Polymer Bulletin. @ Springer-Verlag 1986. Molecular Weight Characteristics of 2-Naphthyl Methacrylate. Copolymers Obtained by Radical Polymerization.
Polymer Bulletin 15, 511-515 (1986)
Polymer Bulletin @ Springer-Verlag 1986
Molecular Weight Characteristics of 2-Naphthyl Methacrylate Copolymers Obtained by Radical Polymerization in Different Solvents Olga Todorova, Ivan Gitsov, and Vesselin Slnlgersky* Central Laboratoryfor Polymers, Bulgarian Academy of Sciences, 1040 Sofia, Bulgaria Dedicated to Professor Ivan M, Panayotov to his 60. birthday with the best wishes
SUMMARY The influence of the chemical nature of the polymerization m e d i u m on the molecular weight characteristics of the copolymers 2-naphthyl m e t h a c r y l a t e / s t y r e n e and 2-napnthyl methac r y l a t e / a c r y l o n i t r i l e was investigated by gel permeation chromatography. The results obtained show that the influence of the nature of the solvent used on the molecular weight characteristics could be a t t r i b u t e d to the different chain transfer c o n s t a n t s . The c o n t r i b u t i o n of the monomer complexes which affects mainly the relative r e a c t i v i t y ratios of the comonomers may be neglected. INTRODUCTION As it is Known different factors may influence the radical polymerization: dipole-dipole and d o n o r - a c c e p t o r interactions, H-bonding, the chemical nature of the solvent etc (I). It has been established that the polarity of the solvent is of primary importance and influences the rate of polymerization as well as t~e tacticity of the polymers obtained. By means of IR- and "H-NMR spectroscopy mainly the influence of the r e a c t i o n m e d i u m on the relative r e a c t i v i t y ratios has been studied. It is interesting to Know how the chemical nature of the solvent affects the m o l e c u l a r weight and the m o l e c u l a r weight d i s t r i b u t i o n which determine the mechanical, theological and other properties of the copolymers obtained. The ~nowledge of these m o l e c u l a r weight c h a r a c t e r i s t i c s (MWC) may enlighten the m e c h a n i s m of polymerization. A fast and convenient method for obtaining these characteristics is the gel permeation c h r o m a t o g r a p h y (GPC). Vsing this method poly(2-naphthyl methacrylates) obtained in different solvents as well as copolymers 2-naphthyl m e t h a c r y l a t e / methyl m e t h a c r y l a t e and benzyl m e t h a c r y l a t e / m e t h y l methacrylate have been sdudied (2). There are no data for t h e MWC of other 2-naphthyl methacrylate copolymers. The present paper r e p r e s e n t s an attempt to investigate via GPC the influence of the chemical nature of the i n t e r a c t i o n m e d i u m - chloroform, benzene, 1,4-dioxane, acetone and acetonitrile, on the molecular weight characteristics (molecular weight and molecular weight distribution) of copolymers 2-naphthyl m e t h a c r y l a t e / s t y r e n e (2-NM/St) and 2-naphthyl m e t h a c r y l a t e / a c r y l o n i t r i l e (2-NM/AN). * To
whom offprint requests should be sent
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EXPERIMENTAL Materials The i n i t i a t o r 2 , 2 ' - a z o i s o b u t y r o n i t r i l e (AIBN) was r e c r y s t a l l i z e d f r o m alcohol, m.p. I02-I03~ 2-Naphthyl methacrylate (2-NM) w a s . s y n t h e s i z e d a c c o r d i n g to (3). A c r y l o n i t r i l e (AN) and styrene (St) w e r e u s e d after distillation. C h l o r o f o r m , benzene, 1 , 4 - d i o x a n e and a c e t o n i t r i l e w e r e d r i e d and d i s t i l l e d prior to use. CopolymerizationL In g l a s s a m p o u l e s to a I m o l / L m o n o m e r s o l u t i o n 0,5 mol % (for 2 - N M / S t ) and 1,0 mol % (.for 2-NM/AN) A I B N w e r e added. After d e g a z a t i o n the sealed a m p o u l e s w e r e h e a t e d in a t h e r m o s t a t at 60~ for a d e f i n i t e time. In all cases i n v e s t i g a t e d , the c o o o l y m e r s formed in a c e t o n i t r i l e p r e c i p i t a t e d during polymer i z a t i o n . In the o t h e r s o l v e n t s the p o l y m e r i z a t i o n w a s h o m o g e neous. In all e x p e r i m e n t s the c o n v e r s i o n was about 10 %. The c o p o l y m e r s o b t a i n e d w e r e p r e c i p i t a t e d and dried u n d e r r e d u c e d p r e s s u r e by ~ n o w n m e t h o d s (4,5). Measurements The GPC a n a l y s e s w e r e p e r f o r m e d on W a t e r s e q u i p m e n t cons i s t i n g of an a u t o m a t i c i n j e c t o r W I S P 710 B~ M 510 pump, R 401 d i f f e r e n t i a l r e f r a c t i v e index d e t e c t o r ~DRI) and M 440 UV det e c t o r ~ ~ = 2~4 . A ~et of four U l t r a s t y r a g e l c o l u m n s w i t h pore sizes 10 ~, 10 , 10 ~ and 500 ~ was used. The f l o w rate of the m o b i l e phase - t e t r a h y d r o f u r a n , was I m L / m i n at 35~ The m o l e c u l a r w e i g h t s of the c o p o l y m e r s i n v e s t i g a t e d w e r e c a l c u l a t e d t o w a r d s p o l y s t y r e n e s t a n d a r d s u s i n g W a t e r s M 730 D a t a Module. By the m o d i f i e d m e t h o d of the u n i v e r s a l c a l i b r a t i o n (6) it was f o u n d out that the r e l a t i o n s of the e l u t i o n v o l u m e s and the m o l e c u l a r w e i g h t s for the h o m o p o l y m e r s of 2 - N ~ St and A N lie on the same s t r a i g h t line. ~or the p u r p o s e we u s e d l o w m o l e c u l a r w e i g h t poly-AN, as the h i g h p o l y m e r s of A N w e r e p o o r l y s o l u b l e in t e t r a h y d r o f u r a n . For all c o p o l y m e r s full c o r r e s p o n d e n c e of the e l u t i o n c u r v e s o b t a i n e d by both (DRI and UV) d e t e c t o r s was found. R E S U L T S AND D I S C U S S I O N At the p o l y m e r i z a t i o n of 2 - N M (7) and its c o p o l y m e r i z a t i o n w i t h m e t h y l m e t h a c r y l a t e in d i f f e r e n t s o l v e n t s (8) a dep e n d e n c e of the t a c t i c i t y and the r e l a t i v e r e a c t i v i t y r a t i o s on the p o l a r i t y of the s o l v e n t u s e d has b e e n observed. We have f o u n d the same i n f l u e n c e of the r e a c t i o n m e d i u m at the c o p o l y m e r i z a t i o n of 2 - N N w i t h St (4) and AN (5). We u s e d GPC to check the i n f l u e n c e of the c h e m i c a l n a t u r e of d i f f e r e n t s o l v e n t s on the MWC of these copolymers. The n u m e r i c a l d a t a o b t a i n e d for the MWC of 2 - N M / S t copol y m e r s are g i v e n in Table I and the e l u t i o n curves are shown on F i g u r e I. W i t h i n c r e a s i n g the 2 - N M c o n t e n t s in the c o p o l y mers, i n d e p e n d e n t l y in w h i c h s o l v e n t they are formed, the mol e c u l a r w e i g h t and the p o l y d i s p e r s i t y of the c o p o l y m e r s become higher. On the other side the c o p o l y m e r s f o r m e d in chloroform, b e n z e n e and 1 , 4 - d i o x a n e ( s o l v e n t s w i t h low d i e l e c t r i c constants) e x h i b i t h i g h e r m o l e c u l a r w e i g h t s and p o l y d i s p e r s i t i e s c o m p a r e d to these f o r m e d in a c e t o n e and a c e t o n i t r i l e ( s o l v e n t s
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Table I: GPC analysis lymerization
2-NM content in the copolymer (weight %)
Solvent (dielectric constant) Chloroform (4,7)
35,9 61,6 69,1 44,8 60,& 91,4 36,8 38,5 73,8 38,6 r 77,0 29,6 62,3 81,7
Benzene (,2,3) 1,4-Dioxane (2,2) Acetone (20,7) Acetonitrile (,36,2)
Figure
of 2-NM/St copolymers formed during poin different solvents
I: GPC chromatograms #
~j
f~]1" -~
Mw
Mw/Mn
(GPC)
(GPC)
25 52 53 32 33 59 16 18 51 9 13 28 10 17 25
000 000 000 000 000 000 000 000 000 000 000 000 000 000
000
1,72 2,28 2,91 1,95 2,36 2,51 1,68 1,75 2,08 1,54 1,51 1,74 1,47 1,67 1,95
of 2-NM/St copolymers obtained by polymerization in different solvents (DRI) : chloroform (2-NM content 61,6 weight %) ---: benzene (2-NM content 60,6 weight %) .--: acetonitrile (2-NM content 62,3 weight %)
J [
z'e '3'0 300000 64000
4o v(mt) ~PS
25000
with high dielectric constants). It has been shown that in chloroform there exist complexes 2-NM/2-NM whereas in solvents with high dielectric constants the free monomer molecules predominate (9). Other authors have found a relation between the formation of intermolecular complexes and the propagation of the macroradical (10). Consequently it may be assumed that the complexes mentioned may contribute for the high molecular weights obtained in non-polar solvents. ~or the solution polymerization the average rate of polymerization ~n is given by the equation
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1 __
Pn
IS] =
C M
+
C S - -
[S]
[In] +
C I
~
[S]
K t [Mn" ] +
(i)
Kp [S]
where CM, C S and C I are the chain transfer constants to the monomer, solvent and initiator; IS], [In] and [M] are the molar concentrations of the solvent, initiator and monomer; [Mn" ] is the concentration of the growing macroradicals; K t and K 0 are the chain termination and chain propagation constants~ It is ~nown that the chain transfer has the strongest influence upon the molecular weight of the polymer obtained. The chain transfer constants of AIBN and St are equal to zero (11). For C M of 2-NM ther.~ are no data in the literature but it could be suggested that its value is close to zero, as for its structural analogue methyl methacrylate it is known to be zero (11). The data given show that C S has the strongest influence on the MWC of the copolymers formed. As in acetone C S is 4,1.10 -4 (12) and in chloroform it is 0,5.10-4 (12), the molecular weights of the products obtained in the former solvent are lower. The polydispersity indexes are close to 1,5 indicating predominant chain termination by recombination. In the non-polar solvents, however, the majoriby of the Mw/Mn values are close to 2 which means that the chain termination in these cases proceeds mainly by disproportionation. Table 2 gives the data of the GPC analysis of 2-NM/AN copolymers formed in different solvents. The influence of the reaction medium on the MWC of the copolymers is also obvious. ~or copolymers with similar compositions the molecular weights obtained in chloroform and benzene are lower than in acetone and acetonitrile. With the increase of the molecular weight the polydisoersity also increases. As alrea@y pointed out C I of AIBN is zero, C M of AN may be neglected (13). Therefore for the system 2-NM/AN the molecular weight is predominatly affected by C S. For chloroform, benzene and acetone the C S values of AN are 5,6.10 -4 , 2,5.10 -4 and 1,13.10 -4 which cou]d exolain the changes in the molecular Table
2: GPC analysis lymerization
Solvent (,dielectric constant) Chloroform (4,7) Benzene (2,3) Acetone [20,7) Acetonitrile (36,2)
of 2-NM/AN copolymers in different solvents
2-NM content in the copolymer (weight %) 72,6 85,2 95,0 69,2 77,2 95,3 73,3 80,3 93,4 69,0 85,5 94,9
