Studies on the Anionic Polymerization of Methyl Methacrylate Initiated

21 Studies on the Anionic Polymerization of Methyl Methacrylate Initiated with Butyllithium in Toluene by Using Perdeuterated Monomer

Downloaded by FUDAN UNIV on March 28, 2017 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0166.ch021

KOICHI HATADA, TATSUKI KITAYAMA, KINZO FUMIKAWA, KOJI OHTA, and HEIMEI YUKI Department of Chemistry, Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan

Many papers have been published on the polymerization of methyl methacrylate (MMA) with alkyllithium. It was reported that in the i n i t i a t i o n step an attack of alkyllithium on monomer occurred in the first few seconds and took place on both olefinic and carbonyl double bonds and a considerable amount of oligomer was formed in the early stage of the polymerization (1, 2, 3, 4, 5). Kawabata and Tsuruta (5) studied the reaction mode of butyllithium (BuLi) with MMA in the i n i t i a t i o n step. Glusker and his coworkers postulated the pseudo-cyclization of chain end as a cause of oligomer formation (6). However, it is still unresolved how the butyl group of the i n i t i a t o r is incorporated into the polymer chain, and how the oligomer terminates its further growth. In this a r t i c l e perdeuterated MMA was polymerized with undeuterated BuLi and the resultant polymer and oligomer were studied for the i n i t i a t o r fragment by using H NMR spectroscopy (7a). The undeuterated monomer was also polymerized with BuLi in toluene at -78°C and chromatography and each fraction was analyzed by H NMR and mass spectroscopies (7b). The formation of butane in this polymerization reaction was also studied in some det a i l (7c). 1

1

Experimental

Perdeuterated MMA was prepared in 32% yield from acetone cyanohydrin-d7 and methanol-d4 according to the method of Crawford (8). Bp 100 ~ 101°C. The isotopic purity was found more than 99.7% by NMR using precision coaxial tubing method (9). Undeuterated MMA was obtained from commercial source. Each monomer was stirred over calcium dihydride overnight and vacuum d i s t i l l e d . The d i s t i l l a t e was stirred over fresh calcium dihydride on the vacuum line for 5 hr and r e d i s t i l l e d at room temperature. Butyl isopropenyl ketone was prepared by the r e a c t i o n of methacryloyl c h l o r i d e with BuLi in ether at -78°C. The crude product was p u r i f i e d by the f r a c t i o n a l d i s t i l l a t i o n under reduced n i t r o g e n pressure. Bp 56.5°C...(14mmHg). 1120=1.4363. Anal. Found: 0097-6156/81/0166-0327$05.00/0 © 1981 American Chemical Society McGrath; Anionic Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


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C., 75.92%, H, 11.18%. Calcd f o r C g H O : C., 76.14%; H, 11.18%. The ! H NMR spectrum (10% CCI4 s o l u t i o n ) showed peaks a t 0.92ppm ( t r i p l e t , 3.0 H) assigned to the methyl protons o f b u t y l group, at 1.42ppm ( m u l t i p l e t , 4.1 H) assigned to the protons o f the two methylenes adjacent and next b u t one to the methyl in b u t y l group, at 1.83ppm ( s i n g l e t , 3.0 H) assigned to the α-methyl protons, at 2.60ppm ( t r i p l e t , 2.0 H) assigned to the protons o f methylene group adjacent to the carbonyl group and at 5.64 and 5.84ppm (two m u l t i p l e t s , 2.0 H) assigned t o the β-ρrotons o f v i n y l group. P o l y m e r i z a t i o n was c a r r i e d out in a s e a l e d g l a s s ampoule and terminated by the a d d i t i o n o f a s m a l l amount o f methanol. The r e a c t i o n mixture was poured i n t o a l a r g e amount o f methanol to p r e c i p i t a t e the polymer formed. A f t e r s t a n d i n g it overnight the p r e c i p i t a t e was c o l l e c t e d by f i l t r a t i o n , washed w i t h methanol and d r i e d in vacuo at 60°C. The combined f i l t r a t e s were evaporated to dryness under reduced pressure and the residue was r e d i s s o l v e d in benzene to remove a s m a l l amount o f i n s o l u b l e m a t e r i a l . The methanol-soluble oligomer was f r e e z e - d r i e d from the benzene s o l u tion. In the p o l y m e r i z a t i o n designed t o detect the amount o f l i t h ium methoxide formed, the r e a c t i o n was terminated with a s m a l l amount o f a c e t i c a c i d , and the r e a c t i o n mixture was analyzed f o r methanol by g a s - l i q u i d chromatography. I t was assumed that the methoxide formed during the p o l y m e r i z a t i o n was converted q u a n t i t a t i v e l y t o methanol (10). The p o l y m e r i z a t i o n was a l s o terminated with CH3OH o r CH3OD in the case t o d e t e c t butane. From the v o l a t i l e f r a c t i o n d i s t i l l e d out from the r e a c t i o n mixture on a vacuum l i n e , l o w - b o i l i n g com pounds were c o l l e c t e d by r e d i s t i l l a t i o n and s u b j e c t e d t o the a n a l y s i s by combined gas chromatography-mass spectrometry. Butane (BuH) and monodeuterated butane, CH3CH2CH2CH2D (BuD), employed as a u t h e n t i c samples, were obtained by the r e a c t i o n o f BuLi w i t h CH3OH and CH3OD, r e s p e c t i v e l y . The f r a c t i o n a t i o n o f MMA oligomer was c a r r i e d out by u s i n g a JASCO model FLC-A10 h i g h speed l i q u i d chromatograph w i t h p o l y styrene g e l column. Chloroform was employed as an e l u e n t . The g e l was prepared and k i n d l y given by Dr. Tanaka o f Tokyo U n i v e r s i ty o f A g r i c u l t u r e and Technology. The sample oligomer was sepa r a t e d as a heptane-soluble f r a c t i o n from a methanol-soluble o l i g o mer. Depolymerizations o f polymer and oligomer were performed by heating them a t 300 350°C... under vacuum. The products were c o l l e c t e d in the r e s e r v o i r c o o l e d in l i q u i d n i t r o g e n bath and analyzed by g a s - l i q u i d chromatography. The 1H NMR s p e c t r a o f the polymer and oligomer were measured in nitrobenzene-d5 a t 110°C... on JNM-FX100 F o u r i e r transform NMR spectrometer(JEOL) b e i n g operated at 100MHz. The hydrogen content of sample polymer o r oligomer was determined from the r e l a t i v e i n t e n s i t y o f the s i g n a l o f i n t e r e s t t o the s i g n a l due t o the remaining protons in the nitrobenzene-d5. The absolute i n t e n s i t y

McGrath; Anionic Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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329

Monomer

o f the l a t t e r s i g n a l was measured b y p r e c i s i o n c o a x i a l t u b i n g method ( 9 ) . S p i n - l a t t i c e r e l a x a t i o n t i m e , Τχ, was measured b y the i n v e r s i o n - r e c o v e r y F o u r i e r T r a n s f o r m method. F i e l d d e s o r p t i o n and e l e c t r o n i m p a c t i o n i z a t i o n mass s p e c t r a were t a k e n b y u s i n g a M a t s u d a t y p e d o u b l e f o c u s s i n g s p e c t r o m e t e r (11) e q u i p p e d w i t h s i l i c o n e m i t t e r (12) a n d a JMS-01SG-2 mass spectrometer(JEOL), respectively. Number a v e r a g e m o l e c u l a r w e i g h t was d e t e r m i n e d in b e n z e n e s o l u t i o n b y H i t a c h i 117 v a p o r p r e s s u r e osmometer(VPO) a t 42°C.


Results 1. P o l y m e r i z a t i o n o f MMA-d8 w i t h B u L i in T o l u e n e . Polymeri z a t i o n o f MMA-dg was c a r r i e d o u t in t o l u e n e w i t h B u L i a t -78°C. The r e s u l t s a n d the % NMR s p e c t r a o f the r e s u l t a n t p o l y m e r a n d o l i g o m e r a r e shown in T a b l e 1 and F i g u r e 1 , r e s p e c t i v e l y . The Table I P o l y m e r i z a t i o n o f P e r d e u t e r a t e d MMA w i t h B u L i in T o l u e n e a t -78°C... f o r 5 h r (Za) 3

Yield MnXlO" VPO NMR (mmol) ω Polymer 0.011 26.9 26.8 0.295 Oligomer 1.09 1.63 0.271 0.249 Monomer 5.2mmol, B u L i 0.50mmol, t o l u e n e 1 0 m l . b C a l c u l a t e d f r o m y i e l d and Mn m e a s u r e d b y VPO. (Polymer B u l l e t i n ) b

a

t r i p l e t a t 0.79ppm s h o u l d b e due t o the m e t h y l p r o t o n s in the b u t y l g r o u p , w h i c h o r i g i n a l l y came f r o m the i n i t i a t o r . The s i n g l e t a t 2.57ppm was a s s i g n e d t o the t e r m i n a l m e t h i n e p r o t o n CD (vvCD2~C...-H ), w h i c h was i n t r o d u c e d f r o m m e t h a n o l in the 3

COOCD3

t e r m i n a t i o n r e a c t i o n . T h e s i g n a l d i s a p p e a r e d when the p o l y m e r i z a t i o n was t e r m i n a t e d b y CH3OD i n s t e a d o f CH3OH. The polymer and o l i g o m e r amounted t o 0.011 and 0.249mmol, r e s p e c t i v e l y , b a s e d on the y i e l d a n d the Mn. On the o t h e r h a n d , the c o n t e n t s o f the m e t h i n e p r o t o n in the p o l y m e r a n d o l i g o m e r w e r e m e a s u r e d t o b e 0.011 and 0.167mmol, f r o m w h i c h the m o l e c u l a r w e i g h t s o f the p o l y mer a n d o l i g o m e r w e r e c a l c u l a t e d t o b e 26,800 and 1,630 r e s p e c tively. E a c h m o l e c u l e was assumed t o c o n t a i n one t e r m i n a l m e t h i n e p r o t o n . T h e m o l e c u l a r w e i g h t o f the p o l y m e r t h u s o b t a i n e d was c o n s i s t e n t w i t h t h a t measured b y VPO, b u t the o l i g o m e r showed d i f f e r e n t m o l e c u l a r w e i g h t s b y t h e s e two methods ( T a b l e I ) . The r e s u l t s i n d i c a t e t h a t most o f the p o l y m e r c h a i n was still l i v i n g a t the e n d o f the r e a c t i o n , a n d the s p o n t a n e o u s t e r m i n a t i o n t h r o u g h the f o r m a t i o n o f c y c l i c k e t o n e s t r u c t u r e d i d n o t o c c u r a t the c h a i n end o f the p o l y m e r . I t was r e p o r t e d t h a t the o l i g o m e r c h a i n was e s s e n t i a l l y i n a c t i v e a t the l a t e r s t a g e o f p o l y m e r i z a t i o n , o w i n g t o the p s e u d o -


ANIONIC POLYMERIZATION

330

CH (Butyl 3


group)

PPM(HMDS) Polymer Bulletin Figure 1. H-l NMR spectra of the polymer (A) and oligomer (B) of MMA-d prepared in toluene with BuLi at —78°C... (la). The signals labelled X arose from the remaining protons in the monomer unit of the chain. 8


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331

c y c l i z a t i o i i (6). The d i f f e r e n c e between the molecular weights of the oligomer measured by NMR and VPO shows that about 30% o f the oligomer molecules d i d not contain a t e r m i n a l methine proton (Table H ) , i n d i c a t i n g the p o s s i b i l i t y of t e r m i n a t i o n by true Table II A n a l y s i s of B u t y l Group and Terminal Methine Proton in the Polymer and Oligomer of MMA-dg Prepared in Toluene with BuLi at -78°C...(J7a) 4H9-(total) C4H9COTerminal methine mmol mol/mol mmol mol/mol mmol mol/mol Polymer 0.0209 1.9 0.0107 1.0 0.011 1.0 Oligomer 0.424 1.7 0.182 0.7 0.167 0.7 Represents the number o f b u t y l group or t e r m i n a l methine proton per a molecule o f polymer or oligomer. C


a

a

a

a

c y c l i z a t i o n w i t h a r e l e a s e o f methoxide. However, the remaining 70% of oligomer were still r e a c t i v e to the proton of methanol. I n t e n s i t y measurement of the methyl proton s i g n a l at 0.79ppm i n d i c a t e d that the polymer and oligomer had 1.9 and 1.7 b u t y l group in each molecule, r e s p e c t i v e l y , (Table H ) . The b u t y l group should be i n c o r p o r a t e d not only in the i n i t i a t i o n step but a l s o through the r e a c t i o n of BuLi with carbonyl group. The t r i p l e t at 2.40ppmwas assigned to the protons of the methylene group adjacent to carbonyl group (-COCH2CH2CH2CH3). The resonance turned out a s i n g l e t by the i r r a d i a t i o n at 1.4ppm, where a weak m u l t i p l e t appeared, i n d i c a t i n g that the l a t t e r resonance was a s c r i b e d to the methylene group a f t e r next to the carbonyl group. The contents o f b u t y l carbonyl group in the polymer and oligomer were determined to be 1.0 and 0.7 per a molecule, r e s p e c t i v e l y . Consequently, each one molecule o f the polymer and oligomer had one t e r m i n a l b u t y l group which was introduced in the i n i t i a t i o n step. In the p o l y m e r i z a t i o n of MMA by BuLi the i n i t i a t o r was r e ported to react first with many more carbonyl groups than with v i n y l double bonds at low temperatures (3). T h e r e f o r e , the b u t y l carbonyl group must be i n c o r p o r a t e d through the copolymerization of MMA with b u t y l i s o p r o p e n y l ketone formed by the former r e a c t i o n . Ç3 CH =Ç Ç=0 H

2

OCH3

BuLi ,

9*3 CH -Ç Bu-Ç-OLi 2

OCH3

,

9*3 CH2=Ç + LiOCH Ç=0

3

Bu

Now it w i l l be necessary to e l u c i d a t e the l o c a t i o n o f the b u t y l i s o p r o p e n y l ketone u n i t in the polymer chain. The s p i n l a t t i c e r e l a x a t i o n time, Τχ, o f the protons in the polymer and oligomer was measured. The Τχ of methylene protons adjacent to the carbonyl group was n e a r l y the same l e v e l as the Ύχ of methyl protons in the t e r m i n a l b u t y l group or t e r m i n a l methine proton (Table HI) but much longer than the Τχ o f the protons in i n t e r i o r sequences o f polymer (13). These i n d i c a t e that the b u t y l carbonyl group in the polymer or oligomer l o c a t e s at o r near to the f o r e f r o n t o r the end o f the chain.


ANIONIC

332

POLYMERIZATION

Table HI S p i n - L a t t i c e R e l a x a t i o n Times T i ' s in Second of the Protons in B u t y l Group and the Terminal Methine Proton in Nitrobenzene-d at 110°C... (7a) 5

CH3CH2CH 2 3

polymer Oligomer


a

Co-

CH3CH2CH2CH2CO-

3.9 5.4

3

Terminal methine

1.8 2.1

5.1 6.1

Prepared in toluene by BuLi at -78°C. (Polymer B u l l e ti«)

The r e s u l t s o f the p o l y m e r i z a t i o n terminated 10min a f t e r the i n i t i a t i o n are shown in Table IV. As compared w i t h the r e s u l t s of the p o l y m e r i z a t i o n f o r 5hr, the y i e l d and molecular weight o f the polymer and oligomer were lower, but the number o f b u t y l carbonyl group in one polymer molecule was almost constant r e g a r d l e s s of the p o l y m e r i z a t i o n time. This may i n d i c a t e that the b u t y l i s o p r o p e n y l ketone u n i t in the polymer molecule l o c a t e s at o r near to the f o r e f r o n t of the chain. Table IV P o l y m e r i z a t i o n o f MMA-dg with BuLi in Toluene at -,78°C... f o r lOrnin C4H9-(total)

Yield

Studies on the Anionic Polymerization of Methyl Methacrylate Initiated

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