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2017 Volume 35 Issue 6
2017, 35(6): 693-699
doi: 10.1007/s10118-017-1932-7
Abstract:
A series of host-guest interaction-adjusted polylactide stereocomplex micelles was prepared via the self-assembly of 4-armed poly(ethylene glycol)-block-poly(L-lactide/D-lactide)-cholesterol (4-armed PEG-b-PLLA/PDLA-CHOL) and poly(β-cyclodextrin) (PCD) with the molar ratios of CHOL/β-CD at 1:0.5, 1:1, and 1:2 in an aqueous environment. The hydrodynamic diameters of the micelles ranged from 84.1 nm to 107 nm depending on the molar ratio of CHOL/β-CD. It was shown that the micelle with the largest proportion of PCD possessed excellent abilities in drug release, cell internalization as well as proliferation inhibitory effect toward human A549 lung cancer cells. The results demonstrated that the stereocomplex and host-guest interactions-mediated PLA micelles exhibited great potential in sustained drug delivery.
A series of host-guest interaction-adjusted polylactide stereocomplex micelles was prepared via the self-assembly of 4-armed poly(ethylene glycol)-block-poly(L-lactide/D-lactide)-cholesterol (4-armed PEG-b-PLLA/PDLA-CHOL) and poly(β-cyclodextrin) (PCD) with the molar ratios of CHOL/β-CD at 1:0.5, 1:1, and 1:2 in an aqueous environment. The hydrodynamic diameters of the micelles ranged from 84.1 nm to 107 nm depending on the molar ratio of CHOL/β-CD. It was shown that the micelle with the largest proportion of PCD possessed excellent abilities in drug release, cell internalization as well as proliferation inhibitory effect toward human A549 lung cancer cells. The results demonstrated that the stereocomplex and host-guest interactions-mediated PLA micelles exhibited great potential in sustained drug delivery.
2017, 35(6): 700-712
doi: 10.1007/s10118-017-1938-1
Abstract:
Generalized two-dimensional correlation spectroscopy (2DCOS) and its derivate technique, perturbation correlation moving window (PCMW), have found great potential in studying a series of physico-chemical phenomena in stimuli-responsive polymeric systems. By spreading peaks along a second dimension, 2DCOS can significantly enhance spectral resolution and discern the sequence of group dynamics applicable to various external perturbation-induced spectroscopic changes, especially in infrared (IR), near-infrared (NIR) and Raman spectroscopy. On the basis of 2DCOS synchronous power spectra changing, PCMW proves to be a powerful tool to monitor complicated spectral variations and to find transition points and ranges. This article reviews the recent work of our research group in the application of 2DCOS and PCMW in thermoresponsive polymers, mainly focused on liquid crystalline polymers and lower critical solution temperature (LCST)-type polymers. Details of group motions and chain conformational changes upon temperature perturbation can thus be elucidated at the molecular level, which contribute to the understanding of their phase transition nature.
Generalized two-dimensional correlation spectroscopy (2DCOS) and its derivate technique, perturbation correlation moving window (PCMW), have found great potential in studying a series of physico-chemical phenomena in stimuli-responsive polymeric systems. By spreading peaks along a second dimension, 2DCOS can significantly enhance spectral resolution and discern the sequence of group dynamics applicable to various external perturbation-induced spectroscopic changes, especially in infrared (IR), near-infrared (NIR) and Raman spectroscopy. On the basis of 2DCOS synchronous power spectra changing, PCMW proves to be a powerful tool to monitor complicated spectral variations and to find transition points and ranges. This article reviews the recent work of our research group in the application of 2DCOS and PCMW in thermoresponsive polymers, mainly focused on liquid crystalline polymers and lower critical solution temperature (LCST)-type polymers. Details of group motions and chain conformational changes upon temperature perturbation can thus be elucidated at the molecular level, which contribute to the understanding of their phase transition nature.
2017, 35(6): 713-720
doi: 10.1007/s10118-017-1928-3
Abstract:
Antibacterial thermoplastic polyurethane (TPU) electrospun fiber mats were prepared by adsorption of Ag nanoparticles (Ag NPs) onto TPU/3-aminopropyltriethoxysilane (APS) co-electrospun fiber mats from silver sol. The use of APS can functionalize TPU fibers with amino groups, facilitating the adsorption of Ag NPs. The effects of pH of silver sol and APS content on Ag NP adsorption and antibacterial activity were investigated. Ag NP adsorption was evidenced by TEM, XPS and TGA. Significant Ag NP adsorption occurred at pH = 3-5. The main driving force for Ag NP adsorption is electrostatic interaction between --NH3+ of the fibers and --COO- derived from the -COOH group capped on the surfaces of Ag NPs. The antibacterial activity of the Ag NP-decorated TPU/APS fiber mats was investigated using both gram-negative Escherichia coli and gram-positive Bacillus subtilis. The antibacterial rate increases with increasing APS content up to 5% where the antibacterial rates against both types of bacteria are over 99.9%.
Antibacterial thermoplastic polyurethane (TPU) electrospun fiber mats were prepared by adsorption of Ag nanoparticles (Ag NPs) onto TPU/3-aminopropyltriethoxysilane (APS) co-electrospun fiber mats from silver sol. The use of APS can functionalize TPU fibers with amino groups, facilitating the adsorption of Ag NPs. The effects of pH of silver sol and APS content on Ag NP adsorption and antibacterial activity were investigated. Ag NP adsorption was evidenced by TEM, XPS and TGA. Significant Ag NP adsorption occurred at pH = 3-5. The main driving force for Ag NP adsorption is electrostatic interaction between --NH3+ of the fibers and --COO- derived from the -COOH group capped on the surfaces of Ag NPs. The antibacterial activity of the Ag NP-decorated TPU/APS fiber mats was investigated using both gram-negative Escherichia coli and gram-positive Bacillus subtilis. The antibacterial rate increases with increasing APS content up to 5% where the antibacterial rates against both types of bacteria are over 99.9%.
2017, 35(6): 721-727
doi: 10.1007/s10118-017-1923-8
Abstract:
Half-titanocene complexes bearing dibenzhydryl-substituted aryloxide ligands (2a-2d) were prepared. Among them, 2c adopted a three-legged distorted tetrahedral geometry evidenced by X-ray crystallography. The poly-1, 3-butadiene with high molecular weight and narrow molecular weight distribution was obtained by using these complexes as the catalysts activated with methylaluminoxane (MAO). The catalytic activities of the complexes depended on their structures. The Ti―O―C bond in the complexes with large angle afforded them with higher activity, while Cp*-based complexes exhibited lower activities than the Cp-based analogues. The activity of complex increased with increasing the polymerization temperature while the selectivity remained no change, indicating the high thermal stability. Furthermore, the polymerization of 1, 3-butadiene catalyzed by 2a/MAO at 0 ℃ has been found in a living fashion.
Half-titanocene complexes bearing dibenzhydryl-substituted aryloxide ligands (2a-2d) were prepared. Among them, 2c adopted a three-legged distorted tetrahedral geometry evidenced by X-ray crystallography. The poly-1, 3-butadiene with high molecular weight and narrow molecular weight distribution was obtained by using these complexes as the catalysts activated with methylaluminoxane (MAO). The catalytic activities of the complexes depended on their structures. The Ti―O―C bond in the complexes with large angle afforded them with higher activity, while Cp*-based complexes exhibited lower activities than the Cp-based analogues. The activity of complex increased with increasing the polymerization temperature while the selectivity remained no change, indicating the high thermal stability. Furthermore, the polymerization of 1, 3-butadiene catalyzed by 2a/MAO at 0 ℃ has been found in a living fashion.
2017, 35(6): 728-738
doi: 10.1007/s10118-017-1920-y
Abstract:
A self-healing and recyclable carbon tube/epoxy adhesive was prepared by epoxy monomer with Diels-Alder (DA) bonds, diethylenetriamine and polyethyleneimine modified multi-wall carbon nanotubes (MWCNTs). The self-healing and recyclable ability was attained by thermally reversible Diels-Alder reaction between furan and maleimide in the epoxy monomer. By controlling the molar ratio of furfuryl glycidyl ether and 4, 4'-methylenebis(N-phenylmaleimide), the glass transition temperature and mechanical properties of MWCNTs/epoxy adhesives were varied. The self-healing properties of MWCNTs/epoxy polymers were evaluated by lap shear experiment and the results showed that the MWCNTs/epoxy adhesives exhibited enhanced mechanical properties and excellent self-healing ability under heat stimulus. The healing efficiency was related to the molecule mobility and the conversion of DA reaction between furan and maleimide. The MWCNTs/epoxy adhesives also displayed excellent recyclable ability by transforming into soluble polymer under heating. These materials offer a wide range of possibilities to produce materials with healing and recyclable ability and have the potential to bring great benefits to our daily lives by enhancing the safety, performance, and lifetime of products.
A self-healing and recyclable carbon tube/epoxy adhesive was prepared by epoxy monomer with Diels-Alder (DA) bonds, diethylenetriamine and polyethyleneimine modified multi-wall carbon nanotubes (MWCNTs). The self-healing and recyclable ability was attained by thermally reversible Diels-Alder reaction between furan and maleimide in the epoxy monomer. By controlling the molar ratio of furfuryl glycidyl ether and 4, 4'-methylenebis(N-phenylmaleimide), the glass transition temperature and mechanical properties of MWCNTs/epoxy adhesives were varied. The self-healing properties of MWCNTs/epoxy polymers were evaluated by lap shear experiment and the results showed that the MWCNTs/epoxy adhesives exhibited enhanced mechanical properties and excellent self-healing ability under heat stimulus. The healing efficiency was related to the molecule mobility and the conversion of DA reaction between furan and maleimide. The MWCNTs/epoxy adhesives also displayed excellent recyclable ability by transforming into soluble polymer under heating. These materials offer a wide range of possibilities to produce materials with healing and recyclable ability and have the potential to bring great benefits to our daily lives by enhancing the safety, performance, and lifetime of products.
2017, 35(6): 739-751
doi: 10.1007/s10118-017-1939-0
Abstract:
Various (SiO2/MgO/MgCl2)·TiClx Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified (SiO2/MgO/MgCl2)·TiClx Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher a-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution (MWD) and the lowest average molecular weight (MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.
Various (SiO2/MgO/MgCl2)·TiClx Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified (SiO2/MgO/MgCl2)·TiClx Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher a-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution (MWD) and the lowest average molecular weight (MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.
The Mobility of Threaded α-Cyclodextrins in PR Copolymer and Its Influences on Mechanical Properties
2017, 35(6): 752-763
doi: 10.1007/s10118-017-1913-x
Abstract:
The methylated polyrotaxane (MePR) copolymer was prepared via the methylation of hydroxyl of threaded α-cyclodextrin (α-CDs) in polyrotaxane (PR) copolymer by CH3I/NaH. Its structure was characterized by GPC, IR and NMR. The WXRD and TGA measurements showed the destruction of channel-like crystalline structure in MePR copolymer. The sliding of threaded α-CDs along PEG axis in PR and MePR copolymers was demonstrated by their dielectric spectra that also evidenced the presence of rotating of threaded α-CDs around PEG axis in MePR copolymer. The frequent and vigorous molecular mobility in MePR and PR copolymers was also verified by dynamic mechanical analysis (DMA) and rheological measurement, which was possibly assigned to the sliding and rotating of threaded α-CDs. DMA and rheological results showed that the mobility of α-CDs could simultaneously strengthen and toughen PR copolymer proved by stress-stain curves. In this paper, we report the CD mobility in PR and MePR copolymers. The macroscopic behaviors of PR copolymer, such as mechanical properties in solid state, were also found to be benefited from CD mobility.
The methylated polyrotaxane (MePR) copolymer was prepared via the methylation of hydroxyl of threaded α-cyclodextrin (α-CDs) in polyrotaxane (PR) copolymer by CH3I/NaH. Its structure was characterized by GPC, IR and NMR. The WXRD and TGA measurements showed the destruction of channel-like crystalline structure in MePR copolymer. The sliding of threaded α-CDs along PEG axis in PR and MePR copolymers was demonstrated by their dielectric spectra that also evidenced the presence of rotating of threaded α-CDs around PEG axis in MePR copolymer. The frequent and vigorous molecular mobility in MePR and PR copolymers was also verified by dynamic mechanical analysis (DMA) and rheological measurement, which was possibly assigned to the sliding and rotating of threaded α-CDs. DMA and rheological results showed that the mobility of α-CDs could simultaneously strengthen and toughen PR copolymer proved by stress-stain curves. In this paper, we report the CD mobility in PR and MePR copolymers. The macroscopic behaviors of PR copolymer, such as mechanical properties in solid state, were also found to be benefited from CD mobility.
2017, 35(6): 764-772
doi: 10.1007/s10118-017-1922-9
Abstract:
The microcrystalline structure and microvoid structure in carbon fibers during graphitization process (2300-2700 ℃) were characterized employing laser micro-Raman scattering (Raman), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy (HR-TEM). The crystalline sizes (La, Lc) increased and interlayer spacing (d002) decreased with increasing heat treatment temperature (HTT). The microvoids in the fibers grew up and contacted to the neighbors with the development of microcrystalline. In addition, the preferred orientation of graphite crystallite along fiber axis decreased and microvoids increased. The results are crucial for analyzing the evolution of microstructure of carbon fibers in the process of heat treatment and important for the preparation of high strength and high modulus carbon fibers.
The microcrystalline structure and microvoid structure in carbon fibers during graphitization process (2300-2700 ℃) were characterized employing laser micro-Raman scattering (Raman), X-ray diffraction (XRD), small angle X-ray scattering (SAXS), and high-resolution transmission electron microscopy (HR-TEM). The crystalline sizes (La, Lc) increased and interlayer spacing (d002) decreased with increasing heat treatment temperature (HTT). The microvoids in the fibers grew up and contacted to the neighbors with the development of microcrystalline. In addition, the preferred orientation of graphite crystallite along fiber axis decreased and microvoids increased. The results are crucial for analyzing the evolution of microstructure of carbon fibers in the process of heat treatment and important for the preparation of high strength and high modulus carbon fibers.
2017, 35(6): 773-781
doi: 10.1007/s10118-017-1929-2
Abstract:
Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly(lactic acid) (PLA) blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly(L-lactic acid) and poly(D-lactic acid), the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals (SCs) during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs (142 J/g) and homo-crystals (HCs, 93 J/g) is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.
Classic Avrami model and its modifications have found diverse applications in describing the thermal and phase behaviors of inorganic metals and organic polymers. The direct introduction of classic Avrami equation to offer quantitative analyses of crystallization kinetic parameters for enantiomeric poly(lactic acid) (PLA) blends may, however, lead to contradictory conclusions. As revealed by this study, during the characterization of isothermal melt and cold crystallization for stereocomplex PLA containing equal-weight poly(L-lactic acid) and poly(D-lactic acid), the kinetic parameters yielded by Avrami equation are not in line with the classic crystallization hypotheses or the direct morphological observations. The underlying mechanisms, to some extent, lie in the generation of stereocomplex crystals (SCs) during the cooling/heating which affects the subsequent crystallization dynamics. The huge gap between the melting enthalpies of 100% crystalline SCs (142 J/g) and homo-crystals (HCs, 93 J/g) is most likely responsible for the confusing kinetic parameters acquired from the deduction of Avrami equation, which is based on the integration of enthalpies as a function of crystallization time. This prompts for great care that the classic Avrami equation is not applicable to accurately describe the crystallization kinetics of stereocomplex PLA, given the generation of SCs prior to crystallization and the coexistence of HCs and SCs during crystallization.
Isothermal-crystallization Kinetics and Spherulite Growth of Aliphatic Polyketone/Polyamide-6 Blends
2017, 35(6): 782-792
doi: 10.1007/s10118-017-1936-3
Abstract:
In this research, the morphologies, isothermal-crystallization kinetics, and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied. A single glass-transition temperature (Tg) was determined, and the composition dependence of Tg for these blends was well described by the Kwei equation. The strong intermolecular interaction between the two polymer components was confirmed by melting-point depression. The isothermal-crystallization kinetics were analyzed on the basis of the Avrami approach. A linear increase in the radii of the spherulites with time was observed for all compositions. All the spherulites continued to grow at nearly identical growth rates. With increasing polyamide-6 content, the size of the spherulites in the polyketone/polyamide-6 blends gradually decreased, and the number of spherulites in the blends increased.
In this research, the morphologies, isothermal-crystallization kinetics, and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied. A single glass-transition temperature (Tg) was determined, and the composition dependence of Tg for these blends was well described by the Kwei equation. The strong intermolecular interaction between the two polymer components was confirmed by melting-point depression. The isothermal-crystallization kinetics were analyzed on the basis of the Avrami approach. A linear increase in the radii of the spherulites with time was observed for all compositions. All the spherulites continued to grow at nearly identical growth rates. With increasing polyamide-6 content, the size of the spherulites in the polyketone/polyamide-6 blends gradually decreased, and the number of spherulites in the blends increased.
