New Aspects of the Chemistry of Living Tetrahydrofuran Polymers

acids were found to yield living polymers of THF in which the end groups consisted ... at 25° using both standard differential refractive index and. ...
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2 New Aspects of the Chemistry of Living Tetrahydrofuran Polymers Initiated by Trifluoromethane Sulfonic Anhydride

Ring-Opening Polymerization Downloaded from pubs.acs.org by YORK UNIV on 12/08/18. For personal use only.

SAMUEL SMITH, WILLIAM J. SCHULTZ, and RICHARD A. NEWMARK Central Research Laboratories, 3M Co., 3M Center, St. Paul, MN 55101

Smith and Hubin have d e s c r i b e d the p o l y m e r i z a t i o n o f t e t r a h y d r o f u r a n (THF) u s i n g e i t h e r ( C F S 0 ) 0 o r ( F S O2)2O as i n i t i a t o r s ( 1 ) . These anhydrides o f tne s o - c a l l e d "super" a c i d s were found t o y i e l d l i v i n g polymers o f THF i n which the end groups c o n s i s t e d o f oxonium i o n s i n e q u i l i b r i u m w i t h c o v a l e n t l y bonded e s t e r s . The nature o f the r e a c t i o n s i n the case o f t r i f l i e anhydride i n i t i a t i o n was p o s t u l a t e d t o be as f o l l o w s ( 1 ) . 3

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l 19 S e v e r a l papers have r e c e n t l y appeared i n which n, F and C nmr s p e c t r a l analyses were used t o i n v e s t i g a t e the nature of the macroester-macroion e q u i l i b r i u m which r e s u l t s when a l k y l e s t e r s o f the super a c i d s are used as THF p o l y m e r i z a t i o n i n i t i a ­ t o r s (2-7), The exact determination o f these e q u i l i b r i u m constants i n v a r i o u s r e a c t i o n s o l v e n t s has been an e s p e c i a l l y noteworthy r e s u l t (2b, 3 ) . Very r e c e n t l y , the s u r p r i s i n g l y dramatic e f f e c t of the o v e r a l l c o n c e n t r a t i o n o f poly-THF l i v i n g end groups on the macroester-macroion e q u i l i b r i u m has been r e ­ ported and a t t r i b u t e d t o i o n aggregation e f f e c t s which a c t t o i n c r e a s e the i o n / e s t e r r a t i o ( 8 ) . Two important f e a t u r e s d i s t i n g u i s h THF p o l y m e r i z a t i o n i n i t i a t e d w i t h super a c i d anhydrides from t h a t i n i t i a t e d w i t h the corresponding e s t e r s which have r e c e i v e d so much study. Anhydride i n i t i a t i o n i s much more r a p i d than e s t e r i n i t i a t i o n and i t leads t o a polymer capable o f growing a t both ends, where­ as e s t e r i n i t i a t i o n produces polymer growing a t only one end.

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These d i s t i n c t i o n s prompted us then to study i n some d e t a i l the exact nature of the r e a c t i o n of ( C F S 0 ) 0 w i t h THF. 3

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EXPERIMENTAL NMR s p e c t r a were obtained w i t h a V a r i a n XL-100 spectrometer. ChemicaJgShifts were measured from t e t r a m e t h y l s i l a n e ( h) and CFClg ( F) reference i n t e r n a l standards and s h i f t s are r e ­ corded here as p o s i t i v e when^they are downfield from the r e ­ ference. Samples used f o r F nmr s p e c t r a were withdrawn by s y r i n g e through a septum cap c l o s u r e from a r e a c t i o n v e s s e l which had been maintained at 0 ° d u r i n g the mixing of r e a c t a n t s . A l l r e a c t a n t s had been d i s t i l l e d and great care was e x e r c i s e d to avoid moisture contamination. The ^ F nmr spectrum of the (CF S 0 ) 0 i n i t i a t o r used i n t h i s work i n d i c a t e d at l e a s t 95% p u r i t y , w i t h CF^SOgH and C F S 0 C F c o n s t i t u t i n g the major i m ­ p u r i t i e s and being present In almost equal c o n c e n t r a t i o n s . The nmr s p e c t r a were determined at 2 5 ° , w i t h the f i r s t spectrum obtained 3 minutes a f t e r i n i t i a t i o n of the r e a c t i o n . Mass s p e c t r a were obtained w i t h a CEC 21-110C mass spectrometer and values are reported as molecular mass per u n i t charge, m/e. Molecular weight d i s t r i b u t i o n s were obtained by g e l p e r ­ meation chromatography (GPC) (Waters A s s o c i a t e s Chromatograph) using a set of s i x S t y r a g e l columns, each 122 χ 0.63 cm, which were s e l e c t e d to achieve h i g h r e s o l u t i o n of low molecular weight f r a c t i o n s . The gels £ a d rated pore s i z e s of 10 (3 columns), 1 0 , 10*, and 1 0 A . The molecular weight d i s t r i b ­ u t i o n s were determined i n e i t h e r chloroform or THF s o l u t i o n s at 2 5 ° u s i n g both standard d i f f e r e n t i a l r e f r a c t i v e index and U.V. detectors. The l a t t e r was employed at a wave length of 2540 Â to detect the phenyl end groups of s p e c i a l l y terminated polymeric i n t e r m e d i a t e s . The phenyl groups were appended to r e a c t i v e intermediates by terminating r e a c t i o n s w i t h the a d d i t i o n of a 3-molar excess of sodium phenoxide i n THF s o l u t i o n . Excess NaOC^H5 was o r d i n a r i l y not removed s i n c e i t d i d not i n t e r f e r e with either H nmr or GPC s p e c t r a . 2

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DISCUSSION OF RESULTS 19 F nmr. The a d d i t i o n of ( C F S 0 ) 0 to a cyclohexane s o l u t i o n of THF immediately gave r i s e to the appearance of 3 d i s t i n c t f l u o r i n e a b s o r p t i o n peaks, as shown i n F i g u r e l a . It i s noteworthy that i n every case s t u d i e d the * F nmr i n d i c a t e d that the anhydride, which gives a sharp s i n g l e t peak at -73.2 ppm i n cyclohexane s o l u t i o n , r e a c t s e s s e n t i a l l y i n s t a n t l y on mixing w i t h THF at 2 5 ° . (In one instance a known amount of r e f e r e n c e t r i f l u o r o m e t h y l benzene was added to the r e a c t a n t s o l u t i o n and the l ^ F nmr spectrum was i n t e g r a t e d to prove that these three peaks accounted f o r a l l the f l u o r i n e s d e r i v e d from the anhydride). The F nmr a b s o r p t i o n peaks at - 7 5 . 7 , - 7 5 . 8 , and -78.6 ppm ( u p f i e l d from C F C I 3 ) were assigned to tetramethylene b i s ( t r i f l a t e ) (V) ( i . e . C F S 0 f C H - } 0 S C F ) , macro-triflate 3

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e s t e r IV and m a c r o - t r i f l a t e i o n I I I , r e s p e c t i v e l y , by the f o l l o w i n g c o n s i d e r a t i o n s . ( S t r i c t l y speaking, ^ F nmr observes o n l y the macroester and macroion end groups and does not d i s ­ t i n g u i s h between e i t h e r I I and I I I o r I I and IV, s i n c e I I c o n t r i b u t e s e q u a l l y t o the macroion and macroester peaks.) The assignment o f the peak a t -78.6 ppm to macroion I I I was f a c i l i t a t e d by s t u d y i n g the * F nmr s p e c t r a o f s o l u t i o n s c o n t a i n i n g s o l u b l e t r i f l a t e s a l t s , e.g. NH4O3SCF3 (chemical s h i f t = -78.8 ppm). The assignments o f the peaks a t -75.7 and -75.8 ppm t o V and macroester IV, r e s p e c t i v e l y were made i n a separate study i n which an a u t h e n t i c sample o f V, prepared u s i n g the procedure o f r e f e r e n c e ( 1 ) , was added t o a 10.2 molar s o l u t i o n o f THF i n cyclohexane and an i n i t i a l l y s t r o n g peak a t -75.7 ppm was observed. T h i s peak s l o w l y disappeared to give i n c r e a s i n g l y stronger peaks a t t r i b u t a b l e t o I I I and IV as the slow p o l y m e r i z a t i o n o f THF i n i t i a t e d by V proceeded. (These l ^ F nmr assignments f o r I I I and IV agree v e r y w e l l w i t h the v a l u e s p r e v i o u s l y r e p o r t e d f o r the corresponding l i v i n g t r i f l a t e end groups which had been c h a r a c t e r i z e d under v e r y s i m i l a r experimental c o n d i t i o n s ) (j6). As the p o l y m e r i z a t i o n r e a c t i o n i n i t i a t e d by (CF^SO^^O progressed a t 25° the peak a t t r i b u t e d t o V s l o w l y and s t e a d i l y decreased, w h i l e the c o n c e n t r a t i o n s o f both macroester and macroion i n c r e a s e d , as i l l u s t r a t e d i n the k i n e t i c data o f Table I . 19 TABLE I . R e l a t i v e C o n c e n t r a t i o n s o f Products by F nmr Versus P o l y m e r i z a t i o n Time a t 25°. Reactant C o n c e n t r a t i o n s : (CF SO£) 0 - 0.079 M; THF i n Cyclohexane = 10.2 M. Reaction Time (min.) CF^SO^CH^^O^SCF^ Macroester Macroion 3 ^36 58 7 10 33 59 8 30 16 70 11 74 10 77 13 280 3 79 18 3

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I t i s i n t e r e s t i n g t o note t h a t the macroion/macroester r a t i o increased as V was d e p l e t e d , a f i n d i n g which seems t o accord w i t h the r e p o r t t h a t the e q u i l i b r i u m shown i n Equation (3) s h i f t s t o produce more macroion as a consequence o f the o v e r a l l i n c r e a s e i n the c o n c e n t r a t i o n o f poly-THF l i v i n g end groups Ç8). An otherwise i d e n t i c a l experiment t o t h a t shown i n Table I was performed i n which the v e r y p o l a r s o l v e n t , nitromethane, was s u b s t i t u t e d f o r the non-polar cyclohexane. I n t h i s case V was formed i n almost the same p r o p o r t i o n (32% a f t e r 4 minutes a t 25°), but macroion c o n c e n t r a t i o n predominated over macroester, I I I - 47% and IV - 21% a f t e r 4 minutes. (This spectrum i s shown i n F i g u r e l b . ) The i n c r e a s e i n the d i e l e c t r i c constant o f the medium would, o f course, be expected t o s h i f t t h e e q u i l i b r i u m i n the d i r e c t i o n o f macroion f o r m a t i o n , a s i t u a t i o n which had indeed been found p r e v i o u s l y ( 3 ) .

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Other s o l v e n t s were i n v e s t i g a t e d as d i l u e n t s i n the r e a c t i o n of (CF3S02>20 w i t h THF. These i n c l u d e d methylene c h l o r i d e , carbon t e t r a c h l o r i d e , nitrobenzene, toluene and o-dichlorobenzene. In each i n s t a n c e l ^ F ^ showed t h a t V formed t o account f o r a t l e a s t 30% of the t o t a l products formed e a r l y i n the r e a c t i o n . The e f f e c t of THF c o n c e n t r a t i o n on the formation of V was exam­ ined i n one case. At THF c o n c e n t r a t i o n s of 10.2 and 5.6 molar i n cyclohexane, V c o n s t i t u t e d 36% and 68%, r e s p e c t i v e l y , of the t o t a l r e a c t i o n products formed a f t e r 3 minutes at 25°. GPC. The d i s c o v e r y t h a t V was being formed and was a c t i n g as a v e r y slow THF p o l y m e r i z a t i o n i n i t i a t o r , as i n d i c a t e d above and i n r e f e r e n c e ( 1 ) , i m p l i e d t h a t f u r t h e r i n f o r m a t i o n concerning the progress of the p o l y m e r i z a t i o n could be gained by i n v e s t i g a t ­ i n g the molecular weight d i s t r i b u t i o n s of products formed d u r i n g the course of the r e a c t i o n u s i n g r e a c t i o n c o n d i t i o n s i d e n t i c a l to those d e s c r i b e d i n Table 1. Toward t h a t end, a f l a s k r e a c t i o n was run i n which a l i q u o t samples were terminated a t v a r i o u s r e a c t i o n stages by quenching w i t h sodium phenoxide. This r e a c t i o n i s known to convert oxonium i o n end groups to phenyl ethers (9) and we e s t a b l i s h e d i n model r e a c t i o n s t h a t i t a l s o converted t r i f l a t e e s t e r s to phenyl e t h e r s . The f i r s t sample quenched a f t e r 3 minutes of r e a c t i o n (8.4% THF conversion) showed a bimodal molecular weight d i s t r i b u t i o n by GPC w i t h w e l l r e s o l v e d peaks a t 21.5 Â and 75 Â end-to-end d i s t a n c e , as shown i n F i g u r e 2. A sample of the e l u e n t at 21.5 1 was separated and d r i e d and the mass spectrum of the product was run. One major peak was found a t m/e 242, corresponding t o the molecular i o n of C6H 0-(CH2>40C6H5 ( V I ) , and t r a c e peaks were observed a t m/e 314 and 386, corresponding t o the THF-dimer and t r i m e r d i phenyl ether molecular i o n s , r e s p e c t i v e l y . The U.V. t r a c e of the GPC, which i s i n d i c a t i v e of the number-average molecular weight (M ) , showed t h a t the 21.5 Â peak c o n s t i t u t e d 35 mole % of the t o t a l product, i n good agreement w i t h the corresponding data shown f o r V i n Table I . As the r e a c t i o n progressed, GPC analyses showed t h a t the d i s t r i b u t i o n became i n c r e a s i n g l y u n i modal. The polymer peak moved up-scale w i t h the simultaneous appearance of a d i s t i n c t i v e , i n c r e a s i n g l y low molecular weight t a i l , as V s l o w l y disappeared by i n i t i a t i n g new polymer chains growing a t both ends. When e q u i l i b r i u m c o n v e r s i o n of THF (69%) was reached a f t e r 90 minutes, the 21.5 Â peak was no longer d i s c e r n i b l e and the and v a l u e s were 13,000 and 19,000, r e s p e c t i v e l y ( p o l y d i s p e r s i t y • 1.5). (The Q f a c t o r f o r c o n v e r t i n g A end-to-end d i s t a n c e t o molecular weight f o r our c a l i b r a t e d column system was 29). (The d i s t r i b u t i o n curve f o r the 90 minute r e a c t i o n product i s a l s o shown i n F i g u r e 2 ) . P r o l o n g a t i o n of the r e a c t i o n f o r an a d d i t i o n a l 3 hours caused the p o l y d i s p e r s i t y to i n c r e a s e to 2.6, f o r reasons which have been i n v e s t i g a t e d independently (10,11). 5

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w Figure 1. F NMR spectrum of products of reaction of 10.2M THF with 0.079U (CF S0 ) 0. Conditions: 3 min at 25°. (a) in cyclohex­ ane, (b) in nitromethane. 19

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Figure 2. Mol wt distribution of phenyl ether-terminated products. [THF] in cyclohexane — 10.2M; [(CF S0 ) 0] = 0.079M. ( ; Product of 3-min reaction (8.4% THF conversion); ( ) product of 90-min reaction (69% THF conversion). s

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The f i r s t order dependence of THF p o l y m e r i z a t i o n r a t e on (CF3S02)2° c o n c e n t r a t i o n has been r e p o r t e d ( 1 ) . However, i n the course of continued s t u d i e s we have observed t h a t as the r e l a t i v e c o n c e n t r a t i o n of anhydride i s i n c r e a s e d beyond about 2 mole p e r ­ cent of the THF c o n c e n t r a t i o n , then a p r e c i p i t a t e occurs e a r l y i n the r e a c t i o n and lower than expected p o l y m e r i z a t i o n r a t e s are observed. We i n v e s t i g a t e d such a r e a c t i o n a t 25° i n which THF c o n c e n t r a t i o n i n cyclohexane was 9.4 M and anhydride concenteationi was 0.47 M. A w h i t e p r e c i p i t a t e was observed to form a t the be­ g i n n i n g of the r e a c t i o n . A l i q u o t samples of the s t i r r e d r e a c t i o n m i x t u r e were withdrawn a f t e r 5, 15, and 120 minutes of r e a c t i o n , quenched w i t h sodium phenoxide and the r e s u l t i n g , now homogeneous s o l u t i o n s were examined by GPC. A l l molecular weight d i s t r i b u ­ t i o n s were found to be t r i m o d a l as shown by the simultaneous U.V. and d i f f e r e n t i a l r e f r a c t i v e index t r a c e s of the product formed i n the 15-minute r e a c t i o n (Figure 3 ) . The mass spectrum of the d r i e d t o t a l sample removed a f t e r 15 minutes of r e a c t i o n was obtained and t h i s i s shown i n F i g u r e 4. Strong fragmentation peaks are seen a t m/e v a l u e s of 55, 77, 94, 107, 149 and 221, corresponding t o the r e s p e c t i v e r a d i c a l or molecular i o n s d e r i v e d from the o l i g o m e r i c d i p h e n y l e t h e r s : C4H7, C6H5, C6H5OH, C H50CH , C6H50C4H and C H ( O C 4 H ) . The h i g h mass p o r t i o n of the spectrum depended on the i n l e t temperature as expected f o r a mixture of o l i g o m e r s . At r e l a t i v e l y low temper­ a t u r e a s i g n i f i c a n t peak a t m/e 242 i s d e t e c t e d f o r V I . A t h i g h e r temperature a much s t r o n g e r peak a t m/e 386 i s observed, corresponding to the t r i m e r molecular i o n C ^ ^ O - f C 4 ^ 0 ) 3 0 ^ 5 ( V I I ) . Only t r a c e peaks were d e t e c t e d f o r m/e v a l u e s c o r r ­ esponding t o o t h e r o l i g o m e r i c poly-THF d i p h e n y l e t h e r s . On t h i s b a s i s , assignments were made f o r the GPC peaks: 21.5 A • V I ; 35 Â = V I I . The t r i m e r (VII) assignment was confirmed by an experiment i n which the elu«iit of the GPC peak a t 35 Â was c o l l e c t e d and d r i e d . The mass spectrum of t h i s sample showed the expected i n t e n s e molecular i o n peak a t m/e 386. I n f r a r e d a n a l y s i s f o r hydroxy groups proved n e g a t i v e . The % nmr spectrum showed the expected 1.5 tetramethylene oxide groups/phenoxy group. T h i s spectrum and the v a r i o u s s p e c i f i c p r o t o n a b s o r p t i o n assignments are shown i n F i g u r e 5. The k i n e t i c data of t h i s r e a c t i o n , based on the a n a l y s i s of the UV t r a c e s of the GPC s p e c t r a , are summarized i n Table I I . 6

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TABLE I I . Product D i s t r i b u t i o n by GPC A n a l y s i s of the P o l y m e r i z ­ a t i o n R e a c t i o n a t 25°. Reactant C o n c e n t r a t i o n s : (CF3S02)2° 0.47 M; THF i n Cyclohexane - 9.4 M. R e l a t i v e Molar Concns. R e a c t i o n Time (min.) of D i p h e n y l E t h e r s Polymer Mol. Wt. VI VII Polymer Mri ^ 5 24 40 36 1,900 4,400 15 15 50 35 2,000 8,400 120 5 40 55 2,100 22,000 =

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Figure 3. Mol wt distribution of phenyl etherterminated products. Reaction conditions: 15 min at 25°. THF in cyclohexane = 9.4M; (CF S0 ) 0 - 0.47U. 3

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Mass spectrum of the total product, identical to that shown in Figure 3.

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Figure 5.

Proton NMR of the GPC eluent at 35 A (see Figure 3).

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I t can be seen t h a t V (the a c t i v e intermediate which gives r i s e to VI) disappeared a t a r a t e which i s c o n s i s t e n t w i t h the p r e v i o u s l y discussed r e s u l t s . On the other hand, the r e a c t i v e intermediate which gives r i s e to V I I remained a t a r e l a t i v e l y constant c o n c e n t r a t i o n f o r the f i r s t 2 hours o f r e a c t i o n . These combined e f f e c t s accounted f o r the unusually l a r g e d i s ­ p a r i t y between ^ and shown i n Table I I . An a u t h e n t i c sample o f V I I was made i n which 0.25 mole THF was added s l o w l y a t -30° t o a s o l u t i o n o f 0.05 mole (CF3S02)20 i n 20 ml. CH Cl2 w h i l e s t i r r i n g , and then warmed t o 25° a f t e r the a d d i t i o n was completed. The r e s u l t i n g d i s p e r s i o n was then d i l u t e d w i t h 50 ml CH2CI2, f i l t e r e d and washed s u c c e s s i v e l y w i t h CH2CI2 and then THF. A white c r y s t a l l i n e product, now known to be the THF-trimer bisoxonium s a l t , 2

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3


>

was obtained i n q u a n t i t a t i v e y i e l d , based on the s t a r t i n g an­ hydride. This s a l t was converted t o the d i p h e n y l ether V I I by adding 5 g. t o a s o l u t i o n o f 10 g NaOCfc^ i n a mixture o f THF and e t h a n o l , and then separated by p r e c i p i t a t i n g i t i n water and p u r i f i e d by repeated water washing. Proton nmr and mass s p e c t r a l analyses proved t h a t the f i n a l product was V I I i n t h a t they were i d e n t i c a l t o the s p e c t r a o f the product separated by GPC, as discussed above. The bisoxonium i o n s a l t V I I I decomposes on m e l t i n g t o g i v e 1 mole o f b i s e s t e r V and 2 moles o f THF (12). V I I I i s s p a r i n g l y s o l u b l e i n THF a t 25° and very s l o w l y disappears over s e v e r a l hours by i n i t i a t i n g p o l y m e r i z a t i o n . I t i s very s o l u b l e i n nitromethane, i n which s o l v e n t i t has been found to polymerize THF as r a p i d l y as (CF3S02)20 i n i t i a t i o n . Mechanisms o f Formation o f Monomer B i s e s t e r V and Trimer B i s ­ oxonium S a l t V I I I . The i n i t i a t i o n r e a c t i o n shown i n Equation (1) has been p o s t u l a t e d t o g i v e r i s e t o the oxonium i o n s a l t I . (High e l e c t r i c a l c o n d u c t i v i t y i s manifest immediately f o l l o w i n g the a d d i t i o n o f the anhydride t o THF a t 25°). I t i s now b e l i e v e d t h a t I disappears r a p i d l y by f o l l o w i n g e i t h e r o f two r e a c t i o n pathways having q u i t e competitive r a t e s . One i n v o l v e s nucleo­ p h i l i c a d d i t i o n o f THF t o I (Equation 2) and t h i s r a p i d l y leads to the formation o f higher polymers. The a l t e r n a t i v e pathway i s a cage r e a c t i o n i n which the CF3SO3 anion n u c l e o p h i l i c a l l y a t t a c k s the oxonium i o n t o open the r i n g t o form V. This view i s c o n s i s t e n t w i t h the f a c t s t h a t s o l v e n t p o l a r i t y does not a f f e c t the r e l a t i v e y i e l d o f V (suggesting a cage r e a c t i o n o f the contact i o n p a i r ) , and the r e l a t i v e y i e l d o f V i n c r e a s e s as THF c o n c e n t r a t i o n i s decreased, as discussed p r e v i o u s l y . V i s a s t a b l e compound and l ^ F nmr shows t h a t i t i s not i n e q u i l i b ­ rium w i t h I ( 1 ) . V then disappears s l o w l y as i t i n i t i a t e s THF p o l y m e r i z a t i o n a t a r a t e which appears to be s i m i l a r t o t h a t o f e t h y l t r i f l a t e (4).

RING-OPENING POLYMERIZATION

22

The f a c t t h a t V appears t o form under a l l c o n d i t i o n s o f r e a c t i n g (CF3S02>20 w i t h THF and then behaves as a slow p o l y ­ m e r i z a t i o n i n i t i a t o r i n d i c a t e s t h a t the p r e v i o u s l y reported narrow molecular weight d i s t r i b u t i o n ( p o l y d i s p e r s i t y o f 1.08) f o r a poly-THF prepared a t -10° was probably i n e r r o r ( 1 ) . I t i s l i k e l y that the e r r o r might be a t t r i b u t e d t o the use o f GPC columns i n the e a r l i e r work which were not s u i t e d to r e s o l v e low molecular weight f r a c t i o n s . As s t a t e d p r e v i o u s l y , V I I I forms as a d i s t i n c t species only when a r e l a t i v e l y h i g h c o n c e n t r a t i o n o f anhydride i s employedI t i s important to note that the t r i m e r i s the lowest oligomer b i s ( t r i f l a t e ) which i s capable o f e x i s t i n g as a bisoxonium s a l t . Thus, i n Equation (3) the e q u i l i b r a t i o n between macrodication I I I and macrodiester IV can come i n t o p l a y only a t the t r i m e r stage. I f V I I I forms a t a c o n c e n t r a t i o n greater than i t s very low s a t u r a t i o n c o n c e n t r a t i o n , then i t p r e c i p i t a t e s , thus d r i v i n g the e q u i l i b r i u m e s s e n t i a l l y a l l the way toward bisoxonium i o n t r i f l a t e s a l t . As higher oligomer b i s ( t r i f l a t e s ) s l o w l y form, these are very s o l u b l e i n THF and the normal e q u i l i b r i u m be­ tween macroester and macroion i s r e - e s t a b l i s h e d .

ABSTRACT A detailed examination of the reaction of THF with (CF S0 ) has been carried out and two prominently distinct oligomeric species have been found to be produced as intermed­ iates during the polymerization which yields living products whose end groups consist of ions and esters in equilibrium. First, the ring-opened tetramethylene bis(triflate) ester is produced in all cases studied and its behavior as a relatively sluggish THF polymerization initiator causes the otherwise narrow molecular weight distribution to skew toward the low end. Second, at relatively high initial anhydride concentrations, 3

2

2

the bisoxonium ion salt,

•2CF SO , forms and 3

3

separates as a pure crystalline precipitate. Reaction mech­ anisms are postulated to account for the surprising formation of these compounds during THF polymerization. ACKNOWLEDGEMENT We are indebted to Dr. Peter F. Cullen for providing the GPC analyses. LITERATURE CITED Smith, S., and Hubin, A.J., J. Macromol. Sci. - Chem., (1973), A7, 1399. 2. Kobayashi, S., Danda, Η., and Saegusa, T., (a) Bull. Chem. Soc. of Japan (1973), 46, 3214, (b) Macromol., (1974), 7., 415. 3. Matyjaszewski, K., and Penczek, S., J. Polym. Sci. - Chem. Ed., (1974) 12, 1905. 1.

2.

SMITH ET AL.

Living

Tetrahydrofuran

Polymers

4. Matyjaszewski, Κ., Kubisa, P., and Penczek, S., J. Polym. Sci. Chem. Ed., (1975), 13, 763. 5. Matyjaszewski, Κ., Buyle, A.M., and Penczek, S., J. Polym. Sci. - Letters Ed., (1976), 14, 125. 6. Wu, T.K., and Pruckmayr, G., Macromol., (1975), 8, 77. 7. Pruckmayr, G., and Wu, T.K., Macromol., (1975) 8, 954. 8. Matyjaszewski, K. and Penczek, S., J . Polym. Sci. - Chem. Ed. (1977), 15, 247. 9. Saegusa, T., and Matsumoto, S., J. Polym Sci., (1968), A6, 1559. 10. Rosenberg, B.A., Ludvig, E.B., Gantmakher, A.R., and Medvedev, S.S., J. Polym. Sci., (1967), C16, 1917. 11. Croucher, T.G., and Wetton, R.E., Polymer, 17, (1976), 205. 12. Cash, D.J., personal communication.