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2002 Volume 20 Issue 4
2002, 20(4): 285-290
Abstract:
To allow anisotropies of optical properties in a magnetic field, nitroxide radical is introduced into the ortho-position of the phenylene ring in the side chain. A new azobenzene side-chain polymer (TEMPO-PAZ) containing TEMPOradical was synthesized. The polymer has a good solubility in organic solvents. The ESR spectrum of the polymer indicatedthree absorption lines characteristic of TEMPO radical. The optical phase conjugated responses (I4) of the polymer films were investigated by degenerate four-wave mixing (DFWM).The experimental results showed that optical phase conjugated response of the TEMPO-PAZ could be easily controlled by choosing the appropriate direction of magnetic field presumably due to the nitroxide radical in the TEMPO-PAZ molecular structure.For the polymer investigated here,the nitroxide radical was introduced to increase optical phase conjugated response intensity in a magnetic field,aiming originally at searching for a new photo-active organic magnetic multifunctional materials.
To allow anisotropies of optical properties in a magnetic field, nitroxide radical is introduced into the ortho-position of the phenylene ring in the side chain. A new azobenzene side-chain polymer (TEMPO-PAZ) containing TEMPOradical was synthesized. The polymer has a good solubility in organic solvents. The ESR spectrum of the polymer indicatedthree absorption lines characteristic of TEMPO radical. The optical phase conjugated responses (I4) of the polymer films were investigated by degenerate four-wave mixing (DFWM).The experimental results showed that optical phase conjugated response of the TEMPO-PAZ could be easily controlled by choosing the appropriate direction of magnetic field presumably due to the nitroxide radical in the TEMPO-PAZ molecular structure.For the polymer investigated here,the nitroxide radical was introduced to increase optical phase conjugated response intensity in a magnetic field,aiming originally at searching for a new photo-active organic magnetic multifunctional materials.
2002, 20(4): 291-307
Abstract:
The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail.The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents showthat two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly take place at sites of tertiary carbon,secondary carbon,and especially allylic carbon when available.The high resolution 13C-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H-and Y-type links and that their concentrations are of the same order.The fluorescence,ESR,13C and 1H-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP(PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl(K·)radical intermediates.Two new PPB products:an isomer of benzpinacol with quinoid structure,1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2,5-cyclohexadiene and three kinds of α-alkyl-benzhydrols have been detected and identified.These results provide new experimental evidence for elucidating the reaction mechanism in the BP-hotoinitiated crosslinking of polyethylene.
The radical intermediates, the crosslink microstructures, and the reaction mechanism of benzophenone (BP)-photoinitiated crosslinking of low-density polyethylene (LDPE) and model compounds (MD) have been reviewed in detail.The spin-trapping electron spin resonance (ESR) spectra obtained from the LDPE/BP systems with spin-trap agents showthat two kinds of polymer radical intermediates are mainly formed: tertiary carbon and secondary carbon radicals. The spin-trapping ESR studies of MD/BP systems give further evidence that photocrosslinking reactions of PE predominantly take place at sites of tertiary carbon,secondary carbon,and especially allylic carbon when available.The high resolution 13C-NMR spectra obtained from LDPE and MD systems show that the crosslink microstructures have H-and Y-type links and that their concentrations are of the same order.The fluorescence,ESR,13C and 1H-NMR spectra from the PE and MD systems demonstrate that the main photoreduction product of BP(PPB) is benzpinacol formed by the recombination of two diphenylhydroxymethyl(K·)radical intermediates.Two new PPB products:an isomer of benzpinacol with quinoid structure,1-phenylhydroxymethylene-4-diphenylhydroxymethyl-2,5-cyclohexadiene and three kinds of α-alkyl-benzhydrols have been detected and identified.These results provide new experimental evidence for elucidating the reaction mechanism in the BP-hotoinitiated crosslinking of polyethylene.
2002, 20(4): 309-316
Abstract:
Polyphenol film deposited on platinum foil can continuously grow with time during the electrolysis of a phenolsolution consisting of 0. 1 mol L-1 phenol, 3 mol L-1 NaOH and 0.5 mol L-1 Na2SO4, as has been proved by the methods ofsweep potential, constant potential and constant current, and visible spectra during the electrolysis of phenol. A polyphenolfilm with thickness of 0.11 mm was obtained by the electrolysis of phenol at a constant potential of 0.70 V (versus Ag/AgCl with saturated KCl solution).Polyphenol film is inactive and stable in 2 mol L-1H2SO4 solution,neutral solution and 3 mol L-1 NaOH solution and in the potential range between -0.95 and 1.35 V.The usable potential range is dependent on the pH value.Polyphenol has an ESR signal with a g factor of 2.0049.The conductivity of polyphenol is 1.2×10-4 S cm-1.In the solution of polyphenol dissolved in DMSO,the mobility of polyphenol anions is 8×10-9m2s-1V-1 at 20℃.
Polyphenol film deposited on platinum foil can continuously grow with time during the electrolysis of a phenolsolution consisting of 0. 1 mol L-1 phenol, 3 mol L-1 NaOH and 0.5 mol L-1 Na2SO4, as has been proved by the methods ofsweep potential, constant potential and constant current, and visible spectra during the electrolysis of phenol. A polyphenolfilm with thickness of 0.11 mm was obtained by the electrolysis of phenol at a constant potential of 0.70 V (versus Ag/AgCl with saturated KCl solution).Polyphenol film is inactive and stable in 2 mol L-1H2SO4 solution,neutral solution and 3 mol L-1 NaOH solution and in the potential range between -0.95 and 1.35 V.The usable potential range is dependent on the pH value.Polyphenol has an ESR signal with a g factor of 2.0049.The conductivity of polyphenol is 1.2×10-4 S cm-1.In the solution of polyphenol dissolved in DMSO,the mobility of polyphenol anions is 8×10-9m2s-1V-1 at 20℃.
2002, 20(4): 317-323
Abstract:
The self-diffesion of water, ethanol and water-ethanol mixtures in chitosan (CS) membranes crosslinked byaqueous H2SO4 solution and uncrosslinked membrane was measured using pulsed-field gradient (PFG) nuclear magneticresonance (NMR) spectroscopy to obtain the partial solubilities and self-diffusion coefficients. An attempt was made toexplain the transport properties of water and ethanol through the CS membrane. It was concluded that there are two types ofchannel water and ethanol diffusate transfer.The water was localized in the hydrophilic ionic region formed by the ionized groups,and the ethanol was localized in the hydrophobic amorphous network of the polymer.There was a good agreement between the separation factors estimated from PFG-NMR data and those obtained by pervaporation testing.
The self-diffesion of water, ethanol and water-ethanol mixtures in chitosan (CS) membranes crosslinked byaqueous H2SO4 solution and uncrosslinked membrane was measured using pulsed-field gradient (PFG) nuclear magneticresonance (NMR) spectroscopy to obtain the partial solubilities and self-diffusion coefficients. An attempt was made toexplain the transport properties of water and ethanol through the CS membrane. It was concluded that there are two types ofchannel water and ethanol diffusate transfer.The water was localized in the hydrophilic ionic region formed by the ionized groups,and the ethanol was localized in the hydrophobic amorphous network of the polymer.There was a good agreement between the separation factors estimated from PFG-NMR data and those obtained by pervaporation testing.
2002, 20(4): 325-332
Abstract:
Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by thephosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and effects on CPCsfrom monocalcium phosphate monohydrate (MCPM) and calcium oxide (CaO) or dicalcium phosphate dihydrate (DCPD)and calcium hydroxide [Ca(OH)2] were investigated. Addition of P-chitin (Mw = 2.60×104; degree of substitution, DS =0.68) to the liquid phase in amounts up to 3 wt% for MCPM and CaO cements or 1.5 wt% for DCPD and Ca(OH)2 cements could enhance the mechanical strength considerably,while little influence on the setting time was observed.However,further addition of P-chitin will cause no setting.
Phosphorylated chitins (P-chitins) as the additives of calcium phosphate cements (CPCs) were prepared by thephosphorylation of chitin with phosphorus pentoxide in methanesulfonic acid. Their physical properties and effects on CPCsfrom monocalcium phosphate monohydrate (MCPM) and calcium oxide (CaO) or dicalcium phosphate dihydrate (DCPD)and calcium hydroxide [Ca(OH)2] were investigated. Addition of P-chitin (Mw = 2.60×104; degree of substitution, DS =0.68) to the liquid phase in amounts up to 3 wt% for MCPM and CaO cements or 1.5 wt% for DCPD and Ca(OH)2 cements could enhance the mechanical strength considerably,while little influence on the setting time was observed.However,further addition of P-chitin will cause no setting.
2002, 20(4): 333-337
Abstract:
NiCl2(bpy) catalyzed polycondensation between p-dibromobenzene and m-dibromobenzene has been carried outunder vdrious conditions. The polycondensation endows the copolymer with an Mn of 2300 (by GPC, polystyrene standards)and good solubility in organic solvents. The fluorescence spectra of the copolymer measured with tetrahydrofuran solutionshows an emission maximum (λmax) at 372.8 nm, whereas for the film the maximum shifts to 436.6 nm.
NiCl2(bpy) catalyzed polycondensation between p-dibromobenzene and m-dibromobenzene has been carried outunder vdrious conditions. The polycondensation endows the copolymer with an Mn of 2300 (by GPC, polystyrene standards)and good solubility in organic solvents. The fluorescence spectra of the copolymer measured with tetrahydrofuran solutionshows an emission maximum (λmax) at 372.8 nm, whereas for the film the maximum shifts to 436.6 nm.
2002, 20(4): 339-345
Abstract:
Based on thermal analysis, the isothermal and nonisothemal crystallization kinetics of Ziegler-Natta catalyzedlinear low density polyethylene (Z-N LLDPE) and metallocene catalyzed LLDPE (m-LLDPE) were studied. Treating theresults with the Avrami equation and the Ozawa equation, the crystallization constant lgk and the Avrami exponent n wereobtained. Some other crystallization parameters were also discussed. According to the different characteristics of the chain structures of Z-N LLDPE and metallocene LLDPE,their crystallization behaviors were analyzed.It is indicated that the homogeneity and heterogeneity of the two polymers act in different way during the crystallization process of polymers,including the nucleation and the growth of crystals under various conditions.
Based on thermal analysis, the isothermal and nonisothemal crystallization kinetics of Ziegler-Natta catalyzedlinear low density polyethylene (Z-N LLDPE) and metallocene catalyzed LLDPE (m-LLDPE) were studied. Treating theresults with the Avrami equation and the Ozawa equation, the crystallization constant lgk and the Avrami exponent n wereobtained. Some other crystallization parameters were also discussed. According to the different characteristics of the chain structures of Z-N LLDPE and metallocene LLDPE,their crystallization behaviors were analyzed.It is indicated that the homogeneity and heterogeneity of the two polymers act in different way during the crystallization process of polymers,including the nucleation and the growth of crystals under various conditions.
2002, 20(4): 347-352
Abstract:
Based on successive multiple-step isothermal crystallization and self-nucleation annealing methods, a novel semi-quantitative method for the characterization of segment distribution in linear low density polyethylene (LLDPE) wasestablished by treating the thermal analysis data using the Gibbs-Thomson equation. The method was used to describe thesegment distribution of Ziegler-Natta catalyzed LLDPE (Z-N LLDPE), metallocene catalyzed LLDPE (m-LLDPE) and two conunercial LLDPEs with wide molecular weight distribution.The differences of the results obtained from the two thermally treated samples were compared.The results of segment distribution of the polymers were discussed according to their microstructure data and were compared with their characteristics.It can be deduced from the results that this characterization method is effective to characterize the sequence structure of the branched ethylene copolymers.
Based on successive multiple-step isothermal crystallization and self-nucleation annealing methods, a novel semi-quantitative method for the characterization of segment distribution in linear low density polyethylene (LLDPE) wasestablished by treating the thermal analysis data using the Gibbs-Thomson equation. The method was used to describe thesegment distribution of Ziegler-Natta catalyzed LLDPE (Z-N LLDPE), metallocene catalyzed LLDPE (m-LLDPE) and two conunercial LLDPEs with wide molecular weight distribution.The differences of the results obtained from the two thermally treated samples were compared.The results of segment distribution of the polymers were discussed according to their microstructure data and were compared with their characteristics.It can be deduced from the results that this characterization method is effective to characterize the sequence structure of the branched ethylene copolymers.
2002, 20(4): 353-360
Abstract:
A novel tetrafunctional initiator, C [CH2O (CH2)3 OOCCH(Br)CH3]4 (1), was synthesized through the reaction oftetraol with α-bromopropionyl chloride, and then was used as initiator of atom transfer radical polymerization (ATRP) in thepreparation of 4-armed polystyrene (PSt) with narrow polydispersity. The structure, molecular weight and molecular weightdistribution (MWD) of each arm were studied by 1H-NMR and GPC data of hydrolyzed products of the 4-armed PSt.The ATRP of St using 1/CuBr/bpy as initiator system is of "living" character based on the following evidence:narrow MWD,constant concentration of chain radical during the polymerization,control of molecular weight by the molar ratio of monomer consumed to 1.The 4-armed poly(St-b-P-nitrophenyl methacrylate)[poly(St-b-NPMA)] was prepared by the ATRP of NPMA using 4-armed PSt with terminal bromine as the initiator,and characterized by FT-IR,1H-NMR spectra and GPC curves.The micelles with PSt as core,and PNPMA as shell were formed by dropping DMSO into a solution of 4-armed poly(St-b-NPMA) in DMF,as proved by laser light scatter(LLS) method.
A novel tetrafunctional initiator, C [CH2O (CH2)3 OOCCH(Br)CH3]4 (1), was synthesized through the reaction oftetraol with α-bromopropionyl chloride, and then was used as initiator of atom transfer radical polymerization (ATRP) in thepreparation of 4-armed polystyrene (PSt) with narrow polydispersity. The structure, molecular weight and molecular weightdistribution (MWD) of each arm were studied by 1H-NMR and GPC data of hydrolyzed products of the 4-armed PSt.The ATRP of St using 1/CuBr/bpy as initiator system is of "living" character based on the following evidence:narrow MWD,constant concentration of chain radical during the polymerization,control of molecular weight by the molar ratio of monomer consumed to 1.The 4-armed poly(St-b-P-nitrophenyl methacrylate)[poly(St-b-NPMA)] was prepared by the ATRP of NPMA using 4-armed PSt with terminal bromine as the initiator,and characterized by FT-IR,1H-NMR spectra and GPC curves.The micelles with PSt as core,and PNPMA as shell were formed by dropping DMSO into a solution of 4-armed poly(St-b-NPMA) in DMF,as proved by laser light scatter(LLS) method.
2002, 20(4): 361-368
Abstract:
Ti-incorporated mesoporous silica materials with pore diameters of 3-4 nm have been prepared via the co-hydrolysis and co-condensation reactions, that is the sol-gel reactions, of titanium (IV) tetrabutoxide and tetraethylorthosilicate in the presence of tartaric acid as template, followed by extraction with ethanol to remove the templatemolecules. The materials were characterized in detail by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption test, powder X-ray diffraction,transmission electron microscopy and X-ray energy disperisve spectroscopy.The results indicate that the Ti-containing silica materials have large specific surface areas(ca.1200 m2g-1) and pore volumes (ca/ 0.900 cm3g-1). The mesoporosity arises from disordered interconnecting channels or pores.The Ti-incorporated silicas exhibit catalytic activity for the ring-opening polymerization of ε-caprolactone,otherwise,the pure mesoporous silica material shows on catalytic activity under the identical conditions.
Ti-incorporated mesoporous silica materials with pore diameters of 3-4 nm have been prepared via the co-hydrolysis and co-condensation reactions, that is the sol-gel reactions, of titanium (IV) tetrabutoxide and tetraethylorthosilicate in the presence of tartaric acid as template, followed by extraction with ethanol to remove the templatemolecules. The materials were characterized in detail by Fourier transform infrared spectroscopy, nitrogen adsorption-desorption test, powder X-ray diffraction,transmission electron microscopy and X-ray energy disperisve spectroscopy.The results indicate that the Ti-containing silica materials have large specific surface areas(ca.1200 m2g-1) and pore volumes (ca/ 0.900 cm3g-1). The mesoporosity arises from disordered interconnecting channels or pores.The Ti-incorporated silicas exhibit catalytic activity for the ring-opening polymerization of ε-caprolactone,otherwise,the pure mesoporous silica material shows on catalytic activity under the identical conditions.
2002, 20(4): 369-375
Abstract:
A series of cellulose acetate membranes were prepared by using formamide as additive, and then were hydrolyzedin 4 wt% aqueous NaOH solution for 8 h to obtain regenerated cellulose membranes. The dependence of degree ofsubstitution, structure, porous properties, solubility and thermal stability on hydrolysis time was studied by chemical titration,Fourier transform infrared spectroscopy, scanning electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry, respectively.The results indicated that the pore size of the regenerated cellulose membranes was slightly smaller than that of cellulose acetate membrane,while solvent-resistance,crystallinity and thermostability were significantly improved.This work provides a simple way to prepare the porous cellulose membranes,which not only kept the good pore characteristics of cellulose acetate membranes,but also possessed solvent-resistance,high crystallinity and thermostability.Therefore,the application range of cellulose acetate membranes can be expanded.
A series of cellulose acetate membranes were prepared by using formamide as additive, and then were hydrolyzedin 4 wt% aqueous NaOH solution for 8 h to obtain regenerated cellulose membranes. The dependence of degree ofsubstitution, structure, porous properties, solubility and thermal stability on hydrolysis time was studied by chemical titration,Fourier transform infrared spectroscopy, scanning electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry, respectively.The results indicated that the pore size of the regenerated cellulose membranes was slightly smaller than that of cellulose acetate membrane,while solvent-resistance,crystallinity and thermostability were significantly improved.This work provides a simple way to prepare the porous cellulose membranes,which not only kept the good pore characteristics of cellulose acetate membranes,but also possessed solvent-resistance,high crystallinity and thermostability.Therefore,the application range of cellulose acetate membranes can be expanded.
2002, 20(4): 377-380
Abstract:
The synergistic effects of silicotungstic acid (SiW12) as a carelyst in the phosphorus-nitrogen compounds AM-based intumescent flame-retardant (IFR) polypropylene (PP) were studied using the limiting oxygen index(LOI), the UL-94test, thermogravimetric analysis (TGA), real time Fourier transform infrared (FTIR), laser Raman spectroscopy (LRS). TheLOI data show that SiW12 added to PP/IFR systems has a synergistic FR effect with an IFR additive named AM. The TGA data show that SiW12 apparently increases the thermal stability of the PP/IFR systems at high temperature(T>500℃).The FTIR results provide the positive evidence that IFR can improve the thermal stability of PP and SiW12 can information a higher rate of formation of phosphoric acid and its derivatives.The LRS measurements provide useful information on the carbonaceous microstructures.In short,a suitable amount of SiW12(1.5 wt%) exerts synergistic effects with the IFR by increasing the LOI value and the thermal stability at high temperature and promoting the formation of charred structures on the burning PP surface.
The synergistic effects of silicotungstic acid (SiW12) as a carelyst in the phosphorus-nitrogen compounds AM-based intumescent flame-retardant (IFR) polypropylene (PP) were studied using the limiting oxygen index(LOI), the UL-94test, thermogravimetric analysis (TGA), real time Fourier transform infrared (FTIR), laser Raman spectroscopy (LRS). TheLOI data show that SiW12 added to PP/IFR systems has a synergistic FR effect with an IFR additive named AM. The TGA data show that SiW12 apparently increases the thermal stability of the PP/IFR systems at high temperature(T>500℃).The FTIR results provide the positive evidence that IFR can improve the thermal stability of PP and SiW12 can information a higher rate of formation of phosphoric acid and its derivatives.The LRS measurements provide useful information on the carbonaceous microstructures.In short,a suitable amount of SiW12(1.5 wt%) exerts synergistic effects with the IFR by increasing the LOI value and the thermal stability at high temperature and promoting the formation of charred structures on the burning PP surface.
2002, 20(4): 381-383
Abstract:
The monomolecular particle agglomerates of polystyrenes were obtained by freeze-drying of its very dilutesolutions of 1.3×10-5-2.0×10-5 g/mL in benzene: cylcohexane (100:1) solvents, and they were annealed at roomtemperature for hundred days before use. According to13C-NMR measurement the polystyrenes should be practically atactic.The number average molecular weights of the samples are 2.80×103, 2.00×104, and 1.55×106, respectively. The freeze-dried aPS with a molecular weight higher than 104 show two new IR absorption bands at 1098 and 1261 cm-1,which are absent in the normal αPS and freeze-dried styrene oligomer.It was also found that the low molecular weight samples can only form powders,whereas the freeze-dried αPS with higher molecular weight form a mixture of powders and fibrils,of which the longer fibrils show a much stronger 1261 cm-1 band than the shorter fibrils and the powder.It seems that the 1261 cm-1 band corresponds to the stacking behavior of monomolecular particles.
The monomolecular particle agglomerates of polystyrenes were obtained by freeze-drying of its very dilutesolutions of 1.3×10-5-2.0×10-5 g/mL in benzene: cylcohexane (100:1) solvents, and they were annealed at roomtemperature for hundred days before use. According to13C-NMR measurement the polystyrenes should be practically atactic.The number average molecular weights of the samples are 2.80×103, 2.00×104, and 1.55×106, respectively. The freeze-dried aPS with a molecular weight higher than 104 show two new IR absorption bands at 1098 and 1261 cm-1,which are absent in the normal αPS and freeze-dried styrene oligomer.It was also found that the low molecular weight samples can only form powders,whereas the freeze-dried αPS with higher molecular weight form a mixture of powders and fibrils,of which the longer fibrils show a much stronger 1261 cm-1 band than the shorter fibrils and the powder.It seems that the 1261 cm-1 band corresponds to the stacking behavior of monomolecular particles.
