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2007 Volume 25 Issue 5
2007, 25(5): 431-435
Abstract:
A novel method to prepare crosslinked polyethyleneimine (CPEI) hollow nanospheres was reported. Uniform silica nanospheres were used as templates, 3-aminopropyl trimethoxysilane (APS) was immobilized on the surface of silica nanospheres as couple agent. Aziridine was initiated ring-opening polymerization with the amino groups in APS to form polyethyleneimine (PEI) shell layer. 1,4-Butanediol diacrylate was utilized to crosslink PEI polymeric shell. The silica nanospheres in core were etched by hydrofluoric acid to obtain hollow CPEI nanospheres. The hollow nanospheres were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA).
A novel method to prepare crosslinked polyethyleneimine (CPEI) hollow nanospheres was reported. Uniform silica nanospheres were used as templates, 3-aminopropyl trimethoxysilane (APS) was immobilized on the surface of silica nanospheres as couple agent. Aziridine was initiated ring-opening polymerization with the amino groups in APS to form polyethyleneimine (PEI) shell layer. 1,4-Butanediol diacrylate was utilized to crosslink PEI polymeric shell. The silica nanospheres in core were etched by hydrofluoric acid to obtain hollow CPEI nanospheres. The hollow nanospheres were characterized by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA).
2007, 25(5): 437-440
Abstract:
A novel EVA/unmodified nano-magnesium hydroxide (NMH)/silicone rubber ternary nanocomposite was prepared by using a special compound flame retardant of NMH and silicone rubber (CFR). The flammability of the ternary composite was studied by cone calorimeter test (CCT). Synergistic effect on flame retardancy was found between silicone rubber and NMH. EVA/CFR ternary nanocomposite showed the lowest peak heat release rate (PHRR) and mass loss rate (MLR) among the samples of virgin EVA, EVA composites. The synergistic flame retardancy of silicone rubber and NMH in EVA system is attributed to the enhanced char layers in the condensed phase that prevents the heat and mass transfer in the fire.
A novel EVA/unmodified nano-magnesium hydroxide (NMH)/silicone rubber ternary nanocomposite was prepared by using a special compound flame retardant of NMH and silicone rubber (CFR). The flammability of the ternary composite was studied by cone calorimeter test (CCT). Synergistic effect on flame retardancy was found between silicone rubber and NMH. EVA/CFR ternary nanocomposite showed the lowest peak heat release rate (PHRR) and mass loss rate (MLR) among the samples of virgin EVA, EVA composites. The synergistic flame retardancy of silicone rubber and NMH in EVA system is attributed to the enhanced char layers in the condensed phase that prevents the heat and mass transfer in the fire.
2007, 25(5): 441-445
Abstract:
Using a core (142 nm) made of linear polystyrene (PS) chains as a seed, we further polymerized a thin layer of cross-linked PS shell (7 nm) on it in water to form a core-shell particle. Such a particle swells in toluene, which enables linear PS chains inside the core to gradually diffuse out through the porous shell. Using a combination of static and dynamic laser light scattering, we examined the chain diffusion process by following the change of the scattering intensity (i.e. the average molar mass of the particles). For the first time, we have revealed that the diffusion exhibits three stages. In the first stage, the chain diffusion through the shell is even faster than their translational diffusion in a dilute solution. The three stages respectively correspond to the change of the solution in the core from concentrated to semidilute and then from semidilute to dilute.
Using a core (142 nm) made of linear polystyrene (PS) chains as a seed, we further polymerized a thin layer of cross-linked PS shell (7 nm) on it in water to form a core-shell particle. Such a particle swells in toluene, which enables linear PS chains inside the core to gradually diffuse out through the porous shell. Using a combination of static and dynamic laser light scattering, we examined the chain diffusion process by following the change of the scattering intensity (i.e. the average molar mass of the particles). For the first time, we have revealed that the diffusion exhibits three stages. In the first stage, the chain diffusion through the shell is even faster than their translational diffusion in a dilute solution. The three stages respectively correspond to the change of the solution in the core from concentrated to semidilute and then from semidilute to dilute.
2007, 25(5): 447-459
Abstract:
By incorporating copper sulfate (CuSO4) particles into acrylonitrile butadiene rubber (NBR) followed by heat pressing, a novel vulcanization method is developed in rubber through the formation of coordination crosslinking. This method totally differs from traditional covalent or non-covalent vulcanization approaches of rubber. No other vulcanizing agent or additional additive is involved in this process. By analyzing the results of DMA, XPS and FT-IR, it is found that the crosslinking of CuSO4 particles filled NBR was induced by in situ coordination between nitrogen atoms of nitrile groups (―CN) and copper ions (Cu2+) from CuSO4. SEM and EDX results revealed the generation of a core (CuSO4 solid particle)-shell (adherent NBR) structure, which leads to a result that the crosslinked rubber has excellent mechanical properties. Moreover, poly(vinyl chloride) (PVC) and liquid acrylonitrile-butadiene rubber (LNBR) were used as mobilizer to improve the coordination crosslinking of CuSO4/NBR. The addition of PVC or LNBR could lead to higher crosslink density and better mechanical properties of coordination vulcanizates. In addition, crystal water in CuSO4 played a positive role to coordination crosslinking of rubber because it decreased the metal point of CuSO4 and promoted the metal ionization.
By incorporating copper sulfate (CuSO4) particles into acrylonitrile butadiene rubber (NBR) followed by heat pressing, a novel vulcanization method is developed in rubber through the formation of coordination crosslinking. This method totally differs from traditional covalent or non-covalent vulcanization approaches of rubber. No other vulcanizing agent or additional additive is involved in this process. By analyzing the results of DMA, XPS and FT-IR, it is found that the crosslinking of CuSO4 particles filled NBR was induced by in situ coordination between nitrogen atoms of nitrile groups (―CN) and copper ions (Cu2+) from CuSO4. SEM and EDX results revealed the generation of a core (CuSO4 solid particle)-shell (adherent NBR) structure, which leads to a result that the crosslinked rubber has excellent mechanical properties. Moreover, poly(vinyl chloride) (PVC) and liquid acrylonitrile-butadiene rubber (LNBR) were used as mobilizer to improve the coordination crosslinking of CuSO4/NBR. The addition of PVC or LNBR could lead to higher crosslink density and better mechanical properties of coordination vulcanizates. In addition, crystal water in CuSO4 played a positive role to coordination crosslinking of rubber because it decreased the metal point of CuSO4 and promoted the metal ionization.
2007, 25(5): 461-472
Abstract:
The oxidative polycondensation reaction conditions of 4-[(4-hydroxybenzylidene) amino] phenol (4-HBAP) were studied with H2O2, air oxygen and NaOCl in an aqueous alkaline medium between 50 and 90°C. The structures of the obtained monomer and polymer were confirmed by FT-IR, UV-Vis, 1H- and 13C-NMR and elemental analysis. The characterization was made by TG-DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of poly[4-(4-hydroxybenzylidene amino) phenol] (P-4-HBAP) was found to be 48.3% (for H2O2 oxidant), 80.5% (for air O2 oxidant) and 86.4% (for NaOCl oxidant). According to the SEC analysis, the number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of P-4-HBAP was found to be 8950, 10970 g mol-1 and 1.225, respectively, using H2O2; and 11610, 15190 g mol-1 and 1.308 respectively, using air O2 and 7900, 9610 g mol-1 and 1.216, respectively, using NaOCl. According to TG-DTA analyses, P-4-HBAP was more stable than 4-HBAP against thermal decomposition. The weight loss of P-4-HBAP was found to be 49.27% at 1000°C. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) values calculated from electrochemical measurement. Electrochemical energy gaps (Eg) of 4-HBAP and P-4-HBAP were found to be 5.46, 5.28; 2.26, 2.67; 3.20 and 2.61 eV, respectively. According to UV-Vis measurements, optical band gap (Eg) of 4-HBAP and P-4-HBAP were found to be 3.34 and 3.01 eV, respectively. Also, antimicrobial activities of 4-HBAP and P-4-HBAP were examined against selected some bacteria. The electrical conductivity of the polymer was measured after doping with iodine.
The oxidative polycondensation reaction conditions of 4-[(4-hydroxybenzylidene) amino] phenol (4-HBAP) were studied with H2O2, air oxygen and NaOCl in an aqueous alkaline medium between 50 and 90°C. The structures of the obtained monomer and polymer were confirmed by FT-IR, UV-Vis, 1H- and 13C-NMR and elemental analysis. The characterization was made by TG-DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of poly[4-(4-hydroxybenzylidene amino) phenol] (P-4-HBAP) was found to be 48.3% (for H2O2 oxidant), 80.5% (for air O2 oxidant) and 86.4% (for NaOCl oxidant). According to the SEC analysis, the number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of P-4-HBAP was found to be 8950, 10970 g mol-1 and 1.225, respectively, using H2O2; and 11610, 15190 g mol-1 and 1.308 respectively, using air O2 and 7900, 9610 g mol-1 and 1.216, respectively, using NaOCl. According to TG-DTA analyses, P-4-HBAP was more stable than 4-HBAP against thermal decomposition. The weight loss of P-4-HBAP was found to be 49.27% at 1000°C. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) values calculated from electrochemical measurement. Electrochemical energy gaps (Eg) of 4-HBAP and P-4-HBAP were found to be 5.46, 5.28; 2.26, 2.67; 3.20 and 2.61 eV, respectively. According to UV-Vis measurements, optical band gap (Eg) of 4-HBAP and P-4-HBAP were found to be 3.34 and 3.01 eV, respectively. Also, antimicrobial activities of 4-HBAP and P-4-HBAP were examined against selected some bacteria. The electrical conductivity of the polymer was measured after doping with iodine.
2007, 25(5): 473-481
Abstract:
20 wt% polyamide 12 (PA1212) pellets were dissolved in molten caprolactam. The caprolactam was then catalyzed at 180°C and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the resultant polyamide 6 (PA6) and PA1212. Mechanical blends with same ingredient were prepared through melt blending on a twin-screw extruder. Scanning electron microscopy (SEM) observation revealed that contrary to the mechanical blends with small spherulites embedded in the matrix, no phase-separation existed in the in situ blends. The results of thermal analysis by differential scanning calorimetry (DSC) showed that single melting peak and crystallization peak existed for the in situ blends, while two melting and crystallization peaks appeared for the mechanical blends. The in situ blend film and the mixed blend film, both cast from a dilute formic acid solution with a concentration of 0.5 g/L, remained similar crystallization and melting behavior as above. It is proved by solution 13C-NMR analysis that transamidation took place during the in situ blending, and it is suggested that the combination of temperature increasing and the basic surrounding derived from NaOH during polymerization resulted in the occurrence of transamidation. Furthermore, it is proposed that the interchange reaction between PA1212 and PA6 also resulted from the degradative reaction during the anionic polymerization.
20 wt% polyamide 12 (PA1212) pellets were dissolved in molten caprolactam. The caprolactam was then catalyzed at 180°C and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the resultant polyamide 6 (PA6) and PA1212. Mechanical blends with same ingredient were prepared through melt blending on a twin-screw extruder. Scanning electron microscopy (SEM) observation revealed that contrary to the mechanical blends with small spherulites embedded in the matrix, no phase-separation existed in the in situ blends. The results of thermal analysis by differential scanning calorimetry (DSC) showed that single melting peak and crystallization peak existed for the in situ blends, while two melting and crystallization peaks appeared for the mechanical blends. The in situ blend film and the mixed blend film, both cast from a dilute formic acid solution with a concentration of 0.5 g/L, remained similar crystallization and melting behavior as above. It is proved by solution 13C-NMR analysis that transamidation took place during the in situ blending, and it is suggested that the combination of temperature increasing and the basic surrounding derived from NaOH during polymerization resulted in the occurrence of transamidation. Furthermore, it is proposed that the interchange reaction between PA1212 and PA6 also resulted from the degradative reaction during the anionic polymerization.
2007, 25(5): 483-490
Abstract:
The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [] and Huggins constant (KH) of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 1060°C. The intrinsic viscosity, RH, Rg, A2, and ( S 2)1/2 (calculated from viscosity data) and “a” values of nylon 12 are found to be higher in m-cresol than in sulphuric acid. All these parameters decrease with the increase in water contents in sulphuric acid. The refractive index increment, KH and activation energy show an opposite trend to that of []. The intrinsic viscosity, RH, Rg, A2, and ( S 2)1/2 have maximum values around 3040°C in sulphuric acid/water system, whereas in m-cresol they fall at about 20°C. It has been concluded that the variation in size, interaction parameter (second virial coefficient), [] and KH of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents, selective adsorption, hydrogen bonding and conformational transitions. It has also been concluded that the increase in temperature first enhances the quality of the solvent, encourages hydrogen bonding and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. However, the addition of water to sulphuric acid continuously deteriorates the solvent quality. This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.
The refractive index increment, dynamic and static laser light scattering, intrinsic viscosity [] and Huggins constant (KH) of nylon 12 have been measured in m-cresol and sulphuric acid/water system at 1060°C. The intrinsic viscosity, RH, Rg, A2, and ( S 2)1/2 (calculated from viscosity data) and “a” values of nylon 12 are found to be higher in m-cresol than in sulphuric acid. All these parameters decrease with the increase in water contents in sulphuric acid. The refractive index increment, KH and activation energy show an opposite trend to that of []. The intrinsic viscosity, RH, Rg, A2, and ( S 2)1/2 have maximum values around 3040°C in sulphuric acid/water system, whereas in m-cresol they fall at about 20°C. It has been concluded that the variation in size, interaction parameter (second virial coefficient), [] and KH of the polymer solutions with the alteration in solvent composition and temperature are the out come of change in thermodynamic quality of solvents, selective adsorption, hydrogen bonding and conformational transitions. It has also been concluded that the increase in temperature first enhances the quality of the solvent, encourages hydrogen bonding and specific adsorption, and then deteriorates, bringing conformational transitions in the polymer molecules. However, the addition of water to sulphuric acid continuously deteriorates the solvent quality. This characteristic of the solvent system brings conformational changes in the polymer especially at low temperatures.
2007, 25(5): 491-500
Abstract:
2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and maleic acid (MA) copolymerized with different feed ratios using N,N-dimethylformamide as a solvent and benzoyl peroxide (Bz2O2) as an initiator at 70°C. Structure and composition of copolymers for a wide range of monomer feed were determined by elemental analysis (content of N for AMPS-units). Monomer reactivity ratios for AMPS (M1)-MA (M2) pair were determined by the application of conventional linearization methods such as Fineman-Ross (F-R), Kelen-Tüds (KT) and Extended Kelen-Tüds (EKT) and a nonlinear error invariable model method using a computer program RREVM. The characterizations were done by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) thermal gravimetry analysis (TGA), and and X-ray diffraction. The antimicrobial effects of polymers were also tested on various bacteria, and yeast.
2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and maleic acid (MA) copolymerized with different feed ratios using N,N-dimethylformamide as a solvent and benzoyl peroxide (Bz2O2) as an initiator at 70°C. Structure and composition of copolymers for a wide range of monomer feed were determined by elemental analysis (content of N for AMPS-units). Monomer reactivity ratios for AMPS (M1)-MA (M2) pair were determined by the application of conventional linearization methods such as Fineman-Ross (F-R), Kelen-Tüds (KT) and Extended Kelen-Tüds (EKT) and a nonlinear error invariable model method using a computer program RREVM. The characterizations were done by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) thermal gravimetry analysis (TGA), and and X-ray diffraction. The antimicrobial effects of polymers were also tested on various bacteria, and yeast.
2007, 25(5): 501-507
Abstract:
A direct difference method has been developed for Non-Newtonian power law fluids to solve the simultaneous non-linear partial differential equations of melt spinning, and to determine the critical draw ratio for draw resonance. The results show that for shear thin fluids, the logarithm of the critical draw ratio has a well defined linear relationship with the power index for isothermal and uniform tension melt spinning. When the power index approaches zero, the critical draw ratio points at unity, indicating no melt spinning can be processed stably for such fluids. For shear thick fluids, the critical draw ratio increases in a more rapid way with increasing the power index.
A direct difference method has been developed for Non-Newtonian power law fluids to solve the simultaneous non-linear partial differential equations of melt spinning, and to determine the critical draw ratio for draw resonance. The results show that for shear thin fluids, the logarithm of the critical draw ratio has a well defined linear relationship with the power index for isothermal and uniform tension melt spinning. When the power index approaches zero, the critical draw ratio points at unity, indicating no melt spinning can be processed stably for such fluids. For shear thick fluids, the critical draw ratio increases in a more rapid way with increasing the power index.
2007, 25(5): 509-517
Abstract:
A novel cross-linking process using two high molecular weight aromatic poly(thioether)s, which were synthesized by the reactions of 4,4-thiobisbenzenethiol with 4,4-difluorobenzophenone and 4,4-difluorodiphenylsulfone, respectively, and commercially available lower molecular weight poly(p-phenylene sulfide) was investigated. These reactions were carried out in bulk by the addition of silver tetrafluroborate and -dibromo-p-xylene at 190°C over a period of 45 min. Furthermore, the same procedure could be modified to cross-link compression-molded films of these three polymers. The thermal and solubility behaviors of these polymers before and after cross-linking reactions, are presented.
A novel cross-linking process using two high molecular weight aromatic poly(thioether)s, which were synthesized by the reactions of 4,4-thiobisbenzenethiol with 4,4-difluorobenzophenone and 4,4-difluorodiphenylsulfone, respectively, and commercially available lower molecular weight poly(p-phenylene sulfide) was investigated. These reactions were carried out in bulk by the addition of silver tetrafluroborate and -dibromo-p-xylene at 190°C over a period of 45 min. Furthermore, the same procedure could be modified to cross-link compression-molded films of these three polymers. The thermal and solubility behaviors of these polymers before and after cross-linking reactions, are presented.
2007, 25(5): 519-523
Abstract:
Natural rubber latex (NRL) and methyl methacrylate (MMA) grafted rubber latex were blended in different ratios and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature. The tensile properties, swelling ratio and permanent set were measured. The maximum tensile strength and modulus at 500% elongation were obtained at an absorbed dose of 8 kGy. Modulus increases from 6.99 MPa to 9.87 MPa for an increase in proportion of MMA grafted rubber from 40% to 60% in the blend at similar absorbed dose. Elongation at break and swelling ratio decrease with increasing absorbed dose as well as the MMA grafted rubber content in the blends. The decreasing trend of permanent set is high up to 5 kGy absorbed dose, and beyond that dose it becomes almost flat.
Natural rubber latex (NRL) and methyl methacrylate (MMA) grafted rubber latex were blended in different ratios and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature. The tensile properties, swelling ratio and permanent set were measured. The maximum tensile strength and modulus at 500% elongation were obtained at an absorbed dose of 8 kGy. Modulus increases from 6.99 MPa to 9.87 MPa for an increase in proportion of MMA grafted rubber from 40% to 60% in the blend at similar absorbed dose. Elongation at break and swelling ratio decrease with increasing absorbed dose as well as the MMA grafted rubber content in the blends. The decreasing trend of permanent set is high up to 5 kGy absorbed dose, and beyond that dose it becomes almost flat.
2007, 25(5): 525-533
Abstract:
We use the pruned-enriched Rosenbluth method to investigate systemically the segment density profiles of compact polymer chains confined between two parallel plane walls. The non-adsorption case of adsorption interaction energy = 0 and the weak adsorption case of = 1 are considered for the compact polymer chains with different chain lengths N and different separation distances between two walls D. Several special entropy effects on the confined compact polymer chains, such as a damped oscillation in the segment density profile for the large separation distance D, are observed and discussed for different separation distances D in the non-adsorption case. In the weak adsorption case, investigations on the segment density profiles indicate that the competition between the entropy and adsorption effects results in an obvious depletion layer. Moreover, the scaling laws of the damped oscillation period Td and the depletion layer width Ld are obtained for the confined compact chains. Most of these results are obtained for the first time so far as we know, which are expected to understand the properties of the confined compact polymer chains more completely.
We use the pruned-enriched Rosenbluth method to investigate systemically the segment density profiles of compact polymer chains confined between two parallel plane walls. The non-adsorption case of adsorption interaction energy = 0 and the weak adsorption case of = 1 are considered for the compact polymer chains with different chain lengths N and different separation distances between two walls D. Several special entropy effects on the confined compact polymer chains, such as a damped oscillation in the segment density profile for the large separation distance D, are observed and discussed for different separation distances D in the non-adsorption case. In the weak adsorption case, investigations on the segment density profiles indicate that the competition between the entropy and adsorption effects results in an obvious depletion layer. Moreover, the scaling laws of the damped oscillation period Td and the depletion layer width Ld are obtained for the confined compact chains. Most of these results are obtained for the first time so far as we know, which are expected to understand the properties of the confined compact polymer chains more completely.
2007, 25(5): 535-539
Abstract:
The NR/modified montmorillonite (EMT) nano-composites were prepared by mechanical mixing and reacting in situ with glycidyl methacrylate. Under 30 kW•m2 of heat flux, the combustion behavior of the nano-composites was studied with cone calorimetry, and PHRR, THR, EHC, TSR and MLR were tested. The results showed that the nano-composite had improved mechanical properties and flame retardance properties, and to some extent, the nano-composite had smoke suppress effect. Compared with pure NR, the PHRR, EHC and SPR of the nano-composite reduced by 34%, 21% and 16.8%, respectively.
The NR/modified montmorillonite (EMT) nano-composites were prepared by mechanical mixing and reacting in situ with glycidyl methacrylate. Under 30 kW•m2 of heat flux, the combustion behavior of the nano-composites was studied with cone calorimetry, and PHRR, THR, EHC, TSR and MLR were tested. The results showed that the nano-composite had improved mechanical properties and flame retardance properties, and to some extent, the nano-composite had smoke suppress effect. Compared with pure NR, the PHRR, EHC and SPR of the nano-composite reduced by 34%, 21% and 16.8%, respectively.
2007, 25(5): 541-544
Abstract:
Ring-opening polymerization of ε-caprolactone has been carried out by using rare earth Schiff base complexes: lanthanide tris(N-phenyl-3,5-di-t-butylsalicylaldiminato)s [Ln(OPBS)3] as single component catalyst for the first time. The influences of different rare earth elements, monomer and catalyst concentration as well as reaction time on the polymerization were investigated. Mechanism studies showed that monomer inserts into the active site with the acyl-oxygen bond scission rather than the break of alkyl-oxygen bond.
Ring-opening polymerization of ε-caprolactone has been carried out by using rare earth Schiff base complexes: lanthanide tris(N-phenyl-3,5-di-t-butylsalicylaldiminato)s [Ln(OPBS)3] as single component catalyst for the first time. The influences of different rare earth elements, monomer and catalyst concentration as well as reaction time on the polymerization were investigated. Mechanism studies showed that monomer inserts into the active site with the acyl-oxygen bond scission rather than the break of alkyl-oxygen bond.
