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2002 Volume 20 Issue 3
2002, 20(3): 191-196
Abstract:
Solid phase transition of the a form crystals to the β form crystals in syndiotactic polystyrene (sPS) samples hasoccurred in supercritical CO2. This transformation is different from those detected under other conditions. The effects ofsome factors (e.g time, temperature, and pressure) on the solid phase transformation of sPS in supercritical CO2 wereanalyzed in detail. Experimental results show that longer time, higher temperature or higher pressure favors the transformation of the α form crystals to the β form crystals.
Solid phase transition of the a form crystals to the β form crystals in syndiotactic polystyrene (sPS) samples hasoccurred in supercritical CO2. This transformation is different from those detected under other conditions. The effects ofsome factors (e.g time, temperature, and pressure) on the solid phase transformation of sPS in supercritical CO2 wereanalyzed in detail. Experimental results show that longer time, higher temperature or higher pressure favors the transformation of the α form crystals to the β form crystals.
2002, 20(3): 197-203
Abstract:
An initial investigation on the roughness and frictional properties of the self-assembled thin films frompolyelectrolytes is presented. Star-shaped C60-poly(styrene-maleic anhydride) was successful prepared. The multilayer thinfilms have been fabricated on mica with diazoresin as the cationic polyelectrolyte and hydrolyzed star-shaped C60-poly(styrene-maleic anhydride) as the anionic polyelectrolyte via self-assembly technique. The crosslinking structure of the films is formed from the conversion of ionic bond to covalent bond after UV irradiation.AFM/FFM investigations provide insights into the roughness and frictional properties on a microscale.The roughness depends strongly on the number of film layers in the case of C60-containing films.The frictional forces of the films exhibited a well behaved non-linear relationship in response to the change of applied load.It supports the prediction of enhanced load-bearing property of C60-containing thin films.
An initial investigation on the roughness and frictional properties of the self-assembled thin films frompolyelectrolytes is presented. Star-shaped C60-poly(styrene-maleic anhydride) was successful prepared. The multilayer thinfilms have been fabricated on mica with diazoresin as the cationic polyelectrolyte and hydrolyzed star-shaped C60-poly(styrene-maleic anhydride) as the anionic polyelectrolyte via self-assembly technique. The crosslinking structure of the films is formed from the conversion of ionic bond to covalent bond after UV irradiation.AFM/FFM investigations provide insights into the roughness and frictional properties on a microscale.The roughness depends strongly on the number of film layers in the case of C60-containing films.The frictional forces of the films exhibited a well behaved non-linear relationship in response to the change of applied load.It supports the prediction of enhanced load-bearing property of C60-containing thin films.
2002, 20(3): 205-211
Abstract:
An unsymmetric 2,6-bis(imino)pyridine iron(II) complex 1' was synthesized. The relationship between catalyststructure and its activity in ethylene polymerization is discussed. The kinetic behavior of ethylene polymerization and theeffects of polymerization conditions such as temperature, aluminum/iron molar ratio on the activity of catalyst and thecharacteristics of polyethylene were reported. The unsymmetric catalyst 1' has a good catalytic performance of 3.47 ×106gPE·mol-1·Fe·h-1 at 40℃ with aluminum/iron molar ratio = 2500.A dependence of catalyst activity on the methylaluminoxane(MAO) concentration and reaction temperature was found.The molecular weight (MW) of polythylene with broad dispersity is about 104-105g/mol.The melting temperature and branching of polyethylenes vary with changing reaction temperature and aluminum/iron molar ratio.
An unsymmetric 2,6-bis(imino)pyridine iron(II) complex 1' was synthesized. The relationship between catalyststructure and its activity in ethylene polymerization is discussed. The kinetic behavior of ethylene polymerization and theeffects of polymerization conditions such as temperature, aluminum/iron molar ratio on the activity of catalyst and thecharacteristics of polyethylene were reported. The unsymmetric catalyst 1' has a good catalytic performance of 3.47 ×106gPE·mol-1·Fe·h-1 at 40℃ with aluminum/iron molar ratio = 2500.A dependence of catalyst activity on the methylaluminoxane(MAO) concentration and reaction temperature was found.The molecular weight (MW) of polythylene with broad dispersity is about 104-105g/mol.The melting temperature and branching of polyethylenes vary with changing reaction temperature and aluminum/iron molar ratio.
2002, 20(3): 213-217
Abstract:
A novel ligand (3), in which the indenyl group is linked to a β-diketone moiety through a three-carbon bridge, andits titanium complex (4) were synthesized. The titanium complex was employed as a metallocene analog with co-catalystmethylaluminoxane (MAO) in catalytic syndiospecific polymerization of styrene to give highly syndiotactic polystyrene(s-PS, 96%-97%). Polymerization temperature (Tp) strongly influenced the catalytic activity and syndiotacticity of theproduced PS. The activities of catalyst 4 increase from 1.84×106 to 3.26 ×106 gPS/molTi ·h with the increase of Tg from 60℃ to 80℃ and the syndiotacticities of the produced s-PS also increase slightly.Then,both the catalytic activity and the syndiotacticity of PS decrease at Tp of 90℃.
A novel ligand (3), in which the indenyl group is linked to a β-diketone moiety through a three-carbon bridge, andits titanium complex (4) were synthesized. The titanium complex was employed as a metallocene analog with co-catalystmethylaluminoxane (MAO) in catalytic syndiospecific polymerization of styrene to give highly syndiotactic polystyrene(s-PS, 96%-97%). Polymerization temperature (Tp) strongly influenced the catalytic activity and syndiotacticity of theproduced PS. The activities of catalyst 4 increase from 1.84×106 to 3.26 ×106 gPS/molTi ·h with the increase of Tg from 60℃ to 80℃ and the syndiotacticities of the produced s-PS also increase slightly.Then,both the catalytic activity and the syndiotacticity of PS decrease at Tp of 90℃.
2002, 20(3): 219-224
Abstract:
A new heat-resistant, soluble polymer, poly(phenyl-1,2,4-triazine imide), has been prepared via a two-step methodof polycondensation of N,N'-bis(4-benzil)pyromellitimide and terephthalamidrazone in cresol, followed by curing at highertemperature. The rigid 1,2,4-triazine group increases the solubility of the polyimide so that the polymer is soluble in cresol,N-methyl-2-pyrrolidone (NMP), trifluoroacetic acid and concentrated sulfuric acid, etc. Thermogravimetric analysis (TGA) indicates that this novel polyimide has good thermal stability with a high decomposition temperature of 447℃ in air and of 423 ℃ in N2.It has a tensile strength of 107.4 MPa with an elongation at break of around 7.6%.
A new heat-resistant, soluble polymer, poly(phenyl-1,2,4-triazine imide), has been prepared via a two-step methodof polycondensation of N,N'-bis(4-benzil)pyromellitimide and terephthalamidrazone in cresol, followed by curing at highertemperature. The rigid 1,2,4-triazine group increases the solubility of the polyimide so that the polymer is soluble in cresol,N-methyl-2-pyrrolidone (NMP), trifluoroacetic acid and concentrated sulfuric acid, etc. Thermogravimetric analysis (TGA) indicates that this novel polyimide has good thermal stability with a high decomposition temperature of 447℃ in air and of 423 ℃ in N2.It has a tensile strength of 107.4 MPa with an elongation at break of around 7.6%.
2002, 20(3): 225-229
Abstract:
A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K2CO3 to produce high molecular weight polymers which can be dissolved in some polar solvents such as chloroform and nitrobenzene at room temperature and can be easily cast into flexible,yellowish and transparent films.PPESK is an amorphous polymer having a decomposition temperature above 400℃,which indicates that it has high thermal staility.At the same time,the thermal properties of PPESKs with dicyandiamide (DICY) as curing agent indicated that the heat-resistance properties of the PPESKs are improved after curing.The apparent activation energy(△E) of the cross-linking reaction and the reaction order(n) of PPESK/DICY were found to be 52.2 kJ/mol and ca.1.0,respectively.Therefore,the cross-linking reaction is approximately a first order reaction.
A kind of novel heat-resistant, high performance engineering thermoplastic phthalazinone poly(aryl ether sulfoneketone) (PPESK) containing a carboxyl group in its side chain was prepared by the nucleophilic displacement reaction of 4-(4-hydroxylphenyl)-1(2H)-phthalazinone with di(4-chlorophenyl) sulfone, 4,4'-difluoro-benzophenone and phenolphthalin insulfolane in the presence of K2CO3 to produce high molecular weight polymers which can be dissolved in some polar solvents such as chloroform and nitrobenzene at room temperature and can be easily cast into flexible,yellowish and transparent films.PPESK is an amorphous polymer having a decomposition temperature above 400℃,which indicates that it has high thermal staility.At the same time,the thermal properties of PPESKs with dicyandiamide (DICY) as curing agent indicated that the heat-resistance properties of the PPESKs are improved after curing.The apparent activation energy(△E) of the cross-linking reaction and the reaction order(n) of PPESK/DICY were found to be 52.2 kJ/mol and ca.1.0,respectively.Therefore,the cross-linking reaction is approximately a first order reaction.
2002, 20(3): 231-235
Abstract:
Nanometer calcium carbonate was modified with Frechet type polyether dendrons bearing a COOH group at thefocal point by a wet-coating technique in dichloromethane at room temperature. The interaction between CaCO3 and thedendritic modifier was proven by IR and mass spectroscopy of the modified CaCO3 after thorough extraction withdichloromethane. The amount of tightly bonded organic modifier was estimated by TGA. It was shown that the amount ofbonded molecules decreased with increasing generation number due to the larger number of branches.Compared to unmodified CaCO3,the modified CaCO3 possess different dispersibility in water and in organic solvents.
Nanometer calcium carbonate was modified with Frechet type polyether dendrons bearing a COOH group at thefocal point by a wet-coating technique in dichloromethane at room temperature. The interaction between CaCO3 and thedendritic modifier was proven by IR and mass spectroscopy of the modified CaCO3 after thorough extraction withdichloromethane. The amount of tightly bonded organic modifier was estimated by TGA. It was shown that the amount ofbonded molecules decreased with increasing generation number due to the larger number of branches.Compared to unmodified CaCO3,the modified CaCO3 possess different dispersibility in water and in organic solvents.
2002, 20(3): 237-241
Abstract:
A resistive humidity sensor was prepared based on sodium polystyrenesulfonate (NaPSS)/TiO2 nanocomposites,and its electrical response to humidity was examined. The sensor exhibits better linearity, smaller hysteresis (2 on humidity response of sensors was discussed.
A resistive humidity sensor was prepared based on sodium polystyrenesulfonate (NaPSS)/TiO2 nanocomposites,and its electrical response to humidity was examined. The sensor exhibits better linearity, smaller hysteresis (2 on humidity response of sensors was discussed.
2002, 20(3): 243-252
Abstract:
The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) compositewere investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples,one with various CB contents in the composites and the other with various γ-irradiation doses in HDPE/CB compositecontaining 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value inHDPE/CB composite is about 16.7 wt% and the suitable γ-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad.The result observed for the second set of samples suggests that γ-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure.Therefore,a suitable irradiation dose,about 20 Mrad,can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure,so that the positive temperature coefficient(PTC) effect remains while the negative temperature coefficient(NTC) effect is suppressed.A new interpretation of the conductive mechanism,which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.
The microstructure and conductive mechanism of high density polyethylene/carbon black (HDPE/CB) compositewere investigated by positron annihilation lifetime spectroscopy (PALS). The PALS were measured in two series of samples,one with various CB contents in the composites and the other with various γ-irradiation doses in HDPE/CB compositecontaining 20 wt% CB. It was found that CB particles distribute in the amorphous regions, the CB critical content value inHDPE/CB composite is about 16.7 wt% and the suitable γ-irradiation dose for improving the conductive behavior of HDPE/CB composite is about 20 Mrad.The result observed for the second set of samples suggests that γ-irradiation causes not only cross-linking in amorphous regions but also destruction of the partial crystalline structure.Therefore,a suitable irradiation dose,about 20 Mrad,can induce sufficient cross-linking in the amorphous regions without enhancing the decomposition of crystalline structure,so that the positive temperature coefficient(PTC) effect remains while the negative temperature coefficient(NTC) effect is suppressed.A new interpretation of the conductive mechanism,which might provide a more detailed explanation of the PTC effect and the NTC effect has been proposed.
2002, 20(3): 253-259
Abstract:
An experimental study was carried out to investigate the effects of isopropoxy tri(dioctyl pyrophosphoryl) titanatecoupling agent on the mechanical performance, rheological property and microstructures of polyethylene highly loaded withaluminum hydroxide (Al(OH)3) composite. It was found that the addition of coupling agent results in reduced tensile strengthand increased percentage elongation of the filled systems. Silane crosslinkable polyethylene substituting for polyethylene as matrix improves the tensile strngth of the composite,while the percentage elongation of the composite still remains at a desired level.Melt viscosity of the composite will be improved by addition of titanate coupling agent.Microstructures of the composites were also studied by means of the scanning electron microscopy(SEM) technique.SEM micrographs reveal that finer dispersion of Al(OH)3 will be obtained upon treatment of titanate and a transition from brittle to tough fracture takes place before and after silane crosslinking structure is introduced into polyethylene highly filled with Al(OH)3 composite.
An experimental study was carried out to investigate the effects of isopropoxy tri(dioctyl pyrophosphoryl) titanatecoupling agent on the mechanical performance, rheological property and microstructures of polyethylene highly loaded withaluminum hydroxide (Al(OH)3) composite. It was found that the addition of coupling agent results in reduced tensile strengthand increased percentage elongation of the filled systems. Silane crosslinkable polyethylene substituting for polyethylene as matrix improves the tensile strngth of the composite,while the percentage elongation of the composite still remains at a desired level.Melt viscosity of the composite will be improved by addition of titanate coupling agent.Microstructures of the composites were also studied by means of the scanning electron microscopy(SEM) technique.SEM micrographs reveal that finer dispersion of Al(OH)3 will be obtained upon treatment of titanate and a transition from brittle to tough fracture takes place before and after silane crosslinking structure is introduced into polyethylene highly filled with Al(OH)3 composite.
2002, 20(3): 261-267
Abstract:
Atom transfer radical polymerization (ATRP) using cuprous chloride/2,2'-bipyridine (bipy) was applied to graftpolymerization of styrene on the surface of silica nanoparticles to synthesize polymer-inorganic hybrid nanoparticles. 2-(4-Chloromethylphenyl) ethyltriethoxysilane (CTES) was immobilized on the surface of silica nanoparticles throughcondensation reaction of the silanol groups on silica with triethoxysilane group of CTES. Then ATRP of St was initiated by this surface-modified silica manoparticles bearing benzyl chloride groups,and formed PSt graft chains on the surface of silica nanoparticles.The thickness of the graft chains increased with reaction time.End group analysis confirmed the occurrence of ATRP.Thermal analysis indicated that thermal stabilization of these resulting hybrid nanoparticles also increases with polymerization conversion.The results above show that this "grafting from" reaction could be used for the preparation of polymer-inorganic hybrid nanoparticles with controlled structure of the polymer's end groups.
Atom transfer radical polymerization (ATRP) using cuprous chloride/2,2'-bipyridine (bipy) was applied to graftpolymerization of styrene on the surface of silica nanoparticles to synthesize polymer-inorganic hybrid nanoparticles. 2-(4-Chloromethylphenyl) ethyltriethoxysilane (CTES) was immobilized on the surface of silica nanoparticles throughcondensation reaction of the silanol groups on silica with triethoxysilane group of CTES. Then ATRP of St was initiated by this surface-modified silica manoparticles bearing benzyl chloride groups,and formed PSt graft chains on the surface of silica nanoparticles.The thickness of the graft chains increased with reaction time.End group analysis confirmed the occurrence of ATRP.Thermal analysis indicated that thermal stabilization of these resulting hybrid nanoparticles also increases with polymerization conversion.The results above show that this "grafting from" reaction could be used for the preparation of polymer-inorganic hybrid nanoparticles with controlled structure of the polymer's end groups.
2002, 20(3): 269-274
Abstract:
We used a thermally reversible hybrid gel made of billions of physically jam-packed swollen thermally sensitivepoly(N-isopropyl-acrylamide) chemical microgels. Laser light scattering study on a series of such hybrid gels formed atdifferent gelling rates and temperatures revealed that the position-dependence of the scattering speckle pattern(staticnonergodicity) came from large voids formed during the sol-gel transition. With a proper preparation, such a nonergodicity could be completely removed indicating that the static nonergodicity generally observed in a gel is not intrinsic,but comes from the clustering"island" structure formed during the gelation process.
We used a thermally reversible hybrid gel made of billions of physically jam-packed swollen thermally sensitivepoly(N-isopropyl-acrylamide) chemical microgels. Laser light scattering study on a series of such hybrid gels formed atdifferent gelling rates and temperatures revealed that the position-dependence of the scattering speckle pattern(staticnonergodicity) came from large voids formed during the sol-gel transition. With a proper preparation, such a nonergodicity could be completely removed indicating that the static nonergodicity generally observed in a gel is not intrinsic,but comes from the clustering"island" structure formed during the gelation process.
