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Some peculiarities of the chemical interaction of polyvinyl acetate) and polypropylene under conditions of thermal degradation
Chemical interaction of poly(viny1 acetate) and polypropylene
The nature of this distribution
is determined
1961
by the ratio of the relative activities
of the mono- and divinyl compounds. The swelling of the crosslinked polyelectrolytes and their permeability for large organic ions are related to these structural peculiaritiek. Translatedby R. J. A. HENDRY REFERENCES 1. 6. V. SAMSONOV, Ye. B. TROSTYANSKAYA and 6. E. YEHUN, Ionnyi obmen. Sorbtsiya organicheskikh veshchestv (Ion exchange. The Sorption of Organic Substances). Izd. “Nauka”, 1969 2. V. 8. SOLDATOV, Dissertation, 1968 3. L. GOLDRING, Ionnyi\obmen (Ion Exchange). Izd. “Mir”. 4. E. GLUECKAUF, Proc. Roy. Sot. 268A: 350, 1962 5. J. GRABTREE and E. GLUECKAUF, Trans. Faraday Sot. 59: 2639, 1963 6. R. WILEY, Chem. Ind. 94: 602, 1965 7. R. WHEY and W. MATHEWS, J. Macromolec. Sci. Al: 503, 1967 8. R. WILEY and E. SALE, J. Polymer Sci. 42: 491, 1960 9. J. MAIJNEKY, J. KLABAN and K. DUSEK, Collection of Czechoslav. Chem. Commun. 34: 711, 1969 10. R. R. GRISSBACH, Theory and Pm&ice of Ion Exchange, 1963 11. A. NAREBSKA and J. KOTECKA, Roczn. Chem. 39: 1305, 1965 12. 6. S. KOLESNIKOV, Vysokomol. soyed. 6: 569,1964 (Translated in Polymer Sci. U.S.S.R. 6: 3, 621, 1964)
SOMEPECULIARITIESOFTHECHEMICALINTERACTIONOF POLY(VINYLACETATE)ANDPOLYPROPYLENE UNDER CONDITIONSOFTI'IERMALDEGRADATION* N. YA. KALOFOROV Bourgas Higher Chemico-technological
Institute
(Received 7 December 1970) COMPLEX problems
have to be dealt with by authors investigating chemical interactions involving mixtures of structurally dissimilar polymers under conditions of degradation. In the investigation described in this paper an attempt has been made to elucidate some of the peculiarities of interactions of this type, taking as an example a mixture of atactic polypropylene (PP) and poly(viny1 acetate) (PVA), * Vysokomol.
soyed. A14: No. 8, 1752-1760,
1972.
1982
N.
YA.
KALOFOROV
The literature contains only a limited amount of inform&ion regarding the chemical interaction of PVA with PP under conditions of degradation in a high-viscosity medium. We know from paper [l] that the thermal modification of PP mixed with other polymers and accompanied by simultaneous degradation has been carried out. The obtained products were superior in respect to mechanical properties, fat resistance, and adhesion to paper. A kinetic study of the thermal degradation of low-molecular PP (molecular weight M=5000) at 328-410” in a high-vacuum apparatus was reported in [Z]. This resulted in a gaseous fraction (alkanes, alkenes, dienes, hydrogen, benzene) and s, residue. The kinetics of the thermal degradation of PP with M= 175,000 were also investigated. In the absence of an initiating agent (benzophenone, etc.) no crosslinking is induced in atactic or isoatactic PP by UV irradiation [3]. The degradation and crosslinking of PVA were investigated at relatively low temperatures (213, 235, 240”), in BUCUO, to prevent degradation of the yin chain [4]. The resulting insoluble residue and volatile products contained mainly acetic acid * and a small amount of ketene and CO,. The kinetics of the initiation and the chain process of elimination of acetic acid leading to the formation of double bonds were analysed in papers [4, 51. The degradation kinetics were investigated at higher temperatures (250-302’) in a 10-6mm vacuum [6]. It is clear from the cited paper that the molecular weight of the sample being investigated does not influence the rate of thermal degredation. EXPERIMENTAL Preparation of the mixtures. The mixtures were prepared in a vessel immersed in a bath containing silicone oil, under the following conditions: weight ratio of atactic PP : PVA =4 : 1, temperature of silicone oil, 130-140”; the mixing was done manually in the course of 20-25 min. Heat treatment. The experiments were performed in glass ampoules measuring 100 x x 10 mm, in nitrogen. An aluminium unit with an electric coil was used to heat the samples. The reaction temperatures were: 270&2, 300f2, 370&3#‘, and in some of the experiments 200f2, 23552 and 335&2’. The heating times were 5, 10, 20, 30, 40, 50, and 60min, and in some cases the time wss either longer or shorter. After the heat treatment the samples were cooled in air. _Fractionation. The residues of the PP and PVA were separated from the crosslinked part of the polymers by extraction with chloroform. The crosslinked product was separated by filtration, washed with pure chloroform, and dried to constant weight. The filtrate was concentrated by evaporation to 30 ml at a temperature below 50”. To precipitate the PP methyl alcohol was added to a glass containing the solution to bring the total volume up to 90 ml. The solution was evaporated to N 30 ml, after which methyl alcohol was again added to bring the volume to 90 ml, and this procedure wss repeated three times. The obtained suspension was centrifuged for 20 mm at the rate of 6000 rev/mint The PVA solution separated by centrifugation was placed in another glass, evaporated at 50’ and dried to constant weight. The product which had precipitated on the bottom and on the walls of the vessel was dissolved in chloroform (added in two 15 ml batches) and placed in a glass containing the PP obtained by precipitation with methyl alcohol. The solvent was evaporated * The mechanism of the elimination of acetic acid is regarded as a chain reaction initiated by an acetic acid molecule detached from the end of the polymer chain or (if the chain reaction starts accidentally) by means of thermal breaking of the carbon-oxygen bond with simultaneous splitting off of a hydrogen from an adjacent carbon atom belonging to the same chain or to another chain. t In the absence of a suspension the centrifugation was not carried out; the PP was simply decanted from methanol solution and washed three times with 15 ml of methanol.
Chemical interaction of poly(viny1 acetate) and polypropylene
1963
at 50” and the residue dried to constant weight. The weight of volatile products formed as a result of heat treatment was determined as the difference between the weight of the original sample and that of all the obtained products (crosslinked polymer, PP residue and PVA residue). DISCUSSION
OF RESULTS
The following products were obtained using the methods outlined above: volatile substances, a chloroform-insoluble product, a chloroform-soluble fraction precipitable with methyl alcohol, and a fraction non-precipitable with methyl alcohol. In addition a suspended product (turbidity) was formed in certain cases. The fact that the volatile product consists of acetic acid is borne out both by our experimental results (also by the smell of acetic acid) and by data in the literature. For example, up to the moment when the maximum amount of crosslinked product (see Fig. 1) is obtained at temperatures of 235, 270 and 300”,. the shape of the degradation curve is very similar to that for PVA by itself [4], despite the different conditions of the experiments. Then we also know from the literature that the volatile products of PVA degradation consist mainly of acetic acid [4, 61. At relatively low temperatures (below 270’) or with only a short period of heat treatment (as used in this investigation) solid non-swelling products and chloroform-insoluble products are formed (in relatively small amounts). At higher temperatures ( ~270”) or with longer period of heat treatment a nonswelling and chloroform-insoluble product is formed (in relatively large amounts). Finally at the highest temperatures ( ~370’) or with a longer period of heat treatment the product formed in relatively small amounts is non-swelling and chloroform-insoluble. TABLE 1 .CONTENTOF PP INTHE PRODUCTS OF HEAT TREATMENT* (Weight ratio of PP : PVA in original mixtures= 4 : 1) Time, mm
T, “C 300
2.6
300 300 370
4.5 10.0 10.0
* Baaedon
the
Product of heat treatment PP fraction in the form of a thin suspension Ditto Crosslinked product Ditto
PP content, % 91.7 94.7 3.25 090
results ofpyrolytic gaschromtowwhy
The degradation of PVA involving the formation of acetic acid in. vacua starts at temperatures above 190” [2]. This is a chain radical process whereby, according to Graesie [4], double bonds appear in the chain. In view of this it would be logical to assume that the formation of these structures is facilitated by more rigorous conditions of heat treatment (by higher temperatures and longer periods of heat treatment).
1964
N. YA.
KALOFOROV
According to the published inform&ion the degradation of PP in vacw) to macromolecular radicals and to non-mdicel residues containing saturated and unsaturated bonds at the chin ends [2] takes place at temperatures above 275” [l]. In the light of these findings one must assume that the formation of PP macroradicals is preceded by the appearance of double bonds in the PVA, and so at temperatures above 275” there could well be more marked interaction of the PP macroradicals with double bonds formed in the PVA. This leads to the formation of graft copolymers or block copolymers. There are data in the literature bearing out the possibility of this type of interaction [7]. Equally possible would be the formation of copolymer based,on PVA with PP chains grafted to the methyl group of the acetate residues. The grafting of polyethylene to PVA was described in [S] where it was found that the polyethylene chains are grafted mainly to the methyl groups of the acetate residues, though some of the chains were linked directly to the main chain.
One may assume that the structure in question (graft copolymer or block copolymers), which must precede the crosslinking, is not strongly marked in our case in view of the small amount of PP in the crosslinked product (Fig. 2). The formation of graft copolymers and block copolymers is further limited by the attainment of the degradation temperature (270”) of PP. In view of the above factors and the results given in Tables 1 and 2 one may conclude that the solid chloroform-insoluble product obtained under the relatively rigorous conditions of heat treatment (above 270’) results mainly from the branched PVA formed under the relatively mild conditions of heat treatment (and to a far lesser extent results from the graft copolymer or block copolymer). /
TABLE 2. EFFECTOFTHECONDITIONS OFHEATTREATMENT ON~ROSSLINKING
Weight ratio PP : PVA
T, “C
Time, min
Amount of crosslinked product, wt. %
270 270 200 270 300 370 200 270 300 370
3 5 10 20 5 10 10 20 5 -
0.12 0.93 0.00 0.00 0.00 0.00 0.00 64.81 69.80 Explosion
1: 1 I:1 5:o 5:o 5:o 5:o 0:5 0:5 0:5 0:5
-
The chloroform-soluble fraction which is nevertheless precipitable by methyl alcohol is apparently PP. Pyrolytic gas chromatographic analysis of the PP fraction obtained by centrifugation of a very thin suspension after the precipitation of PP bymethanol (see Table 1) showed that the amount of PP in the suspension may exceed 9 1%.
Chemical interaction of poly(viny1 acetate) and polypropylene
1966
The fraction that dissolves in chloroform but is not precipitable with methyl alcohol is apparently PVA. Under the conditions of heat treatment referred to above a suspension appears at different moments during the fractionation process, i.e. during the dissolution of the homopolymers in chloroform, and during the precipitation of PP with methyl alcohol, or after the precipitation. The heat treatment of a mixture of PP and PVA under more rigorous conditions resulted, when the reaction mixture was dissolved in chloroform, in a yellowish suspension which was readily precipitable by means of centrifugation. This is probably a solid product of degradation with a low degree of crosslinking. This suspension could be called a micro-gel as distinct from a macro-gel (cross1 linked product) that has a high degree of crosslinking. Under the conditions of our experiments we found that a very thin suspension was formed in the case of a long period of degradation at low temperatures, or with a short period of heat treatment at higher temperatures. A similar but more pronounced effect was observed when the weight ratio of atactic PP : PVA was altered to 1 : 1. When the mixture of polymers is subjected to a longer period of heat treatment at 200” (10, 20, 30 min) the suspension appearing after precipit’ation by methyl alcohol was precipitable by means of centrifugation. This shows that PVA with a higher degree of branching is obtained. With a relatively short period of heat treatment (from 1 to 2.5 min) at 270 and 300”the very thin suspension that is formed after precipitation of the mixture by methanol cannot be precipitated even by ultracentrifugation, which points to a low degree of branching in the PVA structure. With a 3-min period of heat treatment the addition of methanol leads to the formation of a suspension that is precipitable by centrifugation, indicating that the PVA has a high degree of branching. The processes of degradation and crosslinking are inseparably linked: the formation of volatile products results simultaneously in the appearance of the crosslinked product (Fig. 1). In other words the crosslinking process is accompanied by the formation of a volatile product, namely acetic acid. It was found by calculation that the maximum amount of acetic acid that may be formed from a mixture of atactic PP and PVA (4 : 1) is 13*96o/oon the total weight of the mixture. The experimental results show that considerable amounts of acetate groups (the ascending branches of the curves in Fig. 1) are incorporated into the structure of crosslinked products obtained at temperatures below 300’. For example, at the crosslinking peak corresponding to 270” (see Fig. 1, curves I’, 2’) the volatile products (acetic acid) amount to 3.70% compared with 5*32o/oat 300’ (Fig. 1, curves I”, 2”). In other words, up to the moment when the maximum amount of crosslinked product is attained, most of the PVA blocks in the structure of the latter undergo no structural change. During the period in question the acetate groups are apparently stabilized.
1966
N. YA. KALOFOROV
There is a complete lack of any published data relating to studies of the process of crosslinking in mixtures of PVA and atactic PP leading to self-stabilization and carbonization, and consequently to retarded degradation. From the point of view of the modification of polymers, these problems are of interest on accomrt of the polyvinylacetate unsaturated structure being found together with the polypropylene structure (the latter only in quite small amounts) in addition to the crosslinking.
Time
, min
FIU. 1. Kinetics of the form&ion of vol&ile (I-1”) and crosslinked products (Z-Z”) at 235 (I, Z), 270 (I’, 2’) and 300” (I”, 2”).
After the maximum has been reached an abrupt fall is seen on the kinetic curves for the formation of the crosslinked product, pointing to a marked change in structure. For this reason the time corresponding to the maximum might be termed “the moment of transition”. One would expect the moment in question to mark the onset of rapid formation of acetic acid from the PVA blocks incorporated into the crosslinked product. If this is correct, the amount of PP in the crosslinked product will no doubt be the more markedly increased the higher the temperature rises, since the degradation of the crosslinked product will be accelerated at elevated temperatures after the moment of transition. This is borne out by the results of pyrolytic gas chromatographic analysis (see Fig. 2a, curves 1, 2). The crosslinked product we obtained was a modified PP conjugated system based on PVA. When the ratio of atactic PP to PVA=4 : 1, tt rise in temperature above 235’ and an increase in the time of heat treatment result in the colour of the crosslinked product changing from bright-yellow to deep dark-brown (see Table 3).
Chemical interaction of poly(viny1 acetate) and polypropylene
1967
This points to a rise in the number of conjugated bonds [4]. The deeper colouring of the crosslinked product could be taken as a qualitative indication of a lower degree of stabilization of the acetate groups.
PP,% 6-
a
4-
2-
0
.?a
M7
60
Time, min
FIU. 2
FIU. 3
FIU. 2. Kinetics of change in the PP content of the crosslinked product (a); ditto in relation to amount of original mixture (b) at 270 (1) and 300’ (2). FIG. 3. Kinetics of the formation of volatile products, during degradation, from a mixture of PP+PVA at 235 (I), 270 (Z), 300 (3) 335 (4) and 370’ (5).
As the temperature rises and the time of heat treatment is prolonged, the size of the resulting blakes is reduced, and they become rougher to the touch (Table 2). This is due to the breakdown of the three-dimensional structure as a result of the breaking of the crosslinks. It is therefore clear that in the case of higher temperatures and longer periods of heat treatment micro-gelation is the natural final stage of a process of reduction in the size of particles of the crosslinked product. During the period of crosslinking (before the “moment of transition”) at 270 and 300’ (Fig. 1, curves I’, 2’, I”, 2”) the degradation of the crosslinked product is less strongly marked. This is substantiated by the relatively bright colouring of flakes of the crosslinked product (varying from pale yellow to yellow, Table 3). During the period of time in question the total amount of degradation is largely
N. YA. KAT,OPO~OV
1968
determined by the degradation of the individual PVA. This is confirmed by the fact that the degradation curve at 280” prior to the “moment of transition” (Fig. 1, curve 1’) is similar to the degradation curve for the individual PVA [4]. It could be assumed that after the “moment of transition” the stabilization TARLE3. EFFECTOFTHECONDITIONS OFHEATTREATMENT ONTHEEXTERNAL APPEARANCE OF THE CROSSLINIEED PRODUCT Weight ratio PP:PVA 4:l
5:o
0:5
T, "C
Time mm
Commiuution capacity
External appearance of product
-200 200 200 270
10 20 30 15
A white powder Ditto Ditto Large bright yellow flakes
270
20
Large yellow flakes
270
23
Ditto
27;
30
270 270
40 60
300
4.5
Yellow particleswith some deepening of oolour Dark yellow particles Particlesvaryiug from darkyellow to bright-brown Large bright-yellow flakes
300 300
5 10
300
20
Bright-yellow flakes Particlesvarying from bright-yellow to yellow Yellow particles
300
30
Dark-yellow particles
300
40
300 370 370 370 200 270 300 370 200 270 300
60 10 20 30 10 20 5 10 10 20 5
Partiolesvarying from darkyellow to brown Ditto Bright-brownparticles Dark-brown particles Deep dark-brownpar&lea White resinousmass Ditto 9, ,, Br’dwuresinousmass Ditto
Can be commmuted only with difficulty Can be commiuuted only with difllculty (typical.crosslinked product) May be commiuuted to a flue powder Ditto Ditto Ditto Cannot be commiuuted or only with di&ulty (typical crosslinked product) Ditto Can be commiuuted to fine soft powder Can be commiuuted to soft powder Cau be commiuuted to flue soft powder Ditto 1, 2, ,; ,, 2, 3, ,1 9, Bryttle product
/ 1Ditto -
Chemical interaction of poly(viny1 acetate) and polypropylene
1969
of the acetate groups, would be reduced ,as a. result of the lower degree of crosslinking. This would probably account for the considerable rate of degradation of the crosslinked product immediately after this moment (Fig. 1, curve 2’) and the corresponding changes in the shape of the degradation curve (curve I’). The curves of degradation and crosslinking become more and more like mirror curves, as the shape of the degradation curve characterizing the amount of volatile products is now largely determined by the nature of the crosslinking curve, i.e. by the formation of volatile products during the degradation of the crosslinked product. The fact that after the “moment of transition” the high rate of degradation of the crosslinked product is largely due to the formation of acetic acid is confirmed by the colour of the product turning much deeper (Table 3), and by the amount of the PVA fraction (less than 1.70% on the total amount of the mixture). The problem arises as to. whether only acetic acid is formed during the breakdown of the product (is it a case of plain degradation determined by the TABLE
4. CARBONIZATION
AND DECARBONIZATI~N
OF THE CROSSY~D
PRODUCT
(Weight ratio of PP:PVA=4:1)
-
of PVA in the crosslinked product (on weight of original mix-
Amount
T,“C
Time, min
210
300
20 23 30 40 4.5 10 20 30 40 60
the crosslinked product, yo
Amount
in
stabilized acetic acid
ture) % -
-
14.3 16.9
-
Bt
A*
polyeoetylene structures
-
10.6 13.0 6.7 5.2
3.9 -
9.1 -
-
-
4.5 4.0
-
i
*
-
I -
-
-
4.3 6.4 -
1-l 0.8 -
6.9 a.4 8.8 9.2
3.5 4.1 4.9 5.1
-
A* ia the amount of product9 determined during the degradation of the crosalinkedproduct in relation to the weight of the original mixtore,%. Bt is the amount of acetic acid formed during the degradation of the individual PVA in relation to the weight of the original mixture,%.
yield of volatile products (Fig. 1, curve 1’) or does the degradation of the crosslinked product result not only in the formation acetic acid, but also in the formation of considerable amounts of chloroform-soluble (or partially soluble) polymer? If the second assumption were correct, the degradation of the crosslinked product would inevitably pass through the stage of micro-gel formation with the gel appearing as a typical suspension. The absence of any micro-gel in the interval
1970
N.
YA.
KALOFOROV
of time investigated by us means that the crosslinked product degrades mainly to acetic acid. In view of this the following conclusions may be drawn. It is seen from Fig. 1 (curves 1’, Z’, I”, 2”) that the yield of volatile substances during the degradation exceeds the corresponding yield due solely to the degradation of the crosslinked product (Table 4). The difference between these two values is the amount of acetic acid formed during the degradation of the individual PVA (the PVA fraction in the mixture) (Table 4). This difference increases with rising temperature from 270 to 300”, and with increase in the time of heat treatment at 300”. This is due to the relative weakening of the process of degradation of the crosslinked product owing to the smaller number of acetate groups in the latter, which is confirmed by the lower degree of curvature of the curves. All the calculations in respect to the stabilization of acetate groups (carbonization) and decarbonization of the latter refer to cases where degradation of PVA in the crosslinked product to acetic acid both before and after the crosslinking would be impossible. The PVA does actually undergo degradation after the crosslinking, but to a much lesser extent (as it is incorporated into the stabilized structure of the crosslinked product) than the individual PVA. Therefore the numbers appearing in the last two columns of Table 3 are only approximate. The error in calculating the amount of acetic acid formed at 270’ is much less than 0.5 x 3.7% because the total amount of acetic acid obtained during the degradation of the individual PVA at 270’ during a 23 min period (the major part of the total) and during the degradation of PVA in the crosslinked product (the lesser part of the total) amounted to 3.7%. It is seen from Fig. 3 that the degradation curves at 370 and 335” have a steep slope after 10 min, in contrast to the curve for 300”. One may assume that the PVA structure is transformed under these conditions into polyacetylene structure which, as we know, possesses relatively high heat resistance. If this assumption is correct, then in the temperature region 335 to 370’ both the individual PP and the PP of the crosslinked product are transformed into volatile substances after ten minutes’ heat treatment. The results of pyrolytic gas chromatographic confirm the anticipated very low content of PP in the crosslinked product obtained at 370” (Table 1); this is convincing evidence of the validity of the assumptions made above. It should be noted that in the case of heat treatment at 300” the PP content of the crosslinked product according to the results of the gas chromatographic analysis is relatively quite low (Fig. 2a), though it is considerably higher than the PP content of the product obtained at 370” (see Table 1). The procedure adopted for these experiments is convenient in that the nature of the separate processes may be elucidated. For example, it is seen that approximately steady-state conditions prevail in respect to the top portions of the curves in Fig. 3 at 300, 270 and 235’, which shows that the process of formation of acetic acid has been completed. At the same time at temperatures of 370 and 335” the degradation of the PP (both the individual PP and that incorporated into
1971
Chemical interaction of poly(viny1 acetate) and polypropylene the structure
of the crosslinked
of equilibrium. The degradation
product)
of the individual
prevent
the attainment
PVA proceeds
of any state
with an explosion
at the
very outset of heating at 370” (Table 2), which shows that a critical state has been reached
where the least change in pressure will be reflected
in volume.
Therefore
in the investigation
in a huge change
of processes involving
the formation
of considerable amounts of volatile substances the successful application of our method will call for the use of large ampoules and the appropriate heating apparatus. In conclusion
the author wishes to thank Yu. A. Tkhorik
in this investigation
for his assistance
and for a number of valuable observations. CONCLUSIONS
(1) The heat treatment of a mixture of polypropylene (PP) and polyvinylacetate (PVA) under conditions of thermal degradation results in volatile substances, a crosslinked product and unreacted PP and PVA. The amount of products obtained varies according to the conditions of heat treatment. The amount
of crosslinked
prodmt
obtained
at each temperature
increases up to
a particular moment, and is thereafter greatly reduced, which points to a marked structural change, namely a lower degree of crosslinking and a higher content of PP in the crosslinked product. (2) Up to the point
where the maximum
amount
of crosslinked
product
is obtained the stabilization of the acetate groups in the crosslinked product continues, and thereafter the degradation of these groups takes place. During the period of the stabilization total amount of degradation individual PVA. (3) The content
of acetate groups of the crosslinked is largely
determined
of PP in the crosslinked
and increases with rising temperature of the crosslinked product. (4) The interrelation
product
by the degradation
product
is relatively
the
of the
quite low,
after an abrupt change in the structure
and interdependence
of the processes
of degradation
and crosslinking is demonstrated-along with the formation of volatile products the simultaneous appearance of the crosslinked product is observed. . (5) The method used in this investigation makes the nature of the individual processes: the fact that degradation processes approach the equilibrium state of the process of elimination of acetic acid; the absence at 370 and 335” points to the degradation of PP.
it possible to determine at 300, 270 and 235’ the points to the completion of steady-state conditions
Translated by R. J. A.
HENDRY
REFERENCES 1. U.S. Pat. 3121070, 1964; Chem. Abstrs 60: 108243, 1964 2. 6. MADORSKII, Termicheskoye razlozhenie organicheskikh polimerov (Thermal Decomposition of Organic Polymers). p. 106, Izd. “Mir”, 126, 187, 1967 3. J. R. JXATTON, J. B. JACRSON and R. 6. J. MILLRR, Polymer 8: 41, 1967
1972
V. V. KoasHllg et al.
4. N. GRASSIE, Khimiya protesssov destruktsiipolimerov (Chemistryof Polymer Degradation Processes).p. 229, 136, 1959 6. Ii. H. 6. JELINEK, Degradation of Vinyl Polymers, N. Y., p. 142, 1955 6. A. SERVOTT and V. DESRYE, Trans. Internat. Symposium on Polymers, p. 207, 1967, Izd. “Mir” 1968 7. R. TSEREiA, Block and Graft Copolymers, p. 124, Izd. “Mir” 221 240 1964 8. K. MARVELL, Introduction to the Organic Chemistry of Polkers,‘p. ldl, 1961
SYNTHESISAND INVESTIGATIONOF POLYAMIDES BASED ONp-CARBORANEDICARBOXYLICACID* V. V. KORSHAK,L. G. KOMAROVA and N. I. BEKASOVA Heteroorganic Compounds Institute, U.S.S.R. Academy of Sciences (Received 7 December 1970)
IN PREVIOUSpapers [l-4] we described polyamides with m-carborane rings in the main chain. In this investigation our aim was to prepare polyamides containing p-carborane rings and then to investigate their properties and compare them with those of the polyamides based on m-carboranedicarboxylic acid. The polyamides were prepared by polycondensation of p-carboranedicarboxylic acid dichloride with aromatic and aliphatic diamines under the conditions that were optimal for the synthesis of the polyamides of m-carboranedicarboxylic acid, i.e. by solution polycondensation in tetrahydrofuran (THF) with equimolar ratios of the initial reactants, the concentration of the latter being 0.2 mole/l. [I, 21. The polycondensation was carried out in the presence of triethylamine for 1 hr. The reaction proceeds in accordance with the following scheme:
* Vysokomol. soyed. A14: No. 8, 1761-1765, 1972.
The nature of this distribution
is determined
1961
by the ratio of the relative activities
of the mono- and divinyl compounds. The swelling of the crosslinked polyelectrolytes and their permeability for large organic ions are related to these structural peculiaritiek. Translatedby R. J. A. HENDRY REFERENCES 1. 6. V. SAMSONOV, Ye. B. TROSTYANSKAYA and 6. E. YEHUN, Ionnyi obmen. Sorbtsiya organicheskikh veshchestv (Ion exchange. The Sorption of Organic Substances). Izd. “Nauka”, 1969 2. V. 8. SOLDATOV, Dissertation, 1968 3. L. GOLDRING, Ionnyi\obmen (Ion Exchange). Izd. “Mir”. 4. E. GLUECKAUF, Proc. Roy. Sot. 268A: 350, 1962 5. J. GRABTREE and E. GLUECKAUF, Trans. Faraday Sot. 59: 2639, 1963 6. R. WILEY, Chem. Ind. 94: 602, 1965 7. R. WHEY and W. MATHEWS, J. Macromolec. Sci. Al: 503, 1967 8. R. WILEY and E. SALE, J. Polymer Sci. 42: 491, 1960 9. J. MAIJNEKY, J. KLABAN and K. DUSEK, Collection of Czechoslav. Chem. Commun. 34: 711, 1969 10. R. R. GRISSBACH, Theory and Pm&ice of Ion Exchange, 1963 11. A. NAREBSKA and J. KOTECKA, Roczn. Chem. 39: 1305, 1965 12. 6. S. KOLESNIKOV, Vysokomol. soyed. 6: 569,1964 (Translated in Polymer Sci. U.S.S.R. 6: 3, 621, 1964)
SOMEPECULIARITIESOFTHECHEMICALINTERACTIONOF POLY(VINYLACETATE)ANDPOLYPROPYLENE UNDER CONDITIONSOFTI'IERMALDEGRADATION* N. YA. KALOFOROV Bourgas Higher Chemico-technological
Institute
(Received 7 December 1970) COMPLEX problems
have to be dealt with by authors investigating chemical interactions involving mixtures of structurally dissimilar polymers under conditions of degradation. In the investigation described in this paper an attempt has been made to elucidate some of the peculiarities of interactions of this type, taking as an example a mixture of atactic polypropylene (PP) and poly(viny1 acetate) (PVA), * Vysokomol.
soyed. A14: No. 8, 1752-1760,
1972.
1982
N.
YA.
KALOFOROV
The literature contains only a limited amount of inform&ion regarding the chemical interaction of PVA with PP under conditions of degradation in a high-viscosity medium. We know from paper [l] that the thermal modification of PP mixed with other polymers and accompanied by simultaneous degradation has been carried out. The obtained products were superior in respect to mechanical properties, fat resistance, and adhesion to paper. A kinetic study of the thermal degradation of low-molecular PP (molecular weight M=5000) at 328-410” in a high-vacuum apparatus was reported in [Z]. This resulted in a gaseous fraction (alkanes, alkenes, dienes, hydrogen, benzene) and s, residue. The kinetics of the thermal degradation of PP with M= 175,000 were also investigated. In the absence of an initiating agent (benzophenone, etc.) no crosslinking is induced in atactic or isoatactic PP by UV irradiation [3]. The degradation and crosslinking of PVA were investigated at relatively low temperatures (213, 235, 240”), in BUCUO, to prevent degradation of the yin chain [4]. The resulting insoluble residue and volatile products contained mainly acetic acid * and a small amount of ketene and CO,. The kinetics of the initiation and the chain process of elimination of acetic acid leading to the formation of double bonds were analysed in papers [4, 51. The degradation kinetics were investigated at higher temperatures (250-302’) in a 10-6mm vacuum [6]. It is clear from the cited paper that the molecular weight of the sample being investigated does not influence the rate of thermal degredation. EXPERIMENTAL Preparation of the mixtures. The mixtures were prepared in a vessel immersed in a bath containing silicone oil, under the following conditions: weight ratio of atactic PP : PVA =4 : 1, temperature of silicone oil, 130-140”; the mixing was done manually in the course of 20-25 min. Heat treatment. The experiments were performed in glass ampoules measuring 100 x x 10 mm, in nitrogen. An aluminium unit with an electric coil was used to heat the samples. The reaction temperatures were: 270&2, 300f2, 370&3#‘, and in some of the experiments 200f2, 23552 and 335&2’. The heating times were 5, 10, 20, 30, 40, 50, and 60min, and in some cases the time wss either longer or shorter. After the heat treatment the samples were cooled in air. _Fractionation. The residues of the PP and PVA were separated from the crosslinked part of the polymers by extraction with chloroform. The crosslinked product was separated by filtration, washed with pure chloroform, and dried to constant weight. The filtrate was concentrated by evaporation to 30 ml at a temperature below 50”. To precipitate the PP methyl alcohol was added to a glass containing the solution to bring the total volume up to 90 ml. The solution was evaporated to N 30 ml, after which methyl alcohol was again added to bring the volume to 90 ml, and this procedure wss repeated three times. The obtained suspension was centrifuged for 20 mm at the rate of 6000 rev/mint The PVA solution separated by centrifugation was placed in another glass, evaporated at 50’ and dried to constant weight. The product which had precipitated on the bottom and on the walls of the vessel was dissolved in chloroform (added in two 15 ml batches) and placed in a glass containing the PP obtained by precipitation with methyl alcohol. The solvent was evaporated * The mechanism of the elimination of acetic acid is regarded as a chain reaction initiated by an acetic acid molecule detached from the end of the polymer chain or (if the chain reaction starts accidentally) by means of thermal breaking of the carbon-oxygen bond with simultaneous splitting off of a hydrogen from an adjacent carbon atom belonging to the same chain or to another chain. t In the absence of a suspension the centrifugation was not carried out; the PP was simply decanted from methanol solution and washed three times with 15 ml of methanol.
Chemical interaction of poly(viny1 acetate) and polypropylene
1963
at 50” and the residue dried to constant weight. The weight of volatile products formed as a result of heat treatment was determined as the difference between the weight of the original sample and that of all the obtained products (crosslinked polymer, PP residue and PVA residue). DISCUSSION
OF RESULTS
The following products were obtained using the methods outlined above: volatile substances, a chloroform-insoluble product, a chloroform-soluble fraction precipitable with methyl alcohol, and a fraction non-precipitable with methyl alcohol. In addition a suspended product (turbidity) was formed in certain cases. The fact that the volatile product consists of acetic acid is borne out both by our experimental results (also by the smell of acetic acid) and by data in the literature. For example, up to the moment when the maximum amount of crosslinked product (see Fig. 1) is obtained at temperatures of 235, 270 and 300”,. the shape of the degradation curve is very similar to that for PVA by itself [4], despite the different conditions of the experiments. Then we also know from the literature that the volatile products of PVA degradation consist mainly of acetic acid [4, 61. At relatively low temperatures (below 270’) or with only a short period of heat treatment (as used in this investigation) solid non-swelling products and chloroform-insoluble products are formed (in relatively small amounts). At higher temperatures ( ~270”) or with longer period of heat treatment a nonswelling and chloroform-insoluble product is formed (in relatively large amounts). Finally at the highest temperatures ( ~370’) or with a longer period of heat treatment the product formed in relatively small amounts is non-swelling and chloroform-insoluble. TABLE 1 .CONTENTOF PP INTHE PRODUCTS OF HEAT TREATMENT* (Weight ratio of PP : PVA in original mixtures= 4 : 1) Time, mm
T, “C 300
2.6
300 300 370
4.5 10.0 10.0
* Baaedon
the
Product of heat treatment PP fraction in the form of a thin suspension Ditto Crosslinked product Ditto
PP content, % 91.7 94.7 3.25 090
results ofpyrolytic gaschromtowwhy
The degradation of PVA involving the formation of acetic acid in. vacua starts at temperatures above 190” [2]. This is a chain radical process whereby, according to Graesie [4], double bonds appear in the chain. In view of this it would be logical to assume that the formation of these structures is facilitated by more rigorous conditions of heat treatment (by higher temperatures and longer periods of heat treatment).
1964
N. YA.
KALOFOROV
According to the published inform&ion the degradation of PP in vacw) to macromolecular radicals and to non-mdicel residues containing saturated and unsaturated bonds at the chin ends [2] takes place at temperatures above 275” [l]. In the light of these findings one must assume that the formation of PP macroradicals is preceded by the appearance of double bonds in the PVA, and so at temperatures above 275” there could well be more marked interaction of the PP macroradicals with double bonds formed in the PVA. This leads to the formation of graft copolymers or block copolymers. There are data in the literature bearing out the possibility of this type of interaction [7]. Equally possible would be the formation of copolymer based,on PVA with PP chains grafted to the methyl group of the acetate residues. The grafting of polyethylene to PVA was described in [S] where it was found that the polyethylene chains are grafted mainly to the methyl groups of the acetate residues, though some of the chains were linked directly to the main chain.
One may assume that the structure in question (graft copolymer or block copolymers), which must precede the crosslinking, is not strongly marked in our case in view of the small amount of PP in the crosslinked product (Fig. 2). The formation of graft copolymers and block copolymers is further limited by the attainment of the degradation temperature (270”) of PP. In view of the above factors and the results given in Tables 1 and 2 one may conclude that the solid chloroform-insoluble product obtained under the relatively rigorous conditions of heat treatment (above 270’) results mainly from the branched PVA formed under the relatively mild conditions of heat treatment (and to a far lesser extent results from the graft copolymer or block copolymer). /
TABLE 2. EFFECTOFTHECONDITIONS OFHEATTREATMENT ON~ROSSLINKING
Weight ratio PP : PVA
T, “C
Time, min
Amount of crosslinked product, wt. %
270 270 200 270 300 370 200 270 300 370
3 5 10 20 5 10 10 20 5 -
0.12 0.93 0.00 0.00 0.00 0.00 0.00 64.81 69.80 Explosion
1: 1 I:1 5:o 5:o 5:o 5:o 0:5 0:5 0:5 0:5
-
The chloroform-soluble fraction which is nevertheless precipitable by methyl alcohol is apparently PP. Pyrolytic gas chromatographic analysis of the PP fraction obtained by centrifugation of a very thin suspension after the precipitation of PP bymethanol (see Table 1) showed that the amount of PP in the suspension may exceed 9 1%.
Chemical interaction of poly(viny1 acetate) and polypropylene
1966
The fraction that dissolves in chloroform but is not precipitable with methyl alcohol is apparently PVA. Under the conditions of heat treatment referred to above a suspension appears at different moments during the fractionation process, i.e. during the dissolution of the homopolymers in chloroform, and during the precipitation of PP with methyl alcohol, or after the precipitation. The heat treatment of a mixture of PP and PVA under more rigorous conditions resulted, when the reaction mixture was dissolved in chloroform, in a yellowish suspension which was readily precipitable by means of centrifugation. This is probably a solid product of degradation with a low degree of crosslinking. This suspension could be called a micro-gel as distinct from a macro-gel (cross1 linked product) that has a high degree of crosslinking. Under the conditions of our experiments we found that a very thin suspension was formed in the case of a long period of degradation at low temperatures, or with a short period of heat treatment at higher temperatures. A similar but more pronounced effect was observed when the weight ratio of atactic PP : PVA was altered to 1 : 1. When the mixture of polymers is subjected to a longer period of heat treatment at 200” (10, 20, 30 min) the suspension appearing after precipit’ation by methyl alcohol was precipitable by means of centrifugation. This shows that PVA with a higher degree of branching is obtained. With a relatively short period of heat treatment (from 1 to 2.5 min) at 270 and 300”the very thin suspension that is formed after precipitation of the mixture by methanol cannot be precipitated even by ultracentrifugation, which points to a low degree of branching in the PVA structure. With a 3-min period of heat treatment the addition of methanol leads to the formation of a suspension that is precipitable by centrifugation, indicating that the PVA has a high degree of branching. The processes of degradation and crosslinking are inseparably linked: the formation of volatile products results simultaneously in the appearance of the crosslinked product (Fig. 1). In other words the crosslinking process is accompanied by the formation of a volatile product, namely acetic acid. It was found by calculation that the maximum amount of acetic acid that may be formed from a mixture of atactic PP and PVA (4 : 1) is 13*96o/oon the total weight of the mixture. The experimental results show that considerable amounts of acetate groups (the ascending branches of the curves in Fig. 1) are incorporated into the structure of crosslinked products obtained at temperatures below 300’. For example, at the crosslinking peak corresponding to 270” (see Fig. 1, curves I’, 2’) the volatile products (acetic acid) amount to 3.70% compared with 5*32o/oat 300’ (Fig. 1, curves I”, 2”). In other words, up to the moment when the maximum amount of crosslinked product is attained, most of the PVA blocks in the structure of the latter undergo no structural change. During the period in question the acetate groups are apparently stabilized.
1966
N. YA. KALOFOROV
There is a complete lack of any published data relating to studies of the process of crosslinking in mixtures of PVA and atactic PP leading to self-stabilization and carbonization, and consequently to retarded degradation. From the point of view of the modification of polymers, these problems are of interest on accomrt of the polyvinylacetate unsaturated structure being found together with the polypropylene structure (the latter only in quite small amounts) in addition to the crosslinking.
Time
, min
FIU. 1. Kinetics of the form&ion of vol&ile (I-1”) and crosslinked products (Z-Z”) at 235 (I, Z), 270 (I’, 2’) and 300” (I”, 2”).
After the maximum has been reached an abrupt fall is seen on the kinetic curves for the formation of the crosslinked product, pointing to a marked change in structure. For this reason the time corresponding to the maximum might be termed “the moment of transition”. One would expect the moment in question to mark the onset of rapid formation of acetic acid from the PVA blocks incorporated into the crosslinked product. If this is correct, the amount of PP in the crosslinked product will no doubt be the more markedly increased the higher the temperature rises, since the degradation of the crosslinked product will be accelerated at elevated temperatures after the moment of transition. This is borne out by the results of pyrolytic gas chromatographic analysis (see Fig. 2a, curves 1, 2). The crosslinked product we obtained was a modified PP conjugated system based on PVA. When the ratio of atactic PP to PVA=4 : 1, tt rise in temperature above 235’ and an increase in the time of heat treatment result in the colour of the crosslinked product changing from bright-yellow to deep dark-brown (see Table 3).
Chemical interaction of poly(viny1 acetate) and polypropylene
1967
This points to a rise in the number of conjugated bonds [4]. The deeper colouring of the crosslinked product could be taken as a qualitative indication of a lower degree of stabilization of the acetate groups.
PP,% 6-
a
4-
2-
0
.?a
M7
60
Time, min
FIU. 2
FIU. 3
FIU. 2. Kinetics of change in the PP content of the crosslinked product (a); ditto in relation to amount of original mixture (b) at 270 (1) and 300’ (2). FIG. 3. Kinetics of the formation of volatile products, during degradation, from a mixture of PP+PVA at 235 (I), 270 (Z), 300 (3) 335 (4) and 370’ (5).
As the temperature rises and the time of heat treatment is prolonged, the size of the resulting blakes is reduced, and they become rougher to the touch (Table 2). This is due to the breakdown of the three-dimensional structure as a result of the breaking of the crosslinks. It is therefore clear that in the case of higher temperatures and longer periods of heat treatment micro-gelation is the natural final stage of a process of reduction in the size of particles of the crosslinked product. During the period of crosslinking (before the “moment of transition”) at 270 and 300’ (Fig. 1, curves I’, 2’, I”, 2”) the degradation of the crosslinked product is less strongly marked. This is substantiated by the relatively bright colouring of flakes of the crosslinked product (varying from pale yellow to yellow, Table 3). During the period of time in question the total amount of degradation is largely
N. YA. KAT,OPO~OV
1968
determined by the degradation of the individual PVA. This is confirmed by the fact that the degradation curve at 280” prior to the “moment of transition” (Fig. 1, curve 1’) is similar to the degradation curve for the individual PVA [4]. It could be assumed that after the “moment of transition” the stabilization TARLE3. EFFECTOFTHECONDITIONS OFHEATTREATMENT ONTHEEXTERNAL APPEARANCE OF THE CROSSLINIEED PRODUCT Weight ratio PP:PVA 4:l
5:o
0:5
T, "C
Time mm
Commiuution capacity
External appearance of product
-200 200 200 270
10 20 30 15
A white powder Ditto Ditto Large bright yellow flakes
270
20
Large yellow flakes
270
23
Ditto
27;
30
270 270
40 60
300
4.5
Yellow particleswith some deepening of oolour Dark yellow particles Particlesvaryiug from darkyellow to bright-brown Large bright-yellow flakes
300 300
5 10
300
20
Bright-yellow flakes Particlesvarying from bright-yellow to yellow Yellow particles
300
30
Dark-yellow particles
300
40
300 370 370 370 200 270 300 370 200 270 300
60 10 20 30 10 20 5 10 10 20 5
Partiolesvarying from darkyellow to brown Ditto Bright-brownparticles Dark-brown particles Deep dark-brownpar&lea White resinousmass Ditto 9, ,, Br’dwuresinousmass Ditto
Can be commmuted only with difficulty Can be commiuuted only with difllculty (typical.crosslinked product) May be commiuuted to a flue powder Ditto Ditto Ditto Cannot be commiuuted or only with di&ulty (typical crosslinked product) Ditto Can be commiuuted to fine soft powder Can be commiuuted to soft powder Cau be commiuuted to flue soft powder Ditto 1, 2, ,; ,, 2, 3, ,1 9, Bryttle product
/ 1Ditto -
Chemical interaction of poly(viny1 acetate) and polypropylene
1969
of the acetate groups, would be reduced ,as a. result of the lower degree of crosslinking. This would probably account for the considerable rate of degradation of the crosslinked product immediately after this moment (Fig. 1, curve 2’) and the corresponding changes in the shape of the degradation curve (curve I’). The curves of degradation and crosslinking become more and more like mirror curves, as the shape of the degradation curve characterizing the amount of volatile products is now largely determined by the nature of the crosslinking curve, i.e. by the formation of volatile products during the degradation of the crosslinked product. The fact that after the “moment of transition” the high rate of degradation of the crosslinked product is largely due to the formation of acetic acid is confirmed by the colour of the product turning much deeper (Table 3), and by the amount of the PVA fraction (less than 1.70% on the total amount of the mixture). The problem arises as to. whether only acetic acid is formed during the breakdown of the product (is it a case of plain degradation determined by the TABLE
4. CARBONIZATION
AND DECARBONIZATI~N
OF THE CROSSY~D
PRODUCT
(Weight ratio of PP:PVA=4:1)
-
of PVA in the crosslinked product (on weight of original mix-
Amount
T,“C
Time, min
210
300
20 23 30 40 4.5 10 20 30 40 60
the crosslinked product, yo
Amount
in
stabilized acetic acid
ture) % -
-
14.3 16.9
-
Bt
A*
polyeoetylene structures
-
10.6 13.0 6.7 5.2
3.9 -
9.1 -
-
-
4.5 4.0
-
i
*
-
I -
-
-
4.3 6.4 -
1-l 0.8 -
6.9 a.4 8.8 9.2
3.5 4.1 4.9 5.1
-
A* ia the amount of product9 determined during the degradation of the crosalinkedproduct in relation to the weight of the original mixtore,%. Bt is the amount of acetic acid formed during the degradation of the individual PVA in relation to the weight of the original mixture,%.
yield of volatile products (Fig. 1, curve 1’) or does the degradation of the crosslinked product result not only in the formation acetic acid, but also in the formation of considerable amounts of chloroform-soluble (or partially soluble) polymer? If the second assumption were correct, the degradation of the crosslinked product would inevitably pass through the stage of micro-gel formation with the gel appearing as a typical suspension. The absence of any micro-gel in the interval
1970
N.
YA.
KALOFOROV
of time investigated by us means that the crosslinked product degrades mainly to acetic acid. In view of this the following conclusions may be drawn. It is seen from Fig. 1 (curves 1’, Z’, I”, 2”) that the yield of volatile substances during the degradation exceeds the corresponding yield due solely to the degradation of the crosslinked product (Table 4). The difference between these two values is the amount of acetic acid formed during the degradation of the individual PVA (the PVA fraction in the mixture) (Table 4). This difference increases with rising temperature from 270 to 300”, and with increase in the time of heat treatment at 300”. This is due to the relative weakening of the process of degradation of the crosslinked product owing to the smaller number of acetate groups in the latter, which is confirmed by the lower degree of curvature of the curves. All the calculations in respect to the stabilization of acetate groups (carbonization) and decarbonization of the latter refer to cases where degradation of PVA in the crosslinked product to acetic acid both before and after the crosslinking would be impossible. The PVA does actually undergo degradation after the crosslinking, but to a much lesser extent (as it is incorporated into the stabilized structure of the crosslinked product) than the individual PVA. Therefore the numbers appearing in the last two columns of Table 3 are only approximate. The error in calculating the amount of acetic acid formed at 270’ is much less than 0.5 x 3.7% because the total amount of acetic acid obtained during the degradation of the individual PVA at 270’ during a 23 min period (the major part of the total) and during the degradation of PVA in the crosslinked product (the lesser part of the total) amounted to 3.7%. It is seen from Fig. 3 that the degradation curves at 370 and 335” have a steep slope after 10 min, in contrast to the curve for 300”. One may assume that the PVA structure is transformed under these conditions into polyacetylene structure which, as we know, possesses relatively high heat resistance. If this assumption is correct, then in the temperature region 335 to 370’ both the individual PP and the PP of the crosslinked product are transformed into volatile substances after ten minutes’ heat treatment. The results of pyrolytic gas chromatographic confirm the anticipated very low content of PP in the crosslinked product obtained at 370” (Table 1); this is convincing evidence of the validity of the assumptions made above. It should be noted that in the case of heat treatment at 300” the PP content of the crosslinked product according to the results of the gas chromatographic analysis is relatively quite low (Fig. 2a), though it is considerably higher than the PP content of the product obtained at 370” (see Table 1). The procedure adopted for these experiments is convenient in that the nature of the separate processes may be elucidated. For example, it is seen that approximately steady-state conditions prevail in respect to the top portions of the curves in Fig. 3 at 300, 270 and 235’, which shows that the process of formation of acetic acid has been completed. At the same time at temperatures of 370 and 335” the degradation of the PP (both the individual PP and that incorporated into
1971
Chemical interaction of poly(viny1 acetate) and polypropylene the structure
of the crosslinked
of equilibrium. The degradation
product)
of the individual
prevent
the attainment
PVA proceeds
of any state
with an explosion
at the
very outset of heating at 370” (Table 2), which shows that a critical state has been reached
where the least change in pressure will be reflected
in volume.
Therefore
in the investigation
in a huge change
of processes involving
the formation
of considerable amounts of volatile substances the successful application of our method will call for the use of large ampoules and the appropriate heating apparatus. In conclusion
the author wishes to thank Yu. A. Tkhorik
in this investigation
for his assistance
and for a number of valuable observations. CONCLUSIONS
(1) The heat treatment of a mixture of polypropylene (PP) and polyvinylacetate (PVA) under conditions of thermal degradation results in volatile substances, a crosslinked product and unreacted PP and PVA. The amount of products obtained varies according to the conditions of heat treatment. The amount
of crosslinked
prodmt
obtained
at each temperature
increases up to
a particular moment, and is thereafter greatly reduced, which points to a marked structural change, namely a lower degree of crosslinking and a higher content of PP in the crosslinked product. (2) Up to the point
where the maximum
amount
of crosslinked
product
is obtained the stabilization of the acetate groups in the crosslinked product continues, and thereafter the degradation of these groups takes place. During the period of the stabilization total amount of degradation individual PVA. (3) The content
of acetate groups of the crosslinked is largely
determined
of PP in the crosslinked
and increases with rising temperature of the crosslinked product. (4) The interrelation
product
by the degradation
product
is relatively
the
of the
quite low,
after an abrupt change in the structure
and interdependence
of the processes
of degradation
and crosslinking is demonstrated-along with the formation of volatile products the simultaneous appearance of the crosslinked product is observed. . (5) The method used in this investigation makes the nature of the individual processes: the fact that degradation processes approach the equilibrium state of the process of elimination of acetic acid; the absence at 370 and 335” points to the degradation of PP.
it possible to determine at 300, 270 and 235’ the points to the completion of steady-state conditions
Translated by R. J. A.
HENDRY
REFERENCES 1. U.S. Pat. 3121070, 1964; Chem. Abstrs 60: 108243, 1964 2. 6. MADORSKII, Termicheskoye razlozhenie organicheskikh polimerov (Thermal Decomposition of Organic Polymers). p. 106, Izd. “Mir”, 126, 187, 1967 3. J. R. JXATTON, J. B. JACRSON and R. 6. J. MILLRR, Polymer 8: 41, 1967
1972
V. V. KoasHllg et al.
4. N. GRASSIE, Khimiya protesssov destruktsiipolimerov (Chemistryof Polymer Degradation Processes).p. 229, 136, 1959 6. Ii. H. 6. JELINEK, Degradation of Vinyl Polymers, N. Y., p. 142, 1955 6. A. SERVOTT and V. DESRYE, Trans. Internat. Symposium on Polymers, p. 207, 1967, Izd. “Mir” 1968 7. R. TSEREiA, Block and Graft Copolymers, p. 124, Izd. “Mir” 221 240 1964 8. K. MARVELL, Introduction to the Organic Chemistry of Polkers,‘p. ldl, 1961
SYNTHESISAND INVESTIGATIONOF POLYAMIDES BASED ONp-CARBORANEDICARBOXYLICACID* V. V. KORSHAK,L. G. KOMAROVA and N. I. BEKASOVA Heteroorganic Compounds Institute, U.S.S.R. Academy of Sciences (Received 7 December 1970)
IN PREVIOUSpapers [l-4] we described polyamides with m-carborane rings in the main chain. In this investigation our aim was to prepare polyamides containing p-carborane rings and then to investigate their properties and compare them with those of the polyamides based on m-carboranedicarboxylic acid. The polyamides were prepared by polycondensation of p-carboranedicarboxylic acid dichloride with aromatic and aliphatic diamines under the conditions that were optimal for the synthesis of the polyamides of m-carboranedicarboxylic acid, i.e. by solution polycondensation in tetrahydrofuran (THF) with equimolar ratios of the initial reactants, the concentration of the latter being 0.2 mole/l. [I, 21. The polycondensation was carried out in the presence of triethylamine for 1 hr. The reaction proceeds in accordance with the following scheme:
* Vysokomol. soyed. A14: No. 8, 1761-1765, 1972.