Polymer Bulletin Polymer Bulletin26, 377- 382 (1991) 9 Springer-Verlag 1991 Synthesis of telechelic monodispersed dithiols Bruno Ameduri 1, Khalid Berrada 1, Bernard Boutevin 1'*, Roy D. Bowden 2, and Lucia Pereira 1 1URA D11930 CN RS, Ecole Nationale Sup6rieu re de Chimie de Montpellier, 8, Rue Ecole Normale, F-34053 Montpellier C6dex 1, France 21.C.1.,Chemicals and Polymers Limited, Research and Technology Department, The Heath, Runcorn, Cheshire WA7 4QD, UK Summary The synthesis of novel telechelic m o n o d i s p e r s e d dithiols from a nonconjugated diene and an a , w -dithiol is presented. The batch reaction produced a p o l y d i s p e r s e d mixture of dithiols separable with difficulty whereas a dropwise addition of diene onto an excess of dithiol in the presence of peroxide led selectively and q u a n t i t a t i v e l y to the addition product : dithiol-diene-dithiol. Introduction The importance of m o n o d i s p e r s e d telechelic dithiols has been greatly increasing as evidence by the wide range of applications. For instance, these compounds are interesting forerunners of m u l t i b l o c k copolymers (1,2), prepolymers (3), polyurethanes (4) and elastomers (5). Numerous publications and patents have been published showing further novel applications : in optic materials (6), in textile (7), and in photocuring coatings produced by the thiol-ene process (8,9). Each of these reactivity of two mercapto above examples end-group. exploits the enhanced Since 1857 (1O) , it has been well known that the addition of the -SH end-group onto an ethylenic double bond occurs by a radical mechanism (11,12) giving the a n t i - M a r k o v n i k o v product. The reaction between an d , ~ dithiol and a nonconjugated diene is a polyaddition (13) in which the end groups and the molecular weight of the products are controlled by the stoichiometry of the reaction according to the following chemical scheme, in the case of 1,3-benzenedithiol and 1,4-divinylbenzene (14) : S ~H HS exces~dr / CH - ( / - ~ - C H 2 C H 2 HS~SH + H2C=CH__Q_CH=CH2 equimolar[ S \ excess *To whom offprint requests should be sent of diene \-~ 2 S ~H ~ J n SC2H4__G_C2H4] n- 378 Thus, an e x c e s s of d i t h i o l p r o d u c e s a m i x t u r e w h i c h e x h i b i t s p r e d o m i n a n t l y m e r c a p t 0 c h a i n ends, w h e r e a s an e x c e s s of d i e n e leads to e t h y l e n i c f u n c t i o n a l i t y , m a i n l y (14). N u y k e n et al. (14) s h o w e d that the e n d - g r o u p t i t r a t i o n can be u s e d to d e t e r m i n e the m o l e c u l a r w e i g h t s b e l o w 5,000. U s u a l l y , they u s e d a s y s t e m in w h i c h r e a c t a n t s w e r e a r o m a t i c (14-19), or in w h i c h the d i t h i o l , itself, was e i t h e r a l i p h a t i c (20) or a r o m a t i c (21). Similarly, the G e r m a n t e a m c a r r i e d out polyadditions of a r o m a t i c d i t h i o l s o n t o t r i p l e b o n d s (14,17,22) ( l , 4 - d i e t h y n y l - b e n z e n e i n s t e a d of d i v i n y l b e n z e n e as s c h e m e above). M o r e o v e r , the o n l y s t u d y i n v o l v i n g b o t h a l i p h a t i c r e a c t a n t s was performed in 1951 in w h i c h the authors wished to obtain p o l y d i s p e r s e d o l i g o m e r s (of m o l e c u l a r w e i g h t s b e l o w 1,000) w h i c h h a d unsaturated and mercapto end-groups (13). So far, no dithiol c o n t a i n i n g a h e t e r o a t o m has b e e n u s e d in t h e s e a d d i t i o n reactions. This article pesents an effective telechelic monodispersed dithiols obtained from dithiols. Results and synthesis aliphatic of novel dienes and Discussion 1 , 5 - h e x a d i e n e or 1 , 9 - d e c a d i e n e a n d an e x c e s s of 2 - m e r c a p t o e t h y l e t h e r w e r e u s e d as r e a c t a n t s in the p r e s e n c e of peroxides, the r e a c t i o n p r o c e e d i n g a c c o r d i n g to the f o l l o w i n g s c h e m e : H2C=CH-(CH2)x-CH=CH 2 + HSCH2CH2OCH2CH2SH x=2 or 6 (excess) ~ radical HS(CH2}20(CH2)2S(CH2)x+4S(CH2)20(CH2)2SH A, x 1 ~ ) Batch-reaction We chose several initial molar ratios (R) o [dithiol]/[l,5-hexadiene] = R = 2.0 or 3.0 or 4.0 . o A f t e r 3 h reaction, we n o t e d the GPC c h r o m a t o g r a m of the r e a c t i o n m e d i u m e x h i b i t e d a p o l y d i s p e r s e d b e h a v i o r . in which (figure i) We o b s e r v e l o g i c a l l y t h a t the lower the Ro, the h i g h e r the m o l e c u l a r w e i g h t of the t e l o m e r s obtained. W h a t e v e r R , the m e d i u m is o c o m p o s e d of a m i x t u r e of s e v e r a l d i t h i o l s T(DT) :. n TDT T (DT) T (DT) : Hs (cH2) 2~ (cH2) 2 s (cH2) 6s (cH2) 2~ (c~2) 2sH 2 : HS(CH2)20(CH2)2S [(CH2)6S(CH2)20(CH2)2S ]2 }{ 3 : HS(CH2)20(CH2)2S [(CH2)6S(CM2)20(Cn2)2S ]3 }{ 379 TDT T(DT)2~ ~ T I I .~1 !A,. '~. P.a! ! t .R'l, T(DT) 3 I I #Nil* *~ .~d |'.| ; ,', Ill',', i' / 1111 w- -~--x A II R R . . . . . i,.| lilt = 2.0 O =3.0 O R =4.0 O lid |] [1 f/IV '-\Jill I ! ! 24 28 32 Ve(ml) Figure 1 : GPC chromatogram of 2-mercaptoethyl ether reaction) which can methods. only be separated the (T) with product of the addition of onto 1 , 5 - h e x a d i e n e (D) (batch difficulty using conventional Such a p o l y d i s p e r s e d product did not r e p r e s e n t the goal we wished to reach ; thus, this method of obtaining monodispersed t e l e c h e l i c dithiols s e l e c t i v e l y is not valid. The same c o n c l u s i o n is r e a c h e d when 1 , 9 - d e c a d i e n e is used. 2 ~ ) By dropwise addition of diene This m e t h o d consists of a slow dropwise addition of 1 , 5 - h e x a d i e n e into a large excess of ~ , I~ dithiol c o n t a i n i n g initiator (peroxide). 30 m i n u t e s after the total addition of diene, the GPC c h r o m a t o g r a p h of the m e d i u m (figure 2) exhibits peak only which c o r r e s p o n d s to a product, the m o l e c u l a r weight which is g r e a t e r than those of the reactants. The reaction quantitative. The IH NMR spectrum (figure 3) of the o b t a i n e d dithiol the the the one of is shows: -6 * the signal at 1.55 i0 assigned to the p r e s e n c e of the -SH end-group ; * the absence of the signal of the ethylenic p r o t o n s in the 5.5-7.0 -6 i0 range which is evidence that the reaction of 1 , 5 - h e x a d i e n e is total ; * a signal at 1.35 10 -6 due to the inner m e t h y l e n e groups b e t w e e n both' t h i o e t h e r bridges. This comes from the addition product of the thiol accross the double bonds. 380 J ' 24 I I 28 32 Ve(ml) Figure ! 3.6 2 : GPC c h r o m a t o g r a m of the p r o d u c t obtained 30 min complete dropwise addition of 1,5-hexadiene 2 - m e r c a p t o e t h y l ether a I 3.2 2.8 i ! 2.4 2.0 (i0 -6 ) Figure 3 : IH NMR s p e c t r u m of A,2 after onto i 1.6 381 t . . . . . . 80 i 60 .__ | 40 ., .,, 20 6 (10-61 Figure 4 : 13C NMR spectrum of A,_~2 The 13C NMR spectrum (figure 4) exhibits 7 singlets assigned to the different carbon atoms of the dithiol A,2 (table i). The methylene groups located in the p o s i t i o n ~ t o the oxygen atom (70.37 and 72.21 I0- ) are shifted further towards high fields than are ~hose in ~ position either to the thioether bridge (31.31 and 32.24 i0--) or the end-groups. This peak appears at 24.02 10 -6 which is characteristic of the thio group. HS CH 2 CH 2 O CH 2 CH 2 S CH 2 CH 2 CH 2 A,2 (Fig.4) 24.02 72.21 70.37 32.24 31.31 29.30 28.02 A,6 24.25 72.48 70.66 32.61 31.52 29.70 29.34 Table i : 13C NMR characteristics of A,_~2 and A,__~6 CH 2 CH 2 29.09 28.73 382 A similar dropwise addition of 1,9-decadiene into the 2 - m e r c a p t o e t h y l E t h e r produces the expected d , w dithiol q u a n t i t a tively A,6. Its 3C NMR c h a r a c t e r i s t i c s are also listed in table i. Conclusion The synthesis of long chain m o n o d i s p e r s e d telechelic dithiols can be acheived by slow dropwise addition of a n o n e o n j u g a t e d diene into an excess of ~ , w dithiols with peroxidic initiation. This synthesis is very simple and quick and produced the expected telechelic dithiols selectively and quantitatively. Such new dithiols are interesting intermediates for the p r o d u c t i o n of precursors of w e l l - d e f i n e d structured polymers. 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