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Acidity of polyurethane semicarbazide in dimethylformamide
Acidity of polyurethane semicarbazide in dimethylformamide
1429
7. A. S. MICHAELS and H. I. BIXLER, J. Polymer Sci. 50: 329, 1961 8. G. K. BORESKOV, Geterogennyi kataliz (Heterogeneous Catalysis). p. 238, Moscow, 1986 9. R. MONTARIF,L, IVth Internat. Congress on Catalysis. Symposium III, Novosibirsk, 1968
Polymer Science U.S.S.R. Vol. 31, No. 6, pp. 1429-1432, Printed in Poland
1989
0032-3950/89 $10.00+.00 (~) 1990PergamonPressVie
ACIDITY OF POLYURETHANE SEMICARBAZIDE IN DIMETHYLFORMAMIDE* N. F. BABCHENKO,V. N. TOLMACHEVand L. A. LOMAKO A. M. Gor'kii Kharkov State University
(Received 25 December 1987)
Acidity in dimethylformamideof two modificationsof polyurethane semicarbazide and of corresponding model compounds was studied by potentiometric titration. The characteristic dissociationconstants pK0 of the polymers were calculated. The temperature dependence of pKo was measured between 298 and 358 K. Thermodynamic characteristics of dissociation were determined for the polymericand model compounds. The entropic term was found to be decisive for the free energy of dissociation. The electrostatic contribution to the free energy, zlGe~, was calculated and shown to be important for polymer dissociation. POLYURETHANE semicarbazide (PUS) in dimethylformamide (DMFA) solutions is known to form complexes with ions ef transition metals [1], but its acido-basic pro perties have not been studied as yet. It is the aim of this work to determine the acid'ty of PUS in DMFA between 298 and 353 K. Two types of PUS were investigated, based on dihydrazides of isophthalic (PUS-l, M~= 13 x 103) and adipic acids (PUS-2, M~= 104). Synthesis and identification of the polymers containing urethane and semicarbazide groups have been described elsewhere [1]. Potentiometric titration was performed at ionic strength of 0.1 with a glass electrode calibrated by DMFA buffer solutions [2]; a solution of tetramethylammonium hydroxide in isopropanol was the titrant. Three model compounds were also studied: phenylurethane (PU) as a low-molar-mass analog of the urethane group on both polymers, 1-benzoyl-4-phenylsemicarbazide (BPSC), and 1-acetyl-4-phenylsemicarbazide (APSC). The latter two compounds, which model the respective semicarbazide groups in PUS-I and PUS-2, were synthesized according to [3]. As shown by Fig. 1, bends appear on the titration curves of PUS-1 and PUS-2. By analogy with BPSC and APSC they can be attributed to dissociation of semicarbazide groups in the polymers. PU does not exhibit any acidity in DMFA; hence, we * Vysokomol. soyed. A31: No. 6, 1303-1305, 1989.
1430
N. F, BABCHBNKOet aL THERMODYNAMIC CHARACTERISTICS OF DISSOCIATION
Compound
pKo* at T, K 313 328
298 PUS-1 PUS-2 BPSC APSC
12.6 15.2 13.8 15.9
12.6 15.5 13.9 16-5
12.9 15-7 14-2 16.6
343
358
298
13.0 15.9 14.4 17.4
13.1 16.2 14-6 17-8
72 87 78 91
AG° (kJ/mole) at T, K 313 328 343 76 93 83 99
81 99 89 104
358
86 104 94 114
90 111 100 122
* Values of pK. presented for the model compounds.
may postulate negligible dissociation of urethane groups in PUS-1 and PUS-2. The values of pK, determined from the titration curves for ,APSC and BPSC are collected in Table 1. The apparent dissociation constants of the polymers, pK.p~, were calculated according to Katchalsky [4], pH=PK0+log 1
+ApK(0t),
and
pK.pp = PKo + z/pK (0t)= pH - log 1 - 0t where Ko is the characteristic dissociation constant, = is the degree of dissociation, and the term dpK(~t) respects electrostatic and other interactions between the charges on the chain. ETmV
1
,.
2
,
pK pp
6O0
40~0 j ~
" 15
~ f
13 2
#
V, cm s
I
I
O.4
O.6
I
0.8 o~
FIG. 2 FlO. 1 Fie. 1. Potentiometric titration curves: D M F A (1), ASPC (2), BPSC (3), PUS-I (4), and PUS-2 (5). Fie. 2. pK=pp as a function of the degree of dissociation = at 298 (I, 1'), 313 (2, 2'), 328 (3, 3'), 343 (4, 4'), and 358 K (5, 5') for PUS-1 (1-5) and PUS-2 (1'-5').
Acidity of polyurethane semicarbazide in dimethylformamide
1431
OF PUS-l, PUS-2 AND OF THE MODDELCOMPOUNDS -AH °,
kJ/mole 23 38 31 62
-
AS
o,
e.G.
320 420 370 510
AG,I (kJ/mole) at T, K 358 313 I 328 343 42 117 70 t 92 105 23 23 t 37 61 298
-
drier,
k J/mole 315 410
-
ASct, e.u,
1200 1370
The latter are responsible for the dependence of the calculated values pK, pp on ~. The character of the curves obtained for PUS-l, along with the results of viscometric titration which proved the absence of conformational transition s in the polymer, allowed us to assume that the electrostatic effect predominates. Dissociation of PUS-2 includes the simultaneous action o f electrostatic, conformational, solvation, and other effects
[51. The quantities pKo for PUS-1 and PUS-2 were obtained by extrapolation of the linear segments of the functions pKapp=f(a) to a = 0 (with an error of -1-0.3). The quantity ziG ° was calculated by the known method from the values of pKo and pKa. The electrostatic contribution dGc~ to the free energy of dissociation was estimated fl'om the dependence pK~pp=f(~t) according to [6, 7] (see Table 1). A confrontation of pKo for PUS-I and PUS-2 with the values of pK, of the model compounds indicates the semicarbazide group in the polymer to be more acidic. The data in Table 1 show that the magnitude of AG,~ is comparable to and in some instances even higher than the contribution of dissociation proper, AGc. The acidity of PUS-1 and PUS-2 is but weakly influenced by temperature; only a small increase of pKo is discernible. An approximate evaluation of thermodynamic characteristics o f dissociation shows that the entropic term predominates in the studied compounds. The temperature dependence of ztGcj is more strongly pronounced. The results show that the electrostatic interaction between charges attached to polymer segments is characterized by substantial, negative changes of both entropy and enthalpy and their contributions to the overall change of free energy dGe~ are comFarable. Thus, the acid-basic properties of PUS, are given by the character of functional groups and by effects associated with the behaviour of polymer chains in solution. Translated by M. KuafN REFERENCES
1. N. F. BABCHENKO, L. A. LOMAKO and V. N. TOLMACHEV, Izv. vuzov, Khimia i khim. tekhnologia 27: 1218, 1984 2. A, V. KRAVCHINA and L. L. SPIVAK, Vestnik Kharkovsk. u-ta, p. 17, 1974 3. T. CURTIUS, Prakt. Chem. 50: 275, 1894 4. H. MORAWETZ, Makromolekuly v rastvore (Macromolecules in Solution). 398 pp., Moscow, 1967 5. N. A. PLATi~, A. D. LITMANOVICH and O. V. NOA, Makromolekulyarnye reaktsii (Polymer Reactions). 255 pp., Moscow, 1977
1432
A.A. GOr.BuNov et aL
6. G. N. NEKRASOVA, O. B. PTITSYN and A. V. ANUFRIEVA, Vysokomol. soyed. A7: 913, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 5, 1008, 1965) 7. L. V. MIROSHNIK, A. V. ALEKSANDROV and V. N. TOLMACHEV, Vysokomol. soyed. A29: 107, 1987 (Translated in Polymer Sci. U.S.S.R. 29: 1,121, 1987)
PolymerScienceU.S.S.R.Vol. 31, No. 6, pp. 1432--1437.1989 Printedia Poland
0032-3950189$10.00+.00 ~) 1990l~rs~aon ~ pie
DETERMINATION OF POLYMER POLYDISPERSITY BY GEL PERMEATION CHROMATOGRAPHY WITHOUT PRELIMINARY CALIBRATION* '
A. A. Gom~trNov, A. M. SKVORTSOVand M. B. T ~ N m K O V Leningrad Chemical and Pharmaceutical Institute (Received 25 December 1987)
A method which uses exclusivelythe ehromatogram of the investigated sample is proposed for the determination of polymer polydispersityby gel permeation chromatography without resort to calibration by standards. A universal dependence between the reciprocal slope of the calibration curve and the distribution coefficient,which lies behind the proposed method, was te~ted experimentally. Determination of polydispersity without calibration is documented on the example of dextram. POLYMOLECULARITY(polydispersity in molar mass) is oae of the most important characteristics of polymers. Polymolecularity is fully characterized by the molecular mass distribution (MMD) functions, either number, f,(M), weight, fw(M), or z-average dis' tribution, f,(M) [11. Each is characterized by the corresponding mean Ms (i--n, w, or z) and variance o'2. The relative width ~,~=udMs or the polydispersity index Us [1, 2] Us=l+
_~2 (~d
(D
are often used as quantitative characteristics of polymolecularity. The index U~is defined as the ratio of two molecular weight averages; e.g., Un=M~,] [M, or U~,---M,[M w. Gel permeation chromatography (GPC) is the most effective method for the determination of polymolecularity [3]. The following procedure is usually adopted [2, 3]. By means of narrow-distribution standards a calibration curve is first established as a dependence of molecular mass M on retention volume VR= Vo+ VrK (where Vo and Vpare the volumes of the mobile and stationary phases in the column,, K is the dis* Vysokomol. soyed. A31: No. 6, 1306-1310) 1989.
1429
7. A. S. MICHAELS and H. I. BIXLER, J. Polymer Sci. 50: 329, 1961 8. G. K. BORESKOV, Geterogennyi kataliz (Heterogeneous Catalysis). p. 238, Moscow, 1986 9. R. MONTARIF,L, IVth Internat. Congress on Catalysis. Symposium III, Novosibirsk, 1968
Polymer Science U.S.S.R. Vol. 31, No. 6, pp. 1429-1432, Printed in Poland
1989
0032-3950/89 $10.00+.00 (~) 1990PergamonPressVie
ACIDITY OF POLYURETHANE SEMICARBAZIDE IN DIMETHYLFORMAMIDE* N. F. BABCHENKO,V. N. TOLMACHEVand L. A. LOMAKO A. M. Gor'kii Kharkov State University
(Received 25 December 1987)
Acidity in dimethylformamideof two modificationsof polyurethane semicarbazide and of corresponding model compounds was studied by potentiometric titration. The characteristic dissociationconstants pK0 of the polymers were calculated. The temperature dependence of pKo was measured between 298 and 358 K. Thermodynamic characteristics of dissociation were determined for the polymericand model compounds. The entropic term was found to be decisive for the free energy of dissociation. The electrostatic contribution to the free energy, zlGe~, was calculated and shown to be important for polymer dissociation. POLYURETHANE semicarbazide (PUS) in dimethylformamide (DMFA) solutions is known to form complexes with ions ef transition metals [1], but its acido-basic pro perties have not been studied as yet. It is the aim of this work to determine the acid'ty of PUS in DMFA between 298 and 353 K. Two types of PUS were investigated, based on dihydrazides of isophthalic (PUS-l, M~= 13 x 103) and adipic acids (PUS-2, M~= 104). Synthesis and identification of the polymers containing urethane and semicarbazide groups have been described elsewhere [1]. Potentiometric titration was performed at ionic strength of 0.1 with a glass electrode calibrated by DMFA buffer solutions [2]; a solution of tetramethylammonium hydroxide in isopropanol was the titrant. Three model compounds were also studied: phenylurethane (PU) as a low-molar-mass analog of the urethane group on both polymers, 1-benzoyl-4-phenylsemicarbazide (BPSC), and 1-acetyl-4-phenylsemicarbazide (APSC). The latter two compounds, which model the respective semicarbazide groups in PUS-I and PUS-2, were synthesized according to [3]. As shown by Fig. 1, bends appear on the titration curves of PUS-1 and PUS-2. By analogy with BPSC and APSC they can be attributed to dissociation of semicarbazide groups in the polymers. PU does not exhibit any acidity in DMFA; hence, we * Vysokomol. soyed. A31: No. 6, 1303-1305, 1989.
1430
N. F, BABCHBNKOet aL THERMODYNAMIC CHARACTERISTICS OF DISSOCIATION
Compound
pKo* at T, K 313 328
298 PUS-1 PUS-2 BPSC APSC
12.6 15.2 13.8 15.9
12.6 15.5 13.9 16-5
12.9 15-7 14-2 16.6
343
358
298
13.0 15.9 14.4 17.4
13.1 16.2 14-6 17-8
72 87 78 91
AG° (kJ/mole) at T, K 313 328 343 76 93 83 99
81 99 89 104
358
86 104 94 114
90 111 100 122
* Values of pK. presented for the model compounds.
may postulate negligible dissociation of urethane groups in PUS-1 and PUS-2. The values of pK, determined from the titration curves for ,APSC and BPSC are collected in Table 1. The apparent dissociation constants of the polymers, pK.p~, were calculated according to Katchalsky [4], pH=PK0+log 1
+ApK(0t),
and
pK.pp = PKo + z/pK (0t)= pH - log 1 - 0t where Ko is the characteristic dissociation constant, = is the degree of dissociation, and the term dpK(~t) respects electrostatic and other interactions between the charges on the chain. ETmV
1
,.
2
,
pK pp
6O0
40~0 j ~
" 15
~ f
13 2
#
V, cm s
I
I
O.4
O.6
I
0.8 o~
FIG. 2 FlO. 1 Fie. 1. Potentiometric titration curves: D M F A (1), ASPC (2), BPSC (3), PUS-I (4), and PUS-2 (5). Fie. 2. pK=pp as a function of the degree of dissociation = at 298 (I, 1'), 313 (2, 2'), 328 (3, 3'), 343 (4, 4'), and 358 K (5, 5') for PUS-1 (1-5) and PUS-2 (1'-5').
Acidity of polyurethane semicarbazide in dimethylformamide
1431
OF PUS-l, PUS-2 AND OF THE MODDELCOMPOUNDS -AH °,
kJ/mole 23 38 31 62
-
AS
o,
e.G.
320 420 370 510
AG,I (kJ/mole) at T, K 358 313 I 328 343 42 117 70 t 92 105 23 23 t 37 61 298
-
drier,
k J/mole 315 410
-
ASct, e.u,
1200 1370
The latter are responsible for the dependence of the calculated values pK, pp on ~. The character of the curves obtained for PUS-l, along with the results of viscometric titration which proved the absence of conformational transition s in the polymer, allowed us to assume that the electrostatic effect predominates. Dissociation of PUS-2 includes the simultaneous action o f electrostatic, conformational, solvation, and other effects
[51. The quantities pKo for PUS-1 and PUS-2 were obtained by extrapolation of the linear segments of the functions pKapp=f(a) to a = 0 (with an error of -1-0.3). The quantity ziG ° was calculated by the known method from the values of pKo and pKa. The electrostatic contribution dGc~ to the free energy of dissociation was estimated fl'om the dependence pK~pp=f(~t) according to [6, 7] (see Table 1). A confrontation of pKo for PUS-I and PUS-2 with the values of pK, of the model compounds indicates the semicarbazide group in the polymer to be more acidic. The data in Table 1 show that the magnitude of AG,~ is comparable to and in some instances even higher than the contribution of dissociation proper, AGc. The acidity of PUS-1 and PUS-2 is but weakly influenced by temperature; only a small increase of pKo is discernible. An approximate evaluation of thermodynamic characteristics o f dissociation shows that the entropic term predominates in the studied compounds. The temperature dependence of ztGcj is more strongly pronounced. The results show that the electrostatic interaction between charges attached to polymer segments is characterized by substantial, negative changes of both entropy and enthalpy and their contributions to the overall change of free energy dGe~ are comFarable. Thus, the acid-basic properties of PUS, are given by the character of functional groups and by effects associated with the behaviour of polymer chains in solution. Translated by M. KuafN REFERENCES
1. N. F. BABCHENKO, L. A. LOMAKO and V. N. TOLMACHEV, Izv. vuzov, Khimia i khim. tekhnologia 27: 1218, 1984 2. A, V. KRAVCHINA and L. L. SPIVAK, Vestnik Kharkovsk. u-ta, p. 17, 1974 3. T. CURTIUS, Prakt. Chem. 50: 275, 1894 4. H. MORAWETZ, Makromolekuly v rastvore (Macromolecules in Solution). 398 pp., Moscow, 1967 5. N. A. PLATi~, A. D. LITMANOVICH and O. V. NOA, Makromolekulyarnye reaktsii (Polymer Reactions). 255 pp., Moscow, 1977
1432
A.A. GOr.BuNov et aL
6. G. N. NEKRASOVA, O. B. PTITSYN and A. V. ANUFRIEVA, Vysokomol. soyed. A7: 913, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 5, 1008, 1965) 7. L. V. MIROSHNIK, A. V. ALEKSANDROV and V. N. TOLMACHEV, Vysokomol. soyed. A29: 107, 1987 (Translated in Polymer Sci. U.S.S.R. 29: 1,121, 1987)
PolymerScienceU.S.S.R.Vol. 31, No. 6, pp. 1432--1437.1989 Printedia Poland
0032-3950189$10.00+.00 ~) 1990l~rs~aon ~ pie
DETERMINATION OF POLYMER POLYDISPERSITY BY GEL PERMEATION CHROMATOGRAPHY WITHOUT PRELIMINARY CALIBRATION* '
A. A. Gom~trNov, A. M. SKVORTSOVand M. B. T ~ N m K O V Leningrad Chemical and Pharmaceutical Institute (Received 25 December 1987)
A method which uses exclusivelythe ehromatogram of the investigated sample is proposed for the determination of polymer polydispersityby gel permeation chromatography without resort to calibration by standards. A universal dependence between the reciprocal slope of the calibration curve and the distribution coefficient,which lies behind the proposed method, was te~ted experimentally. Determination of polydispersity without calibration is documented on the example of dextram. POLYMOLECULARITY(polydispersity in molar mass) is oae of the most important characteristics of polymers. Polymolecularity is fully characterized by the molecular mass distribution (MMD) functions, either number, f,(M), weight, fw(M), or z-average dis' tribution, f,(M) [11. Each is characterized by the corresponding mean Ms (i--n, w, or z) and variance o'2. The relative width ~,~=udMs or the polydispersity index Us [1, 2] Us=l+
_~2 (~d
(D
are often used as quantitative characteristics of polymolecularity. The index U~is defined as the ratio of two molecular weight averages; e.g., Un=M~,] [M, or U~,---M,[M w. Gel permeation chromatography (GPC) is the most effective method for the determination of polymolecularity [3]. The following procedure is usually adopted [2, 3]. By means of narrow-distribution standards a calibration curve is first established as a dependence of molecular mass M on retention volume VR= Vo+ VrK (where Vo and Vpare the volumes of the mobile and stationary phases in the column,, K is the dis* Vysokomol. soyed. A31: No. 6, 1306-1310) 1989.