Login In
2008 Volume 26 Issue 4
STUDY ON THE PREPARATION AND PERFORMANCES OF P(VAc-MMA) POLYMER ELECTROLYTES FOR LITHIUM ION BATTERY
2008, 26(4): 375-380
Abstract:
A random copolymer P(VAc-MMA) was synthesized via seeded emulsion copolymerization with vinyl acetate (VAc) and methyl methacrylate (MMA) as monomers, and the polymer electrolytes comprising blend of corresponding copolymer P(VAc-MMA) as a host polymer and LiClO4 as a dopant were prepared by solution casting technique. Performances of the synthesized copolymer and prepared polymer membrane and electrolyte were studied by FTIR, XRD, TG, DSC, mechanical testing and AC impedance. According to the study of FTIR and DSC, it was found that P(VAc-MMA) had been formed. XRD indicates that the amorphous nature in copolymer increased with increasing the ratio of VAc in monomers, resulting in expedite migration of ions. The polymer electrolytes based on P(VAc-MMA) possess excellent thermal stability, fine mechanical performance and high ionic conductivity. The maximum ionic conductivity value was found to reach 1.27 × 10－3 S·cm－1 at 25°C. The temperature dependence of the polymer electrolyte complexes appeared to obey Arrhenius equation.
A random copolymer P(VAc-MMA) was synthesized via seeded emulsion copolymerization with vinyl acetate (VAc) and methyl methacrylate (MMA) as monomers, and the polymer electrolytes comprising blend of corresponding copolymer P(VAc-MMA) as a host polymer and LiClO4 as a dopant were prepared by solution casting technique. Performances of the synthesized copolymer and prepared polymer membrane and electrolyte were studied by FTIR, XRD, TG, DSC, mechanical testing and AC impedance. According to the study of FTIR and DSC, it was found that P(VAc-MMA) had been formed. XRD indicates that the amorphous nature in copolymer increased with increasing the ratio of VAc in monomers, resulting in expedite migration of ions. The polymer electrolytes based on P(VAc-MMA) possess excellent thermal stability, fine mechanical performance and high ionic conductivity. The maximum ionic conductivity value was found to reach 1.27 × 10－3 S·cm－1 at 25°C. The temperature dependence of the polymer electrolyte complexes appeared to obey Arrhenius equation.
2008, 26(4): 381-391
Abstract:
Poly(amino acid) has been widely utilized in drug delivery, tissue engineering and biomedical materials. The biomaterials based on poly(glutamic acid) are usually modified via copolymerization with other monomers such as L-aspartic acid to improve the uncontrolled degradation rate. The ring-opening homo- and co-polymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and β-benzyl-L-aspartate N-carboxyanhydride (BLA-NCA) were carried out in solution by using triethylamine (TEA) as initiator. The BLG-NCA homopolymerization could take place even at －30οC and molecular weight of poly(γ-benzyl-L-glutamate) decreased with increasing polymerization temperature. The BLA-NCA polymerization did not occur at －10οC and was needed to be carried out at 25οC to improve the polymerization. Poly(γ-benzyl-L-glutamate) and poly(β-benzyl-L-aspartate) with unimodal molecular weigh distribution and weight average molecular weight (Mw) of 32100 and 4000 could be obtained at 25οC. The copolymers of γ-benzyl L-glutamate and β-benzyl L-aspartate with unimodal molecular weight distribution and Mw ranging from 5600 to 24600 could be prepared. The useful copolymers of poly(L-glutamic acid-co-L-aspartic acid) were further prepared by removal of benzyl groups.
Poly(amino acid) has been widely utilized in drug delivery, tissue engineering and biomedical materials. The biomaterials based on poly(glutamic acid) are usually modified via copolymerization with other monomers such as L-aspartic acid to improve the uncontrolled degradation rate. The ring-opening homo- and co-polymerization of γ-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) and β-benzyl-L-aspartate N-carboxyanhydride (BLA-NCA) were carried out in solution by using triethylamine (TEA) as initiator. The BLG-NCA homopolymerization could take place even at －30οC and molecular weight of poly(γ-benzyl-L-glutamate) decreased with increasing polymerization temperature. The BLA-NCA polymerization did not occur at －10οC and was needed to be carried out at 25οC to improve the polymerization. Poly(γ-benzyl-L-glutamate) and poly(β-benzyl-L-aspartate) with unimodal molecular weigh distribution and weight average molecular weight (Mw) of 32100 and 4000 could be obtained at 25οC. The copolymers of γ-benzyl L-glutamate and β-benzyl L-aspartate with unimodal molecular weight distribution and Mw ranging from 5600 to 24600 could be prepared. The useful copolymers of poly(L-glutamic acid-co-L-aspartic acid) were further prepared by removal of benzyl groups.
2008, 26(4): 393-398
Abstract:
Glycolic acid was polymerized under vacuum in the presence and absence of nano sized clay. The added clay catalyzed the condensation polymerization which can be confirmed by recording FTIR spectroscopy and intrinsic viscosity (IV) values. The relative intensity of C＝O/CH is increased while increasing the amount of clay. DSC showed the appearance of multiple endotherms of poly(glycolic acid). TGA showed the percentage weight residue remain above 750°C for polymer-nano composite system was 21% and hence proved the flame retardancy (char forming) nature. TEM confirmed the nano size of the clay used to catalyze the condensation reaction. The intrinsic viscosity value was increased with the increase of percentage weight of Hectorite type clay.
Glycolic acid was polymerized under vacuum in the presence and absence of nano sized clay. The added clay catalyzed the condensation polymerization which can be confirmed by recording FTIR spectroscopy and intrinsic viscosity (IV) values. The relative intensity of C＝O/CH is increased while increasing the amount of clay. DSC showed the appearance of multiple endotherms of poly(glycolic acid). TGA showed the percentage weight residue remain above 750°C for polymer-nano composite system was 21% and hence proved the flame retardancy (char forming) nature. TEM confirmed the nano size of the clay used to catalyze the condensation reaction. The intrinsic viscosity value was increased with the increase of percentage weight of Hectorite type clay.
2008, 26(4): 399-404
Abstract:
Chloro ethane dimethyl sulfoxide, C2H5Cl·DMSO (ECl·DMSO) was prepared by interaction of acrylic acid with conc. Hydrochloric acid in dimethyl sulfoxide (DMSO) and subsequent decarboxylation with H2O2 solution. The formation of the compound was confirmed by spectral and analytical methods; the molecular weight was determined by cryoscopic method. The solubility of poly(vinyl alcohol) (PVA) in different solvents or mixed solvents at 40οC, 50οC and 60οC temperature in the presence of 0.01% of ECl·DMSO was determined. It turned out that ECl·DMSO helps dissolution of PVA, and is very effective catalyst in the preparation of esters and acetals of PVA.
Chloro ethane dimethyl sulfoxide, C2H5Cl·DMSO (ECl·DMSO) was prepared by interaction of acrylic acid with conc. Hydrochloric acid in dimethyl sulfoxide (DMSO) and subsequent decarboxylation with H2O2 solution. The formation of the compound was confirmed by spectral and analytical methods; the molecular weight was determined by cryoscopic method. The solubility of poly(vinyl alcohol) (PVA) in different solvents or mixed solvents at 40οC, 50οC and 60οC temperature in the presence of 0.01% of ECl·DMSO was determined. It turned out that ECl·DMSO helps dissolution of PVA, and is very effective catalyst in the preparation of esters and acetals of PVA.
2008, 26(4): 405-414
Abstract:
The preparation and properties of asymmetric poly(vinyldiene fluoride) (PVDF) membranes are described in this study. Membranes were prepared from a casting solution of PVDF, N,N-dimethylacetamide (DMAc) solvent and water-soluble poly(ethylene glycol) (PEG) additives by immersing them in water as coagulant medium. Experiments showed that when PEG molecular weight increased, the changes in the resultant membranes’ morphologies and properties showed a transition point at PEG6000. This indicated that PEG with a relatively low molecular weight was used as a pore-forming agent to enhance pure water flux and reduce solute rejection of membranes, but PEG was used as a pore-reducing agent with a further increment of PEG molecular weight to result in pure water flux decreasing and solute rejection increasing. Finally, combined with the precipitation rates of different membrane-forming systems, the membrane formation mechanism describing PEG mobility was discussed extensively basing on the length changes of PEG molecular chains and the affinity between PEG and casting solution. The results offered a better understanding of effects of PEG additives on membrane structure and properties.
The preparation and properties of asymmetric poly(vinyldiene fluoride) (PVDF) membranes are described in this study. Membranes were prepared from a casting solution of PVDF, N,N-dimethylacetamide (DMAc) solvent and water-soluble poly(ethylene glycol) (PEG) additives by immersing them in water as coagulant medium. Experiments showed that when PEG molecular weight increased, the changes in the resultant membranes’ morphologies and properties showed a transition point at PEG6000. This indicated that PEG with a relatively low molecular weight was used as a pore-forming agent to enhance pure water flux and reduce solute rejection of membranes, but PEG was used as a pore-reducing agent with a further increment of PEG molecular weight to result in pure water flux decreasing and solute rejection increasing. Finally, combined with the precipitation rates of different membrane-forming systems, the membrane formation mechanism describing PEG mobility was discussed extensively basing on the length changes of PEG molecular chains and the affinity between PEG and casting solution. The results offered a better understanding of effects of PEG additives on membrane structure and properties.
2008, 26(4): 415-423
Abstract:
Three ansa-metallocenes (Me2C)(Me2Si)Cp2TiCl2 (1), [(CH2)5C](Me2Si)Cp2TiCl2 (2) and (Me2C)(Me2Si)Cp2ZrCl2 (3) with larger dihedral angles and longer distance from metal to the center of Cp planes were synthesized and used as catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). In the case of ethylene polymerization, compared the feature structures of unbridged metallocenes, singly bridged metallocenes and doubly bridged metallocenes 1, 2, 3, there exhibit the relationship between structural characteristics and the catalytic properties with behavior of polymers. And the view that the dimensions of the short dimethylsilylene and isopropylidene bridges of metallocene 3 do not match the co-ordination requirement of the larger zirconium atom can also explain the result for ethylene polymerization. Catalyzed by complexes 1 and 2 respectively, the copolymerizations of ethylene with 1-hexene, 1-octene, especially the long chain α-olefins (1-tetradecene, 1-hexadecene) were investigated, and showed high incorporations and comonomer effects in almost all the examples. The melting points of the copolymers are approximately 4%－31% below those of the homopolymers, and the enthalpies of fusion decrease greatly due to the lower crystallinity. The microstructures of the copolymer were analyzed with 13C-NMR to determine the comonomer sequence distributions and number–average sequence lengths. Comparison between results for the complexes 1 and 2 with different bridging groups respectively showed that the nature of the bridge has a significant effect on both the incorporation and sequence distribution of the α-olefin. Because of the bridges in ansa-metallocene complexes, the copolymerization behavior was different in using catalyst 1 and catalyst 2.
Three ansa-metallocenes (Me2C)(Me2Si)Cp2TiCl2 (1), [(CH2)5C](Me2Si)Cp2TiCl2 (2) and (Me2C)(Me2Si)Cp2ZrCl2 (3) with larger dihedral angles and longer distance from metal to the center of Cp planes were synthesized and used as catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). In the case of ethylene polymerization, compared the feature structures of unbridged metallocenes, singly bridged metallocenes and doubly bridged metallocenes 1, 2, 3, there exhibit the relationship between structural characteristics and the catalytic properties with behavior of polymers. And the view that the dimensions of the short dimethylsilylene and isopropylidene bridges of metallocene 3 do not match the co-ordination requirement of the larger zirconium atom can also explain the result for ethylene polymerization. Catalyzed by complexes 1 and 2 respectively, the copolymerizations of ethylene with 1-hexene, 1-octene, especially the long chain α-olefins (1-tetradecene, 1-hexadecene) were investigated, and showed high incorporations and comonomer effects in almost all the examples. The melting points of the copolymers are approximately 4%－31% below those of the homopolymers, and the enthalpies of fusion decrease greatly due to the lower crystallinity. The microstructures of the copolymer were analyzed with 13C-NMR to determine the comonomer sequence distributions and number–average sequence lengths. Comparison between results for the complexes 1 and 2 with different bridging groups respectively showed that the nature of the bridge has a significant effect on both the incorporation and sequence distribution of the α-olefin. Because of the bridges in ansa-metallocene complexes, the copolymerization behavior was different in using catalyst 1 and catalyst 2.
2008, 26(4): 425-432
Abstract:
Direct melt/solid polycondensation of lactic acid (LA) was carried out to obtain high molecular weight poly(lactic acid) (PLA) by a process using various catalysts in the first-step melt polycondensation, and followed solid polycondensation by using p-toulenesulfonic acid monohydrate (TSA) as the catalyst in the second step. Effects of various catalysts and reaction temperature on the molecular weight and crystallinity of resulting PLA polymers were examined. It was shown that SnCl2·2H2O/TSA, SnCl2·2H2O/succinic anhydride, and SnCl2·2H2O/maleic anhydride binary catalysts should be effective binary catalysts to obtain high molecular weight PLA of more than 1.2× 105. A conventional melt spinning method was used to spin PLA fibers, which displayed tensile strength of (382.76 ± 1.41) MPa and tensile modulus of (4.36 ± 0.07) GPa.
Direct melt/solid polycondensation of lactic acid (LA) was carried out to obtain high molecular weight poly(lactic acid) (PLA) by a process using various catalysts in the first-step melt polycondensation, and followed solid polycondensation by using p-toulenesulfonic acid monohydrate (TSA) as the catalyst in the second step. Effects of various catalysts and reaction temperature on the molecular weight and crystallinity of resulting PLA polymers were examined. It was shown that SnCl2·2H2O/TSA, SnCl2·2H2O/succinic anhydride, and SnCl2·2H2O/maleic anhydride binary catalysts should be effective binary catalysts to obtain high molecular weight PLA of more than 1.2× 105. A conventional melt spinning method was used to spin PLA fibers, which displayed tensile strength of (382.76 ± 1.41) MPa and tensile modulus of (4.36 ± 0.07) GPa.
2008, 26(4): 433-441
Abstract:
Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures. Upon irradiation with UV light (366 nm), fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C. The later color was switched back to the original color when the films were irradiated with white light. The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at its λmax of 525 nm. The first-order plots of photocoloration reaction shows two distinct linear lines. The slopes of which corresponding to the first-order rate constants k1 and k2, where k1 is the rate constant at initial reaction times and k2 is that at late reaction times. These results suggest the plausible presence of two conformers of the ring opened form 1-E which reacts in sequence. On the other hand, photobleaching reaction shows a simple first-order reaction rate. It was found that for photocoloration reaction, the rate constant at initial reaction times is slower than that at late reaction times. Similarly, the photocoloration reaction is slower than the photobleaching reaction and both reactions increases with increasing the annealing temperatures. It was found that there was almost complete loss of photochemical fatigue resistance of fulgide 1 doped in polystyrene polymer film irrespective of the annealing temperature.
Fulgide 1-E doped in polystyrene polymer films was heated at various annealing temperatures. Upon irradiation with UV light (366 nm), fulgide 1-E undergoes a conrotatory ring closure to the pink colored closed form 1-C. The later color was switched back to the original color when the films were irradiated with white light. The kinetics of photocoloration and photobleaching processes were followed spectrophotometrically by monitoring the absorbance of the ring closed product 1-C at its λmax of 525 nm. The first-order plots of photocoloration reaction shows two distinct linear lines. The slopes of which corresponding to the first-order rate constants k1 and k2, where k1 is the rate constant at initial reaction times and k2 is that at late reaction times. These results suggest the plausible presence of two conformers of the ring opened form 1-E which reacts in sequence. On the other hand, photobleaching reaction shows a simple first-order reaction rate. It was found that for photocoloration reaction, the rate constant at initial reaction times is slower than that at late reaction times. Similarly, the photocoloration reaction is slower than the photobleaching reaction and both reactions increases with increasing the annealing temperatures. It was found that there was almost complete loss of photochemical fatigue resistance of fulgide 1 doped in polystyrene polymer film irrespective of the annealing temperature.
2008, 26(4): 443-454
Abstract:
The synthesis of two new methacrylates such as 2-[(cyclohexylideneamino)oxy]-2-oxoethyl methylacrylate (CHOEMA) and 2-[(cyclopentylideneamino)oxy]-2-oxoethyl methylacrylate (CPOEMA) are described. The monomers produced from the reaction of corresponding cyclohexanone O-(2-chloroacetyl) oxime and cyclopentanone O-(2-chloroacetyl) oxime with sodium methacrylate was polymerized in 1,4-dioxane solution at 65οC using AIBN as an initiator. The monomers and their polymers were characterized by IR, 1H- and 13C-NMR spectroscopy. The glass transition temperature of the polymers was investigated by DSC and the apparent thermal decomposition activation energies (Ed) were calculated by Ozawa and multiple heating rate kinetics (MHRK) method using the Shimadzu TGA thermobalance. By using gel permeation chromatography, weight-average (Mw) and number-average (Mn) molecular weights and polydispersity indices of the polymers were determined. The antibacterial and antifungal effects of the monomers and polymers were also investigated on various bacteria and fungi. The photochemical properties of the polymers were investigated by UV and FTIR spectra.
The synthesis of two new methacrylates such as 2-[(cyclohexylideneamino)oxy]-2-oxoethyl methylacrylate (CHOEMA) and 2-[(cyclopentylideneamino)oxy]-2-oxoethyl methylacrylate (CPOEMA) are described. The monomers produced from the reaction of corresponding cyclohexanone O-(2-chloroacetyl) oxime and cyclopentanone O-(2-chloroacetyl) oxime with sodium methacrylate was polymerized in 1,4-dioxane solution at 65οC using AIBN as an initiator. The monomers and their polymers were characterized by IR, 1H- and 13C-NMR spectroscopy. The glass transition temperature of the polymers was investigated by DSC and the apparent thermal decomposition activation energies (Ed) were calculated by Ozawa and multiple heating rate kinetics (MHRK) method using the Shimadzu TGA thermobalance. By using gel permeation chromatography, weight-average (Mw) and number-average (Mn) molecular weights and polydispersity indices of the polymers were determined. The antibacterial and antifungal effects of the monomers and polymers were also investigated on various bacteria and fungi. The photochemical properties of the polymers were investigated by UV and FTIR spectra.
2008, 26(4): 455-463
Abstract:
A new method to synthesize a degradable terminal amino group-containing copolymer, poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-PCL-NH2), was developed in the following three steps: (1) the ring-opening polymerization (ROP) of ε-caprolactone from the Schiff base prepared from benzaldehyde and ethanolamine (Ph―CH＝NCH2CH2OH) used as an initiator to obtain heterobifunctional poly(ε-caprolactone) with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH2CH2N＝CH―Ph); (2) the coupling reaction of two reactive precursors, a hydroxy-terminated HO-PCL-CH2CH2N＝CH―Ph and α-monocarboxy-ω-monomethoxy poly(ethylene glycol) (CMPEG) to synthesize MPEG-PCL-CH2CH2N＝CH―Ph; (3) the conversion of the ―N＝CH―Ph end-group into NH2 end-group by acidification of acetic acid to obtain MPEG-PCL-NH2. The structures from the precursors to the terminal amino group-containing copolymer were confirmed by 1H-NMR and their molecular weights were measured by gel permeation chromatography. The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell. The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.
A new method to synthesize a degradable terminal amino group-containing copolymer, poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG-PCL-NH2), was developed in the following three steps: (1) the ring-opening polymerization (ROP) of ε-caprolactone from the Schiff base prepared from benzaldehyde and ethanolamine (Ph―CH＝NCH2CH2OH) used as an initiator to obtain heterobifunctional poly(ε-caprolactone) with one terminal Schiff base group and one hydroxyl group (HO-PCL-CH2CH2N＝CH―Ph); (2) the coupling reaction of two reactive precursors, a hydroxy-terminated HO-PCL-CH2CH2N＝CH―Ph and α-monocarboxy-ω-monomethoxy poly(ethylene glycol) (CMPEG) to synthesize MPEG-PCL-CH2CH2N＝CH―Ph; (3) the conversion of the ―N＝CH―Ph end-group into NH2 end-group by acidification of acetic acid to obtain MPEG-PCL-NH2. The structures from the precursors to the terminal amino group-containing copolymer were confirmed by 1H-NMR and their molecular weights were measured by gel permeation chromatography. The amphiphilic terminal amino group-containing copolymer could self-assemble into micelles in an aqueous system with PCL block as the core and PEG block as the shell. The micelle formation of the terminal amino group-containing block copolymer was studied by fluorescent probe technique and the existence of critical micellar concentration (cmc) confirmed the amphiphilic nature of the resulting copolymer. ESEM and DLS analysis of the micelles revealed a homogeneous spherical morphology and a unimodal size distribution.
2008, 26(4): 465-473
Abstract:
Dust-free semidilute and concentrated polystyrene (PS) solutions in different solvents were prepared by slow evaporation and in situ anionic polymerization, which removes the effects of troublesome artifacts such as dust contamination and concentration gradient. The dynamics was reexamined by a combination of static and dynamic laser light scattering. In benzene and toluene (good solvents for PS), only one fast diffusive mode of polymer chains can be observed when the concentration (c) is up to 20%, which is attributed to thermally agitated fluctuation of “blobs” or chain segments. Static and dynamic correlation lengths (ξS and ξD) are scaled with c as ξS (or ξD) ~ C－0.72 ± 0.02. In cyclohexane, whose quality decreases with temperature in the range 32－50°C, an additional slow mode of polymer chains can be observed. Such a slow mode is viewed more obviously at a large scattering angle even in a concentrated solution with high chain entanglement. The present study indicates that the slow mode is due to the solvent quality.
Dust-free semidilute and concentrated polystyrene (PS) solutions in different solvents were prepared by slow evaporation and in situ anionic polymerization, which removes the effects of troublesome artifacts such as dust contamination and concentration gradient. The dynamics was reexamined by a combination of static and dynamic laser light scattering. In benzene and toluene (good solvents for PS), only one fast diffusive mode of polymer chains can be observed when the concentration (c) is up to 20%, which is attributed to thermally agitated fluctuation of “blobs” or chain segments. Static and dynamic correlation lengths (ξS and ξD) are scaled with c as ξS (or ξD) ~ C－0.72 ± 0.02. In cyclohexane, whose quality decreases with temperature in the range 32－50°C, an additional slow mode of polymer chains can be observed. Such a slow mode is viewed more obviously at a large scattering angle even in a concentrated solution with high chain entanglement. The present study indicates that the slow mode is due to the solvent quality.
2008, 26(4): 475-479
Abstract:
An aromatic heterocyclic Schiff base neodymium complex bearing thiazole was synthesized and its activity in the ring-opening polymerization of ε-caprolactone (CL) was examined. The conditions of the CL/Nd molar ratio, monomer concentration, polymerization time and temperature were investigated. Activities of ca.171 kg/Nd·h were obtained under the optimum condition (CL/Nd = 1600 (molar ratio), [CL] = 2.26 mol L－1, 1 h at 50οC), giving a poly(ε-caprolactone) (PCL) of number-average molecular weight Mn = 5.4 × 104 and molecular weight distribution MWD = 1.96. The conversion of CL monomer as high as 94% was observed after polymerized for one hour. The mechanism of coordination polymerization has also been illustrated.
An aromatic heterocyclic Schiff base neodymium complex bearing thiazole was synthesized and its activity in the ring-opening polymerization of ε-caprolactone (CL) was examined. The conditions of the CL/Nd molar ratio, monomer concentration, polymerization time and temperature were investigated. Activities of ca.171 kg/Nd·h were obtained under the optimum condition (CL/Nd = 1600 (molar ratio), [CL] = 2.26 mol L－1, 1 h at 50οC), giving a poly(ε-caprolactone) (PCL) of number-average molecular weight Mn = 5.4 × 104 and molecular weight distribution MWD = 1.96. The conversion of CL monomer as high as 94% was observed after polymerized for one hour. The mechanism of coordination polymerization has also been illustrated.
2008, 26(4): 481-487
Abstract:
Poly(silphenylene-siloxane)s had been synthesized through dehydrocarbon polycondensation of 1,4-bis(dimethylsilyl)benzene (BDSB) and dialkoxysilane. The polymer composition and structure was characterized by 29Si-NMR. The influence of temperature, B(C6F5)3 concentration and monomer structure on the composition and the microstructure of the copolymers were investigated. It shows that elevating reaction temperature or using substrate (R’O)2R2R1Si with bulk organic group of R1 or R2 augments the run number value of the polymers, resulting in more alternating structure. Polymers with lower run number are obtained while increasing the B(C6F5)3 concentration. Using dimethyldimethoxysilane in stead of dimethyldiethoxysilane as monomer, the products are more alternating. Owing to the cyclization reaction of the side products of Si―H/Si―OMe exchange reaction, the mole ratio of diorganosiloxane unit and silphenylene unit in the copolymers is some 28/72－36/64, much lower than the mole ratio of the fed monomers, 50/50.
Poly(silphenylene-siloxane)s had been synthesized through dehydrocarbon polycondensation of 1,4-bis(dimethylsilyl)benzene (BDSB) and dialkoxysilane. The polymer composition and structure was characterized by 29Si-NMR. The influence of temperature, B(C6F5)3 concentration and monomer structure on the composition and the microstructure of the copolymers were investigated. It shows that elevating reaction temperature or using substrate (R’O)2R2R1Si with bulk organic group of R1 or R2 augments the run number value of the polymers, resulting in more alternating structure. Polymers with lower run number are obtained while increasing the B(C6F5)3 concentration. Using dimethyldimethoxysilane in stead of dimethyldiethoxysilane as monomer, the products are more alternating. Owing to the cyclization reaction of the side products of Si―H/Si―OMe exchange reaction, the mole ratio of diorganosiloxane unit and silphenylene unit in the copolymers is some 28/72－36/64, much lower than the mole ratio of the fed monomers, 50/50.
2008, 26(4): 489-494
Abstract:
By means of the wet chemical surface modification, the surface of CeO2 was modified by vinyltrimethoxysilane (VTMS). Infrared spectroscopy was used to investigate the structure of the modified CeO2 and the result showed that VTMS has been attached onto the surface of CeO2. Effect of VTMS concentration on the active index of the modified CeO2 was also studied, and the result indicated that the active index of the modified CeO2 increases with the increase of VTMS concentration and the optimal concentration of VTMS is 10 wt%. The effect of the modified CeO2 on the tear strength of silicone rubber before and after aging was studied and it was found that in comparison with the unmodified CeO2 the addition of the modified CeO2 results in the significant increase of the tear strength before ageing due to the increase of the crosslinking density of silicone rubber under the experimental conditions. The tear strength of silicone rubber filled with the modified CeO2 after ageing is higher than that with the unmodified CeO2, indicating that the modification of CeO2 can improve the heat-resistance of silicone rubber.
By means of the wet chemical surface modification, the surface of CeO2 was modified by vinyltrimethoxysilane (VTMS). Infrared spectroscopy was used to investigate the structure of the modified CeO2 and the result showed that VTMS has been attached onto the surface of CeO2. Effect of VTMS concentration on the active index of the modified CeO2 was also studied, and the result indicated that the active index of the modified CeO2 increases with the increase of VTMS concentration and the optimal concentration of VTMS is 10 wt%. The effect of the modified CeO2 on the tear strength of silicone rubber before and after aging was studied and it was found that in comparison with the unmodified CeO2 the addition of the modified CeO2 results in the significant increase of the tear strength before ageing due to the increase of the crosslinking density of silicone rubber under the experimental conditions. The tear strength of silicone rubber filled with the modified CeO2 after ageing is higher than that with the unmodified CeO2, indicating that the modification of CeO2 can improve the heat-resistance of silicone rubber.
2008, 26(4): 495-500
Abstract:
Hydrophobic nano silica sol (HNSS) was incorporated into polyvinylmethylsiloxane to prepare reinforced high-temperature vulcanized (HTV) silicone rubber. HTV silicone rubber filled with 40 phr HNSS showed excellent mechanical and optical properties: the tensile strength reached 11.7 MPa and the optical transmittance was higher than 90%. Possible reasons for reinforcement and transparency were discussed on the basis of the bound rubber percentage, total crosslink density, and SEM analysis. Our work suggests that HNSS is effective for reinforcement of HTV silicone rubber to endow excellent mechanical and optical properties.
Hydrophobic nano silica sol (HNSS) was incorporated into polyvinylmethylsiloxane to prepare reinforced high-temperature vulcanized (HTV) silicone rubber. HTV silicone rubber filled with 40 phr HNSS showed excellent mechanical and optical properties: the tensile strength reached 11.7 MPa and the optical transmittance was higher than 90%. Possible reasons for reinforcement and transparency were discussed on the basis of the bound rubber percentage, total crosslink density, and SEM analysis. Our work suggests that HNSS is effective for reinforcement of HTV silicone rubber to endow excellent mechanical and optical properties.
2008, 26(4): 501-506
Abstract:
An attempt has been made in the present work to prepare poly(vinyl borate), PVBO and its calcium derivative by homogeneous esterification of PVA with boric acid in non-aqueous medium in the presence of a catalyst ethyl nitrate dimethyl sulfoxide. The compounds were characterized by IR and 1H-NMR spectra. Conductivities were determined from 30οC to 90οC in solid state within a frequency range of 42 Hz to 100 kHz. The compounds so formed showed ionic conductivity and their conductivities were dependent on frequencies used. It is found that the addition of Ca2+ ion increases the ionic conductivity of PVBO appreciably. The conductivity of PVBO-Ca increases rapidly after 50οC. The total ionic transport number and activation energy of the copolymers were also determined.
An attempt has been made in the present work to prepare poly(vinyl borate), PVBO and its calcium derivative by homogeneous esterification of PVA with boric acid in non-aqueous medium in the presence of a catalyst ethyl nitrate dimethyl sulfoxide. The compounds were characterized by IR and 1H-NMR spectra. Conductivities were determined from 30οC to 90οC in solid state within a frequency range of 42 Hz to 100 kHz. The compounds so formed showed ionic conductivity and their conductivities were dependent on frequencies used. It is found that the addition of Ca2+ ion increases the ionic conductivity of PVBO appreciably. The conductivity of PVBO-Ca increases rapidly after 50οC. The total ionic transport number and activation energy of the copolymers were also determined.
2008, 26(4): 507-512
Abstract:
Enhanced stability of polyplexes in physiological condition was an important prerequisite for successful systemic gene delivery. Herein novel method was reported to develop stable gene vector by nanotechnology. Thiolated polyplexes were constructed and then cross-linked with gold nanoparticles (AuNPs) by gold-thiol interactions. TEM pictures showed that AuNPs were attached to the shell of spherical polyplexes. The hybrid gene vector was stable enough in physiological condition and maintained efficient transfection, which showed great potential in gene delivery research and application.
Enhanced stability of polyplexes in physiological condition was an important prerequisite for successful systemic gene delivery. Herein novel method was reported to develop stable gene vector by nanotechnology. Thiolated polyplexes were constructed and then cross-linked with gold nanoparticles (AuNPs) by gold-thiol interactions. TEM pictures showed that AuNPs were attached to the shell of spherical polyplexes. The hybrid gene vector was stable enough in physiological condition and maintained efficient transfection, which showed great potential in gene delivery research and application.
