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1999 Volume 17 Issue 2
1999, 17(2): 99-111
Abstract:
The complexation of thiophene with a Lewis acid with moderate acidity as a solvent, such as BF_3-ethyl ether (BFEE) remarkedly lowered the electrochemical polymerization potential. The positively chargedmetal surface of electrode in the process of electrochemical deposition enhanced the coordination interactionbetween π-electrons of thiophene unit and the metal, which makes thiophene rings lie parallel to the surfaceof electrode, resulting in a highly ordered polymeric structure. Because of the large intra-chain transfer integrals,the transport of charge is believed to be principally along the conjugated chains,which is much greater than the inter-chain hopping.The specific electrical resistance across the polythiophene film thickness is more than 104 times than that along the surface plane of the film.In this paper we review the recent development of polymerization technique by low potential electrochemical method performed in our lab and several electrical devices in which the compact polythiophene films,such as anionic and cationic sieves,and laminate film junction of undoped polythiophene derivaties were used.
The complexation of thiophene with a Lewis acid with moderate acidity as a solvent, such as BF_3-ethyl ether (BFEE) remarkedly lowered the electrochemical polymerization potential. The positively chargedmetal surface of electrode in the process of electrochemical deposition enhanced the coordination interactionbetween π-electrons of thiophene unit and the metal, which makes thiophene rings lie parallel to the surfaceof electrode, resulting in a highly ordered polymeric structure. Because of the large intra-chain transfer integrals,the transport of charge is believed to be principally along the conjugated chains,which is much greater than the inter-chain hopping.The specific electrical resistance across the polythiophene film thickness is more than 104 times than that along the surface plane of the film.In this paper we review the recent development of polymerization technique by low potential electrochemical method performed in our lab and several electrical devices in which the compact polythiophene films,such as anionic and cationic sieves,and laminate film junction of undoped polythiophene derivaties were used.
1999, 17(2): 113-122
Abstract:
The synthesis and characterization of amphiphilic copolymers of poly(dimethyl siloxane)(PDMS),poly(ethylene oxide)(PEO), and heparin(Hep) were investigated. These multiblock copolymers wereidentified using 1H-NMR, FTIR, end group analysis, and sulfur elemental analysis. The multiblockcopolymers were characterized by using DSC and X-ray diffractometry. The glass transition temperature,crystalline melting characteristics, annealing effect, and cold crystallization of the block copolymers weredetermined by DSC.The crystallinity of the block copolymers was also determined by X-ray diffraction method.
The synthesis and characterization of amphiphilic copolymers of poly(dimethyl siloxane)(PDMS),poly(ethylene oxide)(PEO), and heparin(Hep) were investigated. These multiblock copolymers wereidentified using 1H-NMR, FTIR, end group analysis, and sulfur elemental analysis. The multiblockcopolymers were characterized by using DSC and X-ray diffractometry. The glass transition temperature,crystalline melting characteristics, annealing effect, and cold crystallization of the block copolymers weredetermined by DSC.The crystallinity of the block copolymers was also determined by X-ray diffraction method.
1999, 17(2): 123-128
Abstract:
New highly stereoregular 2, 3 -di- O-(p-azidobenzyl )-(1 →5 ) - α-D -ribofuranan was synthesized byselective ring-opening polymerization of 1, 4-anhydro-2, 3 - di-O -(p-azidobenzyl )-α-D -ribopyranose(ADABR) using phosphorus pentafluoride or tin tetrachloride as catalyst at low temperature indichloromethane. The monomer was obtained by the reaction of p - bromomethyl -phenyleneazide with 1, 4 -anhydro-α-D-ribose in DMF. The structure of poly(ADANR) was identified by specific rotation and 13C-NMR spectroscopy.Acid chloride-AgCl4 complex catalyst such as CH2=C(CH3)C+OClO4- used in the polymerization resulted in polymers with mixed stryctures,i.e.(1→5)-α-D-ribofuranosidic and (1→4)-β-D-ribopyranosidic units.However,with C6H5C+OClO4- as catalyst,pure(1→5)-α-D-ribofuranan was obtained.The effects of catalyst,polymerization temperature and time on polymer stereoregularity were examined,and the mechanism of the ring-opning polymerization was discussed.
New highly stereoregular 2, 3 -di- O-(p-azidobenzyl )-(1 →5 ) - α-D -ribofuranan was synthesized byselective ring-opening polymerization of 1, 4-anhydro-2, 3 - di-O -(p-azidobenzyl )-α-D -ribopyranose(ADABR) using phosphorus pentafluoride or tin tetrachloride as catalyst at low temperature indichloromethane. The monomer was obtained by the reaction of p - bromomethyl -phenyleneazide with 1, 4 -anhydro-α-D-ribose in DMF. The structure of poly(ADANR) was identified by specific rotation and 13C-NMR spectroscopy.Acid chloride-AgCl4 complex catalyst such as CH2=C(CH3)C+OClO4- used in the polymerization resulted in polymers with mixed stryctures,i.e.(1→5)-α-D-ribofuranosidic and (1→4)-β-D-ribopyranosidic units.However,with C6H5C+OClO4- as catalyst,pure(1→5)-α-D-ribofuranan was obtained.The effects of catalyst,polymerization temperature and time on polymer stereoregularity were examined,and the mechanism of the ring-opning polymerization was discussed.
1999, 17(2): 129-134
Abstract:
Fe3O4/Polystyrene(PSt) magnetic particles with core/shell structure have been prepared in thepresence of Fe3O4 magnetic fluid in ethanol/water medium by dispersion polymeriation of styrene. A Fe3O4particle formation mechanism was proposed. According to this mechanism, the size of particle nuclei isdetermined by the extent of aggregation of Fe3O4 /oligomer. Magnetic particles with diameter ranging from 5to 200 μm were prepared under different reaction conditions. Some polymerization parameters such as the concentration of monomer,stabilizer,initiator,and ethanol which affect particle size and size distribution are discussed and their effect on particle formation are explained by the proposed mechanism.
Fe3O4/Polystyrene(PSt) magnetic particles with core/shell structure have been prepared in thepresence of Fe3O4 magnetic fluid in ethanol/water medium by dispersion polymeriation of styrene. A Fe3O4particle formation mechanism was proposed. According to this mechanism, the size of particle nuclei isdetermined by the extent of aggregation of Fe3O4 /oligomer. Magnetic particles with diameter ranging from 5to 200 μm were prepared under different reaction conditions. Some polymerization parameters such as the concentration of monomer,stabilizer,initiator,and ethanol which affect particle size and size distribution are discussed and their effect on particle formation are explained by the proposed mechanism.
1999, 17(2): 135-140
Abstract:
13C-NMR 1H-decoupled spectra of styrene polymers were assigned by comparison with modelcompounds, then used in measurements of number average molecular weights. The higher limit of an exactdetermination of the end group signal is less than a molecular weight of 104. For polymer samples withMn3, the results obtained from 13C-NMR spectra of saturated carbon region are in excellent agreementwith the values determined by 1H-NMR, SEC, and VPO methods, while the results from 13C-NMR spectra of phenyl C-1 carbon region are somewhta higher than the values determined by other methods.
13C-NMR 1H-decoupled spectra of styrene polymers were assigned by comparison with modelcompounds, then used in measurements of number average molecular weights. The higher limit of an exactdetermination of the end group signal is less than a molecular weight of 104. For polymer samples withMn3, the results obtained from 13C-NMR spectra of saturated carbon region are in excellent agreementwith the values determined by 1H-NMR, SEC, and VPO methods, while the results from 13C-NMR spectra of phenyl C-1 carbon region are somewhta higher than the values determined by other methods.
1999, 17(2): 141-144
Abstract:
Metallocene based polyethylenes were prepared by SINOPEC's "metallocene adduct" technologyin a gas phase fluidized bed model reactor. The 13C-NMR spectra of ethylene/1 -butene (S-34) and ethylene/1-hexene(S-43) copolymers were studied in a manner analogous to that established by Hsieh and Cheng. Thecomonomer sequence distributions of copolymer samples were obtained. The results show that thesemetallocene based copolymers contain a small amount of butene and hexene, and the EE and EEE sequencesare dominant.
Metallocene based polyethylenes were prepared by SINOPEC's "metallocene adduct" technologyin a gas phase fluidized bed model reactor. The 13C-NMR spectra of ethylene/1 -butene (S-34) and ethylene/1-hexene(S-43) copolymers were studied in a manner analogous to that established by Hsieh and Cheng. Thecomonomer sequence distributions of copolymer samples were obtained. The results show that thesemetallocene based copolymers contain a small amount of butene and hexene, and the EE and EEE sequencesare dominant.
1999, 17(2): 145-150
Abstract:
By mechanism-transformation (anionic→ cationic) poly(styrene- b-2-ethyl -2-oxazoline) diblockcopolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene blockcapped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as 1H-NMR, IR,DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight and narrow molecular weight distributio.
By mechanism-transformation (anionic→ cationic) poly(styrene- b-2-ethyl -2-oxazoline) diblockcopolymer, PS-b-PEOx, was synthesized in two steps. The first step is the polymerization of styrene blockcapped with ethylene oxide and its tosylation; the second step is the cationic ring-opening polymerization of2-ethyl-2-oxazoline. The products were thoroughly characterized by various methods, such as 1H-NMR, IR,DMA, TEM and SAXS. The results show that the copolymer obtained possesses high molecular weight and narrow molecular weight distributio.
1999, 17(2): 151-158
Abstract:
Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymerchain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense incontinuum mechanics. A power law dependence of shear modulus of polymer melts on detC, referred to asenvelope volume, is proposed. Based on those assumptions and the non-linear relation of shear modulus, aphenomenological viscoelastic model is derived. The model is tested in simple shear flow, simple elongational flow,oscillatory shear flow,and relaxation process after flow suddenly stopped.The results show that the model works well to predict the change of internal structure and viscoelastic performance of polymer melts in flow fields.
Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymerchain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense incontinuum mechanics. A power law dependence of shear modulus of polymer melts on detC, referred to asenvelope volume, is proposed. Based on those assumptions and the non-linear relation of shear modulus, aphenomenological viscoelastic model is derived. The model is tested in simple shear flow, simple elongational flow,oscillatory shear flow,and relaxation process after flow suddenly stopped.The results show that the model works well to predict the change of internal structure and viscoelastic performance of polymer melts in flow fields.
1999, 17(2): 159-163
Abstract:
The morphological characterizations of poly(N -vinylcarbazole)(PVCZ) obtained by asymmetricallystereoselective polymerization were studied using x-ray diffraction pattern, DSC and GPC. The results showthat the PVCZs have lower crystallinities (11.0～18.6%) and lower melting heats (2.2～7.5 J/g), but thedegree of crystallinities of the PVCZ samples obtained using the organic salts (acid) with chiral orstereodifferentiating ligands are higher than that using radical and general protonic initiator. It has shown that the crystallization is directly related to the pecking density of the hexagonal array of the rodlike molecules formed from the helical chain.
The morphological characterizations of poly(N -vinylcarbazole)(PVCZ) obtained by asymmetricallystereoselective polymerization were studied using x-ray diffraction pattern, DSC and GPC. The results showthat the PVCZs have lower crystallinities (11.0～18.6%) and lower melting heats (2.2～7.5 J/g), but thedegree of crystallinities of the PVCZ samples obtained using the organic salts (acid) with chiral orstereodifferentiating ligands are higher than that using radical and general protonic initiator. It has shown that the crystallization is directly related to the pecking density of the hexagonal array of the rodlike molecules formed from the helical chain.
1999, 17(2): 165-1170
Abstract:
Poly(aniline- co-o-aminobenzenesulfonic acid) (PAOABSA) as a water soluble conducting polymerwas synthesized by chemical polymerization. The productivity and the room-temperature conductivity of thecopolymer were measured as a function of the reaction conditions, such as reaction temperature, the ratio ofoxidant to monomer and the degree of sulfonation defined as the ratio of sulfur to nitrogen atoms(S/N). Themain results obtained are summarized as follows : (1) lower reaction temperature (at about 0℃) is favorable for the enhancement of the room-temperature conductivity of the copolymer;(2)higher content of oxidant is unfavorable for increasing the room-temperature conductivity of the copolymer;(3)both productivity and room-temperature conductivity of the copolymer decrease with increase of the degree of sulfonation which was always lower than 0.5 even an excess of ο-aminobenzenesulfonic acid was added,probably because the reactivity ratio of aniline (γ1=2.99±0.05)is much higher than that of ο-aminobenzenesulfonic acid(γ2=0.06±0.02) estimated by using Fineman-Ross method and least square method.
Poly(aniline- co-o-aminobenzenesulfonic acid) (PAOABSA) as a water soluble conducting polymerwas synthesized by chemical polymerization. The productivity and the room-temperature conductivity of thecopolymer were measured as a function of the reaction conditions, such as reaction temperature, the ratio ofoxidant to monomer and the degree of sulfonation defined as the ratio of sulfur to nitrogen atoms(S/N). Themain results obtained are summarized as follows : (1) lower reaction temperature (at about 0℃) is favorable for the enhancement of the room-temperature conductivity of the copolymer;(2)higher content of oxidant is unfavorable for increasing the room-temperature conductivity of the copolymer;(3)both productivity and room-temperature conductivity of the copolymer decrease with increase of the degree of sulfonation which was always lower than 0.5 even an excess of ο-aminobenzenesulfonic acid was added,probably because the reactivity ratio of aniline (γ1=2.99±0.05)is much higher than that of ο-aminobenzenesulfonic acid(γ2=0.06±0.02) estimated by using Fineman-Ross method and least square method.
1999, 17(2): 171-184
Abstract:
In order to improve the processibility in thermoplastic polyimides, a new method, termed the"reactive plasticizer" approach, has been proposed. This method uses a small amount (5～15 mol%) of a lessactivated, weak nucleophilic diamine co-monomer as a "reactive plasticizer" to obtain copolyimide resinswhich possess relatively low viscosity at low temperatures and can be readily processed through the autoclavecycle at low pressures. During a high temperature treatment, the reactive plasticizers join the reaction to form high molecular weight copolyimides,and the preferred material properties are thus achieved.The most effective reactive plasticizer is aromatic heterocyclic diamines,such as 2,6-diaminopyridine diamine (DAP),and the transimidization involved with a reactive plasticizer has been proposed to play a major role for the success of this approach.In order to understand the transimidization mechanism,three steps have been taken in this research:first,a copolyimide system of 50% of DAP and 50% 1,4-bis[4-aminophenoxy]benzene diamine (DODA) with 100% of 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride (Ultem DA) is prepared.Second,several specifically designed polyimide mixture systems were used,and they consist of two homopolyimides:one is Ultem DA-DODA,and the other is Ultem DA-DAP.The third step is to investigate two mixture systems in which Ultem DA-DODA is mixed with DAP monomer solution and Ultem DA-DAP is mixed with DODA monomer solution.For all systems,with increasing degree of transimidization upon heat-treatment,the chain structures and their thermal and dynamic mechanical transition behaviors are investigated via one-dimensional and two-dimensional nuclear magnetic resonance,differential scanning calorimetry,and dynamic mechanical analysis experiments.Experimental results indicate that in the mixture of two homopolyimides,transimidization takes place much more effciently in solution than in the melt.For the two mixtures with monomer solutions,the transimidization can only be found in the mixture of Ultem DAP/DODA system in p-chlorophenol,and this process does not effectively occur in the Ultem DODA/DAP system in p-chlorophenol,indicating that free DODA can efficiently attack the imide linkage of Ultem DA-DAP.The final product resulting form the transimidization in the mixtures is a random copolyimide with a major population of DAP as end groups for the copolymer system.
In order to improve the processibility in thermoplastic polyimides, a new method, termed the"reactive plasticizer" approach, has been proposed. This method uses a small amount (5～15 mol%) of a lessactivated, weak nucleophilic diamine co-monomer as a "reactive plasticizer" to obtain copolyimide resinswhich possess relatively low viscosity at low temperatures and can be readily processed through the autoclavecycle at low pressures. During a high temperature treatment, the reactive plasticizers join the reaction to form high molecular weight copolyimides,and the preferred material properties are thus achieved.The most effective reactive plasticizer is aromatic heterocyclic diamines,such as 2,6-diaminopyridine diamine (DAP),and the transimidization involved with a reactive plasticizer has been proposed to play a major role for the success of this approach.In order to understand the transimidization mechanism,three steps have been taken in this research:first,a copolyimide system of 50% of DAP and 50% 1,4-bis[4-aminophenoxy]benzene diamine (DODA) with 100% of 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl] propane dianhydride (Ultem DA) is prepared.Second,several specifically designed polyimide mixture systems were used,and they consist of two homopolyimides:one is Ultem DA-DODA,and the other is Ultem DA-DAP.The third step is to investigate two mixture systems in which Ultem DA-DODA is mixed with DAP monomer solution and Ultem DA-DAP is mixed with DODA monomer solution.For all systems,with increasing degree of transimidization upon heat-treatment,the chain structures and their thermal and dynamic mechanical transition behaviors are investigated via one-dimensional and two-dimensional nuclear magnetic resonance,differential scanning calorimetry,and dynamic mechanical analysis experiments.Experimental results indicate that in the mixture of two homopolyimides,transimidization takes place much more effciently in solution than in the melt.For the two mixtures with monomer solutions,the transimidization can only be found in the mixture of Ultem DAP/DODA system in p-chlorophenol,and this process does not effectively occur in the Ultem DODA/DAP system in p-chlorophenol,indicating that free DODA can efficiently attack the imide linkage of Ultem DA-DAP.The final product resulting form the transimidization in the mixtures is a random copolyimide with a major population of DAP as end groups for the copolymer system.
1999, 17(2): 185-188
Abstract:
Several supported zirconocene catalysts were prepared by using MgCl2·6H2O as a precursor forproducing an active support. Such catalysts combined with methylaluminoxane (MAO) obtained by reactingMgCl2·6H2O with AlMe3 show good activity for ethylene polymerization similar to that of anhydrousMgCl2 supported zirconocene catalyst.
Several supported zirconocene catalysts were prepared by using MgCl2·6H2O as a precursor forproducing an active support. Such catalysts combined with methylaluminoxane (MAO) obtained by reactingMgCl2·6H2O with AlMe3 show good activity for ethylene polymerization similar to that of anhydrousMgCl2 supported zirconocene catalyst.
1999, 17(2): 189-192
Abstract:
The first TEMPO-mediated "living" free radical polymerization of liquid crystallinemonomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene(MPCS), was carried out at 130℃ withBPO as an initiator. The molecular weight of the polymer can be varied from rather low values to highvalues while maintaining narrow polydispersity. It was observed that the polymerization of MPCSproceeded much faster than that of styrene. A tentative explanation for this fast polymerization wassuggested.
The first TEMPO-mediated "living" free radical polymerization of liquid crystallinemonomer, 2, 5-bis[(4-methoxyphenyl)oxycarbonyl]styrene(MPCS), was carried out at 130℃ withBPO as an initiator. The molecular weight of the polymer can be varied from rather low values to highvalues while maintaining narrow polydispersity. It was observed that the polymerization of MPCSproceeded much faster than that of styrene. A tentative explanation for this fast polymerization wassuggested.
1999, 17(2): 193-196
Abstract:
Some diacetylene-containing copolyesters with different ratios of dipropargyl 1,10-decanate anddipropargyl terephthalate were synthesized. Properties of these copolymers were characterized by differentialscanning calorimetry and polarizing optical microscopy. The copolymer could be cross-linked easily by UVirradiation in a liquid crystal matrix without adding any photoinitiator. The preliminary studies showed thatthe diacetylene-containing polymer network can assist liquid crystal molecules to align with the external electric field,thus reducing the response time of display devices.
Some diacetylene-containing copolyesters with different ratios of dipropargyl 1,10-decanate anddipropargyl terephthalate were synthesized. Properties of these copolymers were characterized by differentialscanning calorimetry and polarizing optical microscopy. The copolymer could be cross-linked easily by UVirradiation in a liquid crystal matrix without adding any photoinitiator. The preliminary studies showed thatthe diacetylene-containing polymer network can assist liquid crystal molecules to align with the external electric field,thus reducing the response time of display devices.
