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Structural features of the polymeric complex of naphthalene with iodine
Polymer Science U.S.S.R. Vol. 30, No. 11, lap. 2435-2439, 1988 Printed in Poland
0032-3950/88 $10.00+.00 ~ 1990 Pergamon Press plc
STRUCTURAL FEATURES OF THE POLYMERIC COMPLEX OF NAPHTHALENE WITH IODINE* A. M. ARZUMANYAN,I. L. ARUTYUNYANand A. A. MATNISHYAN Armenian Branch of the All-Union Research Institute of Reagents and SpeciallyPure Chemicals (Received 2 June 1987)
Methods of IR, UV and PMR spectroscopy have been used to investigatethe structure of soluble naphthalene oligomers obtained by polycondensationof naphthalene in presence of iodine at 100-120°C. It is shown that propagation of the oligomer chain occurs, in the main, in positions 1,4 and 2,6. The oligomerscontain dihydronaphthalenestructural fragments which persist in the polymericcomplexes of naphthalene and are defects disturbing conjugation of the system. EARLIER it was shown that at 200-250°C naphthalene in presence of iodine forms insoluble, non-fusible black polymeric complexes of scene structure with further development of the planar structures and simultaneous formation of ion-radical salts [l, 2]. The polymeric complexes of naphthalene (PNC) with iodine display semiconductor properties with maximum specific electrical conductivity a = 10-3 f2-1.cm-x. Because of poor solubility the structure of the PNCs has been insufficiently studied. In this respect investigation of soluble low molecular weight oligomeric products may give a better idea of the structure and mechanism of formation of the PNCs. On polymerization of naphthalene in a low temperature regime (100-120°C) with the molar ratio iodine : naphthalene=2 : 1 a soluble, low molecular weight fraction of a light brown colour with M,,~300-400 and containing 1-2 ~ iodine was obtained by hot extraction with benzene from the reaction medium. In the IR spectra of the naphthalene oligomer absorption bands are present characteristic of condensed aromatic systems in the regions 470, 620, 750, 870, 950 and 970 cm- 1 ( C - H deformation vibrations); 1015, 1125, 1260, 1360, 1585 and 1590 cm -1 (valent C - C and C = C ) a n d 3020 and 3050 cm -~ (valent C - H ) (Fig. la). The presence in the oligomer of aromatic units is indicated by the PMR spectra: the presence of the resonance lines of the ~ and fl groups of the protons characteristic of naphthalene in the region 7.8 (~) and 7"5 (fl) ppm. (Fig. lb). Comparison of the IR spectra of the oligomer with those for polynaphthalenes obtained by polycondensation of various dibromonaphthalene derivatives [3] and chosen by us as model compounds showed that propagation of the oligomer chain occurs mainly in positions 1,4 and 2 , 6 - t h e presence in the IR spectra of the absorption bands of * Vysokomol. soyed..4,30: No. 11, 2281-2283, 1988, 2435
2436
A.M. ARZUMAN'YANet aL f
(2
'i
I
1
32
28
12
16
8
i
v. 10-2, cm -1
D, apb.un
b
1.0
0.5 I
l
8
7
.I
I
2
#,,pprn
250 300 350 ~/OOA,nm
F[o. 1. IR (a), PMR (b)and UV (c) spectra of oligomeric fraction of naphthalene (soluble in benzene): a-spectrum recorded in film; b-in deuteroacetone de; c-in liquid paraffin. 1,4-substituted naphthalenes in the region 1430 and 1480 cm -1 and 2,6-substituted in the region 810, 845 and 870 cm-1. Such substitutions in naphthalene may lead to the formation of isolated protons the signals of which are observed in the P M R spectrum in the region 6.9 and 8.3 ppm in the form of singlets. Investigations of the IR spectra of oligomeric naphthalene also revealed absorption bands of the CH2 group in the region 1445, 2850 and 2925 cm -1, the absorption band of the valent vibrations of the bond -C=Cin the region 1630 cm-1 and cis extraplanar deformation vibrations of the = CH bond in the region 690 cm-1. It should be noted that the identification of the cis-bond = C H - from the characteristic absorption band in the region 965 cm -1 is impossible in view of the presence in the same region of absorption characteristic of arommic structures. These findings point to the presence in the oligomer of structural fragments of dihydronaphthalene as cortfirmed by the presence in the P M R spectrum of the resonance lines of the protons of the CH2 group in the region 1.75 ppm and a weak signal of the protons of the = C H group in the region 4.2 ppm. The tbrmation of dihydronaphthalene structures is accompanied by fall in the degree of conjugation of the system and the appearance of substituted benzene rings (structures I and II). The signals of the protons and also the absorption bands of the benzene
Structural features of polymeric complex of naphthalene with iodine
2437
ring have been observed in PMR- (7.23 ppm) and the UV- (256 nm) spectra, respectively
| II I
ll)
The presence io the UV spectrum of absorption bands in the region 220 and 230 nm (Fig. lc) characteristic of the diene [4] also confirms the formation of the structural fragment 1 in the oligomer chain. The absorptions in the region 320 nm and the longwave decay coming within the visible region point to the presence in the oligomeric fraction of fragments with a high degree of conjugation (structure III and IV) •~ - - ~ \ \
\,
J
\ ~/
\, III
/
~-
IV
The formation of the latter governs the absence in the UV spectra of the characteristic absorption bands of the naphthalene ring. A similar phenomenon is already observed on passing from benzene to diphenyl and polyphenylenes [5]. On heating (250°C) the oligomeric products with iodine (weight ratio oligomer : :iodine= 1 : 1) there is further polycondensation with formation of PNCs. It should be noted that in the IR spectra of the ONC with iodine obtained the absorption bands of the CH2 group were also detected. The dihydronaphthalene structural fragments in the polymeric naphthalene complex are defects disturbing the conjugation of the system which also accounts for the comparatively low values of specific electrical conductivity. The formation of reduced structural fragments is apparently connected with secondary reactions of hydrogen iodide formed during polycondensation. On thermal treatment of the polymers to 450°C these defects do not disappear indicating the high stability of the latter linked with the difficulty of dehydrogenation of higher dihydroacenes [5]. It was shown by DTA that polymerization of naphthalene is accompanied by numerous thermal effects (Fig. 2). At the initial stage of the process the DTA curve shows an endothermal peak at 78°C corresponding to the melting point of naphthalene. 120 °
78 °
180 °
112 °
Fro. 2. DTA curve plotted during polymerization of naphthalene in presence of iodine.
2438
A . M . ARZUMANYANet al.
Many aromatic compounds (benzene, pyridine, etc.) complex with iodine already at room temperature [6] while naphthalene in the solid phase does not complex with iodine [7]. Above the melting point in the liquid phase probably there is complexing of iodine with naphthalene reflected in an exothermal effect in the DTA curve with maximum at 93°C. The endothermal peak with a maximum at 112°C corresponds to the melting point of iodine. At this temperature in the DTA curve the onset of another wide (112-150°C) exothermal effect is observed with a maximum at 120°C. As shown above at this temperature the main reaction products (91 Yo) are soluble oligomeric compounds. In the complex the C - H bond as a result of polarization is more reactive and, therefore, in presence of an excess of iodine the naphthalene complex formed is capable of condensing to dimeric and trimerie products. Further rise in the temperature of the reaction mass leads to the appearance in the DTA curve of a wide (150-200°C) exothermal peak with maximum at 180°C. At this temperature the main reaction product is an insoluble naphthalene polymer of acene structure [1] with further development of the planar structures (the latter explains such a wide exothermal effect in the DTA curve). The IR spectra of the polymeric samples were recorded with the UR-20 spectrometer in thin films and KBr pellets. The PMR spectra were recorded with the Tesla spectrometer with the working frequency 100 MHz with the internal standard TMC i n d6-acetone. The Specord spectrometer was used for recording the UV spectra with liquid paraffin as solvent with a concentration 10 -3 mole/l. The MW of the oligomers was determined by the Raast method in diphenyl and naphthalene. Iodine and naphthalene were purified by sublimation controlled by TLC. DTA was with the DSM-2M differential scanning microcalorimeter. The oligomeric product of naphthalene was synthesized as follows. Five grams (0.039 moles) naphthalene and 19.5 g (0.077 moles) iodine were placed in a reflux flask. The reaction temperature was held at 110°C for 3 hr. At the end of the synthesis the reaction mass was cleared of free iodine and naphthalene by extraction with ethanol in a Soxhlct apparatus for 30 hr. After drying in vacuo at 1.33 Pa to constant weight we obtained 6.1 g resin from which we recovered 5.5 g (915/o) oligomer soluble in DMFA and containing 30~/o iodine with M=450-500 and 0"5 g (9~o) insoluble polymer containing 20~o iodine. The oligomer was extracted with benzene in a Soxhlet apparatus for 20 hr, then the benzene solution was Washed with KOH solution. After separating the benzene layer and driving off the solvent in vacuo 13-3 Pa we obtained 0.5 g (9~/o for the oligomer) of a fraction with M=300-400 soluble in benzene and containing 1-2% iodine. Thermal treatment of the oligomer in presence of iodine: 1 g oligomer (fraction soluble in benzene and I g) iodine were heated for 2 hr at 250°C in a sealed ampoule. After clearing the polymer of iodine residues and oligomers by sublimation and washing with DMFA we recovered 1.28 g of the polymer containing 22~o iodine. The polymeric naphthalene complex was thermally treated in sealed ampoules in an inert medium at 450°C for 2 hr. Translated by A. CROZ't
REFERENCES I. A. A. MATNISHYAN, A. M. ARZUMANYAN, L. S. GRIGORYAN, V. N. NIKOGOSOV, I. L. ARUTYUNYAN, S. G. GRIGORYAN, R. S. ASATRYAN, A. L, MANUKYAN and R. O. MATEVOSYAN, Armen. khim. zh. 38: 590, 1985 2. A. A. MATNISHYAN, I. L. ARUTYUNYAN, L. S. GRIGORYAN and A. A. OVCHINNIKOV Dokl. Akad. Nauk SSSR 277:1149, 1984
Patterns of strengthening polyheteroarylene on thermal treatment
2439
3. M. SATO, K. KACRIGAMA and K. SOMENO, Makromolek. Chem. 134: 2241, 1983 4. H. M. JAFFE and M. ORCHIN, Theory and Applications of Ultraviolet Spectroscopy. N.Y., 1962 5. E. KLAHR, Politsiklicheskiye ugievodorody (Polycyclic Hydrocarbons). Vol. 1, pp. 89, 66, Moscow, 1971 6. R. S. MULLIKEN, J. Organ. Chem. Soc. 72: 600, 1950 7. S. ARANSON, J. KLAHR and L. STEMP, J. Solid State Chem. 34: 347, 1980
Polymer Science U.S.S.R. Vol. 30, No. 11, pp. 2439-2444, 1988 Printed in Poland
0032-3950188 $10.00+ .00 © 1990 Pergamon Press plc
PATTERNS OF STRENGTHENING POLYHETEROARYLENE ON THERMAL TREATMENT* A. V. SAVITSKII an d I. L. FROLOVA Ioffe Physicotechnical Institute, Leningrad (Received 2 June 1987)
On the basis of the kinetic concept of strength the authors propose a model of the rearrangement of the molecular structure of polyheteroarylene in the course of its thermal treatment. The experiment showed good agreement between the calculated and experimental data and permitted calculation of the energy of the potential barrier of rearrangement of structure the value of which was 17+8 kJ/mole.
STRENGTHENING on t h e r m a l t r e a t m e n t o f fibres a n d films o f a r o m a t i c P A s has a l r e a d y been s t u d i e d f o r a n u m b e r o f years. I n [I, 2] the a u t h o r s investigated t h e s t r u c t u r a l a n d m o l e c u l a r features o f the r e a r r a n g e m e n t s a n d e l u c i d a t e d t h e influence o f the p r e h i s t o r y o f the fibre ( a n i s o t r o p y o f s o l u t i o n s [3] a n d the c o n d i t i o n s o f f o r m a t i o n [4]) on the s t r e n g t h e n i n g value. In [5, 6] it was s h o w n t h a t in terms o f the kinetic t h e o r y o f f r a c t u r e s t r e g g t h e n i n g o f t h e p o l y m e r s c o n s i d e r e d on t h e r m a l t r e a t m e n t is b r o u g h t a b o u t b y rise in the initial a c t i v a t i o n e n e r g y o f the process o f f r a c t i o n Uo w i t h n o c h a n g e in the struct u r a l coetticient ~, f r o m the Z h u r k o v e q u a t i o n . I n t h e p r e s e n t w o r k we s t u d y the p a t t e r n s o f s t r e n g h e n i n g on t h e r m a l t r e a t m e n t o f p o l y h e t e r o a r y l e n e ('PHA) fibres. The freshly formed, hereafter referred to as initial, fibre was thermally treated either in a low inertia laboratory vacuum oven or by drawing over a contact heater. The strength of the fibres at different temperatures was determined by the technique described in [7, 8] on the ZT-40 machine fitted with a contact heater. In the vacuum oven the fibres were thermally treated in the form of a coil free or fixed on a rigid coiler at different temperatures controlled with a thermocouple. Heating was carried out at a * Vysokomol. soyed. A30: No. 11, 2285-2289, 1988.
0032-3950/88 $10.00+.00 ~ 1990 Pergamon Press plc
STRUCTURAL FEATURES OF THE POLYMERIC COMPLEX OF NAPHTHALENE WITH IODINE* A. M. ARZUMANYAN,I. L. ARUTYUNYANand A. A. MATNISHYAN Armenian Branch of the All-Union Research Institute of Reagents and SpeciallyPure Chemicals (Received 2 June 1987)
Methods of IR, UV and PMR spectroscopy have been used to investigatethe structure of soluble naphthalene oligomers obtained by polycondensationof naphthalene in presence of iodine at 100-120°C. It is shown that propagation of the oligomer chain occurs, in the main, in positions 1,4 and 2,6. The oligomerscontain dihydronaphthalenestructural fragments which persist in the polymericcomplexes of naphthalene and are defects disturbing conjugation of the system. EARLIER it was shown that at 200-250°C naphthalene in presence of iodine forms insoluble, non-fusible black polymeric complexes of scene structure with further development of the planar structures and simultaneous formation of ion-radical salts [l, 2]. The polymeric complexes of naphthalene (PNC) with iodine display semiconductor properties with maximum specific electrical conductivity a = 10-3 f2-1.cm-x. Because of poor solubility the structure of the PNCs has been insufficiently studied. In this respect investigation of soluble low molecular weight oligomeric products may give a better idea of the structure and mechanism of formation of the PNCs. On polymerization of naphthalene in a low temperature regime (100-120°C) with the molar ratio iodine : naphthalene=2 : 1 a soluble, low molecular weight fraction of a light brown colour with M,,~300-400 and containing 1-2 ~ iodine was obtained by hot extraction with benzene from the reaction medium. In the IR spectra of the naphthalene oligomer absorption bands are present characteristic of condensed aromatic systems in the regions 470, 620, 750, 870, 950 and 970 cm- 1 ( C - H deformation vibrations); 1015, 1125, 1260, 1360, 1585 and 1590 cm -1 (valent C - C and C = C ) a n d 3020 and 3050 cm -~ (valent C - H ) (Fig. la). The presence in the oligomer of aromatic units is indicated by the PMR spectra: the presence of the resonance lines of the ~ and fl groups of the protons characteristic of naphthalene in the region 7.8 (~) and 7"5 (fl) ppm. (Fig. lb). Comparison of the IR spectra of the oligomer with those for polynaphthalenes obtained by polycondensation of various dibromonaphthalene derivatives [3] and chosen by us as model compounds showed that propagation of the oligomer chain occurs mainly in positions 1,4 and 2 , 6 - t h e presence in the IR spectra of the absorption bands of * Vysokomol. soyed..4,30: No. 11, 2281-2283, 1988, 2435
2436
A.M. ARZUMAN'YANet aL f
(2
'i
I
1
32
28
12
16
8
i
v. 10-2, cm -1
D, apb.un
b
1.0
0.5 I
l
8
7
.I
I
2
#,,pprn
250 300 350 ~/OOA,nm
F[o. 1. IR (a), PMR (b)and UV (c) spectra of oligomeric fraction of naphthalene (soluble in benzene): a-spectrum recorded in film; b-in deuteroacetone de; c-in liquid paraffin. 1,4-substituted naphthalenes in the region 1430 and 1480 cm -1 and 2,6-substituted in the region 810, 845 and 870 cm-1. Such substitutions in naphthalene may lead to the formation of isolated protons the signals of which are observed in the P M R spectrum in the region 6.9 and 8.3 ppm in the form of singlets. Investigations of the IR spectra of oligomeric naphthalene also revealed absorption bands of the CH2 group in the region 1445, 2850 and 2925 cm -1, the absorption band of the valent vibrations of the bond -C=Cin the region 1630 cm-1 and cis extraplanar deformation vibrations of the = CH bond in the region 690 cm-1. It should be noted that the identification of the cis-bond = C H - from the characteristic absorption band in the region 965 cm -1 is impossible in view of the presence in the same region of absorption characteristic of arommic structures. These findings point to the presence in the oligomer of structural fragments of dihydronaphthalene as cortfirmed by the presence in the P M R spectrum of the resonance lines of the protons of the CH2 group in the region 1.75 ppm and a weak signal of the protons of the = C H group in the region 4.2 ppm. The tbrmation of dihydronaphthalene structures is accompanied by fall in the degree of conjugation of the system and the appearance of substituted benzene rings (structures I and II). The signals of the protons and also the absorption bands of the benzene
Structural features of polymeric complex of naphthalene with iodine
2437
ring have been observed in PMR- (7.23 ppm) and the UV- (256 nm) spectra, respectively
| II I
ll)
The presence io the UV spectrum of absorption bands in the region 220 and 230 nm (Fig. lc) characteristic of the diene [4] also confirms the formation of the structural fragment 1 in the oligomer chain. The absorptions in the region 320 nm and the longwave decay coming within the visible region point to the presence in the oligomeric fraction of fragments with a high degree of conjugation (structure III and IV) •~ - - ~ \ \
\,
J
\ ~/
\, III
/
~-
IV
The formation of the latter governs the absence in the UV spectra of the characteristic absorption bands of the naphthalene ring. A similar phenomenon is already observed on passing from benzene to diphenyl and polyphenylenes [5]. On heating (250°C) the oligomeric products with iodine (weight ratio oligomer : :iodine= 1 : 1) there is further polycondensation with formation of PNCs. It should be noted that in the IR spectra of the ONC with iodine obtained the absorption bands of the CH2 group were also detected. The dihydronaphthalene structural fragments in the polymeric naphthalene complex are defects disturbing the conjugation of the system which also accounts for the comparatively low values of specific electrical conductivity. The formation of reduced structural fragments is apparently connected with secondary reactions of hydrogen iodide formed during polycondensation. On thermal treatment of the polymers to 450°C these defects do not disappear indicating the high stability of the latter linked with the difficulty of dehydrogenation of higher dihydroacenes [5]. It was shown by DTA that polymerization of naphthalene is accompanied by numerous thermal effects (Fig. 2). At the initial stage of the process the DTA curve shows an endothermal peak at 78°C corresponding to the melting point of naphthalene. 120 °
78 °
180 °
112 °
Fro. 2. DTA curve plotted during polymerization of naphthalene in presence of iodine.
2438
A . M . ARZUMANYANet al.
Many aromatic compounds (benzene, pyridine, etc.) complex with iodine already at room temperature [6] while naphthalene in the solid phase does not complex with iodine [7]. Above the melting point in the liquid phase probably there is complexing of iodine with naphthalene reflected in an exothermal effect in the DTA curve with maximum at 93°C. The endothermal peak with a maximum at 112°C corresponds to the melting point of iodine. At this temperature in the DTA curve the onset of another wide (112-150°C) exothermal effect is observed with a maximum at 120°C. As shown above at this temperature the main reaction products (91 Yo) are soluble oligomeric compounds. In the complex the C - H bond as a result of polarization is more reactive and, therefore, in presence of an excess of iodine the naphthalene complex formed is capable of condensing to dimeric and trimerie products. Further rise in the temperature of the reaction mass leads to the appearance in the DTA curve of a wide (150-200°C) exothermal peak with maximum at 180°C. At this temperature the main reaction product is an insoluble naphthalene polymer of acene structure [1] with further development of the planar structures (the latter explains such a wide exothermal effect in the DTA curve). The IR spectra of the polymeric samples were recorded with the UR-20 spectrometer in thin films and KBr pellets. The PMR spectra were recorded with the Tesla spectrometer with the working frequency 100 MHz with the internal standard TMC i n d6-acetone. The Specord spectrometer was used for recording the UV spectra with liquid paraffin as solvent with a concentration 10 -3 mole/l. The MW of the oligomers was determined by the Raast method in diphenyl and naphthalene. Iodine and naphthalene were purified by sublimation controlled by TLC. DTA was with the DSM-2M differential scanning microcalorimeter. The oligomeric product of naphthalene was synthesized as follows. Five grams (0.039 moles) naphthalene and 19.5 g (0.077 moles) iodine were placed in a reflux flask. The reaction temperature was held at 110°C for 3 hr. At the end of the synthesis the reaction mass was cleared of free iodine and naphthalene by extraction with ethanol in a Soxhlct apparatus for 30 hr. After drying in vacuo at 1.33 Pa to constant weight we obtained 6.1 g resin from which we recovered 5.5 g (915/o) oligomer soluble in DMFA and containing 30~/o iodine with M=450-500 and 0"5 g (9~o) insoluble polymer containing 20~o iodine. The oligomer was extracted with benzene in a Soxhlet apparatus for 20 hr, then the benzene solution was Washed with KOH solution. After separating the benzene layer and driving off the solvent in vacuo 13-3 Pa we obtained 0.5 g (9~/o for the oligomer) of a fraction with M=300-400 soluble in benzene and containing 1-2% iodine. Thermal treatment of the oligomer in presence of iodine: 1 g oligomer (fraction soluble in benzene and I g) iodine were heated for 2 hr at 250°C in a sealed ampoule. After clearing the polymer of iodine residues and oligomers by sublimation and washing with DMFA we recovered 1.28 g of the polymer containing 22~o iodine. The polymeric naphthalene complex was thermally treated in sealed ampoules in an inert medium at 450°C for 2 hr. Translated by A. CROZ't
REFERENCES I. A. A. MATNISHYAN, A. M. ARZUMANYAN, L. S. GRIGORYAN, V. N. NIKOGOSOV, I. L. ARUTYUNYAN, S. G. GRIGORYAN, R. S. ASATRYAN, A. L, MANUKYAN and R. O. MATEVOSYAN, Armen. khim. zh. 38: 590, 1985 2. A. A. MATNISHYAN, I. L. ARUTYUNYAN, L. S. GRIGORYAN and A. A. OVCHINNIKOV Dokl. Akad. Nauk SSSR 277:1149, 1984
Patterns of strengthening polyheteroarylene on thermal treatment
2439
3. M. SATO, K. KACRIGAMA and K. SOMENO, Makromolek. Chem. 134: 2241, 1983 4. H. M. JAFFE and M. ORCHIN, Theory and Applications of Ultraviolet Spectroscopy. N.Y., 1962 5. E. KLAHR, Politsiklicheskiye ugievodorody (Polycyclic Hydrocarbons). Vol. 1, pp. 89, 66, Moscow, 1971 6. R. S. MULLIKEN, J. Organ. Chem. Soc. 72: 600, 1950 7. S. ARANSON, J. KLAHR and L. STEMP, J. Solid State Chem. 34: 347, 1980
Polymer Science U.S.S.R. Vol. 30, No. 11, pp. 2439-2444, 1988 Printed in Poland
0032-3950188 $10.00+ .00 © 1990 Pergamon Press plc
PATTERNS OF STRENGTHENING POLYHETEROARYLENE ON THERMAL TREATMENT* A. V. SAVITSKII an d I. L. FROLOVA Ioffe Physicotechnical Institute, Leningrad (Received 2 June 1987)
On the basis of the kinetic concept of strength the authors propose a model of the rearrangement of the molecular structure of polyheteroarylene in the course of its thermal treatment. The experiment showed good agreement between the calculated and experimental data and permitted calculation of the energy of the potential barrier of rearrangement of structure the value of which was 17+8 kJ/mole.
STRENGTHENING on t h e r m a l t r e a t m e n t o f fibres a n d films o f a r o m a t i c P A s has a l r e a d y been s t u d i e d f o r a n u m b e r o f years. I n [I, 2] the a u t h o r s investigated t h e s t r u c t u r a l a n d m o l e c u l a r features o f the r e a r r a n g e m e n t s a n d e l u c i d a t e d t h e influence o f the p r e h i s t o r y o f the fibre ( a n i s o t r o p y o f s o l u t i o n s [3] a n d the c o n d i t i o n s o f f o r m a t i o n [4]) on the s t r e n g t h e n i n g value. In [5, 6] it was s h o w n t h a t in terms o f the kinetic t h e o r y o f f r a c t u r e s t r e g g t h e n i n g o f t h e p o l y m e r s c o n s i d e r e d on t h e r m a l t r e a t m e n t is b r o u g h t a b o u t b y rise in the initial a c t i v a t i o n e n e r g y o f the process o f f r a c t i o n Uo w i t h n o c h a n g e in the struct u r a l coetticient ~, f r o m the Z h u r k o v e q u a t i o n . I n t h e p r e s e n t w o r k we s t u d y the p a t t e r n s o f s t r e n g h e n i n g on t h e r m a l t r e a t m e n t o f p o l y h e t e r o a r y l e n e ('PHA) fibres. The freshly formed, hereafter referred to as initial, fibre was thermally treated either in a low inertia laboratory vacuum oven or by drawing over a contact heater. The strength of the fibres at different temperatures was determined by the technique described in [7, 8] on the ZT-40 machine fitted with a contact heater. In the vacuum oven the fibres were thermally treated in the form of a coil free or fixed on a rigid coiler at different temperatures controlled with a thermocouple. Heating was carried out at a * Vysokomol. soyed. A30: No. 11, 2285-2289, 1988.