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Synthesis and investigation of stereo regular copolymers of propylene and isoprene
SYNTHESIS AND INVESTIGATION OF STEREO REGULAR COPOLYMERS OF PROPYLENE AND ISOPRENE* N. S. VOLKOVA. G. V. K HUTAREVA, B. A. KRENTSEL', Z. A. ROGOVIN
and A. V. TOPCHIEV Moscow Textile Institute and the Institute for Petrochemical Synthesis, USSR Academy of Sciences
(Receipted ] July 1959) THREADS and films of stereoregular polypropylene possess a number of technically valuable properties but they have important shortcomings which limit their use in a number of crucial fields, in particular the production of highstrength cord. This shortcoming consists of the comparatively low softening temperature and, correspondingly, the noteworthy decrease in strength of polypropylene threads on raising the temperature. Thus, on raising the temperature to 80 ° the strength of a filament is reduced to 40 per cent and at 100 ° the filaments begin to flow. If one were to succeed in eliminating this shortcoming, the possibility of using high-strength elastic polypropylene filaments for the production of cord would become a reality. One of the possible answers to this complicated and practically important problem is the formation of a small number of chemical bonds between the propylenemacromolecules. The formation of chemical bonds (vulcanization) to propylene m a y be carried out in various ways. One of the most interesting methods is the synthesis of polypropylene containing a small quantity of diene units (e.g. isoprene) with subsequent vulcanization at the position of the double bond in the copolymer obtained (as in the vulcanization of butylrubber). Starting from this postulate we synthesized copolymers of polypropylene and isoprene and carried out preliminary experiments on their vulcanization; the results obtained are set out in brief in this article. Synthesis of copolymers of propylene and isoprene. The copolymerization of propylene with isoprene was carried out in an autoclave at 8-10 atm. in the presence of catalysts based on organoaluminium compounds and titanium chloride according to two methods previously described by us [2]. Dry, thoroughly purified n-heptane was used as solvent. The catalyst concentration in the heptane solution was 4 per cent by weight. The catalysts used for the copolymerization were AI(C~Hs)a~-TiC14 and AI(C2Hs)a@TiCI 3. The conditions and results of these experiments are put in Table ]. * Vysokomol. soe(iin, l: No. 12, 1758-1763. 1959. 140
S t e r e o r e g u l a r c o p o l y m e r s of p r o p y l e n e a n d isoprene
141
At the end of the copolymerization the reaction mixture was reacted with absolute isopropanol to destroy the residual catalyst and the copolymer obtained was dried to constant weight in vacuum at 50-60 ° . For example, the following were determined: the degree of unsaturation, the specific viscosity in deca|in at 120 °, the melting temperature and the yield of copolymer. At the same time the amount of amorphous fraction was determined by dissolving it in toluene at 20°; in order to compare the generality of the method, the solubility of the copolymer in ether and heptane was determined. An increase in the concentration of isoprene noticeably lowered the yield of copolymer in the reaction with the catalyst AI(C~H~)ad-TiCI4; at the same time the content of amorphous fraction, soluble in ether, increased. TABLE 1. PREPARATIVE CONDITIONS AND PItOPERTIES OF PItOPYLENE/ISOPRENE Concentration of isoprene (wt. °o)
~ Polymer i obtained (g) i
specfiic viscosity [~]
i
i i M.p. (:C) i~
Solubility (wt °,o) ~ ' in e t h e r
C o n t e n t of ,ii i s o t a c t i c
i in p e n t o n e ! c o p o l y m e r
i
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPOLYMER
i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
i
S y s t e m AI(CzHs)3+TiCI4: m o l a r r a t i o of Al(C2Hs)3: TiC14==3:I; cxperim,~ntal t e m l ) e r a t u r e 0 1.0 2.5 5.0 7.5 10.0
148 133 103 3~t 22 20
1-80 1.60 1.50 1.30
1.58 1.60
!157-162 r 155-158 1150-156 1148-157 142-149 150-156
30.0 34.0 33.0 41.0 60.0 56-(P
25.0 26.0 29.0 31.0 25-5 32-0
!
45.(! 40.0 38-0 28.0 14-5 12.~)
S'~.st.em AI(C2Hs)3-.~,I'iCI:~: m o l a r vali,~ of AI(-,~Hs):~: TiCla:= I:1 : t e m p e r a t u r e of th(" ,~xperiment 0 2.5 5-0 7.5
210 19q~ 19ql 195
1.80 1.80 1.50 2.00
! 156- I ti0 154-160 154- 163 143-150
13.0 15.0 15.5 16.0
41.0 59.0 52.5 27.0
46.0 36.0 32.0 57.0
The number of diene groups in the copolymer obtained was estimated by the number of double bonds. The uusaturation was determined by reaction with the ]nterhalogeu ICl which added to the copolymer at the double bond. This method is generally used for butyl-rub!)er containing 1-5 per cent of diene (butadiene or isoprene). The data obtained, which is displayed in Table 2, shows that the number of double bonds in the copolymer increases regularly with the increase in quantity of isoprene used in the copolymerization reaction. The distribution of the isoprene residues between the crystalline and amorphous fractions of the polypropylene was unequal. The main quantity of isoprene, characterized by the presence of double bonds (degree of unsaturation),
N. S. VOLKOVA et al.
142
TABLE 2. I~'r'LUE~CE 0~" THE QUANTITY OF 1SOPRENE USED IN TUE POLYMERIZATION ON THE UNSATURATIO2ffOF THE COPOLYMER OBTAINED
Concentration of isoprene in p e n t o n o s o l u t i o n
U n s a t u r a t i o n o f t h e c o p o l y m e r (wt. %) ]I 0"375 0"455 0"974
1.0 2-5 5.0 7.5 10.0
0"510 1"260 1"840
1'33--1"54
l~ote. Copolymer I was obtained ~with the catalyst At (C2Hs)~+TiCI4; Copolynmr 1[ with the catalyst A1 (C2H5)3+ TiCI3.
is found in the amorphous fraction (Table 3). Such a distribution is quite understandable because with an increase in the isoprene content of the copolymer molecule the regularity of its structure decreases; correspondingly the crystallinity of the sample decreases and its solubility in toluene increases.
Investigation of the possibility of vulcanizing the propylene/isoprene copolymer. Samples of the copolymer with a degree of unsaturation of 1.33-1.8 per cent were taken for investigating the possibility of vulcanization i.e. a sample with
¢0 $
3/!/
; IZ~ E
o
4'o
/z'o
,¢0
Temperat ure (°C) FIG. 1. T h e r m o e h e m i e a l p r o p e r t i c s : (1) p o l y p r o p y l e n e , (2) c o p o l y m e r w i t h l°io, (3) e o p o l y m e r w i t h 5 % , (4) w i t h 1 0 ~ o f isoprene.
the same unsaturation as preparations of butyl-rubber which was a degree of unsaturation of 1.4-1.5 per cent. Methods used for vulcanizing various types of rubber, in particular butyl rubber, were used for vulcanizing the copolymer. (a) Vulcanization with sulphur in the presence of accelerators (using the method as for vulcanizing butyl rubber).
IStereo r e g u l a r c o p o l y m e r s o f p r o p y l e n e a n d i s o p r e n e
143
"FABLE 3. T H E DEGREE OF UNSATURATION OF CRYSTALLINE AND AMORPHOUS FRACTIOlqS OF THE PROPYLENE/ISOPRENB COPOLYMER
Descril)tion of the preparation
Cone. of isoprene in h e p t a n e sol.
(wt. %)
1. U n f r a c t i o n a t e d copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction 2. U n f r a c t i o n a t ed copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction 3. U n f r a c t i o n a t e d copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction 4. U n f r a c t i o n a t e d copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction
5
10
2.5
7.5
Qtty. of product,
% wt. of the copolymer
Unsatttrtl lion
Application
(%)
100
0-974
62"4
0"124
29.82
2.11
100
1.34-1.54
68"6
0.28-0.37
26-6
4.2-4.75
100
0.506
87.4
0.0
10.2
1'3
100
1.81
87"2
O.422
ll.0
6.05
Polymerization was carried o u t in t h e p r e s e n c e o f t h e c a t a l y s t A l ( C z H ~), + TiC14
The
salnt~
Polymerization was carried o u t in t h e p r e s e n c e o f t h e catalyst Al(CtHs) a ~ TiCl,
The ~ a m e
Note. Tile fractionation was carried out by fractional solution in toluene at 20% In these conditions the amorphous fract ion is d iasolved [3]. The introduction of a larger or smaller number of isoprene groups into the macromolccule eopolymer (by adding to the eopolymerization front 1 to 10 per cent of isoprene) does not influence the character of the thormomeehanical curves of these eopolyulers and, consequently, the change ill fluidity of" the co|)olymtq'.
Composition of the vulcanizing mixture (in g per 100 g of polymer): sulp h u r - 2 . 0 , t h i u r a m - - l . 3 , "kaptaks"--0.65, zinc oxide--5.0, stearin--3.0; vulcanization temperature 100-145°; duration 30-120min. Vulcanization was carried out in a press. Because stereoregular polypropylene has little stability to oxidative dest.ruction at high temperature, then, to eliminate the side effects of the process of oxidative destruction, mixtures of the copolymer with the vulcanization
144
N . S . VOLKOVA eg al.
reagents were mixed in a rolling mill, and heating of the mixtm'e was carried out in parallel in air and under vacuum in sealed tubes from which the air had been previously removed down to a pressure of 10-e ram. (b) The ultrafast vulcanization method by reacting the copolymer with sulphur monochloride (either as gaseous S~C12or as a 5°/o solution of S2CI2 in benzene). Length of reaction 15-60 min, temperature 20 °. Treatment with the benzene solution of sulphur monochloride ensures some swelling of the copolymer and thus increases the possibility of diffusion of the vulcanization reagent into the polymer. i
5
ZOi
: l/li/
n6~ -d 12c E
~0
zb
eb
,;0
,~a
Tern perature (*C)
&'
FI6. 2. T h e m n o e h e m i c a l p r o p e r t i e s o f t h e c o p o l y m e r a f t e r v u l c a n i z a t i o n : (1) c o p o l y m e r h e a t e d t o I00 ° for GL., (2) to 150 ° for 2 h r , (3) cop01ymer h e a t e d to 150 ° for 2 hr, (4) a t 100 ° for 6 hr, in n i t r o g e n , (5) c o p o l y m e r h e a t e d t o 150 ° for 2 hi', (6) to 100 ° for 6 hr, in v a c u u m .
The following estimations were carried out to determine the amount of chemical bonding between the copolymer molecules resulting from the treatment described: (a) the quantity of combined sulphur after vulcanization; (b) the change in the degree of unsaturation of the copolymer; (c) the change in the character of the thermomechanical curves of the copolymer before and after vulcanization. The quantity of combined sulphur in the sample after vulcanization was determined by the method adopted in the resin i n d u s t r y - - t h e free sulphur is extracted with acetone from the sample submitted to vulcanization and subsequently the quantity of combined (non-extractable) sulphur is determined by normal methods. However, control experiments showed that it was impossible to remove free sulphur from thick rolled samples of the copolymer or polypropylene. Thus, for example, polypropylene, rolled with a sulphur preparation and then extracted with acetone for 26-36 hr, contained 0.9 per cent combined sulphur. Cyclohexane was used in place of acetone to increase the extraction temperature; but this solvent did not permit the complete removal of sulphur
Stereo regular copolymers of propylene and isoprene
145
from polypropylene. Therefore one cannot use the determination of the quantity of combined sulphur as a characteristic of the number of chemical bonds formed between the macromolecules. The change in properties of the polymer as a result of the formation of chemical bonds between the macromolecules is demonstrated by the character of the thermomechanical curve (the change in fluidity of the material on increasing the temperature) which is determined by various methods, in particular by Kargin's balance. When chemical bonds between the maeromolecules appear the fluidity of the material should fall sharply, but in the presence of a large number of bonds, the polymer in general should not flow on increasing the temperature. The character of the thermomechanical curve should also change sharply. Trials showed that chemical bonds between the copolymer macromolecules were not formed on vulcanization under the conditions described above. As is evident from Fig. 2, the thermomechanical curves of the copolymer did not change after rolling with a vulcanization mixture and after heating either in air or in vacuum for various times and various temperatures. There was no change in the degree of unsaturation either. It is obvious that chemical bonds were not fornmd between the macromoteeules in the vulcanization conditions described; negative results were obtained with both variants of sulphur mouochloride vulcanization.
zool 700
~/,7
.~ /66
166 = IgO E
tZn
b
~-..~.1=// ~
.//
/'7
.I"
~2
z,f~
Ternpcratu(°C) re FIe;. 3. Thermochemieal properties: (1) initial fraction, (2) amorphous fraction of the copolymer, vulcanized in air, (3) same in vacuum.
Temperature (°C) FIG. 4. Thermoehemical properties before and after irradiation: (1) amorphous fraction irradiated with ?-rays (50 million roentgen), (2) tile same, not irradiated, (3) unfraetionated specimen SPI-12, irradiated in air (150 million roentgen). (4) the same in vacuum (150 nfillion roentgen), (5) the same sample, not, irradiated.
To elucidate the possibility of vulcanization of the propylene/isoprene copolymer with sulphur, the vulcanization was carried out with the amorphous fraction of the copolymer which had the highest degree of unsaturation (6.11 per cent). This fraction was mixed with a vulcanizing mixture in the rolling mill 10 Polymer I & 2
146
N.S. VOLKOVAe~al.
and submitted to heating under the same conditions; but as is evident from Fig, 3, the character of the thermomeehanical curve for this fraction also did not change after vulcanization. Therefore, we a t t e m p t e d to use physical methods, especially irradiation with ~,-rays, instead of chemical methods, for forming chemical b o n d s between the macromolecules of the copolymer. The stereoregular copolymer of propylene and isoprene synthesized by us was irradiated with r-rays of varying intensity.* A radiation dose of 15 to 150 million roentgen was used, either in air or in high vacuum. The change in the n u mb er of double bonds and in the molecular weight (by viscometric measurements) were determined for the irradiated samples, and thermomeehanical curves were constructed. The results obtained are put in Table 4 and Fig. 4. As can be seen from these data, a considerable destruction of the copolymer takes place when it is irradiated at various intensities in air, and this leads to a lowering of the initial t e m per a t ur e of flow of the material after irradiation. Chemical bonds between the macromolecules are not formed in these conditions of t r e a t m e n t and consequently the character of the thermomechanical curves of these preparations is not changed. Formation of chemical bonds between the macromolecules is observed or irradiation in vacuum with the maximum dose used b y us - - 150 million r o e n t g e n - - a n d this is confirmed by the sharp change in the thermomechanical curve of this preparation. The data in Fig. 4 show t h a t this preparation does not soften at the t em perat ure at which the initial sample of polypropylene begins to flow (160 °) and this material does T A B L E 4. CHANGES IN T H E D E G R E E Ok' UNSATURATION AN]) T H E VALUE OF T H E SPECIFIC VI8COSITY FOR. PREPARATIONS OF T H E COPOLYME~ OF P R O P Y L E N E AND ISOPRENE AFTER IRRADIATION
Condition of irradiation
Dose (min) r 15 15 50 50 150 150
Properties of the preparation
Degree of unsaturation Character (%) of the .................... medium before after irradiation irradiation Air Vaeutt~n Air Vacuum Ah" Vacuum
1"8 1"8 1"8 1"8 1"8 1'8
0.47 0.98 0.54 0.97 0'71 0.95
Spec. viscosity of a 0.125% solution before I after irradiation]irradiation 0"4 0.4 0.4 0.4 0"4 0"4
0.07 0.37 0"07 insoluble 0.014 insoluble
Note. A copolymer of propylene with 7.5% isoprene, made with the catalyst A1(C2It5)3+ TiCb, u:as used for th e irradiation.
* The irradiation was carried out at. the Karpov Physico-chemieal institute by Iu. M. Malinskii, to whom we convey our thanks.
Stereo regular copolymers of propylene and isoprene
147
not melt at much higher temperatures even up to 280 ° . Evidently under these conditions vulcanization of the stereoregular copolymer of propylene and isoprene can be carried out. SUMMARY
(1) Stereoregular copolymers of the propylene with isoprene containing a small number of diene groups have been synthesized. (2) The possibility of vulcanizing the copolymers obtained has been investigated. I t has been shown t h a t the formation of chemical bonds between the macromolecules does not place when chemical methods of vulcanization are used. (3) Vulcanization of the stereoregular copolymer of propylene and isoprene can only be carried out by irradiation with high intensity rays in vacuum. Translated by M. J. NEWLANDS
REFERENCES
1. S. A. NECHAEVA and Z. A. RO{~OVIN, Khimieheskie volokna 1: 6, 1959 2. A. V. TOPCHIEV, V. A. KRENTSEL', I. M. TOLCHINSKII and {L A. {~ARNISI-IEVSKAIA,
Dokl. Akad. Nauk SSSR 114: 113, 1957 3. Z. A. ROGOVIN and T. V. DRUZHININA, Nauchn. dokl. vyssh, shkoly. 1: 139, 1958
10*
and A. V. TOPCHIEV Moscow Textile Institute and the Institute for Petrochemical Synthesis, USSR Academy of Sciences
(Receipted ] July 1959) THREADS and films of stereoregular polypropylene possess a number of technically valuable properties but they have important shortcomings which limit their use in a number of crucial fields, in particular the production of highstrength cord. This shortcoming consists of the comparatively low softening temperature and, correspondingly, the noteworthy decrease in strength of polypropylene threads on raising the temperature. Thus, on raising the temperature to 80 ° the strength of a filament is reduced to 40 per cent and at 100 ° the filaments begin to flow. If one were to succeed in eliminating this shortcoming, the possibility of using high-strength elastic polypropylene filaments for the production of cord would become a reality. One of the possible answers to this complicated and practically important problem is the formation of a small number of chemical bonds between the propylenemacromolecules. The formation of chemical bonds (vulcanization) to propylene m a y be carried out in various ways. One of the most interesting methods is the synthesis of polypropylene containing a small quantity of diene units (e.g. isoprene) with subsequent vulcanization at the position of the double bond in the copolymer obtained (as in the vulcanization of butylrubber). Starting from this postulate we synthesized copolymers of polypropylene and isoprene and carried out preliminary experiments on their vulcanization; the results obtained are set out in brief in this article. Synthesis of copolymers of propylene and isoprene. The copolymerization of propylene with isoprene was carried out in an autoclave at 8-10 atm. in the presence of catalysts based on organoaluminium compounds and titanium chloride according to two methods previously described by us [2]. Dry, thoroughly purified n-heptane was used as solvent. The catalyst concentration in the heptane solution was 4 per cent by weight. The catalysts used for the copolymerization were AI(C~Hs)a~-TiC14 and AI(C2Hs)a@TiCI 3. The conditions and results of these experiments are put in Table ]. * Vysokomol. soe(iin, l: No. 12, 1758-1763. 1959. 140
S t e r e o r e g u l a r c o p o l y m e r s of p r o p y l e n e a n d isoprene
141
At the end of the copolymerization the reaction mixture was reacted with absolute isopropanol to destroy the residual catalyst and the copolymer obtained was dried to constant weight in vacuum at 50-60 ° . For example, the following were determined: the degree of unsaturation, the specific viscosity in deca|in at 120 °, the melting temperature and the yield of copolymer. At the same time the amount of amorphous fraction was determined by dissolving it in toluene at 20°; in order to compare the generality of the method, the solubility of the copolymer in ether and heptane was determined. An increase in the concentration of isoprene noticeably lowered the yield of copolymer in the reaction with the catalyst AI(C~H~)ad-TiCI4; at the same time the content of amorphous fraction, soluble in ether, increased. TABLE 1. PREPARATIVE CONDITIONS AND PItOPERTIES OF PItOPYLENE/ISOPRENE Concentration of isoprene (wt. °o)
~ Polymer i obtained (g) i
specfiic viscosity [~]
i
i i M.p. (:C) i~
Solubility (wt °,o) ~ ' in e t h e r
C o n t e n t of ,ii i s o t a c t i c
i in p e n t o n e ! c o p o l y m e r
i
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
COPOLYMER
i. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
i
S y s t e m AI(CzHs)3+TiCI4: m o l a r r a t i o of Al(C2Hs)3: TiC14==3:I; cxperim,~ntal t e m l ) e r a t u r e 0 1.0 2.5 5.0 7.5 10.0
148 133 103 3~t 22 20
1-80 1.60 1.50 1.30
1.58 1.60
!157-162 r 155-158 1150-156 1148-157 142-149 150-156
30.0 34.0 33.0 41.0 60.0 56-(P
25.0 26.0 29.0 31.0 25-5 32-0
!
45.(! 40.0 38-0 28.0 14-5 12.~)
S'~.st.em AI(C2Hs)3-.~,I'iCI:~: m o l a r vali,~ of AI(-,~Hs):~: TiCla:= I:1 : t e m p e r a t u r e of th(" ,~xperiment 0 2.5 5-0 7.5
210 19q~ 19ql 195
1.80 1.80 1.50 2.00
! 156- I ti0 154-160 154- 163 143-150
13.0 15.0 15.5 16.0
41.0 59.0 52.5 27.0
46.0 36.0 32.0 57.0
The number of diene groups in the copolymer obtained was estimated by the number of double bonds. The uusaturation was determined by reaction with the ]nterhalogeu ICl which added to the copolymer at the double bond. This method is generally used for butyl-rub!)er containing 1-5 per cent of diene (butadiene or isoprene). The data obtained, which is displayed in Table 2, shows that the number of double bonds in the copolymer increases regularly with the increase in quantity of isoprene used in the copolymerization reaction. The distribution of the isoprene residues between the crystalline and amorphous fractions of the polypropylene was unequal. The main quantity of isoprene, characterized by the presence of double bonds (degree of unsaturation),
N. S. VOLKOVA et al.
142
TABLE 2. I~'r'LUE~CE 0~" THE QUANTITY OF 1SOPRENE USED IN TUE POLYMERIZATION ON THE UNSATURATIO2ffOF THE COPOLYMER OBTAINED
Concentration of isoprene in p e n t o n o s o l u t i o n
U n s a t u r a t i o n o f t h e c o p o l y m e r (wt. %) ]I 0"375 0"455 0"974
1.0 2-5 5.0 7.5 10.0
0"510 1"260 1"840
1'33--1"54
l~ote. Copolymer I was obtained ~with the catalyst At (C2Hs)~+TiCI4; Copolynmr 1[ with the catalyst A1 (C2H5)3+ TiCI3.
is found in the amorphous fraction (Table 3). Such a distribution is quite understandable because with an increase in the isoprene content of the copolymer molecule the regularity of its structure decreases; correspondingly the crystallinity of the sample decreases and its solubility in toluene increases.
Investigation of the possibility of vulcanizing the propylene/isoprene copolymer. Samples of the copolymer with a degree of unsaturation of 1.33-1.8 per cent were taken for investigating the possibility of vulcanization i.e. a sample with
¢0 $
3/!/
; IZ~ E
o
4'o
/z'o
,¢0
Temperat ure (°C) FIG. 1. T h e r m o e h e m i e a l p r o p e r t i c s : (1) p o l y p r o p y l e n e , (2) c o p o l y m e r w i t h l°io, (3) e o p o l y m e r w i t h 5 % , (4) w i t h 1 0 ~ o f isoprene.
the same unsaturation as preparations of butyl-rubber which was a degree of unsaturation of 1.4-1.5 per cent. Methods used for vulcanizing various types of rubber, in particular butyl rubber, were used for vulcanizing the copolymer. (a) Vulcanization with sulphur in the presence of accelerators (using the method as for vulcanizing butyl rubber).
IStereo r e g u l a r c o p o l y m e r s o f p r o p y l e n e a n d i s o p r e n e
143
"FABLE 3. T H E DEGREE OF UNSATURATION OF CRYSTALLINE AND AMORPHOUS FRACTIOlqS OF THE PROPYLENE/ISOPRENB COPOLYMER
Descril)tion of the preparation
Cone. of isoprene in h e p t a n e sol.
(wt. %)
1. U n f r a c t i o n a t e d copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction 2. U n f r a c t i o n a t ed copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction 3. U n f r a c t i o n a t e d copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction 4. U n f r a c t i o n a t e d copolymer (a) c r y s t a l l i n e fraction (b) a m o r p h o u s fraction
5
10
2.5
7.5
Qtty. of product,
% wt. of the copolymer
Unsatttrtl lion
Application
(%)
100
0-974
62"4
0"124
29.82
2.11
100
1.34-1.54
68"6
0.28-0.37
26-6
4.2-4.75
100
0.506
87.4
0.0
10.2
1'3
100
1.81
87"2
O.422
ll.0
6.05
Polymerization was carried o u t in t h e p r e s e n c e o f t h e c a t a l y s t A l ( C z H ~), + TiC14
The
salnt~
Polymerization was carried o u t in t h e p r e s e n c e o f t h e catalyst Al(CtHs) a ~ TiCl,
The ~ a m e
Note. Tile fractionation was carried out by fractional solution in toluene at 20% In these conditions the amorphous fract ion is d iasolved [3]. The introduction of a larger or smaller number of isoprene groups into the macromolccule eopolymer (by adding to the eopolymerization front 1 to 10 per cent of isoprene) does not influence the character of the thormomeehanical curves of these eopolyulers and, consequently, the change ill fluidity of" the co|)olymtq'.
Composition of the vulcanizing mixture (in g per 100 g of polymer): sulp h u r - 2 . 0 , t h i u r a m - - l . 3 , "kaptaks"--0.65, zinc oxide--5.0, stearin--3.0; vulcanization temperature 100-145°; duration 30-120min. Vulcanization was carried out in a press. Because stereoregular polypropylene has little stability to oxidative dest.ruction at high temperature, then, to eliminate the side effects of the process of oxidative destruction, mixtures of the copolymer with the vulcanization
144
N . S . VOLKOVA eg al.
reagents were mixed in a rolling mill, and heating of the mixtm'e was carried out in parallel in air and under vacuum in sealed tubes from which the air had been previously removed down to a pressure of 10-e ram. (b) The ultrafast vulcanization method by reacting the copolymer with sulphur monochloride (either as gaseous S~C12or as a 5°/o solution of S2CI2 in benzene). Length of reaction 15-60 min, temperature 20 °. Treatment with the benzene solution of sulphur monochloride ensures some swelling of the copolymer and thus increases the possibility of diffusion of the vulcanization reagent into the polymer. i
5
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FI6. 2. T h e m n o e h e m i c a l p r o p e r t i e s o f t h e c o p o l y m e r a f t e r v u l c a n i z a t i o n : (1) c o p o l y m e r h e a t e d t o I00 ° for GL., (2) to 150 ° for 2 h r , (3) cop01ymer h e a t e d to 150 ° for 2 hr, (4) a t 100 ° for 6 hr, in n i t r o g e n , (5) c o p o l y m e r h e a t e d t o 150 ° for 2 hi', (6) to 100 ° for 6 hr, in v a c u u m .
The following estimations were carried out to determine the amount of chemical bonding between the copolymer molecules resulting from the treatment described: (a) the quantity of combined sulphur after vulcanization; (b) the change in the degree of unsaturation of the copolymer; (c) the change in the character of the thermomechanical curves of the copolymer before and after vulcanization. The quantity of combined sulphur in the sample after vulcanization was determined by the method adopted in the resin i n d u s t r y - - t h e free sulphur is extracted with acetone from the sample submitted to vulcanization and subsequently the quantity of combined (non-extractable) sulphur is determined by normal methods. However, control experiments showed that it was impossible to remove free sulphur from thick rolled samples of the copolymer or polypropylene. Thus, for example, polypropylene, rolled with a sulphur preparation and then extracted with acetone for 26-36 hr, contained 0.9 per cent combined sulphur. Cyclohexane was used in place of acetone to increase the extraction temperature; but this solvent did not permit the complete removal of sulphur
Stereo regular copolymers of propylene and isoprene
145
from polypropylene. Therefore one cannot use the determination of the quantity of combined sulphur as a characteristic of the number of chemical bonds formed between the macromolecules. The change in properties of the polymer as a result of the formation of chemical bonds between the macromolecules is demonstrated by the character of the thermomechanical curve (the change in fluidity of the material on increasing the temperature) which is determined by various methods, in particular by Kargin's balance. When chemical bonds between the maeromolecules appear the fluidity of the material should fall sharply, but in the presence of a large number of bonds, the polymer in general should not flow on increasing the temperature. The character of the thermomechanical curve should also change sharply. Trials showed that chemical bonds between the copolymer macromolecules were not formed on vulcanization under the conditions described above. As is evident from Fig. 2, the thermomechanical curves of the copolymer did not change after rolling with a vulcanization mixture and after heating either in air or in vacuum for various times and various temperatures. There was no change in the degree of unsaturation either. It is obvious that chemical bonds were not fornmd between the macromoteeules in the vulcanization conditions described; negative results were obtained with both variants of sulphur mouochloride vulcanization.
zool 700
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Ternpcratu(°C) re FIe;. 3. Thermochemieal properties: (1) initial fraction, (2) amorphous fraction of the copolymer, vulcanized in air, (3) same in vacuum.
Temperature (°C) FIG. 4. Thermoehemical properties before and after irradiation: (1) amorphous fraction irradiated with ?-rays (50 million roentgen), (2) tile same, not irradiated, (3) unfraetionated specimen SPI-12, irradiated in air (150 million roentgen). (4) the same in vacuum (150 nfillion roentgen), (5) the same sample, not, irradiated.
To elucidate the possibility of vulcanization of the propylene/isoprene copolymer with sulphur, the vulcanization was carried out with the amorphous fraction of the copolymer which had the highest degree of unsaturation (6.11 per cent). This fraction was mixed with a vulcanizing mixture in the rolling mill 10 Polymer I & 2
146
N.S. VOLKOVAe~al.
and submitted to heating under the same conditions; but as is evident from Fig, 3, the character of the thermomeehanical curve for this fraction also did not change after vulcanization. Therefore, we a t t e m p t e d to use physical methods, especially irradiation with ~,-rays, instead of chemical methods, for forming chemical b o n d s between the macromolecules of the copolymer. The stereoregular copolymer of propylene and isoprene synthesized by us was irradiated with r-rays of varying intensity.* A radiation dose of 15 to 150 million roentgen was used, either in air or in high vacuum. The change in the n u mb er of double bonds and in the molecular weight (by viscometric measurements) were determined for the irradiated samples, and thermomeehanical curves were constructed. The results obtained are put in Table 4 and Fig. 4. As can be seen from these data, a considerable destruction of the copolymer takes place when it is irradiated at various intensities in air, and this leads to a lowering of the initial t e m per a t ur e of flow of the material after irradiation. Chemical bonds between the macromolecules are not formed in these conditions of t r e a t m e n t and consequently the character of the thermomechanical curves of these preparations is not changed. Formation of chemical bonds between the macromolecules is observed or irradiation in vacuum with the maximum dose used b y us - - 150 million r o e n t g e n - - a n d this is confirmed by the sharp change in the thermomechanical curve of this preparation. The data in Fig. 4 show t h a t this preparation does not soften at the t em perat ure at which the initial sample of polypropylene begins to flow (160 °) and this material does T A B L E 4. CHANGES IN T H E D E G R E E Ok' UNSATURATION AN]) T H E VALUE OF T H E SPECIFIC VI8COSITY FOR. PREPARATIONS OF T H E COPOLYME~ OF P R O P Y L E N E AND ISOPRENE AFTER IRRADIATION
Condition of irradiation
Dose (min) r 15 15 50 50 150 150
Properties of the preparation
Degree of unsaturation Character (%) of the .................... medium before after irradiation irradiation Air Vaeutt~n Air Vacuum Ah" Vacuum
1"8 1"8 1"8 1"8 1"8 1'8
0.47 0.98 0.54 0.97 0'71 0.95
Spec. viscosity of a 0.125% solution before I after irradiation]irradiation 0"4 0.4 0.4 0.4 0"4 0"4
0.07 0.37 0"07 insoluble 0.014 insoluble
Note. A copolymer of propylene with 7.5% isoprene, made with the catalyst A1(C2It5)3+ TiCb, u:as used for th e irradiation.
* The irradiation was carried out at. the Karpov Physico-chemieal institute by Iu. M. Malinskii, to whom we convey our thanks.
Stereo regular copolymers of propylene and isoprene
147
not melt at much higher temperatures even up to 280 ° . Evidently under these conditions vulcanization of the stereoregular copolymer of propylene and isoprene can be carried out. SUMMARY
(1) Stereoregular copolymers of the propylene with isoprene containing a small number of diene groups have been synthesized. (2) The possibility of vulcanizing the copolymers obtained has been investigated. I t has been shown t h a t the formation of chemical bonds between the macromolecules does not place when chemical methods of vulcanization are used. (3) Vulcanization of the stereoregular copolymer of propylene and isoprene can only be carried out by irradiation with high intensity rays in vacuum. Translated by M. J. NEWLANDS
REFERENCES
1. S. A. NECHAEVA and Z. A. RO{~OVIN, Khimieheskie volokna 1: 6, 1959 2. A. V. TOPCHIEV, V. A. KRENTSEL', I. M. TOLCHINSKII and {L A. {~ARNISI-IEVSKAIA,
Dokl. Akad. Nauk SSSR 114: 113, 1957 3. Z. A. ROGOVIN and T. V. DRUZHININA, Nauchn. dokl. vyssh, shkoly. 1: 139, 1958
10*