Cellulose ViscosityâMolecular-Weight Relationships by Gel

5

Downloaded by UNIV OF NEW SOUTH WALES on September 18, 2015 | http://pubs.acs.org Publication Date: April 21, 1981 | doi: 10.1021/bk-1981-0150.ch005

Cellulose Viscosity-Molecular-Weight Relationships by Gel Permeation ChromatographyLow-Angle Laser Light Scattering J. J. C A E L , R. E . CANNON, and A. O. DIGGS International Paper Company, Corporate Research Center, P.O. Box 797, Tuxedo Park, N Y 10987 For years the determination o f polymer molecular weights has served as an important process and q u a l i t y c o n t r o l parameter as many f i n a l end use and p h y s i c a l p r o p e r t i e s o f the polymer are c l o s e l y r e l a t e d t o i t s molecular weight and/or molecular weight d i s t r i b u t i o n (MWD). H i s t o r i c a l l y , such methods as membrane osmometry, l i g h t s c a t t e r i n g , e t c . have achieved considerable u t i l i t y i n determining polymer molecular weights (e.g. number and weight-average). A t best, a knowledge o f each o f these averages f o r a given polymer y i e l d s i n f o r m a t i o n on the breadth o f the d i s t r i b u t i o n ; however, the a c t u a l d i s t r i b u t i o n i s unknown and can only be i n f e r r e d . For MWD determinations, g e l permeation chromatography (GPC) has gained wide acceptance as a p r e f e r r e d method. I t i s a l i q u i d chromatographic technique based upon the p r i n c i p l e o f s i z e e x c l u s i o n whereby a macromolecule i s separated on the b a s i s o f molecular s i z e o r hydrodynamic volume i n d i l u t e s o l u t i o n . T h i s i s achieved by the a c t i o n o f v a r i o u s column packing m a t e r i a l s having c o n t r o l l e d , pore s i z e d i s t r i b u t i o n s . The weight f r a c t i o n or c o n c e n t r a t i o n o f polymer e l u t e d during the s e p a r a t i o n process i s measured by a c o n c e n t r a t i o n s e n s i t i v e d e t e c t o r (e.g. UV, IR, or d i f f e r e n t i a l r e f r a c t o m e t e r ) . In conventional GPG the raw data represent the e l u t i o n volume d i s t r i b u t i o n o f the polymer sample by weight, and as a r e s u l t , a transformation t o molecular weights i s r e q u i r e d . T h i s , i s g e n e r a l l y achieved by a c a l i b r a t i o n procedure which uses Mark-Houwink c o e f f i c i e n t s (K and «) d e r i v e d from both the polymer under i n v e s t i g a t i o n and u s u a l l y narrow d i s t r i b u t i o n , p o l y s t y r e n e standards. The accuracy o f MWD data and a s s o c i a t e d molecular weight averages obtained from such a c a l i b r a t i o n method can be q u i t e v a r i a b l e and i s u l t i m a t e l y dependent upon the c o r r e c t n e s s o f K and f o r the polymer/solvent pair. a

In the pulp and paper i n d u s t r y , GPC has been a p p l i e d not only i n measuring c e l l u l o s e molecular weights and MWDs, but a l s o i n f o l l o w i n g i t s degradation as a consequence o f v a r i o u s p u l p i n g , b l e a c h i n g and v i s c o s e processes. In the i n i t i a l a p p l i c a t i o n s o f 0097-6156/81/0150-0043$05.00/0 © 1981 American Chemical Society

In Solution Properties of Polysaccharides; Brant, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


44

SOLUTION PROPERTIES OF

POLYSACCHARIDES

GPC to study c e l l u l o s e , c e l l u l o s e t r i n i t r a t e d e r i v a t i v e was employed (1, 2). While t h i s d e r i v a t i v e i s s o l u b l e i n a wide range of organic s o l v e n t s commonly used i n GPC, the use of the t r i n i t r a t e has s e v e r a l disadvantages C_3). F i r s t , the n i t r a t i o n procedure can cause s i g n i f i c a n t chain s c i s s i o n , thereby causing the MWD of the t r i n i t r a t e to d i f f e r from that of the underivatized cellulose. In a d d i t i o n , the s t a b i l i t y of the t r i n i t r a t e i s l i m i t e d , and there can a l s o be c o n s i d e r a b l e v a r i a b i l i t y i n the degree o f s u b s t i t u t i o n . The l a t t e r e f f e c t i s r a t h e r c r i t i c a l as both the GPC d e t e c t o r output and polymer hydrodynamic volume are a f u n c t i o n of the degree of s u b s t i t u t i o n . Recently, v a r i o u s workers have proposed that the c e l l u l o s e t r i c a r b a n i l a t e (CTC) d e r i v a t i v e be employed i n GPC a p p l i c a t i o n s (3_, 4_, _5, 6) . T h i s d e r i v a t i v e i s s t a b l e and complete t r i s u b s t i t u t i o n i s obtained. More importantly, degradation during the d e r i v a t i z a t i o n i s bel i e v e d to be e l i m i n a t e d . The s t r u c t u r a l formula f o r CTC i s shown i n F i g u r e 1. I d e a l l y , the most accurate way to determine the MWD o f a polymer by GPC i s to l i n k a molecular weight d e t e c t o r to the o u t l e t of the l a s t GPC column. To accomplish t h i s , we have c o n f i g u r e d a low angle l a s e r l i g h t s c a t t e r i n g (LALLS) photometer t o the GPC apparatus. Two inherent design f e a t u r e s f a c i l i t a t e i t s use i n absolute MWD determinations. The f i r s t i s the a b i l i t y to measure the i n t e n s i t y of s c a t t e r e d r a d i a t i o n a t angles as low as 2-3 from the primary beam, thereby circumventing the angular e x t r a p o l a t i o n of data to zero angle such as r e q u i r e d i n a Zimm p l o t (7). The second f e a t u r e i s the 0.008 ml flow-through sample c e l l which minimizes both post-column s o l u t e mixing and homodyne b e a t i n g e f f e c t s . An a d d i t i o n a l consequence of t h i s c o n f i g u r a t i o n i s the a b i l i t y to determine Mark-Houwink coeff i c i e n t s on broad MWD l i n e a r homopolymers without recourse to f r a c t i o n a l p r e c i p i t a t i o n and i n t r i n s i c v i s c o s i t y procedures. Ins trumentation F i g u r e 2 shows a schematic of the GPC/LALLS system. The GPC instrument i s a Waters A s s o c i a t e s model ALC-201 high pressure l i q u i d chromatograph having ^our y - S t y r a g e l columns^ connected i n s e r i e s with p o r o s i t i e s of 10 A, 10 A, 10 A, and 10 A. Connected to the l a s t GPC column i s a Chromatix KMX-6 low angle l a s e r l i g h t s c a t t e r i n g photometer u t i l i z i n g p o l a r i z e d r a d i a t i o n from a 2.0 mW HeNe l a s e r a t 632.8 nm. D e t a i l s of the LALLS photometer and i t s o p t i c a l system have been d e s c r i b e d elsewhere (8) . In order to measure the c o n c e n t r a t i o n of s o l u t e e l u t i n g from the GPC columns, the o u t l e t of the LALLS 0.008 ml flow-through c e l l i s connected to a V a r i a n VARI-CHROM v a r i a b l e wavelength UV d e t e c t o r o p e r a t i n g a t 254 nm. A l l connections u t i l i z e d 1/16" s t a i n l e s s s t e e l tubing having an i n t e r n a l diameter of 0.008" with low dead-volume, Luer type f i t t i n g s i n order to minimize mixing effects.


Cellulose


CAEL ET AL.

45

Viscosity

Figure 1. -

H

O

DUAL PEN STRIP CHART RECORDER

SOLVENT RESERVOIR

SOLVENT PUMP

Structural formula for cellulose tricarbanilate

SAMPLE LOOP

GPC COLUMNS

LALLS PHOTOMETER

VARIABLE WAVELENGTH UV. DETECTOR

SOLVENT WASTE

INITIALIZE DATA ACQUISITION

CENTRONICS PRINTER/PLOTTER USER KEYBOARD

ANALOG/DIGITAL CONVERTER

LSI 11 MICROPROCESSOR 28K RAM

DUAL FLOPPY DISK STORAGE

CALCOMP DIGITAL INCREMENTAL PLOTTER

Figure 2.

Schematic of the GPC/LALLS

configuration


46


POLYSACCHARIDES

For o n - l i n e data a c q u i s i t i o n and a n a l y s i s the analog s i g n a l s from both LALLS and UV d e t e c t o r s are d i g i t i z e d by a Chromatix LDS-2 l a b o r a t o r y data system. The e s s e n t i a l components of t h i s system are a D i g i t a l Equipment LSI-11 microprocessor having 28K words of random access memory, a FORTRAN compiler, a Centronics dot matrix p r i n t e r / p l o t t e r and a dual floppy d i s k f o r mass storage. In a d d i t i o n , we have i n t e r f a c e d to t h i s c o n f i g u r a t i o n a Calcomp model 1012 four-pen d i g i t a l incremental p l o t t e r which p r o v i d e s added f l e x i b i l i t y i n the p r e s e n t a t i o n o f r e s u l t s .


M a t e r i a l s and Methods A l l c e l l u l o s e samples used i n t h i s work were d e r i v e d from bleached, hardwood k r a f t pulps having a h e m i c e l l u l o s e content of 2% or l e s s . The b a s i c procedure used f o r the p r e p a r a t i o n o f CTC d e r i v a t i v e s i s to r e a c t the c e l l u l o s e with phenyl!socyanate i n p y r i d i n e C3* _4, 6) a t 80 C (9) . T y p i c a l l y , 0.5 grams of dry c e l l u l o s e i s added to 540 ml o f anhydrous p y r i d i n e followed by slow a d d i t i o n o f excess phenylisocyanate. A f t e r r e a c t i n g f o r 16-24 hours, the s o l u t i o n i s cooled to 70 C, and 40 ml of methanol i s added i n order to remove unreacted phenylisocyanate. The CTC i s i s o l a t e d by p r e c i p i t i t i o n i n t o and washing by methanol, followed by d i s s o l u t i o n i n t o acetone, p r e c i p i t a t i o n i n t o water, and subsequent vacuum d r y i n g . The n i t r o g e n content of a l l CTC p r e p a r a t i o n s was determined by the semi-micro K j e l d a h l method i n order to assess the degree of s u b s t i t u t i o n . A l l samples had n i t r o g e n contents i n the range 7.89-8.06% ( t h e o r e t i c a l content 8.08%) which corresponds to degrees o f s u b s t i t u t i o n from 2.91 to 2.99. For both GPC/LALLS and i n t r i n s i c v i s c o s i t y measurements, Burdick & Jackson d i s t i l l e d - i n - g l a s s , UV grade t e t r a h y d r o f u r a n (THF) was used. GPC/LALLS experiments were conducted a t a constant, p u l s e - f r e e s o l v e n t f l o w - r a t e of 1.0 ml/min. Solute concentrations were 0.1% (w/vol.) and the volume o f i n j e c t e d s o l u t i o n ranged from 0.3 ml to 0.5 ml. Intrinsic viscosities f o r CTC i n THF were measured a t 25°C i n a Cannon-Ubbelhode f o u r bulb shear d i l u t i o n c a p i l l a r y viscometer (Size 50). Kinetic energy c o r r e c t i o n s were n e g l i g i b l e and the data were c o r r e c t e d f o r shear e f f e c t s by e x t r a p o l a t i o n of n /c to zero shear r a t e (io).

s

p

GPC/LALLS Methodology For a macromolecule i n d i l u t e s o l u t i o n i n a one-component s o l v e n t , the r e l a t i o n s h i p between the excess Rayleigh f a c t o r and the weight-average molecular weight, M , i s given by the f l u c t u a t i o n theory of l i g h t s c a t t e r i n g (11) as Kc/R(0,c) = 1/M

2

P(0) + 2A c/P(0) + 3A c /P(9) +


(1)

5.

CAEL E T AL.

Cellulose

Viscosity.

41

where K=

2

2

C2TT n /^N) Cdn/dc)

2

2

(l+cos 0)

C2)

and c i s the s o l u t e concentration i n g/ml, R(0,c) i s the excess Rayleigh f a c t o r f o r unpolarized i n c i d e n t r a d i a t i o n a t the s c a t t e r i n g angle 0, n i s the r e f r a c t i v e index o f the s o l u t i o n , X i s the wavelength i n vacuo, N i s Avogadro's number, while A and A are the second and t h i r d v i r i a l c o e f f i c i a n t s . The term P(0) i s the form f a c t o r which i s a f u n c t i o n o f the s i z e and shape o f the macromolecule i n s o l u t i o n and represents the modul a t i o n o f the i n t e n s i t y o f s c a t t e r e d r a d i a t i o n due to the f i n i t e s i z e o f the molecule and t o i t s d e v i a t i o n from s p h e r i c i t y . The term dn/dc i s the s p e c i f i c r e f r a c t i v e index increment and represents the change i n s o l u t i o n r e f r a c t i v e index as a f u n c t i o n o f s o l u t e concentration. I f experiments are conducted i n the l i m i t of zero s c a t t e r i n g angle where P(0) = 1 as w e l l as a t s u f f i c i e n t l y low concentrations where only the second v i r i a l c o e f f i c i e n t need be considered, then eq. (1) reduces t o q


2

Kc/R(0,c) = 1/M + 2A„c w 2

(3)

For the determination o f molecular weights and a s s o c i a t e d MWDs, both A^ and dn/dc are measured i n advance. Although the c e l l u l o s e specimens used i n t h i s a n a l y s i s have c h a r a c t e r i s t i c broad MWDs W^/M^ = 1.8-4.0), a s i n g l e determination o f A from a r e p r e s e n t a t i v e CTC p r e p a r a t i o n was considered appropriate f o r a l l subsequent determinations of M and the MWD. T h i s was achieved by using the LALLS photometer o f f - l i n e and by extrapol a t i n g s c a t t e r i n g data from a d i l u t i o n s e r i e s at © = 4*5-5^ usjing eq. (3). The value o f determined was 3.5 x 10 ml-mole/g Likewise, dn/dc was determined f o r the same CTC p r e p a r a t i o n i n THF a t 632.8 nm on a Chromatix KMX-16 l a s e r d i f f e r e n t i a l r e f r a c tometer, and r e s u l t e d i n a value o f 0.163 ml/g. In F i g u r e 3 are shown computer p l o t s o f the UV and LALLS detector response curves as a f u n c t i o n o f e l u t i o n volume f o r a r e p r e s e n t a t i v e CTC. One obvious feature i s the r e l a t i v e d i f ference i n the response of the two detectors as the sample molecular weight decreases with i n c r e a s i n g e l u t i o n volume. T h i s i s a consequence o f the f a c t that the UV absorbance i s a l i n e a r f u n c t i o n o f the s o l u t e concentration while R(0,c) i s a f u n c t i o n o f both concentration and molecular weight. The molecular weight o f s o l u t e e l u t i n g w i t h i n a given volume element i s c a l c u l a t e d from a form of eq. (3) 4

Kc./R(e c.) = 1/M f

+ 2A c 2

(4)

jL

The concentration o f s o l u t e a t the i

t

h

p o i n t i s given by

c. = mx./CV.Sx.) I i l l

(5)

American Chemical Society Library 1155

16th St. N . W .

In Solution Properties of Polysaccharides; Brant, D.; Washington, D. G. 20038 ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

48


POLYSACCHARIDES

where m i s the t o t a l mass of s o l u t e i n j e c t e d , V. i s the volume of s o l u t i o n corresponding to the i volume element, and x. i s the amplitude of the UV s i g n a l a t V.. T y p i c a l l y , 100 values of M. are c a l c u l a t e d across the chromatogram which allow number, weight, and z-average molecular weights to be determined from the r e l a t i o n s M

n

= Ec./Z(c./M.) i l l

(6)

M

= Zc.M./Zc. (7) 1 1 1 2 M = Zc.M. /Ic.M. (8) z 11 11 In a d d i t i o n , both d i f f e r e n t i a l and i n t e g r a l absolute molecular weight d i s t r i b u t i o n s can be generated as shown i n F i g u r e 4a and b, r e s p e c t i v e l y . I t should be pointed out that i n the c a l c u l a t i o n of M. by eq. (4), the assumption i s made £|j t the resol u t i o n of columns i s p e r f e c t and that each i f r a c t i o n which e l u t e s i s monodisperse i n molecular weight. In a c t u a l i t y , M. i s a weighted average due to both the f i n i t e r e s o l u t i o n charact e r i s t i c s of the columns and to mixing e f f e c t s which can occur i n each of the UV and LALLS d e t e c t o r c e l l s . While t h i s does not e f f e c t the accuracy of M , the d e r i v e d values f o r M and will tend to be somewhat g r e a t e r and l e s s than t h e i r true values, respectively.


w

a

Results and D i s c u s s i o n Accuracy and R e p r o d u c i b i l i t y of GPC/LALLS. In Table I are shown molecular weight averages obtained from four successive analyses of the same CTC sample i n order to assess the r e l a t i v e accuracy and consistency o f the GPC/LALLS technique. As can be seen, the r e p r o d u c i b i l i t y of the technique i s q u i t e good with the average TABLE I REPRODUCIBILITY OF GPC/LALLS Run # 1 2 3 4 Average =

M

n

M

w

M

z

331,269 318,615 320,666 319,534

577,855 579,268 581,239 583,255

1,035,150 1,016,520 1,024,100 1,015,190

322,521±2%

580,404±0.5%

1,022,74011.2%

e r r o r of measurement ranging from 2% f o r M to 0.5% f o r M . S i m i l a r l y , i n F i g u r e 5 i s shown the agreement between determined by GPC/LALLS and the corresponding zero shear i n t r i n s i c


CAEL E T A L .

Cellulose

Viscosity

(A)


0C >

(B)

Elution Volume (ml)

Figure 3.

10*

Experimental UV(A) and LALLS (B)detector response curves for CTC in THF

10

5

10

6

Molecular Weight

Figure 4.

10?

10*

10

5

10

6

10?

Molecular Weight

Differential (A) and integral (B) molecular-weight distributions derived from the data of Figure 3


50

SOLUTION PROPERTIES O F POLYSACCHARIDES

v i s c o s i t y obtained from a s e r i e s o f CTC p r e p a r a t i o n s covering a wide range o f sample molecular weights and having v a r i a b l e MWDs. In T a b l e I I , the values o f M obtained by both GPC/LALLS and i n t r i n s i c v i s c o s i t y methods are compared. As can be seen from F i g u r e 5, the values o f M determined by GPC/LALLS c o r r e l a t e TABLE I I


tple 1 2 3 4 5 6 7 8 9

[n]

w

M ° w

2,170,000 1,768,200 1,466,300 1,386,200 1,166,700 1,026,000 601,000 463,800 302,100

2,025,000 1,282,400 1,147,500 992,200 910,900 783,700 528,800 461,800 285,700

a

881.0 716.2 652.3 577.3 537.4 473.5 340.3 303.7 202.9

^zero shear v i s c o s i t y (ml/g) i n THF a t 25 C from GPC/LALLS °from the r e l a t i o n [n] = KM* with K = 0.0053 and « = 0.84 (.6) w e l l with the measured i n t r i n s i c v i s c o s i t i e s ; however, i n a l l cases the M d e r i v e d from GPC/LALLS i s s y s t e m a t i c a l l y l a r g e r than those determined from the Mark-Houwink r e l a t i o n s h i p . Although the use o f a s i n g l e valued A^ f o r the c a l c u l a t i o n o f M. throughout the MWD can be expected t o introduce some u n c e r t a i n t y i n the der i v e d molecular weight averages, we do not expect the d i f f e r e n c e s t o be o f the magnitude observed from the data o f Table I I . Rather, we b e l i e v e the d i f f e r e n c e s i n molecular weight a r i s i n g from these two techniques are a consequence o f inherent e r r o r s i n K and « f o r CTC i n THF, s i n c e t h e i r accuracy i s dependent i d e a l l y upon the a b i l i t y t o e s t a b l i s h a l o g [n] v s . l o g M r e l a t i o n s h i p from monodisperse f r a c t i o n s o f the polymer. Convent i o n a l f r a c t i o n a l p r e c i p i t a t i o n methods r a r e l y ever achieve monod i s p e r s i t y o f the order a t t a i n a b l e from a n i o n i c p o l y m e r i z a t i o n , and i t i s not uncommon f o r e r r o r s o f 10% i n K and to r e s u l t i n a 20% e r r o r i n the d e r i v e d molecular weight. Likewise, while i s not s t r o n g l y dependent on such d i s p e r s i o n e f f e c t s , the value o f K i s c o n s i d e r a b l y more s e n s i t i v e due to the long e x t r a p o l a t i o n of data to v a n i s h i n g molecular weight. a

a

Determination o f K and « from GPC/LALLS. The major assumption i n h e r e n t i n u s i n g GPC f o r the determination o f polymer molecular weights and MWDs i s t h a t i n s o l u t i o n the macromolecule i s chromat o g r a p h i c a l l y f r a c t i o n a t e d according to i t s hydrodynamic volume. Unless monodisperse f r a c t i o n s o f the polymer i n question are a v a i l a b l e , one g e n e r a l l y c a l i b r a t e s the GPC system by chromato-


5.

CAEL

E T AL.

Cellulose

51

Viscosity

graphing a s e r i e s o f a n i o n i c a l l y polymerized polystyrene (PS) standards which span s e v e r a l decades o f molecular weight and which have n e a r l y monodisperse d i s t r i b u t i o n s . Using t h i s procedure most commercial GPC columns allow a l i n e a r r e l a t i o n s h i p between l o g M vs. e l u t i o n volume (V) such that


log M

p s

= a + b*V

(9)

where a and b represent the y - a x i s i n t e r c e p t and slope o f the l o g M vs. V p l o t . To convert the polystyrene c a l i b r a t i o n p l o t i n t o a c e l l u l o s e t r i c a r b a n i l a t e p l o t , use i s made o f the theory of F l o r y and Fox (11) i n which the hydrodynamic volume o f a polymer i n d i l u t e s o l u t i o n i s r e l a t e d t o i t s molecular weight and i n t r i n s i c v i s c o s i t y by a u n i v e r s a l constant, 0: 2 3/2 hydrodynamic volume = [n]M = © (R ) g

(10)

2 and (R ) i s the mean square r a d i u s o f g y r a t i o n . From the assumpt i o n t n a t under the same experimental c o n d i t i o n s d i f f e r e n t p o l y mers having the same hydrodynamic volume w i l l be e l u t e d from the columns w i t h i n the same volume element, [

R

L

] P

S

"PS -

[Tll

M

c r c crc

and the s u b s c r i p t s r e f e r t o the p a r t i c u l a r molecular s p e c i e s . S u b s t i t u t i o n o f the Mark-Houwink r e l a t i o n f o r [n] i n eq. C l l ) yields 1+oc l+oc K M_ = K_ M _ (12) PS PS CTC CTC P

S

C

T

C

which upon l o g a r i t h m i c transformation r e s u l t s i n the r e l a t i o n log M _ CTC

log

PS

+ C1+* ) l o g M^ - l o g K PS PS * CTC • — — n

(13)

^crc As a r e s u l t o f eqs. (9-13), each PS molecular weight standard can be converted through use o f Mark-Houwink c o e f f i c i e n t s from PS and CTC i n t o a corresponding CTC molecular weight. These CTC molecular weights form the b a s i s o f a new c a l i b r a t i o n curve log ^

CTC

= a ' +b

(.14)

where a " and b ^ have the same meanings as i n eq. (9) but are primed so as t o d i s t i n g u i s h them from the PS c o e f f i c i e n t s . In F i g u r e 6 i s shown the c a l i b r a t i o n curve f o r CTC i n THF which r e s u l t s from eq. (13). The Mark-Houwink c o e f f i c i e n t s used f o r i t s generation are K = 0.00203, « = 0.678 f o r p o l y s t y r e n e (_4) and K = 0.0053, « = 0.84 f o r CTC (6). A l s o d e p i c t e d i s the corresponding CTC molecular weight data obtained from a s i n g l e , broad d i s t r i b u t i o n sample by GPC/LALLS. With the exception o f


52

SOLUTION PROPERTIES O F

POLYSACCHARIDES


the

low molecular weight r e g i o n o f the d i s t r i b u t i o n ( i . e .

x = log K and

log M

p

b = -log K

PS

a

cr c

/(i+ ) ere'

i t i s p o s s i b l e from a p l o t o f l o g M vs. x to c a l c u l a t e K and f o r CTC i n THF from a s i n g l e broad MWD sample which has been c h r o m a t i c a l l y f r a c t i o n a t e d . T h i s i s achieved by t a k i n g a p p r o p r i ate values o f M from the l i n e a r r e g i o n o f the GPC/LALLS data of F i g u r e 6 and a s s o c i a t i n g them with the corresponding molecular weights o f the p o l y s t y r e n e c a l i b r a t i o n standards ( i . e . p a i r w i s e values o f M^^ and M^„ are those which e l u t e w i t h i n the same CT C PS volume element). Values o f K and r e s u l t i n g from t h i s procedure are shown i n Table I I I which a l s o compares p u b l i s h e d values a

TABLE I I I COMPARISON OF MARK-HOUWINK COEFFICIENTS FOR CTC IN THF K

«

0.0043 0.0053 0.00201 0.00251

0.84 0.84 0.92 0.89

Method

Reference

GPC/LALLS t h i s work viscosity/light scattering (6) viscosity/light scattering (3) viscosity/light scattering C4)

determined by other workers. We have repeated t h i s procedure on a number o f CTC preparat i o n s and have found i n v a r i a b l y e x c e l l e n t superimposition o f GPC/LALLS molecular weight data i n the l i n e a r domain o f the l o g CTC " l volume p l o t o f F i g u r e 6, which we view as i n d i c a t i v e o f the accuracy o f the derived K and . C e r t a i n l y , our success with t h i s method i s due i n p a r t t o the use o f narrow d i s t r i b u t i o n p o l y s t y r e n e standards i n which K, «, and a s s o c i a t e d M

V S

e

u

t

i

o

n

a



Figure 5.

Correlation of M w

w

(GPC/LALLS)

determined by GPC/LALLS and measured zero shear intrinsic viscosity in THF for broad-distribution CTC

log M


54


SOLUTION PROPERTIES O F POLYSACCHARIDES

J 22

I

I

I

I

L

24

26

28

30

32

Elution Volume (ml) Figure 6.

Comparison of GPC calibration curves for CTC derived from intrinsic viscosity (WhM-)

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