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2002 Volume 20 Issue 6
2002, 20(6): 497-508
Abstract:
The effect of time-temperature treatment on morphology of polyethylene-polypropylene (PE-PP) blends wasstudied to establish a relationship between thermal history, morphology and mechanical properties. Polypropylene (PP)homopolymers were used to blend with various polyethylenes (PE), including high density polyethylene (HDPE), lowdensity polyethylene (LDPE), linear low density polyethylene (LLDPE), and very and ultra low density polyethylene(VLDPE and ULDPE). The majority of the blends were prepared at a ratio of PE:PP=80:20,while blends of PP and LLDPE were prepared at various compositions.Thermal treatment was carried out at temperatures between the crystallization temperatures of PP and PEs to allow PP to crystallize first from the blends.On cooling further,PE crystallized too.A very diffuse PP spherulite morphology in the PE matrix was formed in some partially miscible blends when PP was less than 20% by mass.Droplet-matrix structures were developed in other blends with either PP or PE as dispersed domains in a continuous matrix,depending on the composition ratio.The scanning electron microscopy(SEM) images displayed a fibrillar structure of PP spherulite in the LLDPE-PP(80:20) and large droplets of PP in the HDPE-PP(80:20) blend,providing larger surface area and better bonding in the LLDPE-PP(80:20) blends.This explains why the blends with diffuse spherulite morphology showed greater improvement in tensile properties than droplet-matrix morphology blends after time-temperature treatment.
The effect of time-temperature treatment on morphology of polyethylene-polypropylene (PE-PP) blends wasstudied to establish a relationship between thermal history, morphology and mechanical properties. Polypropylene (PP)homopolymers were used to blend with various polyethylenes (PE), including high density polyethylene (HDPE), lowdensity polyethylene (LDPE), linear low density polyethylene (LLDPE), and very and ultra low density polyethylene(VLDPE and ULDPE). The majority of the blends were prepared at a ratio of PE:PP=80:20,while blends of PP and LLDPE were prepared at various compositions.Thermal treatment was carried out at temperatures between the crystallization temperatures of PP and PEs to allow PP to crystallize first from the blends.On cooling further,PE crystallized too.A very diffuse PP spherulite morphology in the PE matrix was formed in some partially miscible blends when PP was less than 20% by mass.Droplet-matrix structures were developed in other blends with either PP or PE as dispersed domains in a continuous matrix,depending on the composition ratio.The scanning electron microscopy(SEM) images displayed a fibrillar structure of PP spherulite in the LLDPE-PP(80:20) and large droplets of PP in the HDPE-PP(80:20) blend,providing larger surface area and better bonding in the LLDPE-PP(80:20) blends.This explains why the blends with diffuse spherulite morphology showed greater improvement in tensile properties than droplet-matrix morphology blends after time-temperature treatment.
2002, 20(6): 509-515
Abstract:
The film formation process of micro-PS particles (diameter 742 nm) and nano-PS particles (diameter 29 nm) wasstudied by atomic force microscopy and differential scanning calorimetry. During a step heating process, the particles wereannealed for 0.5 h at each selected temperature. It was found that the deformation and interdiffusion temperatures of themicro-PS particles are ca. 120-130℃ and 140-150℃, that of the nano-PS particles are 90℃ and 100-110℃ respectively.The DSC traces of nano-PS particles showed that there was an exothermic peak near Tg after annealing for 0.5 h at the selected temperatures below 90℃ ;otherwise,the exothermic peak disappeared after annealing at 100℃ or above.Compared with the micro-PS particles,the sintering process of nano-PS particles occurs at much lower temperature determined by the confined state of polymer chains with higher conformational energy in nano-particles,and completes in a much narrower temperature range driven mainly by the larger total surface energy.
The film formation process of micro-PS particles (diameter 742 nm) and nano-PS particles (diameter 29 nm) wasstudied by atomic force microscopy and differential scanning calorimetry. During a step heating process, the particles wereannealed for 0.5 h at each selected temperature. It was found that the deformation and interdiffusion temperatures of themicro-PS particles are ca. 120-130℃ and 140-150℃, that of the nano-PS particles are 90℃ and 100-110℃ respectively.The DSC traces of nano-PS particles showed that there was an exothermic peak near Tg after annealing for 0.5 h at the selected temperatures below 90℃ ;otherwise,the exothermic peak disappeared after annealing at 100℃ or above.Compared with the micro-PS particles,the sintering process of nano-PS particles occurs at much lower temperature determined by the confined state of polymer chains with higher conformational energy in nano-particles,and completes in a much narrower temperature range driven mainly by the larger total surface energy.
2002, 20(6): 517-524
Abstract:
The electrochemical polymerization of catechol on platinum has been carried out using repeated potential cyclingbetween-0.2 and 1.1 V (versus SCE). The electrolytic solution consisted of 0.2 mol dm-3 catechol, 0.5 mol dm-3 NaCl and0.1 mol dm-3 Na2HPO4 with pH 8.72. Catechol can not be polymerized at pH≥10.12. Polycatechol has an electrochemicalactivity at pH≤4. The anodic and cathodic peak potentials of polycatechol shift towards more negative values as the pH of the solution increases from 1 to 4.The electrochemical activity of polycatechol hardly changes in this pH region,but it decreases slowly with time.This is caused by oxygen in air,which leads to an irreversible oxidation of polycatechol.This property is favorable for protecting metals from corrosion.Raman and FTIR spectra of polycatechol and catechol are quite different.AFM images of polycatechol films provide evidence that the image of the oxidized state of polycatechol is markedly different from that of the reduced one.This difference is caused by doping and dedoping of polycatechol.
The electrochemical polymerization of catechol on platinum has been carried out using repeated potential cyclingbetween-0.2 and 1.1 V (versus SCE). The electrolytic solution consisted of 0.2 mol dm-3 catechol, 0.5 mol dm-3 NaCl and0.1 mol dm-3 Na2HPO4 with pH 8.72. Catechol can not be polymerized at pH≥10.12. Polycatechol has an electrochemicalactivity at pH≤4. The anodic and cathodic peak potentials of polycatechol shift towards more negative values as the pH of the solution increases from 1 to 4.The electrochemical activity of polycatechol hardly changes in this pH region,but it decreases slowly with time.This is caused by oxygen in air,which leads to an irreversible oxidation of polycatechol.This property is favorable for protecting metals from corrosion.Raman and FTIR spectra of polycatechol and catechol are quite different.AFM images of polycatechol films provide evidence that the image of the oxidized state of polycatechol is markedly different from that of the reduced one.This difference is caused by doping and dedoping of polycatechol.
2002, 20(6): 525-530
Abstract:
The copolymerization of styrene (St) with maleic anhydride (MAh) under gamma radiation at room temperature inthe presence of benzyl dithiobenzoate (BDTB) was found to display "living" nature evidenced by constant concentration ofchain radicals during the copolymerization, linear evolution of molecular weights with conversion and narrow molecularweight distribution (Msub>w/Mn = 1.23-1.35). The compositional analysis and the sequence structural information of the copolymers obtained from DEPT (Distortionless Enhancement by Polarization Transfer ) experiments demonstrate that the copolymers obtained also possess strictly alternating structure.
The copolymerization of styrene (St) with maleic anhydride (MAh) under gamma radiation at room temperature inthe presence of benzyl dithiobenzoate (BDTB) was found to display "living" nature evidenced by constant concentration ofchain radicals during the copolymerization, linear evolution of molecular weights with conversion and narrow molecularweight distribution (Msub>w/Mn = 1.23-1.35). The compositional analysis and the sequence structural information of the copolymers obtained from DEPT (Distortionless Enhancement by Polarization Transfer ) experiments demonstrate that the copolymers obtained also possess strictly alternating structure.
2002, 20(6): 531-536
Abstract:
Poly(methyl methacrylate/ethyl acrylate/acrylic acid) hydrosols were prepared by employing soap-freepolymerization, and (acrylic acid/butyl acrylate) oligomer was used as the polymeric surfactant The effect of reactioncondition on the morphology and particle size of the hydrosols was investigated. The minimum amount of acrylic acid in thehydrosols is 2%. The maximum weight average molecular weight (Mw) of polymer that assures soap-free emulsion conversion into hydrosol is about 1.2×105-1.3×105.The particle transforming process was investigated,and an obvious change of particle diameter and morphology was observed.
Poly(methyl methacrylate/ethyl acrylate/acrylic acid) hydrosols were prepared by employing soap-freepolymerization, and (acrylic acid/butyl acrylate) oligomer was used as the polymeric surfactant The effect of reactioncondition on the morphology and particle size of the hydrosols was investigated. The minimum amount of acrylic acid in thehydrosols is 2%. The maximum weight average molecular weight (Mw) of polymer that assures soap-free emulsion conversion into hydrosol is about 1.2×105-1.3×105.The particle transforming process was investigated,and an obvious change of particle diameter and morphology was observed.
2002, 20(6): 537-541
Abstract:
Polysiloxane bearing pendant quaternary ammonium groups (PSI) was used to modify the surface properties ofepoxy resins. In the cured resin, PSI formed the dispersed phase. Remarkable enrichment and gradient distribution ofpolysiloxane on the surface region of the epoxy resins were demonstrated by XPS analysis. The composition and propertiesof the surface of PSI-modified epoxy resin, which is in contact with the mold, are dependent on the material of the mold.Through the incorporation of PSI,epoxy resins with low surface energy and low friction coefficient were obtained.Polysiloxane with lower ionic group content shows a higher degree of enrichment on the resin surface and leads to a higher contact angle against water,while the polysiloxane having optimum compatibility with the epoxy resin shows a greater effect in reducing the static friction coefficient of the resin against glass.
Polysiloxane bearing pendant quaternary ammonium groups (PSI) was used to modify the surface properties ofepoxy resins. In the cured resin, PSI formed the dispersed phase. Remarkable enrichment and gradient distribution ofpolysiloxane on the surface region of the epoxy resins were demonstrated by XPS analysis. The composition and propertiesof the surface of PSI-modified epoxy resin, which is in contact with the mold, are dependent on the material of the mold.Through the incorporation of PSI,epoxy resins with low surface energy and low friction coefficient were obtained.Polysiloxane with lower ionic group content shows a higher degree of enrichment on the resin surface and leads to a higher contact angle against water,while the polysiloxane having optimum compatibility with the epoxy resin shows a greater effect in reducing the static friction coefficient of the resin against glass.
2002, 20(6): 543-550
Abstract:
A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphologyin phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed tochange the potential field around the dispersed pedicles near the wall. This additional potential interaction between the solidwall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. The gradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coakescence mechanism.The effect of interfacial tension on the gradient morphology is also discussed.
A fast coalescence mechanism is proposed to account for the wall effect on the formation of gradient morphologyin phase separated polymer blends during quiescent annealing. The existence of solid wall with high polarity is believed tochange the potential field around the dispersed pedicles near the wall. This additional potential interaction between the solidwall and the dispersed particles causes faster coalescence of the dispersed particles near the wall than in the bulk. The gradient phase morphology thus formed can be predicted by combining the wall-particle interaction and the touch-coakescence mechanism.The effect of interfacial tension on the gradient morphology is also discussed.
2002, 20(6): 551-557
Abstract:
The montmorillonites (MMTs), layered, smectite-type silicates, were premodified by two different methods priorto the polymer melt intercalation. In one case MMTs were modified with cetyltrimethylammonium bromide (CTAB), andtermed as organomontmorillonites (OMMTs); in the other case MMTs were modified by nylon, and the products were calledmodified montmorillonites (MMMTs). The effects of CTAB and nylon on the MMTs were investigated by using TG andWAXD. The results show that interlayer spacings of CTAB and nylon modified MMTs are larger than that of sodium MMTs.Then polyamide 66 (PA 66)/MMT nanocomposites were obtained through the method of melt intercalation of polymers.The nanocomposites were characterized by WAXD,TEM and Molau experiments.The results indicate that the MMTs disperse homogeneously in the PA 66 matrix.The mechanical properties of nanocomposites,such as tensile properties and flexural properties,were also measured and show a tendency to increase with increase of MMT content and reach the maximum values at 5phr MMT content.The heat distortion temperature (HDT) of the nanocomposites(7 phr) is about 32 K higher than that of pure PA 66.
The montmorillonites (MMTs), layered, smectite-type silicates, were premodified by two different methods priorto the polymer melt intercalation. In one case MMTs were modified with cetyltrimethylammonium bromide (CTAB), andtermed as organomontmorillonites (OMMTs); in the other case MMTs were modified by nylon, and the products were calledmodified montmorillonites (MMMTs). The effects of CTAB and nylon on the MMTs were investigated by using TG andWAXD. The results show that interlayer spacings of CTAB and nylon modified MMTs are larger than that of sodium MMTs.Then polyamide 66 (PA 66)/MMT nanocomposites were obtained through the method of melt intercalation of polymers.The nanocomposites were characterized by WAXD,TEM and Molau experiments.The results indicate that the MMTs disperse homogeneously in the PA 66 matrix.The mechanical properties of nanocomposites,such as tensile properties and flexural properties,were also measured and show a tendency to increase with increase of MMT content and reach the maximum values at 5phr MMT content.The heat distortion temperature (HDT) of the nanocomposites(7 phr) is about 32 K higher than that of pure PA 66.
2002, 20(6): 559-564
Abstract:
Silicone rubber (SIR) shows superior performance when used outdoors, but its surface can be transformed frominherently hydrophobic to hydrophilic by the adsorption of contaminants. Al(OH)3, Al2O3, quartz powder and active carbonwere selected as authentic contaminants. Hydrophobicity of the surface was determined using contact angle measurement.The results indicate that the adsorbability of the contaminants can strongly affect the hydrophobicity of contaminated SIR surface. The incrrasing rate of contact angle of specimens contaminated by Al(OH)3 was much faster than that by Al2O3 and quartz due to the adsorption of migrated low molecular weight (LMW) polydimethylsiloxanes.Specimens contaminated by active carbon could achieve surface hydrophobicity within 15 min because active carbon has high adsorbability.Surfaces of contaminated ultrapure SIR,polytetrafluoroethylene(PTFE) and glass remain hydrophilic because they contain no mobile LMW components.The addition of oligomeric polydimethylsiloxanes has little effect on the hydrophobicity of contaminants covered on SIR surface.
Silicone rubber (SIR) shows superior performance when used outdoors, but its surface can be transformed frominherently hydrophobic to hydrophilic by the adsorption of contaminants. Al(OH)3, Al2O3, quartz powder and active carbonwere selected as authentic contaminants. Hydrophobicity of the surface was determined using contact angle measurement.The results indicate that the adsorbability of the contaminants can strongly affect the hydrophobicity of contaminated SIR surface. The incrrasing rate of contact angle of specimens contaminated by Al(OH)3 was much faster than that by Al2O3 and quartz due to the adsorption of migrated low molecular weight (LMW) polydimethylsiloxanes.Specimens contaminated by active carbon could achieve surface hydrophobicity within 15 min because active carbon has high adsorbability.Surfaces of contaminated ultrapure SIR,polytetrafluoroethylene(PTFE) and glass remain hydrophilic because they contain no mobile LMW components.The addition of oligomeric polydimethylsiloxanes has little effect on the hydrophobicity of contaminants covered on SIR surface.
2002, 20(6): 565-572
Abstract:
Hybrid mesoporous polystyrene-silica materials were successfully prepared through HCl-catalyzed sol-gelreactions of tetraethyl orthosilicate (TEOS) and triethoxysilyl-functionalized polystyrene obtained via atom transfer radicalpolymerization (ATRP) of styrene, in the presence of citric acid (CA) as non-surfactant template or pore-forming agent andfollowed by ethanol extraction to remove template molecules. The materials were characterized by infrared spectroscopy (IR), N2 adsorption-desorption measurements,powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM).The results indicate that the materials prepared with 50 wt%-60 wt% template contents have average pore sized of 2-3 nm and large surface areas(ca.886 m2/g) as well as high pore volumes (ca.0.53 cm3/g) The mesoporosity arises from interconnected channels and pores with disordered arrangements.The pore diameters and pore volumes increase as the template content is increased.The pore diameters show a little change upon heating at 200℃ overnight.However,the materials do not have good hydrothermal stability.
Hybrid mesoporous polystyrene-silica materials were successfully prepared through HCl-catalyzed sol-gelreactions of tetraethyl orthosilicate (TEOS) and triethoxysilyl-functionalized polystyrene obtained via atom transfer radicalpolymerization (ATRP) of styrene, in the presence of citric acid (CA) as non-surfactant template or pore-forming agent andfollowed by ethanol extraction to remove template molecules. The materials were characterized by infrared spectroscopy (IR), N2 adsorption-desorption measurements,powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM).The results indicate that the materials prepared with 50 wt%-60 wt% template contents have average pore sized of 2-3 nm and large surface areas(ca.886 m2/g) as well as high pore volumes (ca.0.53 cm3/g) The mesoporosity arises from interconnected channels and pores with disordered arrangements.The pore diameters and pore volumes increase as the template content is increased.The pore diameters show a little change upon heating at 200℃ overnight.However,the materials do not have good hydrothermal stability.
2002, 20(6): 573-577
Abstract:
X-ray photoelectron spectroscopy and Raman spectroscopy were used to determine the chemical change ofpolyphenylsilsesquioxane (PPSQ) during pyrolysis in flowing nitrogen. Two temperature ranges were found for pyrolysedPPSQ below and above 600℃, respectively. The former is related to the rearrangement of PPSQ backbone and the latterreflects that most of backbone structure of PPSQ might be broken down and unorganized. Carbon formed in carbonization of PPSQ sample pyrolysed at 900℃ should be sp3 bonded carbon with crystallite size effects or defects.
X-ray photoelectron spectroscopy and Raman spectroscopy were used to determine the chemical change ofpolyphenylsilsesquioxane (PPSQ) during pyrolysis in flowing nitrogen. Two temperature ranges were found for pyrolysedPPSQ below and above 600℃, respectively. The former is related to the rearrangement of PPSQ backbone and the latterreflects that most of backbone structure of PPSQ might be broken down and unorganized. Carbon formed in carbonization of PPSQ sample pyrolysed at 900℃ should be sp3 bonded carbon with crystallite size effects or defects.
2002, 20(6): 579-584
Abstract:
A novel polymer containing the sucrose group was synthesized by radical polymerization from an enzymaticallyprepared monomer, l'-O-vinyledipoyl-sucrose (VAS). Transesterification reaction of sucrose with divinyl adipate inanhydrous pyridine catalyzed by an alkaline protease from Bacillus subtilis at 60℃ for 7 days gave VAS (yield 55%) withoutany blocking/deblocking steps. The vinyl sucrose ester could be polymerized with potassium persulfate and H2O2 as initiatorto give poly(l'-O-vinyladipoyl-sucrose)with Mn=33,000 and Mw=53,200,Mw/Mn=1.61.The polymer was biodegradable.After 6 days in aqueous buffer (pH 7),this alkaline protease could degrade poly(1′-O-vinyladipoyl-sucrose) to Mn of ca. 1080,Mw/Mn=3.30(37℃),and Mn of ca.5200,Mw/Mn=2.44(4℃).The polymer containing the sucrose branch would be a functional material in various application fields.
A novel polymer containing the sucrose group was synthesized by radical polymerization from an enzymaticallyprepared monomer, l'-O-vinyledipoyl-sucrose (VAS). Transesterification reaction of sucrose with divinyl adipate inanhydrous pyridine catalyzed by an alkaline protease from Bacillus subtilis at 60℃ for 7 days gave VAS (yield 55%) withoutany blocking/deblocking steps. The vinyl sucrose ester could be polymerized with potassium persulfate and H2O2 as initiatorto give poly(l'-O-vinyladipoyl-sucrose)with Mn=33,000 and Mw=53,200,Mw/Mn=1.61.The polymer was biodegradable.After 6 days in aqueous buffer (pH 7),this alkaline protease could degrade poly(1′-O-vinyladipoyl-sucrose) to Mn of ca. 1080,Mw/Mn=3.30(37℃),and Mn of ca.5200,Mw/Mn=2.44(4℃).The polymer containing the sucrose branch would be a functional material in various application fields.
2002, 20(6): 585-590
Abstract:
An epoxy-terminated hyperbranched aromatic polyester (P3) was synthesized from a hyperbranched aromaticpolyester containing carboxylic acid end groups (P1), which was derived from the condensation polymerization of the AB_2monomer, 5-acetoxyisophthalic acid. Polymer P1 was converted into the polymeric acid chloride by reaction with thionylchloride. The acid chloride was reacted with ethanol and glycidol to form a poly(ethyl ester) (P2) and an epoxy terminatedmaterial (P3), respectively.The reaction conditions in each step of these processes had to be controlled very carefully to avoid unwanted cross-linking reactions.The characterization of products and intermediates,including molecualr weight distributions and thermal properties,are reported.
An epoxy-terminated hyperbranched aromatic polyester (P3) was synthesized from a hyperbranched aromaticpolyester containing carboxylic acid end groups (P1), which was derived from the condensation polymerization of the AB_2monomer, 5-acetoxyisophthalic acid. Polymer P1 was converted into the polymeric acid chloride by reaction with thionylchloride. The acid chloride was reacted with ethanol and glycidol to form a poly(ethyl ester) (P2) and an epoxy terminatedmaterial (P3), respectively.The reaction conditions in each step of these processes had to be controlled very carefully to avoid unwanted cross-linking reactions.The characterization of products and intermediates,including molecualr weight distributions and thermal properties,are reported.
2002, 20(6): 591-593
Abstract:
Electrostatic layer-by-layer self-assembly multilayer films were successfully fabricated from C60-ethylenediamineadduct (C60-EDA) and DNA. Under visible light irradiation, DNA is ready to be cleaved and the films are destroyed.
Electrostatic layer-by-layer self-assembly multilayer films were successfully fabricated from C60-ethylenediamineadduct (C60-EDA) and DNA. Under visible light irradiation, DNA is ready to be cleaved and the films are destroyed.
