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1998 Volume 16 Issue 2
1998, 16(2): 97-105
Abstract:
The statistical counting method for the computer simulation of the ther-modynamic quantities of polymer solution has been reviewed. The calculating results fora single athermal chain confirm the theory of the renormalization group. The results forthe athermal solution are consistent with the scaling law of the osmotic pressure with theexponent 2.25. The results for a single chain with the segmental interaction are in a goodagreement with the exact results obtained by the direct counting method. The results for a single chain with the segmental interaction are in a good agreement with the exact results obtained by the direct counting method.The results for the polymer solution show us that the Flory-Huggins parameter is strongly dependent on both the polymer concentration and the interaction energy between segments.
The statistical counting method for the computer simulation of the ther-modynamic quantities of polymer solution has been reviewed. The calculating results fora single athermal chain confirm the theory of the renormalization group. The results forthe athermal solution are consistent with the scaling law of the osmotic pressure with theexponent 2.25. The results for a single chain with the segmental interaction are in a goodagreement with the exact results obtained by the direct counting method. The results for a single chain with the segmental interaction are in a good agreement with the exact results obtained by the direct counting method.The results for the polymer solution show us that the Flory-Huggins parameter is strongly dependent on both the polymer concentration and the interaction energy between segments.
1998, 16(2): 106-116
Abstract:
The oxidative polymerization of aryl sulfoxides provides a novel polysulfo-nium compound, poly(methylsulfonio-1,4-phenylenethio-1,4-phenylene cation) in quantita-tive yield. The polymerization proceeds efficiently in an acidic solution under atmosphericconditions. Oxygen, chemical and electrochemical oxidations are available. Vanadyl acety-lacetonate and cerium ammonium nitrate act as an effective catalyst for the oxygen ox-idative polymerization. The polymerization mechanism involves multielectron oxidation of the sulfides followed by successive electrophilic substitution.The resulting polyarylenesulfonium cations are useful as a soluble precursor for the synthesis of high molecular weight (Mw>105)poly(thio arylne)s.
The oxidative polymerization of aryl sulfoxides provides a novel polysulfo-nium compound, poly(methylsulfonio-1,4-phenylenethio-1,4-phenylene cation) in quantita-tive yield. The polymerization proceeds efficiently in an acidic solution under atmosphericconditions. Oxygen, chemical and electrochemical oxidations are available. Vanadyl acety-lacetonate and cerium ammonium nitrate act as an effective catalyst for the oxygen ox-idative polymerization. The polymerization mechanism involves multielectron oxidation of the sulfides followed by successive electrophilic substitution.The resulting polyarylenesulfonium cations are useful as a soluble precursor for the synthesis of high molecular weight (Mw>105)poly(thio arylne)s.
1998, 16(2): 117-125
Abstract:
Based on the property that carboxymethylcellulose (CMC ) can be de-graded to anhydroglucose residues by cellulase, the rate constant (K) of enzymatic degra-dation of CMC synthesized in the benzene-ethanol medium has been determined. Further-morel experimental equation K = 2.71× 10-2(DS)-1.2 reflecting the relationship betweenK and the degree of substitution (DS) is correlated and used to describe chemical mi-crostructure uniformity of the distribution of substituents along chains effectively. Chain structure parameters of enzymatic degradation products of CMC — the number of chain breaks and the percentage of glucose released have been also measured.Average length of substituted and unsubstituted chain segments are calculated simultaneously.Through the study of static and dynamic procedures of enzymatic degradation,the method to characterize the distribution of substituents of CMC along the chain has been improved.
Based on the property that carboxymethylcellulose (CMC ) can be de-graded to anhydroglucose residues by cellulase, the rate constant (K) of enzymatic degra-dation of CMC synthesized in the benzene-ethanol medium has been determined. Further-morel experimental equation K = 2.71× 10-2(DS)-1.2 reflecting the relationship betweenK and the degree of substitution (DS) is correlated and used to describe chemical mi-crostructure uniformity of the distribution of substituents along chains effectively. Chain structure parameters of enzymatic degradation products of CMC — the number of chain breaks and the percentage of glucose released have been also measured.Average length of substituted and unsubstituted chain segments are calculated simultaneously.Through the study of static and dynamic procedures of enzymatic degradation,the method to characterize the distribution of substituents of CMC along the chain has been improved.
1998, 16(2): 126-132
Abstract:
The polymerization mechanism is described by the conductance changewith the time during the polymerization. The mechanism can be explained by the equi-librium feature (i.e. main ion-pairs) between the free ions and the ion-pairs dissociated bythe organic salt (-) Sp*+ (+) CSA*- (An asterisk represents the chirality) and the schemeof the polymerization process is described mainly by the charge transfer complexes havingchiral induction power.
The polymerization mechanism is described by the conductance changewith the time during the polymerization. The mechanism can be explained by the equi-librium feature (i.e. main ion-pairs) between the free ions and the ion-pairs dissociated bythe organic salt (-) Sp*+ (+) CSA*- (An asterisk represents the chirality) and the schemeof the polymerization process is described mainly by the charge transfer complexes havingchiral induction power.
1998, 16(2): 133-141
Abstract:
Based on perfect rotational isomeric state model of polyethylene chainwithout any torsional stretch or chain twisting, the separation distance between a zig-zagsegment and its re-entry ones in lamella has been investigated. The intervals were definedby a pair of quantum numbers (kx, ky) according to the formula: D=0.153/(31/2)((8kx2+16ly2)1/2)(nm)kx and ky are integers just as the lattice coordinates on the respective & and α- axes ofthe crystal lattices for polyethylene. The crystal lattices of polyethylene can be accessible by the re-entry stems,whether it is adjacent fold or not.Conformations,until 14-bond fold,of the fold part were investigated.The sequence TTGTTG'G'TTGGTTG possesses the lowest average conformation energy per bond for (110) fold,and TGTTG'G'TTTG' for (020) fold.TTTGGTGGTTGTG'etc.for(200) fold.
Based on perfect rotational isomeric state model of polyethylene chainwithout any torsional stretch or chain twisting, the separation distance between a zig-zagsegment and its re-entry ones in lamella has been investigated. The intervals were definedby a pair of quantum numbers (kx, ky) according to the formula: D=0.153/(31/2)((8kx2+16ly2)1/2)(nm)kx and ky are integers just as the lattice coordinates on the respective & and α- axes ofthe crystal lattices for polyethylene. The crystal lattices of polyethylene can be accessible by the re-entry stems,whether it is adjacent fold or not.Conformations,until 14-bond fold,of the fold part were investigated.The sequence TTGTTG'G'TTGGTTG possesses the lowest average conformation energy per bond for (110) fold,and TGTTG'G'TTTG' for (020) fold.TTTGGTGGTTGTG'etc.for(200) fold.
1998, 16(2): 142-146
Abstract:
Papain (Papainase, EC 3.4.22.2) was immobilized on porous silica beadsby cross linking with glutaraldehyde. The thermal activation of this immobilized papainin aqueous system was found at a temperature range from 50 to 90℃. The higher thetemperature, the more active the immobilized papain will possess. At the same time,the durability of the immobilized papain on heating was greatly improved. The effect ofadditives and salts on the activity of the immobilized papain were also studied. The results showed that the additives and some of the salts studied could markedly enhance the activity of the immobilized papain at elevated temperature.
Papain (Papainase, EC 3.4.22.2) was immobilized on porous silica beadsby cross linking with glutaraldehyde. The thermal activation of this immobilized papainin aqueous system was found at a temperature range from 50 to 90℃. The higher thetemperature, the more active the immobilized papain will possess. At the same time,the durability of the immobilized papain on heating was greatly improved. The effect ofadditives and salts on the activity of the immobilized papain were also studied. The results showed that the additives and some of the salts studied could markedly enhance the activity of the immobilized papain at elevated temperature.
1998, 16(2): 147-154
Abstract:
The dynamic elasticity of linoleic acid monolayer on a subphase of10-4mol/L TbCl3 at various surface pressure has been measured by means of dynamic oscil-lation method in measuring the change of surface pressure caused by periodic compression-expansion cycles of the barrier. The elasticity of monolayer increases with increasing ofsurface pressure linearly. The linoleic acid polymer monolayer has been obtained underUV-irradiation in situ when keeping a constant surface pressure. But the elasticity of the resulting polymerized monolayer is even smaller than that of its corresponding monomer monolayer.The elasticity of the polymerized linoleic acid monolayer decreases with increasing polymerization time.The explanation based on entropy has been presented.
The dynamic elasticity of linoleic acid monolayer on a subphase of10-4mol/L TbCl3 at various surface pressure has been measured by means of dynamic oscil-lation method in measuring the change of surface pressure caused by periodic compression-expansion cycles of the barrier. The elasticity of monolayer increases with increasing ofsurface pressure linearly. The linoleic acid polymer monolayer has been obtained underUV-irradiation in situ when keeping a constant surface pressure. But the elasticity of the resulting polymerized monolayer is even smaller than that of its corresponding monomer monolayer.The elasticity of the polymerized linoleic acid monolayer decreases with increasing polymerization time.The explanation based on entropy has been presented.
1998, 16(2): 155-163
Abstract:
A series of slightly crosslinked polyethylenes (SXLPE) was prepared by aone-step method using dicumyl peroxide as crosslinking agent in a Haake Mixer. The gelcontents G (Soxhlet extracted) of the samples are in the range from 5% to 20% by weight.Their shear viscosity, crystallization and melting behavior, dynamic mechanical propertiesand shape recovery effect were systematically investigated in terms of the content of thecrosslinking agent. It shows that under certain experimental conditions the SXLPE's may exhibit good shape fixation ability and shape memory properties,which are similar to those of the commercially available shape memory polyethylenes prepared by gamma-irradiation technique.However the shape memory behavior of these samples is not very stable due to their low crosslinking degree,or gel content.Thus their application is limited in special cases with fast strain fixing procedures.
A series of slightly crosslinked polyethylenes (SXLPE) was prepared by aone-step method using dicumyl peroxide as crosslinking agent in a Haake Mixer. The gelcontents G (Soxhlet extracted) of the samples are in the range from 5% to 20% by weight.Their shear viscosity, crystallization and melting behavior, dynamic mechanical propertiesand shape recovery effect were systematically investigated in terms of the content of thecrosslinking agent. It shows that under certain experimental conditions the SXLPE's may exhibit good shape fixation ability and shape memory properties,which are similar to those of the commercially available shape memory polyethylenes prepared by gamma-irradiation technique.However the shape memory behavior of these samples is not very stable due to their low crosslinking degree,or gel content.Thus their application is limited in special cases with fast strain fixing procedures.
1998, 16(2): 164-169
Abstract:
Hydrophobically modified poly(4-vinyl pyridines) by alkyl bromides arekinds of polysoap similar to the surfactant. Properties of dilute solutions were studiedthrough the viscosity measurements in pure water and NaCl solutions. In aqueous solu-tions of polysoaps hydrophobic interaction can be attributed to aggregation of hydrophobicgroups of the polysoap main chains. The hydrophobic groups of polysoap can aggregate toform hydrophobic microdomains (micelles) in aqueous solution. This is a compact confor-mation.The formation of such microdomains is a process of dynamic equilibrium.
Hydrophobically modified poly(4-vinyl pyridines) by alkyl bromides arekinds of polysoap similar to the surfactant. Properties of dilute solutions were studiedthrough the viscosity measurements in pure water and NaCl solutions. In aqueous solu-tions of polysoaps hydrophobic interaction can be attributed to aggregation of hydrophobicgroups of the polysoap main chains. The hydrophobic groups of polysoap can aggregate toform hydrophobic microdomains (micelles) in aqueous solution. This is a compact confor-mation.The formation of such microdomains is a process of dynamic equilibrium.
1998, 16(2): 170-175
Abstract:
A fully characterised natural rubber latex was subjected to mechanicaldegradation by stirring at intervals. The resistance to oxidative degradation of the differentsamples were studied by measuring the Plasticity retention indices (PRI). The results show that there is an enhancement of the PRI from 57% for the undegradedrubber to 79% for the one-hour degraded sample. Further degradation resulted in decreaseof PRI as time of degradation increased. Therefore, the one-hour degraded sample is aspecial rubber with high oxidation resistance which is of great importance in engineering.
A fully characterised natural rubber latex was subjected to mechanicaldegradation by stirring at intervals. The resistance to oxidative degradation of the differentsamples were studied by measuring the Plasticity retention indices (PRI). The results show that there is an enhancement of the PRI from 57% for the undegradedrubber to 79% for the one-hour degraded sample. Further degradation resulted in decreaseof PRI as time of degradation increased. Therefore, the one-hour degraded sample is aspecial rubber with high oxidation resistance which is of great importance in engineering.
1998, 16(2): 176-184
Abstract:
The physical aging behavior of atactic polystyrene (aPS) films achievedunder different drawing conditions has been studied by optical birefringence and modulatedifferential scanning calorimeter (m.d.s.c.). The results show that on annealing at specifictemperature below glass transition temperatue (Tg), the enthalpy relaxation (△H) and Tg decrease with increasing of birefringence (△n). On the other hand, the effect of moleculardraw ratio (MDR) is confusing: △H and Tg decrease with increasing of MDR in the early stage of aging,but the MDR's effect become unobvious with the development of aging. It may be concluded that the ordered domain generated by the drawing below or above glass transition temperature will affect the development of physical aging behavior.The viewpoint of cohesional entanglement is used to account for the above observations.
The physical aging behavior of atactic polystyrene (aPS) films achievedunder different drawing conditions has been studied by optical birefringence and modulatedifferential scanning calorimeter (m.d.s.c.). The results show that on annealing at specifictemperature below glass transition temperatue (Tg), the enthalpy relaxation (△H) and Tg decrease with increasing of birefringence (△n). On the other hand, the effect of moleculardraw ratio (MDR) is confusing: △H and Tg decrease with increasing of MDR in the early stage of aging,but the MDR's effect become unobvious with the development of aging. It may be concluded that the ordered domain generated by the drawing below or above glass transition temperature will affect the development of physical aging behavior.The viewpoint of cohesional entanglement is used to account for the above observations.
1998, 16(2): 185-192
Abstract:
Two acetylene polymers containing cyanobiphenyl-based mesogens,poly { 10-[ ((4'- cyano-4-biphenylyl ) oxy ) carbonyl] - 1 -decyne } (PA8CN ), which has a relativelyfiexible polyalkyne backbone, and poly {[4-(((12-((4'-cyano-4-biphenylyl)oxy)dodecyl)oxy)carbonyl) phenyl]-acetylene} (PB12CN), which has a fairly rigid poly (phenylacetylene )backbone, were synthesized using respectively WCl6 and [Rh(nbd)Cl]2 as the catalysts.PA8CN exhibits enantiotropic interdigitated smectic A phase (SAd) over a temperature range as wide as ca.100℃,whereas PB12CN is non-mesomorphic,demonstrating that the backbone rigidity plays an important role in determining the liquid crystallinity of the polyacetylenes.
Two acetylene polymers containing cyanobiphenyl-based mesogens,poly { 10-[ ((4'- cyano-4-biphenylyl ) oxy ) carbonyl] - 1 -decyne } (PA8CN ), which has a relativelyfiexible polyalkyne backbone, and poly {[4-(((12-((4'-cyano-4-biphenylyl)oxy)dodecyl)oxy)carbonyl) phenyl]-acetylene} (PB12CN), which has a fairly rigid poly (phenylacetylene )backbone, were synthesized using respectively WCl6 and [Rh(nbd)Cl]2 as the catalysts.PA8CN exhibits enantiotropic interdigitated smectic A phase (SAd) over a temperature range as wide as ca.100℃,whereas PB12CN is non-mesomorphic,demonstrating that the backbone rigidity plays an important role in determining the liquid crystallinity of the polyacetylenes.
