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Polyamides from fluoroalkylphenylenediamines and isophthalic acid
Polyamides from fluoroalkylphenylenediamines and isophthalic acid 59. 60. 61. 62. 63. 64. 65. 66. 67.
11 l 0
A. L. $EGRI~, Macromolecules h 93, 1968 F. HEATLEY and F. A. BOVEY, Maoromolecules 2: 241, 1969 T. YOSCHINO and J. KOMIYAMA, J. P o l y m e r Sci. B3: 311, 1965 L. CAVAI.;.I, C. (3. BORSINI, G. CARRAVO and G. CONFALONIERI, J. Polymer Sci. A - l , 8: 801, 1970 / L. B. STROGANOV, Yu. A. TARAN, N. A. PLATE a n d T. ZEIFERT, Vysokomol. soyed. A l 6 : 2147, 1974 (Translated in P o l y m e r Sei. U.S.S.R. 16: 9, 2489, 1974) J. P I T H A and R. N. JONES, Canadian J. Chem. 44: 3031, 1966 L. B. STROGANOV, Yu. A. TARAN a n d N. A. PLATE, Zh. fiz. khim. 49: 2696, 1975 N. M. SERGEYEV, Zh. strukt, khim. 7: 356, 1966 V. D. MOI3HEL, Macromolceules 2: 537, 1966
POLYAMIDES FROM FLUOROALKYLPHENYLENEDIAMINES AND ISOPHTHALIC ACID* B. F. 1WAr,rcH~XO, E. V. SHELUD'KO~nd O. N. TSYPINA I n s t i t u t e of the Chemistry of Macromolecular Compounds, Ukr. S.S.R. A c a d e m y of Sciences (Received 7 October 1974) The effect of fluoroalkyl substituents on the properties of polyphenyleneisophthalamides has been studied. I n t r b d u c t i o n of fluoroalkyl substituents in the meta position with respect to the amide groups imparts improved solubility, resistance to thermaloxidative degradation a n d hydrolysis, and greatly increased low temperature resistance to the fluorinated polyamides, in comparison with the unfluorinated polymer "Fenilon". W h e n the same substituents are a t t a c h e d to the ortho position with respect to the amide groups the heat resistance of the polyamides is reduced.
IT is well known that aromatic polyamides have high heat resistance [1]. In many instances the melting points of aromatic polyamides is higher than the thermal decomposition temperature, which makes moulding of such polymers from the melt difficult or impossible. Therefore production of articles, such as fibres, from these polymers must be carried out from hot solutions in concentrated sulphuric acid, or the amide salt system must be used. Polyamides that combine high heat resistance with solubility in ordinary solvents could be very promising from the practical point of view. Aromatic polyamides containing fluorine have received little study. It is known [2, 5] that in order to obtain heat resistant polyamides it is necessary to separate the fluorinated substituents from the amino or carboxyl functional groups by some thermally stable non-fluorinated fragment. It is also known that * Vysokomol. soyed. AI8: No. 5, 980-983, 1976.
B. F. M~ICEENKO eta/. p o l y a m i d e s f r o m t e r e p h t h a l i c acid a n d p h e n y l e n e d i a m l n e s [6] h a v e b e t t e r hea~ resistance t h a n p o l y m e r s f r o m t h e s a m e d i a m i n e s a n d i s o p h t h a l i c acid [7], b u t t h e y are less soluble a n d h a v e p o o r e r processing characteristics. I t S e e m e d o f i n t e r e s t to s y n t h e s i z e a r o m a t i c p o l y a m i d e s f r o m fluoroalkyIp h e n y l e n e d i a m i n e s a n d i s o p h t h a l i c acid a n d to c o m p a r e t h e i r p r o p e r t i e s w i t h u n f l u o r i n a t e d p o l y a m i d e s of s i m i l a r s t r u c t u r e . T h e f o r m u l a e of t h e r e p e a t i n g u n i t s of t h e p01yamides s y n t h e s i z e d are g i v e n below CF3 1 // ~ --HN--()--NHC0--,)--C0--(l);
CFa
i ?h--NHC0--~\~--C0 --HN--~J ~/~
CuF~ I
CaF7 I //
~HN
(II);
(III); - - H N - - ( )
~
~)
(IV);
CH I ~
~
--NHCO-- ~
--CO--
--NH The polyamides V ("Fenilon") and ¥ I , from 2,4-toluylenediamine and isophthalic acid, which do not contain fluorine, were prepared under similar conditions for comparison. 1-Trifluoromethyl-2,5-and 3,5-phenylenediamines were prepared by the conventional method and purified by vacuum distillation. Products with m. p. 56-57 ° and 88-89 ° respectively were used [8]. 1-Perfluoropropyl-2,5- and 3,5-phenylenediamines were prepared by the-usual method and purified by vacuum distillation, products with m.p. 66-67 ° and 93-94 ° respectively being used [9]. Metaphenylenediamine and 2,4-toluylenediamine were PROPERTIES
Polyamide
I II III IV V ¥I
Yield, ~o
97 92 97 90 94 91
[~/], dl/g
0"70 0"61 0'66 0-52 0-57 0'42
OF S Y N T H E S I Z E D P O L Y A M I D E S
Thermal de- / Loss in composition t temperaweight at ture, °C 500 °C, ~o 390 350 380 340 360 340
14"2 25"4 20"6 37"0 19"5 17"5
Loss in weight ~/o after heating with HaOH
H,SOa
32.0 80.0 8"5 33.4 30.2 36.3
1.3 0.9 0-9 1.5 7.7 3.0
purified by sublimation i n v a c u o and products with m.p. 63-64 ° and 98-99 ° respectively were used. Isophthalyl chloride was prepared from isophthalic acid and PC15, and purified by vacuum distillation, m.p. 41 °. Lithium chloride and N-methyl-2-pyrrolidone were purified and dried by the usual methods.
Polyamides from fluoroalkylphenylenediamines and isophthalic acid
1121
Polymers I-VI were synthesized by the conventional method [10], using the l~-methyl2-pyrrolidone-lithium chloride amide salt system. The structure of the polyamidcs was confirmed by analysis for fluorine (polyamides I-IV) and for nitrogen (V and VI) and by IR spectroscopy. The intrinsic viscosity of the polymers was determined in DMF (I-IV and ~Y) or sulphuric acid (polymer V) at 20°. Thermal analysis of the polymers was carried out in a derivatograph at a rate of heating of 6 deg/min. Films of the polyamides were examined under a MIN-8 polarizing microscope. The hydrolytic stability of the polymers was determined as the loss in weight after samples had been heated with a twentyfold excess of 10% I~aOH or 10~o H~SO4 for 6 hr at 100°. The samples taken for hydrolysis were in the form of uniform powders, obtained by precipitation by alcohol from solution in DMF. The loss in weight was measured directly by weighing, with a precision of ~0-0001 g. The average of three parallel measurements are given in the Table. Films of the polyamides were prepared by evaporation of solutions in N-methyl-2-pyrrolidone, followed by drying to constant weight i n vacuo. The low temperature resistance was judged by the absence of mechanical damage after films had been bent several times around a rod of diameter 1 mm in liquid nitrogen. The properties of the polymers are given in the Table. I n t r o d u c t i o n of perfluoroalkyl s u b s t i t u e n t s into t h e macromolecule of polyamides i m p r o v e s their solubility in organic solvents. F o r e x a m p l e I - I V a n d V I are soluble in DMF, N - m e t h y l - 2 - p y r r o l i d o n e and h e x a m e t h y l t r i a m i d o p h o s p h a t e , whereas V a t 20 ° is soluble only in c o n c e n t r a t e d H2SO 4. I n N - m e t h y l - 2 - p y r r o l i d o n e it is soluble only a t high t e m p e r a t u r e s . P o l y a m i d e I I I , which is derived f r o m perfluoropropyl-3,5-phenylenediamine, has p a r t i c u l a r l y high solubility. I n addition to t h e solvents m e n t i o n e d a b o v e it is soluble a t 20 ° also in ketones, such as acetone. T h e intrinsic viscosity of p o l y m e r s I - V I is fairly high a n d o f similar m a g n i t u d e , which p e r m i t s comparison of the physicochomieal properties o f these polymers. I n t r o d u c t i o n of fluorine containing s u b s t i t u e n t s in t h e m e t a position with respect to the amide groups raises the decomposition t e m p e r a t u r e of the p o l y m e r s b y 20-30 °, in comparison w i t h t h e unfluorinated polymers V a n d V I (Figure). P o l y a m i d e s I I and IV, where the same s u b s t i t u e n t s are in the ortho position w i t h respect to the amide groups, h a d lower h e a t resistance. The decomposition t e m p e r a t u r e s of polyamides I I a n d I V are 350 a n d 340 ° respectively. Special e x p e r i m e n t s have shown t h a t when I I a n d I V are h e a t e d i s o t h e r m a l l y in air a t these t e m p e r a t u r e s H F is present a m o n g the gaseous d e g r a d a t i o n p r o d u c t s . H e n c e in these instances t h e nearness of the fluorinated s u b s t i t u e n t a n d the amide g r o u p in space a n d their conjugation p r o m o t e elimination of h y d r o g e n fluoride. T h e r e f o r e t h e r m a l d e g r a d a t i o n is complicated b y chemical d e g r a d a t i o n o f the perfluoroalkyl groups, a n d amide linkages u n d e r the influence of H F . The D T G curves also indicate the multistage n a t u r e of t h e r m a l d e g r a d a t i o n of PAs I I and IV. A t 500 ° t h e t h e r m a l stability of the polyamides according t o the loss in weight varies in the following order: I > V I > V > I I I > I I > I V . Films of all the polyamides, deposited on a glass slide, were e x a m i n e d u n d e r t h e polarizing microscope. I t was f o u n d t h a t I a n d I I I , despite t h e presence
B . F. M ~ a ~ e m a w ~ o ~ o/.
1122
of fluoroalkyl groups in the chain, begin to crystallize at 100°, already during the course of evaporation of the solvent, Probably crystallization of I and I I I is assisted by increase in interchain interaction, caused by additional hydrogen bonding of the C--H...F--C type, which creates favourable conditions for suitable orientation and packing of the polymer chains. All the other polymers, including the unfluorinatcd polyamides V and VI, do not crystallize under these conditions. I t is known in the literature that Fenilon crystallizes at about 350 ° [11].
.
qO
E -
V
10
,YO0
qo0
6O0
T,oG
TGA curves of polyamides I-VI. Heated in air at the rate of 6 deg/min. Addition of fluoroalkyl substituents into polyamide molecules increases their resistance to boiling aqueous solutions oi mineral acids. Alkalis break down fluorinated polyamides to a considerably greater extent than acids. Hydrolysis in an alkaline medium begins with attack of the HO- ion on the carbon atom of the carbonyl group. The greater the partial positive charge on the carbon atom of the carbonyl group the easier is alkaline hydrolysis of the amide grouping. This process is aided by electron accepter substituents in the ortho position with respect to the amide group. Hence polymers II and IV break down to a greater extent under alkaline conditions. Polyamido I I I has high resistance to alkalis. In this polyamide the perfluoroalkyl substituent is in the meta position with respect to the amide groups and it therefore affects the electron density on the carbon atom of the carbonyl group to a considerably smaller extent. It must however increase the hydrophobic character of the PA chain and to some extent retard hydrolysis. It should be noted that in hydrolysis of polymers II and IV the perfluoroalkyl substituents are involved as well as the amide groups, because fluorine ions are found in the solution. Thus in order to improve the properties of polyamides fluoroalkyl substituents must be attached in the meta position with respect to the amide groups. The ability to form films is also dependent on the relative positions of the amide groups and fluorinated substituents. Polymers II, IV and VI, in which the fluorinated or non-fluorinated substituents are in the ortho position to the amide groups,
Polyamides from fluoroalkylphenylenediamines and isophthalic acid
1123
f o r m b r i t t l e films. P o l y m e r s I a n d I I I , w h i c h c o n t a i n t h e s e g r o u p i n g s in t h e m ~ a position, easily f o r m films w i t h s a t i s f a c t o r y s t r e n g t h characteristics. T h e tensile s t r e n g t h a t b r e a k o f t h e s e films in t h e u n o r i e n t a t e d s t a t e is 300 k g / c m 2 a t a n e l o n g a t i o n o f 1 0 ~ . P o l y m e r V f o r m s b r i t t l e films. A n i n t e r e s t i n g p r o p e r t y o f films o f I a n d I I I is t h e i r h i g h r e s i s t a n c e t o low t e m p e r a t u r e s . T h e y do n o t b e c o m e b r i t t l e e v e n a t - - 195 °, a t w h i c h t e m p e r a t u r e t h e y c a n b e b e n t r e p e a t e d l y w i t h o u t breaking. All t h e fluorine c o n t a i n i n g p o l y a m i d e s h a v e r e d u c e d f l a m m a b i l i t y . W h e n r e m o v e d f r o m t h e f l a m e o f t h e b u r n e r t h e y slowly s t o p b u r n i n g , w h e r e a s t h e non-fluorinated polymers V and VI continue to burn. Tr~te~
5y E. O. PHILLIPS
REFERENCES
1. V. V. KORSHAK and T. M. FRUNZE, Sinteticheslde geteroteepnye poliamidy (Synthetic Hetero-chain Polyamides). Izd. Akad. Nauk SSSR, 1962 2. B. F. MALICHENKO, Z. S. PRIgHOD'KO and N. N. SEMENIgHINA, Vysokomol. soyed AIS: 966, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 4, 1089, 1971) 3. B. F. MALICHENKO, L. Sh. SHAGELISHVI~, A. A. KACHAN, L. L. CHERVYATSOVA, G. L BELOKONEVA and G. P. TATAUROV, Vysokomol. soyed. A13: 809, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 4, 912, 1971) 4. B. F. MALICHENKO, V. V. SERIKOVA, L. L. CHERVYATSOVA, A. A. KACHAN and G. I. MORYUK, Vysokomol. soyed. BI4: 423, 1972 (Not translated in Polymer ScL U.S.S.R.) 5. G.S. KOLESNIKOV, O. Ya. FEDOTOVA, G. S. MATVELASHVILI and Ye. V. GUTSALYU~ Vysokomol. soyed. A12: 528, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 3, 594, 1970) 6. M. M. KOTON, Uspekhi khlmii 81" 153, 1962 7. Ye. L. KRASNOV, V. M. SAVINOV, L.B. SOKOLOV, V. I. LOGUNOVA, V.K. BELYAKOVA and T. A. POLYAKOVA, Vysokomol. soyed. 8" 380, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 3, 413, 1966) 8. I. KAN and M. YASUO, J. Chem. Soc. Japan, Ind. Chem. Sec. 69" 2229, 1966 9. B. F. MALICHENKO and O. N. TSYPIN, Zh. obshch, khim. 89- 2515, 1969 10. A. A. FEDOROV, V. M. SAVINOV and L. R. SOKOLOV, Vysokomol. soyed. A12: 2185, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 10, 2475, 1970) 11. G. A. KUZNETSOV, V. D. GERASIMOV, L. N. FOMENKO, A. I. MAKLAKOV, G. G. PIMENOV and L. B. SOKOLOY, Yysokomol. soyed. 7: 1592, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 9, 1763, 1965)
11 l 0
A. L. $EGRI~, Macromolecules h 93, 1968 F. HEATLEY and F. A. BOVEY, Maoromolecules 2: 241, 1969 T. YOSCHINO and J. KOMIYAMA, J. P o l y m e r Sci. B3: 311, 1965 L. CAVAI.;.I, C. (3. BORSINI, G. CARRAVO and G. CONFALONIERI, J. Polymer Sci. A - l , 8: 801, 1970 / L. B. STROGANOV, Yu. A. TARAN, N. A. PLATE a n d T. ZEIFERT, Vysokomol. soyed. A l 6 : 2147, 1974 (Translated in P o l y m e r Sei. U.S.S.R. 16: 9, 2489, 1974) J. P I T H A and R. N. JONES, Canadian J. Chem. 44: 3031, 1966 L. B. STROGANOV, Yu. A. TARAN a n d N. A. PLATE, Zh. fiz. khim. 49: 2696, 1975 N. M. SERGEYEV, Zh. strukt, khim. 7: 356, 1966 V. D. MOI3HEL, Macromolceules 2: 537, 1966
POLYAMIDES FROM FLUOROALKYLPHENYLENEDIAMINES AND ISOPHTHALIC ACID* B. F. 1WAr,rcH~XO, E. V. SHELUD'KO~nd O. N. TSYPINA I n s t i t u t e of the Chemistry of Macromolecular Compounds, Ukr. S.S.R. A c a d e m y of Sciences (Received 7 October 1974) The effect of fluoroalkyl substituents on the properties of polyphenyleneisophthalamides has been studied. I n t r b d u c t i o n of fluoroalkyl substituents in the meta position with respect to the amide groups imparts improved solubility, resistance to thermaloxidative degradation a n d hydrolysis, and greatly increased low temperature resistance to the fluorinated polyamides, in comparison with the unfluorinated polymer "Fenilon". W h e n the same substituents are a t t a c h e d to the ortho position with respect to the amide groups the heat resistance of the polyamides is reduced.
IT is well known that aromatic polyamides have high heat resistance [1]. In many instances the melting points of aromatic polyamides is higher than the thermal decomposition temperature, which makes moulding of such polymers from the melt difficult or impossible. Therefore production of articles, such as fibres, from these polymers must be carried out from hot solutions in concentrated sulphuric acid, or the amide salt system must be used. Polyamides that combine high heat resistance with solubility in ordinary solvents could be very promising from the practical point of view. Aromatic polyamides containing fluorine have received little study. It is known [2, 5] that in order to obtain heat resistant polyamides it is necessary to separate the fluorinated substituents from the amino or carboxyl functional groups by some thermally stable non-fluorinated fragment. It is also known that * Vysokomol. soyed. AI8: No. 5, 980-983, 1976.
B. F. M~ICEENKO eta/. p o l y a m i d e s f r o m t e r e p h t h a l i c acid a n d p h e n y l e n e d i a m l n e s [6] h a v e b e t t e r hea~ resistance t h a n p o l y m e r s f r o m t h e s a m e d i a m i n e s a n d i s o p h t h a l i c acid [7], b u t t h e y are less soluble a n d h a v e p o o r e r processing characteristics. I t S e e m e d o f i n t e r e s t to s y n t h e s i z e a r o m a t i c p o l y a m i d e s f r o m fluoroalkyIp h e n y l e n e d i a m i n e s a n d i s o p h t h a l i c acid a n d to c o m p a r e t h e i r p r o p e r t i e s w i t h u n f l u o r i n a t e d p o l y a m i d e s of s i m i l a r s t r u c t u r e . T h e f o r m u l a e of t h e r e p e a t i n g u n i t s of t h e p01yamides s y n t h e s i z e d are g i v e n below CF3 1 // ~ --HN--()--NHC0--,)--C0--(l);
CFa
i ?h--NHC0--~\~--C0 --HN--~J ~/~
CuF~ I
CaF7 I //
~HN
(II);
(III); - - H N - - ( )
~
~)
(IV);
CH I ~
~
--NHCO-- ~
--CO--
--NH The polyamides V ("Fenilon") and ¥ I , from 2,4-toluylenediamine and isophthalic acid, which do not contain fluorine, were prepared under similar conditions for comparison. 1-Trifluoromethyl-2,5-and 3,5-phenylenediamines were prepared by the conventional method and purified by vacuum distillation. Products with m. p. 56-57 ° and 88-89 ° respectively were used [8]. 1-Perfluoropropyl-2,5- and 3,5-phenylenediamines were prepared by the-usual method and purified by vacuum distillation, products with m.p. 66-67 ° and 93-94 ° respectively being used [9]. Metaphenylenediamine and 2,4-toluylenediamine were PROPERTIES
Polyamide
I II III IV V ¥I
Yield, ~o
97 92 97 90 94 91
[~/], dl/g
0"70 0"61 0'66 0-52 0-57 0'42
OF S Y N T H E S I Z E D P O L Y A M I D E S
Thermal de- / Loss in composition t temperaweight at ture, °C 500 °C, ~o 390 350 380 340 360 340
14"2 25"4 20"6 37"0 19"5 17"5
Loss in weight ~/o after heating with HaOH
H,SOa
32.0 80.0 8"5 33.4 30.2 36.3
1.3 0.9 0-9 1.5 7.7 3.0
purified by sublimation i n v a c u o and products with m.p. 63-64 ° and 98-99 ° respectively were used. Isophthalyl chloride was prepared from isophthalic acid and PC15, and purified by vacuum distillation, m.p. 41 °. Lithium chloride and N-methyl-2-pyrrolidone were purified and dried by the usual methods.
Polyamides from fluoroalkylphenylenediamines and isophthalic acid
1121
Polymers I-VI were synthesized by the conventional method [10], using the l~-methyl2-pyrrolidone-lithium chloride amide salt system. The structure of the polyamidcs was confirmed by analysis for fluorine (polyamides I-IV) and for nitrogen (V and VI) and by IR spectroscopy. The intrinsic viscosity of the polymers was determined in DMF (I-IV and ~Y) or sulphuric acid (polymer V) at 20°. Thermal analysis of the polymers was carried out in a derivatograph at a rate of heating of 6 deg/min. Films of the polyamides were examined under a MIN-8 polarizing microscope. The hydrolytic stability of the polymers was determined as the loss in weight after samples had been heated with a twentyfold excess of 10% I~aOH or 10~o H~SO4 for 6 hr at 100°. The samples taken for hydrolysis were in the form of uniform powders, obtained by precipitation by alcohol from solution in DMF. The loss in weight was measured directly by weighing, with a precision of ~0-0001 g. The average of three parallel measurements are given in the Table. Films of the polyamides were prepared by evaporation of solutions in N-methyl-2-pyrrolidone, followed by drying to constant weight i n vacuo. The low temperature resistance was judged by the absence of mechanical damage after films had been bent several times around a rod of diameter 1 mm in liquid nitrogen. The properties of the polymers are given in the Table. I n t r o d u c t i o n of perfluoroalkyl s u b s t i t u e n t s into t h e macromolecule of polyamides i m p r o v e s their solubility in organic solvents. F o r e x a m p l e I - I V a n d V I are soluble in DMF, N - m e t h y l - 2 - p y r r o l i d o n e and h e x a m e t h y l t r i a m i d o p h o s p h a t e , whereas V a t 20 ° is soluble only in c o n c e n t r a t e d H2SO 4. I n N - m e t h y l - 2 - p y r r o l i d o n e it is soluble only a t high t e m p e r a t u r e s . P o l y a m i d e I I I , which is derived f r o m perfluoropropyl-3,5-phenylenediamine, has p a r t i c u l a r l y high solubility. I n addition to t h e solvents m e n t i o n e d a b o v e it is soluble a t 20 ° also in ketones, such as acetone. T h e intrinsic viscosity of p o l y m e r s I - V I is fairly high a n d o f similar m a g n i t u d e , which p e r m i t s comparison of the physicochomieal properties o f these polymers. I n t r o d u c t i o n of fluorine containing s u b s t i t u e n t s in t h e m e t a position with respect to the amide groups raises the decomposition t e m p e r a t u r e of the p o l y m e r s b y 20-30 °, in comparison w i t h t h e unfluorinated polymers V a n d V I (Figure). P o l y a m i d e s I I and IV, where the same s u b s t i t u e n t s are in the ortho position w i t h respect to the amide groups, h a d lower h e a t resistance. The decomposition t e m p e r a t u r e s of polyamides I I a n d I V are 350 a n d 340 ° respectively. Special e x p e r i m e n t s have shown t h a t when I I a n d I V are h e a t e d i s o t h e r m a l l y in air a t these t e m p e r a t u r e s H F is present a m o n g the gaseous d e g r a d a t i o n p r o d u c t s . H e n c e in these instances t h e nearness of the fluorinated s u b s t i t u e n t a n d the amide g r o u p in space a n d their conjugation p r o m o t e elimination of h y d r o g e n fluoride. T h e r e f o r e t h e r m a l d e g r a d a t i o n is complicated b y chemical d e g r a d a t i o n o f the perfluoroalkyl groups, a n d amide linkages u n d e r the influence of H F . The D T G curves also indicate the multistage n a t u r e of t h e r m a l d e g r a d a t i o n of PAs I I and IV. A t 500 ° t h e t h e r m a l stability of the polyamides according t o the loss in weight varies in the following order: I > V I > V > I I I > I I > I V . Films of all the polyamides, deposited on a glass slide, were e x a m i n e d u n d e r t h e polarizing microscope. I t was f o u n d t h a t I a n d I I I , despite t h e presence
B . F. M ~ a ~ e m a w ~ o ~ o/.
1122
of fluoroalkyl groups in the chain, begin to crystallize at 100°, already during the course of evaporation of the solvent, Probably crystallization of I and I I I is assisted by increase in interchain interaction, caused by additional hydrogen bonding of the C--H...F--C type, which creates favourable conditions for suitable orientation and packing of the polymer chains. All the other polymers, including the unfluorinatcd polyamides V and VI, do not crystallize under these conditions. I t is known in the literature that Fenilon crystallizes at about 350 ° [11].
.
qO
E -
V
10
,YO0
qo0
6O0
T,oG
TGA curves of polyamides I-VI. Heated in air at the rate of 6 deg/min. Addition of fluoroalkyl substituents into polyamide molecules increases their resistance to boiling aqueous solutions oi mineral acids. Alkalis break down fluorinated polyamides to a considerably greater extent than acids. Hydrolysis in an alkaline medium begins with attack of the HO- ion on the carbon atom of the carbonyl group. The greater the partial positive charge on the carbon atom of the carbonyl group the easier is alkaline hydrolysis of the amide grouping. This process is aided by electron accepter substituents in the ortho position with respect to the amide group. Hence polymers II and IV break down to a greater extent under alkaline conditions. Polyamido I I I has high resistance to alkalis. In this polyamide the perfluoroalkyl substituent is in the meta position with respect to the amide groups and it therefore affects the electron density on the carbon atom of the carbonyl group to a considerably smaller extent. It must however increase the hydrophobic character of the PA chain and to some extent retard hydrolysis. It should be noted that in hydrolysis of polymers II and IV the perfluoroalkyl substituents are involved as well as the amide groups, because fluorine ions are found in the solution. Thus in order to improve the properties of polyamides fluoroalkyl substituents must be attached in the meta position with respect to the amide groups. The ability to form films is also dependent on the relative positions of the amide groups and fluorinated substituents. Polymers II, IV and VI, in which the fluorinated or non-fluorinated substituents are in the ortho position to the amide groups,
Polyamides from fluoroalkylphenylenediamines and isophthalic acid
1123
f o r m b r i t t l e films. P o l y m e r s I a n d I I I , w h i c h c o n t a i n t h e s e g r o u p i n g s in t h e m ~ a position, easily f o r m films w i t h s a t i s f a c t o r y s t r e n g t h characteristics. T h e tensile s t r e n g t h a t b r e a k o f t h e s e films in t h e u n o r i e n t a t e d s t a t e is 300 k g / c m 2 a t a n e l o n g a t i o n o f 1 0 ~ . P o l y m e r V f o r m s b r i t t l e films. A n i n t e r e s t i n g p r o p e r t y o f films o f I a n d I I I is t h e i r h i g h r e s i s t a n c e t o low t e m p e r a t u r e s . T h e y do n o t b e c o m e b r i t t l e e v e n a t - - 195 °, a t w h i c h t e m p e r a t u r e t h e y c a n b e b e n t r e p e a t e d l y w i t h o u t breaking. All t h e fluorine c o n t a i n i n g p o l y a m i d e s h a v e r e d u c e d f l a m m a b i l i t y . W h e n r e m o v e d f r o m t h e f l a m e o f t h e b u r n e r t h e y slowly s t o p b u r n i n g , w h e r e a s t h e non-fluorinated polymers V and VI continue to burn. Tr~te~
5y E. O. PHILLIPS
REFERENCES
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