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2009 Volume 27 Issue 4
2009, 27(4): 447-454
Abstract:
Spectroscopic studies have revealed that the amount of polyureas formed and the kinetics of their formation in soy based polyurethane systems are considerably different from traditional systems employing ethylene oxide-propylene oxide (EO-PO) based polyols. The aggregation of polyureas was characterized by the hydrogen bonds formed utilizing FTIR spectroscopy. This study offered the opportunity to assign the previously undefined infrared features. The structural transformation is reflected in the segmental relaxation kinetics characterized by spin-spin diffusion most conveniently measured using low field NMR. The reaction kinetics and the products formed are directly related to the hydrophobic nature of the soy based polyols and its inability to disperse water.
Spectroscopic studies have revealed that the amount of polyureas formed and the kinetics of their formation in soy based polyurethane systems are considerably different from traditional systems employing ethylene oxide-propylene oxide (EO-PO) based polyols. The aggregation of polyureas was characterized by the hydrogen bonds formed utilizing FTIR spectroscopy. This study offered the opportunity to assign the previously undefined infrared features. The structural transformation is reflected in the segmental relaxation kinetics characterized by spin-spin diffusion most conveniently measured using low field NMR. The reaction kinetics and the products formed are directly related to the hydrophobic nature of the soy based polyols and its inability to disperse water.
2009, 27(4): 455-464
Abstract:
A new luminescent and thermally stable platinum(II) polyyne polymer trans-[―Pt(PBu3)2C≡CArC≡C―]n (P1) containing the 2,7-fluorene chromophoric spacer substituted by pendant carbazolyl group via long alkyl bridges. The regiochemical structures of these compounds were studied by various spectroscopic analyses. We report the photophysical properties of this group 10 polymetallayne and a comparison was made to its binuclear model complex trans-[Pt(Ph)(PEt3)2C≡CArC≡CPt(Ph)(PEt3)2] (M1) as well as to those with non-carbazole-containing fluorene spacer (P2 and M2). Upon photoexcitation, each of P1 and M1 emits an intense purple-blue fluorescence emission in the near-UV to visible region in dilute fluid solutions at room temperature. Harvesting of organic triplet emissions harnessed through the strong heavy-atom effects of platinum metal was examined and at 77 K, each of the metalated compounds displayed dual emission bands, viz. both the fluorescence and the lower-lying phosphorescence. Spectroscopic results revealed that the formation of excimers was suppressed by introducing carbazole side groups. The spatial extent of the lowest singlet and triplet excitons in P1 and M1 was fully elucidated. Such organometallic poly(fluorenyleneethynylene)s anchored with the carbazole pendants was found to have an improved thermal stability and suppressed aggregation.
A new luminescent and thermally stable platinum(II) polyyne polymer trans-[―Pt(PBu3)2C≡CArC≡C―]n (P1) containing the 2,7-fluorene chromophoric spacer substituted by pendant carbazolyl group via long alkyl bridges. The regiochemical structures of these compounds were studied by various spectroscopic analyses. We report the photophysical properties of this group 10 polymetallayne and a comparison was made to its binuclear model complex trans-[Pt(Ph)(PEt3)2C≡CArC≡CPt(Ph)(PEt3)2] (M1) as well as to those with non-carbazole-containing fluorene spacer (P2 and M2). Upon photoexcitation, each of P1 and M1 emits an intense purple-blue fluorescence emission in the near-UV to visible region in dilute fluid solutions at room temperature. Harvesting of organic triplet emissions harnessed through the strong heavy-atom effects of platinum metal was examined and at 77 K, each of the metalated compounds displayed dual emission bands, viz. both the fluorescence and the lower-lying phosphorescence. Spectroscopic results revealed that the formation of excimers was suppressed by introducing carbazole side groups. The spatial extent of the lowest singlet and triplet excitons in P1 and M1 was fully elucidated. Such organometallic poly(fluorenyleneethynylene)s anchored with the carbazole pendants was found to have an improved thermal stability and suppressed aggregation.
2009, 27(4): 465-477
Abstract:
The optimum reaction conditions of the oxidative polycondensation of 2-(thien-2-yl-methylene)aminophenol (2-TMAP) has been accomplished by using air O2, H2O2 and NaOCl oxidants in an aqueous alkaline medium between 20°C and 90°C. The structures of the monomer and oligomer were confirmed by FT-IR, UV-Vis, 1H-NMR and 13C-NMR and elemental analysis. TGA-DTA, size exclusion chromatography (SEC) techniques and solubility tests were applied for characterization. The 1H-NMR and 13C-NMR data show that the polymerization proceeded with C―C and C―O―C coupling system from ortho and para positions and oxyphenylene. The number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of oligo[2-(thien-2-yl-methylene)aminophenol] (O-2-TMAP) were determined with SEC measurements. Thermal analyses of oligomer-metal complex compounds of O-2-TMAP with Cd+2, Co+2, Cu+2, Zn+2, Fe+2, Zr+4, Ni+2 and Pb+2 ions were investigated in N2 atmosphere in the temperature range of 15 1000°C. The highest occupied molecular orbital and the lowest unoccupied molecular orbital of monomer and oligomer were determined from the onset potentials for n-doping and p-doping, respectively. Optical band gaps (Eg) of 2-TMAP and O-2-TMAP and oligomer-metal complex compounds determined according to UV-Vis measurements. Also, electrical conductivities of O-2-TMAP and its metal complexes measured with four-point probe technique.
The optimum reaction conditions of the oxidative polycondensation of 2-(thien-2-yl-methylene)aminophenol (2-TMAP) has been accomplished by using air O2, H2O2 and NaOCl oxidants in an aqueous alkaline medium between 20°C and 90°C. The structures of the monomer and oligomer were confirmed by FT-IR, UV-Vis, 1H-NMR and 13C-NMR and elemental analysis. TGA-DTA, size exclusion chromatography (SEC) techniques and solubility tests were applied for characterization. The 1H-NMR and 13C-NMR data show that the polymerization proceeded with C―C and C―O―C coupling system from ortho and para positions and oxyphenylene. The number-average molecular weight (Mn), weight-average molecular weight (Mw) and polydispersity index (PDI) values of oligo[2-(thien-2-yl-methylene)aminophenol] (O-2-TMAP) were determined with SEC measurements. Thermal analyses of oligomer-metal complex compounds of O-2-TMAP with Cd+2, Co+2, Cu+2, Zn+2, Fe+2, Zr+4, Ni+2 and Pb+2 ions were investigated in N2 atmosphere in the temperature range of 15 1000°C. The highest occupied molecular orbital and the lowest unoccupied molecular orbital of monomer and oligomer were determined from the onset potentials for n-doping and p-doping, respectively. Optical band gaps (Eg) of 2-TMAP and O-2-TMAP and oligomer-metal complex compounds determined according to UV-Vis measurements. Also, electrical conductivities of O-2-TMAP and its metal complexes measured with four-point probe technique.
2009, 27(4): 479-485
Abstract:
The dependence of polarization fatigue on crystallinity of vinylidene fluoride and trifluoroethylene copolymer films was studied. Experimental data indicated that the higher the crystallinity of the film was, the slower the fatigue rate of the film became. A possible explanation was put forward, and it was regarded that the space charges, trapped at the boundaries of crystallites and/or captured by the defects lying both in amorphous and crystalline phases, should make the major contribution to polarization fatigue.
The dependence of polarization fatigue on crystallinity of vinylidene fluoride and trifluoroethylene copolymer films was studied. Experimental data indicated that the higher the crystallinity of the film was, the slower the fatigue rate of the film became. A possible explanation was put forward, and it was regarded that the space charges, trapped at the boundaries of crystallites and/or captured by the defects lying both in amorphous and crystalline phases, should make the major contribution to polarization fatigue.
2009, 27(4): 487-492
Abstract:
Conductive polyaniline (PAn-M and PAn-O) doped with dodecylbenzene sulfonic acid (DBSA) was synthesized by using emulsion polymerization method in the presence of a constant magnetic field (0.4 T) and the absence of magnetic field, respectively. The effects of magnetic field on the microscopic morphology and orientation structure of PAn were generally analyzed and characterized by using transmission electron microscope (TEM), X-ray diffraction (XRD) and through the conductivity anisotropy of unit resistance of the PAn/PVA(polyvinyl alcohol) composite film. The results showed that, compared with PAn-O, PAn-M had higher crystallinity and more obvious microscopic orientation structure: its particles were arranged orderly and piled into many banded aggregates with a certain length/diameter ratio, after magnetization treatment, it demonstrated a high degree of consistent orientation; PAn-M/PVA composite films showed conductivity anisotropy after magnetization in the film-forming process. The results all fully confirmed that PAn prepared in a magnetic field condition had a high degree of orientation.
Conductive polyaniline (PAn-M and PAn-O) doped with dodecylbenzene sulfonic acid (DBSA) was synthesized by using emulsion polymerization method in the presence of a constant magnetic field (0.4 T) and the absence of magnetic field, respectively. The effects of magnetic field on the microscopic morphology and orientation structure of PAn were generally analyzed and characterized by using transmission electron microscope (TEM), X-ray diffraction (XRD) and through the conductivity anisotropy of unit resistance of the PAn/PVA(polyvinyl alcohol) composite film. The results showed that, compared with PAn-O, PAn-M had higher crystallinity and more obvious microscopic orientation structure: its particles were arranged orderly and piled into many banded aggregates with a certain length/diameter ratio, after magnetization treatment, it demonstrated a high degree of consistent orientation; PAn-M/PVA composite films showed conductivity anisotropy after magnetization in the film-forming process. The results all fully confirmed that PAn prepared in a magnetic field condition had a high degree of orientation.
2009, 27(4): 493-500
Abstract:
The phase behavior of bimodal molecular weight high density polyethylene (BHDPE) in solid state was investigated. Hildebrand solubility parameters (δ) were calculated for the models of blends of higher molecular weight branch polyethylene (HBPE) with different branch contents and lower molecular weight linear polyethylene (LLPE), by using molecular dynamics (MD) simulations. These δ values were then used to calculate the corresponding Flory-Huggins interaction parameter (χ) between HBPE and LLPE models. In order to better understand the compatibility between LLPE and various HBPE, Mesodyn simulations were used to show the density profiles of the blends of LLPE with various HBPE at different compositions. The results indicated that the phase behavior of BHDPE was influenced by both the global branch content of the system and the local branch content, i.e., the branch content of HBPE.
The phase behavior of bimodal molecular weight high density polyethylene (BHDPE) in solid state was investigated. Hildebrand solubility parameters (δ) were calculated for the models of blends of higher molecular weight branch polyethylene (HBPE) with different branch contents and lower molecular weight linear polyethylene (LLPE), by using molecular dynamics (MD) simulations. These δ values were then used to calculate the corresponding Flory-Huggins interaction parameter (χ) between HBPE and LLPE models. In order to better understand the compatibility between LLPE and various HBPE, Mesodyn simulations were used to show the density profiles of the blends of LLPE with various HBPE at different compositions. The results indicated that the phase behavior of BHDPE was influenced by both the global branch content of the system and the local branch content, i.e., the branch content of HBPE.
2009, 27(4): 501-510
Abstract:
Biodegradable blend films composed of chitosan and PEG with various composition ratios were prepared. The chemical structure of the blend films was characterized with FTIR and X-ray, which showed no chemical bond formations but certain interactions probably coming from the hydrogen bonds. Morphologies of these blend films were viewed using AFM and SEM, suggesting that pure chitosan film had a smooth surface structure and the blend films surface showed a plenty of holes with varying size. Through the DMA measurement, it was found that there existed differences in the peak area and position of the blend films, and the peak at the glass transition temperature became significantly weaker and was markedly wider with the increasing content of PEG. The obtained results showed that the crystallinity of chitosan was suppressed and partially destroyed; and this should have an influence on the thermal behaviors and dynamic mechanical properties of the blend films.
Biodegradable blend films composed of chitosan and PEG with various composition ratios were prepared. The chemical structure of the blend films was characterized with FTIR and X-ray, which showed no chemical bond formations but certain interactions probably coming from the hydrogen bonds. Morphologies of these blend films were viewed using AFM and SEM, suggesting that pure chitosan film had a smooth surface structure and the blend films surface showed a plenty of holes with varying size. Through the DMA measurement, it was found that there existed differences in the peak area and position of the blend films, and the peak at the glass transition temperature became significantly weaker and was markedly wider with the increasing content of PEG. The obtained results showed that the crystallinity of chitosan was suppressed and partially destroyed; and this should have an influence on the thermal behaviors and dynamic mechanical properties of the blend films.
2009, 27(4): 511-516
Abstract:
The effect of gas flow rate on crystal structures of electrospun and gas-jet/electrospun poly(vinylidene fluoride) (PVDF) fibers was investigated. PVDF fibers were prepared by electrospinning and gas-jet/electrospinning of its N,N-dimethylformamide (DMF) solutions. The morphology of the PVDF fibers was investigated by scanning electron microscopy (SEM). With an increase of the gas flow rate, the average diameters of PVDF fibers were decreased.The crystal structures and thermal properties of the PVDF fibers were investigated by attenuated Fourier transform infrared spectroscopy (AT-FTIR), wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). It was found that electrospinning and gas-jet/electrospinning of PVDF from its DMF solutions promoted the formation ofβ phase. Moreover, gas-jet/electrospun PVDF fibers exhibited higher crystallinity andβphase content than electrospun fibers did. Similar with electrostatic force, the drawing force of gas jet may induce the conformational change to all-trans (TTTT) planar zigzag conformation, and then promote the formation of theβ phase.
The effect of gas flow rate on crystal structures of electrospun and gas-jet/electrospun poly(vinylidene fluoride) (PVDF) fibers was investigated. PVDF fibers were prepared by electrospinning and gas-jet/electrospinning of its N,N-dimethylformamide (DMF) solutions. The morphology of the PVDF fibers was investigated by scanning electron microscopy (SEM). With an increase of the gas flow rate, the average diameters of PVDF fibers were decreased.The crystal structures and thermal properties of the PVDF fibers were investigated by attenuated Fourier transform infrared spectroscopy (AT-FTIR), wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). It was found that electrospinning and gas-jet/electrospinning of PVDF from its DMF solutions promoted the formation ofβ phase. Moreover, gas-jet/electrospun PVDF fibers exhibited higher crystallinity andβphase content than electrospun fibers did. Similar with electrostatic force, the drawing force of gas jet may induce the conformational change to all-trans (TTTT) planar zigzag conformation, and then promote the formation of theβ phase.
2009, 27(4): 517-524
Abstract:
Exploration and characterization of grafting productions by experimental methods are often cumbersome or sometimes impossible. Therefore, quantum chemistry calculations were performed to characterize the graft sites of epoxy resin. According to the Gibbs free energy criterion of the second law of thermodynamic, the reported graft sites were confirmed, and more important, some unreported graft sites were found. In addition, method of increasing the number of graft sites was studied in this article.
Exploration and characterization of grafting productions by experimental methods are often cumbersome or sometimes impossible. Therefore, quantum chemistry calculations were performed to characterize the graft sites of epoxy resin. According to the Gibbs free energy criterion of the second law of thermodynamic, the reported graft sites were confirmed, and more important, some unreported graft sites were found. In addition, method of increasing the number of graft sites was studied in this article.
2009, 27(4): 525-532
Abstract:
A well-defined m-phenylenediimino-bridged ladder polymethylsiloxane (LP) was first synthesized through a well-defined ladder superstructure (LS) acting as synthetic template, which was self-assembled by concerted interaction of hydrogen bonding and aromatic π-π stacking of the monomer (M), N,N,-bis(phenyldichlorosilyl)-m-phenylenediamine. Some key characterization data of LP and, in particular, the extremely vulnerable LS with very unstable Si―Cl and Si―N groups were given. The molecular weights (Mn) of LS and LP are 5010 and 10480, corresponding to about 15 and 46 monomer units, respectively. To monitor the real in situ status of LS in solution the XRD measurements of special freeze-drying samples were performed, demonstrating two characteristic peaks of ladder structure. Most importantly, both LP and LS display exceedingly sharp resonance absorption peaks with a half peak width (△1/2) as small as 0.3 of MeSi(NH)O2/2 moieties in 29Si-NMR spectra. It is well-known that the higher the regularity of the ladder polysiloxane, the narrower the resonance peak of the siloxane moiety on the ladder backbone, and the smaller the half peak width△1/2. Therefore, the very small values of △1/2 for both LS and LP confirm that both LS and LP possess well-defined ladder structures.
A well-defined m-phenylenediimino-bridged ladder polymethylsiloxane (LP) was first synthesized through a well-defined ladder superstructure (LS) acting as synthetic template, which was self-assembled by concerted interaction of hydrogen bonding and aromatic π-π stacking of the monomer (M), N,N,-bis(phenyldichlorosilyl)-m-phenylenediamine. Some key characterization data of LP and, in particular, the extremely vulnerable LS with very unstable Si―Cl and Si―N groups were given. The molecular weights (Mn) of LS and LP are 5010 and 10480, corresponding to about 15 and 46 monomer units, respectively. To monitor the real in situ status of LS in solution the XRD measurements of special freeze-drying samples were performed, demonstrating two characteristic peaks of ladder structure. Most importantly, both LP and LS display exceedingly sharp resonance absorption peaks with a half peak width (△1/2) as small as 0.3 of MeSi(NH)O2/2 moieties in 29Si-NMR spectra. It is well-known that the higher the regularity of the ladder polysiloxane, the narrower the resonance peak of the siloxane moiety on the ladder backbone, and the smaller the half peak width△1/2. Therefore, the very small values of △1/2 for both LS and LP confirm that both LS and LP possess well-defined ladder structures.
2009, 27(4): 533-542
Abstract:
Ethanol perm-selective PDMS/PVDF composite membranes were prepared by curing polydimethylsiloxane (PDMS) with various cross-linking reagents, such as tetraethoxylsilane (TEOS),γ-aminopropyltriethoxylsilane (APTEOS), phenyltrimethoxylsilane (PTMOS) and octyltrimethoxylsilane (OTMOS) as well. The cross-linking density and surface properties of the PDMS active layer were adjusted by varying cross-linking reagents. The pervaporation performance of PDMS membranes cured with different cross-linking reagents was investigated in detail. As temperature increased, the total flux of the four kinds of membranes all increased exponentially, and the separation factor followed a reversed order. The increase of thickness of PDMS layers depressed the total flux of composite membranes and had no obvious effect on selectivity of ethanol. It was found that the composite membrane cured by PTMOS showed much better separation performance compared with other membranes. A resistance-in-series model was used to investigate and estimate the overall mass transfer coefficients and boundary layer mass transfer coefficients of ethanol and water according to experimental results. The measured diffusivities of ethanol and water in PDMS membranes had a magnitude of 10-10 m2．s-1 and 10-11 m2．s-1 at 313.15 K, respectively.
Ethanol perm-selective PDMS/PVDF composite membranes were prepared by curing polydimethylsiloxane (PDMS) with various cross-linking reagents, such as tetraethoxylsilane (TEOS),γ-aminopropyltriethoxylsilane (APTEOS), phenyltrimethoxylsilane (PTMOS) and octyltrimethoxylsilane (OTMOS) as well. The cross-linking density and surface properties of the PDMS active layer were adjusted by varying cross-linking reagents. The pervaporation performance of PDMS membranes cured with different cross-linking reagents was investigated in detail. As temperature increased, the total flux of the four kinds of membranes all increased exponentially, and the separation factor followed a reversed order. The increase of thickness of PDMS layers depressed the total flux of composite membranes and had no obvious effect on selectivity of ethanol. It was found that the composite membrane cured by PTMOS showed much better separation performance compared with other membranes. A resistance-in-series model was used to investigate and estimate the overall mass transfer coefficients and boundary layer mass transfer coefficients of ethanol and water according to experimental results. The measured diffusivities of ethanol and water in PDMS membranes had a magnitude of 10-10 m2．s-1 and 10-11 m2．s-1 at 313.15 K, respectively.
OXIDATIVE POLYMERIZATION BEHAVIOR OF 2,6-DIMETHYLPHENOL IN AQUEOUS MEDIA WITH POTASSIUM FERRICYANIDE
2009, 27(4): 543-549
Abstract:
The effects of potassium ferricyanide, sodium n-dodecyl sulfate, sodium hydroxide and temperature on the molecular weight and the yield of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) synthesized in an aqueous medium were studied. It was found that oxygen in air had little influence on the oxidative polymerization of 2,6-dimethylphenol (DMP) in the aqueous medium, and potassium ferricyanide was only an oxidant during the oxidative polymerization of DMP. Sodium n-dodecyl sulfate could stabilize polymer particles and facilitate the oxidative polymerization of DMP on the surface of polymer particles, which resulted in the increase of the molecular weight of PPO. The yield and molecular weight of PPO increased significantly with NaOH concentration at first and then decreased with NaOH concentration. The high molecular weight PPO with high yield was obtained at 50°C, but both the yield and molecular weight of PPO decreased with the further increase of temperature.
The effects of potassium ferricyanide, sodium n-dodecyl sulfate, sodium hydroxide and temperature on the molecular weight and the yield of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) synthesized in an aqueous medium were studied. It was found that oxygen in air had little influence on the oxidative polymerization of 2,6-dimethylphenol (DMP) in the aqueous medium, and potassium ferricyanide was only an oxidant during the oxidative polymerization of DMP. Sodium n-dodecyl sulfate could stabilize polymer particles and facilitate the oxidative polymerization of DMP on the surface of polymer particles, which resulted in the increase of the molecular weight of PPO. The yield and molecular weight of PPO increased significantly with NaOH concentration at first and then decreased with NaOH concentration. The high molecular weight PPO with high yield was obtained at 50°C, but both the yield and molecular weight of PPO decreased with the further increase of temperature.
2009, 27(4): 551-559
Abstract:
The highly reactive polyisobutylenes (PIBs) with α-double bonds (87.5 mol%) or tert-chloro (tert-Cl) groups (95 mol%) could be prepared via the cationic polymerization of isobutylene (IB) coinitiated by BF3 or TiCl4 respectively. The Friedel-Crafts alkylation of diphenylamine (DPA) with the highly reactive PIB with α-double bonds was further conducted under different conditions, such as at different alkylation temperature, in the mixed solvents of CH2Cl2/n-hexane with different solvent polarity and at DPA concentration ([DPA]). The resultant PIBs with sec-arylamino terminal groups were characterized by GPC with RI/UV dual detectors and 1H-NMR spectrum. The experimental results indicated that alkylation efficiency increased with increases in reaction temperature, solvent polarity and [DPA]. The 77 mol% of sec-arylamino terminated PIBs could be obtained in 10/90 (V/V) mixture of nHex/CH2Cl2 with [DPA]/[PIB] of 3.0 at 60°C for 45 h. Moreover, the alkylation of DPA with highly reactive PIBs with mainly tert-Cl terminal groups was also carried out in 10/90 (V/V) mixture of CH2Cl2/nHex with [DPA]/[PIB] = 3.0 at 60°C for 45 h, and almost monoalkylation with 100 mol% sec-arylamino terminal groups could be achieved. These results will help further explorations of the molecular engineering via combination of cationic polymerization with alkylation.
The highly reactive polyisobutylenes (PIBs) with α-double bonds (87.5 mol%) or tert-chloro (tert-Cl) groups (95 mol%) could be prepared via the cationic polymerization of isobutylene (IB) coinitiated by BF3 or TiCl4 respectively. The Friedel-Crafts alkylation of diphenylamine (DPA) with the highly reactive PIB with α-double bonds was further conducted under different conditions, such as at different alkylation temperature, in the mixed solvents of CH2Cl2/n-hexane with different solvent polarity and at DPA concentration ([DPA]). The resultant PIBs with sec-arylamino terminal groups were characterized by GPC with RI/UV dual detectors and 1H-NMR spectrum. The experimental results indicated that alkylation efficiency increased with increases in reaction temperature, solvent polarity and [DPA]. The 77 mol% of sec-arylamino terminated PIBs could be obtained in 10/90 (V/V) mixture of nHex/CH2Cl2 with [DPA]/[PIB] of 3.0 at 60°C for 45 h. Moreover, the alkylation of DPA with highly reactive PIBs with mainly tert-Cl terminal groups was also carried out in 10/90 (V/V) mixture of CH2Cl2/nHex with [DPA]/[PIB] = 3.0 at 60°C for 45 h, and almost monoalkylation with 100 mol% sec-arylamino terminal groups could be achieved. These results will help further explorations of the molecular engineering via combination of cationic polymerization with alkylation.
2009, 27(4): 561-567
Abstract:
The association of poly(N,N-diethylacrylamide) (PDEA) chains has been investigated by a combination of static and dynamic laser light scattering (LLS). Unlike poly(N-isopropylacrylamide) (PNIPAM), PDEA chains can not form the C＝O…H―N hydrogen bonds. Our results demonstrate that a limited number of PDEA chains collapse and associate into metastable globules in dilute solutions. The heating rate has great effect on the mesoglobule size. The formation of such mesoglobules is attributed to the competition between intrachain contraction and interchain association. The stabilization has been explained in terms of viscoelastic effect.
The association of poly(N,N-diethylacrylamide) (PDEA) chains has been investigated by a combination of static and dynamic laser light scattering (LLS). Unlike poly(N-isopropylacrylamide) (PNIPAM), PDEA chains can not form the C＝O…H―N hydrogen bonds. Our results demonstrate that a limited number of PDEA chains collapse and associate into metastable globules in dilute solutions. The heating rate has great effect on the mesoglobule size. The formation of such mesoglobules is attributed to the competition between intrachain contraction and interchain association. The stabilization has been explained in terms of viscoelastic effect.
2009, 27(4): 569-581
Abstract:
The apparent kinetics and cure behavior of novel interpenetrating polymer networks (IPNs) based on cycloaliphatic epoxy resin (CER) and tri-functional acrylate have been investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The results of DSC measurements show that the curing reaction of the TMPTMA component is much earlier than that of the CER component, which can lead to the formation of the IPNs. In contrast to neat anhydride-CER system, the anhydride-CER/TMPTMA systems exhibit relatively lower curing temperatures. The activation energy for initiating the reaction of the anhydride-CER system slightly increases, whereas the activation energy for propagating the reaction markedly reduces during the full IPNs formation. The FT-IR spectroscopic changes are interpreted in terms of curing mechanism of CER and TMPTMA components. The extent of reaction is calculated from FT-IR absorption bands, which depends on the reactive group concentration. The experimental results of FT-IR measurements are in good agreements with those of DSC measurements. The rheological behavior of anhydride-CER/TMPTMA systems during IPNs formation is studied in this paper. It is confirmed that the introduction of TMPTMA monomer into anhydride-epoxy resin has significant effects on the rheological behavior of the system.
The apparent kinetics and cure behavior of novel interpenetrating polymer networks (IPNs) based on cycloaliphatic epoxy resin (CER) and tri-functional acrylate have been investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The results of DSC measurements show that the curing reaction of the TMPTMA component is much earlier than that of the CER component, which can lead to the formation of the IPNs. In contrast to neat anhydride-CER system, the anhydride-CER/TMPTMA systems exhibit relatively lower curing temperatures. The activation energy for initiating the reaction of the anhydride-CER system slightly increases, whereas the activation energy for propagating the reaction markedly reduces during the full IPNs formation. The FT-IR spectroscopic changes are interpreted in terms of curing mechanism of CER and TMPTMA components. The extent of reaction is calculated from FT-IR absorption bands, which depends on the reactive group concentration. The experimental results of FT-IR measurements are in good agreements with those of DSC measurements. The rheological behavior of anhydride-CER/TMPTMA systems during IPNs formation is studied in this paper. It is confirmed that the introduction of TMPTMA monomer into anhydride-epoxy resin has significant effects on the rheological behavior of the system.
2009, 27(4): 583-592
Abstract:
Self assemblies of ABC triblock copolymer thin films on a densely brush-coated substrate were investigated by using the self-consistent field theory. The middle block B and the coated polymer form one phase and the alternating phase A and phase C occur when the film is very thin either for the neutral or selective hard surface (which is opposite to the brush-coated substrate). The lamellar phase is stable on the hard surface when it is neutral and interestingly, the short block tends to stay on this hard surface. The rippled structure forms when the cylindrical phase exists near the surface between grafted polymers and ABC block copolymers. Due to the existence of the hydrophilic brush-coated surface serving as a soft surface of the film, the energy fluctuation existing in the film confined by two hard surfaces disappears. The results are helpful for designing the nanopattern of the film and realizing the functional thin film, such as adding the functional short block A to the BC diblock copolymer.
Self assemblies of ABC triblock copolymer thin films on a densely brush-coated substrate were investigated by using the self-consistent field theory. The middle block B and the coated polymer form one phase and the alternating phase A and phase C occur when the film is very thin either for the neutral or selective hard surface (which is opposite to the brush-coated substrate). The lamellar phase is stable on the hard surface when it is neutral and interestingly, the short block tends to stay on this hard surface. The rippled structure forms when the cylindrical phase exists near the surface between grafted polymers and ABC block copolymers. Due to the existence of the hydrophilic brush-coated surface serving as a soft surface of the film, the energy fluctuation existing in the film confined by two hard surfaces disappears. The results are helpful for designing the nanopattern of the film and realizing the functional thin film, such as adding the functional short block A to the BC diblock copolymer.
2009, 27(4): 593-596
Abstract:
A novel associating polymer P(AEBA) was synthesized by radical polymerization of the cationic amphiphilic monomer, 4-(2-(acryloyloxy)ethoxy)benzyl tri-ethyl ammonium bromide (AEBA), in aqueous solutions. P(AEBA) displays a strong tendency for self-association in aqueous solutions and is sensitive to the external stimulation such as added salt. The associative properties and morphologies of P(AEBA) were studied by fluorescnece probe technique, viscometry and TEM. In dilute salt-free solutions P(AEBA) behaves as polyelectrolyte, while its behavior is similar to that of the polysoap as salt added. Accompanying increasing polymer concentration, polymer aggregation conformation changes from an extended necklace-like structure to a compact globular aggregate corresponding to the viscosity reduction.
A novel associating polymer P(AEBA) was synthesized by radical polymerization of the cationic amphiphilic monomer, 4-(2-(acryloyloxy)ethoxy)benzyl tri-ethyl ammonium bromide (AEBA), in aqueous solutions. P(AEBA) displays a strong tendency for self-association in aqueous solutions and is sensitive to the external stimulation such as added salt. The associative properties and morphologies of P(AEBA) were studied by fluorescnece probe technique, viscometry and TEM. In dilute salt-free solutions P(AEBA) behaves as polyelectrolyte, while its behavior is similar to that of the polysoap as salt added. Accompanying increasing polymer concentration, polymer aggregation conformation changes from an extended necklace-like structure to a compact globular aggregate corresponding to the viscosity reduction.
2009, 27(4): 597-600
Abstract:
The tetrameric neodymium-silsesquioxane cage complex, {[(i-C4H9)7(Si7O12)Nd]4NaCl}, was prepared and used as precursor for the polymerization of isoprene. When activated by AlEt3 in the presence of TMSCl, this POSS-Nd complex (POSS = polyhedral oligomeric silsesquioxane) shows a moderate activity for the polymerization, and the effects of different ratios of Al/Nd, Cl/Nd and time on the polymerization were investigated. Moreover, The POSS-Nd complex may serve as models for the silica-supported rare earth catalyst, and a simplified surface model was also proposed.
The tetrameric neodymium-silsesquioxane cage complex, {[(i-C4H9)7(Si7O12)Nd]4NaCl}, was prepared and used as precursor for the polymerization of isoprene. When activated by AlEt3 in the presence of TMSCl, this POSS-Nd complex (POSS = polyhedral oligomeric silsesquioxane) shows a moderate activity for the polymerization, and the effects of different ratios of Al/Nd, Cl/Nd and time on the polymerization were investigated. Moreover, The POSS-Nd complex may serve as models for the silica-supported rare earth catalyst, and a simplified surface model was also proposed.
