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2011 Volume 29 Issue 4
2011, 29(4): 397-406
doi: 10.1007/s10118-011-1054-6
Abstract:
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2011, 29(4): 407-413
doi: 10.1007/s10118-011-1051-9
Abstract:
Three types of microfibrillated cellulose (MFC) with differences in structure and surface charge were used at low concentration as filler materials in polysodium acrylate superabsorbents (SAPs). The swelling of the composite hydrogels was determined in 0.9% NaCl solution as well as in deionized water. The shear modulus of the samples was determined through uniaxial compression analysis after synthesis and after swelling in 0.9% NaCl solution. Furthermore, the ability to retain filler effects after washing was investigated. The results showed that all of the investigated MFCs had a strong reinforcing effect on the shear modulus after synthesis. The filler effect on swelling and on the associated shear modulus of swollen samples showed a more complicated dependence on structure and surface charge. Finally, it was found that the filler effects were reasonably retained after washing and subsequent drying. The results confirm that MFC holds great potential as a filler material in superabsorbent applications. Furthermore, the results provide some insight on how the structural properties and surface charge of MFC will affect gel properties depending on swelling conditions. This information should be useful in evaluating the use of different types of MFC in future applications.
Three types of microfibrillated cellulose (MFC) with differences in structure and surface charge were used at low concentration as filler materials in polysodium acrylate superabsorbents (SAPs). The swelling of the composite hydrogels was determined in 0.9% NaCl solution as well as in deionized water. The shear modulus of the samples was determined through uniaxial compression analysis after synthesis and after swelling in 0.9% NaCl solution. Furthermore, the ability to retain filler effects after washing was investigated. The results showed that all of the investigated MFCs had a strong reinforcing effect on the shear modulus after synthesis. The filler effect on swelling and on the associated shear modulus of swollen samples showed a more complicated dependence on structure and surface charge. Finally, it was found that the filler effects were reasonably retained after washing and subsequent drying. The results confirm that MFC holds great potential as a filler material in superabsorbent applications. Furthermore, the results provide some insight on how the structural properties and surface charge of MFC will affect gel properties depending on swelling conditions. This information should be useful in evaluating the use of different types of MFC in future applications.
2011, 29(4): 414-420
doi: 10.1007/s10118-011-1053-7
Abstract:
We study the interaction between two like charged surfaces embedded in a solution of oppositely charged multivalent rod-like counterions. The counterions consist of two rigidly bonded point charges, each of valency Z. The strength of the electrostatic coupling increases with increasing surface charge density or valency of the charges. The system is analyzed by employing a self-consistent field theory, which treats the short and long range interactions of the counterions within different approximations. We find that in the weak coupling limit, the interactions are only repulsive. In the intermediate coupling regime, the multivalent rod-like counterions can mediate attractive interactions between the surfaces. For sufficiently long rods, bridging contributes to the attractive interaction. In the strong coupling limit, the charge correlations can contribute to the attractive interactions at short separations between the charged surfaces. Two minima can then appear in the force curve between surfaces.
We study the interaction between two like charged surfaces embedded in a solution of oppositely charged multivalent rod-like counterions. The counterions consist of two rigidly bonded point charges, each of valency Z. The strength of the electrostatic coupling increases with increasing surface charge density or valency of the charges. The system is analyzed by employing a self-consistent field theory, which treats the short and long range interactions of the counterions within different approximations. We find that in the weak coupling limit, the interactions are only repulsive. In the intermediate coupling regime, the multivalent rod-like counterions can mediate attractive interactions between the surfaces. For sufficiently long rods, bridging contributes to the attractive interaction. In the strong coupling limit, the charge correlations can contribute to the attractive interactions at short separations between the charged surfaces. Two minima can then appear in the force curve between surfaces.
2011, 29(4): 421-426
doi: 10.1007/s10118-011-1060-8
Abstract:
Cationic polymers have been receiving much attention as non-viral gene vectors. The aqueous mobile phase was optimized in combination with Shodex OHpak SB columns for size-exclusion chromatography (SEC) analysis of disulfide-containing poly(ethylene imine) (PEI) derivatives used in gene delivery. Addition of acetonitrile in mobile phase was shown to be able to suppress the hydrophobic interactions between polymer analytes and the stationary phase. The absolute molecular weights and distributions of the cationic polymers were determined directly from online SEC-MALS (multi-angle light scattering)/RI (refractive index detector). The results demonstrate that a good SEC separation of disulfide-containing PEI derivatives used in gene delivery with little band broadening was achieved.
Cationic polymers have been receiving much attention as non-viral gene vectors. The aqueous mobile phase was optimized in combination with Shodex OHpak SB columns for size-exclusion chromatography (SEC) analysis of disulfide-containing poly(ethylene imine) (PEI) derivatives used in gene delivery. Addition of acetonitrile in mobile phase was shown to be able to suppress the hydrophobic interactions between polymer analytes and the stationary phase. The absolute molecular weights and distributions of the cationic polymers were determined directly from online SEC-MALS (multi-angle light scattering)/RI (refractive index detector). The results demonstrate that a good SEC separation of disulfide-containing PEI derivatives used in gene delivery with little band broadening was achieved.
2011, 29(4): 431-438
doi: 10.1007/s10118-011-1043-9
Abstract:
Multifunctional organolithium initiator was prepared in cyclohexane solvent. The process started with adding the cyclohexane solution of butadiene to naphthalene-lithium in batches to produce butadiene oligomer dilithium with 4-8 butadiene repeating units. In the first feeding, the maximum loading of cyclohexane and the minimum concentration of butadiene cyclohexane solution must be controlled under Vcyclohexane 1.33VTHF and 40.6cN. Then, SnCl4 was added and eventually the multifunctional organolithium initiator containing Sn atom was synthesized through coupling reaction. Experiment results showed that adding the cyclohexane solution in batches was effective in overcoming some difficulties, such as insolubility of naphthalene-lithium in cyclohexane, low efficiency of naphthalene-lithium in initiating butadiene. In practice, benzene can be replaced by cyclohexane completely, which can not only reduce environmental pollution from benzene, but also overcome the difficulty of solvent recovery caused by similar boiling point between benzene and cyclohexane. Prepared with multifunctional organolithium containing Sn atom as initiator, the star-shaped solution polymerized styrene-butadiene rubber (star S-SBR) with better vulcanization performances, lower rolling resistance and higher wet-skid resistance was obtained.
Multifunctional organolithium initiator was prepared in cyclohexane solvent. The process started with adding the cyclohexane solution of butadiene to naphthalene-lithium in batches to produce butadiene oligomer dilithium with 4-8 butadiene repeating units. In the first feeding, the maximum loading of cyclohexane and the minimum concentration of butadiene cyclohexane solution must be controlled under Vcyclohexane 1.33VTHF and 40.6cN. Then, SnCl4 was added and eventually the multifunctional organolithium initiator containing Sn atom was synthesized through coupling reaction. Experiment results showed that adding the cyclohexane solution in batches was effective in overcoming some difficulties, such as insolubility of naphthalene-lithium in cyclohexane, low efficiency of naphthalene-lithium in initiating butadiene. In practice, benzene can be replaced by cyclohexane completely, which can not only reduce environmental pollution from benzene, but also overcome the difficulty of solvent recovery caused by similar boiling point between benzene and cyclohexane. Prepared with multifunctional organolithium containing Sn atom as initiator, the star-shaped solution polymerized styrene-butadiene rubber (star S-SBR) with better vulcanization performances, lower rolling resistance and higher wet-skid resistance was obtained.
2011, 29(4): 439-449
doi: 10.1007/s10118-011-1045-7
Abstract:
Utilizing the hydrolysis and condensation of the methoxysilyl moieties, organic-inorganic hybrid poly(N-isopropylacrylamide-co-acrylamide-co-3-(trimethoxysilyl)propylmethacrylate) P(NIPAM-co-AM-co-TMSPMA) microgels were prepared via two different methods. The first method was that the microgels were post-fabricated from the cross-linkable linear P(NIPAM-co-AM-co-TMSPMA) terpolymer aqueous solutions above the lower critical solution temperature (LCST) of the terpolymer. For the second method, the microgels were directly synthesized by conventional surfactant free emulsion copolymerization of NIPAM, AM, and TMSPMA. The hydrodynamic diameter and stability of the resultant P(NIPAM-co-AM-co-TMSPMA) microgels strongly depend on the pH and temperature of the microgel aqueous solution. The hydrodynamic diameters of the microgels decreased with increasing the measuring temperature. The phase transition temperature of the microgels was found to be around 34?C, which was independent of the initial terpolymer concentration and shifted to lower temperature with increasing the preparation temperature. Increasing the initial amount of AM will enhance the instability of the microgels at high pH values. Moreover, the P(NIPAM-co-AM-co-TMSPMA) microgels obtained from the linear terpolymer had more homogeneous microstructures as compared with the corresponding NIPAM/AM/TMSPMA microgels prepared by one step emulsion copolymerization as revealed by light scattering measurements.
Utilizing the hydrolysis and condensation of the methoxysilyl moieties, organic-inorganic hybrid poly(N-isopropylacrylamide-co-acrylamide-co-3-(trimethoxysilyl)propylmethacrylate) P(NIPAM-co-AM-co-TMSPMA) microgels were prepared via two different methods. The first method was that the microgels were post-fabricated from the cross-linkable linear P(NIPAM-co-AM-co-TMSPMA) terpolymer aqueous solutions above the lower critical solution temperature (LCST) of the terpolymer. For the second method, the microgels were directly synthesized by conventional surfactant free emulsion copolymerization of NIPAM, AM, and TMSPMA. The hydrodynamic diameter and stability of the resultant P(NIPAM-co-AM-co-TMSPMA) microgels strongly depend on the pH and temperature of the microgel aqueous solution. The hydrodynamic diameters of the microgels decreased with increasing the measuring temperature. The phase transition temperature of the microgels was found to be around 34?C, which was independent of the initial terpolymer concentration and shifted to lower temperature with increasing the preparation temperature. Increasing the initial amount of AM will enhance the instability of the microgels at high pH values. Moreover, the P(NIPAM-co-AM-co-TMSPMA) microgels obtained from the linear terpolymer had more homogeneous microstructures as compared with the corresponding NIPAM/AM/TMSPMA microgels prepared by one step emulsion copolymerization as revealed by light scattering measurements.
2011, 29(4): 450-455
doi: 10.1007/s10118-011-1056-4
Abstract:
Organic microporous materials based on spiroketal and spirothioketal polymers were synthesized through 1,3-dioxol-forming polymerization reaction between pentaerythritol or pentaerythritol tetrathiol and different types of cyclohexa-1,4-dione derivatives. The structure of the prepared polymers was confirmed by NMR spectroscopy and molecular mass measurements. Nitrogen adsorption/desorption isotherms of the prepared polymers show a large amount of nitrogen adsorbed at low relative pressure indicating microporosity. These polymers have Brunauer Emmitt and Teller (BET) surface areas in the range from 492 (m2 g-1) to 685 (m2 g-1). The prepared polymers were found to be useful for pervaporation separation of methanol-toluenemixture with a separation factor up to 12.5 and fluxes, varying between 6.7 10-3 kg/(m2 h) and 13.4 10-3 kg/(m2 h).
Organic microporous materials based on spiroketal and spirothioketal polymers were synthesized through 1,3-dioxol-forming polymerization reaction between pentaerythritol or pentaerythritol tetrathiol and different types of cyclohexa-1,4-dione derivatives. The structure of the prepared polymers was confirmed by NMR spectroscopy and molecular mass measurements. Nitrogen adsorption/desorption isotherms of the prepared polymers show a large amount of nitrogen adsorbed at low relative pressure indicating microporosity. These polymers have Brunauer Emmitt and Teller (BET) surface areas in the range from 492 (m2 g-1) to 685 (m2 g-1). The prepared polymers were found to be useful for pervaporation separation of methanol-toluenemixture with a separation factor up to 12.5 and fluxes, varying between 6.7 10-3 kg/(m2 h) and 13.4 10-3 kg/(m2 h).
2011, 29(4): 456-464
doi: 10.1007/s10118-011-1049-3
Abstract:
Thin wall samples of high density polyethylene (HDPE) were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Youngs modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction (2D-WAXD), gel permeation chromatography (GPC), capillary rheometry and differential scanning calorimetry (DSC), respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.
Thin wall samples of high density polyethylene (HDPE) were prepared via injection molding with different injection speeds ranging from 100 mm/s to 1200 mm/s. A significant decrease in the tensile strength and Youngs modulus was observed with increasing injection speed. In order to investigate the mechanism behind this decrease, the orientation, molecular weight, molecular weight distribution, melt flow rate, crystallinity and crystal morphology of HDPE were characterized using two-dimensional wide-angle X-ray diffraction (2D-WAXD), gel permeation chromatography (GPC), capillary rheometry and differential scanning calorimetry (DSC), respectively. It is demonstrated that the orientation, molecular weight, molecular weight distribution, melt flow rate and crystallinity have no obvious change with increasing injection speed. Nevertheless, the content of extended chain crystals or large folded chain crystals was found to decrease with increasing injection speed. Therefore, it is concluded that the decrease in tensile properties is mainly contributed by the reduced content of extended chain crystals or large folded chain crystals. This study provides industry with valuable information for the application of high speed injection molding.
2011, 29(4): 465-474
doi: 10.1007/s10118-011-1055-5
Abstract:
A novel kind of aromatic diamine, N-(4-(4-(2,6-diphenyl pyridine-4-yl) phenoxy) phenyl)-3,5-diaminobezamide (DPDAB), was synthesized via aromatic nucleophilic substitution of 3,5-dinitrobenzoylchloride with 4-(4-(2,6-diphenylpyridine-4-yl)phenoxy)aniline (DPPA), followed by palladium-catalyzed hydrazine reduction. This monomer was used to prepare polyimides (PIs) based on reaction with several commerically avaiable tetracarboxylic dianhydrides such as pyromellatic dianhydride (PMDA), benzophenone tetracarboxylic acide dianhydride (BTDA) and bicycle [2.2.2] oct-7-ene-2, 3,5,6-tetracarboxylic dianhydride (BCDA). These PIs had inherent viscosity in the range of 0.34-0.76 dL/g and showed good solubility in various aprotic polar solvents. The glass-transition tempratures (Tgs) of the PIs were in the range of184-302C, and showed high thermal stability with 10% weight loss in the temperature range of 360-500C under nitrogen atmosphere.
A novel kind of aromatic diamine, N-(4-(4-(2,6-diphenyl pyridine-4-yl) phenoxy) phenyl)-3,5-diaminobezamide (DPDAB), was synthesized via aromatic nucleophilic substitution of 3,5-dinitrobenzoylchloride with 4-(4-(2,6-diphenylpyridine-4-yl)phenoxy)aniline (DPPA), followed by palladium-catalyzed hydrazine reduction. This monomer was used to prepare polyimides (PIs) based on reaction with several commerically avaiable tetracarboxylic dianhydrides such as pyromellatic dianhydride (PMDA), benzophenone tetracarboxylic acide dianhydride (BTDA) and bicycle [2.2.2] oct-7-ene-2, 3,5,6-tetracarboxylic dianhydride (BCDA). These PIs had inherent viscosity in the range of 0.34-0.76 dL/g and showed good solubility in various aprotic polar solvents. The glass-transition tempratures (Tgs) of the PIs were in the range of184-302C, and showed high thermal stability with 10% weight loss in the temperature range of 360-500C under nitrogen atmosphere.
2011, 29(4): 475-482
doi: 10.1007/s10118-011-1048-4
Abstract:
Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-em-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction temperature, ethylene/propylene molar ratio, aluminium/vanadium (Al/V) molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated. The molecular weight, molecular weight distribution, sequence composition and crystallinity of the products were measured by gel permeation chromatography, 13C-NMR and differential scanning calorimetry analysis, respectively. In comparison to the vanadium and titanium catalysts, the bimetallic catalyst showed higher catalytic activity and better copolymerization performance. The obtained ethylene/propylene copolymers have high molecular weight(105), broad molecular weight distribution, high propylene content with random or short blocked sequence structures(rErP = 1.919), low melting temperatures and low crystallinities (Xc 20%).
Magnesium chloride supported vanadium/titanium bimetallic Ziegler-Natta catalysts with di-em-butyl phthalate as internal donor for copolymerization of ethylene and propylene were prepared. The effects of reaction temperature, ethylene/propylene molar ratio, aluminium/vanadium (Al/V) molar ratio and titanium/vanadium molar ratio on the catalytic activity were investigated. The molecular weight, molecular weight distribution, sequence composition and crystallinity of the products were measured by gel permeation chromatography, 13C-NMR and differential scanning calorimetry analysis, respectively. In comparison to the vanadium and titanium catalysts, the bimetallic catalyst showed higher catalytic activity and better copolymerization performance. The obtained ethylene/propylene copolymers have high molecular weight(105), broad molecular weight distribution, high propylene content with random or short blocked sequence structures(rErP = 1.919), low melting temperatures and low crystallinities (Xc 20%).
2011, 29(4): 483-489
doi: 10.1007/s10118-011-1052-8
Abstract:
Modulated-temperature differential scanning calorimetric and dynamic mechanical analyses and dielectric spectroscopy were used to investigate the glass transition of hydrated wheat gliadin powders with moisture absorption ranged from 2.30 db% to 18.21 db%. Glass transition temperature (Tg) of dry wheat gliadin was estimated according to the Gordon-Taylor equation. Structural heterogeneity at high degrees of hydration was revealed in dielectric temperature and frequency spectra. The activation energies (Ea) of the two relaxations were calculated from Arrhenius equation.
Modulated-temperature differential scanning calorimetric and dynamic mechanical analyses and dielectric spectroscopy were used to investigate the glass transition of hydrated wheat gliadin powders with moisture absorption ranged from 2.30 db% to 18.21 db%. Glass transition temperature (Tg) of dry wheat gliadin was estimated according to the Gordon-Taylor equation. Structural heterogeneity at high degrees of hydration was revealed in dielectric temperature and frequency spectra. The activation energies (Ea) of the two relaxations were calculated from Arrhenius equation.
2011, 29(4): 490-496
doi: 10.1007/s10118-011-1050-x
Abstract:
Bifunctional spherical polyelectrolyte brushes (SPBs) with tunable thermo- and pH-sensitivity are synthesized by combining thermo-controlled emulsion polymerization and photo-emulsion polymerization. They consist of a spherical polystyrene core and a shell of mixed brushes of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) whose composition can be easily modulated by the dose of monomers. The kinetics of SPB synthesis as well as their size change with temperature and pH is determined by dynamic light scattering (DLS). The scanning electron microscopy (SEM) images show that the bifunctional SPBs have a defined spherical morphology with a narrow size distribution.
Bifunctional spherical polyelectrolyte brushes (SPBs) with tunable thermo- and pH-sensitivity are synthesized by combining thermo-controlled emulsion polymerization and photo-emulsion polymerization. They consist of a spherical polystyrene core and a shell of mixed brushes of poly(N-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAA) whose composition can be easily modulated by the dose of monomers. The kinetics of SPB synthesis as well as their size change with temperature and pH is determined by dynamic light scattering (DLS). The scanning electron microscopy (SEM) images show that the bifunctional SPBs have a defined spherical morphology with a narrow size distribution.
2011, 29(4): 497-505
doi: 10.1007/s10118-011-1059-1
Abstract:
The impact propylene copolymer (IPC) and isotactic polypropylene (iPP) were separately selected to prepare laminates with high density polyethylene (HDPE) by hot press. The peel forces of IPC/HDPE and iPP/HDPE laminates were examined, and it was found that the welded joint strength in IPC/HDPE laminate was dramatically higher than that of iPP/HDPE laminate. According to the special microstructure of IPC, the co-crystallization of the ethylene segments in ethylene-propylene block copolymer (EbP) component of IPC and the PE chain in HDPE was proposed to explain the high-strength welding. The DSC results indicated that there indeed existed some interaction between IPC and HDPE, and the crystallizable PE component in IPC could affect the crystallization of HDPE. The scanning electron microscope (SEM) observations of IPC/HDPE blends demonstrated that HDPE tended to stay with the PE-rich EbP chains to form the dispersed phase, indicating the good miscibility between HDPE and EbP components of IPC. According to the above results, the effect of co-crystallization of the PE components of the IPC and HDPE on the high weld strength of IPC/HDPE laminate was confirmed.
The impact propylene copolymer (IPC) and isotactic polypropylene (iPP) were separately selected to prepare laminates with high density polyethylene (HDPE) by hot press. The peel forces of IPC/HDPE and iPP/HDPE laminates were examined, and it was found that the welded joint strength in IPC/HDPE laminate was dramatically higher than that of iPP/HDPE laminate. According to the special microstructure of IPC, the co-crystallization of the ethylene segments in ethylene-propylene block copolymer (EbP) component of IPC and the PE chain in HDPE was proposed to explain the high-strength welding. The DSC results indicated that there indeed existed some interaction between IPC and HDPE, and the crystallizable PE component in IPC could affect the crystallization of HDPE. The scanning electron microscope (SEM) observations of IPC/HDPE blends demonstrated that HDPE tended to stay with the PE-rich EbP chains to form the dispersed phase, indicating the good miscibility between HDPE and EbP components of IPC. According to the above results, the effect of co-crystallization of the PE components of the IPC and HDPE on the high weld strength of IPC/HDPE laminate was confirmed.
2011, 29(4): 506-512
doi: 10.1007/s10118-011-1058-2
Abstract:
Two highly soluble aromatic polyimides were synthesized successfully from a diamine with two tert-butyl groups (MBTBA) and dianhydrides with a thioether or sulfone moiety (DTDA and DSDA). Both of them showed excellent solubility in common solvents such as chloroform, tetrahydrofuran and dioxane at the room temperature. The number-average molecular weight was 6.0 104 and 8.3 104 according to gel permeation chromatography relative to a polystyrene standard, and the polydispersity index was 1.80 and 1.82 respectively. The glass-transition temperatures of them were 286C and 314C (or 315C and 358C) respectively, as measured by differential scanning calorimetry (or dynamic mechanical analysis). The 5% weight loss temperature of both was near 490C in N2 by thermogravimetric analysis. These results indicated that the tert-butyl pendent groups reduced the interactions among polymer chains and the thioether or sulfone moiety was flexible which may improve their solubility in conventional organic solvents without the loss of thermal stability. Transparent and flexible films of the two polyimides were obtained via solution casting. The MBTBA-DTDA membrane had higher storage moduli than those of the MBTBA-DSDA membrane.
Two highly soluble aromatic polyimides were synthesized successfully from a diamine with two tert-butyl groups (MBTBA) and dianhydrides with a thioether or sulfone moiety (DTDA and DSDA). Both of them showed excellent solubility in common solvents such as chloroform, tetrahydrofuran and dioxane at the room temperature. The number-average molecular weight was 6.0 104 and 8.3 104 according to gel permeation chromatography relative to a polystyrene standard, and the polydispersity index was 1.80 and 1.82 respectively. The glass-transition temperatures of them were 286C and 314C (or 315C and 358C) respectively, as measured by differential scanning calorimetry (or dynamic mechanical analysis). The 5% weight loss temperature of both was near 490C in N2 by thermogravimetric analysis. These results indicated that the tert-butyl pendent groups reduced the interactions among polymer chains and the thioether or sulfone moiety was flexible which may improve their solubility in conventional organic solvents without the loss of thermal stability. Transparent and flexible films of the two polyimides were obtained via solution casting. The MBTBA-DTDA membrane had higher storage moduli than those of the MBTBA-DSDA membrane.
2011, 29(4): 513-519
doi: 10.1007/s10118-010-1028-0
Abstract:
The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130?C were investigated by means of optical microscopy, AFM and X-ray diffraction. The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably, which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition. The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals. It is further demonstrated that except for the different crystal orientation, the PE does not influence the crystalline modification and crystallinity of the PLA.
The crystalline structure and morphology of the PLA crystallized isothermally from the glassy state on highly oriented PE substrates at 130?C were investigated by means of optical microscopy, AFM and X-ray diffraction. The results indicate that the PE substrate influences the crystallization behavior of PLA remarkably, which leads to the growth of PLA crystals on PE substrate always in edge-on form rather than the twisted lamellar crystals from edge-on to flat-on when crystallizing the PLA on glass surface under the same condition. The edge-on PLA lamellae on the PE substrate are preferentially arranged with their long axes in the chain direction of the PE substrate crystals. It is further demonstrated that except for the different crystal orientation, the PE does not influence the crystalline modification and crystallinity of the PLA.
2011, 29(4): 427-430
doi: 10.1007/s10118-011-1057-3
Abstract:
A biodegradable tumor targeting nano-probe based on poly(e-caprolactone)-b-poly(ethylene glycol) block copolymer (PCL-b-PEG) micelle functionalized with a magnetic resonance imaging (MRI) contrast agent diethylenetriaminepentaacetic acid-gadolinium (DTPA-Gd3+)on the shell and a near-infrared (NIR) dye in the core for magnetic resonance and optical dual-modality imaging was prepared. The longitudinal relaxivity (r1) of the PCL-b-PEG-DTPA-Gd3+micelle was 13.4 (mmol/L)-1s-1, three folds of that of DTPA-Gd3+, and higher than that of many polymeric contrast agents with similar structures. The in vivo optical imaging of a nude mouse bearing xenografted breast tumor showed that the dual-modality micelle preferentially accumulated in the tumor via the folic acid-mediated active targeting and the passive accumulation by the enhanced permeability and retention (EPR) effect. The results indicated that the dual-modality micelle is a promising nano-probe for cancer detection and diagnosis.
A biodegradable tumor targeting nano-probe based on poly(e-caprolactone)-b-poly(ethylene glycol) block copolymer (PCL-b-PEG) micelle functionalized with a magnetic resonance imaging (MRI) contrast agent diethylenetriaminepentaacetic acid-gadolinium (DTPA-Gd3+)on the shell and a near-infrared (NIR) dye in the core for magnetic resonance and optical dual-modality imaging was prepared. The longitudinal relaxivity (r1) of the PCL-b-PEG-DTPA-Gd3+micelle was 13.4 (mmol/L)-1s-1, three folds of that of DTPA-Gd3+, and higher than that of many polymeric contrast agents with similar structures. The in vivo optical imaging of a nude mouse bearing xenografted breast tumor showed that the dual-modality micelle preferentially accumulated in the tumor via the folic acid-mediated active targeting and the passive accumulation by the enhanced permeability and retention (EPR) effect. The results indicated that the dual-modality micelle is a promising nano-probe for cancer detection and diagnosis.
