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2010 Volume 28 Issue 5
2010, 28(5): 673-683
doi: 10.1007/s10118-010-9114-x
Abstract:
The graft copolymerization of N,N-dimethylacrylamide onto alginate by free radical polymerization using potassium peroxymonosulphate-sarbose as a redox pair in an inert atmosphere was investigated. The reaction conditions for maximum grafting have been optimized by varying the reaction variables, including the concentration of N,N-dimethylacrylamide (7 × 10-2 mol/L to 23 × 10-2 mol/L), potassium peroxymonosulphate (2 × 10-3 mol/L to 18 × 10-3 mol/L), sarbose (0.4 × 10-3 mol/L to 3.4 × 10-3 mol/L), sulphuric acid (1 × 10-3 mol/L to 8 × 10-3 mol/L) and alginic acid (0.4 g/L to 1.8 g/L) along with time duration (60 min to 180 min) and temperature (25oC to 45oC). Water swelling capacity, metal ion sorption and flocculation studies of the synthesized graft copolymer have been performed. The graft copolymer has been characterized by FTIR spectroscopy and thermogravimetric analysis.
The graft copolymerization of N,N-dimethylacrylamide onto alginate by free radical polymerization using potassium peroxymonosulphate-sarbose as a redox pair in an inert atmosphere was investigated. The reaction conditions for maximum grafting have been optimized by varying the reaction variables, including the concentration of N,N-dimethylacrylamide (7 × 10-2 mol/L to 23 × 10-2 mol/L), potassium peroxymonosulphate (2 × 10-3 mol/L to 18 × 10-3 mol/L), sarbose (0.4 × 10-3 mol/L to 3.4 × 10-3 mol/L), sulphuric acid (1 × 10-3 mol/L to 8 × 10-3 mol/L) and alginic acid (0.4 g/L to 1.8 g/L) along with time duration (60 min to 180 min) and temperature (25oC to 45oC). Water swelling capacity, metal ion sorption and flocculation studies of the synthesized graft copolymer have been performed. The graft copolymer has been characterized by FTIR spectroscopy and thermogravimetric analysis.
2010, 28(5): 685-694
doi: 10.1007/s10118-010-9120-z
Abstract:
An optically active bulky aromatic diacid chiral monomer, (2S)-4-[(4-methyl-2-phthalimidylpentanoyl-amino)benzoylamino]isophthalic acid (1), containing a rigid phthalimide and flexible L-leucine pendent group was synthesized in five steps. A fast and clean method for direct polyamidation reaction of monomer 1 with various aromatic diamines under microwave irradiation and conventional heating was performed. The polymerization reactions provided optically active polyamides with high yields and inherent viscosities in the range of 0.36-0.74 dL/g. Their thermal properties were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry. TGA thermograms show that the polymers are thermally stable, 10% weight loss temperatures are in excess of 385°C, and char yields at 800°C are higher than 56%. The data obtained from TGA were used to study the kinetics of thermal decomposition of the resulting polymers. The interpretation of kinetic parameters (E, ΔH,ΔS andΔG) of thermal decomposition stages was evaluated using Coats and Redfern equation.
An optically active bulky aromatic diacid chiral monomer, (2S)-4-[(4-methyl-2-phthalimidylpentanoyl-amino)benzoylamino]isophthalic acid (1), containing a rigid phthalimide and flexible L-leucine pendent group was synthesized in five steps. A fast and clean method for direct polyamidation reaction of monomer 1 with various aromatic diamines under microwave irradiation and conventional heating was performed. The polymerization reactions provided optically active polyamides with high yields and inherent viscosities in the range of 0.36-0.74 dL/g. Their thermal properties were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry. TGA thermograms show that the polymers are thermally stable, 10% weight loss temperatures are in excess of 385°C, and char yields at 800°C are higher than 56%. The data obtained from TGA were used to study the kinetics of thermal decomposition of the resulting polymers. The interpretation of kinetic parameters (E, ΔH,ΔS andΔG) of thermal decomposition stages was evaluated using Coats and Redfern equation.
2010, 28(5): 695-704
doi: 10.1007/s10118-010-9119-5
Abstract:
A series of new optically active poly(amide-imide)s were synthesized by direct polycondensation reaction of 4,4'-diaminochalcone with several N-trimellitylimido-L-amino acids using a tosyl chloride (TsCl), pyridine (Py) and dimethylformamide (DMF) system as condensing agent. The resulting thermally stable poly(amide-imide)s were obtained in good to high yields and inherent viscosities ranging between 0.35 dL/g and 0.58 dL/g and were characterized with FTIR, 1H-NMR, CHN, Ultraviolet, TGA and DTG techniques.
A series of new optically active poly(amide-imide)s were synthesized by direct polycondensation reaction of 4,4'-diaminochalcone with several N-trimellitylimido-L-amino acids using a tosyl chloride (TsCl), pyridine (Py) and dimethylformamide (DMF) system as condensing agent. The resulting thermally stable poly(amide-imide)s were obtained in good to high yields and inherent viscosities ranging between 0.35 dL/g and 0.58 dL/g and were characterized with FTIR, 1H-NMR, CHN, Ultraviolet, TGA and DTG techniques.
2010, 28(5): 705-713
doi: 10.1007/s10118-010-9110-1
Abstract:
Poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) nanofiber membranes with improved hydrophilicity and protein fouling resistance via surface graft copolymerization of hydrophilic monomers were prepared. The surface modification involves atmospheric pressure glow discharge plasma (APGDP) pretreatment followed by graft copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA). The success of the graft modification with PEGMA on the PVDF-HFP fibrous membrane is ascertained by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared measurements (ATR-FTIR). The hydrophilic property of the nanofiber membranes is assessed by water contact angle measurements. The results show that the PEGMA grafted PVDF-HFP nanofiber membrane has a water contact angle of 0o compared with the pristine value of 132o. The protein adsorption was effectively reduced after PEGMA grafting on the PVDF-HFP nanofiber membrane surface. The PEGMA polymer grafting density on the PVDF-HFP membrane surface is measured by the gravimetric method, and the filtration performance is characterized by the measurement of water flux. The results indicate that the water flux of the grafted PVDF-HFP fibrous membrane increases significantly with the increase of the PEGMA grafting density.
Poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) nanofiber membranes with improved hydrophilicity and protein fouling resistance via surface graft copolymerization of hydrophilic monomers were prepared. The surface modification involves atmospheric pressure glow discharge plasma (APGDP) pretreatment followed by graft copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA). The success of the graft modification with PEGMA on the PVDF-HFP fibrous membrane is ascertained by X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared measurements (ATR-FTIR). The hydrophilic property of the nanofiber membranes is assessed by water contact angle measurements. The results show that the PEGMA grafted PVDF-HFP nanofiber membrane has a water contact angle of 0o compared with the pristine value of 132o. The protein adsorption was effectively reduced after PEGMA grafting on the PVDF-HFP nanofiber membrane surface. The PEGMA polymer grafting density on the PVDF-HFP membrane surface is measured by the gravimetric method, and the filtration performance is characterized by the measurement of water flux. The results indicate that the water flux of the grafted PVDF-HFP fibrous membrane increases significantly with the increase of the PEGMA grafting density.
2010, 28(5): 715-720
doi: 10.1007/s10118-010-9121-y
Abstract:
The hydroxyl-terminated polybutadiene (HTPB) possessing high content of 1,4-units was synthesized by anionic polymerization of butadiene, using alkyllithium containing silicon-protected hydroxyl group as initiator and cyclohexane as solvent. The polymers were characterized by GPC, IR and 1H-NMR. The mechanical properties of cured films were also evaluated. The results show that the content of 1,4-units for HTPBs made by anionic polymerization reaches up to 90%. The molecular weight distribution is very narrow (≤ 1.05). The functionality of hydroxyl groups approaches 2. Compared with free radical HTPB, the elongation at break of anionic HTPB films increased by 70%, while the tensile strength remained nearly unchanged. This new HTPB can be very useful in solid propellant.
The hydroxyl-terminated polybutadiene (HTPB) possessing high content of 1,4-units was synthesized by anionic polymerization of butadiene, using alkyllithium containing silicon-protected hydroxyl group as initiator and cyclohexane as solvent. The polymers were characterized by GPC, IR and 1H-NMR. The mechanical properties of cured films were also evaluated. The results show that the content of 1,4-units for HTPBs made by anionic polymerization reaches up to 90%. The molecular weight distribution is very narrow (≤ 1.05). The functionality of hydroxyl groups approaches 2. Compared with free radical HTPB, the elongation at break of anionic HTPB films increased by 70%, while the tensile strength remained nearly unchanged. This new HTPB can be very useful in solid propellant.
2010, 28(5): 721-729
doi: 10.1007/s10118-010-9115-9
Abstract:
The asymmetric polyamide-6 (PA6) membranes were prepared by thermally induced phase separation. From the scanning electron microscopy (SEM) images, it is observed that with the increase of silicon dioxide (SiO2) content the structure of obtained membranes gradually varied from cellular structure to large ball-shaped cluster aggregates. Subsequently, with the addition of SiO2, pure water flux increased first and then decreased, while rejection showed the opposite trend. Besides, raising the coagulation bath temperature was favorable to increase pure water flux. Consequently, different membrane morphologies and performance were obtained by changing SiO2 content and coagulation bath temperature.
The asymmetric polyamide-6 (PA6) membranes were prepared by thermally induced phase separation. From the scanning electron microscopy (SEM) images, it is observed that with the increase of silicon dioxide (SiO2) content the structure of obtained membranes gradually varied from cellular structure to large ball-shaped cluster aggregates. Subsequently, with the addition of SiO2, pure water flux increased first and then decreased, while rejection showed the opposite trend. Besides, raising the coagulation bath temperature was favorable to increase pure water flux. Consequently, different membrane morphologies and performance were obtained by changing SiO2 content and coagulation bath temperature.
2010, 28(5): 731-743
doi: 10.1007/s10118-010-9125-7
Abstract:
A novel calix[4]arene derivative 2 with amino functional groups at the lower rim was first prepared via introduction of nitro functional groups and amination of the dinitro derivative of calix[4]arene. The optically active monomers were synthesized by dehydration of L-leucine (and L-isoleucine) and 3,3',4,4'-benzophenonetetracarboxylic-3,3',4,4'-dianhydride (3) followed by reaction with thionyl chloride to form 5a and 5b. Two methods, polymerization under microwave irradiation and solution polymerization in CH2Cl2/TEA, were then employed to carry out the condensation polymerization of 2 with the optically active monomers 5a and 5b, respectively. The polymerization conditions affected the kind of resulting polymers, poly(amide-imide)s (PAIs) 6a and 6b and poly(ester-imide)s (PEIs) 6a' and 6b' were obtained selectively in good yields and moderate inherent viscosities. Sorption-extraction experiments were carried out using cram picrate extraction method and verified good binding ability of the resulting calixarene-based polymers towards silver, alkali metal and toxic heavy metal cations. Also thermogravimetric analysis indicated that the resulting PAIs and PEIs were thermally stable.
A novel calix[4]arene derivative 2 with amino functional groups at the lower rim was first prepared via introduction of nitro functional groups and amination of the dinitro derivative of calix[4]arene. The optically active monomers were synthesized by dehydration of L-leucine (and L-isoleucine) and 3,3',4,4'-benzophenonetetracarboxylic-3,3',4,4'-dianhydride (3) followed by reaction with thionyl chloride to form 5a and 5b. Two methods, polymerization under microwave irradiation and solution polymerization in CH2Cl2/TEA, were then employed to carry out the condensation polymerization of 2 with the optically active monomers 5a and 5b, respectively. The polymerization conditions affected the kind of resulting polymers, poly(amide-imide)s (PAIs) 6a and 6b and poly(ester-imide)s (PEIs) 6a' and 6b' were obtained selectively in good yields and moderate inherent viscosities. Sorption-extraction experiments were carried out using cram picrate extraction method and verified good binding ability of the resulting calixarene-based polymers towards silver, alkali metal and toxic heavy metal cations. Also thermogravimetric analysis indicated that the resulting PAIs and PEIs were thermally stable.
2010, 28(5): 745-751
doi: 10.1007/s10118-010-9130-x
Abstract:
Using synchrotron SAXS and WAXS, we investigated crystalline structures including crystallite size, lamellar thickness, long spacing of syndiotactic polypropylene (sPP) and poly(ethylene-co-octene) (PEcO) that crystallized from the sheared melt. The independence of the shear effects on the crystalline structures and the shear related lamellar orientation indicate the stable mesophase. Experiments on the different shear effects on polymer various crystalline structures confirm the multi-step polymer crystallization process.
Using synchrotron SAXS and WAXS, we investigated crystalline structures including crystallite size, lamellar thickness, long spacing of syndiotactic polypropylene (sPP) and poly(ethylene-co-octene) (PEcO) that crystallized from the sheared melt. The independence of the shear effects on the crystalline structures and the shear related lamellar orientation indicate the stable mesophase. Experiments on the different shear effects on polymer various crystalline structures confirm the multi-step polymer crystallization process.
2010, 28(5): 753-759
doi: 10.1007/s10118-010-9116-8
Abstract:
The effect of ammonium sulfamate (AS) content on the flame retardancy of polyamide 6 (PA6) was studied. It is found that the limiting oxygen index (LOI) of PA6 increases with the increase of AS content and the flame retardancy of PA6 is significantly improved. The morphology of the residues after combustion was examined by means of scanning electron microscopy (SEM). SEM results show that AS facilitates the formation of the intumescent char layer with honeycomb-like structure, which inhibits the transfer of heat and mass, and thus improves the flame retardancy of PA6. The thermal degradation of AS flame retarded PA6 was studied by thermogravimetric analysis (TGA). The Kissinger method was applied to estimate the activation energy (Ea) of the degradation. The activation energy of the thermal degradation of PA6 decreases by adding AS, indicating that AS can promote the degradation of PA6.
The effect of ammonium sulfamate (AS) content on the flame retardancy of polyamide 6 (PA6) was studied. It is found that the limiting oxygen index (LOI) of PA6 increases with the increase of AS content and the flame retardancy of PA6 is significantly improved. The morphology of the residues after combustion was examined by means of scanning electron microscopy (SEM). SEM results show that AS facilitates the formation of the intumescent char layer with honeycomb-like structure, which inhibits the transfer of heat and mass, and thus improves the flame retardancy of PA6. The thermal degradation of AS flame retarded PA6 was studied by thermogravimetric analysis (TGA). The Kissinger method was applied to estimate the activation energy (Ea) of the degradation. The activation energy of the thermal degradation of PA6 decreases by adding AS, indicating that AS can promote the degradation of PA6.
2010, 28(5): 761-770
doi: 10.1007/s10118-010-9138-2
Abstract:
Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid (PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate (SSS) onto electron beam (EB) irradiated poly(vinylidene fluoride) (PVDF) films were established. The physico-chemical properties of the membranes such as ion exchange capacity, water swelling and proton conductivity were correlated with the degree of grafting (G, %) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The membranes were found to undergo substantial structural changes in forms of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the variation in G (%) and the preparation method. The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e. radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation. The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.
Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid (PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate (SSS) onto electron beam (EB) irradiated poly(vinylidene fluoride) (PVDF) films were established. The physico-chemical properties of the membranes such as ion exchange capacity, water swelling and proton conductivity were correlated with the degree of grafting (G, %) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The membranes were found to undergo substantial structural changes in forms of ionic sites increase, hydrophilicity enhancement, hydrophobicity reduction and crystallinity decrease with the variation in G (%) and the preparation method. The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e. radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation. The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.
2010, 28(5): 771-780
doi: 10.1007/s10118-010-9141-7
Abstract:
Poly(benzanthrone-co-thiophene), a new conducting copolymer, was successfully prepared by direct anodic oxidation of benzanthrone and thiophene (Th) in a binary solvent system containing boron trifluoride diethyl etherate (BFEE) and acetonitrile (ACN). The as-formed copolymer film electrodeposited with monomer feed ratio of benzanthrone/Th = 1:1 at the applied potential of 1.3 V versus Ag/AgCl exhibited the advantages of both polybenzanthrone and polythiophene, such as active electrochemical behavior, excellent thermal stability, relatively high electrical conductivity and mechanical properties. UV-Vis spectroscopy, 1H-NMR and SEM were used to characterize and investigate the structures and morphologies of the copolymers. Fluorescence spectroscopy studies revealed that the obtained copolymer films show strong emission at about 525 nm. Moreover, the emitting properties of the copolymers could be tuned by changing some parameters during the electropolymerization process, such as monomer feed ratio.
Poly(benzanthrone-co-thiophene), a new conducting copolymer, was successfully prepared by direct anodic oxidation of benzanthrone and thiophene (Th) in a binary solvent system containing boron trifluoride diethyl etherate (BFEE) and acetonitrile (ACN). The as-formed copolymer film electrodeposited with monomer feed ratio of benzanthrone/Th = 1:1 at the applied potential of 1.3 V versus Ag/AgCl exhibited the advantages of both polybenzanthrone and polythiophene, such as active electrochemical behavior, excellent thermal stability, relatively high electrical conductivity and mechanical properties. UV-Vis spectroscopy, 1H-NMR and SEM were used to characterize and investigate the structures and morphologies of the copolymers. Fluorescence spectroscopy studies revealed that the obtained copolymer films show strong emission at about 525 nm. Moreover, the emitting properties of the copolymers could be tuned by changing some parameters during the electropolymerization process, such as monomer feed ratio.
2010, 28(5): 781-788
doi: 10.1007/s10118-010-9140-8
Abstract:
The stability of poly(vinyl alcohol) (PVA) nanofibrous mats in water media was improved by post-electrospinning treatments. Bifunctional glutaraldehyde (GA) in methanol was used as a crosslinking agent to stabilize PVA nanofiber, but fiber twinning was observed frequently, and the highly porous structure of PVA nanofibrous mats was destroyed when the crosslinked fiber was soaked in water. To overcome this shortcoming, chitosan (CS) was introduced into the PVA spinning solution to prepare PVA/CS composite nanofibers. Their treatment in GA/methanol solution could retain the fiber morphology of PVA/CS nanofibers and porous structure of PVA/CS nanofibrous mats even if they were soaked in aqueous solutions for 1 month. Scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were applied to characterize the physicochemical structure and thermal properties of PVA nanofibers. It was found that the water resistance of PVA nanofibrous mats was enhanced because of the improvement of the degree of crosslinking and crystallinity in the electrospun PVA fibers after soaking in GA/methanol solution.
The stability of poly(vinyl alcohol) (PVA) nanofibrous mats in water media was improved by post-electrospinning treatments. Bifunctional glutaraldehyde (GA) in methanol was used as a crosslinking agent to stabilize PVA nanofiber, but fiber twinning was observed frequently, and the highly porous structure of PVA nanofibrous mats was destroyed when the crosslinked fiber was soaked in water. To overcome this shortcoming, chitosan (CS) was introduced into the PVA spinning solution to prepare PVA/CS composite nanofibers. Their treatment in GA/methanol solution could retain the fiber morphology of PVA/CS nanofibers and porous structure of PVA/CS nanofibrous mats even if they were soaked in aqueous solutions for 1 month. Scanning electron microscopy (SEM), X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) were applied to characterize the physicochemical structure and thermal properties of PVA nanofibers. It was found that the water resistance of PVA nanofibrous mats was enhanced because of the improvement of the degree of crosslinking and crystallinity in the electrospun PVA fibers after soaking in GA/methanol solution.
2010, 28(5): 789-799
doi: 10.1007/s10118-010-9144-4
Abstract:
Elastic behavior of 4-branched star polymer chain with different chain length N adsorbed on attractive surface is investigated using steered molecular dynamics (SMD) simulation method based on the united-atom (UA) model for branched alkanes. The simulation is realized by pulling up the chain via a linear spring with a constant velocity v = 0.005 nm/ps. At the beginning, the chain lies extensionally on adsorbed surface and suffers continuous deformations during the tensile process. Statistical parameters as mean-square radii of gyration S2xy, S2z, shape factor δ, describing the conformational changes, sectional density den which gives the states of the chain, and average surface attractive energy Ua, average total energy U, average force f probed by the spring, which characterize the thermodynamic properties, are calculated in the stimulant process. Remarkably, distinguishing from the case in linear chains that there only exists one long plateau in the curve of f , the force plateau in our study for star chains is multiple, denoting different steps of desorption, and this agrees well with the experimental results in essence. We find during the tensile process, there are three characteristic distances Zc, Zt and Z0 from the attractive surface, and these values vary with N. When Z = Zc, the chain is stripped from the surface, but due to the form of wall-monomer interaction, the surface retains weak influence on the chain till Z = Zc. From Z = Zt, parameters Ua, U and f respectively reach a stable value, while the shape and the size of the chain still need adjustments after Zt till Z0 to reach their equilibrium states. Specifically, for short chain of N = 41, Zt and Z0 are incorporated. These results may help us to deepen the knowledge about the elastic behavior of adsorbed star polymer chains.
Elastic behavior of 4-branched star polymer chain with different chain length N adsorbed on attractive surface is investigated using steered molecular dynamics (SMD) simulation method based on the united-atom (UA) model for branched alkanes. The simulation is realized by pulling up the chain via a linear spring with a constant velocity v = 0.005 nm/ps. At the beginning, the chain lies extensionally on adsorbed surface and suffers continuous deformations during the tensile process. Statistical parameters as mean-square radii of gyration S2xy, S2z, shape factor δ, describing the conformational changes, sectional density den which gives the states of the chain, and average surface attractive energy Ua, average total energy U, average force f probed by the spring, which characterize the thermodynamic properties, are calculated in the stimulant process. Remarkably, distinguishing from the case in linear chains that there only exists one long plateau in the curve of f , the force plateau in our study for star chains is multiple, denoting different steps of desorption, and this agrees well with the experimental results in essence. We find during the tensile process, there are three characteristic distances Zc, Zt and Z0 from the attractive surface, and these values vary with N. When Z = Zc, the chain is stripped from the surface, but due to the form of wall-monomer interaction, the surface retains weak influence on the chain till Z = Zc. From Z = Zt, parameters Ua, U and f respectively reach a stable value, while the shape and the size of the chain still need adjustments after Zt till Z0 to reach their equilibrium states. Specifically, for short chain of N = 41, Zt and Z0 are incorporated. These results may help us to deepen the knowledge about the elastic behavior of adsorbed star polymer chains.
2010, 28(5): 801-806
doi: 10.1007/s10118-010-9158-y
Abstract:
Multi-walled carbon nanotubes (MWNTs) and chitosan (CS) composite rods with layer-by-layer structure were prepared via in situ precipitation method. On the one hand, some MWNTs fragments with open tips played the role of nuclear agent to improve the crystallinity of CS. On the other hand, MWNTs embedded in CS matrix to absorb energy when the composite rods were destroying. Nanotubes pulled out from CS matrix, and lots of holes remained, so MWNTs could endure external stress effectively. The bending strength and bending modulus of CS/MWNTs rods (100/0.5, W/W) arrived at 130.7 MPa and 4.4 GPa respectively, increased by 34.3% and 7.3% compared with those of pure CS rods. Consequently, CS/MWNTs composite rods with excellent mechanical properties could be a novel device used for bone fracture internal fixation.
Multi-walled carbon nanotubes (MWNTs) and chitosan (CS) composite rods with layer-by-layer structure were prepared via in situ precipitation method. On the one hand, some MWNTs fragments with open tips played the role of nuclear agent to improve the crystallinity of CS. On the other hand, MWNTs embedded in CS matrix to absorb energy when the composite rods were destroying. Nanotubes pulled out from CS matrix, and lots of holes remained, so MWNTs could endure external stress effectively. The bending strength and bending modulus of CS/MWNTs rods (100/0.5, W/W) arrived at 130.7 MPa and 4.4 GPa respectively, increased by 34.3% and 7.3% compared with those of pure CS rods. Consequently, CS/MWNTs composite rods with excellent mechanical properties could be a novel device used for bone fracture internal fixation.
2010, 28(5): 807-817
doi: 10.1007/s10118-010-9164-0
Abstract:
Hollow poly(divinylbenzene-co-methacrylic acid) (P(DVB-co-MAA)) microspheres were prepared by the selective dissolution of the non-crosslinked poly(methacrylic acid) (PMAA) mid-layer in ethanol from the corresponding silica/PMAA/P(DVB-co-MAA) tri-layer hybrid microspheres, which were afforded by a three-stage reaction. Silica/PMAA core-shell hybrid microspheres were prepared by the second-stage distillation polymerization of methacrylic acid (MAA) via the capture of the oligomers and monomers with the aid of the vinyl groups on the surface of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified silica core, which was prepared by the Stber hydrolysis as the first stage reaction. The tri-layer hybrid microspheres were synthesized by the third-stage distillation precipitation copolymerization of functional MAA monomer and divinylbenzene (DVB) crosslinker in presence of silica/PMAA particles as seeds, in which the efficient hydrogen-bonding interaction between the carboxylic acid groups played as a driving force for the construction of monodisperse hybrid microspheres with tri-layer structure. The morphology and the structure of silica core, silica/PMAA core-shell particles, the tri-layer hybrid microspheres and the corresponding hollow polymer microspheres with movable silica cores were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS).
Hollow poly(divinylbenzene-co-methacrylic acid) (P(DVB-co-MAA)) microspheres were prepared by the selective dissolution of the non-crosslinked poly(methacrylic acid) (PMAA) mid-layer in ethanol from the corresponding silica/PMAA/P(DVB-co-MAA) tri-layer hybrid microspheres, which were afforded by a three-stage reaction. Silica/PMAA core-shell hybrid microspheres were prepared by the second-stage distillation polymerization of methacrylic acid (MAA) via the capture of the oligomers and monomers with the aid of the vinyl groups on the surface of 3-(methacryloxy)propyl trimethoxysilane (MPS)-modified silica core, which was prepared by the Stber hydrolysis as the first stage reaction. The tri-layer hybrid microspheres were synthesized by the third-stage distillation precipitation copolymerization of functional MAA monomer and divinylbenzene (DVB) crosslinker in presence of silica/PMAA particles as seeds, in which the efficient hydrogen-bonding interaction between the carboxylic acid groups played as a driving force for the construction of monodisperse hybrid microspheres with tri-layer structure. The morphology and the structure of silica core, silica/PMAA core-shell particles, the tri-layer hybrid microspheres and the corresponding hollow polymer microspheres with movable silica cores were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS).
2010, 28(5): 819-828
doi: 10.1007/s10118-010-9166-y
Abstract:
A series of 3-arm ABC and AA'B and 4-arm ABCD, AA'BC and AA'A"B heteroarm star polymers comprising one poly(4-methylphenyl vinyl sulfoxide) segment and other segments such as polystyrene, poly(α-methylstyrene), poly(4-methoxystyrene) and poly(4-trimethylsilylstyrene) were synthesized by living anionic polymerization based on diphenylethylene (DPE) chemistry. The DPE-functionalized polymers were synthesized by iterative methodology, and the objective star polymers were prepared by two distinct methodologies based on anionic polymerization using DPE-functionalized polymers. The first methodology involves an addition reaction of living anionic polymer with excess DPE-functionalized polymer and a subsequent living anionic polymerization of 4-methylphenyl vinyl sulfoxide (MePVSO) initiated from the in situ formed polymer anion with two or three polymer segments. The second methodology comprises an addition reaction of DPE-functionalized polymer with excess sec-BuLi and a following anionic polymerization of MePVSO initiated from the in situ formed polymer anion and 3-methyl-1,1-diphenylpentyl anion as well. Both approaches could afford the target heteroarm star polymers with predetermined molecular weight, narrow molecular weight distribution (Mw/Mn 1.03) and desired composition, evidenced by SEC, 1H-NMR and SLS analyses. These polymers can be used as model polymers to investigate structure-property relationships in heteroarm star polymers.
A series of 3-arm ABC and AA'B and 4-arm ABCD, AA'BC and AA'A"B heteroarm star polymers comprising one poly(4-methylphenyl vinyl sulfoxide) segment and other segments such as polystyrene, poly(α-methylstyrene), poly(4-methoxystyrene) and poly(4-trimethylsilylstyrene) were synthesized by living anionic polymerization based on diphenylethylene (DPE) chemistry. The DPE-functionalized polymers were synthesized by iterative methodology, and the objective star polymers were prepared by two distinct methodologies based on anionic polymerization using DPE-functionalized polymers. The first methodology involves an addition reaction of living anionic polymer with excess DPE-functionalized polymer and a subsequent living anionic polymerization of 4-methylphenyl vinyl sulfoxide (MePVSO) initiated from the in situ formed polymer anion with two or three polymer segments. The second methodology comprises an addition reaction of DPE-functionalized polymer with excess sec-BuLi and a following anionic polymerization of MePVSO initiated from the in situ formed polymer anion and 3-methyl-1,1-diphenylpentyl anion as well. Both approaches could afford the target heteroarm star polymers with predetermined molecular weight, narrow molecular weight distribution (Mw/Mn 1.03) and desired composition, evidenced by SEC, 1H-NMR and SLS analyses. These polymers can be used as model polymers to investigate structure-property relationships in heteroarm star polymers.
2010, 28(5): 829-840
doi: 10.1007/s10118-010-9188-5
Abstract:
Random copolyester of poly(ε-caprolactone-co-L-lactide) (PCLA) with a 50:50 feeding molar ratio was synthesized via the ring-opening polymerization and functionalized by the end-capping reaction with acryloyl chloride. The resulting acrylated PCLA was then fabricated into small diameter tubular scaffolds by electrospinning technique and the formed scaffolds were followed by photocrosslinking under UV irradiation in the absence of photoinitiator. The mechanical strengths including tensile, suture retention and burst pressure were greatly enhanced after the photocrosslinking. The in vitro degradation data clearly revealed that the mechanical properties of the crosslinked scaffolds still remained after one month degradation in PBS solution, while those of the non-crosslinked ones lost heavily. The cytotoxicity assay on the mouse fibroblast L929 cells was conducted via MTT measurement. Furthermore, the observation on endothelial and fibroblast cell adhesion and proliferation was also made by using scanning electron microscopy (SEM). The initiator-free photocrosslinked tubular scaffolds show the potential to be used in vascular tissue engineering.
Random copolyester of poly(ε-caprolactone-co-L-lactide) (PCLA) with a 50:50 feeding molar ratio was synthesized via the ring-opening polymerization and functionalized by the end-capping reaction with acryloyl chloride. The resulting acrylated PCLA was then fabricated into small diameter tubular scaffolds by electrospinning technique and the formed scaffolds were followed by photocrosslinking under UV irradiation in the absence of photoinitiator. The mechanical strengths including tensile, suture retention and burst pressure were greatly enhanced after the photocrosslinking. The in vitro degradation data clearly revealed that the mechanical properties of the crosslinked scaffolds still remained after one month degradation in PBS solution, while those of the non-crosslinked ones lost heavily. The cytotoxicity assay on the mouse fibroblast L929 cells was conducted via MTT measurement. Furthermore, the observation on endothelial and fibroblast cell adhesion and proliferation was also made by using scanning electron microscopy (SEM). The initiator-free photocrosslinked tubular scaffolds show the potential to be used in vascular tissue engineering.
2010, 28(5): 841-847
doi: 10.1007/s10118-010-0044-4
Abstract:
A newly natural fine template, kapok fiber, for microtube preparation was reported. Large scale microtubes with high length/diameter ratio and controllable wall thickness and morphology have been successfully fabricated with this template. It is a wildly available, low-cost, environmental friendly and fine structured natural template for microtubes. Its thin wall thickness is only about 1-2 μm that means the whole template material is tiny and easy for removing. Even there is any residue the amount can be ignored. When the template is covered with a shell component, hollow structured microtube could be obtained by removing the thin inner template, and its shape could be the same as that of the original template (positive copy of the template’s shape). The products have high length/diameter ratio and uniform tubular structure. By further modifying the fabricating methods, facile fabrication not only exists for polypyrrole (PPy) in electrochemical deposition, but also for many other organic and inorganic materials. The surface morphology and wall thickness of the resultant microtubes can be easily modulated by controlling the processing conditions. This natural fiber is predicted to be a fine template for fabricating large scale microtubes with large cavity and high length/diameter ratio.
A newly natural fine template, kapok fiber, for microtube preparation was reported. Large scale microtubes with high length/diameter ratio and controllable wall thickness and morphology have been successfully fabricated with this template. It is a wildly available, low-cost, environmental friendly and fine structured natural template for microtubes. Its thin wall thickness is only about 1-2 μm that means the whole template material is tiny and easy for removing. Even there is any residue the amount can be ignored. When the template is covered with a shell component, hollow structured microtube could be obtained by removing the thin inner template, and its shape could be the same as that of the original template (positive copy of the template’s shape). The products have high length/diameter ratio and uniform tubular structure. By further modifying the fabricating methods, facile fabrication not only exists for polypyrrole (PPy) in electrochemical deposition, but also for many other organic and inorganic materials. The surface morphology and wall thickness of the resultant microtubes can be easily modulated by controlling the processing conditions. This natural fiber is predicted to be a fine template for fabricating large scale microtubes with large cavity and high length/diameter ratio.
