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Synthesis and study of polyalkoxyphosphazenes
Polymer Science U.S.S.R, Vol. 26, "No.1, pp, 156-161, 1984
0032-3950/84 $10.00+.00 © 1985 Pergamon Press Ltd.
Printed in Poland
S Y N T H E S I S A N D STUDY OF POLYALKOXYPHOSPHAZENES* V. V. KIREYEV, F. A. BITTIROVA, G. I. MITROPOL'SKAYA, A . K . MIKITAYEV, V. S. PAPKOV a n d M. N . ILqNA D. I. Mendeleyev Chemico-Technological Institute, Moscow Institute of High Molar Mass Compounds, Kabardin-Balkh State University
(Received 25 May 1982) Polydialkoxyphosphazenes with long-chain lateral radicals were synthesized and identified and the presence of a certain order in the position of lateral radicals, established. Polydialkoxyphosphazenes are chemically inert and do not practically change in weight and reduced viscosity during prolonged retention in solutions of mineral acids and alkalies; under conditions of isothermal heating a reduction is observed in these indices. Mechanical and thermo-mechanical characteristics of polydialkoxyphosphazenes were examined.
AMONG the many polyphosphazenes special interest is attached to polyorganoxyphosphazenes readily formed during the treatment of polydiehlorophosphazene with alkali metal alcoholates or phenates [1]. However, up to recently practically no polyphosphazenes were known with long aliphatic radicals in the lateral chain. A report was given previously [2] of the synthesis of polydi-(n-octyloxy)phosphazene (POP); a description is given in this paper of the preparation of polydi-(n-hexyloxy)phosphazene (PHP) and polydi-(n-dodecyloxy)phosphazene (PDP) and a comparative study made of some properties of these three polymers. Raw materials, n-Hexanol and n-dodecanol were dried with freshly calcined calcium oxide and distilled (b.p. 157 and 255-259 °, respectively). Purification of the initial hexaehlorocyclotriph0sphazene and its polymerization were carried out by methods previously described [1]. PHP and PDP were synthesized in the same way as POP [2], by the treatment of polydichlorophosphazene with an excess of corresponding alcoholates in dry diethylene glycol. The polymers were separated and purified, as previously [2]. Methods of investigation. Reduced viscosity and gas-permeability of polymers were measured, as before [2]. X-ray studies were carried out in a URS-50I device with CuK~ radiation. Creep in air and in various media and thermo-mechanical investigations were carried out in a Zhurkov device using constant stress. Mechanical measurements were carried out in a Polyani type device. I R spectra were recorded in an IKS-22 device using films obtained from polymer solutions in chloroform. P M R spectra were obtained in a VS-497 device at an operating frequency of 60 MHz for solutions of the substances examined in deuterochloroform, alp N M R spectra were recorded using a Bruker HX-90 device (operating frequency 36'43 MHz) for polymer solutions in deuterochloroform using 85 % H3PO4 as external standard. Potentiometric titration of alcoholic solutions of * Vysokomol. soyed. A26: No. 1, 140-144, 1984. 1~6
Synthesis and study of polyalkoxyphosphazenes
157
samples of the reaction mixture when synthesizing polymers was carried out using a HC1 alcoholic solution and an LPM-60M potentiometer with an automatic titration unit. The degree of substitution of chlorine atoms in polydichlorophosphazene when preparing P H P and PDP, the same as for the synthesis of POP [2] was monitored by potentiometric titration of the unreacted alcoholate, using IR spectra and elemental analysis. As shown by Table 1, at a temperature of 130-140 ° synthesis of P H P and P D P may be carried out for 40 and 80 hr, respectively; under these conditions practically complete substitution of chlorine atoms for alkoxyradicals is achieved. Absorption bands in the range of 550-600, 2700-2800 and 3200-3400 c m - 1, typical of bond-stretching vibrations of P - C 1 , P - O H and N - H groups, respectively are absent from IR spectra of the polymers obtained; this also proves that substitution is complete. alp N M R spectra of PHP and PDP are characterized by the presence of a singlet signal in the range of - 8 . 0 - + 8 . 3 p.p.m. Chemical shifts at 4.5, 1.5 and 0.8 p.p.m. in P M R spectra of polyalkoxyphosphazenes correspond to O - C H 2 , (CH2),, and C H 3 groups. Intensity ratios of proton signals of alkoxy groups of polymers synthesized are given below; these are values found from P M R spectra and calculated values. Polymer I n t e n s i t y ratio o f p r o t o n signals o f OCH2 : CH2 : CHa groups, found from PMR spectra calculated
PItP
POP
PDP
1-9:8.0:3.0 2 :8 :3
2.1:12,0:3.0 2 : 12 : 3
2.4:19.5:3.1 2 : 20 : 3
Proton signals of P - OH and N - H groups are absent from P M R spectra of polymers; this also proves that substitution is complete and secondary hydrolytic reactions are absent. P H P and PDP are soluble in chloroform, ethyl ether, benzene and on heating in CCI~ and chlorobenzene; they are insoluble in water, mineral acids and organic solvents such as acetone, ethanol and DMF. P H P and PDP were subjected to fractional precipitation from 1 ~ solution in benzene with acetone. Initial polymers and their fractions have the same elemental composition, which agrees with the calculated value, the same chemical shift values in alp N M R spectra (8.1-8.2 p.p.m.) and identical IR spectra. However, anomalies TABLE ]. VARIATION OF CHLORINE CONTENT DURING THE SYNTHESIS* OF P H P AND P D P Chlorine content (~) Reaction time, hr
during the synthesis of PHP
1.5 8'5 20.0
13.8 10.0 1 "2
* In diethylene glycol at 130-140°C.
Chlorine content (%) R e a c t i o n time, h r
PDP 25.1 20.8 15'3
40.0 60-0 80-0
during the synthesis of PHP
PDP
Traces ,, ,,
8.2 3.1 Traces
V . V . KaREYEV et al.
158
are observed for initial polymers and their fractions in the concentration dependence of reduced viscosity, which hinder the determination of intrinsic viscosity. These anomalies may be caused, the same way as in the case of POP [2], by the formation of macromolecular associates in solution which gradually break down in the course of dilution, thus increasing viscosity. During isothermal heating in air of PHP and PDP at 140° a gradual reduction takes place in weight and reduced viscosity, this being more typical of PHP than PDP. During heating for 10 hr at 140° weight loss for PHP is 15 Yo, while reduced viscosity of a 0.5 ~ solution decreases from 0.38 to 0.13 dl/g. For PDP weight loss under these conditions only reaches 5 ~ , while viscosity decreases from 0.20 to 0.15-0.19 dl/g. At the same time in 5 ~ dilute solutions of KOH and HCI breakdown processes are less strongly expressed (Table 2). The same as for POP [2], the low heat stability of the polyalkoxyphosphazenes studied may be caused by the steric interaction of bulky lateral substituents destabilizing the main chain and by damage to the main macromolecular chain [3]. In spite of the low value of its reduced viscosity, which is 0.20 dl/g for PDP, this polymer forms flexible elastic films from solution in chloroform, in contrast with PHP even though the reduced viscosity of this polymer is 0.38 dl/g. N M R pulse spectroscopy and a dielectric method were previously used to study relaxation properties of POP, PHP and PDP; two main ranges of relaxation were found and a relation derived between transition points and dimensions of lateral radicals [4]. Results of relaxation methods of investigation agree with data of differential scanning calorimetry* (Fig. 1). The thermogram of POP plotted while heating shows an endothermic peak of melting at 0 ° (273°K); a sharper exothermic peak appears at - 1 3 ° (260°K) on the cooling curve, which is typical of crystallization. The heat of crystallization and melting, found from the area of these peaks is 14.5 cal/g. The difference in melting points and crystallization temperatures (0 and - 1 3 °) corresponds to differences normally observed in these parameters for high molecular weight compounds. The difference in temperatures of phase transition obtained from calorimetric and relaxation measurements [4] is also TABLE2. VARIATION OF THE WEIGHT AND REDUCED VISCOSITY OF P H P AND P D P DURINGRETENTIONIN AIR AND IN 5 ~/o DILUTE SOLUTIONS OF HCI AND K O H
Polymer
PHP PDP
l .
Variation of ~/,ea, dl/g (numerator) and weight loss, ~ (denominator) o n retaining polymers for 100 hr at 140 ° in air
in 5 % K O H
in 5 y, HCI
0"30
0'05
0.08
55.0
3.5
5-1
0.13 15.0
0 1"5
0.01 2.4
* Calorimetric measurements were carried out by Yu. K. Godovskii, to whom the authors arc very grateful.
Synthesis and study of polyalkoxyphosphazenes
159
within reasonable limits. In contrast with PDP, according to results of differential scanning calorimetry, PHP does not show first order phase transitions. The thermogram of POP, characterized by the existence of an asymmetric endothermic peak at - 7 7 ° (196°K), is unusual. In shape this peak corresponds to phase transition (in case of glass transition it should be S-shaped), however, it is characterized by low heat (-2.45 cal/g). Nevertheless, it probably corresponds to the glass transition, which is in agreement with results of relaxation measurements [4], according to which POP has T, = - 7 8 °. In spite of the absence from thermograms of PHP and POP of peaks that corre spend to phase transition, these polymers show a degree of ordering, as confirmed by diffraction curves, characterized by the existence of an amorphous halo in the angular range of 20"~20 ° and the existence of narrow diffraction peaks in the small angular range.
196K 170K 250K 208K
ZTSK
~"
40 -
318K FIO. 1
260K
0
2 L
i
80
I
I _~
t60 T"
FIo. 2
FIo. 1. Thermo~ams of POP (a) and PDP (b); b: 1-heating (rate 20 deg/min), 2-cooling. FIG. 2. Temperature/deformationcurves of PDP (1, 5) and POP (2--4), plotted with.constant load. 1, 2, 4 - C o m p r e s s i v e load 0.4 (1); 0.1 (2) arid 0.2 MPa (4); 3, 5-tensile stress 0.05 MPa. The position of the diffraction maximum in the range of small angles depends on the length of the lateral alkyl radical; interplanar distance dl increases with an increase in lateral chain length in the P H P - P O P - P D P series. Results of structural methods suggest that coordinated arrangement of lateral chains is observed in PDP with disordered position of the main chain. In PHP and POP elements of ordering of lateral chains only begin to show, as confirmed by X-ray analysis, but are unconfirmed thermodynamically. The structural features of polyalkoxyphosphazenes affect thermodynamic and mechanical characteristics. In view of the fact that strong elastic films only form from PDP and POP, these polymers were examined.
160
V. V, IOR~YEV et al.
By the action of a compressive load of 1>0.1 MPa immediately after melting at 20 to 30 ° PDP flows (Fig. 2). A similar curve was also plotted for POP, although in this temperature range no phase transition was observed. The order in the arrangement of lateral octyl radicals is evidently disrupted in this temperature range and the restrictions imposed by this order on the mobility of the main chain are removed. These assumptions confirm the curves plotted under a load insufficient for flow. In this case temperature/deformation curves have a form, which is typical of the linear amorphous polymer. After breaking the order of the side chains and after the appearance of segmental mobility in the interval of 20-30 ° high-elastic deformation is formed; the greater the load, the higher this value (Fig. 2, curves 2 and 3). The flow of both polymers takes place in the interval of 150 to 170°, which is in agreement with results of relaxation measurements [4]. Therefore, the temperature range observed on temperature/deformation curves, where high-elastic deformation starts to take place is the melting range of liquidcrystalline structures in the polymers. As a result of disrupting the order of side groups segmental mobility becomes possible and high-elastic properties emerge (provided the actual load is insufficient for viscous flow).
lO
2
~
6
a
3
\ ....
!
l
~
10
t
I
30 ~,% Fro. 1
]
I
I
I 30
I 60
90
I
T[me, min Fie. 2
FIG. 3. Elongationcurves: 1-POP, 2-PDP. FIG. 4. Creep curves of PDP (a), POP (b) when a = 3"4 MPa; b: 1 -air, 2 - blood plasma, 3 - water. These conclusions are in agreement with elongation curves plotted at room temperature (Fig. 3), i.e. under conditions close to initial disruption of the order of side chains. PDP and POP films first have a relatively high initial tensile strength: P O P - 10.0, P D P - 9 . 5 MPa. The increasing load results in the disruption of order in side chains at lower temperature, i.e. in forced melting, as observed in the case of recrystallization in crystalline polymers. Having become isotropic the polymer rapidly flows (Fig. 2, curves 1, 4).
Synthesis and study of polyalkoxyphosphazenes
161
Creep curves of the polyalkoxyphosphazenes (Fig. 4) show satisfactory agreement with temperature/deformation curves and elongation curves. By the action of a constant load of 3.4 MPa a deformation of the order of 4-5 70 is formed rapidly, which is made up of reversible high-elastic and "irreversible" deformation; the latter is made up of two c o m p o n e n t s - f o r c e d , high-elastic and plastic, irreversible deformation of flow; the proportion of the latter increases on increasing the duration of heating, while the closer the experimental temperature to the temperature of disruption of the order in side chains, the higher the proportion of the former. The hydrophobic nature of the polymers examined, which is due to the existence of long alkyl radicals has the result that creep curves coincide when using various liquid media (water, blood plasma) (Fig. 4). Permeabilities were determined for POP and PDP films obtained using 02, N2 and Ar; their values are between those of natural rubber and polydimethylsiloxanes. Films based on the polyalkoxyphosphazenes indicated have reduced flammability. Tranalated by E. SEMERE REFERENCES
1. G. ALLCOCK, Fosforazotistyye soyedinaniya, p. 416, Mir, Moscow, 1976 2. F. A. BITTIROVA, V. V. KIREYEV and A. K. MIKITAYEV, Vysokomol. soyed. B23: 30, 1981 (Not translated in Polymer Sci. U.S.S.R.) 3. M. N. ALEXANDER, C. R. DESPER, P. L. SAGALYN and N. S. SCHNEIDER, Macromolecules 10: 721, 1977 4. I. B. SOKOLO¥SKAYA, V. V. KOCHERVINSKII, V. V. K1REYEV, V. V. KORSHAK, Yu. V.
ZELENEV and F. A. BITTIROVA, Dokl. AN SSSR 256: 911, 1981
0032-3950/84 $10.00+.00 © 1985 Pergamon Press Ltd.
Printed in Poland
S Y N T H E S I S A N D STUDY OF POLYALKOXYPHOSPHAZENES* V. V. KIREYEV, F. A. BITTIROVA, G. I. MITROPOL'SKAYA, A . K . MIKITAYEV, V. S. PAPKOV a n d M. N . ILqNA D. I. Mendeleyev Chemico-Technological Institute, Moscow Institute of High Molar Mass Compounds, Kabardin-Balkh State University
(Received 25 May 1982) Polydialkoxyphosphazenes with long-chain lateral radicals were synthesized and identified and the presence of a certain order in the position of lateral radicals, established. Polydialkoxyphosphazenes are chemically inert and do not practically change in weight and reduced viscosity during prolonged retention in solutions of mineral acids and alkalies; under conditions of isothermal heating a reduction is observed in these indices. Mechanical and thermo-mechanical characteristics of polydialkoxyphosphazenes were examined.
AMONG the many polyphosphazenes special interest is attached to polyorganoxyphosphazenes readily formed during the treatment of polydiehlorophosphazene with alkali metal alcoholates or phenates [1]. However, up to recently practically no polyphosphazenes were known with long aliphatic radicals in the lateral chain. A report was given previously [2] of the synthesis of polydi-(n-octyloxy)phosphazene (POP); a description is given in this paper of the preparation of polydi-(n-hexyloxy)phosphazene (PHP) and polydi-(n-dodecyloxy)phosphazene (PDP) and a comparative study made of some properties of these three polymers. Raw materials, n-Hexanol and n-dodecanol were dried with freshly calcined calcium oxide and distilled (b.p. 157 and 255-259 °, respectively). Purification of the initial hexaehlorocyclotriph0sphazene and its polymerization were carried out by methods previously described [1]. PHP and PDP were synthesized in the same way as POP [2], by the treatment of polydichlorophosphazene with an excess of corresponding alcoholates in dry diethylene glycol. The polymers were separated and purified, as previously [2]. Methods of investigation. Reduced viscosity and gas-permeability of polymers were measured, as before [2]. X-ray studies were carried out in a URS-50I device with CuK~ radiation. Creep in air and in various media and thermo-mechanical investigations were carried out in a Zhurkov device using constant stress. Mechanical measurements were carried out in a Polyani type device. I R spectra were recorded in an IKS-22 device using films obtained from polymer solutions in chloroform. P M R spectra were obtained in a VS-497 device at an operating frequency of 60 MHz for solutions of the substances examined in deuterochloroform, alp N M R spectra were recorded using a Bruker HX-90 device (operating frequency 36'43 MHz) for polymer solutions in deuterochloroform using 85 % H3PO4 as external standard. Potentiometric titration of alcoholic solutions of * Vysokomol. soyed. A26: No. 1, 140-144, 1984. 1~6
Synthesis and study of polyalkoxyphosphazenes
157
samples of the reaction mixture when synthesizing polymers was carried out using a HC1 alcoholic solution and an LPM-60M potentiometer with an automatic titration unit. The degree of substitution of chlorine atoms in polydichlorophosphazene when preparing P H P and PDP, the same as for the synthesis of POP [2] was monitored by potentiometric titration of the unreacted alcoholate, using IR spectra and elemental analysis. As shown by Table 1, at a temperature of 130-140 ° synthesis of P H P and P D P may be carried out for 40 and 80 hr, respectively; under these conditions practically complete substitution of chlorine atoms for alkoxyradicals is achieved. Absorption bands in the range of 550-600, 2700-2800 and 3200-3400 c m - 1, typical of bond-stretching vibrations of P - C 1 , P - O H and N - H groups, respectively are absent from IR spectra of the polymers obtained; this also proves that substitution is complete. alp N M R spectra of PHP and PDP are characterized by the presence of a singlet signal in the range of - 8 . 0 - + 8 . 3 p.p.m. Chemical shifts at 4.5, 1.5 and 0.8 p.p.m. in P M R spectra of polyalkoxyphosphazenes correspond to O - C H 2 , (CH2),, and C H 3 groups. Intensity ratios of proton signals of alkoxy groups of polymers synthesized are given below; these are values found from P M R spectra and calculated values. Polymer I n t e n s i t y ratio o f p r o t o n signals o f OCH2 : CH2 : CHa groups, found from PMR spectra calculated
PItP
POP
PDP
1-9:8.0:3.0 2 :8 :3
2.1:12,0:3.0 2 : 12 : 3
2.4:19.5:3.1 2 : 20 : 3
Proton signals of P - OH and N - H groups are absent from P M R spectra of polymers; this also proves that substitution is complete and secondary hydrolytic reactions are absent. P H P and PDP are soluble in chloroform, ethyl ether, benzene and on heating in CCI~ and chlorobenzene; they are insoluble in water, mineral acids and organic solvents such as acetone, ethanol and DMF. P H P and PDP were subjected to fractional precipitation from 1 ~ solution in benzene with acetone. Initial polymers and their fractions have the same elemental composition, which agrees with the calculated value, the same chemical shift values in alp N M R spectra (8.1-8.2 p.p.m.) and identical IR spectra. However, anomalies TABLE ]. VARIATION OF CHLORINE CONTENT DURING THE SYNTHESIS* OF P H P AND P D P Chlorine content (~) Reaction time, hr
during the synthesis of PHP
1.5 8'5 20.0
13.8 10.0 1 "2
* In diethylene glycol at 130-140°C.
Chlorine content (%) R e a c t i o n time, h r
PDP 25.1 20.8 15'3
40.0 60-0 80-0
during the synthesis of PHP
PDP
Traces ,, ,,
8.2 3.1 Traces
V . V . KaREYEV et al.
158
are observed for initial polymers and their fractions in the concentration dependence of reduced viscosity, which hinder the determination of intrinsic viscosity. These anomalies may be caused, the same way as in the case of POP [2], by the formation of macromolecular associates in solution which gradually break down in the course of dilution, thus increasing viscosity. During isothermal heating in air of PHP and PDP at 140° a gradual reduction takes place in weight and reduced viscosity, this being more typical of PHP than PDP. During heating for 10 hr at 140° weight loss for PHP is 15 Yo, while reduced viscosity of a 0.5 ~ solution decreases from 0.38 to 0.13 dl/g. For PDP weight loss under these conditions only reaches 5 ~ , while viscosity decreases from 0.20 to 0.15-0.19 dl/g. At the same time in 5 ~ dilute solutions of KOH and HCI breakdown processes are less strongly expressed (Table 2). The same as for POP [2], the low heat stability of the polyalkoxyphosphazenes studied may be caused by the steric interaction of bulky lateral substituents destabilizing the main chain and by damage to the main macromolecular chain [3]. In spite of the low value of its reduced viscosity, which is 0.20 dl/g for PDP, this polymer forms flexible elastic films from solution in chloroform, in contrast with PHP even though the reduced viscosity of this polymer is 0.38 dl/g. N M R pulse spectroscopy and a dielectric method were previously used to study relaxation properties of POP, PHP and PDP; two main ranges of relaxation were found and a relation derived between transition points and dimensions of lateral radicals [4]. Results of relaxation methods of investigation agree with data of differential scanning calorimetry* (Fig. 1). The thermogram of POP plotted while heating shows an endothermic peak of melting at 0 ° (273°K); a sharper exothermic peak appears at - 1 3 ° (260°K) on the cooling curve, which is typical of crystallization. The heat of crystallization and melting, found from the area of these peaks is 14.5 cal/g. The difference in melting points and crystallization temperatures (0 and - 1 3 °) corresponds to differences normally observed in these parameters for high molecular weight compounds. The difference in temperatures of phase transition obtained from calorimetric and relaxation measurements [4] is also TABLE2. VARIATION OF THE WEIGHT AND REDUCED VISCOSITY OF P H P AND P D P DURINGRETENTIONIN AIR AND IN 5 ~/o DILUTE SOLUTIONS OF HCI AND K O H
Polymer
PHP PDP
l .
Variation of ~/,ea, dl/g (numerator) and weight loss, ~ (denominator) o n retaining polymers for 100 hr at 140 ° in air
in 5 % K O H
in 5 y, HCI
0"30
0'05
0.08
55.0
3.5
5-1
0.13 15.0
0 1"5
0.01 2.4
* Calorimetric measurements were carried out by Yu. K. Godovskii, to whom the authors arc very grateful.
Synthesis and study of polyalkoxyphosphazenes
159
within reasonable limits. In contrast with PDP, according to results of differential scanning calorimetry, PHP does not show first order phase transitions. The thermogram of POP, characterized by the existence of an asymmetric endothermic peak at - 7 7 ° (196°K), is unusual. In shape this peak corresponds to phase transition (in case of glass transition it should be S-shaped), however, it is characterized by low heat (-2.45 cal/g). Nevertheless, it probably corresponds to the glass transition, which is in agreement with results of relaxation measurements [4], according to which POP has T, = - 7 8 °. In spite of the absence from thermograms of PHP and POP of peaks that corre spend to phase transition, these polymers show a degree of ordering, as confirmed by diffraction curves, characterized by the existence of an amorphous halo in the angular range of 20"~20 ° and the existence of narrow diffraction peaks in the small angular range.
196K 170K 250K 208K
ZTSK
~"
40 -
318K FIO. 1
260K
0
2 L
i
80
I
I _~
t60 T"
FIo. 2
FIo. 1. Thermo~ams of POP (a) and PDP (b); b: 1-heating (rate 20 deg/min), 2-cooling. FIG. 2. Temperature/deformationcurves of PDP (1, 5) and POP (2--4), plotted with.constant load. 1, 2, 4 - C o m p r e s s i v e load 0.4 (1); 0.1 (2) arid 0.2 MPa (4); 3, 5-tensile stress 0.05 MPa. The position of the diffraction maximum in the range of small angles depends on the length of the lateral alkyl radical; interplanar distance dl increases with an increase in lateral chain length in the P H P - P O P - P D P series. Results of structural methods suggest that coordinated arrangement of lateral chains is observed in PDP with disordered position of the main chain. In PHP and POP elements of ordering of lateral chains only begin to show, as confirmed by X-ray analysis, but are unconfirmed thermodynamically. The structural features of polyalkoxyphosphazenes affect thermodynamic and mechanical characteristics. In view of the fact that strong elastic films only form from PDP and POP, these polymers were examined.
160
V. V, IOR~YEV et al.
By the action of a compressive load of 1>0.1 MPa immediately after melting at 20 to 30 ° PDP flows (Fig. 2). A similar curve was also plotted for POP, although in this temperature range no phase transition was observed. The order in the arrangement of lateral octyl radicals is evidently disrupted in this temperature range and the restrictions imposed by this order on the mobility of the main chain are removed. These assumptions confirm the curves plotted under a load insufficient for flow. In this case temperature/deformation curves have a form, which is typical of the linear amorphous polymer. After breaking the order of the side chains and after the appearance of segmental mobility in the interval of 20-30 ° high-elastic deformation is formed; the greater the load, the higher this value (Fig. 2, curves 2 and 3). The flow of both polymers takes place in the interval of 150 to 170°, which is in agreement with results of relaxation measurements [4]. Therefore, the temperature range observed on temperature/deformation curves, where high-elastic deformation starts to take place is the melting range of liquidcrystalline structures in the polymers. As a result of disrupting the order of side groups segmental mobility becomes possible and high-elastic properties emerge (provided the actual load is insufficient for viscous flow).
lO
2
~
6
a
3
\ ....
!
l
~
10
t
I
30 ~,% Fro. 1
]
I
I
I 30
I 60
90
I
T[me, min Fie. 2
FIG. 3. Elongationcurves: 1-POP, 2-PDP. FIG. 4. Creep curves of PDP (a), POP (b) when a = 3"4 MPa; b: 1 -air, 2 - blood plasma, 3 - water. These conclusions are in agreement with elongation curves plotted at room temperature (Fig. 3), i.e. under conditions close to initial disruption of the order of side chains. PDP and POP films first have a relatively high initial tensile strength: P O P - 10.0, P D P - 9 . 5 MPa. The increasing load results in the disruption of order in side chains at lower temperature, i.e. in forced melting, as observed in the case of recrystallization in crystalline polymers. Having become isotropic the polymer rapidly flows (Fig. 2, curves 1, 4).
Synthesis and study of polyalkoxyphosphazenes
161
Creep curves of the polyalkoxyphosphazenes (Fig. 4) show satisfactory agreement with temperature/deformation curves and elongation curves. By the action of a constant load of 3.4 MPa a deformation of the order of 4-5 70 is formed rapidly, which is made up of reversible high-elastic and "irreversible" deformation; the latter is made up of two c o m p o n e n t s - f o r c e d , high-elastic and plastic, irreversible deformation of flow; the proportion of the latter increases on increasing the duration of heating, while the closer the experimental temperature to the temperature of disruption of the order in side chains, the higher the proportion of the former. The hydrophobic nature of the polymers examined, which is due to the existence of long alkyl radicals has the result that creep curves coincide when using various liquid media (water, blood plasma) (Fig. 4). Permeabilities were determined for POP and PDP films obtained using 02, N2 and Ar; their values are between those of natural rubber and polydimethylsiloxanes. Films based on the polyalkoxyphosphazenes indicated have reduced flammability. Tranalated by E. SEMERE REFERENCES
1. G. ALLCOCK, Fosforazotistyye soyedinaniya, p. 416, Mir, Moscow, 1976 2. F. A. BITTIROVA, V. V. KIREYEV and A. K. MIKITAYEV, Vysokomol. soyed. B23: 30, 1981 (Not translated in Polymer Sci. U.S.S.R.) 3. M. N. ALEXANDER, C. R. DESPER, P. L. SAGALYN and N. S. SCHNEIDER, Macromolecules 10: 721, 1977 4. I. B. SOKOLO¥SKAYA, V. V. KOCHERVINSKII, V. V. K1REYEV, V. V. KORSHAK, Yu. V.
ZELENEV and F. A. BITTIROVA, Dokl. AN SSSR 256: 911, 1981