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1965 Volume 7 Issue 2
1965, 7(2): 79-84
Abstract:
Ten benzene and substituted benzene diazonium fluoroborates were synthesized and obtained in colourless crystalline form. These compounds with Mohr's salt containing small amount of copper ion as impurity were used as redox initiator for the polymerizations of acrylonitrile in aqueous solution. Rates of polymerization initiated by different substituted benzene diazonium fluoroborates were studied. Results show that the rate of polymerization with different substituents could be correlated by the Hammett equa-tion.
Ten benzene and substituted benzene diazonium fluoroborates were synthesized and obtained in colourless crystalline form. These compounds with Mohr's salt containing small amount of copper ion as impurity were used as redox initiator for the polymerizations of acrylonitrile in aqueous solution. Rates of polymerization initiated by different substituted benzene diazonium fluoroborates were studied. Results show that the rate of polymerization with different substituents could be correlated by the Hammett equa-tion.
1965, 7(2): 85-95
Abstract:
The effects of irradiation atmosphere，irradiation dose，and heating rate upon the thermoluminescence of γ-irradiated polyethylene sheet were studied． It is found that off the glow curve there appear three main peaks between 77°K and 273°K with irradiation doses up to 9×105 rads，but the number of peaks is reduced to two as the dose is in-creased to or over 2×106 rads．At low irradiation dose,the effect of oxygen is pro-nounced，while peak I (the low temperature peak) seems to remain unchanged．Furthermore．an endothermal peak with its temperature location close to glow peak I，is observed on the DTA (differential thermal analysis) diagram of an irradia'ted poly- ethylene powder sample．Contrary to the glow peaks，this endothermal peak disappears after repeated irradiation，even on repeated DTA testing．This indicates that the glow peak I and the endothermal peak are of different origin．but it is considered that the factors determining the temperature locations for the appearance of these two peaks might be the same．By separating the main peaks from each other，the values of activation energy for peak I and III have been determined to be 0.22 eV and 1.2 eV respectively．However．the value for peak III is nearly identical with that obtained by the method of changing heating rate，while the difference between the values for peak I is fairly large．By tom-paring the experimental curve with the calculated ones，it is shown that the results ob-tained by the peak-separating method is more reasonable．
The effects of irradiation atmosphere，irradiation dose，and heating rate upon the thermoluminescence of γ-irradiated polyethylene sheet were studied． It is found that off the glow curve there appear three main peaks between 77°K and 273°K with irradiation doses up to 9×105 rads，but the number of peaks is reduced to two as the dose is in-creased to or over 2×106 rads．At low irradiation dose,the effect of oxygen is pro-nounced，while peak I (the low temperature peak) seems to remain unchanged．Furthermore．an endothermal peak with its temperature location close to glow peak I，is observed on the DTA (differential thermal analysis) diagram of an irradia'ted poly- ethylene powder sample．Contrary to the glow peaks，this endothermal peak disappears after repeated irradiation，even on repeated DTA testing．This indicates that the glow peak I and the endothermal peak are of different origin．but it is considered that the factors determining the temperature locations for the appearance of these two peaks might be the same．By separating the main peaks from each other，the values of activation energy for peak I and III have been determined to be 0.22 eV and 1.2 eV respectively．However．the value for peak III is nearly identical with that obtained by the method of changing heating rate，while the difference between the values for peak I is fairly large．By tom-paring the experimental curve with the calculated ones，it is shown that the results ob-tained by the peak-separating method is more reasonable．
1965, 7(2): 96-104
Abstract:
The effect of various organic redox of tertiary buryl hydroperoxide．amine(TBH-amine) system on the title polymerization of acrylonitrile was studied．It was observed that the structure of amine bears a significant influence both on the rate of polymerization and Oil the percentage of conversion．The decreasing order of the rates of polymeriza-tion for various amines was as follows：(C2H5)3N，HEA>TEA>DMA，MEA>TEA-HCl．in which the TBH-TEA redox showed to be the best one with sufficiently high rate of polymerization and high percentage of conversion．Moreover，some parallel relationship between the rate of polymerization and duration of induction was observed，i.e., shorter duration of induction with higher rate of polymerization and vice versa．For tertia'ry amine．TBH systems．the induction period of polymerization was shown to bear a somewhat parallel relationship with the pK b of amine，i．e．，smaller pKh with shorter duration of induction and vice versa．
The effect of various organic redox of tertiary buryl hydroperoxide．amine(TBH-amine) system on the title polymerization of acrylonitrile was studied．It was observed that the structure of amine bears a significant influence both on the rate of polymerization and Oil the percentage of conversion．The decreasing order of the rates of polymeriza-tion for various amines was as follows：(C2H5)3N，HEA>TEA>DMA，MEA>TEA-HCl．in which the TBH-TEA redox showed to be the best one with sufficiently high rate of polymerization and high percentage of conversion．Moreover，some parallel relationship between the rate of polymerization and duration of induction was observed，i.e., shorter duration of induction with higher rate of polymerization and vice versa．For tertia'ry amine．TBH systems．the induction period of polymerization was shown to bear a somewhat parallel relationship with the pK b of amine，i．e．，smaller pKh with shorter duration of induction and vice versa．
1965, 7(2): 105-111
Abstract:
A method for the rapid estimation of the shelf life of rubber vulcanizates by means of chemical stress relaxation measurements is described．The method is based on the consideration that the temperature dependence of the times required to reach variOUS depths of the relaxation process as chara'cterized bv the relative stresses f/fo，may be expressed by an Arrhenius type relation，so that a plot of the relaxation times at different temperatures at which a given relative stress is reached vs 1/T should be a straight line．Then relaxation times at room temperature can be obtained by extrapolation．Two vulcanizates of butvl and nitrile rubber were chosen for investigation as these rubbers show quite different behaviours in chemical relaxation．All experimental results support the present consideration and the shelf life of rubber vulcanizates can be easily estimated from the experimental data．
A method for the rapid estimation of the shelf life of rubber vulcanizates by means of chemical stress relaxation measurements is described．The method is based on the consideration that the temperature dependence of the times required to reach variOUS depths of the relaxation process as chara'cterized bv the relative stresses f/fo，may be expressed by an Arrhenius type relation，so that a plot of the relaxation times at different temperatures at which a given relative stress is reached vs 1/T should be a straight line．Then relaxation times at room temperature can be obtained by extrapolation．Two vulcanizates of butvl and nitrile rubber were chosen for investigation as these rubbers show quite different behaviours in chemical relaxation．All experimental results support the present consideration and the shelf life of rubber vulcanizates can be easily estimated from the experimental data．
1965, 7(2): 112-119
Abstract:
The effect of different initiators and solvents on the title polymerization was studied．An isotactic crystalline polymer with melting range 183—193° was obtained when t-butyl acrylate was polymerized at room temperature with LiAlH4 or NaH as anionic initiator in hexane or toluene as solvent．When tetrahydrofuran (THF) was used as solvent, an amorphous polymer with softening range of 75°一90°was obtained．NaBH4 in hexane or toluene would not initiate the polymerization unless pyridine or THF was used as solvent，but an amorphous polymer was the product．For the hydride of alkali metal or its complex initiated anionic polymerization of the title vinyl monomer，the mechanism of hydride transfer to β-carbon atom of the monomer molecule was proposed．
The effect of different initiators and solvents on the title polymerization was studied．An isotactic crystalline polymer with melting range 183—193° was obtained when t-butyl acrylate was polymerized at room temperature with LiAlH4 or NaH as anionic initiator in hexane or toluene as solvent．When tetrahydrofuran (THF) was used as solvent, an amorphous polymer with softening range of 75°一90°was obtained．NaBH4 in hexane or toluene would not initiate the polymerization unless pyridine or THF was used as solvent，but an amorphous polymer was the product．For the hydride of alkali metal or its complex initiated anionic polymerization of the title vinyl monomer，the mechanism of hydride transfer to β-carbon atom of the monomer molecule was proposed．
1965, 7(2): 120-126
Abstract:
In our previous report,by considering both monomolecular and bimolecular me-chanism of cyclopolymerization，the following kinetic relation was obtained：一d[M]-d[m]一A+B-[M] where [M] is the monomer concentration，[m] is the pendent double bond concentration and both A and B are constants．This equation was verified further in this report by polymerizing methacrylic anhydride under different temperatures．In all cases，一d[M]-d[m] gave a linear relation with 1／[M] as expected，and the intercepts of the plots obtained were 2．9，2.15 and 1.7 at temperatures of 60°，40°and 25℃ respectively．It was also found that the values of the ratio of the bimolecular rate to the monomolecular rate were 2.7 [M]，2.0 [M] & 1.4 [M] at 60°，40°and 25℃ respectively and thus decrease as temperature decreases．The energy of activation of bimolecular cyclopolymerization was found tO be 3.7 kcal／mole higher than that of monomolecular reaction．
In our previous report,by considering both monomolecular and bimolecular me-chanism of cyclopolymerization，the following kinetic relation was obtained：一d[M]-d[m]一A+B-[M] where [M] is the monomer concentration，[m] is the pendent double bond concentration and both A and B are constants．This equation was verified further in this report by polymerizing methacrylic anhydride under different temperatures．In all cases，一d[M]-d[m] gave a linear relation with 1／[M] as expected，and the intercepts of the plots obtained were 2．9，2.15 and 1.7 at temperatures of 60°，40°and 25℃ respectively．It was also found that the values of the ratio of the bimolecular rate to the monomolecular rate were 2.7 [M]，2.0 [M] & 1.4 [M] at 60°，40°and 25℃ respectively and thus decrease as temperature decreases．The energy of activation of bimolecular cyclopolymerization was found tO be 3.7 kcal／mole higher than that of monomolecular reaction．
