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Solubility parameter components of some polyurethanes
Eur. Polym. J. Vol. 28, No. 1, pp. 53-55, 1992 Printed in Great Britain. All rights reserved
0014-3057/92$5.00+ 0.00 Copyright © 1992PergamonPress plc
SOLUBILITY PARAMETER COMPONENTS OF SOME POLYURETHANES RYSZARD MIECZKOWSKI Institute of Chemistry, N. Copernicus University, 87100 Torufi, Poland (Received 15 November 1990; in revised form 24 May 1991)
Abstract--The components of the solubility parameter of some polyurethanes have been determined. The determination is based on the application of three mixtures of solvents. For each mixture, the point of maximum interaction between the mixture and the polyurethane was obtained from the maximum value of the intrinsic viscosity. The calculation of the solubility parameter components is based on the application of the three points of maximum interaction for each examined polymer. The following components of solubility parameters, and total parameters have been obtained: for polyurethane obtained from poly(ethylene oxide) and 1,6-hexamethylene diisocyanate: Jd=17.6+0.1, Jp=3.5+0.2, 6h=9.0+0.1, ~o=20.1 +0.2, for polyurethane from poly(propylene oxide) and 1,6-hexamethylene diisocyanate: c5d = 16.8 __+0.8, Jp = 4.4 _+0.2, 6h = 6.8 _ 0.3, C~o = 18.6 ___+0.9, for polyurethane from poly(ethylene adipate) and 1,6-bexamethylene diisocyanate: c~ = 17.2 + 1.7, 6p = 4.5 + 0.8, 6h = 9.3 + 0.1, ~o = 20.1 + 1.7; all values are in (J/ml) j/2.
INTRODUCTION
EXPERIMENTAL PROCEDURES
In a previous paper [1], the components of the solubility parameters of some polyols have been determined. It seemed interesting to determine these values for polyurethanes obtained from the examined polyois, The concept of solubility parameter was developed for the mixing of a non-polar system [2], and has
Materials The polyols (PEO, PPO, PEA) were purified as described previously [1]. 1,6-Hexamethylene diisocyanate (HDI) (Merck-Schuchardt) was purified by distillation under reduced pressure in an atmosphere of dry N 2. The --NCO group content was found analytically to be 49.9 wt% [8]. Its density was 1.046 g/ml. Polyurethanes were synthesized by a one-step technique. A chosen polyol, carefully dried, was melted at 353 K and HDI diisocyanate was added. The polyaddition of polyol/diisocyanate at a molar ratio of 0.9 was carried out at 353 K in N 2. The polymers obtained from PEO and PEA were dissolved in acetone, precipitated by ethanol and dried at 303 K under reduced pressure. The polymer obtained from PPO was dried at 353 K under reduced pressure. The number-average molecular weight, M n, of polyurethanes was determined from the hydroxyl end-group content [7]. Values of ~ , were found to be 21,000 for polyurethane obtained from PEO and HDI-PU1, 20,000 for PU from PPO and HDI-PU2 and 19,500for PU from PEA and HDI-PU3. The solvents used for polymers were purified by standard methods [9]. The purities were tested by measurements of refractive index and density. Viscosity measurements were made at 298 K using an Ubbelohde viscometer for the polymer solutions in the mixed solvents in the concentration range 0.01 to 0.05 g/ml. The intrinsic viscosity [t/] was determined by extrapolating viscosity-concentration plots i.e. r/$pagainst c; [r/] was the intercept at c = 0.
also been applied to polar system [3]. In the case of the polymer studied, the solubility parameter is treated as a vector composed of the three following components, dispersion 6d, polar 6p and hydrogen bonding 6h. In the present study, the method of determination of solubility parameters, described elsewhere [4, 5], has been used. This method is based on the determination of values of volume fraction of as solvent (qS~) for three different mixtures of two solvents corresponding to maximum interaction between the mixed solvents and a polymer. For every mixture of solvents, the empirical value of ~b~ could be obtained from the maximum value of intrinsic viscosity [6]. The three values of qS~ were substituted into three equations in the form of: I P,(ai -- bi) -
~ C~s (ai - bi)2
~=t 1 +
bi(a~- b i )
~- 0
(1)
i=l
where Pi is the component of the solubility parameter of a polymer; for example: p~ is the dispersion component of the solubility parameter of a polymer; ai is the component of the first solvent and bi is the component of the second solvent; for instance, a 2 is the component of polar bonding of solvent a and b3 is the hydrogen bonding component of solvent b.
RESULTS AND DISCUSSION For each polymer, three mixtures of solvents were chosen viz.: for P U I , I benzene-acetone, II dioxane-acetone, III benzene-ethyl acetate; for PU2, I benzene-acetone, II dioxane-acetone, III benzene-methyl ethyl ketone; 53
54
RYSZARD MIECZKOWSKI
Table 1. Dependence of intrinsic viscosities of PUI and PU2 solutions on the volume fraction of the components of mixtures PUI
Case No.
Mixture
PU2
4,
[r/] (ml/g)
4,
[~/] (ml/g)
1 2 3 4 5
Benzene-acetone 4, = volume fraction of acetone
0.47 0.49 0.50 0.51 0.53
15.00 15.45 15.60 15.50 15.20
0.55 0.61 0.62 0.63 0.65
17.50 18.80 19.15 19.05 18.75
6 7 8 9 10
Acetone-dioxane 4s = volume fraction of acetone
0.18 0.21 0.22 0.23 0.25
26.05 27.15 28.35 27.50 27.40
0.38 0.40 0.41 0.42 0.45
24.10 24.00 25.30 24.85 23.27
11 12 13 14 15
Ethyl a~tatc-benzene 4, = volume fraction of ethyl acetate
0.97 0.95 0.94 0.93 0.90
23.15 24.00 24.55 24.10 23.13
16 17 18 19 20
Benzene--methyl ethyl ketone 4, = volume fraction of benzene
0.26 0.28 0.29 0.30 0.32
14.53 15.90 16.55 16.05 15.45
for PU3, I toluene-methanol, II chloroformmethanol, III n-butyl chloride-methanol, Tables 1 and 2 show the dependence of intrinsic viscosities of polymer solutions on the volume fractions of components of the mixtures. Upon the assumption that in the best mixture the value of [r/] for a polymer solution shows a maximum, we have obtained the following maxima for PU1 for mixture I--~bi~to~, =0.50 +0.01; for mixture II--$a~ton e = 0.22 + 0.01 and for mixture III-$,thyla~tat~ = 0.94 + 0.01. The components of the parameters of the pure solvents and non-solvents from literature values [10] and ~b~ obtained from the maximum values [r/] (Table 1) were put into the three equations (1), the solution of which gave the values of the solubility parameter components for PUI:pl = 17.6 + 0.1 = c5d, p~ = 3.5 + 0.2 = 3p and Ps = 9.0 _ 0.1 = 6h. In the same way, the components of solubility parameters for PU2 and PU3 were obtained (Table 3). The method for estimating the single (total) solubility parameter, described by Small [11], is based on
the assumption that the cohesive energy is an additive property related to the structure of the polymers. According to Small ~
= -dpy~F -
(2) M where F is the group attractive constant, M is the molecular weight of the repeating unit, dp is the density of the polymer. The total solubility parameters of polyurethanes now obtained were compared with the single parameters calculated from equation (2) by adopting Hoy's [12] molar attraction constants (Table 3). The total solubility parameters for polyols [1] and for polyurethanes obtained from these polyols are very similar. For polyurethanes the solubility parameters are a little larger [0.1-0.3 (J/ml) 1/2] than for polyols from which the polyurethanes were obtained. The solubility parameter components are rather different. The dispersion components are larger by [0.3-0.9 (J/ml) ~/~] for polyurethanes than for the corresponding polyols. The polar components for
Table 2. Dependence of intrinsic viscosities of PU3 solutions on the volume fractions of the components of mixtures Case No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
4,
[~/] (ml/g)
Toluene-methanol 4s = volume fraction of toluene
Mixture
0.650 0.655 0.660 0.665 0.670
20.05 20.22 20.66 20.50 20.22
Chloroform-methanol 4s = volume fraction of chloroform
0.790 0.795 0.800 0.805 0.810 0.690 0.695 0.700 0.705 0.710
30.25 32.71 35.42 34.10 32.05 16.74 17.22 17.72 16.85 16.50
n-Butyl chloride-methanol 4s = volume fraction of n-butyl chloride
Solubility parameter components of some polyurethanes "la~
.~mty parameters and their components for polyurethanes. All solubility parameters in (J/ml)I/: Polyurethane ,5o 6d 6p 6h PUl 20.1 +0.2 17.6-+0.1 3.5+0.2 9.0-+0.1 d = 1.15g/ml 20.7a PU2 18.6-+0.9 16.8-+0.8 4.4+0.2 6.8-+0.3 d = 1.1 g/ml 18.8a PU3 20.1 + 1.7 17.2+ 1.7 4.5 + 0.8 9.3 _+0.1 d = 1.2g/ml 20.1a Total solubility parameters calculated from equation (2) according to Hoy [111 group attractive constants.
p o l y u r e t h a n e s are smaller by [0.5-1.5 (J/ml) ~:2] t h a n for polyols, a n d a similar situation is observed for the h y d r o g e n b o n d i n g c o m p o n e n t s which are smaller by [0.1-0.6 (J/ml) ~/2] for polyurethanes. It is not surprising because, after the poly addition, the molecules o f p o l y u r e t h a n e s c o n t a i n the new n o n - p o l a r - - C H 2 groups f r o m H D I a n d u r e t h a n e groups; they have a smaller tendency to form hydrogen bonds t h a n the hydroxyl groups in polyols.
55
The total solubility parameters found for the examined polyurethanes are in excellent agreement with the values calculated from e q u a t i o n (2) by a d o p t i n g Hoy's molar attraction constants. REFERENCES
1. R. Mieczkowski. Eur. Polym. J. 27, 377 (1991). 2. J. H. Hildebrand and R. L. Scott. Regular Solutions. Prentice-Hall, New York (1962). 3. C. M. Hansen. J. Paint Tech. 39, 105, 505 (1967). 4. R. Mieczkowski. Eur. Polym. J. 24, 1185 (1988). 5. R. Mieczkowski. Eur. Polym. J. 25, 1055 (1989). 6. J. M. Sosa. Structure-Solubility Relationships in Polymers. Academic Press, New York (1977). 7. J. S. Fritz and G. H. Schenk. Analyt. Chem. 31, 93 (1959). 8. Pensez Plastiques. 12, 370/371, (1965). 9. A. J. Vogel. Preparatyka organiczna. WNT, Warszawa (1964), 10. D. W. Van Krewelen. Properties of Polymers. Elsevier, Amsterdam (1976). 11. P. A. Small. J. appl. Chem. 3, 71 (1953). 12. K. L. Hoy. J. Paint Techn. 42, 76 (1970).
0014-3057/92$5.00+ 0.00 Copyright © 1992PergamonPress plc
SOLUBILITY PARAMETER COMPONENTS OF SOME POLYURETHANES RYSZARD MIECZKOWSKI Institute of Chemistry, N. Copernicus University, 87100 Torufi, Poland (Received 15 November 1990; in revised form 24 May 1991)
Abstract--The components of the solubility parameter of some polyurethanes have been determined. The determination is based on the application of three mixtures of solvents. For each mixture, the point of maximum interaction between the mixture and the polyurethane was obtained from the maximum value of the intrinsic viscosity. The calculation of the solubility parameter components is based on the application of the three points of maximum interaction for each examined polymer. The following components of solubility parameters, and total parameters have been obtained: for polyurethane obtained from poly(ethylene oxide) and 1,6-hexamethylene diisocyanate: Jd=17.6+0.1, Jp=3.5+0.2, 6h=9.0+0.1, ~o=20.1 +0.2, for polyurethane from poly(propylene oxide) and 1,6-hexamethylene diisocyanate: c5d = 16.8 __+0.8, Jp = 4.4 _+0.2, 6h = 6.8 _ 0.3, C~o = 18.6 ___+0.9, for polyurethane from poly(ethylene adipate) and 1,6-bexamethylene diisocyanate: c~ = 17.2 + 1.7, 6p = 4.5 + 0.8, 6h = 9.3 + 0.1, ~o = 20.1 + 1.7; all values are in (J/ml) j/2.
INTRODUCTION
EXPERIMENTAL PROCEDURES
In a previous paper [1], the components of the solubility parameters of some polyols have been determined. It seemed interesting to determine these values for polyurethanes obtained from the examined polyois, The concept of solubility parameter was developed for the mixing of a non-polar system [2], and has
Materials The polyols (PEO, PPO, PEA) were purified as described previously [1]. 1,6-Hexamethylene diisocyanate (HDI) (Merck-Schuchardt) was purified by distillation under reduced pressure in an atmosphere of dry N 2. The --NCO group content was found analytically to be 49.9 wt% [8]. Its density was 1.046 g/ml. Polyurethanes were synthesized by a one-step technique. A chosen polyol, carefully dried, was melted at 353 K and HDI diisocyanate was added. The polyaddition of polyol/diisocyanate at a molar ratio of 0.9 was carried out at 353 K in N 2. The polymers obtained from PEO and PEA were dissolved in acetone, precipitated by ethanol and dried at 303 K under reduced pressure. The polymer obtained from PPO was dried at 353 K under reduced pressure. The number-average molecular weight, M n, of polyurethanes was determined from the hydroxyl end-group content [7]. Values of ~ , were found to be 21,000 for polyurethane obtained from PEO and HDI-PU1, 20,000 for PU from PPO and HDI-PU2 and 19,500for PU from PEA and HDI-PU3. The solvents used for polymers were purified by standard methods [9]. The purities were tested by measurements of refractive index and density. Viscosity measurements were made at 298 K using an Ubbelohde viscometer for the polymer solutions in the mixed solvents in the concentration range 0.01 to 0.05 g/ml. The intrinsic viscosity [t/] was determined by extrapolating viscosity-concentration plots i.e. r/$pagainst c; [r/] was the intercept at c = 0.
also been applied to polar system [3]. In the case of the polymer studied, the solubility parameter is treated as a vector composed of the three following components, dispersion 6d, polar 6p and hydrogen bonding 6h. In the present study, the method of determination of solubility parameters, described elsewhere [4, 5], has been used. This method is based on the determination of values of volume fraction of as solvent (qS~) for three different mixtures of two solvents corresponding to maximum interaction between the mixed solvents and a polymer. For every mixture of solvents, the empirical value of ~b~ could be obtained from the maximum value of intrinsic viscosity [6]. The three values of qS~ were substituted into three equations in the form of: I P,(ai -- bi) -
~ C~s (ai - bi)2
~=t 1 +
bi(a~- b i )
~- 0
(1)
i=l
where Pi is the component of the solubility parameter of a polymer; for example: p~ is the dispersion component of the solubility parameter of a polymer; ai is the component of the first solvent and bi is the component of the second solvent; for instance, a 2 is the component of polar bonding of solvent a and b3 is the hydrogen bonding component of solvent b.
RESULTS AND DISCUSSION For each polymer, three mixtures of solvents were chosen viz.: for P U I , I benzene-acetone, II dioxane-acetone, III benzene-ethyl acetate; for PU2, I benzene-acetone, II dioxane-acetone, III benzene-methyl ethyl ketone; 53
54
RYSZARD MIECZKOWSKI
Table 1. Dependence of intrinsic viscosities of PUI and PU2 solutions on the volume fraction of the components of mixtures PUI
Case No.
Mixture
PU2
4,
[r/] (ml/g)
4,
[~/] (ml/g)
1 2 3 4 5
Benzene-acetone 4, = volume fraction of acetone
0.47 0.49 0.50 0.51 0.53
15.00 15.45 15.60 15.50 15.20
0.55 0.61 0.62 0.63 0.65
17.50 18.80 19.15 19.05 18.75
6 7 8 9 10
Acetone-dioxane 4s = volume fraction of acetone
0.18 0.21 0.22 0.23 0.25
26.05 27.15 28.35 27.50 27.40
0.38 0.40 0.41 0.42 0.45
24.10 24.00 25.30 24.85 23.27
11 12 13 14 15
Ethyl a~tatc-benzene 4, = volume fraction of ethyl acetate
0.97 0.95 0.94 0.93 0.90
23.15 24.00 24.55 24.10 23.13
16 17 18 19 20
Benzene--methyl ethyl ketone 4, = volume fraction of benzene
0.26 0.28 0.29 0.30 0.32
14.53 15.90 16.55 16.05 15.45
for PU3, I toluene-methanol, II chloroformmethanol, III n-butyl chloride-methanol, Tables 1 and 2 show the dependence of intrinsic viscosities of polymer solutions on the volume fractions of components of the mixtures. Upon the assumption that in the best mixture the value of [r/] for a polymer solution shows a maximum, we have obtained the following maxima for PU1 for mixture I--~bi~to~, =0.50 +0.01; for mixture II--$a~ton e = 0.22 + 0.01 and for mixture III-$,thyla~tat~ = 0.94 + 0.01. The components of the parameters of the pure solvents and non-solvents from literature values [10] and ~b~ obtained from the maximum values [r/] (Table 1) were put into the three equations (1), the solution of which gave the values of the solubility parameter components for PUI:pl = 17.6 + 0.1 = c5d, p~ = 3.5 + 0.2 = 3p and Ps = 9.0 _ 0.1 = 6h. In the same way, the components of solubility parameters for PU2 and PU3 were obtained (Table 3). The method for estimating the single (total) solubility parameter, described by Small [11], is based on
the assumption that the cohesive energy is an additive property related to the structure of the polymers. According to Small ~
= -dpy~F -
(2) M where F is the group attractive constant, M is the molecular weight of the repeating unit, dp is the density of the polymer. The total solubility parameters of polyurethanes now obtained were compared with the single parameters calculated from equation (2) by adopting Hoy's [12] molar attraction constants (Table 3). The total solubility parameters for polyols [1] and for polyurethanes obtained from these polyols are very similar. For polyurethanes the solubility parameters are a little larger [0.1-0.3 (J/ml) 1/2] than for polyols from which the polyurethanes were obtained. The solubility parameter components are rather different. The dispersion components are larger by [0.3-0.9 (J/ml) ~/~] for polyurethanes than for the corresponding polyols. The polar components for
Table 2. Dependence of intrinsic viscosities of PU3 solutions on the volume fractions of the components of mixtures Case No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
4,
[~/] (ml/g)
Toluene-methanol 4s = volume fraction of toluene
Mixture
0.650 0.655 0.660 0.665 0.670
20.05 20.22 20.66 20.50 20.22
Chloroform-methanol 4s = volume fraction of chloroform
0.790 0.795 0.800 0.805 0.810 0.690 0.695 0.700 0.705 0.710
30.25 32.71 35.42 34.10 32.05 16.74 17.22 17.72 16.85 16.50
n-Butyl chloride-methanol 4s = volume fraction of n-butyl chloride
Solubility parameter components of some polyurethanes "la~
.~mty parameters and their components for polyurethanes. All solubility parameters in (J/ml)I/: Polyurethane ,5o 6d 6p 6h PUl 20.1 +0.2 17.6-+0.1 3.5+0.2 9.0-+0.1 d = 1.15g/ml 20.7a PU2 18.6-+0.9 16.8-+0.8 4.4+0.2 6.8-+0.3 d = 1.1 g/ml 18.8a PU3 20.1 + 1.7 17.2+ 1.7 4.5 + 0.8 9.3 _+0.1 d = 1.2g/ml 20.1a Total solubility parameters calculated from equation (2) according to Hoy [111 group attractive constants.
p o l y u r e t h a n e s are smaller by [0.5-1.5 (J/ml) ~:2] t h a n for polyols, a n d a similar situation is observed for the h y d r o g e n b o n d i n g c o m p o n e n t s which are smaller by [0.1-0.6 (J/ml) ~/2] for polyurethanes. It is not surprising because, after the poly addition, the molecules o f p o l y u r e t h a n e s c o n t a i n the new n o n - p o l a r - - C H 2 groups f r o m H D I a n d u r e t h a n e groups; they have a smaller tendency to form hydrogen bonds t h a n the hydroxyl groups in polyols.
55
The total solubility parameters found for the examined polyurethanes are in excellent agreement with the values calculated from e q u a t i o n (2) by a d o p t i n g Hoy's molar attraction constants. REFERENCES
1. R. Mieczkowski. Eur. Polym. J. 27, 377 (1991). 2. J. H. Hildebrand and R. L. Scott. Regular Solutions. Prentice-Hall, New York (1962). 3. C. M. Hansen. J. Paint Tech. 39, 105, 505 (1967). 4. R. Mieczkowski. Eur. Polym. J. 24, 1185 (1988). 5. R. Mieczkowski. Eur. Polym. J. 25, 1055 (1989). 6. J. M. Sosa. Structure-Solubility Relationships in Polymers. Academic Press, New York (1977). 7. J. S. Fritz and G. H. Schenk. Analyt. Chem. 31, 93 (1959). 8. Pensez Plastiques. 12, 370/371, (1965). 9. A. J. Vogel. Preparatyka organiczna. WNT, Warszawa (1964), 10. D. W. Van Krewelen. Properties of Polymers. Elsevier, Amsterdam (1976). 11. P. A. Small. J. appl. Chem. 3, 71 (1953). 12. K. L. Hoy. J. Paint Techn. 42, 76 (1970).