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2009 Volume 27 Issue 3
2009, 27(3): 297-306
Abstract:
The adsorption amount of poly(styrene sulfonate) and poly(dimethyldiallyl ammonium chloride) (PSS/PDDA) self-assembled multilayer membranes in designed dipping solvents were measured by UV-Vis-spectroscopy and quartz crystal microbalance (QCM). Intrinsic viscosities of PSS and PDDA in corresponding dipping solvents were determined by an Ubbelohde viscometer. It is found that the adsorption amount of PSS/PDDA self-assembled multilayer membranes built up in different dipping solutions, added salt concentration, pH of solution and solvent quality, respectively changed oppositely with the corresponding intrinsic viscosity of PSS and PDDA in dipping solvents. A negative relation between the adsorption amount and intrinsic viscosity was revealed, and explained in term of the concept of excluded volume of polymer molecule in dilute solutions.
The adsorption amount of poly(styrene sulfonate) and poly(dimethyldiallyl ammonium chloride) (PSS/PDDA) self-assembled multilayer membranes in designed dipping solvents were measured by UV-Vis-spectroscopy and quartz crystal microbalance (QCM). Intrinsic viscosities of PSS and PDDA in corresponding dipping solvents were determined by an Ubbelohde viscometer. It is found that the adsorption amount of PSS/PDDA self-assembled multilayer membranes built up in different dipping solutions, added salt concentration, pH of solution and solvent quality, respectively changed oppositely with the corresponding intrinsic viscosity of PSS and PDDA in dipping solvents. A negative relation between the adsorption amount and intrinsic viscosity was revealed, and explained in term of the concept of excluded volume of polymer molecule in dilute solutions.
2009, 27(3): 307-315
Abstract:
The phase behaviors of symmetric diblock copolymer thin films confined between two hard, parallel and diversified patterned surfaces are investigated by three-dimensional dissipative particle dynamics (DPD) simulations. The induction of diversified patterned surfaces on phase separation of symmetric diblock copolymer films in snapshots, density profiles and concentration diagrams of the simulated systems are presented. The phase separations can be controlled by the patterned surfaces. In the meantime, the mean-square end-to-end distance of the confined polymer chains is also discussed. Surface-induced phase separation for diblock copolymers can help us to create novel and controlled nanostructured materials.
The phase behaviors of symmetric diblock copolymer thin films confined between two hard, parallel and diversified patterned surfaces are investigated by three-dimensional dissipative particle dynamics (DPD) simulations. The induction of diversified patterned surfaces on phase separation of symmetric diblock copolymer films in snapshots, density profiles and concentration diagrams of the simulated systems are presented. The phase separations can be controlled by the patterned surfaces. In the meantime, the mean-square end-to-end distance of the confined polymer chains is also discussed. Surface-induced phase separation for diblock copolymers can help us to create novel and controlled nanostructured materials.
2009, 27(3): 327-334
Abstract:
A series of poly(dimethylsiloxane) (PDMS)-4,4’-diphenylmethanediisocyanate(MDI)-poly(ethylene glycol) (PEG) multiblock copolymers were synthesized by employing two-step growth polymerization and investigated by AFM, XPS, contact angle system, protein adsorption and platelets adhesion measurements, respectively. It was found that as the molecular weight of PDMS increased, the surface of copolymers had increasing phase separation, while the increase in the molecular weight of PEG decreased the phase separation extents of the copolymer surface. XPS and contact angle measurements showed that the greater the phase separation extent was, the lower both the surface enrichment of PDMS and the surface free energy of the copolymer film were. The protein adsorption experiments indicated that the best phase separation did not exhibit the best biocompatibility.
A series of poly(dimethylsiloxane) (PDMS)-4,4’-diphenylmethanediisocyanate(MDI)-poly(ethylene glycol) (PEG) multiblock copolymers were synthesized by employing two-step growth polymerization and investigated by AFM, XPS, contact angle system, protein adsorption and platelets adhesion measurements, respectively. It was found that as the molecular weight of PDMS increased, the surface of copolymers had increasing phase separation, while the increase in the molecular weight of PEG decreased the phase separation extents of the copolymer surface. XPS and contact angle measurements showed that the greater the phase separation extent was, the lower both the surface enrichment of PDMS and the surface free energy of the copolymer film were. The protein adsorption experiments indicated that the best phase separation did not exhibit the best biocompatibility.
2009, 27(3): 335-341
Abstract:
New amphoteric hydrogels based on carboxyethylchitosans (CECH) with various degrees of substitution (DS) were prepared using different amounts of epichlorohydrin (ECH) as the crosslinking agent. The equilibrium swelling ratio (SW) was determined as functions of pH and salt concentration. The hydrogels show typical amphoteric character responding to pH change of the external medium. At isoelectric point (IEP), the hydrogels shrink. The DS value has important effect on the swelling properties of the hydrogels. When the DS of N-carboxyethylchitosan increases from 0.32 to 0.72, the equilibrium swelling ratio (SW) of the hydrogel changes from 76 to 290 at pH 7.3 and from 117 to 499 at pH 11.3. A marked volume decrease was observed in hydrogels with increasing salt concentration in the surrounding solution. The viscoelastic properties of the hydrogels were studied by oscillatory shear measurements under small-deformation conditions. The elastic modulus G, of all the samples has no dependence on frequency and is one order of magnitude larger than the loss modulus G,,, corresponding to a strong gel behavior.
New amphoteric hydrogels based on carboxyethylchitosans (CECH) with various degrees of substitution (DS) were prepared using different amounts of epichlorohydrin (ECH) as the crosslinking agent. The equilibrium swelling ratio (SW) was determined as functions of pH and salt concentration. The hydrogels show typical amphoteric character responding to pH change of the external medium. At isoelectric point (IEP), the hydrogels shrink. The DS value has important effect on the swelling properties of the hydrogels. When the DS of N-carboxyethylchitosan increases from 0.32 to 0.72, the equilibrium swelling ratio (SW) of the hydrogel changes from 76 to 290 at pH 7.3 and from 117 to 499 at pH 11.3. A marked volume decrease was observed in hydrogels with increasing salt concentration in the surrounding solution. The viscoelastic properties of the hydrogels were studied by oscillatory shear measurements under small-deformation conditions. The elastic modulus G, of all the samples has no dependence on frequency and is one order of magnitude larger than the loss modulus G,,, corresponding to a strong gel behavior.
2009, 27(3): 343-350
Abstract:
To enhance the impact strength of polyamide 6, hydrolytic polymerization modification by the polyaminoamide-g-poly(ethylene glycol) (PAAEG) derivatives with poly(ethylene glycol) (PEG) molecular weight of 400-010000 was studied. Amide groups of polyaminoamide segments were postulated to form hydrogen bonding with polyamide 6, and hydroxy groups of PAAEG units were expected to react with carboxylic acid groups of polyamide 6 forming copolymers during the polymerization. The improved compatibility in amorphous regions of blends has been confirmed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) of fracture surfaces. The effects of PAAEG on the water absorption and notch sensitivity of blends were investigated, using water uptake measurement and mechanical testings, respectively. For comparison, pure polyamide 6 and the blend of PEG/polyamide 6 were also investigated. The addition of PAAEG retarded the crystallization of polyamide 6, but did not make remarkable influences on its crystalline structure. As a consequence of the strong interactions between the dispersed phases and polyamide 6 matrices, PAAEG was a more suitable additive for improving the notched impact strength of polyamide 6 than PEG.
To enhance the impact strength of polyamide 6, hydrolytic polymerization modification by the polyaminoamide-g-poly(ethylene glycol) (PAAEG) derivatives with poly(ethylene glycol) (PEG) molecular weight of 400-010000 was studied. Amide groups of polyaminoamide segments were postulated to form hydrogen bonding with polyamide 6, and hydroxy groups of PAAEG units were expected to react with carboxylic acid groups of polyamide 6 forming copolymers during the polymerization. The improved compatibility in amorphous regions of blends has been confirmed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) of fracture surfaces. The effects of PAAEG on the water absorption and notch sensitivity of blends were investigated, using water uptake measurement and mechanical testings, respectively. For comparison, pure polyamide 6 and the blend of PEG/polyamide 6 were also investigated. The addition of PAAEG retarded the crystallization of polyamide 6, but did not make remarkable influences on its crystalline structure. As a consequence of the strong interactions between the dispersed phases and polyamide 6 matrices, PAAEG was a more suitable additive for improving the notched impact strength of polyamide 6 than PEG.
2009, 27(3): 351-358
Abstract:
Thermosetting acrylic coatings were prepared by using carboxyl acid group-containing acrylic oligomer and curing with titanium-oxo-clusters which were first pre-hydrolyzed from titanium n-butoxide. The curing ability of the titanium-oxo-cluster was examined using a microdielectric analytical (DEA) curing monitor, Fourier transformed infrared spectroscopy (FTIR), and Soxhlet extraction experiments, and the properties of the resulted coatings were investigated with pendulum hardness tester, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and ultraviolet-visible spectrometer. The effect of titania-oxo-cluster in leading acrylic oligomers to form thermosetting acrylic coatings was confirmed. An increasing pendulum hardness and modulus of acrylic coatings with increasing titania content was observed, which resulted from the increment of crosslinking degree rather than of the titania content. The thermosetting acrylic/titania coatings also showed better thermal stability and higher UV-blocking properties than those coatings using organic curing agent.
Thermosetting acrylic coatings were prepared by using carboxyl acid group-containing acrylic oligomer and curing with titanium-oxo-clusters which were first pre-hydrolyzed from titanium n-butoxide. The curing ability of the titanium-oxo-cluster was examined using a microdielectric analytical (DEA) curing monitor, Fourier transformed infrared spectroscopy (FTIR), and Soxhlet extraction experiments, and the properties of the resulted coatings were investigated with pendulum hardness tester, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA) and ultraviolet-visible spectrometer. The effect of titania-oxo-cluster in leading acrylic oligomers to form thermosetting acrylic coatings was confirmed. An increasing pendulum hardness and modulus of acrylic coatings with increasing titania content was observed, which resulted from the increment of crosslinking degree rather than of the titania content. The thermosetting acrylic/titania coatings also showed better thermal stability and higher UV-blocking properties than those coatings using organic curing agent.
2009, 27(3): 359-366
Abstract:
Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate-co-sodium methacrylate) [P(HEMA-co-SMA)] hydrogels with different compositions were prepared to be used as intravaginal rings, and their gelation time, water content, mechanical properties and morphology were investigated. The water content of PHEMA and P(HEMA-co-SMA) hydrogels decreased as the concentration of the monomer and the degree of crosslinking increased, while the water content significantly increased as the content of SMA, the hydrophilic monomer, increased. The increasing of the concentration of the crosslinking agent affected the tensile and flexural properties highly. The presence of a proper small amount of SMA also led the tensile and flexural modulus to move to a higher level. The results showed that P(HEMA-co-SMA) hydrogel with high drug load and good mechanical properties at optimum preparation conditions can be prepared for intravaginal rings to deliver nonhormonal contraceptives. These results may be applied to prepare better intravaginal drug delivery devices.
Poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(2-hydroxyethyl methacrylate-co-sodium methacrylate) [P(HEMA-co-SMA)] hydrogels with different compositions were prepared to be used as intravaginal rings, and their gelation time, water content, mechanical properties and morphology were investigated. The water content of PHEMA and P(HEMA-co-SMA) hydrogels decreased as the concentration of the monomer and the degree of crosslinking increased, while the water content significantly increased as the content of SMA, the hydrophilic monomer, increased. The increasing of the concentration of the crosslinking agent affected the tensile and flexural properties highly. The presence of a proper small amount of SMA also led the tensile and flexural modulus to move to a higher level. The results showed that P(HEMA-co-SMA) hydrogel with high drug load and good mechanical properties at optimum preparation conditions can be prepared for intravaginal rings to deliver nonhormonal contraceptives. These results may be applied to prepare better intravaginal drug delivery devices.
2009, 27(3): 367-374
Abstract:
The monomer reactivity ratios of free radical copolymerization of styrene and methyl methacrylate in carbon dioxide at vapor-liquid equilibrium state (vlCO2) at 65°C and under 7.5-8.5 MPa were measured. The experimental results showed that, in comparison with the data in bulk copolymerization, the monomer reactivity ratio of St in vlCO2 increased acompanied by a somewhat decrease in that of MMA. Further analysis of the sequence distributions of these copolymers by 1H-NMR spectra indicated that there was a significant bootstrap effect in this system. The local monomer concentrations in the proximity of growing free radicals, rather than the true reactivity of monomers or free radicals, were altered by the presence of vlCO2, leading to the change in monomer reactivity ratios.
The monomer reactivity ratios of free radical copolymerization of styrene and methyl methacrylate in carbon dioxide at vapor-liquid equilibrium state (vlCO2) at 65°C and under 7.5-8.5 MPa were measured. The experimental results showed that, in comparison with the data in bulk copolymerization, the monomer reactivity ratio of St in vlCO2 increased acompanied by a somewhat decrease in that of MMA. Further analysis of the sequence distributions of these copolymers by 1H-NMR spectra indicated that there was a significant bootstrap effect in this system. The local monomer concentrations in the proximity of growing free radicals, rather than the true reactivity of monomers or free radicals, were altered by the presence of vlCO2, leading to the change in monomer reactivity ratios.
2009, 27(3): 375-380
Abstract:
A mild and facile way was used to prepare poly(nitriloethylenenitrilovinylene)-grafted multi-walled carbon nanotubes (MWCNTs-g-PNENV) nanocomposites via the “grafting to” method. The MWCNTs-g-PNENV nanocomposites are well dispersible in polar solvents such as water, tetrahydrofuran and ethanol. Chemical structure of the resulting product was characterized by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA). FTIR showed that the “grafting to” process belonged to covalent attachment mechanisms. TEM observations indicated that the MWCNTs were coated with a uniform PNENV layer, and the MWCNTs existed as a hard backbone. TGA data also showed that the PNENV shell was successfully grafted to the side wall of MWCNTs.
A mild and facile way was used to prepare poly(nitriloethylenenitrilovinylene)-grafted multi-walled carbon nanotubes (MWCNTs-g-PNENV) nanocomposites via the “grafting to” method. The MWCNTs-g-PNENV nanocomposites are well dispersible in polar solvents such as water, tetrahydrofuran and ethanol. Chemical structure of the resulting product was characterized by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and thermal gravimetric analysis (TGA). FTIR showed that the “grafting to” process belonged to covalent attachment mechanisms. TEM observations indicated that the MWCNTs were coated with a uniform PNENV layer, and the MWCNTs existed as a hard backbone. TGA data also showed that the PNENV shell was successfully grafted to the side wall of MWCNTs.
2009, 27(3): 381-386
Abstract:
Self-vulcanizing blends of phenol hydroxy silicone rubber (PHSR) and fluoroelastomer (FPM) were prepared. Vulcanized rubbers with lower glass transition temperature (Tg) were successfully obtained. The results of dynamic mechanical analysis (DMA) show that the vulcanized FPM/PHSR (10 phr) blend has only one Tg temperature, demonstrating the well compatibility between FPM and PHSR. The thermogravimetric analysis (TGA) demonstrates that the PHSR do little damage to the thermal stability of FPM. The vulcanization characteristics of the FPM/PHSR blends were analyzed by using oscillating disc rheometer (ODR). The results show that FPM/PHSR blends have smaller Smin values and longer scorch time than that of FPM with the same level of bisphenol AF curing agent. It means that FPM/PHSR blends have better processability and curing security. Better mechanical properties can be gained for FPM/PHSR blends at appropriate level of PHSR.
Self-vulcanizing blends of phenol hydroxy silicone rubber (PHSR) and fluoroelastomer (FPM) were prepared. Vulcanized rubbers with lower glass transition temperature (Tg) were successfully obtained. The results of dynamic mechanical analysis (DMA) show that the vulcanized FPM/PHSR (10 phr) blend has only one Tg temperature, demonstrating the well compatibility between FPM and PHSR. The thermogravimetric analysis (TGA) demonstrates that the PHSR do little damage to the thermal stability of FPM. The vulcanization characteristics of the FPM/PHSR blends were analyzed by using oscillating disc rheometer (ODR). The results show that FPM/PHSR blends have smaller Smin values and longer scorch time than that of FPM with the same level of bisphenol AF curing agent. It means that FPM/PHSR blends have better processability and curing security. Better mechanical properties can be gained for FPM/PHSR blends at appropriate level of PHSR.
2009, 27(3): 387-392
Abstract:
Biopolymer chitosan was used to modify the mechanical properties of soluble eggshell membrane protein (SEP) films. The SEP/chitosan blend films were prepared by solution casting from 10% aqueous acetic acid. Tensile strength and elongation at break of the blend films increased with increasing amount of chitosan. Microphase separation was observed by field emission scanning electron microscopy, although interaction between the two components was revealed by FTIR. The biocompatibility of SEP/chitosan blend films containing 10%-50% of chitosan, as demonstrated by cell culture of NIH3T3, was much better than that of pure chitosan.
Biopolymer chitosan was used to modify the mechanical properties of soluble eggshell membrane protein (SEP) films. The SEP/chitosan blend films were prepared by solution casting from 10% aqueous acetic acid. Tensile strength and elongation at break of the blend films increased with increasing amount of chitosan. Microphase separation was observed by field emission scanning electron microscopy, although interaction between the two components was revealed by FTIR. The biocompatibility of SEP/chitosan blend films containing 10%-50% of chitosan, as demonstrated by cell culture of NIH3T3, was much better than that of pure chitosan.
2009, 27(3): 393-398
Abstract:
Polypropylene (PP)/multi-walled carbon nanotube (MWCNT)/calcium carbonate (CaCO3) composites are prepared by melt mixing using two types of CaCO3 of different sizes. The electrical resistivities of the composites with the two types of CaCO3 are all lower than those of the corresponding PP/MWCNT composites at various MWCNT loadings (1 wt%-5 wt%). The morphology of the composites is investigated by field emission scanning electron microscopy (FESEM). The crystallization behavior of PP in the composites is characterized by differential scanning calorimetry (DSC). The storage modulus, as measured by dynamic mechanical analysis (DMA), increases significantly by the presence of CaCO3.
Polypropylene (PP)/multi-walled carbon nanotube (MWCNT)/calcium carbonate (CaCO3) composites are prepared by melt mixing using two types of CaCO3 of different sizes. The electrical resistivities of the composites with the two types of CaCO3 are all lower than those of the corresponding PP/MWCNT composites at various MWCNT loadings (1 wt%-5 wt%). The morphology of the composites is investigated by field emission scanning electron microscopy (FESEM). The crystallization behavior of PP in the composites is characterized by differential scanning calorimetry (DSC). The storage modulus, as measured by dynamic mechanical analysis (DMA), increases significantly by the presence of CaCO3.
2009, 27(3): 399-405
Abstract:
The living cationic polymerization of 4-[2-(tert-butyldimethylsiloxy)ethyl]styrene (TBDMES) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) (50/50 V/V) solvent mixture at -80°C. The initiator 1,1-diphenylethylene (DPE) capped 2-chloro-2,4,4-trimethylpentane (TMPCl) was formed in situ in conjunction with titanium tetrachloride (TiCl4). The Lewis acidity of TiCl4 was decreased by the addition of titanium(IV) isopropoxide (Ti(OiPr)4) to accomplish living polymerization of TBDMES. Hydrolysis of poly(TBDMES) in the presence of tetra-butylammonium fluoride yielded poly[4-(2-hydroxyethyl)styrene] (poly(HOES)). FT-IR, NMR and DSC demonstrated the hydrolysis was complete.
The living cationic polymerization of 4-[2-(tert-butyldimethylsiloxy)ethyl]styrene (TBDMES) was studied in methylcyclohexane (MeChx)/methylchloride (MeCl) (50/50 V/V) solvent mixture at -80°C. The initiator 1,1-diphenylethylene (DPE) capped 2-chloro-2,4,4-trimethylpentane (TMPCl) was formed in situ in conjunction with titanium tetrachloride (TiCl4). The Lewis acidity of TiCl4 was decreased by the addition of titanium(IV) isopropoxide (Ti(OiPr)4) to accomplish living polymerization of TBDMES. Hydrolysis of poly(TBDMES) in the presence of tetra-butylammonium fluoride yielded poly[4-(2-hydroxyethyl)styrene] (poly(HOES)). FT-IR, NMR and DSC demonstrated the hydrolysis was complete.
2009, 27(3): 407-414
Abstract:
The effects of the chain length, active end group and concentration on the association of living polystyryllithium (PS-Li+) chains in benzene were examined by a combination of static and dynamic laser light scattering in a cuvette equipped with a high-vacuum stopcock. The results show that long PS-Li+ chains (Mw 1 × 104) usually form dimers in the solution. In contrast, shorter PS-Li+ chains exhibit two relaxation modes, where the fast mode is related to the translational diffusion of the living chain dimers. The end capping of the living chain with bulky 1,1-diphenylethene (DPE) leads to an intensity increase of the slow mode, indicating that the slow mode is not due to the chain aggregates but to temporal aggregates or long-range density fluctuation induced by weak electrostatic dipole-dipole interaction between ionic pairs at the chain ends.
The effects of the chain length, active end group and concentration on the association of living polystyryllithium (PS-Li+) chains in benzene were examined by a combination of static and dynamic laser light scattering in a cuvette equipped with a high-vacuum stopcock. The results show that long PS-Li+ chains (Mw 1 × 104) usually form dimers in the solution. In contrast, shorter PS-Li+ chains exhibit two relaxation modes, where the fast mode is related to the translational diffusion of the living chain dimers. The end capping of the living chain with bulky 1,1-diphenylethene (DPE) leads to an intensity increase of the slow mode, indicating that the slow mode is not due to the chain aggregates but to temporal aggregates or long-range density fluctuation induced by weak electrostatic dipole-dipole interaction between ionic pairs at the chain ends.
2009, 27(3): 415-426
Abstract:
Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.
Bioactive SiO2-CaO-P2O5 gel (BAG) nanoparticles with 40 nm in diameter were synthesized by the sol-gel route and further modified via the ring-opening polymerization of lactide on the surface of particles. Surface modified BAG (mBAG) was introduced in poly(L-lactide) (PLLA) matrix as bioactive filler. The dispersibility of mBAG in PLLA matrix was much higher than that of rough BAG particles. Tensile strength of the mBAG/PLLA composite could be increased to 61.2 MPa at 2 wt% filler content from 53.4 MPa for pure PLLA. The variation of moduli of the BAG/PLLA and mBAG/PLLA composites always showed an enhancement tendency with the increasing content of filler loading. The SEM photographs of the fracture surfaces showed that mBAG could be homogeneously dispersed in the PLLA matrix, and the corrugated deformation could absorb the rupture energy effectively during the breaking of materials. In vitro bioactivity tests showed that both BAG and mBAG particles could endow the composites with ability of the calcium sediment in SBF, but the surface modification of BAG particles could weaken this capability to some extent. Biocompatibility tests showed that both BAG and mBAG particles could facilitate the attachment and proliferation of the marrow cells on the surface of the composite. All these results showed that the mBAG/PLLA composite would be a promising material for bone tissues regeneration.
2009, 27(3): 427-433
Abstract:
Anionic polymerization of methyl methacrylate (MMA), n-butyl methacrylate (nBMA) and glycidyl methacrylate (GMA) initiated by nBuCu(NCy2)Li (1) in tetrahydrofuran (THF) at -50°C to-10°C was investigated. It was found that the polymerization of MMA and nBMA initiated by 1 proceeded quantitatively in THF to afford PMMA and PBMA with polydispersity index 1.15-1.30 and nearly 100% initiator efficiencies at -10°C. The molecular weights increased linearly with the ratio of [monomer]/[1]. However, a post-polymerization experiment carried out on this system revealed a double polymer peak by GPC when fresh monomer was added after an interval of 10 min. Polymerization of styrene could be initiated by 1, but the initiator efficiency was low.
Anionic polymerization of methyl methacrylate (MMA), n-butyl methacrylate (nBMA) and glycidyl methacrylate (GMA) initiated by nBuCu(NCy2)Li (1) in tetrahydrofuran (THF) at -50°C to-10°C was investigated. It was found that the polymerization of MMA and nBMA initiated by 1 proceeded quantitatively in THF to afford PMMA and PBMA with polydispersity index 1.15-1.30 and nearly 100% initiator efficiencies at -10°C. The molecular weights increased linearly with the ratio of [monomer]/[1]. However, a post-polymerization experiment carried out on this system revealed a double polymer peak by GPC when fresh monomer was added after an interval of 10 min. Polymerization of styrene could be initiated by 1, but the initiator efficiency was low.
2009, 27(3): 435-445
Abstract:
The service life of a polyolefin product depends to large extent on the type and amount of the antioxidants added. During the manufacturing, storage and use of the product the antioxidants are depleted by physical processes and chemical degradation, and this impairs its long-term performance. The initial and in-use oxidation stability is often characterized and monitored by the measurement of the oxidative induction time (OIT), and service life predictions are based on the rate of decrease of the OIT value. To study the correlation between the OIT value and the actual antioxidant concentration, eight random arrays of high-impact polypropylene (PP) strands stabilized using six different antioxidant packages (composed of Irgafos 168, Irganox 1010 and 1330, Chimassorb 944) were immersed in hot water (80°C and 90°C) and oven aged in air (80°C) for more than two years, and the change of OIT values and antioxidant concentrations was measured. For phosphitic and phenolic stabilizers water immersion is generally a more critical aging condition than oven aging in air, while for the hindered amine stabilizers (HAS) the opposite was observed. As expected, a linear correlation between OIT values and concentrations was found for the “classical” package of phosphitic and phenolic stabilizers. In the case of Irganox 1330, the change of the OIT values during aging was considerably slower than the change of concentration. Even when zero concentration was reached according to the vanishing peak height in the chromatogram, a considerable OIT value was still measurable. This may be due to unidentified degradation products of Irganox 1330 which still act as antioxidants in the long run. Addition of HAS (Chimassorb 944) seems to enhance the initial OIT of stabilized phenolic samples and the long-term effectiveness of the phenolic stabilization under air oven aging conditions. However, the marked long-term effectiveness of the HAS itself and the slow change with time of the concentration were not detectable by OIT measurements above the PP melting point of about 170°C.
The service life of a polyolefin product depends to large extent on the type and amount of the antioxidants added. During the manufacturing, storage and use of the product the antioxidants are depleted by physical processes and chemical degradation, and this impairs its long-term performance. The initial and in-use oxidation stability is often characterized and monitored by the measurement of the oxidative induction time (OIT), and service life predictions are based on the rate of decrease of the OIT value. To study the correlation between the OIT value and the actual antioxidant concentration, eight random arrays of high-impact polypropylene (PP) strands stabilized using six different antioxidant packages (composed of Irgafos 168, Irganox 1010 and 1330, Chimassorb 944) were immersed in hot water (80°C and 90°C) and oven aged in air (80°C) for more than two years, and the change of OIT values and antioxidant concentrations was measured. For phosphitic and phenolic stabilizers water immersion is generally a more critical aging condition than oven aging in air, while for the hindered amine stabilizers (HAS) the opposite was observed. As expected, a linear correlation between OIT values and concentrations was found for the “classical” package of phosphitic and phenolic stabilizers. In the case of Irganox 1330, the change of the OIT values during aging was considerably slower than the change of concentration. Even when zero concentration was reached according to the vanishing peak height in the chromatogram, a considerable OIT value was still measurable. This may be due to unidentified degradation products of Irganox 1330 which still act as antioxidants in the long run. Addition of HAS (Chimassorb 944) seems to enhance the initial OIT of stabilized phenolic samples and the long-term effectiveness of the phenolic stabilization under air oven aging conditions. However, the marked long-term effectiveness of the HAS itself and the slow change with time of the concentration were not detectable by OIT measurements above the PP melting point of about 170°C.
