Login In
2003 Volume 21 Issue 5
2003, 21(5): 499-503
Abstract:
On the basis of hydrogen bonding directed layer-by-layer (LbL) assembly we have fabricated two multilayersystems, poly(acrylic acid) bearng spironaphthoxazine (PAA-SO)/poly(4-vinylpyridine) and carboxyl-terminated polyetherdendrimer (dendrimer-COOH)/poly(4-vinylpyridine). UV-Vis spectroscopy indicates that either PAA-SO or dendrimer-COOH can be released from the corresponding multilayer assemblies upon immerssion in a basic aqueous solution.Furthermore, the rate of molecule release can be controlled either by changing the pH value or by adjusting the layer structure.
On the basis of hydrogen bonding directed layer-by-layer (LbL) assembly we have fabricated two multilayersystems, poly(acrylic acid) bearng spironaphthoxazine (PAA-SO)/poly(4-vinylpyridine) and carboxyl-terminated polyetherdendrimer (dendrimer-COOH)/poly(4-vinylpyridine). UV-Vis spectroscopy indicates that either PAA-SO or dendrimer-COOH can be released from the corresponding multilayer assemblies upon immerssion in a basic aqueous solution.Furthermore, the rate of molecule release can be controlled either by changing the pH value or by adjusting the layer structure.
2003, 21(5): 505-514
Abstract:
As a long-term project aimed at developing super polyolefin blends, in this paper we summarize our work on themechanical reinforcement and phase morphology of polyolefin blends achieved by dynamic packing injection molding(DPIM). The main feature of this technology is that the specimen is forced to move repeatedly in the model by two pistonsthat move reversibly with the same frequency during cooling, which results in preferential orientation of the dispersed phaseas well as the matrix. The typical morphology of samples obtained via DPIM is a shear-induced morphology with a core in the center,an oriented zone surrounding the core and a skin layer in the cross-section areas.Shear-induced phase dissolution at a higher shear rate but phase separation at low shhear rates is evident from AFM examination of LLDPE/PP (50/50) blends.The super polyolefin blends having high modulus (1.9-2.2 GPa),high tensile strength(100-120 MPa) and high impact strength(6 times as that of pure HDPE) have been prepared by controlling the phase separation,molecular orientation and crystal morphology.
As a long-term project aimed at developing super polyolefin blends, in this paper we summarize our work on themechanical reinforcement and phase morphology of polyolefin blends achieved by dynamic packing injection molding(DPIM). The main feature of this technology is that the specimen is forced to move repeatedly in the model by two pistonsthat move reversibly with the same frequency during cooling, which results in preferential orientation of the dispersed phaseas well as the matrix. The typical morphology of samples obtained via DPIM is a shear-induced morphology with a core in the center,an oriented zone surrounding the core and a skin layer in the cross-section areas.Shear-induced phase dissolution at a higher shear rate but phase separation at low shhear rates is evident from AFM examination of LLDPE/PP (50/50) blends.The super polyolefin blends having high modulus (1.9-2.2 GPa),high tensile strength(100-120 MPa) and high impact strength(6 times as that of pure HDPE) have been prepared by controlling the phase separation,molecular orientation and crystal morphology.
2003, 21(5): 515-520
Abstract:
The influence of the condensed structure of poly(styrene-co-acrylonitrile) (SAN) and traces of tetrahydrofuran(THF) that remained in titanyl phthalocyanine (TiOPc)/SAN films after fabrication on the photoconductive stability ofTiOPc/SAN composites is studied. The results reveal that the existence of traces of THF results in the increase of thephotoconductivity and the charging voltage. The main facors responsible for the unstable photoconductivity of thephotoconductors are believed to be the relaxation of SAN and the slow volatilization of THF.
The influence of the condensed structure of poly(styrene-co-acrylonitrile) (SAN) and traces of tetrahydrofuran(THF) that remained in titanyl phthalocyanine (TiOPc)/SAN films after fabrication on the photoconductive stability ofTiOPc/SAN composites is studied. The results reveal that the existence of traces of THF results in the increase of thephotoconductivity and the charging voltage. The main facors responsible for the unstable photoconductivity of thephotoconductors are believed to be the relaxation of SAN and the slow volatilization of THF.
2003, 21(5): 521-526
Abstract:
A new copolymer was synthesized by free radical polymerization in solution from methyl 3α-methylacryloyl-7α, 12α-dihydroxy-5β-cholan-24-oate (MACAME) and maleic anhydride (MAN). The copolymer was characterized by FT-IR and functional group analysis. The reactivity ratios of the two monomers were estimated [r1 = 11.6 (MACAME), r2 = 0.01(MAN)] by conducting a series of copolymerizations with a variety of monomer feed compositions and analyzing thecopolymer composition. Thermogravimetric and differential scanning calorimetric analyses of the samples indicate that the copolymer possesses good thermal stability.The temperature at which the copolymer samples experienced a 10% weight loss (TWL) is over 287℃,and the Tg ranged from 174 to 185℃ for the copolymers.
A new copolymer was synthesized by free radical polymerization in solution from methyl 3α-methylacryloyl-7α, 12α-dihydroxy-5β-cholan-24-oate (MACAME) and maleic anhydride (MAN). The copolymer was characterized by FT-IR and functional group analysis. The reactivity ratios of the two monomers were estimated [r1 = 11.6 (MACAME), r2 = 0.01(MAN)] by conducting a series of copolymerizations with a variety of monomer feed compositions and analyzing thecopolymer composition. Thermogravimetric and differential scanning calorimetric analyses of the samples indicate that the copolymer possesses good thermal stability.The temperature at which the copolymer samples experienced a 10% weight loss (TWL) is over 287℃,and the Tg ranged from 174 to 185℃ for the copolymers.
2003, 21(5): 527-531
Abstract:
Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by "rebuilding" cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination.In the meantime,we recapture the findings from the search for suitable OLED packaging materials,in particular polymer composites,which provide both heat dissipation and moisture resistance,in addition to electrical insulation.
Organic Light Emitting Devices (OLED) have attracted much attention recently, for their applications in futureFlat Panel Displays and lighting products. However, their fast degradation remained a major obstacle to theircommercialization. Here we present a brief summary of our studies on both extrinsic and intrinsic causes for the fastdegradation of OLEDs. In particular, we focus on the origin of the dark spots by "rebuilding" cathodes, which confirms thatthe growth of dark spots occurs primarily due to cathode delamination.In the meantime,we recapture the findings from the search for suitable OLED packaging materials,in particular polymer composites,which provide both heat dissipation and moisture resistance,in addition to electrical insulation.
2003, 21(5): 533-539
Abstract:
The aqueous polymerization of acrylamide and crosslinking with N,N-methylenebisacrylamide afforded hydrogelsdisplaying high levels of light scattering (poor optical clarity). Enhancement of the optical clarity within a polyacrylamide(PAm) hydrogel was accomplished through the implementation of "refractive index matching". Water-soluble additives wereutilised to better match the refractive index inhomogeneities throughout a given hydrogel. This resulted in lower light scattering within the system and hence improved clarity.Amino acids,sugars,polymers,and other water-soluble additives such as glycerol were investigated by this methodology.Most addditives investigated displayed potential for effectively reducing the light scattering within a PAm hydrogel as a function of increased additive concentration.On increasing the refractive index of the water medium,the overall refractive index of a PAm hydrogel was also observed to increase.This provided a quantitative means of determining the effectiveness of a given additive for improving the optical clarity within a hydrogel.
The aqueous polymerization of acrylamide and crosslinking with N,N-methylenebisacrylamide afforded hydrogelsdisplaying high levels of light scattering (poor optical clarity). Enhancement of the optical clarity within a polyacrylamide(PAm) hydrogel was accomplished through the implementation of "refractive index matching". Water-soluble additives wereutilised to better match the refractive index inhomogeneities throughout a given hydrogel. This resulted in lower light scattering within the system and hence improved clarity.Amino acids,sugars,polymers,and other water-soluble additives such as glycerol were investigated by this methodology.Most addditives investigated displayed potential for effectively reducing the light scattering within a PAm hydrogel as a function of increased additive concentration.On increasing the refractive index of the water medium,the overall refractive index of a PAm hydrogel was also observed to increase.This provided a quantitative means of determining the effectiveness of a given additive for improving the optical clarity within a hydrogel.
2003, 21(5): 541-550
Abstract:
The N--N linkage in hydrazine is thermally stable when it is tetrasubstituted and there are electron-withdrawinggroups attached to the nitrogen atoms. Our research on the synthesis of polymers contaning N--N linkages is reviewed. The N,N-bisimide structure has been introduced in the backbone of polymers as well as a pendant group in poly(aryl ether)s togive very thermoxidatively stable polymers with very high glass transition temperatures. Most of the polymers form tough,flexible films. N-Aminotriazoles also form stable imides by reaction with anhydrides and these N-imidotriazole groups have been introduced as pendent groups on poly(aryl ether)s.The polymers are highly fluorescent materials.Three methods for the synthesis of polymers containing the tetrasubstituted-azine structure will be discussed:(1) oxidative coupling of bisimines;(2) condensation of bishydrazones with diketones;(3)poly(aryl ether azines)from the azine formed from 4-fluororbenzo-phenone by reaction with salts of bisphenols.
The N--N linkage in hydrazine is thermally stable when it is tetrasubstituted and there are electron-withdrawinggroups attached to the nitrogen atoms. Our research on the synthesis of polymers contaning N--N linkages is reviewed. The N,N-bisimide structure has been introduced in the backbone of polymers as well as a pendant group in poly(aryl ether)s togive very thermoxidatively stable polymers with very high glass transition temperatures. Most of the polymers form tough,flexible films. N-Aminotriazoles also form stable imides by reaction with anhydrides and these N-imidotriazole groups have been introduced as pendent groups on poly(aryl ether)s.The polymers are highly fluorescent materials.Three methods for the synthesis of polymers containing the tetrasubstituted-azine structure will be discussed:(1) oxidative coupling of bisimines;(2) condensation of bishydrazones with diketones;(3)poly(aryl ether azines)from the azine formed from 4-fluororbenzo-phenone by reaction with salts of bisphenols.
2003, 21(5): 551-556
Abstract:
Hybrids of intercalative nitrile-butadiene rubber/organomodified bentonite (NBR/OMB) were prepared by thelatex intercalation technique. Investigation of their mechanical properties and the microstructore of NBR/OMB showed thatthe organomodified bentonite is an effective toughener for NBR. Transmission electronic microscopy (TEM) and X-rnydiffraction (XRD) tests showed that the NBR macromolecule could be intercalated into the galleries of bentonite.Incorporation of NBR/OMB hybrids as tougheners into poly(vinyl chloride)(PVC) results in a substantial increase in the impact strength of PVC,but little decrease in its tensile strength and flexural strength,compared to the unmodified PVC.
Hybrids of intercalative nitrile-butadiene rubber/organomodified bentonite (NBR/OMB) were prepared by thelatex intercalation technique. Investigation of their mechanical properties and the microstructore of NBR/OMB showed thatthe organomodified bentonite is an effective toughener for NBR. Transmission electronic microscopy (TEM) and X-rnydiffraction (XRD) tests showed that the NBR macromolecule could be intercalated into the galleries of bentonite.Incorporation of NBR/OMB hybrids as tougheners into poly(vinyl chloride)(PVC) results in a substantial increase in the impact strength of PVC,but little decrease in its tensile strength and flexural strength,compared to the unmodified PVC.
2003, 21(5): 557-562
Abstract:
Polyethylene (PE) grafting 4-vinylpyridine copolymers has been produced as powders of different rushes by theirradiation method. After treatment with methylaluminoxane (MAO), the copolymers were used as supports for Cp2ZrCl2catalyst Results of X-ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, ultraviolet spectroscopy andscanning electron microscope measurements show that the catalytic sites have been linked through MAO on the PE-graft-4-vinylpyridine (PEVP). The percentages of grafting 4-vinylpyridine and supported Cp2ZrCl2 depend on the size of polyethylene powder.The smaller the polyethylene powder,the more percent of 4-vinylpyridine groups and Cp2ZrCl2 exist on the polyethylene chains,and the PEVP-supported catalyst has a relatively high activity for ethylene polymerization.
Polyethylene (PE) grafting 4-vinylpyridine copolymers has been produced as powders of different rushes by theirradiation method. After treatment with methylaluminoxane (MAO), the copolymers were used as supports for Cp2ZrCl2catalyst Results of X-ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, ultraviolet spectroscopy andscanning electron microscope measurements show that the catalytic sites have been linked through MAO on the PE-graft-4-vinylpyridine (PEVP). The percentages of grafting 4-vinylpyridine and supported Cp2ZrCl2 depend on the size of polyethylene powder.The smaller the polyethylene powder,the more percent of 4-vinylpyridine groups and Cp2ZrCl2 exist on the polyethylene chains,and the PEVP-supported catalyst has a relatively high activity for ethylene polymerization.
2003, 21(5): 563-567
Abstract:
In this paper, the damage to methyl silicone rubber induced by irradiation with protons of 150 keV energy wasstudied. The surface morphology, tensile strength, Shore hardness, cross-linking density and glass transition temperaturewere examined. Positron annihilation lifetime spectrum analysis (PALS) was perfomed to reveal the damage mechanisms ofthe rubber. The results showed that tensile strength and Shore hardness of the rubber increased first and then decreased withincreasing irradiation fluence. The PALS characteristics τ3 and i3,as well as the free volume Vf,decreased with increasing irradiation fluence up to 1015cm-2,and then increased slowly.It indicates that proton irradiation causes a decrease of free volume in the methyl silicone rubber when the fluence is less than 1015cm-2,while the free volume increases when the fluence is greater than 1015cm-2.The results on cross-linking density indicate that the cross-linking induced by proton irradiation is dominant at smaller proton fluences,increasing the tensile strength and Shore hardness of the rubber,while the degradation of rubber dominates at greater fluence,leading to a decrease of tensile strength and Shore hardness.
In this paper, the damage to methyl silicone rubber induced by irradiation with protons of 150 keV energy wasstudied. The surface morphology, tensile strength, Shore hardness, cross-linking density and glass transition temperaturewere examined. Positron annihilation lifetime spectrum analysis (PALS) was perfomed to reveal the damage mechanisms ofthe rubber. The results showed that tensile strength and Shore hardness of the rubber increased first and then decreased withincreasing irradiation fluence. The PALS characteristics τ3 and i3,as well as the free volume Vf,decreased with increasing irradiation fluence up to 1015cm-2,and then increased slowly.It indicates that proton irradiation causes a decrease of free volume in the methyl silicone rubber when the fluence is less than 1015cm-2,while the free volume increases when the fluence is greater than 1015cm-2.The results on cross-linking density indicate that the cross-linking induced by proton irradiation is dominant at smaller proton fluences,increasing the tensile strength and Shore hardness of the rubber,while the degradation of rubber dominates at greater fluence,leading to a decrease of tensile strength and Shore hardness.
2003, 21(5): 569-573
Abstract:
The self-assembly of five narrowly distributed novel rod-coil diblock copolymers, poly(styrene-block-(2, 5-bis[4-methoxy-phenyl]oxycarbonyl) styrene) (PS-b-PMPCS), in p-xylene, a selective solvent at room temperature, was studied. Therod-coil copolymers, which have the same PS length but different PMPCS length, were synthesized by 2,2,6,6-tetramethyl-I-piperidinyloxy (TEMPO) mediated living free radical polymerization. The influence of the rod length on the self-assembly morphology was studied by transmission electron microscopy (TEM). At a concentration of 2.0 mg/mL,those copolymers with relatively shorter PMPCS length (copolymers 1 and 2) form individual spherical micelles;those with relatively longer PMPCS length(copolymer 3 and 4) form "pearl chains"coexisting with individual spherical micelles;the ones with longest PMPCS length form "pearl chains"coexisting with occasionally formed nanofibees.The diameter of all the morphologies was controlled by the rod length.This gives us a way to govern the self-assembly morphology by altering the length of one block in the block copolymer.
The self-assembly of five narrowly distributed novel rod-coil diblock copolymers, poly(styrene-block-(2, 5-bis[4-methoxy-phenyl]oxycarbonyl) styrene) (PS-b-PMPCS), in p-xylene, a selective solvent at room temperature, was studied. Therod-coil copolymers, which have the same PS length but different PMPCS length, were synthesized by 2,2,6,6-tetramethyl-I-piperidinyloxy (TEMPO) mediated living free radical polymerization. The influence of the rod length on the self-assembly morphology was studied by transmission electron microscopy (TEM). At a concentration of 2.0 mg/mL,those copolymers with relatively shorter PMPCS length (copolymers 1 and 2) form individual spherical micelles;those with relatively longer PMPCS length(copolymer 3 and 4) form "pearl chains"coexisting with individual spherical micelles;the ones with longest PMPCS length form "pearl chains"coexisting with occasionally formed nanofibees.The diameter of all the morphologies was controlled by the rod length.This gives us a way to govern the self-assembly morphology by altering the length of one block in the block copolymer.
