Synthesis and characteristics of polystyryl derivatives of aluminium

0032-3950/79/1201-3062507.50fl)

Polymer Science U.S.S.R.VoL 21, pp. 3062-3068.

G PergamonPress Ltd. 1980.Printed in Poland

SYNTHESIS AND CHARACTERISTICS, OF POLYSTYRYL DERIVATIVES OF ALUMINIUM* L . V. ZAMOISKAYA, E . S. GANKINA, YE. YE. K~VER a n d Y r . B. MILOVSKAr), I n s t i t u t e of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences

(Received 25 December 1978) To synthesize organo-aluminium compounds with a polystyryl radical (PS)n. •A1Eta-n, thermal polymerization of styrene was carried out in the presence of A1Eta as a chain transfer agent. I t was established that by changing the ratio of monomer : :chain transfer agent, the length of the polymer radical m a y be adjusted over a wide range ( P = 2-800); a high degree of subhtitution of ethyl groups m a y only be observed for radicals of comparatively low molecular weight ( P = 2 - 3 0 ) . A study was made of the formation mechanism of (PS)nA1Et3-n. Results prove that the main method of formation is by a hemolytic reaction, which takes place with free polystyryl radicals. Step-by-step introduction of the monomer at the A1-- C bond has been little investigated. Synthesis and study of the behavjour of (PS)nA1Et3-n are of interest because these compounds are used as components of the A1Ra-acy] peroxide type initiating system.

A1Rs-)-cYT, peroxide type systems (R being the high molecular weight radical) are sources of high molecular weight free radicals and are therefore used to prepare block copolymers under conditions of low temperature radical polymerization [1-3]. Synthesis of organo-aluminium compounds with a high molecular weight radical (A1-HM) is the first stage in developing and studying systems of this kind. The preparation of A1-HM compounds is difficult since the conventional method used for the synthesis of high molecular weight compounds with an alkali or alkaline earth counter ion, namely anionic polymerization--cannot be carried out for A1 alkyls. A special method of solving this problem involves the use of the well known ability of alkyl aluminium to take part in hemolytic reactions as a chain transfer agent. The mechanism of action of alkyl aluminium involves the exchange of the radical combined with A1 for a free radical; under conditions of radical polymerization this process results in the formation of AI-HM [4, 5]. Thermal polymerization of styrene in the presence of A1Et8 as a chain transfer agent was selected in this study as a source of high molecular weight radicals. Polystyryl derivatives of aluminium were formed as a result. The use of these compounds as an aluminium component of initiating systems enables ABA type block copolymer structures to be obtained in the case of polymerization of meth* Vysokomol. soyed. A21: No. 12, 2773-2778, 1979. 3062

Polystyryl derivatives of aluminium

3063

acrylates (where A is the styrene block and B, the methaerylate block) as a consequence of the recombination mechanism of rupture of growing chains prevailing at low temperatures [6]. This structure of blocl~-copolymers cannot be achieved under conditions of anionic and radical (polyperoxide initiators) processes, which explains the interest in the systems studied. This investigation is aimed at establishing the regularities of the process of synthesizing p01ystyryl derivatives of A1 since the information in the literature does not answer a number of problems related to the behaviour of the system selected for synthesis (styrene+A1Et3). It had to be explained first of all to w h a t extent the A1Et3 function is limited even with high degrees of conversion b y tho role of the chain transfer agent, i.e. the fact that the presence of AIEt~ does not prevent 100% conversion of the monomer.* Furthermore, it was essential to establish a relation between conditions of synthesis (concentration of of reacting components) and parameters of the polystyrylaluminium formed (PS)nA1Eta_n,* namely the number of n-PS chains combined with A1 and the degree of polymerization/5 of the PS chain. Using results it became possible to examine in more detail the formation mechanism of styryl derivatives of aluminium. Styryl was polymcrized at 120 °. The concentration of A1Eta varied between 7 × 10 -a and 7 × 10 -1 mole/1, with the retention of constant initial concentration of the monomer (6 mole/l.), toluene being the solvent. In every case the process took place until the monomer had been used up completely, the process lasting for ~ 8 days. This was established dilatometrically using oligomer samples with /5=--2-4, of comparatively low viscosity and b y determining polymer yield from the dry residue. During the reaction A1Et3 was completely converted to compounds containing polystyryl groups at the A1 atom. This conclusion was reached while retaining the proportion of active A1-- C bond with a simultaneous reduction in the content of ethyl groups in the end product, compared with A1Et3 ~ (Table). Using low molecular weight samples 1 and 2 it was shown that two ethyl groups are fully substituted and the third is partially substituted in them. According to experimental results and information in the literature [4], t h e process m a y be expressed using equations P S ' + A 1 E t s :*-(PS)A1Et2+Et"

(1)

E t ' + M -. E t M ' + m M -* PS" (PS)A1Et2+PS" -~ (PS)2A1Et+Et" etc.

(3)

where M is the monomer. * The reaction mixture containing the end product was later used without further purification. The absence of the monomer was therefore a condition of synthesis. t These compounds are hereafter denoted in the text as PS-A1. $ Methods of determining the concentration of PS-A1 and the contents of ethyl groutm in it were described in the experimental part.

~064

L. V. ZAMOISKAYAet al.

A study of MWD of low molecular weight samples 1-3 (Table) by thin layer Chromatography (TLC) shows that the fraction corresponding to high molecular weight PS, which could be formed during thermal polymerization without A1Ets, is absent. MW of the main fraction of oligomers corresponds to values ,obtained cryoscopically. As an example Fig. la shows TLC of sample 1. Diphenyl a n d oligostyrene identified by MW (GPC) were used to identify spots on chromatographic patterns. It can be seen that two spots correspond to the dimer. The upper o n e corresponds to the dimer formed as a result of homolytie reaction (1)-(3).* A combination of all these facts proves that during polymerization practically all the styrene is transferred to PS-A1 and that MW of the polymer chain is determined by chain transfer to A1Et 3 (]~trans to A1Eta at 100 ° being 17 [4]). Results obtained for oligo-derivatives of A1 suggest that all ethyl groups in A1Eta have approximately the same reactivity. Establishing the relation between .concentration conditions of the process and values of ~ a n d / ~ result in formula (4), which is confirmed by tabulated information (samples 1-3) /5= [M]/[hl]~

(4)

It can be seen that MW values found experimentally and calculated using t'ormula (4) show fairly satisfactory agreement. The degree of substitution of ethyl groups (i.e. the n value) in the case of high molecular weight products (samples 4 and 6) cannot be determined experimentally. Approximate characteristics of these compounds may be derived from the g value using the same formula (4). Within the range of cases examined • he value of ~ tends to one. For samples 1-3 of the Table there is a steady reduction in g with an increase in the length of the macroradical. The existence o f a similar relation for high molecular weight products may be confirmed indir e c t l y by an increased homopolymer yield during the synthesis of block copolymers as polymer chain length in the alumininm component of the initiating system increases. A reduction in the reactivity of ethyl groups in PS-A1, in proportion t o substitution, is evidently the consequence of the screening effect of long polyJner chains. The length of the polystyrene chain linked with A1 is determined by
Polystyryl derivatives of aluminium

3065

of AI, shown using low molecular weighs compounds [3], is also observed for higk molecular weight PS-AI, making it possible for these substances to be used as components of the initiating system. The regularities derived explain the selection of concentration conditions of the process. In particular, the lower limit of A1Et 8 concentration corresponds to characteristics of the product obtained, which are close to limiting properties, bearing in mind polymer chain length and therefore, the value of ~, which is close to one. The conditions selected are also determined by the ease of subsequent work with PS-A1 solutions, bearing in mind the concentration of A1--C-bonds and the viscosity of the solution used. SYNTHESIS

OF POLYSTYRYL

DERIVATIVES

OF ALUMINIUM a

([styrene]=6 mole/1.; 120 °, 8 days, solvent--toluene) Conditions of synthesis F~xpt., :No.

[A1Eta],

mole/1.

0"75 0'50 0.11 0"015 0"007 without A1

Characteristics of PS-A1

number of rema[styrcb, ining Et ene]/ /[All mole/1, groups, % of theory 8

12 55 00 50

0.71 0.48 0-10 0.014

13 27 40

MW of PS

number of PS groups in PS-/kl

I

found c

ealcu lated d

J•w M.

ne

233 ! 300 355 540 3000 2500 25; 18; 26 -78; 52; 109 -210; 161; 316 --

1-~ 2"( 2-(

2 4 30 300 800 2000

2.6 2.2 1-8 1"5; 2-2 1.0; 1-6

a The e x p e r i m e n t s were reproduced repeatedly. b See e x p e r i m e n t a l p a r t for m e t h o d s of determination. c M W o f samples 1 a n d 2 was f o u n d cryoseopically, o f sample 3, b y T C L using s t a n d a r d materials, 4-6, b y OPC; for the last three the n u m b e r s in the column correspond to values M y × 10 -~, Mn × 10 -~ a n d M ~ × 10 -3. a According to f o r m u l a (4). e The v a l u e o f ~ in e x p e r i m e n t s 1-3 was derived b y a n a l y s i n g the reaction product b y a gas-volumetric m e t h o d . while in e x p e r i m e n t s 4 a n d 5 n was calculated f r o m f o r m u l a (4) using ~lv a n d ~ ' . , w i t h corresponding values being shown in t h e column.

As n o t e d previously, a l k y l a l u m i n i u m does n o t f u n c t i o n as a p o l y m e r i z a t i o n i n i t i a t o r of anionic t y p e . T h e o n l y process k n o w n f r o m results in t h e l i t e r a t u r e is p o l y m e r i z a t i o n of e t h y l e n e using these c o m p o u n d s , resulting in A1-HM [9]. On t h e o t h e r h a n d , a l k y l - a l n m i n i z a t i o n to f o r m low m o l e c u l a r weight a d d i t i o n p r o d u c t s is described in detail in t h e literature. F o r styrene, in p a r t i c u l a r , the f o r m a t i o n of a n a d d i t i o n p r o d u c t was o b s e r v e d w i t h a yield close to t h e t h e o r e t i c a l , w i t h a s t o i c h i o m e t r i c r a t i o of s t y r e n e : A1 ~<1, a t a t e m p e r a t u r e of 60-70 ° [10]. I t w a s i n t e r e s t i n g to e x p l a i n to w h a t e x t e n t u n d e r t h e conditions u s e d in t h i s s t u d y (styrene : Al>>l, 120 °) e t h y l a n d s t y r y l g r o u p s of a n o r g a n o - a l u m i n i u m

3066

L.V.

ZA~OZS~rA e2 aL

oompomzd may take part in the process, which is equivalent to chain extension not only by a radical type reaction (1-3), but also by a non-radical type reaction b y the step-by-step introduction of the monomer at the A1--C bond. To answer this problem, a study was made using (PS)nA1Et3-, (samples 1 and 2, Table) as initial organic alnminium compound (transfer agent).

•

f

t #

e/'

•

#2 t

'

•

, , Lb

|

3'

abcd Fzo. 1

Ii i e

a

b

c

d

Fro. 2

~ o . 1. TLC of oligostyrenes in a cyclohexane-toluene system (volumetric ratio 11:0-3): a - - s a m p l e 1 before the reaction; b - - a f t e r the reaction; s t a n d a r d samples; c - - d i p h e n y l ; d--oligostyrene ~vith M ~ 9 0 0 ( l ' - - t r i m e r ; 2 ' - - t e t r a m e r ; 3 ' - - p e n t a m e r ) . F r o . 2. TLC of polystyrenes in a cyclohexane-benzene-acetone system (volumetric ratio 12 : 4 : 0-2): a - - s a m p l e 2 {Table) after the reaction (main fraction); b - d - - s t a n d a r d samples of polystyrene with M ~ 9 × l0 S, 2 × 108, 4 × 108, respectively.

When the reaction takes place by a homolytic mechanism it can be expected that the ethyl groups in PS-A1 are substituted for a high molecular weight polystyryl radical. The end product in this case contains high molecular weight fractions, of which MW depends on the content of ethyl groups in PS-A1 and the oligomer fraction corresponds to MW of the initial oligostyrene. When the process takes place by the step-by-step addition of styrene molecules to an A1--C bond, as observed for the polymerization of ethylene, chain extension could be expected to take place for all the three A1--C bonds. The type of process was evaluated on the basis of the number of ethyl groups combined with A1 (gasvolumetric analysis) and the proportion of products (TLC) (see Figs lb and 2} separated and identified according to MW and MWD. As a result of the participation of oligostyryl-A1 in the reaction, compolmds are formed, which contain a few ethyl groups (e.g. for sample 1~ of the initial product is 2.6, after the reaction, 2.85). Results for sample 2 indicate that MW of the main fraction IV of the polymer formed (TLC with standard preparations results in M ~ 4 × × 10a, Fig. 2) is close to the value of M~--6× 10a, calculated from eqn. (4), based on the number of ethyl groups in the compound used in the reaction (100%). Similar regularities were also derived for a process with sample 1; MW of the main fraction, calculated 3× 103, found ~ 1.5× 103. Practically all the oligostyrene introduced in the reaction was isolated in the form of a low molecular weight fraction (ibr sample 2 of fraction 1'). A comparison of chromatographic curves of the initial oligostyrene and that obtained after the reaction (Fig.. la, b) indi-

Polystyrylderivatives of alumlninm

3067.

eates an increase of initialoligomer chains, which is confirmed by a higher intensity of spots, corresponding to oligomer fractions, with an increase of M W . A h i g h m o l e c u l a r w e i g h t p r o d u c t is f o r m e d in this p r o c e s s in a small p r o p o r t i o n . F o r s a m p l e 2 o n l y 9 % o f t h e o l i g o m e r o f initial f r a c t i o n I c h a n g e s i n t o t h e solid p o l y m e r ( f r a c t i o n 2') as a r e s u l t o f t h e r e a c t i o n . R e s u l t s s u g g e s t t h a t t h e f o r m a t i o n o f s t y r y l d e r i v a t i v e s o f A1 is m a i n l y t h e c o n s e q u e n c e o f h o m o l y t i c r e a c t i o n (1)-(3). A d e s c r i p t i o n is g i v e n o f c h a r a c t e r i s t i c s o f p o l y s t y r e n e * o b t a i n e d b y t h e r m a l p o l y m e r i z a t i o n in t h e p r e s e n c e o f PS-A1 ( / ~ 4 ) as a c h a i n t r a n s f e r a g e n t , [ M ] = 6 mole/1.; [M] : [A1]----55, t o l u e n e b e i n g t h e s o l v e n t a t 120 ° in 8 d a y s . t 3.4 g o l i g o s t y r e n e (from P S - A I ) w a s u s e d in t h e r e a c t i o n . C h a r a c t e r i s t i c s w e r e as follows: f r a c t i o n 1 (filtrate): / ~ = 2 - 9 , w e i g h t 2.18 g; f r a c t i o n 2 (residue): /~----9, w e i g h t 0.87 g. A f t e r t h e r e a c t i o n 16.9 g p o l y m e r w a s s e p a r a t e d c o n s i s t i n g o f f r a c t i o n 1' (filtrate): / ~ = - 2 - 9 , w e i g h t 1-98 g a n d f r a c t i o n 2' (residue): ]5----40, w e i g h t 14.9 g. Methods of purification and preparation for the reaction of solvents and the monomer were described previously [3]. A1Ets--a commercial product--was used as solution in toluene. PS-A1 with 15 ranging from 2 to 300 was synthesized in sealed dilatometers in vacuum (120 °, 8 days). PS-A1 solutions were stored and measured from Sehlenke vessels. PS-A1 w i t h / 5 _ 800 was synthesized in two compartment dilatometers provided with a partition and a calibrated neck part to enable them to be used directly for the synthesis of block eopolymers. The concentration of the active AI--C bond in PS-A1 could not be determined by the indicator method used for alkyl aluminium [11] because of the lower Lewis acidity of styryl derivatives of A1. PS-A1 only forms strong donor-accepter complexes with strong Lewis bases (amines of aliphatic series, pyridine). This property was also used in this study for the quantitative determination of these compounds. Methods of determination involve the following: a NEt3 solution of known concentration was added to the solution of PS-A1, with an excess of the former. The unreacted amine was distilled in vacuum and the reaction mixture rinsed with toluene. The complex was then decomposed with alcohol and the proportion of amine determined (vacuum distillation and HC1 titration). The concentration of PS-A1 was calculated in terms of the composition of the PS-A1.NEta= 1 : 1 complex. 1Results of similar determinations are tabulated. The proportion of unsubstituted ethyl groups in PS-A1 was established by a gas volumetric method, the reaction solution decomposed using a toluene-butanol mixture and the gas liberated was measured (Table). To separate oligostyrene and PS from PS-A1, the reaction mixture was decomposed using ethyl alcohol. The oligostyrene left in the filtrate and the fraction with 15/> 9 and AI(OH)~ were precipitated into residue. To remove AI(OH)a, the residue was dissolved in toluene and centrifuged and the polymer isolated by precipitation into alcohol. The filtrate was freed from solvents by vacuum distillation and the residue (oligomers) dried to constant weight in vacuum. TLC was carried out using strips with K S K silica gel by a method previously described [3].

Translated by E. SEMERE * Conditions of separation of polymers and oligcmers, their separation into fractions are described in the experimental part. t 15.9 g styrene was used in the reaction; po]ymerization took place to the extent o f 93~o during the period indicated. L

3068

A.I.

VOLOZHn~ e t a / . REFERENCES

1. Ye. B. MILOVSKAYA, L. V. ZAMOISKAYA, O. S. MIKHAILYCHEVA, E. S. GANKINA, M. D. VAL'CHIKHINA, S. Ya. MAGARIK, V. S. S K A Z K A and G. V. TARA° SOVA, Auth. Cert. 520373, 1976; Bull. izobr. No. 25, 78, 1976 2. Ye. B. MILOVSKAYA and L. V. ZAMOISKAYA, Vysokomol. seyed. B18S 300, 1976 (Not translated in Polymer Sci. U.S.S.R.) 3. L. V. ZAMOISKAYA, E. S. GANKINA and Ye. B. MILOVSKAYA, Vysokomol. soyed. A18: 1635, 1976 (Translated in Polymer Sci. U.S.S.R. 18: 7, 1873, 1976) 4. T. H A F F and E. PERRY, J. Amer. Chem. Soe. 82: 4277, 1960 5. Ye. B. MILOVSKAYA, Uspekhi khimii 42: 881, 1973 6. Kh. S. BAGDASAR'YAN, Teoriya radikal'noi polimerizatsii (Theory of Radical Polym e r i z a t i o n ) . Izd. " N a u k a " , 1966 '7. I. WIESNER and P. MERWERT, Makromolek. Chem. 165: 1, 1973 8. B. G. BELEN'KII, E. S. GANKINA, V. N. ZGONNIK, T. S. KRASNOVA, Ye. Yu. MELENEVSKAYA and P. P. NEFEDOV, Vysokomol. soyed. B20: 575, 1978 (Not trans-

lated in Polymer Sci. U.S.S.R.) 9. G. ZEISS, (Ed.), K h i m i y a metalloorganicheskikh soyedinenii (Chemistry of Organo-metallic Compounds). Izd. "Mir", 1964 10. L. I. ZAKHARIfIN, V. V. GAVRILENKO, Izv. AN SSSR, Otd. khim. n., 1507, 1959 11. G. A. RAZUVAYEV and A. I. GRAYEVSKII, Dokl. A N SSSR 128: 309, 1959

Polymer ScionceU.S.S.R. Vol. 21, pp. 3068-3072.

0032-3950/79/1201-3068507.50]0

4DPergamon Press Ltd. 1980. Printed in Poland

THERM0-MECHANICAL PROPERTIES OF ORIENTED CYCLOALIPHATIC POLYIMIDES* fl_. T. VOLOZHII~, E . T. KRUT'KO, :N. l~. PROKOPCHUK, L . N . KORZHAVII~ a n d YA. M. PAUSIrKII~ I n s t i t u t e of Organophysical Chemistry, B.S.S.R. A c a d e m y of Sciences (Received 30 December 1978) Cyclo-aliphatic polyimides were synthesized from stereoisomeric dianhydrides o f 1,2,3,4-cyclohexane tetracarboxylic acid with cis- and trans-arrangement of a n h y d r i d e rings in relation to the plane of the eyclohexano ring and a number of a r o m a t i c diamines: p-phenylenediamine, benzidinc, 4,4'-diaminodiphenyloxide a n d 4,4'-diaminodiphenylmethane. A s t u d y was made of thermo-mechanical properties o f oriented model monofilaments prepared from the polyimides indicated. The effect o f the chemical structure of polyimides on structure and physico-mechanical properties was investigated over a wide range of temperature. * Vysokomol. soyed. A21: No. 12, 2779-2783, 1979.