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2000 Volume 18 Issue 3
2000, 18(3): 189-193
Abstract:
The scientific and technical history of polymerization can be divided into three periods, which will be illustratedfor emulsion polymerization. The first period was when emulsion polymers were originally produced, and was developed asan attempt to copy natural rubber latex. Indeed, the natural process is quite different from the synthetic process of emulsionpolymerization, which in fact does not even need an emulsion to be present: the term is a misnomer! The results were functional but limited.In the second period,the first theories appeared,and a huge range of products was made for surface coatings,adhesives,commodity polymers such as SBR,neoprene,etc.The work of the outstanding pioneers was based on limited types of experimental data,and some suppositions are now seen to be incorrect.Nevertheless,many excellent products were made and have evolved to many materials currently in everyday use.The third period of emulsion polymerization is now dawning.The scientific efforts of many teams over previous decades,aided by the advent of new physical techniques for investigation,have resulted in better understanding of the fundamentals of emulsion polymerizations.Some examples from the author's group involve creating novel materials using controlled seeded emulsion polymerization from natural rubber latex and other polyenes.Latex topology and controlled free-radical chemistry can be combined to produce a )a comb polymer with hydrophobic backbone and hydrophilic "teeth",or b )with sufficient in situ compatibilizer between two otherwise incompatible polymers to yield a spatially uniform material down to the nanostructure level,and c)to produce controlled nanostructures.
The scientific and technical history of polymerization can be divided into three periods, which will be illustratedfor emulsion polymerization. The first period was when emulsion polymers were originally produced, and was developed asan attempt to copy natural rubber latex. Indeed, the natural process is quite different from the synthetic process of emulsionpolymerization, which in fact does not even need an emulsion to be present: the term is a misnomer! The results were functional but limited.In the second period,the first theories appeared,and a huge range of products was made for surface coatings,adhesives,commodity polymers such as SBR,neoprene,etc.The work of the outstanding pioneers was based on limited types of experimental data,and some suppositions are now seen to be incorrect.Nevertheless,many excellent products were made and have evolved to many materials currently in everyday use.The third period of emulsion polymerization is now dawning.The scientific efforts of many teams over previous decades,aided by the advent of new physical techniques for investigation,have resulted in better understanding of the fundamentals of emulsion polymerizations.Some examples from the author's group involve creating novel materials using controlled seeded emulsion polymerization from natural rubber latex and other polyenes.Latex topology and controlled free-radical chemistry can be combined to produce a )a comb polymer with hydrophobic backbone and hydrophilic "teeth",or b )with sufficient in situ compatibilizer between two otherwise incompatible polymers to yield a spatially uniform material down to the nanostructure level,and c)to produce controlled nanostructures.
ARCHITECTURE OF LADDER,TUBULAR AND SIEVE-PLATE POLYMERS PREPARED BY STEPWISE COUPLING POLYMERIZATION
2000, 18(3): 195-206
Abstract:
"Stepwise-coupling polymerization" (SCP) is a very useful approach for preparing microstructure-controllableordered network polymers, including soluble one-dimensional ladderlike polymers (LP) and tubular polymers (TP), and two-dimensional sieve-plate polymers. The novel reactive LPs are important precursors of micro-structure controllable polymerssuch as "fishbone-" or "rowboat-"like mesomorphic polymers and their metal complexes as well as tubular polymer (TPs).They are full of great potential for use as advanced materials.
"Stepwise-coupling polymerization" (SCP) is a very useful approach for preparing microstructure-controllableordered network polymers, including soluble one-dimensional ladderlike polymers (LP) and tubular polymers (TP), and two-dimensional sieve-plate polymers. The novel reactive LPs are important precursors of micro-structure controllable polymerssuch as "fishbone-" or "rowboat-"like mesomorphic polymers and their metal complexes as well as tubular polymer (TPs).They are full of great potential for use as advanced materials.
2000, 18(3): 207-208
Abstract:
At the turn of the century, the global polymer industry is undergoing the most rapid and dramatic changes in itshistory. Emerging markets, particularly in Asia, and their polymer consumption are catching up with other parts of the world,creating new business opportunities. Economy of scale, combined with optimized logistic concepts, is becoming a keyeconomic success factor, thus forcing smaller suppliers out of business and creating a major hurdle for newcomers and the introduction of new products.Globalization of polymer customers and cost pressure lead to a consolidation of suppliers and products.Today standard thermoplastics have a dominant position in the market and they will retain this position in future.Engineering thermoplastics are facing growing competition due to the increased of standard polymers.This leads to a displacement process where standard polymers substitute engineering thermoplastics.Simultaneously engineering polymers are pushing into new markets or applications or displacing materials like glass,wood or metal.The recent history and future trends have a strong impact on R & D activity in the polymer industry.Competition on a global scale and increasing cost pressure are turning innovation into an essential precondition of commercial success,thus determining the objectives of industrial polymer research and development.
At the turn of the century, the global polymer industry is undergoing the most rapid and dramatic changes in itshistory. Emerging markets, particularly in Asia, and their polymer consumption are catching up with other parts of the world,creating new business opportunities. Economy of scale, combined with optimized logistic concepts, is becoming a keyeconomic success factor, thus forcing smaller suppliers out of business and creating a major hurdle for newcomers and the introduction of new products.Globalization of polymer customers and cost pressure lead to a consolidation of suppliers and products.Today standard thermoplastics have a dominant position in the market and they will retain this position in future.Engineering thermoplastics are facing growing competition due to the increased of standard polymers.This leads to a displacement process where standard polymers substitute engineering thermoplastics.Simultaneously engineering polymers are pushing into new markets or applications or displacing materials like glass,wood or metal.The recent history and future trends have a strong impact on R & D activity in the polymer industry.Competition on a global scale and increasing cost pressure are turning innovation into an essential precondition of commercial success,thus determining the objectives of industrial polymer research and development.
2000, 18(3): 209-226
Abstract:
The inclusion complex formation of -CD, -CD, and -CD with various water-soluble polymers has beeninvestigated, and the relationship between the chain cross-sectional areas of the polymers and the diameters of the cavities ofcyclodextrins (molecular recognition) was found. Polyrotaxanes and tubular polymers were prepared on the basis ofmolecular recognition. Several kinds of polymers having tetraphenylporphyrin (TPP) and paramagnetic metallotetraphenyl-prophyrin (AgTTP,CuTPP,VOTPP or ZnTPP) have been prepared by radical polymerization of the corresponding monomers.Visible spectra of these polymers show hypochromism in the Soret bands of TPP moieties as compared with those of monomers.Polymer effects were observed in the magnetic behavior and oxygen adsorption of paramagnetic metallotetraphenylporphyrin moieties.Moreover,polymer effects on photophysical and photophysical and photochemical behavior were found in the amphiphilic polymers covalently tethered with small amounts of zinc(II)-tetraphenylporphyrin(ZnTPP).
The inclusion complex formation of -CD, -CD, and -CD with various water-soluble polymers has beeninvestigated, and the relationship between the chain cross-sectional areas of the polymers and the diameters of the cavities ofcyclodextrins (molecular recognition) was found. Polyrotaxanes and tubular polymers were prepared on the basis ofmolecular recognition. Several kinds of polymers having tetraphenylporphyrin (TPP) and paramagnetic metallotetraphenyl-prophyrin (AgTTP,CuTPP,VOTPP or ZnTPP) have been prepared by radical polymerization of the corresponding monomers.Visible spectra of these polymers show hypochromism in the Soret bands of TPP moieties as compared with those of monomers.Polymer effects were observed in the magnetic behavior and oxygen adsorption of paramagnetic metallotetraphenylporphyrin moieties.Moreover,polymer effects on photophysical and photophysical and photochemical behavior were found in the amphiphilic polymers covalently tethered with small amounts of zinc(II)-tetraphenylporphyrin(ZnTPP).
2000, 18(3): 227-237
Abstract:
Fluorene-based alternating and statistical copolymers were synthesized by employing reaction methods of Wittig,Heck and Suzuki. The copolymers were classified into three groups with the photoluminescence (PL) emission maxima at420, 475 and 500 nm, respectively. Statistical copolymers with two chromophores having PL emission maxima at 420 and475 nm emitted light with the emission maximum at 475 nm on photoexcitation at 365 nm and improved the quantumefficiency by the energy transfer. However, the intramolecular energy transfer was inefficient compared to the intermolecular energy transfer when the two chromophores were apart from each other in the range of the Forster critical distance.Fluorene-pyridinedivinylene alternating copolymer was synthesized by the Wittig reaction and found to have physical,electronic and electrochemical properties of the individual units intact.The double-layered light emitting diode(LED) with the statistical copolymer as an emitting layer and the pyridine-containing copolymer as an electron transporting-hole blocking layer,which were sandwiched between ITO and Al,displayed a quantum efficiency of 0.1%.
Fluorene-based alternating and statistical copolymers were synthesized by employing reaction methods of Wittig,Heck and Suzuki. The copolymers were classified into three groups with the photoluminescence (PL) emission maxima at420, 475 and 500 nm, respectively. Statistical copolymers with two chromophores having PL emission maxima at 420 and475 nm emitted light with the emission maximum at 475 nm on photoexcitation at 365 nm and improved the quantumefficiency by the energy transfer. However, the intramolecular energy transfer was inefficient compared to the intermolecular energy transfer when the two chromophores were apart from each other in the range of the Forster critical distance.Fluorene-pyridinedivinylene alternating copolymer was synthesized by the Wittig reaction and found to have physical,electronic and electrochemical properties of the individual units intact.The double-layered light emitting diode(LED) with the statistical copolymer as an emitting layer and the pyridine-containing copolymer as an electron transporting-hole blocking layer,which were sandwiched between ITO and Al,displayed a quantum efficiency of 0.1%.
2000, 18(3): 239-248
Abstract:
Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanningviscoelasticity microscopic (SVM) and lateral force microscopic (LFM) measurements. SVM and LFM measurements werecarried out for films of conventional monodisperse polystyrene (PS) with sec-butyl and proton-terminated end groups atroom temperature. In the case of the number-average molecular weight, Mn, less than ca. 4.0×104, the surface was in a glass-rubber transition state even though the bulk glass transition temperature,Tg was far above room temperature,meaning that the surface molecular motion was fairly active compared with that in the bulk.LFM measurements of the monodisperse PS films at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to the surface mechanical relaxation behavior and also that the surface glass transition temperature,Tg,was depressed in comparison with the bulk one even though the magnitude of MN was fairly high at 1.40×105.The surface molecular motion of monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanning viscoelasticity microscopy (TDSVM).The tgσs for the PS films with Mn of 4.9 × 103 to 1.45×106 measured by TDSVM were smaller than those for the bulk one,with corresponding Ms,and the Tgσs for Mns smaller than ca.4.0 ×104 were lower than room temperature (293 K).The active thermal molecular motion at the polymeric solid surface can be interpreted in terms of an excess free volume near the surface region induced by the surface localization of chain end groups.In the case of Mn=ca.5.0×104,the Tgσs for the α,ω-diamino-terminated PS(α,ω-PS(COOH)2) films were higher than that of the PS film.The change of Tgσ for the PS film with warious chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region depending on the relative hydrophobicity.
Surface molecular motions of amorphous polymeric solids have been directly measured on the basis of scanningviscoelasticity microscopic (SVM) and lateral force microscopic (LFM) measurements. SVM and LFM measurements werecarried out for films of conventional monodisperse polystyrene (PS) with sec-butyl and proton-terminated end groups atroom temperature. In the case of the number-average molecular weight, Mn, less than ca. 4.0×104, the surface was in a glass-rubber transition state even though the bulk glass transition temperature,Tg was far above room temperature,meaning that the surface molecular motion was fairly active compared with that in the bulk.LFM measurements of the monodisperse PS films at various scanning rates and temperatures revealed that the time-temperature superposition was applicable to the surface mechanical relaxation behavior and also that the surface glass transition temperature,Tg,was depressed in comparison with the bulk one even though the magnitude of MN was fairly high at 1.40×105.The surface molecular motion of monodisperse PS with various chain end groups was investigated on the basis of temperature-dependent scanning viscoelasticity microscopy (TDSVM).The tgσs for the PS films with Mn of 4.9 × 103 to 1.45×106 measured by TDSVM were smaller than those for the bulk one,with corresponding Ms,and the Tgσs for Mns smaller than ca.4.0 ×104 were lower than room temperature (293 K).The active thermal molecular motion at the polymeric solid surface can be interpreted in terms of an excess free volume near the surface region induced by the surface localization of chain end groups.In the case of Mn=ca.5.0×104,the Tgσs for the α,ω-diamino-terminated PS(α,ω-PS(COOH)2) films were higher than that of the PS film.The change of Tgσ for the PS film with warious chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region depending on the relative hydrophobicity.
2000, 18(3): 249-254
Abstract:
Studies related to the behavior of different metallocene catalysts for the homopolymerization of 1-octadecene andits copolymerization with ethylene will be presented. The metallocenes: rac-Et(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2 andPh2C(Flu)(Cp)ZrCl2 were chosen for the homopolymerization study. They show important differences in catalytic activity athigh temperatures (≥70℃), with rac-Et(Ind)2ZrCl2 showing the highest activity. At lower temperatures (≤30℃) thedifferences are negligible. For the copolymerization of ethylene with 1-octadecene only the catalysts rac-Et(Ind)2ZrCl2 and rac-Me2Si(Ind)2ZrCl2 were studied.The results show that their catalytic activity is just like that for the homopolymerization of 1-octadecene,with higher activity for the metallocene with the Et-bridged catalyst.13C-NMR analysis shows that the composition of the copolymerization products depends on the catalytic systems.Copolymers obtained with rac-Me2Si(Ind)2ZrCl2 have greater comonomer incorporation.Thermal analysis shows that poly-1-octadecene synthesized with the catalyst rac-Et(Ind)2ZrCl2 is very dependent on the polymerization temperature.The homopolymer obtained at 70 ℃ presents two endothermal peaks at 41℃ and 53℃,as compared with the one obtained at 30℃ which presents one wider peak with a maximum at 67℃.For the catalyst rac-Me2Si(Ind)2ZrCl2 this trend is not observed.The type of metallocene and the reaction time do not significantly change the intrinsic viscosity,but the polymerization temperature changes it drastically,giving higher values at lower temperature.Viscosity measurements on the copolymers show that an increase of comonomer concentration in the feed reduces the molecular weight of the copolymer,and it was also found that for homopolymer,the molecular weight is independent of the catalytic systems.
Studies related to the behavior of different metallocene catalysts for the homopolymerization of 1-octadecene andits copolymerization with ethylene will be presented. The metallocenes: rac-Et(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2 andPh2C(Flu)(Cp)ZrCl2 were chosen for the homopolymerization study. They show important differences in catalytic activity athigh temperatures (≥70℃), with rac-Et(Ind)2ZrCl2 showing the highest activity. At lower temperatures (≤30℃) thedifferences are negligible. For the copolymerization of ethylene with 1-octadecene only the catalysts rac-Et(Ind)2ZrCl2 and rac-Me2Si(Ind)2ZrCl2 were studied.The results show that their catalytic activity is just like that for the homopolymerization of 1-octadecene,with higher activity for the metallocene with the Et-bridged catalyst.13C-NMR analysis shows that the composition of the copolymerization products depends on the catalytic systems.Copolymers obtained with rac-Me2Si(Ind)2ZrCl2 have greater comonomer incorporation.Thermal analysis shows that poly-1-octadecene synthesized with the catalyst rac-Et(Ind)2ZrCl2 is very dependent on the polymerization temperature.The homopolymer obtained at 70 ℃ presents two endothermal peaks at 41℃ and 53℃,as compared with the one obtained at 30℃ which presents one wider peak with a maximum at 67℃.For the catalyst rac-Me2Si(Ind)2ZrCl2 this trend is not observed.The type of metallocene and the reaction time do not significantly change the intrinsic viscosity,but the polymerization temperature changes it drastically,giving higher values at lower temperature.Viscosity measurements on the copolymers show that an increase of comonomer concentration in the feed reduces the molecular weight of the copolymer,and it was also found that for homopolymer,the molecular weight is independent of the catalytic systems.
2000, 18(3): 255-262
Abstract:
Nanostructure fabrication from block copolymers in my group normally involves polymer design, synthesis, self-assembly, selective domain crosslinking, and sometimes selective domain removal. Preparation of thin films withnanochannels was used to illustrate the strategy we took. In this particular case, a linear triblock copolymer polyisoprenc-block-poly(2-cinnamoylethyl methacrylate)-block-poly(t-butyl acrylate), PI-b-PCEMA-b-PtBA, was used. Films, 25 to50 μm thick, were prepared from casting on glass slides a toluene solution of PI-b-PCEMA-b-PtBA and PtBA homopolymer,hPtBA,where hPtBA is shorter than the PtBA block.At the hPtBA mass fraction of 20% relative to the triblock or the total PtBA (hPtBA and PtBA block) volume fraction of 0.44,hPtBA and PtBA formed a seemingly continuous phase in the matrix of PCEMA and PI.Such a block segregation pattern was locked in by photocrosslinking the PCEMA domain.Nanochannels were formed by extracting out hPtBA with solvent.Alternatively,larger channels were obtained from extracting out hPtBA and hydrolyzing the t-butyl groups of the PtBA block.Such membranes were not liquid permeable but had gas permeability constants-6 orders of magnitude higher than that of low-density polyethylene films.
Nanostructure fabrication from block copolymers in my group normally involves polymer design, synthesis, self-assembly, selective domain crosslinking, and sometimes selective domain removal. Preparation of thin films withnanochannels was used to illustrate the strategy we took. In this particular case, a linear triblock copolymer polyisoprenc-block-poly(2-cinnamoylethyl methacrylate)-block-poly(t-butyl acrylate), PI-b-PCEMA-b-PtBA, was used. Films, 25 to50 μm thick, were prepared from casting on glass slides a toluene solution of PI-b-PCEMA-b-PtBA and PtBA homopolymer,hPtBA,where hPtBA is shorter than the PtBA block.At the hPtBA mass fraction of 20% relative to the triblock or the total PtBA (hPtBA and PtBA block) volume fraction of 0.44,hPtBA and PtBA formed a seemingly continuous phase in the matrix of PCEMA and PI.Such a block segregation pattern was locked in by photocrosslinking the PCEMA domain.Nanochannels were formed by extracting out hPtBA with solvent.Alternatively,larger channels were obtained from extracting out hPtBA and hydrolyzing the t-butyl groups of the PtBA block.Such membranes were not liquid permeable but had gas permeability constants-6 orders of magnitude higher than that of low-density polyethylene films.
2000, 18(3): 263-270
Abstract:
Miscibility and crystallization have been studied for polypropylene-polyethylene and polyethylene-polyethyleneblends. In the case of the polypropylene blends the composition of interest is 20% polypropylene. At this composition thepolypropylene has been found to be soluble in linear low density polyethylene but insoluble in high, low and very lowdensity polyethylenes. The miscibility has been concluded from the crystallization kinetics and polarised optical microscopywith a hot stage. Polyethylene-polyethylene blends have been formed from polymers with similar average branching content but where they have different melting temperatures.Important consequences are to introduce long branches into a polyethylene taht only has short branches,and to modify the morphology of a polyethylenes so that haze,gloss and strain hardening are improved.Polyethylene blends must be developed after careful consideration of the branch content and distribution within each of the constituents.It is not sufficient to simply blend polyethylenes,with the desired range of properties,without regard to the miscibility of the blend composition.
Miscibility and crystallization have been studied for polypropylene-polyethylene and polyethylene-polyethyleneblends. In the case of the polypropylene blends the composition of interest is 20% polypropylene. At this composition thepolypropylene has been found to be soluble in linear low density polyethylene but insoluble in high, low and very lowdensity polyethylenes. The miscibility has been concluded from the crystallization kinetics and polarised optical microscopywith a hot stage. Polyethylene-polyethylene blends have been formed from polymers with similar average branching content but where they have different melting temperatures.Important consequences are to introduce long branches into a polyethylene taht only has short branches,and to modify the morphology of a polyethylenes so that haze,gloss and strain hardening are improved.Polyethylene blends must be developed after careful consideration of the branch content and distribution within each of the constituents.It is not sufficient to simply blend polyethylenes,with the desired range of properties,without regard to the miscibility of the blend composition.
2000, 18(3): 271-275
Abstract:
The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors ofthe hydrogels do not conform to Amonton's law F=μW which well describes the friction of solids. The frictional force andits dependence on the load are quite different depending on the chemical structures of the gels, surface properties of theopposing substrates, and the measurement condition. The gel friction is explained in terms of interracial interaction,either attractive or repulsive,between the polymer chain and the solid surface.According to this model,the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case.In the attractive case,the force to detach the adsorbing chain from the substrate appears as fricition.The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction,which supported the repulsion-adsorption model proposed by the authors.
The sliding friction of various kinds of hydrogels has been studied and it was found that the frictional behaviors ofthe hydrogels do not conform to Amonton's law F=μW which well describes the friction of solids. The frictional force andits dependence on the load are quite different depending on the chemical structures of the gels, surface properties of theopposing substrates, and the measurement condition. The gel friction is explained in terms of interracial interaction,either attractive or repulsive,between the polymer chain and the solid surface.According to this model,the friction is ascribed to the viscous flow of solvent at the interface in the repulsive case.In the attractive case,the force to detach the adsorbing chain from the substrate appears as fricition.The surface adhesion between glass particles and gels measured by AFM showed a good correlation with the friction,which supported the repulsion-adsorption model proposed by the authors.
