Molecular Structure of Vinyl ChlorideVinylidene Chloride Copolymers

5 M o l e c u l a r Structure of Vinyl C h l o r i d e - V i n y l i d e n e Chloride Copolymers by Carbon-13

NMR

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1

CHARLES J. CARMAN The B. F. Goodrich Company, Research & Development Center, 9921 Brecksville Road, Brecksville, OH 44141 13

High resolution C nmr is established as perhaps the most discriminating spectroscopic method in recent years for determining the molecular structure of macromolecules. For chlorinated polymers the direct and long range substituent effects of the halogen produce unique C chemical shifts that enable the determination of tacticity in PVC1, average block lengths in vinyl chloride-butadiene copolymers2, and monomer composition and sequence distribution in a variety of vinyl chloride copolymers3. In addition, Keller et al have attempted to apply interpretational analogies to more complicated chlorinated polyalkanes4. The present C nmr analysis of copolymers of vinyl chloride (VCl) and vinylidene chloride (VCl2) demonstrates the value of using internal consistencies for determining monomer composition and sequence distribution. 13

13

Results and Discussion Figure 1 shows the spectra of three copolymers and compares their spectra to that of a PVC sample. The resonances centered around 46 ppm in Figure la are from the CH2 carbon and those resonances in the 5^ ppm region are from the CHC1 carbon. The fine structure in both the methine and methylene regions is from tacticity information. At very low levels of vinylidene chloride, the VCI2 monomer will be flanked by VCl monomer. The isolated structure is shown in Figure 2a. The carbon bearing both chlorine atoms has a chemical shift o^ 87.50 ppm and is identified in Figure lb. The chemical shift at 52.33 ppm in Figure lb is assigned to the methylene carbon adjacent to a vinylidene (or dichloro carbon) structure. 1

Current address: B. F. Goodrich Company, Engineered Products Group, 500 S. Main Street, Akron, OH 44318. 0-8412-0594-9/80/47-142-081$05.00/0 © 1980 American Chemical Society Woodward and Bovey; Polymer Characterization by ESR and NMR ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

82

POLYMER

Figure 1.

13

CHARACTERIZATION

G{ //} NMR spectra of PVC (a) and VCl-VCU C (c), and D (d) J

B Y ESR A N D N M R

Copolymers Β (b),

Woodward and Bovey; Polymer Characterization by ESR and NMR ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

5.

CARMAN

Vinyl

Chloride-Vinylidene

Chloride

CI

83

Copolymers

CI

CI

ι (a)

C -

CH

CI

1

(b)

C -

CH

9

0

2

ι H

ι

C -

0

-I 1

C -

CH„ 2

ι \ H

ι CI

CI

1 1

I1

-j c

1 1

-

CH

1

-

0

z

i1

H

CH

ι I

C

1 - CH,

f

J

C

-

11

CI

CI

CI

CI

1

•H

1 1

CI

CI

CI

I

) C CI

Figure 2.

CH-

-

c

-

CH

9 z

CI

-

C - CH 1 CI

2

C -

r

I I

CH

2

' H

Carbon environment in VCl-VCl, copolymers representing (a) isolated, (b) paired, and (c) greater-than-paired structures


84

POLYMER

CHARACTERIZATION

BY

ESR

AND

NMR

The n e x t h i g h e r s t r u c t u r e f o r m e d w o u l d be p a i r e d VCI2 mono mer. T h i s i s shown i n F i g u r e 2 b . In the p a i r e d s t r u c t u r e , there a r e s t i l l two m e t h y l e n e c a r b o n s w h i c h f o r m t h e VCI2 and V C l junction. T h e r e i s a l s o a u n i q u e m e t h y l e n e b e t w e e n two CCI2 c a r b o n s a t 6O.U9 ppm and t h e c h e m i c a l s h i f t o f t h e CC1 in a p a i r e d s t r u c t u r e a t 85.^9 ppm. As v i n y l i d e n e c h l o r i d e i n c r e a s e s i n c o n c e n t r a t i o n t h e polymer would form g r e a t e r than p a i r e d s e q u e n c e s ; shown i n F i g u r e 2 c . A unique carbon resonance formed from t h i s s t r u c t u r e i s t h e CC1 f l a n k e d by CC1 on e i t h e r s i d e i n the β p o s i t i o n . The c o r r e s p o n d i n g c h e m i c a l s h i f t i s shown a t 8 2 . 8 3 ppm i n F i g u r e I d . The o t h e r c a r b o n s i n t h e (> p a i r e d ) sequence o n l y change t h e r e l a t i v e areas o f t h e o t h e r assignments i n t h e spectrum. A summary o f t h e C c h e m i c a l s h i f t assignments f o r VCI-VCI2 c o p o l y m e r s i s g i v e n i n T a b l e I . To c a l c u l a t e monomer c o m p o s i t i o n , t h e s e c h e m i c a l s h i f t a s s i g n m e n t s must f o l l o w p e a k a r e a r e l a t i o n s h i p s d e d u c e d f r o m i s o l a t e d , p a i r e d , and > p a i r e d s t r u c t u r e s . I s o l a t e d : The m o l e s o f i s o l a t e d VCI2 monomer i s p r o p o r t i o n a l t o t h e i s o l a t e d CC1 carbon area. There i s a l s o produced an a r e a t w i c e t h e i s o l a t e d C C 1 area which i s assigned t o the two f l a n k i n g CH carbons. The PVC CH2 c a r b o n i s r e d u c e d i n a r e a b y an amount e q u a l t o t h e i s o l a t e d C C 1 carbon area. P a i r e d : The m o l e s o f p a i r e d VCI2 monomer p r o d u c e a d i r e c t l y p r o p o r t i o n a t e a r e a f r o m t h e p a i r e d CCI2 c a r b o n and an e q u a l a r e a f r o m t h e o u t e r CH2. T h e r e w i l l a l s o be an a r e a e q u a l t o h a l f t h e p a i r e d CC1 a r e a a s s i g n e d t o t h e i n n e r CH carbon. The PVC CH a r e a i s r e d u c e d i n a r e a by an amount one h a l f t h e p a i r e d CCI2 ( b e c a u s e h a l f t h e o u t e r CH2 a r e a comes f r o m t h e PVC monomer). >Paired: The a r e a r e l a t i o n s h i p s f o r g r e a t e r t h a n p a i r e d depend on t h e l e n g t h s o f t h e c o n t i g u o u s u n i t s . For a run t h r e e u n i t s l o n g t h e r e i s an a r e a f r o m t h e > p a i r e d CCI2 c a r b o n d i r e c t l y p r o p o r t i o n a l t o one t h i r d t h e number o f monomers i n a c o n t i g u o u s sequence. There are c o n t r i b u t i o n s o f t w i c e t h i s a r e a t o b o t h t h e i n n e r CH resonance areas. The PVC CH i s reduced i n a r e a b y h a l f t h e o u t e r CH area. T h e r e f o r e , f o r VC1 sequen c e s (n) a s s i g n e d t o t h e > p a i r e d C C I 2 , t h e a r e a ( n - l ) i s a s s i g n e d t o t h e i n n e r CH . Using these area r e l a t i o n s h i p s the equations i n Table I I were w r i t t e n t o u s e t h e m e a s u r e d peak a r e a s f r o m a c o p o l y m e r o f v i n y l c h l o r i d e t o c a l c u l a t e monomer c o m p o s i t i o n s . The e q u a t i o n s a l s o p r o v i d e c h e c k s on i n t e r n a l c o n s i s t e n c y o f t h e s p e c t r a . These r e l a t i o n s h i p s must h o l d as t h e monomer r a t i o i s v a r i e d o r e r r o r s i n a s s i g n m e n t h a v e b e e n made. E q u a t i o n s ( l ) and (2) a r e s i m p l y two ways o f e x p r e s s i n g t h e CHC1 s p e c t r a l r e g i o n i n t e r m s o f c o n t r i b u t i o n o f PVC m e t h i n e . E q u a t i o n (k) i s a means o f c a l c u l a t i n g the c o n c e n t r a t i o n o f v i n y l c h l o r i d e i n terms of i t s methylene area a f t e r c o r r e c t i n g f o r those methylene carbons t h a t h a v e b e e n s h i f t e d (φ, e q u a t i o n 3) u n d e r t h e CHC1 resonance r e g i o n by v i r t u e o f b e i n g a d j a c e n t t o a CC1 carbon. Equations (5) and (6) a r e two a r e a r e l a t i o n s h i p s t h a t p r o v i d e t h e vinylidene chloride concentration. 2

2

2

1 3

2

2

2

2

2

2

2

2

2

2

2

2

2


5.

Vinyl

CARMAN

Chloride-V

inylidene

Chloride

Copolymers

85

TABLE I 13

C

8

Chemical S h i f t s " f o r VC1-VC1 _ Structure *CHCl

Copolymers

6C

(ppm)

b

55.21, 55.12 5 ^ . 3 5 , 5^.19 53.1+8 53.35 53.22

rr mr mmmm mmmr rmmr CHCl^CHsCHCl

13

rrr rmr rrm mmr + mrm mmm *CC1

2

1+5.80 h^.hl 1+5.07 1+1+. 39 1+3.65

2

isolated paired > paired

87.50 85.09 82.83

CC1 *CH -R 2

2

R = CHC1 R = CCI > paired

a

b

52.33 6O.U9 -53-55

r e l a t i v e t o hexamethgldisiloxane (HMDS), measured i n 1,2,1+,-trichlorobenzene at 373 Κ reference 1


86

POLYMER

CHARACTERIZATION

B Y ESR A N D N M R

TABLE I I

Vinyl

E q u a t i o n s t o C a l c u l a t e Monomer C o m p o s i t i o n o f C h l oorrii dd ee - V i n y l i d e n e C h l o r i dd e C o p o l y m e r s from C NMR A r e a s 1 3

M o l e V C l = P V C ( C H C l ) = ( a r e a CHC1Ï [ ( i s o l a t e d CC1

^_ t o t a l region CC1 + 0.5 (outer CC1

+ (isolated

2

2

VCl

+ 0 . 5 ( o u t e r CC1 (1) :

vLJ

2

VO±

2

2

m o i s ( V C l ) = PVC ( C H C l ) = ( a r e a C H C l ) . . . . t o t a l region

2 ( i s o l a t e d CC1 area) - (outer CC1 area) 2

(2) :

m o i s ( V C l ) = PVC ( C H C l ) = ( a r e a C H C l )

[isolated (inner (3) :

2

CC1 )

+ 0.5 (outer CC1

™

2

t o t a l

)JJJ

a

2

r

e

g

i

o

n

+ (total

CC1

)*™* -

2

CH )J£*] 2

a r e a

i

s

ψ = ( t o t a l CC1 - inner C H ) ~ ( cci ) m o i s V C l = PVC ( C H ) = ( a r e a C H ) + ψ (e.g. s h i f t e d V C l (CH )) 2

a

r

e

o

2

l

a

t

e

d

C C 1

+

*

o

u

t

e

r

a

2

(h):

2

2

2

(5):

m o i s V C 1 = V C 1 (CC1 ) = ( a r e a C C 1 ) . . _ t o t a l region 2

2

2

1 = 2 = 4 or_ t a k e (6):

mois V C 3

2

average a

= V C 1 (CH ) = (inner C H ) ^

2

2

2

V L l

area vci 2

. +

°-

5

(

o

u

„ t

e

r

u

C

l

η Ί 2

)

+ (isolated

2

^area vci 2

mol.

wt. V C l = 6 2 . 5 ; wt. % CI = 5 6 . 6

mol.

wt. V C 1 = 9 7 . 0 ; wt. % C I = 73.2

5 = 6 or take

a

2

2

average


CC1 ) 2


i s 1;

VC1

2

1, .7 2,,2 10, .1 26, .6

A Β C D

VCl

Mol % VC1

Sample

2

C

is 0

56.9 57.1 59.0 62.5

( c)

1 3

TABLE I I I

b — n 0

= N

101 ioi

Ν +

(

0

+ Ν

5 5 . 7 8 , 55.85 5 8 . 6 7 , 58.29 -

(vet)

Wt. % C l

) N

(001) 0 0 0.33 0.U2

(101) 1.0 1.0 0.63 0.U5

0 0 0.0U 0.12

(000)

Distribution

Copolymers

+ Ν 001 000 · ooi 5

2

Relative Triad

NMR A n a l y s i s o f V C 1 - V C 1

Wt. % C l

1 3

3 ,

o

1.00 1.00 1.26 1.50

Observed^

n

88

POLYMER

CHARACTERIZATION

B Y ESR A N D N M R

F o u r V C 1 - V 0 1 c o p o l y m e r s were a n a l y z e d and t h e r e s u l t s a r e summarized i n T a b l e T T I . The i n t e r n a ] , c o n s i s t e n c y c h e c k s from T a b l e I I h e l d . The r e s u l t i n g c h l o r i n e a n a l y s i s ^ o r sample C a g r e e d v e r y w e l l w i t h t h e wet a n a l y t i c a l r e s u l t s . The d i s c r e p a n c y i n sample Λ s u g g e s t s t h e wet r e s u l t s a r e i n e r r o r as t h e r e p o r t e d v a l u e s were l e s s t h a n t h e PVC t h e o r e t i c a l v a l u e . Using t h e observed t r i a d c o n c e n t r a t i o n s i n Table I I I , t h e number a v e r a g e s e q u e n c e l e n g t h s f o r t h e V C 1 monomer were c a l culated using the equation: 2

2

5

Π

Ν + Ν + Ν 101 001 000

=

° " ιοι Ν

°·

+

5

Ν

οοι

/η

ν

'

The o b s e r v e d number a v e r a g e s e q u e n c e l e n g t h s d e v i a t e from t h o s e p r e d i c t e d from B e r n o u l l i a n s t a t i s t i c s , i . e . , n ^ = l/[VCl]„ However, c o r r e s p o n d i n g c a l c u l a t i o n s b a s e d on f i r s t o r d e r M a r k o v i a n s t a t i s t i c s a r e i n e x c e l l e n t agreement. To c a l c u l a t e t h e number a v e r a g e s e q u e n c e l e n g t h u s i n g f i r s t o r d e r _ M a r k o v i a n s t a t i s t i c s , i t i s n e c e s s a r y t o e s t i m a t e PQ^> (for n = l/pg^). The i n f o r m a t i o n t h a t c a n be measured f r o m t h e s p e c t r a i n F i g u r e 1 i s monad and t r i a d c o n c e n t r a t i o n s : ( θ ) , ( l ) , ( 1 0 1 ) , ( 0 0 1 ) , and ( 0 0 0 ) . In this notation vinyl chloridei s r e p r e s e n t e d b y ( ] ) o r v i n y l i d e n e c h l o r i d e b y (θ). U s i n g t h e s e m e a s u r a b l e s t r u c t u r e s an e s t i m a t e f o r ρ was d e r i v e d u s i n g an approach suggested by R a n d a l l - f o r t h e d e t e r m i n a t i o n o f sequence d i s t r i b u t i o n f o r hydrogenated polybutadienes. T h i s can be a c c o m p l i s h e d i n t w o ways; f r o m t h e r a t i o o f ( l 0 l ) / ( 0 0 l ) and f r o m the r a t i o o f ( l 0 l ) / ( 0 ) . E q u a t i o n s (2) t h r o u g h (5) d e s c r i b e t h e o b s e r v a b l e s t r u c t u r e s i n terms o f t r a n s i t i o n p r o b a b i l i t i e s : Q

000 = p 1

0

1

=

001

^

OI

) 2

= 2(p

O = P

^01

( P

1 0

/

o i

PIO

• p

2

(l-P

1 0

) /(p

0 1

/ {

P I

+

0

0 1

+P

1 0

/

(2) (

i o

0 1

)

V

) (P ) ( I - P

Combing t h e s e e q u a t i o n s e n a b l e s one t o e s t i m a t e v a l u e s f o r ^-^ °f two r a t i o s shown as f o l l o w s : r o m

e

n e r

(101)/(001)

= P

(l0l)/(0) - ( p

0 1

0 1

/2(l-P

)

0 1

(6)

)

2

(7)

T a b l e I V shows t h e s e r a t i o s f o r t h e f o u r VC1-VC1 c o p o l y mers. The v a l u e f o r ρ can be c a l c u l a t e d u s i n g b o t h e q u a t i o n s f o r s a m p l e s C and D, a n a a r e i n good a g r e e m e n t . As seen i n 2


Woodward and Bovey; Polymer Characterization by ESR and NMR ACS Symposium Series; American Chemical Society: Washington, DC, 1980. 0.79 0.67

0.79 0.68

1, ,00 0, .630 0. Mi

-

1.909

1.071

Β

C

D

Ό

=

1 / P

01

'calculated

using equation

6

a b s o l u t e c o n c e n t r a t i o n need f o r t h i s r a t i o i s p r o d u c t o f (101) f r o m T a b l e I I I and m o l f r a c t i o n V C 1 2

=

1/

Pl

1. .50

1. ,36

1.1*8

calculated using equation 7

Q

1. ,26

1. ,11

1.26

n

1. ,00

1. ,02

1.00 1.00

Observed

1. ,00

b

Spectra

Bernoullian

C NMR

1 3

1. ,02

n

1.00

01

— e o

1.00

P

-

01

1. ,00

P

d

-

c

Order Markovian

A

1st

(lOl)/(0)

(l0l)/(00l)

a

Sequence L e n g t h s C a l c u l a t e d f r o m

Sample

Number A v e r a g e

TABLE I V

90

POLYMER CHARACTERIZATION BY ESR AND NMR

Table IV, the resulting calculation of VC1 number average se quence length calculated using the first order Markov agrees very well with the observed sequence lengths. There is another way to confirm that the triad distribution cannot result from a random -polymerization. The observed rela tive proportion of the triad structure in Figure Id is (l):(.93):(.26). The corresponding distribution for the triad structure for .266 mole fraction VC1 would be (1):(.36):(.13). Obviously, this comparison confirms from just a consideration of the triad distribution that the polymer does not conform to Bernoullian statistics. The data shown in Tables III and TV show that the C nmr spectra of vinyl chloride-vinylidene chloride copolymers have a redundancy of structural relationships. By analyzing a range of compositions, this system has been found to yield a reasonable description of both monomer composition and monomer sequence distribution. The data also show that this copolymer is a good example of a system best described by first order Markovian statistics as com/oared to Bernoullian statistics. 2

2

1 3

Py-npri m ρ η-f^ η η 1 3

The C nmr spectra were obtained at 22.6 MHz using a Bruker HX90E spectrometer from ho -percent polymer solutions in 1,2,1+trichlorobenzene at 3T3K. The sr>ectral conditions were: π/2 (25ys) , 6 kHz sweepwidth, 16 k fid, 1.5 Hz line broadening, 5 sec rep, rate, number of scans to give good S/N, (usually about 6000), Perdeuterobenzene was added as internal lock. Compositions were calculated from electronic integrals. Acknowledgements I would like to thank M. L. Dannis for supplying the poly mers and R. F. Scourfield for obtaining the nmr spectra. Thanks is also given to The BFGoodrich Company for permission to publish this work. Abstract Carbon-13 nuclear magnetic resonance was used to determine the molecular structure of four copolymers of vinyl chloride and vinylidene chloride. The spectra were used to determine both monomer composition and sequence distribution. Good agreement was found between the chlorine analysis determined from wet analysis and the chlorine analysis determined by the C nmr method. The number average sequence length for vinylidene chloride measured from the spectra fit first order Markovian statistics rather than Bernoullian. The chemical shifts in these copolymers as well as their changes in areas as a function of monomer composition enable these copolymers to serve as model 13


5. CARMAN

Vinyl Chloride-V inylidene Chloride Copolymers 91

compounds for making structural assignments in other chlorinated polymers. Literature Cited 1. C. J. Carman, Macromolecules, 6, 725 (1973). 2. C. E. Wilkes, J. Polym. Sci., Polymer Symposium 60, 161 (1977). 3. F. Keller, Plaste U. Kautschuk, 23, 730 (1976); B. Hosselbarth and F. Keller, Faserforsch. u. Textiltechnik/Z. Polymerforsch., 28, 325 (1971); F. Keller and C. Mugge, ibid, 27, 347 (1976); F. Keller, S. Zepnik, and B. Hosselbarth, ibid, 29, 29 (1978). 4. F. Keller and B. Hosselbarth, Faserforsch. u. Textiltechnik Z. Polymerforsch., 26, 329 (1975); ibid, 27, 453 (1976); ibid, 28 287 (1977); R. Lukas, M. Kolinsky, D. Doskocilova, J. Polym. Sci., 16, 889 (1978). 5. J. C. Randall, "Polymer Sequence Determination: Carbon-13 NMR Method", Academic Press, New York, 1977. 6. J. C. Randall, J. Polym. Sci., Polym. Phys. Ed. 13, 1975 (1975). RECEIVED May 21, 1980.


Molecular Structure of Vinyl ChlorideVinylidene Chloride Copolymers

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