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2014 Volume 32 Issue 11
2014, 32(11): 1419-1430
doi: 10.1007/s10118-014-1527-5
Abstract:
The effect of nanoclay on the phase-separation behavior of poly(methyl methacrylate)/poly(vinyl acetate) (PMMA/PVAc) blends has been mainly investigated by small-angle laser light scattering. It is found that the effect of clay on the thermodynamics and kinetics of phase-separation for PMMA/PVAc blends seems inconsistent. The kinetics phase-separation rate decreases, while the thermodynamics parameters, cloud points Tcand delay time tD of isothermal phase-separation also decrease, and the variation amplitude depends on the matrix composition. The affinity of clay to PMMA results in the composition difference between the border layer and the polymer matrix and further causes the concentration fluctuation at the early stage of phase separation to reduce Tc and tD. On the other hand, the decrease of phase-separation rate is caused by the mechanical barrier effect of clay on the macromolecular diffusion of blend matrix. Hence, such seemingly counterintuitive results on the thermodynamics and kinetics of phase-separation are attributed to different dominant factors.
The effect of nanoclay on the phase-separation behavior of poly(methyl methacrylate)/poly(vinyl acetate) (PMMA/PVAc) blends has been mainly investigated by small-angle laser light scattering. It is found that the effect of clay on the thermodynamics and kinetics of phase-separation for PMMA/PVAc blends seems inconsistent. The kinetics phase-separation rate decreases, while the thermodynamics parameters, cloud points Tcand delay time tD of isothermal phase-separation also decrease, and the variation amplitude depends on the matrix composition. The affinity of clay to PMMA results in the composition difference between the border layer and the polymer matrix and further causes the concentration fluctuation at the early stage of phase separation to reduce Tc and tD. On the other hand, the decrease of phase-separation rate is caused by the mechanical barrier effect of clay on the macromolecular diffusion of blend matrix. Hence, such seemingly counterintuitive results on the thermodynamics and kinetics of phase-separation are attributed to different dominant factors.
2014, 32(11): 1431-1441
doi: 10.1007/s10118-014-1528-4
Abstract:
Eight-arm star-shaped poly(-caprolactone)-block-poly(ethylene glycol)s (SPCL-b-PEG) have been prepared by a combination of controlled ring-opening polymerization (CROP) and coupling reaction. First, eight-arm star-shaped poly(-caprolactone)s (SPCL) with a resorcinarene core were synthesized using octamethyl tetraundecylresorcinarene octaacetate as octa-initiator and yttrium tris(2, 6-di-tert-butyl-4-methylphenolate) [Y(DBMP)3] as catalyst. Then the coupling reaction was carried out between SPCLs and carboxyl-terminated methoxy poly(ethylene glycol)s (mPEG-COOH) in the presence of N, N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), resulting in eight-arm star-shaped SPCL-b-PEGs with controlled molecular weight and well-defined architecture. Furthermore, these amphiphilic eight-arm SPCL-b-PEGs could self-assemble into micelles with low critical micellar concentrations (CMC), which was characterized by fluorescent spectroscopy. Moreover, indomethacin loaded micelles with high drug loading content and high encapsulation efficiency can be prepared, which is probably due to the highly branched architecture. The morphologies of micelles were characterized by transmission electron microscopy (TEM), which exhibited diverse nanostructures as the drug loading contents varied. In vitro drug release of indomethacin from SPCL-b-PEG micelles was carried out in PBS, from which a sustained release behavior was observed. SPCL-b-PEG micelles did not show significant cytotoxicity at copolymer concentrations up to 1000 mg/L, making them very promising for drug delivery.
Eight-arm star-shaped poly(-caprolactone)-block-poly(ethylene glycol)s (SPCL-b-PEG) have been prepared by a combination of controlled ring-opening polymerization (CROP) and coupling reaction. First, eight-arm star-shaped poly(-caprolactone)s (SPCL) with a resorcinarene core were synthesized using octamethyl tetraundecylresorcinarene octaacetate as octa-initiator and yttrium tris(2, 6-di-tert-butyl-4-methylphenolate) [Y(DBMP)3] as catalyst. Then the coupling reaction was carried out between SPCLs and carboxyl-terminated methoxy poly(ethylene glycol)s (mPEG-COOH) in the presence of N, N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), resulting in eight-arm star-shaped SPCL-b-PEGs with controlled molecular weight and well-defined architecture. Furthermore, these amphiphilic eight-arm SPCL-b-PEGs could self-assemble into micelles with low critical micellar concentrations (CMC), which was characterized by fluorescent spectroscopy. Moreover, indomethacin loaded micelles with high drug loading content and high encapsulation efficiency can be prepared, which is probably due to the highly branched architecture. The morphologies of micelles were characterized by transmission electron microscopy (TEM), which exhibited diverse nanostructures as the drug loading contents varied. In vitro drug release of indomethacin from SPCL-b-PEG micelles was carried out in PBS, from which a sustained release behavior was observed. SPCL-b-PEG micelles did not show significant cytotoxicity at copolymer concentrations up to 1000 mg/L, making them very promising for drug delivery.
2014, 32(11): 1442-1449
doi: 10.1007/s10118-014-1534-6
Abstract:
The influence of solvent on the miscibility of polystyrene (PS) and poly (styrene-co-acrylonitrile) (PSAN) blends has been investigated viscometrically. The miscibility of different PS/PSAN blend (30/70, 50/50 and 70/30) compositions in acetone and benzene at 20, 30, and 40℃ was investigated on the basis of the sign of Chee (B and ), and Sun's () criteria. The values of these parameters were evaluated from the analyses of reduced viscosity data of binary (solvent/polymer) and ternary (solvent/polymer1/polymer2) polymer systems. These investigations indicated partial miscibility for both the blend systems. However, PS/PSAN/acetone blend system showed somewhat higher partial miscibility than the PS/PSAN/Benzene blend system highlighting the impact of solvent over the polymer-polymer interactions and hence their miscibility. The results obtained through viscometry were also corroborated by the refractive index and density results for the blends under study. The effect of temperature on miscibility in both the cases was almost negligible.
The influence of solvent on the miscibility of polystyrene (PS) and poly (styrene-co-acrylonitrile) (PSAN) blends has been investigated viscometrically. The miscibility of different PS/PSAN blend (30/70, 50/50 and 70/30) compositions in acetone and benzene at 20, 30, and 40℃ was investigated on the basis of the sign of Chee (B and ), and Sun's () criteria. The values of these parameters were evaluated from the analyses of reduced viscosity data of binary (solvent/polymer) and ternary (solvent/polymer1/polymer2) polymer systems. These investigations indicated partial miscibility for both the blend systems. However, PS/PSAN/acetone blend system showed somewhat higher partial miscibility than the PS/PSAN/Benzene blend system highlighting the impact of solvent over the polymer-polymer interactions and hence their miscibility. The results obtained through viscometry were also corroborated by the refractive index and density results for the blends under study. The effect of temperature on miscibility in both the cases was almost negligible.
2014, 32(11): 1450-1459
doi: 10.1007/s10118-014-1531-9
Abstract:
A new class of unsaturated polyesters based on diethylketone have been prepared by interfacial polymerization of 2, 4-bis(4-hydroxybenzylidene)-3-pentanone (Ⅰ) and 2, 4-bis(4-hydroxy-3-methoxybenzylidene)-3-pentanone (Ⅱ) with 4, 4'-azodibenzoyl chloride and 3, 3'-azodibenzoyl chloride at ambient temperature. The model compounds were synthesized by reaction of (Ⅰ) and (Ⅱ) with benzoyl chloride. The new monomers, model compounds and polyesters have been characterized by different spectral analyses. The polyesters have inherent viscosity of 0.55-0.80 dL/g and moderate number average molecular weight (Mn) in the range of 6150-7400 g/mol. Most of the compounds exhibited their solubility in aprotic solvents while partial solubility in various halogenated organic solvents was observed. The temperatures of 10% weight loss were high (225-330℃) in nitrogen, indicating that these polyesters have excellent thermal stability. Doping with iodine dramatically raised the conductivity and produced brown colored semiconductive polymers with a maximum conductivity of 2.7 10-6 -1cm-1. Moreover, the morphological properties of selected example of polyesters were detected by SEM.
A new class of unsaturated polyesters based on diethylketone have been prepared by interfacial polymerization of 2, 4-bis(4-hydroxybenzylidene)-3-pentanone (Ⅰ) and 2, 4-bis(4-hydroxy-3-methoxybenzylidene)-3-pentanone (Ⅱ) with 4, 4'-azodibenzoyl chloride and 3, 3'-azodibenzoyl chloride at ambient temperature. The model compounds were synthesized by reaction of (Ⅰ) and (Ⅱ) with benzoyl chloride. The new monomers, model compounds and polyesters have been characterized by different spectral analyses. The polyesters have inherent viscosity of 0.55-0.80 dL/g and moderate number average molecular weight (Mn) in the range of 6150-7400 g/mol. Most of the compounds exhibited their solubility in aprotic solvents while partial solubility in various halogenated organic solvents was observed. The temperatures of 10% weight loss were high (225-330℃) in nitrogen, indicating that these polyesters have excellent thermal stability. Doping with iodine dramatically raised the conductivity and produced brown colored semiconductive polymers with a maximum conductivity of 2.7 10-6 -1cm-1. Moreover, the morphological properties of selected example of polyesters were detected by SEM.
2014, 32(11): 1460-1468
doi: 10.1007/s10118-014-1478-x
Abstract:
Using three designed peptides with precisely-controlled charge density and three types of DNAs with different length and flexibility, the effect of charge density on the formation of PEC was studied. Highly charged (KKKK)5 interacts strongly with 21 bp dsDNA to form large complex, followed by precipitation; while the medium charged (KGKG)5 only form complex with 21 bp dsDNA at proper +/- charge ratios; and no prominent complex between weakly charged (KGGG)5 and 21 bp dsDNA is observed at the same conditions. Similar trend is observed when the peptides form complex with 2000 bp DNA or 21nt ssDNA. It is also found that the complex formed by adding peptide to DNA is in random coil conformation, but the complex prepared by the inverse order is in molten globule state. Re-dissolution of the complex occurs only when DNA is added to peptides with similar or shorter length.
Using three designed peptides with precisely-controlled charge density and three types of DNAs with different length and flexibility, the effect of charge density on the formation of PEC was studied. Highly charged (KKKK)5 interacts strongly with 21 bp dsDNA to form large complex, followed by precipitation; while the medium charged (KGKG)5 only form complex with 21 bp dsDNA at proper +/- charge ratios; and no prominent complex between weakly charged (KGGG)5 and 21 bp dsDNA is observed at the same conditions. Similar trend is observed when the peptides form complex with 2000 bp DNA or 21nt ssDNA. It is also found that the complex formed by adding peptide to DNA is in random coil conformation, but the complex prepared by the inverse order is in molten globule state. Re-dissolution of the complex occurs only when DNA is added to peptides with similar or shorter length.
2014, 32(11): 1469-1478
doi: 10.1007/s10118-014-1530-x
Abstract:
p-Nitrophenol imprinted nanoparticles with a size range of 150-300 nm in diameter were prepared through miniemulsion polymerization. The imprinted polymer exhibited higher adsorption capacity for p-nitrophenol than the non-imprinted polymer. The hydrolysis of paraoxon in aqueous phase can be accelerated in the presence of the p-nitrophenol imprinted nanoparticles. The hydrolysis rate of paraoxon incorporated with the imprinted nanoparticles was 2.8310-7 mol/(Lmin), which was about 3.7 times higher compared to the non-imprinted nanoparticles, 12.7 times higher to the spontaneous hydrolysis. The nanoparticles have been mixed with polyacrylonitrile solution and electrospun into nanofibers, which can also be used to accelerate the hydrolysis of paraoxon and conveniently separated from liquid phase for further processing.
p-Nitrophenol imprinted nanoparticles with a size range of 150-300 nm in diameter were prepared through miniemulsion polymerization. The imprinted polymer exhibited higher adsorption capacity for p-nitrophenol than the non-imprinted polymer. The hydrolysis of paraoxon in aqueous phase can be accelerated in the presence of the p-nitrophenol imprinted nanoparticles. The hydrolysis rate of paraoxon incorporated with the imprinted nanoparticles was 2.8310-7 mol/(Lmin), which was about 3.7 times higher compared to the non-imprinted nanoparticles, 12.7 times higher to the spontaneous hydrolysis. The nanoparticles have been mixed with polyacrylonitrile solution and electrospun into nanofibers, which can also be used to accelerate the hydrolysis of paraoxon and conveniently separated from liquid phase for further processing.
2014, 32(11): 1479-1488
doi: 10.1007/s10118-014-1537-3
Abstract:
Water soluble tetraphenylethene-based (TPE) aggregation-induced emission fluorescent organic nanoparticles (FONs) were facilely prepared via Schiff base condensation with polyethylenimine (PEI) and subsequent reduction. The obtained TPE-PEI FONs were characterized by a series of techniques including 1H-NMR, 13C-NMR, gel permeation chromatography, UV absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy, size distribution and zeta potential measurement, and transmission electron microscopy. Biocompatibility evaluation and cell imaging of TPE-PEI FONs were further explored. We demonstrated that such FONs showed intense fluorescence, spherical morphology and excellent biocompatibility, making them very suitable for cell imaging application.
Water soluble tetraphenylethene-based (TPE) aggregation-induced emission fluorescent organic nanoparticles (FONs) were facilely prepared via Schiff base condensation with polyethylenimine (PEI) and subsequent reduction. The obtained TPE-PEI FONs were characterized by a series of techniques including 1H-NMR, 13C-NMR, gel permeation chromatography, UV absorption spectra, fluorescence spectra, Fourier transform infrared spectroscopy, size distribution and zeta potential measurement, and transmission electron microscopy. Biocompatibility evaluation and cell imaging of TPE-PEI FONs were further explored. We demonstrated that such FONs showed intense fluorescence, spherical morphology and excellent biocompatibility, making them very suitable for cell imaging application.
2014, 32(11): 1489-1499
doi: 10.1007/s10118-014-1535-5
Abstract:
To prepare a high-performance epoxy resin with excellent thermal, chemical and corrosion stability, diaminoxanthone (DAX) was used to cure diglycidylether of bisphenol-A (DGEBA)-based epoxy resin and blend of DGEBA with functionalized Fe3O4 nanoparticles. Kinetic parameters of curing and thermal degradation of epoxy resin systems were estimated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The 10% weight loss temperature has been increased from 340℃ to 366℃ and there was an increase in the char yield from 32.6% to 45.3% for the above systems. The corrosion performance of epoxy coated carbon steel was examined by potentiodynamic polarization, along with immersion test in 1.0 mol/L HCl solution. The results showed that epoxy resins cured with DAX had low tendency to corrosion. In addition, the cured epoxy resin containing 10% Fe3O4 had higher anticorrosion activity than bare DGEBA system. The results showed that functionalized Fe3O4 nanoparticles enhanced char formation and improved the thermal stability as well as anticorrosion activity of the resin.
To prepare a high-performance epoxy resin with excellent thermal, chemical and corrosion stability, diaminoxanthone (DAX) was used to cure diglycidylether of bisphenol-A (DGEBA)-based epoxy resin and blend of DGEBA with functionalized Fe3O4 nanoparticles. Kinetic parameters of curing and thermal degradation of epoxy resin systems were estimated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The 10% weight loss temperature has been increased from 340℃ to 366℃ and there was an increase in the char yield from 32.6% to 45.3% for the above systems. The corrosion performance of epoxy coated carbon steel was examined by potentiodynamic polarization, along with immersion test in 1.0 mol/L HCl solution. The results showed that epoxy resins cured with DAX had low tendency to corrosion. In addition, the cured epoxy resin containing 10% Fe3O4 had higher anticorrosion activity than bare DGEBA system. The results showed that functionalized Fe3O4 nanoparticles enhanced char formation and improved the thermal stability as well as anticorrosion activity of the resin.
2014, 32(11): 1500-1506
doi: 10.1007/s10118-014-1532-8
Abstract:
L-lactide (LLA) homopolymerization and copolymerization with -caprolactone (CL) in toluene initiated by tetrahydrosalen-supported yttrium borohydride complex were systematically investigated. A possible mechanism of LLA homopolymerization was proposed according to the 1H-NMR result. In addition, PCL-b-PLLA copolymers were synthesized by sequential addition of monomers and their structure was characterized by GPC, 1H-NMR and 13C-NMR.
L-lactide (LLA) homopolymerization and copolymerization with -caprolactone (CL) in toluene initiated by tetrahydrosalen-supported yttrium borohydride complex were systematically investigated. A possible mechanism of LLA homopolymerization was proposed according to the 1H-NMR result. In addition, PCL-b-PLLA copolymers were synthesized by sequential addition of monomers and their structure was characterized by GPC, 1H-NMR and 13C-NMR.
2014, 32(11): 1507-1514
doi: 10.1007/s10118-014-1536-4
Abstract:
In this paper, methacrylated -PGA (mPGA) precursor was synthesized via reaction between -PGA and glycidyl methacrylate (GMA). Hydrogels from this precursor were prepared under 365 nm ultraviolet irradiation. The swelling behavior and mechanical properties were studied in detail as functions of the degree of substitution (DS), precursor concentration, and environmental pH. Results showed that the crosslink density, swelling kinetics and mechanical properties of the hdyrogel could be tailored by adjusting the DS and concentration of the precursor as well as the environmental pH. Three-dimensional photo-encapsulation of swine cartilage chondrocytes and Live/Dead assay proved the cytocompatibility of the hydrogel.
In this paper, methacrylated -PGA (mPGA) precursor was synthesized via reaction between -PGA and glycidyl methacrylate (GMA). Hydrogels from this precursor were prepared under 365 nm ultraviolet irradiation. The swelling behavior and mechanical properties were studied in detail as functions of the degree of substitution (DS), precursor concentration, and environmental pH. Results showed that the crosslink density, swelling kinetics and mechanical properties of the hdyrogel could be tailored by adjusting the DS and concentration of the precursor as well as the environmental pH. Three-dimensional photo-encapsulation of swine cartilage chondrocytes and Live/Dead assay proved the cytocompatibility of the hydrogel.
2014, 32(11): 1515-1523
doi: 10.1007/s10118-014-1538-2
Abstract:
The effect of particle shape on the rheological behavior of small particle-large polymer chain mixture solutions has been investigated with two model colloidal silica dispersions, one of which is ellipsoidal (BINDZIL20/440) and the other is spherical (TM40). It was found that BINDZIL20/440 series showed shear-thickening at lower shear rates and had a lower upper limit in PEO concentration to demonstrate shear-thickening phenomena. The particle shape was identified as the major factor accounting for these differences. This work enables one to control the rheological behavior of colloid-polymer mixture through simply changing particle geometry instead of performing surface modifications, which could be especially useful in cases where only certain chemicals are allowed, for example in vivo applications.
The effect of particle shape on the rheological behavior of small particle-large polymer chain mixture solutions has been investigated with two model colloidal silica dispersions, one of which is ellipsoidal (BINDZIL20/440) and the other is spherical (TM40). It was found that BINDZIL20/440 series showed shear-thickening at lower shear rates and had a lower upper limit in PEO concentration to demonstrate shear-thickening phenomena. The particle shape was identified as the major factor accounting for these differences. This work enables one to control the rheological behavior of colloid-polymer mixture through simply changing particle geometry instead of performing surface modifications, which could be especially useful in cases where only certain chemicals are allowed, for example in vivo applications.
2014, 32(11): 1524-1534
doi: 10.1007/s10118-014-1533-7
Abstract:
An interesting order-order transition between two different complex nanostructures was observed in a new liquid crystalline linear coil-coil-rod ABC triblock copolymer (triBCP). First, the ABC triBCP, poly(dimethylsiloxane)-b-polystyrene-b-poly{2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PDMS-b-PS-b-PMPCS), was synthesized through sequential atom transfer radical polymerization. The degrees of polymerization of PDMS, PS, and PMPCS blocks are 58, 159, and 106, and the corresponding volume fractions of PDMS, PS, and PMPCS are 0.09, 0.29, and 0.62, respectively. The phase behaviors of the PDMS-b-PS diblock copolymer precursor and the final triblock copolymer were studied by small-angle X-ray scattering, one-dimensional wide-angle X-ray scattering, and transmission electron microscopy experiments. The PDMS-b-PS precursor self-assembles into hexagonally packed cylinders with a relatively small periodic size after thermal annealing. When the triblock copolymer is annealed at a relatively low temperature (120℃) at which the PMPCS block is in the amorphous state, the triBCP forms core-shell hexagonally packed cylinders (CSH) with a relativly large periodic size. After the triBCP is annealed above 140℃ at which the PMPCS block transforms to the liquid crystalline (LC) phase, the nanophase-separated structure transforms to a three-phase four-layer lamellar structure (LAM-3P4L). Thus, accompanied with the transition of the PMPCS blocks from the amorphous state to the LC phase, the order-order transition from CSH to LAM-3P4L occurs in the PDMS-b-PS-b-PMPCS ABC triBCP.
An interesting order-order transition between two different complex nanostructures was observed in a new liquid crystalline linear coil-coil-rod ABC triblock copolymer (triBCP). First, the ABC triBCP, poly(dimethylsiloxane)-b-polystyrene-b-poly{2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PDMS-b-PS-b-PMPCS), was synthesized through sequential atom transfer radical polymerization. The degrees of polymerization of PDMS, PS, and PMPCS blocks are 58, 159, and 106, and the corresponding volume fractions of PDMS, PS, and PMPCS are 0.09, 0.29, and 0.62, respectively. The phase behaviors of the PDMS-b-PS diblock copolymer precursor and the final triblock copolymer were studied by small-angle X-ray scattering, one-dimensional wide-angle X-ray scattering, and transmission electron microscopy experiments. The PDMS-b-PS precursor self-assembles into hexagonally packed cylinders with a relatively small periodic size after thermal annealing. When the triblock copolymer is annealed at a relatively low temperature (120℃) at which the PMPCS block is in the amorphous state, the triBCP forms core-shell hexagonally packed cylinders (CSH) with a relativly large periodic size. After the triBCP is annealed above 140℃ at which the PMPCS block transforms to the liquid crystalline (LC) phase, the nanophase-separated structure transforms to a three-phase four-layer lamellar structure (LAM-3P4L). Thus, accompanied with the transition of the PMPCS blocks from the amorphous state to the LC phase, the order-order transition from CSH to LAM-3P4L occurs in the PDMS-b-PS-b-PMPCS ABC triBCP.
2014, 32(11): 1535-1543
doi: 10.1007/s10118-014-1541-7
Abstract:
This study investigated total warpage of a type of motorcycle seat support made of polypropylene (PP) during the entire process of injection molding and free-cooling after demolding. Finite element modeling (FEM) analysis for injection molding and its associated thermal deformation was carried out in the study. The effects of processing parameters on warpage occurring in different stages were analyzed by Taguchi optimization method. It was found that packing pressure is the major factor that affects warpage in the injection stage, whereas cooling time is the major factor in free-cooling stage. From an overall evaluation, melt temperature affects the total warpage most, followed by cooling time, packing pressure, packing time and mold temperature. The result proved that optimum parameters for minimizing final warpage of the injected parts can be obtained only when the deformation in the entire manufacturing process is addressed in both molding and demolding stages.
This study investigated total warpage of a type of motorcycle seat support made of polypropylene (PP) during the entire process of injection molding and free-cooling after demolding. Finite element modeling (FEM) analysis for injection molding and its associated thermal deformation was carried out in the study. The effects of processing parameters on warpage occurring in different stages were analyzed by Taguchi optimization method. It was found that packing pressure is the major factor that affects warpage in the injection stage, whereas cooling time is the major factor in free-cooling stage. From an overall evaluation, melt temperature affects the total warpage most, followed by cooling time, packing pressure, packing time and mold temperature. The result proved that optimum parameters for minimizing final warpage of the injected parts can be obtained only when the deformation in the entire manufacturing process is addressed in both molding and demolding stages.
2014, 32(11): 1544-1549
doi: 10.1007/s10118-014-1508-8
Abstract:
A new kind of hollow hydrogel microfiber with discontinuous hollow structure was prepared by an ice-segregation-induced self-assembly process. Monodisperse thermo-responsive hollow poly(N-isopropylacrylamide) (PNIPAM) microgels were first synthesized by seed precipitation polymerization using colloidal SiO2 nanoparticles as seeds, followed by removing the silica cores of the formed SiO2/PNIPAM core/shell composite microgels with hydrofluoric acid. Then, the discontinuously hollow hydrogel microfibers were produced by unidirectional freezing of 1 wt% hollow PNIPAM microgel aqueous dispersion in liquid nitrogen bath, followed by freeze-drying to remove the formed ice crystals. Many orderly arrayed dents were observed on the surfaces of the hydrogel microfibers by field-emission scanning electron microscopy, indicating that they are constructed by closely packed monodisperse hollow PNIPAM microgels. The effect of freezing method and the hollow microgel concentration in the aqueous dispersion on the morphological structure of the hollow hydrogel microfibers was investigated.
A new kind of hollow hydrogel microfiber with discontinuous hollow structure was prepared by an ice-segregation-induced self-assembly process. Monodisperse thermo-responsive hollow poly(N-isopropylacrylamide) (PNIPAM) microgels were first synthesized by seed precipitation polymerization using colloidal SiO2 nanoparticles as seeds, followed by removing the silica cores of the formed SiO2/PNIPAM core/shell composite microgels with hydrofluoric acid. Then, the discontinuously hollow hydrogel microfibers were produced by unidirectional freezing of 1 wt% hollow PNIPAM microgel aqueous dispersion in liquid nitrogen bath, followed by freeze-drying to remove the formed ice crystals. Many orderly arrayed dents were observed on the surfaces of the hydrogel microfibers by field-emission scanning electron microscopy, indicating that they are constructed by closely packed monodisperse hollow PNIPAM microgels. The effect of freezing method and the hollow microgel concentration in the aqueous dispersion on the morphological structure of the hollow hydrogel microfibers was investigated.
2014, 32(11): 1550-1563
doi: 10.1007/s10118-014-1519-5
Abstract:
Chemical degradation of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured with an aliphatic amine in supercritical 1-propanol was investigated under different reaction temperature and time. The combination of GC-MS and LC-MS proved that the epoxy resin was decomposed to five main products including phenol, 4-isopropylphenol, 4-isopropenylphenol, bisphenol A, and 4, 4'-(cyclopropane-1, 1-diyl)diphenol. The 13C-NMR results verified the chemical structures of the degradation products. The change of the products' yield with time was evaluated by an effective means of HPLC. In addition, the GPC analysis confirmed the formation of soluble low molecular weight clusters during the degradation reaction. A possible free-radical reaction mechanism was proposed for chemical depolymerization of the epoxy resin in supercritical 1-propanol. After the homolytic cleavage of the aromatic ether linkages, the resulting bisphenol A biradical either produced 4, 4'-(cyclopropane-1, 1-diyl)diphenol after intramolecular rearrangement or generated bisphenol A after capturing hydrogen from 1-propanol.
Chemical degradation of diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured with an aliphatic amine in supercritical 1-propanol was investigated under different reaction temperature and time. The combination of GC-MS and LC-MS proved that the epoxy resin was decomposed to five main products including phenol, 4-isopropylphenol, 4-isopropenylphenol, bisphenol A, and 4, 4'-(cyclopropane-1, 1-diyl)diphenol. The 13C-NMR results verified the chemical structures of the degradation products. The change of the products' yield with time was evaluated by an effective means of HPLC. In addition, the GPC analysis confirmed the formation of soluble low molecular weight clusters during the degradation reaction. A possible free-radical reaction mechanism was proposed for chemical depolymerization of the epoxy resin in supercritical 1-propanol. After the homolytic cleavage of the aromatic ether linkages, the resulting bisphenol A biradical either produced 4, 4'-(cyclopropane-1, 1-diyl)diphenol after intramolecular rearrangement or generated bisphenol A after capturing hydrogen from 1-propanol.
2014, 32(11): 1564-1574
doi: 10.1007/s10118-014-1540-8
Abstract:
In this work, a fluorescent monomer 2-(9-carbazolyl) ethyl vinyl ether (CEVE) was synthesized in our lab, and its photo-induced living cationic copolymerization behavior with isobutyl vinyl ether (IBVE) was investigated in detail using diphenyliodonium chloride (DPICl)/2, 2-dimethoxy-2-phenylacetophenone (DMPA) and zinc bromide (ZnBr2) initiating system in dichloromethane solution at 5℃, -5℃, and -15℃, respectively. The living nature of this copolymerization system was confirmed by adding fresh comonomer method after the copolymerization almost finished. In addition, the obtained fluorescent copolymer poly(IBVE-co-CEVE) has a low glass transition temperature (Tg), below -10℃.
In this work, a fluorescent monomer 2-(9-carbazolyl) ethyl vinyl ether (CEVE) was synthesized in our lab, and its photo-induced living cationic copolymerization behavior with isobutyl vinyl ether (IBVE) was investigated in detail using diphenyliodonium chloride (DPICl)/2, 2-dimethoxy-2-phenylacetophenone (DMPA) and zinc bromide (ZnBr2) initiating system in dichloromethane solution at 5℃, -5℃, and -15℃, respectively. The living nature of this copolymerization system was confirmed by adding fresh comonomer method after the copolymerization almost finished. In addition, the obtained fluorescent copolymer poly(IBVE-co-CEVE) has a low glass transition temperature (Tg), below -10℃.
2014, 32(11): 1575-1580
doi: 10.1007/s10118-014-1539-1
Abstract:
The captioned question has been addressed by the steric effect; namely, the adsorption of proteins on a surface grafted with linear polymer chains decreases monotonically as the grafting density increases. However, there is no quantitative and satisfactory explanation why the adsorption starts to increase when the grafting density is sufficiently high and why polyethylene glycol (PEG) still remains as one of the best polymers to repel proteins. After considering each grafted chain as a molecular spring confined inside a tube made of its surrounding grafted chains, we estimated how its free energy depends on the grafting density and chain length, and calculated its thermal energy-agitated chain conformation fluctuation, enabling us to predict an adsorption minimum at a proper grafting density, which agrees well with previous experimental results. We propose that it is such a chain fluctuation that slows down the adsorption kinetically.
The captioned question has been addressed by the steric effect; namely, the adsorption of proteins on a surface grafted with linear polymer chains decreases monotonically as the grafting density increases. However, there is no quantitative and satisfactory explanation why the adsorption starts to increase when the grafting density is sufficiently high and why polyethylene glycol (PEG) still remains as one of the best polymers to repel proteins. After considering each grafted chain as a molecular spring confined inside a tube made of its surrounding grafted chains, we estimated how its free energy depends on the grafting density and chain length, and calculated its thermal energy-agitated chain conformation fluctuation, enabling us to predict an adsorption minimum at a proper grafting density, which agrees well with previous experimental results. We propose that it is such a chain fluctuation that slows down the adsorption kinetically.
