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Anionic polymerization of organotricyclosilazasiloxanes
0052-$950/80/092162-10507.5010
Polymer Science U.S.S.R. Vol. $2, No. 9, pp. 2162-2171, 1 9 8 0 Printed in Polaud
O 1981 Pergamon Press Ltd.
ANIONIC POLYMERIZATION OF ORGANOTRICYCLOSILAZASILOXANES* ¥~.. A. ZZrDA~OVA, V. S. SVISTUI~OV a n d G. V. KOTRELEV Institute of Hetero-organic Compounds, U.S.S.R. Academy of Sciences
(Received 11 July 1979) /
A study has been made of anionic polymerization of organotricyclosilazasiloxanes, containing two solixane and one disilazane ring in the molecule, in the presence of diammonium or dipotassium salts of polydimethylsiloxane diols, at various temperatures, in solution, in bulk and in the solid state. I t was found that in solution with an ammonium catalyst, rupture of Si-N and Si-O bonds occurs, with formation of a polymer in which the ratio of soluble to insoluble fraction is dependent on the molecular structure and concentration of the original polycyclic compound. I t is shown that in the course of anionic polymerization, intramoleeular rearrangement takes place, resulting in increase in the size of the rings. A comparative assessment of the reactivities of the polycyclic compounds was made, from the rates of heat evolution during the course of the reaction. In bulk in the presence of an ammonium initiator at 60-80°C some micro-scale gel is formed. At 140°C and above in the presence of a dipoC~ssium salt erosslinked polymer is formed. In solid-phase polymerization the yield of polymer is small. Some features of the mechanism of the reaction between organooyclosilazasiloxanes and nueleophilic compounds are discussed. II~ESTIOATIOI~ of t h e anionic p o l y m e r i z a t i o n o f s o m e o r g a n o p o l y c y c l o s i l o x a n e s h a s s h o w n t h a t , d e p e n d i n g on t h e r e a c t i o n conditions a n d t h e m o l e c u l a r s t r u c t u r e o f t h e m o n o m e r , soluble or crosslinked, polycyclic o r g a n o s i l o x a n e p o l y m e r s can be o b t a i n e d [1, 2]. W e felt t h a t it w o u l d b e i n t e r e s t i n g t o s t u d y t h e a n i o n i c p o l y m e r i z a t i o n of polycyclie c o m p o u n d s c o n t a i n i n g silazane rings in t h e m o l e cule as well as p o l y s i l o x a n e f r a g m e n t s , in o r d e r t o discover t h e m a i n correlations in anionic p o l y m e r i z a t i o n o f such ring c o m p o u n d s , a n d t h e possibility o f p r o d u c i n g p o l y m e r s c o n t a i n i n g silicon a n d nitrogen, w i t h h i g h t h e r m a l s t a b i l i t y a n d resista n c e to t h e r m a l oxidation. F o r this p u r p o s e we u s e d tricyclic c o m p o u n d s , c o n t a i n i n g t w o siloxane rings s u r r o u n d e d b y different, organic side g r o u p s a n d o n e disilazane ring [3] tt I Me
Me2
Si
O---SiO$iN (Si--O)r~ R~
Me 1:l1 NSiOSi~O
l~Ie2
*Vysokomol. soyed. A22: No. 9, 1973--1980. 2162
(O--Si).~, B._,
Anionic polymerization of organotricyclosilazasiloxanes
2163~
where R=R'=lVIe, m = 2 (I) and ~ n = 3 (II), or R=Me, R ' = P h and m = 2 (III), or R = P h , R ' = M e and m = 2 (IV). In polymerization of compound I in 43% toluene solution at 60°C, in the presence of the diammonium salt of polydimethylsiloxane diol (DAS), the end product contained 62% of gel fraction. As the concentration of the monomer solution is reduced the quantity of gel decreases, until at concentrations of less than 20% no insoluble product is formed. In the case of compounds I I - I V no gel fraction was formed over the range of monomer concentrations from 10~/o to 40~o. Chromatographic analysis showed that for compounds I and I I at a concentration of 15%, the conversion of monomer was 100% and 70% respectively. The corresponding heats of reaction were ~ 20 and ~ 9 kcal/mole. Analysis of the soluble products shows that in polymerization of these organotricyclosilazasiloxanes, opening of the disilazane ring occurs, as well as opening of the siloxane rings. In the NMR spectra a new peak of methyl protons appears in a stronger field region than the peak of the methyl protons of the cyclodisilazane grouping and is assigned to the methyl protons in the trisilylamino group o f a large-ring compound or of a branched molecule, as was obtained in references [4] and [5].
"
I
3
Time, hr.
5
FIG. 1. Variation in gel-fraction in bulk po]ymezlzation of the cyclic compounds I (1-3) and I V (4 and 5) in the presence of 0.03% of tho potassium catalyst at ]40°C
(1, 4), 160°0 (2) and 180°0 (3, 5).
Investigation of the polymerization of I in the melt at 60°C in the presence of DAS, showed that the heat of reaction is very small, being less than 0-5 kcal] ]mole. The reaction does not develop three-dimensionally and proceeds only as far as formation of microgel, the quantity of which increases as the quantity of catalyst is increased. This effect can be explained by occlusion of the active centre within the polymer, as a result of which, transport of the bulky monomer to the interior Of the gel is hindered. It is possible to avoid formation of mierogel by polymerizing compounds I - I V in bulk in the presence of 0.003% of the dipotassium salt of polydimehtylsiloxane diol (DKS) at 140°C and above. By this means a considerable quantity of gel fraction and soluble oligomer are produced. It is seen from Fig. 1 t h a t increase in temperature reduces the maximal quantity of gel to some e x t e n t ,
.2164
Y~.. A. ZHDANOVA St a/.
A t the same time the quantity of gel is dependent on the organic side groups surrounding the siloxane ring (Fig. 1). At a catalyst concentration of 0.5% the quantity of insoluble product is 44%. As in polymerization in solution, reaction in bulk involves the silazane as well as the siloxane ring. This is indicated by the appearance of new peaks in the NMR spectra of the soluble fraction (0.23 p.p.m, for I, 0.19 p.p.m, for II and 0.08 p.p.m, for I I I and IV), and a general increase in the integral intensity of the methyl-proton peaks of the methyl groups attached to silicon atoms linked to tertiary nitrogen. For example , in polymerization of IV at 160°C the integral intensity of these peaks increases from 1.3 to 1.6. Opening Of the silazane ring and the subsequent conversion of the resulting compounds can be represented in the following Way:
Si--O
Si
/
\
\
/I
() Si--0
O--Si
I / SiOSiN
\
I
/
\
Si
I I/ NSi0Si
0
I
\
I ~+l
I
O--Si
Si--O -, 0
/ \
/
O--Si
\ I
k/
\
S i 0 S i N SiNSi()Si
I
/ Si--O
t I ,
~)
\ \
8i--0 > 0 "
Ko(sio)n K I
\
/ O--S i 1
O(SiO)nK
O-Si Si0SiN--Si--N--Si0Si
\Si--0/~!~/~ i
!i
0 -4- K 0 - - ( - S i 0 - - ) n _ 2 K
]\0--Si/
l
0--Si--O 1 [
1 I "N~
o
N--Si--N--Si0Si
-si-o-si-
->
"
- i-ol
il
, /
~\
[/o-si
~/
\0
I
/~
0--(--Si0--)n--K i
0P
Anionic polymerization of organotricyclosilazasiloxanes
2165
VI
KOSiOSi--O l \ / >>Si--O Si--O o
\
SiOSiN
Si--0
/I/~\
Si Si--N
I
/Si(
K-(-oslt-)~-o It is seen from the reaction scheme that in polymerization of these compounds, an important part is played b y rearrangement with enlargement of the ring, because of reaction of the resulting active centre on a nitrogen atom with a siloxane group. The ability of this active centre to take part in scission of a siloxane bond we confirmed also in the reaction between bis-(trimethylsilyl)amide-sodium with trimethyltriphenylcyclotrisiloxane, which resulted in complete disappearance of the original monomer. Because of the strongly electropositive nature of the silicon atom in a disiloxane ring and of the strain in the ring, polymerization obviously begins according to the above scheme and only after this does active intermolecular interaction take place, with opening of the siloxane rings and formation of crosslinked polymer. Introduction of bulky groups, such as phenyl groups, into the monomer molecule and increase in reaction temperature, should act in favour of predominance of the occurrecnce of rearrangement and cyclization. Polymerization of IV at 200°C in fact produces only soluble oligomers. In the case of compound II, polymerization ends in crosslinking only when the catalyst concentration is increased considerably. Compound I was polymerized in the solid state at 50°C, and this produced only 6-7% of insoluble product. Here the quantity of heat evolved was proportional to the catalyst concentration. It is seen from the X-ray analysis of compound I reported in reference [6], that because of the particular arrangement of the molecules of this compound in the crystal lattice, transfer of an active centre from one molecule to another is hindered or rendered impossible. In order to discover the part played b y the silazane grouping of the molecule in polymerization, we studied the dependence of heat evolution on the concentration of compounds I - I V in solution at 60°C and a constant concentration of DAS. I t was found that decrease in monomer concentration brings about an increase in the amount of heat evolved per unit quantity of monomer. For example, for compound I this increase is from 12.3 to 58.8 kcal/mole, with a change in concentration fl'om 30% to 0.2%. I t is scarcely possible that such a high contribution to the heat of reaction could be made b y opening of cyclic fragments of the molecule. I t is possible that a substantial contribution to the heat of reaction is made b y the energy released b y formation of a stable compound
2166
Y~.. A. ZHDANOVA et al.
between reactive groups of the c a t a l y s t and the silazane ring. Traces of watercan also make some contribution. This is confirmed by a special e x p e r i m e n t carried out in a solvent saturated with water. The increase in heat evolution in the moist solvent was small, however, and could not be attributed to possible hydrolysis of the silazane ring. Moreover hydrolysis of such systems under alkaline conditions is extremely slow and the rate of heat evolution in a moist solvent is the same as in a dry solvent. Since for these tricyclie systems only the total conversion of monomer can be determined, and not of the individual cyclic fragments, it seemed t h a t it would be necessary to carry out model reactions with mixtures of a cyclodisilazane and organosiloxanes, and with a cyclodisilazane alone, in order to clarify separate details of the reaction mechanism, and to separate the heat effect in polymerization of the tricyclie compound into its individual components.We assume that the amount of heat evolved in opening the siloxane parts of t h e molecules of monomers I - I V will not differ substantially from the corresponding quantities for pure organocyclosiloxanes. l~,l~'-bis-(Trimethylsilyl)tetramethylcyclodisilazane (V) was taken as a n example for investigation of the reaction of eyclodisilazane systems with a diammonium catalyst. The dependence o f heat evolution on the concentration o f V and on catalyst concentration was determined. I t was found t h a t as the concentration of V. is decreased at constant catalyst concentration, the specific heat evolution and conversion increase, as in the case of compounds I-IV, b u t when the catalyst concentration is decreased at constant monomer concentration the specific heat evolution and conversion of V decrease. Also on the chromatogram in conformity with the quantity of V reacted, a new peak appears, t ~ e elution t'/une of which corresponds to an eight-membered silazosiloxane ring, the quantity of which is proportional to the catalyst concentration. I t is evident t h a t in the first stage a transitional complex is formed between the catalys~ and the four-membered silazane ring, as follows: Me2
si
M%SiN \
/ "Si Me., iV)
NSiMe3-[- M%NO(SiO)uNM% --~ 1
Me2 Si / \ --~MeaSiN NSiMea \ /",, Si NMe~ Me2" i) / \ (SiO)nNMea
Anionic polymerization of organotricyclosilazasiloxanes
2167
The rate of formation of this complex is so high t h a t it is possible ~o detect a small peak in the heat-evolution curve (Fig. 2). Because it is unstable t h e
W, col~rain 0"05 I
ooa o.ol
i 0
I 5
I
Time, rain
iO
I
"
/5
Fzo. 2. Variation in the rate of heat evolution, W, in reaction of compound V (2.8 × 10-=~mole/l.) with the ammonium catalyst (0.0564 × 10-' mole %). (Here and in Figs. 3-6 the volume of the reaction system is 0.3 ml). !intermediate complex decomposes with evolution of heat and formation of the compound
%/ M%SiN S i N-SiMea
\
O--(--SiO)nNMe~,
"which then becomes converted to the stable ring structure M%SiN Si NSiM%
0--Si--O The latter like the original cyclodisilazane, since it has a strongly electropositive silicon atom situated between two, trisilylaza-substituted nitrogen atoms, can form a stable complex with the active group of the catalyst. An equation was derived on the basis of experimental evidence (Fig. 3), relating :the total heat effect Q to the heats of opening of the silazane ring, qr, and of
2168
YE. A. ZHDANOVA et aL
complex formation, qe. This equation is Q = q r gl P~-~/c g~, where P and gl are the conversion and molar concentration of monomer respectively, and g~ t h e molar concentration of active groups of the catalyst, Graphical solution of the equation at various concentrations of V, gave the values of ql and q2, which are 14.8 and 14.2 kcal/mole respectively (Fig. 4). Satisfactory agreement between the calculated and experimental results were obtained when these values of q ~ and q 3, and the heats of opening of the siloxane rings were used in making up the heat balance in polymerization oE mixtures of ring compound V with 2 moles of hexamethylcyclotrisiloxane (D 3) or of oetamethyleyclotetrasiloxane (D~) (Table). AQ, ca/
A Q cal
0.3
0.3 0.2
0.2
0.1
I
I
0.2
I
"
I 0.6 1"0 ~ql" fO-q~ .q.rnole I
I
0.I
0.!
0.2. , 0"3 " ,.qIP~ tO- ,,q-mole
Fro. 4
:FIG. 3
Fig. 3. Concentration dependence of the heat of reaction, AQ, of compound V with theAmmonium catalyst (0.0564× 10-~ mole ~/o). FIG. 4. Dependence of AQ on glP. The degree of conversion of the individual rings is strongly dependent o n their reactivity. Despite the high reactivity of V, a ring compound like D3, firstly because its concentration of siloxane rings is higher and secondly because, it has similar reactivity, becomes involved in the process as a result of active~ centres formed on the nitrogen a t o m Me~
~Ie3SiNSiNSiM% Me~N+ [
[
~- [Me~SiO]3--~ ,
Me2SiO(SiO)nNMe~ ~,~e2
MeaSiNSiNSiMe3 -~ / \ l M%IN(OSi)3 Me~SiO(SiO)nNM% Me2 [ As a consequence the conversion of Da is greater than the conversion of V, whereas the conversion of the less reactive D 4 is ]ess than that of V. These results give some idea of the ratio of opened siloxane and silazane ring fragments in
Anionic polymerization of organo%ricyclosilazasiloxanes
2169,
tricyclic silazasiloxanes when t h e y polymerize. There is a difference here, however, in that ring opening can occur intramolecularly in compounds I - I V , w h e r e the reaction rate is obviously higher than the rate of the intermolecu]ar reaction represented above. In this respect it is interesting to note that in copolymerizaEXrEm~E~T~ MEASV~mME~TS OF ~EAT EVOLVTm~ LW POLYMEmZATm~ O.¢ CO~POtnCDS I AND
II, A N D
OF THEIR
Quantity, " g
Compound I V + 2[MeSiO]3 II V + 2[M%8iO]4
0.0471 0.0179+0.0281 0.0450 0-0136+0.0259
MODEL
ANALOGUES
Heat evolved, cal
Conversion, %
found
100 22.3 and 75 70 32 and 20
1.3 0.77 0.33 0.37
calculate
0.78 0.38
tion of V with cyelosiloxanes we have two maxima in the heat-evolution curve,. while this is not found in the case of polymerization of the ring compounds I - I V (Fig. 5).
w, cz/Imio
h
0.08 "=
0.04
0
0
I 5 T i m e ~m / n
I Io
f /5
FIG. 5. Heat 6volution in polymerization in solution at 60°C of compound I I (0.48 mole/1.), 1) and of a mixture of D~ (0.33 mole/1.) with V (2).
The comparatively low conversion of the cyclic fragments in c~talytic polymerization of silazasiloxanes, indirectly supports the idea of formation of a stable compound between reactive end groups and eleetropositive silicon atoms situated between two trisilyl-substituted nitrogen atoms in an enlarged ring or in a branched molecule.
:2170
YE. A. Z,~I~A~OVA et ed.
As a result t h e active groups become deactivated and chain growth ceases, i.e. polymerization stops. I t is seen from Fig. 6 that the rate of heat evolution falls over the series I~IV~III~II, possibly because of difference in the reactivity of the siloxane ~part of the molecules of these compounds.
W, c~l/min O.G
1
2
O.Zt
3 0.2
o
0
5
lO Time, min
FIG. 6. Differential heat evolution curves of polymerization in solution at 60°C of
compounds I (1), IV (2), III (3) and II (4). Monomer concentration 0.37 mole]l., quantity of catalyst 0.564 × 10-4 mole ~o. Study of the resistance of these polysilazasiloxanes to thermal oxidation,' :showed t h a t degradation occurs mainly at temperatures above 400°C. I t has been shown previotisly t h a t introduction of silazane fragments into a siloxane chain increases the thermal stability of these polymers Considerably [7, 8]. The results of the present work provide an understanding of the thermal stability of organosilazasiloxanes. Firstly the more electropositive silicon atoms in these polymers, linked to tertiary nitrogen, form stable complexes with various nueleophilic impurities or additives present and increases the energy of activation for degradation, and secondly the nitrogen a t o m itself is a centre of branching, which hinders depolymerization to a considerable extent. Translated by E. O. P~LL~S
Physico-chemical properties of polydiphenylbutadiino
2171
REFERENCES 1. K. A. ANDRIANOV and A. B. ZACHERNYUK, Vysokomol. soyed. A16: 1435, 1974 (Translated in Polymer Sci. U.S.S.R., 16: 7, 1661, 1974) 2. K, A. ANDRIANOV, I. Yu. KLEMENT'EV and V. S. TIKHONOV, Dokl. Akad. Nauk 241: 834, 1978 3. K. A. ANDRIANOV, G. V. KOTRELEV, E. A. ZHDANOVA, T. V. STRELKOVA a n d N. I. PANKOV, Dokl. Akad, Nauk SSSR, 233: 349, 1977 4. K. A. ANDRIANOV, G. V. KOTRELEV, N. A. TEBENEVA, N. V..PERTSOVA, I. I. TVERDOKHLEBOVA, P. A. KURGINYAN, T. A. LARINA and E. G. KHOROSHILOVA, Vysokomol. soyed. A20: 692, 1977 (Translated in Polymer Sci. U.S.S.R. 20: 3, 784, 1977) 5. K. A. ANDRIANOV, G. V. KOTRELEV, E. A. ZHDANOVA, T. V. STRELKOVA, E. S. OBOLONKOVA, V. A. MARTIROSOV and N. I. PANKOV, Vysokomol. soyed. A20: 2355, 1978 (Translated in Polymer Sci. U.S.S.R. 20: I0, 2650, 1978) (~. V. E. SHKLOVER, P. AD'YAASUR~N, Yu. T. STRUCHKOV, E. A. ZHDANOVA, V. S. SVISTUNOV, G. V. KOTRELEV and K. A. ANDRIANOV, Dokl. Akad. Nauk SSSR 241: 377, 1978 7. K. A. ANDRIANOV, G. V. KOTRELEV, A. I. NOGAIDELI, I. V. ZHURAVLEVA, N. G. LEKISHVILI, Yu. I. TOLCHINSKII and V. I. PUSHICH, Vysokomol. soyed. A19: 451, 1977 (Translated in Polymer Sci. U.S.S.R. !9: 3, 515, 1977) 8. K. A. ANDRIANOV, A. I. NOGAIDELI, S. A. PAVLOVA, I. V. ZHURAVLEVA, N. G. LEKISHVILI, Yu. I. TOLINSKII and G. V. KOTRELEV, Soobshch. Akad. Nauk Gruz.SSI~ 78: 97, 1975
Polymer ScienceU.S.S.I~.Vol. 22, No. 9, pp. 2171-2179, 1980 Printed in Poland
0032-3950/80/092171-09507.50/0 © 1981 Pergamonl~rcss Ltd.
SOME OF THE PHYSICO-CHEMICAL PROPERTIES OF POLYDIPHENYLBUTADIINE AND OF ITS FRACTIONS* V. 1K. ~IIsr~, V. I.
FARTU~I-N', /~k. ~ . FOMI~ and M. I. CHERKASHI:b?
Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 12 July 1979) A polydiphenylbutadiine (PPBD) produced by anionic polymerization has been fractionated a n d its integral a~ld differential MWD curves have been plotted. The electron absorption a n d the luminescence spectra of the fractions have shown blocks of conjugation to be present in the first fraction. The polymer solutioas follow the Lambert-Beer law. Electron-microsoopy showed that polymers of diphenylbutadiine and of tolane produced b y anionic a~d thermal polymerizations had a glol~ular structure. A n u m b e r of the P P B D fractions show a correlation of the concentration with the globule size. The con~ection between the composition of the polymers and their eleotro-physical properties has been examined. * Vysokomol. soyod. A22: No. 9, 1981-1987, 1980.
Polymer Science U.S.S.R. Vol. $2, No. 9, pp. 2162-2171, 1 9 8 0 Printed in Polaud
O 1981 Pergamon Press Ltd.
ANIONIC POLYMERIZATION OF ORGANOTRICYCLOSILAZASILOXANES* ¥~.. A. ZZrDA~OVA, V. S. SVISTUI~OV a n d G. V. KOTRELEV Institute of Hetero-organic Compounds, U.S.S.R. Academy of Sciences
(Received 11 July 1979) /
A study has been made of anionic polymerization of organotricyclosilazasiloxanes, containing two solixane and one disilazane ring in the molecule, in the presence of diammonium or dipotassium salts of polydimethylsiloxane diols, at various temperatures, in solution, in bulk and in the solid state. I t was found that in solution with an ammonium catalyst, rupture of Si-N and Si-O bonds occurs, with formation of a polymer in which the ratio of soluble to insoluble fraction is dependent on the molecular structure and concentration of the original polycyclic compound. I t is shown that in the course of anionic polymerization, intramoleeular rearrangement takes place, resulting in increase in the size of the rings. A comparative assessment of the reactivities of the polycyclic compounds was made, from the rates of heat evolution during the course of the reaction. In bulk in the presence of an ammonium initiator at 60-80°C some micro-scale gel is formed. At 140°C and above in the presence of a dipoC~ssium salt erosslinked polymer is formed. In solid-phase polymerization the yield of polymer is small. Some features of the mechanism of the reaction between organooyclosilazasiloxanes and nueleophilic compounds are discussed. II~ESTIOATIOI~ of t h e anionic p o l y m e r i z a t i o n o f s o m e o r g a n o p o l y c y c l o s i l o x a n e s h a s s h o w n t h a t , d e p e n d i n g on t h e r e a c t i o n conditions a n d t h e m o l e c u l a r s t r u c t u r e o f t h e m o n o m e r , soluble or crosslinked, polycyclic o r g a n o s i l o x a n e p o l y m e r s can be o b t a i n e d [1, 2]. W e felt t h a t it w o u l d b e i n t e r e s t i n g t o s t u d y t h e a n i o n i c p o l y m e r i z a t i o n of polycyclie c o m p o u n d s c o n t a i n i n g silazane rings in t h e m o l e cule as well as p o l y s i l o x a n e f r a g m e n t s , in o r d e r t o discover t h e m a i n correlations in anionic p o l y m e r i z a t i o n o f such ring c o m p o u n d s , a n d t h e possibility o f p r o d u c i n g p o l y m e r s c o n t a i n i n g silicon a n d nitrogen, w i t h h i g h t h e r m a l s t a b i l i t y a n d resista n c e to t h e r m a l oxidation. F o r this p u r p o s e we u s e d tricyclic c o m p o u n d s , c o n t a i n i n g t w o siloxane rings s u r r o u n d e d b y different, organic side g r o u p s a n d o n e disilazane ring [3] tt I Me
Me2
Si
O---SiO$iN (Si--O)r~ R~
Me 1:l1 NSiOSi~O
l~Ie2
*Vysokomol. soyed. A22: No. 9, 1973--1980. 2162
(O--Si).~, B._,
Anionic polymerization of organotricyclosilazasiloxanes
2163~
where R=R'=lVIe, m = 2 (I) and ~ n = 3 (II), or R=Me, R ' = P h and m = 2 (III), or R = P h , R ' = M e and m = 2 (IV). In polymerization of compound I in 43% toluene solution at 60°C, in the presence of the diammonium salt of polydimethylsiloxane diol (DAS), the end product contained 62% of gel fraction. As the concentration of the monomer solution is reduced the quantity of gel decreases, until at concentrations of less than 20% no insoluble product is formed. In the case of compounds I I - I V no gel fraction was formed over the range of monomer concentrations from 10~/o to 40~o. Chromatographic analysis showed that for compounds I and I I at a concentration of 15%, the conversion of monomer was 100% and 70% respectively. The corresponding heats of reaction were ~ 20 and ~ 9 kcal/mole. Analysis of the soluble products shows that in polymerization of these organotricyclosilazasiloxanes, opening of the disilazane ring occurs, as well as opening of the siloxane rings. In the NMR spectra a new peak of methyl protons appears in a stronger field region than the peak of the methyl protons of the cyclodisilazane grouping and is assigned to the methyl protons in the trisilylamino group o f a large-ring compound or of a branched molecule, as was obtained in references [4] and [5].
"
I
3
Time, hr.
5
FIG. 1. Variation in gel-fraction in bulk po]ymezlzation of the cyclic compounds I (1-3) and I V (4 and 5) in the presence of 0.03% of tho potassium catalyst at ]40°C
(1, 4), 160°0 (2) and 180°0 (3, 5).
Investigation of the polymerization of I in the melt at 60°C in the presence of DAS, showed that the heat of reaction is very small, being less than 0-5 kcal] ]mole. The reaction does not develop three-dimensionally and proceeds only as far as formation of microgel, the quantity of which increases as the quantity of catalyst is increased. This effect can be explained by occlusion of the active centre within the polymer, as a result of which, transport of the bulky monomer to the interior Of the gel is hindered. It is possible to avoid formation of mierogel by polymerizing compounds I - I V in bulk in the presence of 0.003% of the dipotassium salt of polydimehtylsiloxane diol (DKS) at 140°C and above. By this means a considerable quantity of gel fraction and soluble oligomer are produced. It is seen from Fig. 1 t h a t increase in temperature reduces the maximal quantity of gel to some e x t e n t ,
.2164
Y~.. A. ZHDANOVA St a/.
A t the same time the quantity of gel is dependent on the organic side groups surrounding the siloxane ring (Fig. 1). At a catalyst concentration of 0.5% the quantity of insoluble product is 44%. As in polymerization in solution, reaction in bulk involves the silazane as well as the siloxane ring. This is indicated by the appearance of new peaks in the NMR spectra of the soluble fraction (0.23 p.p.m, for I, 0.19 p.p.m, for II and 0.08 p.p.m, for I I I and IV), and a general increase in the integral intensity of the methyl-proton peaks of the methyl groups attached to silicon atoms linked to tertiary nitrogen. For example , in polymerization of IV at 160°C the integral intensity of these peaks increases from 1.3 to 1.6. Opening Of the silazane ring and the subsequent conversion of the resulting compounds can be represented in the following Way:
Si--O
Si
/
\
\
/I
() Si--0
O--Si
I / SiOSiN
\
I
/
\
Si
I I/ NSi0Si
0
I
\
I ~+l
I
O--Si
Si--O -, 0
/ \
/
O--Si
\ I
k/
\
S i 0 S i N SiNSi()Si
I
/ Si--O
t I ,
~)
\ \
8i--0 > 0 "
Ko(sio)n K I
\
/ O--S i 1
O(SiO)nK
O-Si Si0SiN--Si--N--Si0Si
\Si--0/~!~/~ i
!i
0 -4- K 0 - - ( - S i 0 - - ) n _ 2 K
]\0--Si/
l
0--Si--O 1 [
1 I "N~
o
N--Si--N--Si0Si
-si-o-si-
->
"
- i-ol
il
, /
~\
[/o-si
~/
\0
I
/~
0--(--Si0--)n--K i
0P
Anionic polymerization of organotricyclosilazasiloxanes
2165
VI
KOSiOSi--O l \ / >>Si--O Si--O o
\
SiOSiN
Si--0
/I/~\
Si Si--N
I
/Si(
K-(-oslt-)~-o It is seen from the reaction scheme that in polymerization of these compounds, an important part is played b y rearrangement with enlargement of the ring, because of reaction of the resulting active centre on a nitrogen atom with a siloxane group. The ability of this active centre to take part in scission of a siloxane bond we confirmed also in the reaction between bis-(trimethylsilyl)amide-sodium with trimethyltriphenylcyclotrisiloxane, which resulted in complete disappearance of the original monomer. Because of the strongly electropositive nature of the silicon atom in a disiloxane ring and of the strain in the ring, polymerization obviously begins according to the above scheme and only after this does active intermolecular interaction take place, with opening of the siloxane rings and formation of crosslinked polymer. Introduction of bulky groups, such as phenyl groups, into the monomer molecule and increase in reaction temperature, should act in favour of predominance of the occurrecnce of rearrangement and cyclization. Polymerization of IV at 200°C in fact produces only soluble oligomers. In the case of compound II, polymerization ends in crosslinking only when the catalyst concentration is increased considerably. Compound I was polymerized in the solid state at 50°C, and this produced only 6-7% of insoluble product. Here the quantity of heat evolved was proportional to the catalyst concentration. It is seen from the X-ray analysis of compound I reported in reference [6], that because of the particular arrangement of the molecules of this compound in the crystal lattice, transfer of an active centre from one molecule to another is hindered or rendered impossible. In order to discover the part played b y the silazane grouping of the molecule in polymerization, we studied the dependence of heat evolution on the concentration of compounds I - I V in solution at 60°C and a constant concentration of DAS. I t was found that decrease in monomer concentration brings about an increase in the amount of heat evolved per unit quantity of monomer. For example, for compound I this increase is from 12.3 to 58.8 kcal/mole, with a change in concentration fl'om 30% to 0.2%. I t is scarcely possible that such a high contribution to the heat of reaction could be made b y opening of cyclic fragments of the molecule. I t is possible that a substantial contribution to the heat of reaction is made b y the energy released b y formation of a stable compound
2166
Y~.. A. ZHDANOVA et al.
between reactive groups of the c a t a l y s t and the silazane ring. Traces of watercan also make some contribution. This is confirmed by a special e x p e r i m e n t carried out in a solvent saturated with water. The increase in heat evolution in the moist solvent was small, however, and could not be attributed to possible hydrolysis of the silazane ring. Moreover hydrolysis of such systems under alkaline conditions is extremely slow and the rate of heat evolution in a moist solvent is the same as in a dry solvent. Since for these tricyclie systems only the total conversion of monomer can be determined, and not of the individual cyclic fragments, it seemed t h a t it would be necessary to carry out model reactions with mixtures of a cyclodisilazane and organosiloxanes, and with a cyclodisilazane alone, in order to clarify separate details of the reaction mechanism, and to separate the heat effect in polymerization of the tricyclie compound into its individual components.We assume that the amount of heat evolved in opening the siloxane parts of t h e molecules of monomers I - I V will not differ substantially from the corresponding quantities for pure organocyclosiloxanes. l~,l~'-bis-(Trimethylsilyl)tetramethylcyclodisilazane (V) was taken as a n example for investigation of the reaction of eyclodisilazane systems with a diammonium catalyst. The dependence o f heat evolution on the concentration o f V and on catalyst concentration was determined. I t was found t h a t as the concentration of V. is decreased at constant catalyst concentration, the specific heat evolution and conversion increase, as in the case of compounds I-IV, b u t when the catalyst concentration is decreased at constant monomer concentration the specific heat evolution and conversion of V decrease. Also on the chromatogram in conformity with the quantity of V reacted, a new peak appears, t ~ e elution t'/une of which corresponds to an eight-membered silazosiloxane ring, the quantity of which is proportional to the catalyst concentration. I t is evident t h a t in the first stage a transitional complex is formed between the catalys~ and the four-membered silazane ring, as follows: Me2
si
M%SiN \
/ "Si Me., iV)
NSiMe3-[- M%NO(SiO)uNM% --~ 1
Me2 Si / \ --~MeaSiN NSiMea \ /",, Si NMe~ Me2" i) / \ (SiO)nNMea
Anionic polymerization of organotricyclosilazasiloxanes
2167
The rate of formation of this complex is so high t h a t it is possible ~o detect a small peak in the heat-evolution curve (Fig. 2). Because it is unstable t h e
W, col~rain 0"05 I
ooa o.ol
i 0
I 5
I
Time, rain
iO
I
"
/5
Fzo. 2. Variation in the rate of heat evolution, W, in reaction of compound V (2.8 × 10-=~mole/l.) with the ammonium catalyst (0.0564 × 10-' mole %). (Here and in Figs. 3-6 the volume of the reaction system is 0.3 ml). !intermediate complex decomposes with evolution of heat and formation of the compound
%/ M%SiN S i N-SiMea
\
O--(--SiO)nNMe~,
"which then becomes converted to the stable ring structure M%SiN Si NSiM%
0--Si--O The latter like the original cyclodisilazane, since it has a strongly electropositive silicon atom situated between two, trisilylaza-substituted nitrogen atoms, can form a stable complex with the active group of the catalyst. An equation was derived on the basis of experimental evidence (Fig. 3), relating :the total heat effect Q to the heats of opening of the silazane ring, qr, and of
2168
YE. A. ZHDANOVA et aL
complex formation, qe. This equation is Q = q r gl P~-~/c g~, where P and gl are the conversion and molar concentration of monomer respectively, and g~ t h e molar concentration of active groups of the catalyst, Graphical solution of the equation at various concentrations of V, gave the values of ql and q2, which are 14.8 and 14.2 kcal/mole respectively (Fig. 4). Satisfactory agreement between the calculated and experimental results were obtained when these values of q ~ and q 3, and the heats of opening of the siloxane rings were used in making up the heat balance in polymerization oE mixtures of ring compound V with 2 moles of hexamethylcyclotrisiloxane (D 3) or of oetamethyleyclotetrasiloxane (D~) (Table). AQ, ca/
A Q cal
0.3
0.3 0.2
0.2
0.1
I
I
0.2
I
"
I 0.6 1"0 ~ql" fO-q~ .q.rnole I
I
0.I
0.!
0.2. , 0"3 " ,.qIP~ tO- ,,q-mole
Fro. 4
:FIG. 3
Fig. 3. Concentration dependence of the heat of reaction, AQ, of compound V with theAmmonium catalyst (0.0564× 10-~ mole ~/o). FIG. 4. Dependence of AQ on glP. The degree of conversion of the individual rings is strongly dependent o n their reactivity. Despite the high reactivity of V, a ring compound like D3, firstly because its concentration of siloxane rings is higher and secondly because, it has similar reactivity, becomes involved in the process as a result of active~ centres formed on the nitrogen a t o m Me~
~Ie3SiNSiNSiM% Me~N+ [
[
~- [Me~SiO]3--~ ,
Me2SiO(SiO)nNMe~ ~,~e2
MeaSiNSiNSiMe3 -~ / \ l M%IN(OSi)3 Me~SiO(SiO)nNM% Me2 [ As a consequence the conversion of Da is greater than the conversion of V, whereas the conversion of the less reactive D 4 is ]ess than that of V. These results give some idea of the ratio of opened siloxane and silazane ring fragments in
Anionic polymerization of organo%ricyclosilazasiloxanes
2169,
tricyclic silazasiloxanes when t h e y polymerize. There is a difference here, however, in that ring opening can occur intramolecularly in compounds I - I V , w h e r e the reaction rate is obviously higher than the rate of the intermolecu]ar reaction represented above. In this respect it is interesting to note that in copolymerizaEXrEm~E~T~ MEASV~mME~TS OF ~EAT EVOLVTm~ LW POLYMEmZATm~ O.¢ CO~POtnCDS I AND
II, A N D
OF THEIR
Quantity, " g
Compound I V + 2[MeSiO]3 II V + 2[M%8iO]4
0.0471 0.0179+0.0281 0.0450 0-0136+0.0259
MODEL
ANALOGUES
Heat evolved, cal
Conversion, %
found
100 22.3 and 75 70 32 and 20
1.3 0.77 0.33 0.37
calculate
0.78 0.38
tion of V with cyelosiloxanes we have two maxima in the heat-evolution curve,. while this is not found in the case of polymerization of the ring compounds I - I V (Fig. 5).
w, cz/Imio
h
0.08 "=
0.04
0
0
I 5 T i m e ~m / n
I Io
f /5
FIG. 5. Heat 6volution in polymerization in solution at 60°C of compound I I (0.48 mole/1.), 1) and of a mixture of D~ (0.33 mole/1.) with V (2).
The comparatively low conversion of the cyclic fragments in c~talytic polymerization of silazasiloxanes, indirectly supports the idea of formation of a stable compound between reactive end groups and eleetropositive silicon atoms situated between two trisilyl-substituted nitrogen atoms in an enlarged ring or in a branched molecule.
:2170
YE. A. Z,~I~A~OVA et ed.
As a result t h e active groups become deactivated and chain growth ceases, i.e. polymerization stops. I t is seen from Fig. 6 that the rate of heat evolution falls over the series I~IV~III~II, possibly because of difference in the reactivity of the siloxane ~part of the molecules of these compounds.
W, c~l/min O.G
1
2
O.Zt
3 0.2
o
0
5
lO Time, min
FIG. 6. Differential heat evolution curves of polymerization in solution at 60°C of
compounds I (1), IV (2), III (3) and II (4). Monomer concentration 0.37 mole]l., quantity of catalyst 0.564 × 10-4 mole ~o. Study of the resistance of these polysilazasiloxanes to thermal oxidation,' :showed t h a t degradation occurs mainly at temperatures above 400°C. I t has been shown previotisly t h a t introduction of silazane fragments into a siloxane chain increases the thermal stability of these polymers Considerably [7, 8]. The results of the present work provide an understanding of the thermal stability of organosilazasiloxanes. Firstly the more electropositive silicon atoms in these polymers, linked to tertiary nitrogen, form stable complexes with various nueleophilic impurities or additives present and increases the energy of activation for degradation, and secondly the nitrogen a t o m itself is a centre of branching, which hinders depolymerization to a considerable extent. Translated by E. O. P~LL~S
Physico-chemical properties of polydiphenylbutadiino
2171
REFERENCES 1. K. A. ANDRIANOV and A. B. ZACHERNYUK, Vysokomol. soyed. A16: 1435, 1974 (Translated in Polymer Sci. U.S.S.R., 16: 7, 1661, 1974) 2. K, A. ANDRIANOV, I. Yu. KLEMENT'EV and V. S. TIKHONOV, Dokl. Akad. Nauk 241: 834, 1978 3. K. A. ANDRIANOV, G. V. KOTRELEV, E. A. ZHDANOVA, T. V. STRELKOVA a n d N. I. PANKOV, Dokl. Akad, Nauk SSSR, 233: 349, 1977 4. K. A. ANDRIANOV, G. V. KOTRELEV, N. A. TEBENEVA, N. V..PERTSOVA, I. I. TVERDOKHLEBOVA, P. A. KURGINYAN, T. A. LARINA and E. G. KHOROSHILOVA, Vysokomol. soyed. A20: 692, 1977 (Translated in Polymer Sci. U.S.S.R. 20: 3, 784, 1977) 5. K. A. ANDRIANOV, G. V. KOTRELEV, E. A. ZHDANOVA, T. V. STRELKOVA, E. S. OBOLONKOVA, V. A. MARTIROSOV and N. I. PANKOV, Vysokomol. soyed. A20: 2355, 1978 (Translated in Polymer Sci. U.S.S.R. 20: I0, 2650, 1978) (~. V. E. SHKLOVER, P. AD'YAASUR~N, Yu. T. STRUCHKOV, E. A. ZHDANOVA, V. S. SVISTUNOV, G. V. KOTRELEV and K. A. ANDRIANOV, Dokl. Akad. Nauk SSSR 241: 377, 1978 7. K. A. ANDRIANOV, G. V. KOTRELEV, A. I. NOGAIDELI, I. V. ZHURAVLEVA, N. G. LEKISHVILI, Yu. I. TOLCHINSKII and V. I. PUSHICH, Vysokomol. soyed. A19: 451, 1977 (Translated in Polymer Sci. U.S.S.R. !9: 3, 515, 1977) 8. K. A. ANDRIANOV, A. I. NOGAIDELI, S. A. PAVLOVA, I. V. ZHURAVLEVA, N. G. LEKISHVILI, Yu. I. TOLINSKII and G. V. KOTRELEV, Soobshch. Akad. Nauk Gruz.SSI~ 78: 97, 1975
Polymer ScienceU.S.S.I~.Vol. 22, No. 9, pp. 2171-2179, 1980 Printed in Poland
0032-3950/80/092171-09507.50/0 © 1981 Pergamonl~rcss Ltd.
SOME OF THE PHYSICO-CHEMICAL PROPERTIES OF POLYDIPHENYLBUTADIINE AND OF ITS FRACTIONS* V. 1K. ~IIsr~, V. I.
FARTU~I-N', /~k. ~ . FOMI~ and M. I. CHERKASHI:b?
Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 12 July 1979) A polydiphenylbutadiine (PPBD) produced by anionic polymerization has been fractionated a n d its integral a~ld differential MWD curves have been plotted. The electron absorption a n d the luminescence spectra of the fractions have shown blocks of conjugation to be present in the first fraction. The polymer solutioas follow the Lambert-Beer law. Electron-microsoopy showed that polymers of diphenylbutadiine and of tolane produced b y anionic a~d thermal polymerizations had a glol~ular structure. A n u m b e r of the P P B D fractions show a correlation of the concentration with the globule size. The con~ection between the composition of the polymers and their eleotro-physical properties has been examined. * Vysokomol. soyod. A22: No. 9, 1981-1987, 1980.