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2000 Volume 18 Issue 6
2000, 18(6): 485-491
Abstract:
Theoretical and experimental research has been performed on the interaction curves and stress paths of crystallinepolymeric materials PE and POM under tensile-torsional stress with a linearly intensifying model and in terms of the yield points undergoing Von Mises criterion.
Theoretical and experimental research has been performed on the interaction curves and stress paths of crystallinepolymeric materials PE and POM under tensile-torsional stress with a linearly intensifying model and in terms of the yield points undergoing Von Mises criterion.
2000, 18(6): 493-500
Abstract:
o-Chloro-hexaarylbiimidazole (o-Cl-HABI) can be sensitized efficiently by the dyes 1-ethyl-3'-methyl thiacyaninebromide (C 1), 3,3'-diethyl thiacarbocyanine iodide (C 2), and cyclopentanone 2,5-bis[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene] (C 3) through electron transfer proceses. When exposed to a xenon lamp (filtered by Pyrex glass),the photosensitive systems composed of o-Cl-HABI and the above dyes can produce free radicals which initiate thepolymerization of MMA. The photopolymerization kinetics equation was obtained for the ο-C1-HABI/C2 system,Rp=K[C2]0.75[ο-C1-HABI]0.44[MTA]0.12[MMA]1.0.A comparison of the influence of different dyes on the conversion of MMA photopolymerization was conducted.
o-Chloro-hexaarylbiimidazole (o-Cl-HABI) can be sensitized efficiently by the dyes 1-ethyl-3'-methyl thiacyaninebromide (C 1), 3,3'-diethyl thiacarbocyanine iodide (C 2), and cyclopentanone 2,5-bis[2-(1,3-dihydro-1,3,3-trimethyl-2H-indol-2-ylidene)ethylidene] (C 3) through electron transfer proceses. When exposed to a xenon lamp (filtered by Pyrex glass),the photosensitive systems composed of o-Cl-HABI and the above dyes can produce free radicals which initiate thepolymerization of MMA. The photopolymerization kinetics equation was obtained for the ο-C1-HABI/C2 system,Rp=K[C2]0.75[ο-C1-HABI]0.44[MTA]0.12[MMA]1.0.A comparison of the influence of different dyes on the conversion of MMA photopolymerization was conducted.
2000, 18(6): 501-507
Abstract:
Critical concentrations of α-(1→3)-D-glucan L-FV-Ⅱ from Lentinus edodes were studied by viscometry andfluorescence probe techniques. The dependence of the reduced viscosity on concentration of the glucan in 0.5 mol/L NaOHaqueous solutions with or without urea showed two turning points corresponding to the dynamic contact concentration cs andthe overlap concentration c* of the polymer. The values of cs and c* were found to be 1×10-3 g cm-3 and 1.1×10-2 g cm-3,respectively,for L-FV-II in 0.5 mol/L NaOH aqueous solutions.The two critical concentrations of L-FV-II in 0.5 mol/L NaOH aqueous solutions were also found to be 1.2×10-3g cm-3 for cs and 9.2×10-3g cm-3 for c8 from the concentration dependence of phenanthrene fluorescence intensities.The overlap concentration c* of L-FV-II in 0.5 mol/L NaOH aqueous solutions was lower than that of polystyrene with same molecular weight in benzene,owing to the fact that polysaccharide rends to undergo aggregation caused by intermolecular hydrogen bonding.A normal viscosity behavior of L-FV-II in 0.5mol/L urea/0.5 mol/L NaOH aqueous solutions can still be observed in an extremelt low concentration range at 25℃.
Critical concentrations of α-(1→3)-D-glucan L-FV-Ⅱ from Lentinus edodes were studied by viscometry andfluorescence probe techniques. The dependence of the reduced viscosity on concentration of the glucan in 0.5 mol/L NaOHaqueous solutions with or without urea showed two turning points corresponding to the dynamic contact concentration cs andthe overlap concentration c* of the polymer. The values of cs and c* were found to be 1×10-3 g cm-3 and 1.1×10-2 g cm-3,respectively,for L-FV-II in 0.5 mol/L NaOH aqueous solutions.The two critical concentrations of L-FV-II in 0.5 mol/L NaOH aqueous solutions were also found to be 1.2×10-3g cm-3 for cs and 9.2×10-3g cm-3 for c8 from the concentration dependence of phenanthrene fluorescence intensities.The overlap concentration c* of L-FV-II in 0.5 mol/L NaOH aqueous solutions was lower than that of polystyrene with same molecular weight in benzene,owing to the fact that polysaccharide rends to undergo aggregation caused by intermolecular hydrogen bonding.A normal viscosity behavior of L-FV-II in 0.5mol/L urea/0.5 mol/L NaOH aqueous solutions can still be observed in an extremelt low concentration range at 25℃.
2000, 18(6): 509-513
Abstract:
The polymerization of ethylene by two iron-based catalysts, {[2,6-ArN=C(Me)2C5H3N]FeCl2} (Ar=2,6-C6H3-Me21; 2,6-C6Hv3 (i-Pr)v2 Ⅱ) has been investigated. Catalyst Ⅱ produces higher molecular weight polyethylene (PE) and broadenedpolydispersities relative to catalyst Ⅰ under analogous conditions and all polymers are linear. The kinetic profiles with ironcatalysts showed a smooth pattern during both rate build-up and rate lowering, which are different from the metallocene catalysts. The polymerization activity increases with Al/Fe value and an optimum temperature range at 40～50℃ was observed.The molecular weight of PE decreases with the increase of Al/Fe ratio and rise of polymerization temperature.
The polymerization of ethylene by two iron-based catalysts, {[2,6-ArN=C(Me)2C5H3N]FeCl2} (Ar=2,6-C6H3-Me21; 2,6-C6Hv3 (i-Pr)v2 Ⅱ) has been investigated. Catalyst Ⅱ produces higher molecular weight polyethylene (PE) and broadenedpolydispersities relative to catalyst Ⅰ under analogous conditions and all polymers are linear. The kinetic profiles with ironcatalysts showed a smooth pattern during both rate build-up and rate lowering, which are different from the metallocene catalysts. The polymerization activity increases with Al/Fe value and an optimum temperature range at 40～50℃ was observed.The molecular weight of PE decreases with the increase of Al/Fe ratio and rise of polymerization temperature.
2000, 18(6): 515-520
Abstract:
Polystyrene macromonomers with different molecular weight were prepared by radical polymerization of styrene(St) in benzene using β-methacryloxylethyl 2-N,N-diethyldithiocarbamylacetate (MAEDCA) as a monomer-iniferter.Characterization of the macromonomer by 1H-NMR showed that the end groups were α-methacrylyoxylethyloxycarbonyl-methyl and ω-(N,N-diethyldithiocarbamyl). The macromonomer was difficult to homopolymerize, but it was easilycopolymerized with methyl methacrylate (MMA) initiated by AIBN to form graft copolymers(PMMA-g-PSt) with PSt branches randomly distributed along the PMMA backbone.Copolymerization reaction and the structure of the graft copolymers were strongly affected by Mn and concentration of the macromonomer.The composition and Mn of the purified graft copolymer were determined by 1H-NMR and GPC analysis.
Polystyrene macromonomers with different molecular weight were prepared by radical polymerization of styrene(St) in benzene using β-methacryloxylethyl 2-N,N-diethyldithiocarbamylacetate (MAEDCA) as a monomer-iniferter.Characterization of the macromonomer by 1H-NMR showed that the end groups were α-methacrylyoxylethyloxycarbonyl-methyl and ω-(N,N-diethyldithiocarbamyl). The macromonomer was difficult to homopolymerize, but it was easilycopolymerized with methyl methacrylate (MMA) initiated by AIBN to form graft copolymers(PMMA-g-PSt) with PSt branches randomly distributed along the PMMA backbone.Copolymerization reaction and the structure of the graft copolymers were strongly affected by Mn and concentration of the macromonomer.The composition and Mn of the purified graft copolymer were determined by 1H-NMR and GPC analysis.
2000, 18(6): 521-525
Abstract:
When polyethylene chains are stretched, the chains are regarded as being confined in an infinite cylinder withdecreasing diameter. The conformational properties of polyethylene chains confined in an infinite cylinder are investigatedby using rotational isomeric state model. Using the average conformational energy and entropy and the average length, wecan determine the elastic force f or the fraction of the energy term to the total forcefe/f,where fe=?/?and f=?/?.Comparisons with experimental data are also made.The results of these microscopic calculations are discussed in therms of the macroscopic phenomena of rubber elasticity.
When polyethylene chains are stretched, the chains are regarded as being confined in an infinite cylinder withdecreasing diameter. The conformational properties of polyethylene chains confined in an infinite cylinder are investigatedby using rotational isomeric state model. Using the average conformational energy and entropy and the average length, wecan determine the elastic force f or the fraction of the energy term to the total forcefe/f,where fe=?/?and f=?/?.Comparisons with experimental data are also made.The results of these microscopic calculations are discussed in therms of the macroscopic phenomena of rubber elasticity.
2000, 18(6): 527-533
Abstract:
Heat-resistant silicone gels were synthesized by replacing the single main chain polymethylhydrosiloxane withreactive ladderlike polyhydrosilsesquioxane copolymers. Because of the interaction between polydimethylsiloxane chainsand the ladderlike polysilsesquioxanes chains, the cyclization of the polydimethylsiloxane chains is hindered. The highthermal stability of the ladderlike polymers can improve the thermal stability of the silicone gels without sacrificing their good comprehensive properties.
Heat-resistant silicone gels were synthesized by replacing the single main chain polymethylhydrosiloxane withreactive ladderlike polyhydrosilsesquioxane copolymers. Because of the interaction between polydimethylsiloxane chainsand the ladderlike polysilsesquioxanes chains, the cyclization of the polydimethylsiloxane chains is hindered. The highthermal stability of the ladderlike polymers can improve the thermal stability of the silicone gels without sacrificing their good comprehensive properties.
2000, 18(6): 535-539
Abstract:
Polyvinyl alcohol coated magnetic particles (PVA ferrofluids) have been synthesized by chemical co-precipitationof Fe(Ⅱ)/Fe(Ⅲ) salts in 1.5 mol/L NH4OH solution at 70℃ in the presence of PVA. The resultant colloidal particles havecore-shell structures, in which the iron oxide crystallites form the cores and PVA chains form the shells. The hydrodynamicdiameter of the colloidal particles is in the range of 108 to 155 nm, which increases with increasing PVA concentration from5 wt% to 20 wt%. The size of the magnetic cores is ca.5～10 nm,which is relatively independent of PVA concentration.Under transmission electron microscopic (TEM) examination,the magnetic cores exhibit somewhat irregular shapes varying from spherical,oval,to cubic.Magnetometry measurement revealed that the PVA coated magnetic particles are superparamagnetic.The saturation magnetization of 5 wt% and 20wt% PVA ferrofluids at 300 K is 54 and 49 emu/g,respectively.All the PVA ferrofluids exhibited excellent colloidal stability in pure water and phosphate buffer saline (PBS,pH=7.4).The ferrofluids can remain stable in above solutions for more than three months at 4℃.
Polyvinyl alcohol coated magnetic particles (PVA ferrofluids) have been synthesized by chemical co-precipitationof Fe(Ⅱ)/Fe(Ⅲ) salts in 1.5 mol/L NH4OH solution at 70℃ in the presence of PVA. The resultant colloidal particles havecore-shell structures, in which the iron oxide crystallites form the cores and PVA chains form the shells. The hydrodynamicdiameter of the colloidal particles is in the range of 108 to 155 nm, which increases with increasing PVA concentration from5 wt% to 20 wt%. The size of the magnetic cores is ca.5～10 nm,which is relatively independent of PVA concentration.Under transmission electron microscopic (TEM) examination,the magnetic cores exhibit somewhat irregular shapes varying from spherical,oval,to cubic.Magnetometry measurement revealed that the PVA coated magnetic particles are superparamagnetic.The saturation magnetization of 5 wt% and 20wt% PVA ferrofluids at 300 K is 54 and 49 emu/g,respectively.All the PVA ferrofluids exhibited excellent colloidal stability in pure water and phosphate buffer saline (PBS,pH=7.4).The ferrofluids can remain stable in above solutions for more than three months at 4℃.
2000, 18(6): 541-549
Abstract:
Fully soluble poly[2-methoxy-5-(2'-ethylhexyl)-oxy)-p-phenylenevinylene] (MEH-PPV) was synthesized by theaddition of molecular weight modifiers (chain stopper, free radical scavengers) to a polymerization system containingmonomer, catalyst and a solvent. These PPV products synthesized in this work were characterized by IR, NMR, UV-visiblespectroscopy and GPC. Results show that the Mw of polyphenylvinylene (PPV) can be controlled by the addition of chainstopper (benzyl bromide) and radical inhibitor (2,6-di-tert-butyl-4-methyl phenol).The polymerization mechanism in the presence of these additives was also discussed.A dual mechanism involving carbene for PPV polymerization was proposed.
Fully soluble poly[2-methoxy-5-(2'-ethylhexyl)-oxy)-p-phenylenevinylene] (MEH-PPV) was synthesized by theaddition of molecular weight modifiers (chain stopper, free radical scavengers) to a polymerization system containingmonomer, catalyst and a solvent. These PPV products synthesized in this work were characterized by IR, NMR, UV-visiblespectroscopy and GPC. Results show that the Mw of polyphenylvinylene (PPV) can be controlled by the addition of chainstopper (benzyl bromide) and radical inhibitor (2,6-di-tert-butyl-4-methyl phenol).The polymerization mechanism in the presence of these additives was also discussed.A dual mechanism involving carbene for PPV polymerization was proposed.
2000, 18(6): 551-555
Abstract:
A new kind of polysiloxane containing N,N'-bis(diphenylsilyl)tetraphenylcyclodisilazane was prepared by anionicnon-equilibrium polymerization with a "seed solution" as initiator. The monomer, N,N'-bis(hydroxydiphenylsilyl)-tetraphenyl-cyclodisilazane (BHPTPC), was synthesized via the hydrolysis of N,N'-bis(chlorodiphenylsilyl)tetraphenyl-cyclodisilazane (BCPTPC). A new method for the preparation of BCPTPC is also reported here with high yield and simplermanipulation. The synthesized polysiloxane containing N,N'-bis(diphenylsilyl)tetraphenlycyclodisilazane was characterized by 1H-NMR,29Si-NMR,gel permeation chromatography(GPC)and intrinsic viscosity.
A new kind of polysiloxane containing N,N'-bis(diphenylsilyl)tetraphenylcyclodisilazane was prepared by anionicnon-equilibrium polymerization with a "seed solution" as initiator. The monomer, N,N'-bis(hydroxydiphenylsilyl)-tetraphenyl-cyclodisilazane (BHPTPC), was synthesized via the hydrolysis of N,N'-bis(chlorodiphenylsilyl)tetraphenyl-cyclodisilazane (BCPTPC). A new method for the preparation of BCPTPC is also reported here with high yield and simplermanipulation. The synthesized polysiloxane containing N,N'-bis(diphenylsilyl)tetraphenlycyclodisilazane was characterized by 1H-NMR,29Si-NMR,gel permeation chromatography(GPC)and intrinsic viscosity.
2000, 18(6): 557-564
Abstract:
The molecular structure of polyethylene (PE) samples with various comonomers including propylene, 1-buteneand 1-hexene was investigated by DSC and 13C-NMR techniques. The density of the samples varies from 0.948 g/cm3 to0.917 g/cm3, and the molecular weight determined by the GPC method is in the range of 1～2×105. The branch point contentof the samples was determined by 13C-NMR measurements and was found to be less than 20 per 1000 C atoms along themain chain. Crystallization segregation DSC technique(CSDSC) was used to characterize the branch point distribution or the segment length distribution of PEs.The crystallization segregation was performed in a successive annealing process at decreasing temperatures.The interval of two successive annealing temperatures was 6 K,and the time length of each annealing step was 2.5h.The CSDSC results clearly indicate that all the PE samples used,including some metallocene PEs,more or less exhibit their non-uniformity in segment length distribution,and bimodal or multimodal CSDSC curves were usually observed.For quantitative characterization of the CSDSC curves and the segment length distribution two parameters,the average melting point,TmAV,and the root-mean-square deviation of melting temperature,(△Tm2 AV)1/2 were proposed.TmAV is corresponding to the average segment length due to branching and(△Tm2 AV)1/2 gives information about the width of the segment length distribution.Experimental results show that both the degree of average melting temperature depression and the width of the distribution seem of increase with increasing the branching content and are dependent on the type of comonomers.Very good reproducibility and additivity of the CSDSC method were evidenced experimentally.It was concluded that the CSDSC technique is a sensitive and convenient method for characterizing the segment length distribution of branched polyethylenes and will be of great interest in structure-property relationship studies of crystalline polymers.
The molecular structure of polyethylene (PE) samples with various comonomers including propylene, 1-buteneand 1-hexene was investigated by DSC and 13C-NMR techniques. The density of the samples varies from 0.948 g/cm3 to0.917 g/cm3, and the molecular weight determined by the GPC method is in the range of 1～2×105. The branch point contentof the samples was determined by 13C-NMR measurements and was found to be less than 20 per 1000 C atoms along themain chain. Crystallization segregation DSC technique(CSDSC) was used to characterize the branch point distribution or the segment length distribution of PEs.The crystallization segregation was performed in a successive annealing process at decreasing temperatures.The interval of two successive annealing temperatures was 6 K,and the time length of each annealing step was 2.5h.The CSDSC results clearly indicate that all the PE samples used,including some metallocene PEs,more or less exhibit their non-uniformity in segment length distribution,and bimodal or multimodal CSDSC curves were usually observed.For quantitative characterization of the CSDSC curves and the segment length distribution two parameters,the average melting point,TmAV,and the root-mean-square deviation of melting temperature,(△Tm2 AV)1/2 were proposed.TmAV is corresponding to the average segment length due to branching and(△Tm2 AV)1/2 gives information about the width of the segment length distribution.Experimental results show that both the degree of average melting temperature depression and the width of the distribution seem of increase with increasing the branching content and are dependent on the type of comonomers.Very good reproducibility and additivity of the CSDSC method were evidenced experimentally.It was concluded that the CSDSC technique is a sensitive and convenient method for characterizing the segment length distribution of branched polyethylenes and will be of great interest in structure-property relationship studies of crystalline polymers.
2000, 18(6): 565-568
Abstract:
Spinodal phase separation behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile)(PMMA/SAN)blends was investigated by the time-resolved small angle light scattering (SALS) technique. It was found that the influence oftemperature on the scattering intensity evolution followed the time-temperature superposition principle. The relationshipbetween temperature and the relaxation time of scattering intensity I(t) can be well described by the Williams-Landel-Ferry(WLF) function.
Spinodal phase separation behavior of poly(methyl methacrylate)/poly(styrene-co-acrylonitrile)(PMMA/SAN)blends was investigated by the time-resolved small angle light scattering (SALS) technique. It was found that the influence oftemperature on the scattering intensity evolution followed the time-temperature superposition principle. The relationshipbetween temperature and the relaxation time of scattering intensity I(t) can be well described by the Williams-Landel-Ferry(WLF) function.
2000, 18(6): 569-572
Abstract:
The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic forcemicroscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found thatthe ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of thespherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite under polarizing microscope coincided with its surface characteristics.The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface,while the dark rings coincided with the concave rings.
The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic forcemicroscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found thatthe ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of thespherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite under polarizing microscope coincided with its surface characteristics.The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface,while the dark rings coincided with the concave rings.
