values agree well with each other and also with reported values, which further validates our proposed mechanism. The lateral size of the thickening domain grows linearly with time as long as its thickeness approaches the extended-chain crystal. Such type of growth resembles the direct growth of the polymer crystals from the melt. However, its reltation between the growth rate and the annealing temperature is quite different from that of the growth of polymer crystals: the growth rate increases with the annealing temperature in the thickening case while it decreases with the crystallization temperature in the crystallization case. It indicates that there is an activation process rather than a nucleation process during thickening, which has been attributed to the chain sliding diffusion within the folded-chain crystals.
2018, 0(9): 1221-1227
doi: 10.11777/j.issn1000-3304.2018.18011
Abstract:
Adding stereocomplex (SC) crystals into matrix can effectively improve the hydrolysis resistance and heat-resistance of polylactic acid (PLA). However, the existence of pre-formed SC crystals will increase the processing difficulty because a higher processing temperature is needed. Thus the exploration of inducing SC crystals via external force fields is important. In this paper, ‘quenched’ and ‘annealed’ PLA enantiomer mixtures were studied. The enantiomer mixtures were prepared by solution coprecipitation. Preparation of the ‘quenched’ specimen is done in two steps: hot pressed at 250 °C for 5 min and then quenched in air (15 °C). The method of annealing is done as following: hot pressed at 250 °C for 5 min, annealed at 200 °C for 30 min, and finally quenched in air. The X-ray diffraction patterns indicated that a loose structure with low order degree, named as quasi-ordered phase (QOP), was formed in the two types of the samples. Based on this structure, SC crystals was formed during stretching near the glass transition temperature (Tg) of PLA.The results of infrared spectra indicated that adequate amount of poly(D-lactic acid) (PDLA) is the prerequisite for the induction of SC crystals. There was no SC crystal generated in the specimens with 5% of PDLA, regardless of the treatment used. However, SC crystal appearred in the specimens with 20% of PDLA. This is because that adequate amount of QOP regions can merge and rebuild into complete crystals. In the specimens of high PDLA content, the transition could happen either during annealing or stretching above Tg (e.g., 70 °C). Owing to the self-nucleation and heterogeneous nucleation of QOP, α'-form crystal would be formed concomitantly during annealling. Therefore the former approach cannot generate pure SC crystal. As to the latter approach, depending on the tensile temperature and rate, mesophase, SC crystal and α'-form can be selectively generated. When stretched below Tg (e.g., 50 °C), only mesophase can be obtained beacause of low chain activity. As stretched at 70 °C, the tensile model has a great effect on the induced results. Fast stretching will induce highly pure SC crystals. Otherwise, when given sufficent time for chain segmet adjustment, both SC and α'-form crystals would be induced.
Adding stereocomplex (SC) crystals into matrix can effectively improve the hydrolysis resistance and heat-resistance of polylactic acid (PLA). However, the existence of pre-formed SC crystals will increase the processing difficulty because a higher processing temperature is needed. Thus the exploration of inducing SC crystals via external force fields is important. In this paper, ‘quenched’ and ‘annealed’ PLA enantiomer mixtures were studied. The enantiomer mixtures were prepared by solution coprecipitation. Preparation of the ‘quenched’ specimen is done in two steps: hot pressed at 250 °C for 5 min and then quenched in air (15 °C). The method of annealing is done as following: hot pressed at 250 °C for 5 min, annealed at 200 °C for 30 min, and finally quenched in air. The X-ray diffraction patterns indicated that a loose structure with low order degree, named as quasi-ordered phase (QOP), was formed in the two types of the samples. Based on this structure, SC crystals was formed during stretching near the glass transition temperature (Tg) of PLA.The results of infrared spectra indicated that adequate amount of poly(D-lactic acid) (PDLA) is the prerequisite for the induction of SC crystals. There was no SC crystal generated in the specimens with 5% of PDLA, regardless of the treatment used. However, SC crystal appearred in the specimens with 20% of PDLA. This is because that adequate amount of QOP regions can merge and rebuild into complete crystals. In the specimens of high PDLA content, the transition could happen either during annealing or stretching above Tg (e.g., 70 °C). Owing to the self-nucleation and heterogeneous nucleation of QOP, α'-form crystal would be formed concomitantly during annealling. Therefore the former approach cannot generate pure SC crystal. As to the latter approach, depending on the tensile temperature and rate, mesophase, SC crystal and α'-form can be selectively generated. When stretched below Tg (e.g., 50 °C), only mesophase can be obtained beacause of low chain activity. As stretched at 70 °C, the tensile model has a great effect on the induced results. Fast stretching will induce highly pure SC crystals. Otherwise, when given sufficent time for chain segmet adjustment, both SC and α'-form crystals would be induced.
2018, 0(9): 1228-1235
doi: 10.11777/j.issn1000-3304.2018.18024
Abstract:
The isothermal crystallization kinetics of poly(ethylene oxide) (PEO) droplets was studied by fast scanning calorimetry (FSC) at a scanning rate up to 10000 K/s over a wide temperature range from its glass transition temperature to its melting temperature, and compared with that of PEO bulk sample. It was observed that the nucleation in PEO bulk sample during cooling is unavoidable even at a scanning rate of up to 50000 K/s because of numerous heterogeneity and the observation of an obvious cold crystallization peak in the subsequent heating curves. While the critical cooling rate is much slower when the sample was prepared by film dewetting and dispersed to several droplets smaller than 2 μm in diameter, and a fully amorphous sample could be obtained at a scanning rate of 10000 K/s. Isothermal crystallization of PEO bulk and that of droplets were studied in the time range from 10−2 s to 103 s at varied temperatures from 210 K to 310 K. The half crystallization time at each annealing temperature was calculated by fitting the enthalpy-time curve with a modified Avrami equation. It was found that the total crystallization rate of PEO droplets was systematically decreased by one magnitude in the whole temperature region. When the sample was dispersed into droplets of the size of several microns, the number of heterogeneity in each droplet was much less than that in the bulk or even heterogeneity-free in some droplets, with the average crystallization rate slowing down, especially in the low supercooling region, where heterogeneous nucleation is supposed to be dominant. The slowing down of crystallization rate was also observed at higher supercooling near Tg, where the homogeneous nucleation is considered to dominate the crystallization rate. Because of a slower homogeneous nucleation rate of PEO, the droplets sample with less heterogeneity mainly nucleated from homogeneous nucleation with a slower crystallization rate comparing to the unavoidable heterogeneous nucleation in bulk sample. The confinement of the droplet size may hinder the long-range diffusion of PEO chains and restricted the growth dimension under confinement, which could also be a reason for which a decrease in total crystallization rate of PEO droplets sample was observed.
The isothermal crystallization kinetics of poly(ethylene oxide) (PEO) droplets was studied by fast scanning calorimetry (FSC) at a scanning rate up to 10000 K/s over a wide temperature range from its glass transition temperature to its melting temperature, and compared with that of PEO bulk sample. It was observed that the nucleation in PEO bulk sample during cooling is unavoidable even at a scanning rate of up to 50000 K/s because of numerous heterogeneity and the observation of an obvious cold crystallization peak in the subsequent heating curves. While the critical cooling rate is much slower when the sample was prepared by film dewetting and dispersed to several droplets smaller than 2 μm in diameter, and a fully amorphous sample could be obtained at a scanning rate of 10000 K/s. Isothermal crystallization of PEO bulk and that of droplets were studied in the time range from 10−2 s to 103 s at varied temperatures from 210 K to 310 K. The half crystallization time at each annealing temperature was calculated by fitting the enthalpy-time curve with a modified Avrami equation. It was found that the total crystallization rate of PEO droplets was systematically decreased by one magnitude in the whole temperature region. When the sample was dispersed into droplets of the size of several microns, the number of heterogeneity in each droplet was much less than that in the bulk or even heterogeneity-free in some droplets, with the average crystallization rate slowing down, especially in the low supercooling region, where heterogeneous nucleation is supposed to be dominant. The slowing down of crystallization rate was also observed at higher supercooling near Tg, where the homogeneous nucleation is considered to dominate the crystallization rate. Because of a slower homogeneous nucleation rate of PEO, the droplets sample with less heterogeneity mainly nucleated from homogeneous nucleation with a slower crystallization rate comparing to the unavoidable heterogeneous nucleation in bulk sample. The confinement of the droplet size may hinder the long-range diffusion of PEO chains and restricted the growth dimension under confinement, which could also be a reason for which a decrease in total crystallization rate of PEO droplets sample was observed.
2018, 0(9): 1236-1243
doi: 10.11777/j.issn1000-3304.2017.17286
Abstract:
A series of poly(aryl ether sulfonephthalazinone)s (PPES-Ps) containing pendent carboxyl groups and N-heterocyclicphthalazinone units were derived from phenolphthalin (PPL) and 4-(3-chloro-4-hydroxylphenyl)(2H)-phthalazin-1-one (DHPZ) with 4,4′-dichlorodiphenyl sulfone (DCS) via " one-pot” solution polymerization. The structure of the resulting polymers was elaborately controlled by tailoring the feed ratio of the two diphenols to have a balance between the carboxyl content and the thermal resistance. As evidenced by NMR analysis, the structure of the corrsponding polymers along with the carboxyl content is consistent with those designed. PPES-Ps also exhibit high glass transition temperature (Tg > 260 °C) and excellent thermal stability as well as good solubility, mainly originating from the rigid, bulky, non-coplanar phthalazinone units. As the content of phthalazinone unit increases, both Tg and solubility demostrate an increasing trend. Furthermore, the copolymers with different contents of carboxyl groups are used to reactively toughen 601 epoxy resin. The mechanical and thermal properties of the obtained blending system are investigated in details. The results indicate that the pendant carboxyl groups in PPES-P can efficiently react with the epoxy groups of 601 resin during the thermal curing, leading to cross-linking networks by covalent bonding, which can not only improve the fracture toughness and flexural properties, but also maintain the high Tg of 601 epoxy resin. The impact strength of 601 epoxy resin, reactively toughened by PPES-P13 derived from PPL/DHPZ with the molar ratio of 1:3, is 43% higher than that of unmodified 601 resin. Meanwhile, the fracture of impact specimen shows a toughened fracture character, and no phase separation is observed on the crack surface, even with a high concent (15%) of PPES-P, which means that the reactive carboxyl moiety could enhance the compatibility between the high rigid poly(aryl ether)s and the epoxy resins. The 601 resins, reactively modified with PPES-Ps toughening, are thus expected to be useful in multistage toughening of carbon fiber reinforced resin matrix composites.
A series of poly(aryl ether sulfonephthalazinone)s (PPES-Ps) containing pendent carboxyl groups and N-heterocyclicphthalazinone units were derived from phenolphthalin (PPL) and 4-(3-chloro-4-hydroxylphenyl)(2H)-phthalazin-1-one (DHPZ) with 4,4′-dichlorodiphenyl sulfone (DCS) via " one-pot” solution polymerization. The structure of the resulting polymers was elaborately controlled by tailoring the feed ratio of the two diphenols to have a balance between the carboxyl content and the thermal resistance. As evidenced by NMR analysis, the structure of the corrsponding polymers along with the carboxyl content is consistent with those designed. PPES-Ps also exhibit high glass transition temperature (Tg > 260 °C) and excellent thermal stability as well as good solubility, mainly originating from the rigid, bulky, non-coplanar phthalazinone units. As the content of phthalazinone unit increases, both Tg and solubility demostrate an increasing trend. Furthermore, the copolymers with different contents of carboxyl groups are used to reactively toughen 601 epoxy resin. The mechanical and thermal properties of the obtained blending system are investigated in details. The results indicate that the pendant carboxyl groups in PPES-P can efficiently react with the epoxy groups of 601 resin during the thermal curing, leading to cross-linking networks by covalent bonding, which can not only improve the fracture toughness and flexural properties, but also maintain the high Tg of 601 epoxy resin. The impact strength of 601 epoxy resin, reactively toughened by PPES-P13 derived from PPL/DHPZ with the molar ratio of 1:3, is 43% higher than that of unmodified 601 resin. Meanwhile, the fracture of impact specimen shows a toughened fracture character, and no phase separation is observed on the crack surface, even with a high concent (15%) of PPES-P, which means that the reactive carboxyl moiety could enhance the compatibility between the high rigid poly(aryl ether)s and the epoxy resins. The 601 resins, reactively modified with PPES-Ps toughening, are thus expected to be useful in multistage toughening of carbon fiber reinforced resin matrix composites.
2018, 0(9): 1244-1252
doi: 10.11777/j.issn1000-3304.2018.18005
Abstract:
Blends based on poly(butylene succinate) (PBS) and poly(ethylene glycol-co-cyclohexane-1,4-dimethanolterephthalate) (PETG) were successfully fabricated by a special twin screw extruder. Effects of PETG content and rotating speed on the dispersed size and mechanical properties of the PBS/PETG blends were investigated. The average diameter of PETG phase showed a downwards trend from 2.27 μm to 0.89 μm with increasing rotating speed from 150 r/min to 900 r/min for a blend with 20 wt% of PETG. Meanwhile, the yield strength of the blend was raised from 26.2 MPa to 33.4 MPa. In addition, the elongation at break was also promoted from 13.3% to 133.3%, which indicated a transformation from brittle fracture into ductile fracture as accomplished by high speed extrusion. However, the decrease of the dispersed PETG size was very limited by increasing rotating speed for the blends containing 10 wt% or 30 wt% of PETG. As a result, the yield strength and the elongation at break showed only limited increase in the obtained blends. The relationship between the size of the dispersed phase and mechanical properties of the PBS/PETG blends prepared with different components and at different rotating speeds were analyzed comprehensively. A nearly linear relationship was found between the yield strength and the diameter of the dispersed phase, disregarding the composition and rotating speed. This demonstrated again the importance of the size of the dispersed phase in determining the property of PBS/PETG blends. GPC and DSC results indicated no obvious change in molecular weight and crystallinity of PBS by increasing rotating speed, and the observed property change of the blends was well explained by the change of dispersed phase size induced by high speed rotating. It should be noted that the high speed rotating induced change in the size of the dispersed phase was thermodynamically unstable. The stability of the blends will be investigated in our future work.
Blends based on poly(butylene succinate) (PBS) and poly(ethylene glycol-co-cyclohexane-1,4-dimethanolterephthalate) (PETG) were successfully fabricated by a special twin screw extruder. Effects of PETG content and rotating speed on the dispersed size and mechanical properties of the PBS/PETG blends were investigated. The average diameter of PETG phase showed a downwards trend from 2.27 μm to 0.89 μm with increasing rotating speed from 150 r/min to 900 r/min for a blend with 20 wt% of PETG. Meanwhile, the yield strength of the blend was raised from 26.2 MPa to 33.4 MPa. In addition, the elongation at break was also promoted from 13.3% to 133.3%, which indicated a transformation from brittle fracture into ductile fracture as accomplished by high speed extrusion. However, the decrease of the dispersed PETG size was very limited by increasing rotating speed for the blends containing 10 wt% or 30 wt% of PETG. As a result, the yield strength and the elongation at break showed only limited increase in the obtained blends. The relationship between the size of the dispersed phase and mechanical properties of the PBS/PETG blends prepared with different components and at different rotating speeds were analyzed comprehensively. A nearly linear relationship was found between the yield strength and the diameter of the dispersed phase, disregarding the composition and rotating speed. This demonstrated again the importance of the size of the dispersed phase in determining the property of PBS/PETG blends. GPC and DSC results indicated no obvious change in molecular weight and crystallinity of PBS by increasing rotating speed, and the observed property change of the blends was well explained by the change of dispersed phase size induced by high speed rotating. It should be noted that the high speed rotating induced change in the size of the dispersed phase was thermodynamically unstable. The stability of the blends will be investigated in our future work.
