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2018 Volume Issue 11
2018, 0(11):
Abstract:
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2018, 0(11): 1359-1371
doi: 10.11777/j.issn1000-3304.2018.18146
Abstract:
Coordination-insertion copolymerization of olefins and polar monomers for the preparation of functionalized polyolefins is one of the most important project in the field of olefin polymerization in the past twenty years. Due to the incorporation of functional groups, functionalized polyolefins, as the high value-added polymer materials, are of better surface properties and compatibility than those without any functionality, thus leading to expanding the range of applications. However, the presence of functional groups can also accelerate the chain transfer and chelate to the active central metal in the copolymerization of olefin and polar monomers, therefore this type of copolymerization suffers from lower catalytic activity and lower polymer molecular weight than the corresponding homo-polymerization of the olefins. As a result, the key for the high performance synthesis of functionalized polyolefins is to overcome the problem related to the functional groups of the polar monomers. In this Feature Article, recent research progress on the copolymerization of olefins and polar monomers to achieve the functionalized polyolefins by using late transition metal catalysts will be mostly summarized. Firstly, the milestone catalysts for the synthesis of functionalized polyolefins are introduced, and the latest research progresses on how to overcome the problem of polar monomer by designing nickel and palladium catalysts are highlighted. Then a series of our findings in recent years on the design of the polar monomers for the synthesis of functionalized polyolefins are revealed in detail, including the concept of polar di-vinyl monomers to overcome the problems related to polar monomers (rapid chain transfer reaction and chelation of functional group to active central metal) and the strategy of vinyl furan monomer with secondary coordination effect to synthesize novel functionalized polyolefins (telechelic polyolefin with two reactive endgroups). Finally, future development and long-standing challenges in the community of functionalized polyolefins by the copolymerization of olefins and polar monomers are out looked.
Coordination-insertion copolymerization of olefins and polar monomers for the preparation of functionalized polyolefins is one of the most important project in the field of olefin polymerization in the past twenty years. Due to the incorporation of functional groups, functionalized polyolefins, as the high value-added polymer materials, are of better surface properties and compatibility than those without any functionality, thus leading to expanding the range of applications. However, the presence of functional groups can also accelerate the chain transfer and chelate to the active central metal in the copolymerization of olefin and polar monomers, therefore this type of copolymerization suffers from lower catalytic activity and lower polymer molecular weight than the corresponding homo-polymerization of the olefins. As a result, the key for the high performance synthesis of functionalized polyolefins is to overcome the problem related to the functional groups of the polar monomers. In this Feature Article, recent research progress on the copolymerization of olefins and polar monomers to achieve the functionalized polyolefins by using late transition metal catalysts will be mostly summarized. Firstly, the milestone catalysts for the synthesis of functionalized polyolefins are introduced, and the latest research progresses on how to overcome the problem of polar monomer by designing nickel and palladium catalysts are highlighted. Then a series of our findings in recent years on the design of the polar monomers for the synthesis of functionalized polyolefins are revealed in detail, including the concept of polar di-vinyl monomers to overcome the problems related to polar monomers (rapid chain transfer reaction and chelation of functional group to active central metal) and the strategy of vinyl furan monomer with secondary coordination effect to synthesize novel functionalized polyolefins (telechelic polyolefin with two reactive endgroups). Finally, future development and long-standing challenges in the community of functionalized polyolefins by the copolymerization of olefins and polar monomers are out looked.
2018, 0(11): 1372-1384
doi: 10.11777/j.issn1000-3304.2018.18155
Abstract:
In the past 50 years, the studies of olefin polymerization have achieved great successes in both academia and industry. Polyolefins have huge annual production and wide applications. However, one of their biggest limitations is their nonpolar nature. The introduction of a small amount of polar and functionalized groups can greatly improve many properties, broaden their applications, and increase their business values. Transition metal catalyzed copolymerization of olefin with polar monomers is the most direct route to access polar and functionalized polyolefins, which is also highly challenging. With the " polar monomer problem” as the central theme, this account mainly focuses on the works from our own research group and describes the following topics: modification of existing catalyst systems, development of new catalyst systems, design of new polymerization modulation strategies, and the synthesis and property studies of special polyolefins and polar functionalized polyolefins materials.
In the past 50 years, the studies of olefin polymerization have achieved great successes in both academia and industry. Polyolefins have huge annual production and wide applications. However, one of their biggest limitations is their nonpolar nature. The introduction of a small amount of polar and functionalized groups can greatly improve many properties, broaden their applications, and increase their business values. Transition metal catalyzed copolymerization of olefin with polar monomers is the most direct route to access polar and functionalized polyolefins, which is also highly challenging. With the " polar monomer problem” as the central theme, this account mainly focuses on the works from our own research group and describes the following topics: modification of existing catalyst systems, development of new catalyst systems, design of new polymerization modulation strategies, and the synthesis and property studies of special polyolefins and polar functionalized polyolefins materials.
2018, 0(11): 1385-1399
doi: 10.11777/j.issn1000-3304.2018.18150
Abstract:
As one of the most important stimuli-responsive polymeric materials, shape memory polymers could fix temporary shapes and subsequently recover to the original shape under specific stimuli, and have thus aroused tremendous attention and shown promising applications in many fields such as biomedical, textile, aerospace and so on. The currently developed shape memory polymers are mainly thermo-responsive, in which vitrification or crystallization of the polymer chains are applied as temporary crosslinks to achieve shape memory property, and the shape recovery is induced by heat. In order to realize shape memory performance under mild conditions, supramolecular interactions (hydrogen bonds, host-guest recognition, metal-ligand coordination) and dynamic covalent bonds (boronate ester interactions, Schiff base bonds) have been employed as temporary switches to construct supramolecular shape memory hydrogels (SSMHs). Because of the reversible and dynamic nature of molecular switches, SSMHs could display excellent shape memory behavior at room temperature. In the early stage, only one kind of reversible interaction was utilized to fix one temporary shape in each shape memory cycle, resulting in a dual shape memory effect. Since the number of temporary shapes that could be stabilized normally has a great impact on the potential applications, two or more non-interfering dynamic switches have been incorporated in one system to realize triple or multiple shape memory effect. Moreover, other properties such as self-healing, adhesion, shape deformation and fluorescence have been successfully introduced into SSMHs, a series of multi-functional SSMHs have been developed to broaden their potential applications. In this review, the definition and development of SSMHs are briefly introduced, and recent progress in SSMHs with different kinds of reversible interactions is summarized, followed by the presentation of SSMHs with multiple shape memory effect and multi-functions. Finally, current challenges and future perspectives in this field are also discussed to promote new developing directions.
As one of the most important stimuli-responsive polymeric materials, shape memory polymers could fix temporary shapes and subsequently recover to the original shape under specific stimuli, and have thus aroused tremendous attention and shown promising applications in many fields such as biomedical, textile, aerospace and so on. The currently developed shape memory polymers are mainly thermo-responsive, in which vitrification or crystallization of the polymer chains are applied as temporary crosslinks to achieve shape memory property, and the shape recovery is induced by heat. In order to realize shape memory performance under mild conditions, supramolecular interactions (hydrogen bonds, host-guest recognition, metal-ligand coordination) and dynamic covalent bonds (boronate ester interactions, Schiff base bonds) have been employed as temporary switches to construct supramolecular shape memory hydrogels (SSMHs). Because of the reversible and dynamic nature of molecular switches, SSMHs could display excellent shape memory behavior at room temperature. In the early stage, only one kind of reversible interaction was utilized to fix one temporary shape in each shape memory cycle, resulting in a dual shape memory effect. Since the number of temporary shapes that could be stabilized normally has a great impact on the potential applications, two or more non-interfering dynamic switches have been incorporated in one system to realize triple or multiple shape memory effect. Moreover, other properties such as self-healing, adhesion, shape deformation and fluorescence have been successfully introduced into SSMHs, a series of multi-functional SSMHs have been developed to broaden their potential applications. In this review, the definition and development of SSMHs are briefly introduced, and recent progress in SSMHs with different kinds of reversible interactions is summarized, followed by the presentation of SSMHs with multiple shape memory effect and multi-functions. Finally, current challenges and future perspectives in this field are also discussed to promote new developing directions.
2018, 0(11): 1400-1415
doi: 10.11777/j.issn1000-3304.2018.18175
Abstract:
Ordered mesoporous materials, a family of highly porous nanomaterials, have attracted extensive attentions of many researchers in various fields due to their stable structure, high specific surface area, adjustable pore size, and easily modifiable pore wall. Over 70% reports on mesoporous materials are about amorphous mesoporous materials (e.g., silica), because the traditional templates are widely commercially available and can be used readily for synthesis of amorphous mesoporous materials. However, conventional soft templates are not favorable for the synthesis of crystalline ordered mesoporous metal oxide semiconductors (OMMSs) with unique physical and chemical properties (i.e., light, electricity, magnetism, catalysis, gas sensitivity, etc). Fortunately, this issue is well tackled by the development of interdisciplinary research along with more involvement of polymer researchers into the field of inorganic porous materials. In recent years, various novel block copolymers, particularly those with high carbon residue, high glass transition temperature, and complex-ability, have been synthesized and applied for fabricating porous materials. Remarkable progress has been achieved in using these templates to direct the co-assembly of various precursors for OMMSs synthesis. Starting from the preparation and assembly of polymer templates, this review elucidates systematically the mechanism and assembly behavior between metal oxide precursor and polymer templates. In addition, in-depth discussion is developed on the common three assembly processes, i.e. the metal inorganic salt-polymer template assembly, the metal cluster compounds-polymer template assembly, and the metal nanocrystals-polymer template assembly. Future opportunities and challenges faced by the synthesis and applications of OMMSs based on these novel block copolymer templates are foreseen in the last section.
Ordered mesoporous materials, a family of highly porous nanomaterials, have attracted extensive attentions of many researchers in various fields due to their stable structure, high specific surface area, adjustable pore size, and easily modifiable pore wall. Over 70% reports on mesoporous materials are about amorphous mesoporous materials (e.g., silica), because the traditional templates are widely commercially available and can be used readily for synthesis of amorphous mesoporous materials. However, conventional soft templates are not favorable for the synthesis of crystalline ordered mesoporous metal oxide semiconductors (OMMSs) with unique physical and chemical properties (i.e., light, electricity, magnetism, catalysis, gas sensitivity, etc). Fortunately, this issue is well tackled by the development of interdisciplinary research along with more involvement of polymer researchers into the field of inorganic porous materials. In recent years, various novel block copolymers, particularly those with high carbon residue, high glass transition temperature, and complex-ability, have been synthesized and applied for fabricating porous materials. Remarkable progress has been achieved in using these templates to direct the co-assembly of various precursors for OMMSs synthesis. Starting from the preparation and assembly of polymer templates, this review elucidates systematically the mechanism and assembly behavior between metal oxide precursor and polymer templates. In addition, in-depth discussion is developed on the common three assembly processes, i.e. the metal inorganic salt-polymer template assembly, the metal cluster compounds-polymer template assembly, and the metal nanocrystals-polymer template assembly. Future opportunities and challenges faced by the synthesis and applications of OMMSs based on these novel block copolymer templates are foreseen in the last section.
2018, 0(11): 1416-1421
doi: 10.11777/j.issn1000-3304.2018.18088
Abstract:
Polymerization of myrcene and its copolymerization with butadiene by half-sandwich scandium complexes, (C5Me4SiMe3)Sc(CH2SiMe3)2(THF) (1) and Cp′Sc(CH2C6H4NMe2-o)2 (2: Cp′ = C5Me4SiMe3; 3: Cp′ = C5H5), have been examined. The microstructures and thermal properties of the obtained polymers were characterized by 1H-NMR, 13C-NMR, GPC and DSC. Significant ligand influence on the catalytic activity, selectivity, and polymer molecular weight has been observed in the homopolymerization of myrcene. The scandium complexes 1 and 2 bearing large C5Me4SiMe3 ligand showed relatively low activity (104 g polymer molSc−1 h−1) and preferred 3,4-selectivity (74% for 1 and 61% for 2). The myrcene homopolymers prepared by complexes 1 and 2 have low molecular weight (Mn = 1.7 × 104 − 5.6 × 104) and relatively high glass transition temperature (−48 and −45 °C). The complex 3 bearing small C5H5 ligand showed high activity (105 g polymer molSc−1 h−1) and high cis-1,4-selectivity (95%). The myrcene homopolymers prepared by complex 3 have high molecular weight (Mn = 7.0 × 104 − 2.31 × 105) and low glass transition temperature (Tg = −70 °C). By use of complex 3, the copolymerization of myrcene with butadiene was also achieved for the first time to afford a novel family of rubber materials. The copolymerization reaction was completed within 5 min, irrespective of the monomer feed ratio, and the copolymerization activity was raised to as high as 105 g polymer molSc−1 h−1. The copolymer composition was in agreement with the co-monomer feed ratio, suggesting that both monomers were completely incorporated into their copolymers. The obtained myrcene-butadiene copolymers showed a random monomer sequence distribution, and the cis-1,4 contents of both monomers in the copolymers were more than 92%. All of these copolymers showed a single Tg varing with the myrcene/butadiene ratio. The Tgs of the copolymers with myrcene content of 19 mol% − 75 mol% fell in a range of −95 °C to −71 °C, which are between those of homopolymyrcene (−70 °C) and homopolybutadiene (−107 °C). The Tg of the copolymers decreased with increasing butadiene content. The molecular weight of the myrcene-butadiene copolymers can be controlled simply by changing the monomer/catalyst ratio.
Polymerization of myrcene and its copolymerization with butadiene by half-sandwich scandium complexes, (C5Me4SiMe3)Sc(CH2SiMe3)2(THF) (1) and Cp′Sc(CH2C6H4NMe2-o)2 (2: Cp′ = C5Me4SiMe3; 3: Cp′ = C5H5), have been examined. The microstructures and thermal properties of the obtained polymers were characterized by 1H-NMR, 13C-NMR, GPC and DSC. Significant ligand influence on the catalytic activity, selectivity, and polymer molecular weight has been observed in the homopolymerization of myrcene. The scandium complexes 1 and 2 bearing large C5Me4SiMe3 ligand showed relatively low activity (104 g polymer molSc−1 h−1) and preferred 3,4-selectivity (74% for 1 and 61% for 2). The myrcene homopolymers prepared by complexes 1 and 2 have low molecular weight (Mn = 1.7 × 104 − 5.6 × 104) and relatively high glass transition temperature (−48 and −45 °C). The complex 3 bearing small C5H5 ligand showed high activity (105 g polymer molSc−1 h−1) and high cis-1,4-selectivity (95%). The myrcene homopolymers prepared by complex 3 have high molecular weight (Mn = 7.0 × 104 − 2.31 × 105) and low glass transition temperature (Tg = −70 °C). By use of complex 3, the copolymerization of myrcene with butadiene was also achieved for the first time to afford a novel family of rubber materials. The copolymerization reaction was completed within 5 min, irrespective of the monomer feed ratio, and the copolymerization activity was raised to as high as 105 g polymer molSc−1 h−1. The copolymer composition was in agreement with the co-monomer feed ratio, suggesting that both monomers were completely incorporated into their copolymers. The obtained myrcene-butadiene copolymers showed a random monomer sequence distribution, and the cis-1,4 contents of both monomers in the copolymers were more than 92%. All of these copolymers showed a single Tg varing with the myrcene/butadiene ratio. The Tgs of the copolymers with myrcene content of 19 mol% − 75 mol% fell in a range of −95 °C to −71 °C, which are between those of homopolymyrcene (−70 °C) and homopolybutadiene (−107 °C). The Tg of the copolymers decreased with increasing butadiene content. The molecular weight of the myrcene-butadiene copolymers can be controlled simply by changing the monomer/catalyst ratio.
2018, 0(11): 1422-1429
doi: 10.11777/j.issn1000-3304.2018.18107
Abstract:
With inspiration from the structure of macromolecular thioether generated in the 9H-xanthene-9-thione mediated radical polymerization, five thioethers containing 9-alkyl-9-phenylthio/methylthio-xanthene structure were synthesized. Xanthydrol was selected as the precursor for two 9-substituted xanthene intermediates. 9-(Phenylthio)-9H-xanthene was obtained via a condensation reaction between xanthydrol and thiophenol in the presence of perchloric acid as catalyst. 9-(Methylthio)-9H-xanthene was obtained via the thioetherification of the chlorinated product of xanthydrol with sodium methyl mercaptide. The sulfurated intermediates were deprotonated by n-butyl lithium, and transformed into five target products via substitution reactions with three alkyl halides individually. 1H-NMR, 13C-NMR, FTIR and UV-Vis analyses were conducted to confirm and characterize the thioethers. Afterwards, a systematic study on the polymerization behavior of styrene (St) initiated by the thioethers was carried out in the absence and presence of a thermal initiator. Bulk polymerizations of St were initiated successfully by the thioethers at 80 °C with relatively low monomer conversions, and the reactions exhibited uncontrolled polymerization behaviors without obvious increase in number-average molecular weight (Mn) in the polymerization process with the PDI of polymeric products above 3.0. However, when the thioethers were used together with 2,2'-azobis(2,4-dimethyl)valeronitrile (ABVN) in the solution polymerization of St in toluene at 65 °C, higher monomer conversions compared with those of bulk polymerization and certain controllability could be achieved, reflected by a linear increase in Mn with conversion. Besides, the effects of molar ratio of ABVN to thioether and reaction temperature on the polymerization behavior of St were investigated in detail. A reduction in the molar ratio of ABVN to thioether would cause a reduction in the concentration of propagating radicals, and lead to a decrease in monomer conversion. But the PDI of polymeric product narrowed down indicating a controllable polymerization. Furthermore, elevated reaction temperature brought about an increased concentration of chain radical, and resulted in a relatively low Mn with a broadened PDI.
With inspiration from the structure of macromolecular thioether generated in the 9H-xanthene-9-thione mediated radical polymerization, five thioethers containing 9-alkyl-9-phenylthio/methylthio-xanthene structure were synthesized. Xanthydrol was selected as the precursor for two 9-substituted xanthene intermediates. 9-(Phenylthio)-9H-xanthene was obtained via a condensation reaction between xanthydrol and thiophenol in the presence of perchloric acid as catalyst. 9-(Methylthio)-9H-xanthene was obtained via the thioetherification of the chlorinated product of xanthydrol with sodium methyl mercaptide. The sulfurated intermediates were deprotonated by n-butyl lithium, and transformed into five target products via substitution reactions with three alkyl halides individually. 1H-NMR, 13C-NMR, FTIR and UV-Vis analyses were conducted to confirm and characterize the thioethers. Afterwards, a systematic study on the polymerization behavior of styrene (St) initiated by the thioethers was carried out in the absence and presence of a thermal initiator. Bulk polymerizations of St were initiated successfully by the thioethers at 80 °C with relatively low monomer conversions, and the reactions exhibited uncontrolled polymerization behaviors without obvious increase in number-average molecular weight (Mn) in the polymerization process with the PDI of polymeric products above 3.0. However, when the thioethers were used together with 2,2'-azobis(2,4-dimethyl)valeronitrile (ABVN) in the solution polymerization of St in toluene at 65 °C, higher monomer conversions compared with those of bulk polymerization and certain controllability could be achieved, reflected by a linear increase in Mn with conversion. Besides, the effects of molar ratio of ABVN to thioether and reaction temperature on the polymerization behavior of St were investigated in detail. A reduction in the molar ratio of ABVN to thioether would cause a reduction in the concentration of propagating radicals, and lead to a decrease in monomer conversion. But the PDI of polymeric product narrowed down indicating a controllable polymerization. Furthermore, elevated reaction temperature brought about an increased concentration of chain radical, and resulted in a relatively low Mn with a broadened PDI.
2018, 0(11): 1430-1441
doi: 10.11777/j.issn1000-3304.2018.18075
Abstract:
Two triphenylamines (TPA) based diamine monomers, TPCDA and TPNDA, were successfully designed and synthesized, which were of similar chemical structures but different electronic effects. Both TPCDA and TPNDA exhibit aggregation induced emission (AIE) phenomenon, and show intense emission at 395 and 447 nm in the solid state, respectively. They were polymerized with two dianhydrides (BPADA and HQDPA), respectively, to form four novel polyimides with excellent thermal stability. The fluorescence of the polyimides derived from TPNDA, TPNBPI and TPNHPI, is totally quenched. However, for the TPCDA-based polyimides, TPCBPI and TPCHPI show bright orange photoluminescence at 565 and 585 nm in their films, respectively. By increasing the concentration of TPCBPI and TPNBPI in N-methyl pyrrolidone (NMP) solution, their emission changes from non-luminescence to bright blue emission, followed by a red-shift due to the formation of strong intermolecular charge transfer, and they show green emission at 504 nm and 508 nm at the concentration of 4 mg·mL−1. The photoluminescence of TPCDA-based polyimides is similar to the composite system, where TPA is doped in a polyimide with the same main-chain structure. However, the theoretical calculations for the model units of the resulting polyimides show that both the conjugated TPNDA-based system and the unconjugated TPCDA-based system are non-luminescent due to an inhibited transition from HOMO to LUMO level. Further studies show that the luminescent properties of the TPCDA-based polyimides are owing to the following two reasons: (1) Compared with the TPNDA-based system, the sp3 hybridized carbon atom in the TPCDA-based system separates the TPA structure from the polyimide main chain, which dispels the influence of the intramolecular charge transfer effect of the polyimide on TPA; (2) The relatively independent TPA moieties can have strong intermolecular charge transfer interaction with the polyimide main chains, which leads this system to exhibiting a strong orange fluorescence with a 184 nm red-shift of the max emission wavelength. This work demonstrates a simple strategy to develop aromatic polyimides with high fluorescence for potential applications in organic photoelectric field.
Two triphenylamines (TPA) based diamine monomers, TPCDA and TPNDA, were successfully designed and synthesized, which were of similar chemical structures but different electronic effects. Both TPCDA and TPNDA exhibit aggregation induced emission (AIE) phenomenon, and show intense emission at 395 and 447 nm in the solid state, respectively. They were polymerized with two dianhydrides (BPADA and HQDPA), respectively, to form four novel polyimides with excellent thermal stability. The fluorescence of the polyimides derived from TPNDA, TPNBPI and TPNHPI, is totally quenched. However, for the TPCDA-based polyimides, TPCBPI and TPCHPI show bright orange photoluminescence at 565 and 585 nm in their films, respectively. By increasing the concentration of TPCBPI and TPNBPI in N-methyl pyrrolidone (NMP) solution, their emission changes from non-luminescence to bright blue emission, followed by a red-shift due to the formation of strong intermolecular charge transfer, and they show green emission at 504 nm and 508 nm at the concentration of 4 mg·mL−1. The photoluminescence of TPCDA-based polyimides is similar to the composite system, where TPA is doped in a polyimide with the same main-chain structure. However, the theoretical calculations for the model units of the resulting polyimides show that both the conjugated TPNDA-based system and the unconjugated TPCDA-based system are non-luminescent due to an inhibited transition from HOMO to LUMO level. Further studies show that the luminescent properties of the TPCDA-based polyimides are owing to the following two reasons: (1) Compared with the TPNDA-based system, the sp3 hybridized carbon atom in the TPCDA-based system separates the TPA structure from the polyimide main chain, which dispels the influence of the intramolecular charge transfer effect of the polyimide on TPA; (2) The relatively independent TPA moieties can have strong intermolecular charge transfer interaction with the polyimide main chains, which leads this system to exhibiting a strong orange fluorescence with a 184 nm red-shift of the max emission wavelength. This work demonstrates a simple strategy to develop aromatic polyimides with high fluorescence for potential applications in organic photoelectric field.
2018, 0(11): 1442-1450
doi: 10.11777/j.issn1000-3304.2018.18100
Abstract:
Amphiphilic and conjugated polymers based on poly(phenylenebutadiynylene)s (A-PPB) were designed and synthesized, which were consisted of a hydrophobic rigid conjugated main chain and hydrophilic flexible side chains with carboxylic anions. Structure and degree of polymerization (DP) of the polymers were examined by proton nuclear magnetic resonance (1H-NMR), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The two dimensional self-assembly of the amphiphilic conjugated polymers was investigated in different solvents and their mixtures. The morphology of the aggregates was characterized by transmission electron microscopy (TEM). The results showed that A-PPB in water self-assembled into two-dimentional supramolecular nanosheets (2D-SNS) with size ranged from hundred nanometers to several microns. The thickness of 2D-SNS was measured to be about 5 nm by atomic force microscopy (AFM), indicating a stack of 3 layers. The results of high-resolution TEM (HRTEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD) demonstrated that 2D-SNS was formed by the parallel arrangement of A-PPB, and the distance between the adjacent two A-PPB chains was consistent with the typical π-π stacking distance. On the other hand, A-PPB in methanol formed irregular aggregates because of its high solubility. However, when toluene was added into the methanolsolution of A-PPB, multilayered aggregates were obtained. Moreover, self-assembly of the non-amphiphilic precursor PPB was also examined in a mixed solvent of chloroform and methanol, and the TEM images showed that PPB formed multi-layered aggregates. This result indicated that the amphiphilicity and the electrostatic repulsion of the polymer chains played an important role in the formation of the layered sheets. In addition, DP of A-PPB is also important for 2D self-assembly of the polymers. When DP was 8, amphiphilic oligo(phenylenebutadiynylene)s formed disordered aggregates. In conclusion, this work provides significant information for 2D self-assembly of linear amphiphilic and conjugated polymers.
Amphiphilic and conjugated polymers based on poly(phenylenebutadiynylene)s (A-PPB) were designed and synthesized, which were consisted of a hydrophobic rigid conjugated main chain and hydrophilic flexible side chains with carboxylic anions. Structure and degree of polymerization (DP) of the polymers were examined by proton nuclear magnetic resonance (1H-NMR), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. The two dimensional self-assembly of the amphiphilic conjugated polymers was investigated in different solvents and their mixtures. The morphology of the aggregates was characterized by transmission electron microscopy (TEM). The results showed that A-PPB in water self-assembled into two-dimentional supramolecular nanosheets (2D-SNS) with size ranged from hundred nanometers to several microns. The thickness of 2D-SNS was measured to be about 5 nm by atomic force microscopy (AFM), indicating a stack of 3 layers. The results of high-resolution TEM (HRTEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD) demonstrated that 2D-SNS was formed by the parallel arrangement of A-PPB, and the distance between the adjacent two A-PPB chains was consistent with the typical π-π stacking distance. On the other hand, A-PPB in methanol formed irregular aggregates because of its high solubility. However, when toluene was added into the methanolsolution of A-PPB, multilayered aggregates were obtained. Moreover, self-assembly of the non-amphiphilic precursor PPB was also examined in a mixed solvent of chloroform and methanol, and the TEM images showed that PPB formed multi-layered aggregates. This result indicated that the amphiphilicity and the electrostatic repulsion of the polymer chains played an important role in the formation of the layered sheets. In addition, DP of A-PPB is also important for 2D self-assembly of the polymers. When DP was 8, amphiphilic oligo(phenylenebutadiynylene)s formed disordered aggregates. In conclusion, this work provides significant information for 2D self-assembly of linear amphiphilic and conjugated polymers.
Synthesis of Near-infrared Poly(IB-alt-MAnh)-aza-bodipy and Its Application in Photoacoustic Imaging
2018, 0(11): 1451-1459
doi: 10.11777/j.issn1000-3304.2018.18068
Abstract:
Near-infrared poly(isobutylene-alt-MAnh)-aza-bodipy, which can be used as photoacoustic imaging contrast agent in vivo mice, was synthesized by ring opening reaction of poly(isobutylene-alt-MAnh) with hydroxyl group. Near-infrared organic nanoparticle was formed in water with their hydrodynamic diameter of 60 nm. These nanoparticles were formed with a core of aza-bodipy dye and shell of polymer. Dynamic light scattering (DLS), transmission electron microscopy (TEM) and ultraviolet-visible absorption spectra (UV-Vis) were used to characterize the morphology, size and optical property of the nanoparticles in aqueous solution. The results showed that the nanoparticles had uniform appearance and strong absorption in near-infrared area. Moreover, DLS was used to observe the stability of nanoparticles in serum and the size of nanoparticles was kept pratically constant within 24 h. Photothermal experiment was conducted to study the nanoparticle performance at different power and concentration, which exhibited excellent photothermal performance. MTT assay demonstrated that the nanoparticles had a good biocompatibility and photothermal performance at different concentrations. In addition, the photoacoustic property of the nanoparticles was studied by photoacoustic imaging and the results showed that they had strong photoacoustic signals at a low concentration. Photoacoustic imaging experiments on mice were also studied. It was found that tumor location on mice had a significant photoacoustic signal enhancement after tail vein injection of the nanoparticles. With 24 h of circulation in blood after injection of the nanoparticles, the photoacoustic signal disappeared, which indicated that the nanoparticles had good metabolic and biocompatibility.
Near-infrared poly(isobutylene-alt-MAnh)-aza-bodipy, which can be used as photoacoustic imaging contrast agent in vivo mice, was synthesized by ring opening reaction of poly(isobutylene-alt-MAnh) with hydroxyl group. Near-infrared organic nanoparticle was formed in water with their hydrodynamic diameter of 60 nm. These nanoparticles were formed with a core of aza-bodipy dye and shell of polymer. Dynamic light scattering (DLS), transmission electron microscopy (TEM) and ultraviolet-visible absorption spectra (UV-Vis) were used to characterize the morphology, size and optical property of the nanoparticles in aqueous solution. The results showed that the nanoparticles had uniform appearance and strong absorption in near-infrared area. Moreover, DLS was used to observe the stability of nanoparticles in serum and the size of nanoparticles was kept pratically constant within 24 h. Photothermal experiment was conducted to study the nanoparticle performance at different power and concentration, which exhibited excellent photothermal performance. MTT assay demonstrated that the nanoparticles had a good biocompatibility and photothermal performance at different concentrations. In addition, the photoacoustic property of the nanoparticles was studied by photoacoustic imaging and the results showed that they had strong photoacoustic signals at a low concentration. Photoacoustic imaging experiments on mice were also studied. It was found that tumor location on mice had a significant photoacoustic signal enhancement after tail vein injection of the nanoparticles. With 24 h of circulation in blood after injection of the nanoparticles, the photoacoustic signal disappeared, which indicated that the nanoparticles had good metabolic and biocompatibility.
2018, 0(11): 1460-1466
doi: 10.11777/j.issn1000-3304.2018.18087
Abstract:
Highly thermal conductive and flexible materials are urgently required in the heat management of high-power electronic devices. In this work, a composite film with these required properties, based on graphene and carbonized Chinese art paper, is prepared through a green route. Graphite is directly exfoliated in water in the presence of polyvinylpyrrolidone surfactant into high-quality graphene through a combination of large and small ball milling. The exfoliated graphene is filled into the porous network of the flexible superhydrophilic Chinese art paper through immersion absorption. After drying, the immersed Chinese art paper is mechanically compressed and carbonized at high temperature, leading to a composite film of graphene and carbonized Chinese art paper. TEM shows that the exfoliated graphene nanoplatelets is of layered structure and has a diameter in the range of several hundreds of nanometers to several micrometers. Raman spectroscopy proves that the exfoliated graphene nanoplatelet has a few defects with a low intensity ratio of D peak to G peak (0.25). SEM image shows that the graphene nanoplatelets filled in Chinese art paper are interconnected, which provides continuous channels for phonon transport. Mechanical compression increases the mass density of the composite film and improves the contact between the graphene nanoplatelets. Raman spectroscopy proves that annealing at high temperature decreases the amount of SP3 hybrid carbon. As a result, the resultant composite film of graphene and carbonized Chinese art paper shows excellent thermal conductivity of 258 W/mK, superior to previously reported RGO-polymer composites (0.8 – 19.5 W/mK). The interconnected three-dimensional microfiber network of the carbonized Chinese art paper imparts the composite film with good flexibility, superior to that of the pure graphene film. After 100 bending cycles, the electrical resistance of the composite film remains practically unchanged. Compared with the conventional chemical oxidation-thermal reduction, the present route is environment-friendly, which avoids the use of strong oxidizing acids and does not generate acidic waste water.
Highly thermal conductive and flexible materials are urgently required in the heat management of high-power electronic devices. In this work, a composite film with these required properties, based on graphene and carbonized Chinese art paper, is prepared through a green route. Graphite is directly exfoliated in water in the presence of polyvinylpyrrolidone surfactant into high-quality graphene through a combination of large and small ball milling. The exfoliated graphene is filled into the porous network of the flexible superhydrophilic Chinese art paper through immersion absorption. After drying, the immersed Chinese art paper is mechanically compressed and carbonized at high temperature, leading to a composite film of graphene and carbonized Chinese art paper. TEM shows that the exfoliated graphene nanoplatelets is of layered structure and has a diameter in the range of several hundreds of nanometers to several micrometers. Raman spectroscopy proves that the exfoliated graphene nanoplatelet has a few defects with a low intensity ratio of D peak to G peak (0.25). SEM image shows that the graphene nanoplatelets filled in Chinese art paper are interconnected, which provides continuous channels for phonon transport. Mechanical compression increases the mass density of the composite film and improves the contact between the graphene nanoplatelets. Raman spectroscopy proves that annealing at high temperature decreases the amount of SP3 hybrid carbon. As a result, the resultant composite film of graphene and carbonized Chinese art paper shows excellent thermal conductivity of 258 W/mK, superior to previously reported RGO-polymer composites (0.8 – 19.5 W/mK). The interconnected three-dimensional microfiber network of the carbonized Chinese art paper imparts the composite film with good flexibility, superior to that of the pure graphene film. After 100 bending cycles, the electrical resistance of the composite film remains practically unchanged. Compared with the conventional chemical oxidation-thermal reduction, the present route is environment-friendly, which avoids the use of strong oxidizing acids and does not generate acidic waste water.
