Thermal polymerization of arylacetylenes: 2. Study of linear dimers

Polymer Vol. 38 No. 6, pp. 1449 1459, 1997 © 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0032-3861/97/$17.00 + 0.00

PII: S0032-386I(96)00659-3

ELSEVIER

Thermal polymerization of arylacetylenes: 2. Study of linear dimers S. G a n d o n , P. M i s o n a n d B. S i l l i o n * UMR 102 CNRS-IFP. BP N ° 3, 69390 Vernaison, France (Received 17 June 1996)

Four linear dimers of 4-(hexyloxy)phenylacetylene I have been synthesized and thermally polymerized under the same conditions which were used for I. The polymerization of monomer and linear dimer mixtures was also studied. The reaction products were analysed by chromatography, spectroscopy and spectrometry techniques. The experimental results led us to conclude that the linear dimers are not reaction intermediates of the thermal polymerization of I. © 1997 Elsevier Science Ltd. All rights reserved. (Keywords: thermal

polymerization;

diyne; enynes)

INTRODUCTION

EXPERIMENTAL

In the previous paper 1 we presented the study of the thermal polymerization of 4-(hexyloxy)phenylacetylene I used as an arylacetylenic model compound. Some features of its polymerization were determined such as the formation of about 30% of naphthalenic dimers and benzenic trimers (1-5) and 70% of oligomeric products which depolymerize under extended heating. Previous studies 2-4 have implied linear dimers 5-7 as reaction intermediates of the arylacetylene polymerization in order to explain the formation of either the benzenic trimers 3 or naphthalenic dimers 4. The proposed reaction mechanisms are given in Scheme 1. The formation of 1,2,3-trisubstituted benzenic trimer was explained by a [2+2] cycloaddition. However, no linear dimer has been clearly evidenced during the polymerization. In addition the backbone geometry of any linear dimer is not favourable to the cyclization into naphthalenic dimers and benzenic trimers. This is due to the presence of the triple bond which implies the alignment of four carbon atoms and will not allow an easy cyclization reaction. In order to elucidate whether linear dimers I I - V are really intermediates of the monomer I polymerization, we undertook their synthesis and their thermal polymerization study.

Analyses and polymerization were conducted according to general procedures given in the previous paper I.

Ar RO,~~_.,~ 5

4

1

Ar R

O

~ 5

Starting materials High purity reagents such as methyltriphenylphosphonium bromide, 4-(hexyloxy)benzoyl chloride, cuprous chloride, 1,2-dibromoethane, aluminium chloride, iodine, potassium terbutylate, tetramethylethylenediamine (TMEDA), dimethoxyethane (DME) and the other solvents were purchased from commercial sources and used without further purification. For the synthesis of III, rough zinc powder (PROLABO) must be used. Prior to use diethyl ether was dried over molecular sieves (3A). Every reaction was performed under inert atmosphere and with magnetic stirring. The chemical structures of the synthesized products are presented in Figure 1 as well as an alphabetical indexation of carbon atoms used for 13C n.m.r, description. Preparation of 1,4-di[4~-(hexyloxy)phenyl]-l,3 butadiyne II A solution of 4-(hexyloxy)phenylacetylene I l (36.81 g, 180 mmol) in D M E (45 ml) was added to a mixture of cuprous chloride (3.60g, 36mmol) and of T M E D A (7.19 g, 62 mmol) in DM E (150 ml). The reaction mixture

Ar Ar~~

Ar

Ar

4

2

--Ar = " - - ~ / ~ O R

Ar

Ar

3

r

Ar 4

R = nCsH13

* T o w h o m c o r r e s p o n d e n c e s h o u l d be addressed. Present address: U P R 9031 C N R S , BP N ° 24, 69390 Vernaison, F r a n c e

POLYMER Volume 38 N u m b e r 6 1 9 9 7

1449

Thermal polymerization of arylacetylenes. 2." S. Gandon et al.

A r - ~

Ar o-~-~C

C--C

Ar and polymers

Ar~ n ' ~

diynedimer

r~Ono'~e ~

polymers

Ar Ar~ ~C --CH~-- CH'--Arf E, Z enynedimers

~

R Ar~ Ar

Ar

Ar and polymers

~ C ~ C(Ar)~ CI-~f vinylideneenyne

Ar_~-~

A~

Ar

and polymers

Ar

2 A,'

CE~C monomer

II

[2÷2]

~ rAt

Ar~//Ar monomer

Ar

A r ~

Ar

II I q

Scheme 1

was vigorously stirred at 40°C for 20 h with air bubbling. The reaction was monitored by t.l.c, analysis (cyclohexane). Some dimer II precipitated. Then the reaction mixture was poured into water (200ml) and extracted with toluene (3 × 200ml). The organic layers were washed with water and dried over magnesium sulfate. After solvent evaporation, the resulting yellow powder was dried, then crystallized from cyclohexane to yield pure |I as white needles (34.26g, 85retool, 94%). M.p. = 122-123°C (lit.8: 122.5°C); isotropic liquid transition temperature: 153°C (lit.8: 149.2°C). I.r: 2120 (C_=C). 1H n.m.r.: 7.13 (m, 8H, H arom); 3.95 (t, J = 6.5, 4H, CH20); 1.77 (Q, J = 6.5, 4H, CHzCH20); 1.30 1.50 (m, 12H, CH3(CH2)3); 0.90 (t, J = 6.6, 6H, CH3). ~3C n.m.r.: 14.1 (2C, a); 22.6 (2C, b); 25.7 (2C, d); 29.1 (2C, e); 31.6 (2C, c); 68.1 (2C, f); 72.9 (2C, 1); 81.3 (2C, k); 113.7 (2C, j); 114.6 (4C, h); 134.0 (4C, i); 159.9 (2C, g).

Preparation of 1,4-di[4'- (hexyloxy)phenyl]- 1butene-3-yne Z IIl Zinc powder (7.6g, l l6mmol) was introduced into ethanol (5 ml). After the addition of 1,2-dibromoethane (0.80 g, 4.3 mmol) diluted in ethanol (3 ml), the reaction mixture was heated. When reflux was reached, the heating bath was removed until the self-heating finished. Then a second fraction of 1,2-dibromoethane (0.75g, 40mmol) diluted in ethanol (3 ml) was added and the mixture was heated for 10min under reflux. After cooling down to 50°C the diyne II (11.26g, 28.0retool)

1450

POLYMER Volume 38 N u m b e r 6 1 9 9 7

was added in two portions and the reaction mixture was homogenized with toluene (25 ml). After 3 h 30min at 90c'C (reflux), a second activated zinc fraction [prepared from zinc (3.70g, 56.6mmol) and 1,2-dibromoethane (0.94g, 5.0mmol added in twice)] was added to the reftuxing reaction mixture. After three additional hours of reflux, the conversion of 11 was complete as was determined by t.l.c, analysis (carbon tetrachloride). Cooled to room temperature, the liquid fraction of the reaction mixture was decanted and poured into an aqueous ammonium chloride solution (4.78 g in 40 ml of water). The organic layer and the liquid fractions used for rinsing the residual zinc with toluene and ethanol, were washed together with 2N hydrochloric acid (100ml), then with water (4 × 100ml) until the pH was 7 and finally dried over magnesium sulfate. After filtration and solvent evaporation, the crude product (10.61g) was purified through silical gel column chromatography using pentane as eluent: 9.44g (23.3 mmol, 83%) of pure III were collected. M.p. = 33-34°C. I.r.: 2180 (C~C); 670 ( C H = C H cis). H n.m.r. 7.36 (m, 4H, H a r o m Ph-C=); 7.14 (m, 4H, H arom Ph C~); 6.57 (d, J = 11.9, 1H, CH Ph); 5.76 (d, J 11.9, 1H, C H C=); 3.96 (t, J = 6 . 4 , 2H, CH20); 3.93 (t, J = 6.4, 2H, CH2O); 1.77 (m, 4H, CH, CH~O); 1.30 1.50 3(m, 12H, CH?(CH,)~); 0.90 ( t , ) = 6.5, 6H, CH3). I C n.m.r.: 14.1-(2C,-a-and x); 22.6 (2C, b and w); 25.7 (2C, d and u); 29.19 and 29.24 (e and t); 31.6 (2C, c and v); 68.05 and 68.10 (f and s); 87.4 (in); 95.5 (n); 105.0 (1); 114.2 and 114.6 (2 × 2C,

Thermal polymerization

of arylacetylenes.

2: S. Gandon et al.

ab c de f CH3CH2CH2CH2CH2CH20

h

ab c de f CH3CH2CH2CH2CH2CH20 g\

0

i

-

I

k /j-

P

Q

-

-g-

CH=CH z

O\3

stu

vwx

-

0CH2CH2CH2 CH2CH2CH3

r-

OCH2CH2CH2 CH2CH&H3

/r

III

h

ab c de f CH,CH2CH2CH2CH2CH20

s\

0 h

ab c de f CH,CH2CH2CH2CH&H20

i

-

/IF

0

-

h

abcde f CH3CH2CH2CH2CH2CH20 g\

0

-g&c-

n

9

,

stu

vwx

3

E

IY

i

/i

0

i

-

P o \

CH=CH

-

g\

I

k

P

-

-

5s::

--c”c

=

/j

;H2,-

n \ 3

/

r s t u v w 0CH2CH2CH2CH2CH2CH3

q-

Y Figure 1

Chemical

structures

of linear dimers II-V

and ynone Va

“activated zinc” Al--C-CEC-k

AF-(~C-C=C II

-

II adsorption 21 electronic transfer

Ar

\/

1

2 EtOH desorption WEtO),

AI-WC-C-C-At

d A III Scheme 2

hand q); 115.6 (0); 129.6 (j); 130.2 (2C, i); 132.8 (2C, p); 137.4 (k); 159.2 (2C, g and r).

Preparation of 1,4-di(4’-(hexyloxy)phenyl]-lbutene-3-yne E IV In a quartz flask, a solution of the Z isomer III (1.90 g, 4.7 mmol) in cyclohexane (25 ml) was first bubbled with argon and then irradiated with a mercury lamp beam (300-400nm) located at 60cm away from the reaction flask. After 9 h of irradiation, the solvent was removed

from the reaction mixture to give a residual solid. This solid was washed many times with pentane so that the almost insoluble E enyne IV was isolated from the soluble Z dimer III. The solid fraction was dried under vacuum to give 1.2 g of crude product. After crystallization in cyclohexane, pure dimer IV was collected (0.95 g, 2.4mmo1, 50%). From filtrates the unreacted Z enyne III with some E isomer IV can be recovered and used again for another isomerization reaction. M.p. = 117-118°C. 1.r.: 2200 (C&); 950 (CH=CH tram). ‘H n.m.r.: 7.11 and 7.10 (2m, 8H, H atom); 6.9H (d,

POLYMER

Volume

38 Number

6 1997

1451

Thermal polymerization of arylacetylenes. 2. S. Gandon et al.

ArCOCI

+

Me3SI

C~C

+ Ph3P ~

Ar

CH3, Br

Ib AICI3 / CH2CI 2

tBuOK/Et20

rt

Ar

C~-C

rt

CO

Ar

Ph3P

01"12

,ca

\

J

Y CH2CI2 3 - 5°C

Ar

C:~C ~

C(Ar) ,'" : CH 2

v

Ar = Scheme 3

J = 16.2, 1H, = C H - P h ) ; 6.22 (d, J - 16.2, IH, = C H C - ) ; 3.96 (t, J = 6.5, 2H, CH20); 3.95 (t, J = 6.5, 2H, CH20); 1.72-1.83 (m, 4H, CH2CH20); 1.30-1.50 (m, 12H, CH3(CH2)3); 0.91 (t, J = 6.7, 6H, CH3). 13C n.m.r.: 14.1 (2C, a and x); 22.6 (2C, b and w); 25.7 (2C, d and u); 29.2 (2C, e and t); 31.6 (2C, c and v); 68.1 (2C, fand s); 87.9 (m); 91.1 (n); 105.8 (1); 114.5 and 114.7 (2 × 2C, h and q); 115.5 (o); 127.5 (2C, i); 129.2 (j); 132.9 (2C, p); 140.1 (k); 159.1 and 159.6 (g and r).

Preparation o[ 1,3-di(4'- (hexyloxy)phenyl)-2propynone Va A solution of 1-(hexyloxy)-4-(2-(trimethylsilyl)-ethynyl) benzene 1 lb (5.05g, 18.4mmol) and of 4-(hexyloxy) benzoylchloride (4.0g, 16.6mmol) in dichloromethane (4ml) was added dropwise to an ice bath cooled suspension of aluminium chloride (2.5 g, 18.7mmol) in dichloromethane (15ml). After the addition of rinsing dichloromethane (2 x 4 ml), the reaction mixture was left to return to room temperature and maintained at this temperature for 4 h 30min. Then a few drops of acid chloride were added to complete the reaction. The reaction mixture was poured into aqueous hydrochloric acid (50 ml, 1.25 N) 30 rain later. The organic layer was extracted with dichloromethane (3 × 30ml) then dried over magnesium sulfate. After solvent evaporation, 7.04g of crude product were obtained and percolated on silica gel (140 g) using a mixture of petroleum ether/ ethyl acetate (from 100/0 to 95/5) as eluent to give pure Va (5.26g, 12.9 mmol, 70%). M.p. = 67 68°C. I.r.: 2180 ( C - C ) ; 1630 (C=O). 1H n.m.r.: 7.56 (m, 4H, H a r o m Ph-CO); 7.29 (m, 4H, H arom P h - C = ) ; 4.04 (t, J = 6.5, 2H, CH20); 3.99 (t, J = 6.5, 2H, CH20); 1.74-1.87 (m, 4H, CH2CH20); 1.30 1.50 (in, 12H, C H 3 ( C H 2 ) 3 ) ; 0.91 (t, J = 6.6, 6H, CH3). 13C n.m.r.: 14.1 (2C, a and w); 22.6 (2C, b and v); 25.7 (2C, d and t); 29.1 (2C, e and s); 31.6 (2C, c and u); 68.3 and 68.4 (f and r); 86.8 and 93.6

1452

POLYMER Volume 38 N u m b e r 6 1997

(k and 1); 111.9 (j); 114.3 and 114.9 (2 x 2C, h and p); 130.3 (n); 131.9 (2C, o); 135.0 (2C, i); 161.2 (g): 164.0 (q); 176.8 (m).

Preparation of 2,4-di[4C(hexyloxy)phenyl]-I buten-3-yne V Methyltriphenylphosphonium bromide (3.06 g, 8.6 retool) in ether (15ml) was added to potassium terbutylate (1.0g, 8.9mmol) in ether (5ml) at room temperature. After disappearance of the phosphonium salt, determined by t.l.c, analysis (ethyl acetate/methanol: 50/50) methyltriphenylphosphonium bromide (0.29g, 0.8 mmol) was added again. One hour later, the reaction mixture was cooled down to 5c~C. Then a cool solution of Va (3.06 g, 7.5mmol) in ether (20ml) was added. The reaction was monitored with t.l.c, analysis (cyclohexane/ethyl acetate: 95/5). After 6h at 5°C, the reaction mixture was filtered and the solvent evaporated. The resulting crude product was dissolved in pentane (50ml) and put in the refrigerator so that triphenylphosphine oxide precipitated. After filtration and evaporation the crude product (2.9 g) was purified on silica gel column (150g) using a mixture of petroleum ether and ethyl acetate (98/2) as eluent. The enyne V was isolated pure (t.9g, 4.7mmol, 60%). M . p . = 6 3 6 4 C . I.r.: 2190 (C=C); 880 ( C H 2 ) . IH n.m.r.: 7.26 (m, 4H, H arom Ph C ): 7.15 (m, 4H, H atom Ph C - ) ; 5.82 and 5.60 (2d, J = 0.9 determined at 4 0 0 M H z frequency, 2 × I H, CH2-); 3.96 and 3.97 (2t, J - 6.6, 4H, CH20); 1.72-1.84 (m, 4H, CH_~CH20); 1.25 1.52 (m, 12H, CH3(CH2)3; 0.91 (t, J = 6.7, 6H, CH3). 13C n.m.r.: 14.1 (2C, a and w); 22.6 (2C, b and v); 25.7 (2C, d and t); 29.22 and 29.17 (e and s); 31.6 (2C, c and u); 68.0 (2C, f and r): 87.5 and 90.7 (k and 1); 114.2 and 114.5 (2 x 2C, h and p); 115.0 (m); 117.8 (x); 127.3 (2C, o); 129.8 and 130.1 (j and n); 133.1 (2C, i); 159.28 and 159.33 (g and q).

Thermal polymerization of arylacetylenes. 2: S. Gandon et al. relative p e r c e n t a g e

M

7000 6464

6000 5000

4444 4040

4000 3000

4040

2828

2000

a

1000 0 !

lj

If_! compound

?

IVV

AhL

'~

'k

,,

~w 4000 3835

3500 3000 2500 2000 1500

1417

1628

1426

t

0

1144

I

15

I

I

30

!

I

45

|

60 e l u t i o n t i m e (rain)

1000 Figure 3 H.p.l.c. chromatograms of crude products of the thermal polymerization of: m o n o m e r I (trace a); Z enyne III (trace b); Z enyne III with u.v. detector working at 260 n m (trace c)

500 0

!

U

__11I compound

Iv

_v

I

1,8 1,6 1,4 1,2 1 0,8 0.6 0,4 0,2 0

1,51

!

l_!

IIl compound

[_V

V

Figure 2 Thermal treatment of dimers II V and m o n o m e r I: highest molecular weight (M) detected by SIMS analysis (a); average molecular weight (Mw) and polydispersity ratio (l) measured by s.e.c, analysis (b and c)

R E S U L T S A N D DISCUSSION

Synthesis of l&ear dimers II- V The diyne II was synthesized in high yield (94%) from monomer I using the modified oxidative Glaser coupling 9. The Z enyne III was prepared with complete diastereoselectivity and good yield (83%) from the selective hydrogenation of one triple bond of the diyne II by activated zinc in ethanol solution 10 (Scheme 2).

The E enyne IV was obtained by the photochemical isomerization of the Z enyne III performed in an apolar solvent in the presence of iodine used as catalyst 11' 12. The dimer V was synthesized through a Wittig reaction 13 between the corresponding c~-ynone Va and the methylenephosphonium ylide obtained in situ from potassium terbutylate and methyltriphenylphosphonium bromide (Scheme 3). The c~-ynone was previously prepared from the acylation of lb 1 by the 4-(hexyloxy)benzoyl chloride (Aldrich) in presence of aluminium chloride 14 . To obtain the enyne V with good yield (60%) it is necessary to prepare and isolate it at low temperature (to prevent its polymerization). Moreover, before reacting the c~-ynone with the ylide, it is also necessary to check that the base used to form the ylide is wholly consumed. If not, the cleavage of the c~-ynone 15 takes place leading to the formation of I

(Scheme 4 ). Thermal polymerization of linear dimers II- V Dimers I I - V were sampled according to the experimental procedure described for monomer I and cured according to a gradual thermal step treatment 1. The polymerization of linear dimers leads to the formation of oligomers with higher molecular weight than the polymerization of the monomer I (Figure 2). Moreover h.p.l.c, analyses also show this larger proportion of high molecular weight oligomers in the polymerization products of the linear dimers (traces a and b of Figures 3, 4 and 5). The polymerization of II and V gives almost no naphthalenic dimers and benzenic trimers isolated in the cured product of I. When polymerized, the enynes III and IV form some low

POLYMER Volume 38 N u m b e r 6 1 9 9 7

1453

Thermal polymerization of arylacetylenes. 2: S. Gandon et al. tBuOK Ar

C~---C

CO

Ar

~

[Ar

. + C~---C, K

+

ArCOOtBu ]

"ca 4-

H30

Ar =

-~OnCsH13 Ar

C~C

H

+

ArCOOH

I Scheme 4 Table 1 S.e.c. analysis: average molecular weight M',,, and polydispersity ratio I of the thermal polymerization products of monomer/linear dimer mixtures in x/y molar proportions

Diyne II

Z enyne III

E enyne IV

Vinylidene enyne V

Linear dimer

x/y

M~

1

Mw

I

M,~

I

M,,

1

10/0

1114

1.58

1114

1.58

1114

1.58

1114

1.58

9/1

1504

1.66

1386

1.70

1347

1.63

1358

1.56

5/5

2655

1.65

1533

1.61

1540

1.57

1528

1.46

0/10

3835

1.51

1417

1.53

1426

1.61

1661

1.26

relative percentage

relative percentage

't ,2]L

. . . . . .

I

0

I

I

1$

I

I

30

I

I

45 60 elution time (rain)

relative percentage |.

l

1,

?

.m o

15

30

< 45

60 elution time (rain)

Figure 4 H.p.l.c. chromatograms of crude products of the thermal polymerization of: m o n o m e r I (trace a); E enyne IV (trace b): E enyne IV with u.v. detector working at 2 6 0 n m (trace c)

molecular weight compounds. One of them could be the 2,7-disubstituted naphthalenic dimer 1, but in any case cannot be the 1,7-disubstituted naphthalenic dimer 2, as demonstrated using u.v. detection at 260 nm which is the

1454

POLYMER Volume 38 N u m b e r 6 1997

jtk i

0

I

l$

I

I

30

I

I

I

45 60 elution time (min)

Figure 5 H.p.l.c. chromatograms of crude products of the thermal polymerization of: diyne II (trace a); vinylidene enyne V (trace b)

maximum absorption wavelength of these compounds (traces c of Figures 3 and 4) (unless otherwise specified u.v. detection was at 270 nm). As the polymerization of linear dimers leads to the formation of high molecular weight oligomers in comparison to the m o n o m e r polymerization, we can assume that either the polymerization mechanism is

Thermal polymerization of arylacetylenes. 2: S. Gandon et al. Table 2 S.e.c. analysis: average molecular weight M w and polydispersity ratio I of the products formed during the thermal polymerization of dimers II V and monomer I Compound

Time

Diyne II

Mw I

Z enyne III

3 h (180°C)

4 h (220°C)

7 h 24 min (280°C)

455 1.02

2138 1.21

3629 1.57

Mw I

324 1.04

1255 1.23

1416 1.25

E enyne IV

~t w I

983 1.07

1171 1.16

1578 1.25

Vinylidene enyneV

Mw I

2042 1.45

1698a 1.41

1628 1.31

Monomer I

AIw I

1495 1.51

1534 1.57

1252 1.57

5 h (220°C)

relative pereenta ~e.

relative percentage

V00

S

700 5 5

To a

a

o

io

2"0

30

4'0

fo

50

zo

30

40

50

[6o

51 [~0

1 1

4

/

A

0

b

10

5o

a0

1'0

46

i0

30

46

50

]-60

1 l 11

45

r05

24

1

C ~ (2

~o

1o

20

30

4'0

s~o

o

1o

zo

46

ao

-6 50

~o go

~o

g 0

1'0

20

3'0

46 5"0 elution time (rain)

S : standard arrows indicate new species

::d_ 10

20

30

40 50 elntion time (rain)

S : standard arrows indicate new species

Figure 6 H.p.l.c. chromatograms of crude products of the thermal

Figure 7 H.p.l.c. chromatograms of crude products of the thermal

polymerization of I/II mixtures in molar proportions [u.v. detector working at 254nm]: 10/0 (trace a); 9/1 (trace b); 5/5 (trace c); 0/10 (trace d)

polymerization of l/III mixtures in molar proportions [u.v. detector working at 254nm]: 10/0 (trace a); 9/1 (trace b); 5/5 (trace c); 0/10 (trace d)

POLYMER Volume 38 N u m b e r 6 1 9 9 7

1455

Thermal polymerization of arylacetylenes, 2: S. Gandon et al. different or the propagation rate of the reaction of I I - V to produce oligomers is higher than the rate of their cyclization into naphthalenic dimers (1, 2) and benzenic trimers (3 5). Besides the formation of small quantities of cyclized oligomers could also come from a thermal decomposition of the enyne leading to the m o n o m e r 1. N o w a question arises: what would be the effect of the m o n o m e r presence on the polymerization mechanism of the dimers? So mixtures of m o n o m e r and linear dimers in the m o l a r proportion 9/1 and 5/5 have been polymerized.

Polymerization of monomer-linear dimer mixtures F r o m the s.e.c, results (Table 1 ) it can be pointed out that the molecular weight increases as a function of the dimer concentration. On the other hand h.p.l.c, analyses show two new features for the polymerization of m o n o m e r - d i m e r mixtures:

(a) new species are produced (see arrows, Figures 6 9) with each dimer, (b) in the case of the mixtures with the enynes Ill and IV, the ratios of the produced naphthalenic dimers and benzenic trimers are modified. These results are in agreement with the following conclusions: the linear dimers are not reaction intermediates in the m o n o m e r polymerization. Furthermore a reaction between m o n o m e r and dimer can occur (probably to some extent) during the copolymerization in addition to individual polymerization of each partner.

Relative thermal reactiviO, qf monomer I and dimers 11- V The thermal reactivity of the linear dimers I I - V has been examined and compared with the monomer one. From the d.s.c, measurements (Figure 10), we observed

relative percentage

n0

To

relative percentage

F

5

1 4 a 0

10

20

30

4'0

50

a

1 2 3_ ~ ,

~^.

i'~O

o

f5

'

6o

7~

b 0

1"0

41 1

o

2"0

30

F

40

4 ¸

~

['60 0

'

15

'

b

30

'

~

'

60

310

'

45

'

60

I

I

I

I

5/

lo

2"0

ao

4/

5"

40

50

Too Ts

'

15

'

I

i

~o

d

1o

io

3o

40

~5

5" so

elution time (rain)

S : standard arrows indicate new species

Figure 8 H.p.l.c. chromatograms of crude products of the thermal polymerization of I/IV mixtures in molar proportions [u.v. detector working at 254nrn]: 10/0 (trace a); 9/1 (trace b); 5/5 (trace c): 0/10 (trace d)

1456

P O L Y M E R V o l u m e 38 N u m b e r 6 1 9 9 7

i

0

15

30

45

60

elution time (rain)

Figure 9 H.p.l.c. chromatograms of crude products of the thermal polymerization of I/V mixtures in molar proportions: 10,'0 (trace a); 9/1 (trace b); 5/5 (trace c); 0/10 (tracc d)

Thermal polymerization of arylacetylenes. 2. S. Gandon et al. ~O°C

/

l..]

tempea-('aCtm)~e

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Figure 10 D.s.c.thermograms and polymerizationenthalpies AH: monomer I (trace a); diyne II (trace b); Z enyne llI (trace c); E enyne IV (trace d); vinylidene enyne V (trace e) that the linear dimers, except V, polymerize at higher temperatures than I. A kinetic study has confirmed these results: the thermal reactivity of compounds I - V has been studied under the same curing conditions (thermal step treatment), the s.e.c, analyses (Table 2) show that compounds V and I started to react at 180°C, whereas I I - I V reacted only at 220°C and they did it slowly. Their conversion gets more important only at 280°C. By the end of the thermal treatment unreacted linear dimer still remains (h.p.l.c. analyses, Figures 11-13). The polymerization of the vinylidene dimer V is very different: after 3 h at 180°C there is no more residual V (Figure 14) and high molecular weight compounds are already produced (Table 2). It seems that similarly to the thermal treatment of 11, the average molecular weight of the cured product of V decreases along reaction time and temperature as well as the polydispersity (Table 2). Some low retention time species appear by the end of the thermal treatment (see arrows, Figure 14). It may mean that a depolymerization process happens to yield shorter and more stable oligomers.

CONCLUSION

Are the linear dimers reaction intermediates of the thermal polymerization of the arylacetylene? The experimental results herein described allow us to answer negatively.

Case of the linear dimers II-IV. Their polymerization products (when polymerized with or without the monomer) are very different from the m o n o m e r one. Moreover, if they were reaction intermediates, they should accumulate in the cured product of I because of their lowest reactivity. But it is not the case: they are not observed in h.p.l.c, analyses even if the u.v. detection is used at their m a x i m u m absorption wavelength. Case of the dimer V. Its cured product is very different from the m o n o m e r one and it does not contain any aromatic dimers and trimers 1-5. So we believe V is not an intermediate of the thermal polymerization of I. Therefore, to explain our experimental results, another reaction mechanism has to be suggested ]6.

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Thermal polymerization of arylacetylenes. 2. S. Gandon et al. relative percentage

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1458

POLYMER Volume 38 N u m b e r 6 1 9 9 7

o

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Thermal polymerization of arylacetylenes. 2: S. Gandon et al. relative percentage

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REFERENCES l 2 3 4 5 6 7

Gandon, S., Mison, P., Bartholin, M., Mercier, R., Sillion, B., Geneve, E., Grenier, P. and Grenier-Loustalot, M. F. Polymer 1997, 38, 1439 Kovar, R. F., Ehlers, G. F. L. and Arnold, F. E. J. Polym. Sci., Polym. Chem. Ed. 1977, 15, 1081 Hergenrother, P. M., Sykes, G. F. and Young, P. R. Polym. Prepr., Am. Chem. Soe., Div. Petr. Chem. 1979, 24, 243 Grenier-Loustalot, M. F. High Perform. Polym. 1994, 6, 347 Glaser, C. Ber. der Deutsch. Chem. Gesell. 1869, 2, 422 Straus, F. Ann. Chem. (Justus Liebigs) 1905, 342, 190 Sabourin, E. T. J. Mol. Cat. 1984, 26, 363

8 9 10 11 12 13 14 15 16

Grant, B. Mol. Cryst. Liq. Cryst. 1978, 48, 175 Fritzsche, V. and Hunig, S. Tetrahedron Lett. 1972, 4831 Brandsma, L. 'Preparative Acetylenic Chemistry', Studies in Organic Chemistry, 2nd Edn, Vol. 34, Elsevier, Amsterdam, 1988, p. 284 Sonnet, P. E. Tetrahedron 1980, 36, 557 Muller, E., Staub, H. and Rao, J. M. Tetrahedron Lett. 1970, 773 Wittig, G. and Schoellkopf, U. Chem. Ber. 1954, 87, 1318 Birkoffer, L., Ritter, A. and Uhlenbrauck, H. Chem. Ber. 1963, 96, 3280 Kirillova, L. P., Buzilova, S. R., Serebryakova, E. S. and Vereshchagin, L. I. J. Org. Chem. USSR 1974, 2001 Gandon, S., Mison, P. and Sillion, B. Polymer (submitted)

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