Polymerization and Dilute Solution Characterization of Poly

13

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Polymerization and Dilute Solution Characterization of Poly(dichlorophosphazene) G A R Y L. H A G N A U E R Polymer Research Division, Army Materials and Mechanics Research Center, Watertown, MA 02172

The high temperature, melt p o l y m e r i z a t i o n of h e x a c h l o r o c y c l o triphosphazene (I) t o polydichlorophosphazene [ N P C I 2 ] was first reported i n 1897 ( 1 ) . The polymer was u s u a l l y obtained as a c r o s s l i n k e d m a t r i x ( I I I ) and had many o f t h e p r o p e r t i e s o f a good elastomer (Tg = -66°C) except t h a t i t was h y d r o l y t i c a l l y unstable. Upon exposure t o moist a i r , t h e P-Cl bonds hydrolyze and t h e polymer g r a d u a l l y degrades t o phosphoric a c i d and ammonia. I f the polymer i s swollen i n an organic s o l v e n t and water i s added, the h y d r o l y s i s i s q u i t e r a p i d ( 2 ) . More r e c e n t l y , s o l u b l e "open-chain" polydichlorophosphazene ( I I ) has been prepared by u s i n g h i g h l y pure t r i m e r and l i m i t i n g t h e conversion i n the bulk (ca. 250°C) and s o l u t i o n (ca. 200°C) p o l y m e r i z a t i o n r e a c t i o n s (3)· I n c o n t r a s t to ( I I I ) , ( I I ) by v i r t u e o f i t s s o l u b i l i t y can be rendered hydrol y t i c a l l y s t a b l e by r e p l a c i n g i t s c h l o r i n e atoms w i t h v a r i o u s organic n u c l e o p h i l e s (IV-VI) (3,4_). Hence, t e c h n o l o g i c a l l y promising poly(organo)phosphazenes are obtained i f care i s taken during p o l y m e r i z a t i o n t o avoid g e l a t i o n and t o s e l e c t proper c o n d i t i o n s f o r complete c h l o r i n e s u b s t i t u t i o n ( 4 , 5 ) . Although poly(organo)phosphazenes have been c h a r a c t e r i z e d using d i l u t e s o l u t i o n techniques (4-10), attempts t o c h a r a c t e r i z e polydichlorophosphazene d i r e c t l y have been l i m i t e d (11,12,13). The presence of g e l and the f a c t that polydichlorophosphazene i s moisture s e n s i t i v e g e n e r a l l y have precluded an accurate a n a l y s i s of i t s molecular weight (MW) and molecular weight d i s t r i b u t i o n (MWD). However i t i s now r e a l i z e d t h a t , i f precautions are taken during the p u r i f i c a t i o n and h a n d l i n g o f t h e c y c l i c t r i m e r (I) and i f the p o l y m e r i z a t i o n y i e l d s are kept low, g e l - f r e e p o l y d i c h l o r o phosphazene may be prepared r o u t i n e l y . A more d i f f i c u l t problem to handle has been t h e h y d r o l y t i c i n s t a b i l i t y . Although p o l y d i c h lorophosphazene i s s o l u b l e i n a v a r i e t y o f organic s o l v e n t s , t r a c e amounts o f water cause h y d r o l y s i s w i t h t h e formation of P-OH s i d e groups. I n apolar s o l v e n t s l i k e benzene and t o l u e n e , t h e presence of P-OH groups cause the polymer molecules t o a s s o c i a t e through x

This chapter not subject to U.S. copyright. Published 1980 American Chemical Society

Provder; Size Exclusion Chromatography (GPC) ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

240

SIZE EXCLUSION CHROMATOGRAPHY (GPC)

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13.

HAGNAUER

Polymerization

of Poly(dichlorophosphazene)

241

d i p o l a r i n t e r a c t i o n s ; and depending upon the extent of h y d r o l y s i s , c r o s s l i n k i n g may occur through the formation of P-O-P bonds. In p o l a r s o l v e n t s l i k e acetone and dimethyl formamide, the polymer hydrolyzes r a p i d l y , s o l u t i o n s t u r n t u r b i d and a white p r e c i p i t a t e i s evident w i t h i n a few hours t o s e v e r a l days. In t h i s paper, techniques are described f o r p r e p a r i n g and handling d i l u t e s o l u t i o n s of polydichlorophosphazene. Polymer samples are prepared by the melt p o l y m e r i z a t i o n of hexachlorocyclotriphosphazene i n s e a l e d , evacuated g l a s s ampoules at 250°C. P r e c i p i t a t i o n techniques are used t o separate the polymer from unreacted t r i m e r and low molecular weight p o l y m e r i z a t i o n products, under anhydrous c o n d i t i o n s , the molecular weights and molecular weight d i s t r i b u t i o n s of the polymers are d i r e c t l y and a c c u r a t e l y c h a r a c t e r i z e d . Viscometry, membrane osmometry, l i g h t s c a t t e r i n g and l i q u i d s i z e e x c l u s i o n chromatography (SEC) techniques are a p p l i e d f o r d i l u t e s o l u t i o n c h a r a c t e r i z a t i o n . A d d i t i o n a l l y , SEC i s used t o analyze t r i m e r p u r i t y and t o c h a r a c t e r i z e low and intermediate molecular weight p o l y m e r i z a t i o n r e a c t i o n products. The accuracy of the polymer c h a r a c t e r i z a t i o n i s evaluated and the p o l y m e r i z a t i o n products of t r i m e r obtained from d i f f e r e n t sources are c h a r a c t e r i z e d and compared. Experimental M a t e r i a l s . Hexachlorocyclotriphosphazene ( I ) , a l s o designated as the p h o s p h o n i t r i l i c c h l o r i d e t r i m e r , was obtained from two d i f f e r e n t sources - E t h y l Corp., F e m d a l e , MI and Inabata & Co., Minami-Ku Osaka, Japan. Under the c o n d i t i o n s used f o r polymer i z a t i o n i n t h i s study, the t r i m e r samples obtained from E t h y l Corp. were observed t o form an i n s o l u b l e m a t r i x ( I I I ) ; whereas the Japanese t r i m e r formed s o l u b l e polymer ( I ) . Hence, two batches of t r i m e r (PN-1 and PN-2) from E t h y l Corp. were p u r i f i e d by vacuum d i s t i l l a t i o n , r e c r y s t a l l i z a t i o n from heptane and vacuum s u b l i m a t i o n to remove i n o r g a n i c i m p u r i t i e s , h y d r o l y s i s products and higher molecular weight c y c l i c s and oligomers. A f t e r p u r i f i c a t i o n , the samples were found t o c o n s i s t of pure t r i m e r (mp 114°C) t o the l i m i t s of d e t e c t i o n using d i f f e r e n t i a l scanning c a l o r i m e t r y , gas chromatography and l i q u i d s i z e e x c l u s i o n chromatography. The t r i m e r from Inabata & Co. i s a high q u a l i t y , polymer grade m a t e r i a l produced on a l a r g e s c a l e under the trade name Phosnic 390. Phosnic 390 from two d i f f e r e n t l o t s , I J - 3 and IL-22, was obtained and used f o r p o l y m e r i z a t i o n without f u r t h e r p u r i f i c a t i o n . According to gas and l i q u i d chromatographic analyses, the Phosnic 390 samples c o n s i s t of 91% c y c l i c t r i m e r and 9% c y c l i c tetramer ( i . e . , o c t a chlo rο c y c l o t et rapho sphaz ene). The t r i m e r samples were polymerized i n sealed pyrex ampoules placed i n an aluminum b l o c k oven at 250°C. T y p i c a l l y , the ampoules contained 50g of t r i m e r sealed under vacuum (0.005 t o 0.010 mm Hg) and the r e a c t i o n s were terminated by removing the ampoules from the oven. A f t e r c o o l i n g , the ampoules were opened and the contents removed.


242

SIZE E X C L U S I O N C H R O M A T O G R A P H Y

(GPC)

The t r i m e r samples and the p o l y m e r i z a t i o n r e a c t i o n mixtures were s t o r e d under vacuum and handled i n a dry box under a blanket of dry n i t r o g e n . Dried s o l v e n t s were used and precautions were taken to exclude moisture d u r i n g i s o l a t i o n and h a n d l i n g of the polymers. In each case, the r e a c t i o n mixture was d i s s o l v e d i n 80ml benzene and the polymer was p r e c i p i t a t e d w i t h 400ml n_-pentane. About 10-20% of the t r i m e r and other low MW components are r e t a i n e d i n the polymer f r a c t i o n at t h i s stage. To completely remove t r i m e r , the polymer was d i s s o l v e d and p r e c i p i t a t e d a second time. Solvent was removed, v i a a Rotavapor-R instrument, from the s o l u b l e , low molecular weight f r a c t i o n s and both the polymer and the low MW f r a c t i o n s were d r i e d and s t o r e d under vacuum. To remove water, the benzene was azeotroped and d i s t i l l e d over CaH . The n-pentane was s t o r e d over L i M H ^ and d i s t i l l e d over CaH . Toluene was d i s t i l l e d over CaH . Toluene from Burdick & Jackson, Muskegon, MI could a l s o be used f o r d i l u t e s o l u t i o n c h a r a c t e r i z a t i o n without any adverse e f f e c t s on polymer s o l u b i l i t y . Tetrahydrofuran (THF) was d r i e d over molecular s i e v e s and doubly d i s t i l l e d over CaH . The s o l v e n t s were blanketed w i t h n i t r o g e n to maintain dryness. 2

2

2

2

D i l u t e S o l u t i o n C h a r a c t e r i z a t i o n . The polydichlorophosphazene samples were c h a r a c t e r i z e d w i t h toluene as the s o l v e n t at 25°C. The polymers were completely s o l u b l e i n d i l u t e s o l u t i o n and f i l t e r e d w i t h no d i f f i c u l t y through 0.8μ and 5u membrane f i l t e r s . The t r i m e r samples and low MW f r a c t i o n s were d i s s o l v e d and analyzed i n THF s o l u t i o n . S o l u t i o n s were prepared i n an i n e r t atmosphere and kept under a blanket of n i t r o g e n except f o r short i n t e r v a l s during which t r a n s f e r or i n j e c t i o n o p e r a t i o n s were conducted as r e q u i r e d f o r c e r t a i n analyses. Cannon-Ubbelohde d i l u t i o n viscometers were employed f o r i n t r i n s i c v i s c o s i t y [η] determinations and number-average molecular weights MniOS) were obtained u s i n g a Mechrolab model 501 membrane osmometer. L i g h t s c a t t e r i n g measurements were made u s i n g a FICA 50 instrument operated w i t h u n p o l a r i z e d l i g h t of wavelength λ = 5461Â and c a l i b r a t e d w i t h benzene (Rg = 1.58 χ 1 0 ~ cm" ). The average v a l u e of the r e f r a c t i v e index increment as determined using a Brice-Phoenix d i f f e r e n t i a l refractometer was (dn/dc) = 0.0635 ml/g. A computer program i n c o r p o r a t i n g a polynomial equation for the l e a s t - s q u a r e s a n a l y s i s of data and a p l o t t i n g r o u t i n e f o r the c o n t r u c t i o n of_Zimm p l o t s was used t o evaluate weight-average molecular weights M^(LS), second v i r i a l c o e f f i c i e n t s A and z-average r a d i i of g y r a t i o n ( S ) 3 « A Waters ALC/GPC-244 instrument w i t h 6000A s o l v e n t d e l i v e r y system, U6K i n j e c t o r , R400 r e f r a c t i v e index (RI) d e t e c t o r and h i g h performance columns was used f o r l i q u i d s i z e e x c l u s i o n chromato graphy (SEC). A Spectra P h y s i c s SP4000 data system w i t h SP4020 data i n t e r f a c e and SP4050 p r i n t e r / p l o t t e r was a p p l i e d t o format and i n t e g r a t e data. The f o l l o w i n g c o n d i t i o n s were used f o r a n a l y z i n g the polydichlorophosphazene samples: 5

0

2

2


1

13.

HAGNAUER

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Sample c o n c e n t r a t i o n - 2yg/ul I n j e c t i o n volume - 50ul Mobile phase - toluene Flow r a t e - 1 ml/min Columns - yBondagel 2000Â, E - l i n e a r , 125 A D e t e c t i o n - RI 16X, SP4050 A t t e n u a t i o n 10 Chart speed - 4 cm/min A n a l y s i s time - 10 min T o t a l p l a t e count 10 p l a t e s D i s c r e t e area segments were computed over f o u r second time i n t e r v a l s d u r i n g polymer e l u t i o n and b a s e l i n e c o r r e c t i o n s were made. The raw data were t r a n s f e r r e d t o a Hewlett Packard HP9830 computer f o r e v a l u a t i o n and p l o t t i n g . The f o l l o w i n g c o n d i t i o n s were used t o analyze the t r i m e r samples and low MW f r a c t i o n s : Sample c o n c e n t r a t i o n - lug/μΐ I n j e c t i o n volume - 5 0 y l Mobile phase - THF Flow r a t e - 2ml/min Columns - (2) Shodex GPC A-800/S columns + (3) 100A y S t y r a g e l columns D e t e c t i o n - RI 16X, SP4050 A t t e n u a t i o n 10 Chart speed - lcm/min A n a l y s i s time - 24 min T o t a l p l a t e count - 2(10**) p l a t e s Polydichlorophosphazene and c y c l i c t r i m e r and tetramer standards were used f o r c a l i b r a t i o n . Standard methods were a p p l i e d f o r i n t e g r a t i n g peak areas. Gas chromatographic and mass s p e c t r o s c o p i c analyses were run using a F i n n i g a n GC/MS instrument w i t h an e l e c t r o n i o n i z a t i o n d e t e c t o r a t 70eV. Separations were achieved u s i n g 3% D e x s i l 300 on 100/200 Supelcoport i n a 5 - f t χ 1/4-in g l a s s column programmed from 100° t o 280°C a t 20°C/min. h

R e s u l t s and D i s c u s s i o n P o l y m e r i z a t i o n times and y i e l d s are given i n Table I . The polymers and oligomer f r a c t i o n s are designated according t o t h e batch o r l o t number o f the t r i m e r from which they were d e r i v e d . The % polymer i s based on the a c t u a l weights o f t r i m e r used f o r p o l y m e r i z a t i o n and polymer recovered from the second p r e c i p i t a t i o n . The values i n p a r e n t h e s i s i n c l u d e the weight of polymer (ca. 3-8%) r e t a i n e d i n the s o l u b l e oligomer f r a c t i o n s as determined by SEC a n a l y s i s . As shown i n F i g u r e 1, high MW polymer r e t a i n e d i n the s o l u b l e oligomer f r a c t i o n s e l u t e s a t the e x c l u s i o n l i m i t (670s) as a sharp peak f o l l o w e d by another peak (705s) o r a t a i l o f h i g h MW oligomers and a s e r i e s o f i n t e r m e d i a t e MW oligomers (880, 950, 990, 1040, 1070, 1100s). The c y c l i c tetramer e l u t e s as a shoulder (1170s) on the t r i m e r peak (1250s). The peaks a t 1300 and 1390s are due t o r e s i d u a l s o l v e n t s from p r e c i p i t a t i o n and d r y i n g . I t i s



Time (hrs)

100

89

45

21.5

Sample

PN-1

PN-2

IJ-3

IL-22

(30.8)

23.6(31.4)

23.4(26.0)

27

24.1

% Polymer

-

4.0

7.8

43.2

56.8

18.4

12.4

35.0

2.4

% Intermediate % Total MW Oligomers Conversion

1.8

% High MW Oligomers

P o l y m e r i z a t i o n Times and Y i e l d s

Table I

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noted t h a t the c y c l i c tetramer does not appear i n the PN-1 and -2 r e a c t i o n products. Comparable polymer y i e l d s are obtained f o r the four samples; however, the Phosnic 390 samples I J - 3 and IL-22 have a p p r e c i a b l y more high and intermediate MW oligomer products. Nearly h a l f the t r i m e r i n the Phosnic 390 samples undergoes conversion compared to 35% f o r the p u r i f i e d t r i m e r . F i n a l l y , i t i s noted that the Phosnic 390 samples achieve s i m i l a r polymer y i e l d s i n about o n e - f i f t h to one-half the time as the pure PN t r i m e r s . These observations suggest t h a t the Phosnic 390 samples may c o n t a i n component (s) t h a t behave as c a t a l y s t s o r a c c e l e r a t o r s and that a l s o tend t o i n c r e a s e the h i g h and intermediate MW oligomer y i e l d s . Besides t h e t r i m e r , the only component i d e n t i f i e d (by GC/MS and SEC) i n the Phosnic 390 samples i s the c y c l i c tetramer. However, i t i s d i f f i c u l t t o understand how the tetramer might be a c c e l e r a t i n g t r i m e r p o l y m e r i z a t i o n s i n c e t h e tetramer i s r e p o r t e d to polymerize slower that the t r i m e r and r e q u i r e a higher p o l y m e r i z a t i o n temperature (14,15). M e t a l s , s u l f u r and oxygen-bearing compounds ( a l c o h o l s , e t h e r s , ketones and c a r b o x y l i c a c i d s ) , as w e l l as the surfaces o f g l a s s r e a c t i o n tubes, have been reported t o enhance the p o l y m e r i z a t i o n r a t e (14,16-21). But i t i s noted that such r a t e enhancers a l s o tend t o promote c r o s s l i n k i n g and the formation o f an i n s o l u b l e m a t r i x ( I I I ) . Since the p o l y m e r i z a t i o n products were s o l u b l e and s i n c e i t i s u n l i k e l y that the r a t e enhancers would i n t e n t i o n a l l y have been added t o Phosnic 390, t h e i r presence i s q u e s t i o n a b l e . More l i k e l y , the d i f f e r e n c e s i n p o l y m e r i z a t i o n are caused by the presence o f t r a c e i m p u r i t i e s . For example, t r a c e amounts o f phosphorus p e n t a c h l o r i d e from the t r i m e r s y n t h e s i s and o f water as a contaminant may be present i n t h e Phosnic 390 samples. A l l c o c k and coworkers found that very low concentrations o f water (0.02 t o 0.1 mol %) i n the c y c l i c t r i m e r markedly a c c e l e r a t e s the p o l y m e r i z a t i o n r e a c t i o n and have proposed a mechanism f o r c a t a l y s i s based upon t h e formation o f chlorophosphazene h y d r o l y s i s products (22). With t r a c e amounts o f water present d u r i n g p o l y m e r i z a t i o n , they a l s o found t h a t the i n t r i n s i c v i s c o s i t y o f the polymer ( I I ) decreased w i t h i n c r e a s i n g water c o n c e n t r a t i o n but apparently t h a t no high o r intermediate MW oligomers are formed. However, s m a l l amounts o f PCI5 (0.02 mol%) added t o the t r i m e r does r e s u l t i n the formation o f low MW p o l y m e r i z a t i o n products (22). Consequently, the d i f f e r e n c e s i n the y i e l d s and products obtained w i t h the Phosnic 390 and PN samples as w e l l as the Phosnic 390 I J - 3 and IL-22 samples themselves may be a t t r i b u t e d t o v a r i a t i o n s i n the amounts o f t r a c e water and PCI5.

In a l l cases the p o l y m e r i z a t i o n products were f u l l y s o l u b l e i n toluene and the toluene s o l u t i o n s were well-behaved. That i s , the d i l u t e polymer s o l u t i o n s f i l t e r e d through 0.8μ membrane f i l t e r s w i t h no c l o g g i n g ; normal Huggins constants (23) k pj0.5 were obtained from the v i s c o m e t r i c analyses; and r e g u l a r Zimm p l o t s were obtained from the l i g h t s c a t t e r i n g analyses (Figure 2 ) . To evaluate f u r t h e r f


246

SIZE E X C L U S I O N C H R O M A T O G R A P H Y ( G P C )

Figure 2.

Zimm plot for poly(dichlorophosphazene) Sample IL-22


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Poly(dichlorophosphazene)

247

the v a l i d i t y of the polymer h a n d l i n g and c h a r a c t e r i z a t i o n techniques, sample PN-1 was d i v i d e d i n t o t h r e e s e c t i o n s a f t e r p o l y m e r i z a t i o n . Each s e c t i o n was handled s e p a r a t e l y t o determine the average polymer y i e l d (Table I ) and the polymers PN-la, - l b and - l c were c h a r a c t e r i z e d a t d i f f e r e n t times over a p e r i o d o f one month. The d i l u t e s o l u t i o n parameters are l i s t e d i n Table I I . A l l the samples have h i g h molecular weights and broad molecular weight d i s t r i b u t i o n s . The parameters are c o n s i s t e n t f o r samples P N - l a , - l b and - l c w i t h i n the usual l i m i t s of experimental e r r o r expected for the d i l u t e s o l u t i o n techniques. This means t h a t the parameters for PN-2 are s i g n i f i c a n t l y d i f f e r e n t from those o f the PN-1 polymers. Although both t r i m e r s were p u r i f i e d , t r a c e d i f f e r e n c e s i n t r i m e r p u r i t y o r p o l y m e r i z a t i o n c o n d i t i o n s e v i d e n t l y were r e s p o n s i b l e f o r the higher VL^ and ί% values and the broader MWD o f PN-2. Similarly, most parameter values f o r I J - 3 and IL-22 were d i f f e r e n t not only from those o f the PN-1 and -2 polymers but a l s o from those obtained for one another. The low values o f the second v i r i a l c o e f f i c i e n t A i n d i c a t e t h a t toluene i s a thermodynamically poor s o l v e n t and perhaps a Θ s o l v e n t f o r polydichlorophosphazene; w h i l e the [η] and (S^, * values are comparable t o values o f the parameters obtained f o r other h i g h MW polymers i n Θ s o l v e n t s (24). For a l i n e a r polymer, the values o f [η] and (s ^* i n a Θ s o l v e n t are the lowest values the parameters may assume without the s o l v e n t becoming a non-solvent. However, i f the polymer i s branched, the values o f [η] and (β\** w i l l be l e s s than those obtained f o r t h e l i n e a r polymer o f i d e n t i c a l MW. The [η] and (s \** values obtained for polydichlorophosphazene are no lower than expected f o r the polymer i n a Θ s o l v e n t . Therefore, i f the polydichlorophosphazene samples are branched, they do not appear t o be h i g h l y branched. F i n a l l y , i t i s noted t h a t , r e g a r d l e s s o f d i f f e r e n c e s i n p o l y d i s p e r s i t y , the polymers have s i m i l a r φ ^ / Μ values which suggests that they have a s i m i l a r chain s t r u c t u r e a l b e i t l i n e a r o r branched. A t y p i c a l SEC e l u t i o n p r o f i l e f o r polydichlorophosphazene i s shown i n F i g u r e 3. A l l the samples e l u t e d between 330 and 500 seconds w i t h only s l i g h t d i f f e r e n c e s i n the shapes o f t h e i r chromatograms, i . e . , PN-1 and -2 had broader, more symmetrical chromatograms than I J - 3 and IL-22. No low MW peaks due t o t r i m e r or r e s i d u a l oligomers were e v i d e n t . Upon a n a l y s i s , the c y c l i c t r i m e r had an e l u t i o n time o f 525 seconds. The polymers were compatible w i t h the uBondagel column packing such t h a t , as long as d i l u t e s o l u t i o n s were i n j e c t e d and anhydrous c o n d i t i o n s were maintained, no i n c r e a s e s i n column back pressure o r changes i n e l u t i o n times were observed. Upon c a l i b r a t i n g the columns w i t h narrow MWD p o l y s t y r e n e standards, i t was noted t h a t the polydichlorophosphazenes e l u t e d over a r e l a t i v e l y s t r a i g h t r e g i o n o f the c a l i b r a t i o n p l o t . There fore a two parameter e q u a t i o n , 2

1

2

5

2

2

ζ

log M i

= c + ο

ν

Cit. A

ι

American C t a i c a f S o c i a l / L'.Tcry 1155 16th Gl. M, W.

Provder; Size Exclusion Chromatography (GPC) Washington. D. C. Society: 20036 ACS Symposium Series; American Chemical Washington, DC, 1980.

(1)


0.941

-

1.68

IL-22

1.35

PN-lc

U-3

1.46

PN-lb

PN-2

-

PN-la

Sample

n

4.15

3.24

5.2

4.3

4.3

3.8

5

6

1.81

0.896

3.77

2.45

2.56

2.17

w

w

4.36

2.77

7.3

5.7

6.0

5.7

n

M M (OS) M (LS) M (LS)/M (OS) (dl/g) (g/mol) (g/mol) (10- ) (10- ) 5

4.17

0

5.38

0.32

0.34

0.28

2

774

570

1230

874

801

813

2

z

w

0.33

0.36

0.40

0.31

0.25

0.31

T * /M (LS) (ml-mol/g) (Â) (Â -mol/g) (1(T )

Polydichlorophosphazene Dilute Solution Parameters

Table II

13.

HAGNAUER

Polymerization of Poly(dichlorophosphazene)

249

Figure 3. SEC analysis of poly(dichlorophosphazene) Sample IL-22


250

SIZE EXCLUSION CHROMATOGRAPHY (GPC)

where c and ci are constants, was calculated from the molecular weights Mi and elution times t i of the standards eluting during the same interval as the polydichlorophosphazenes. Using Eq.l and the polydichlorophosphazene segment areas A^, number- and weightaverage molecular weights were evaluated Q

fi

n "

Σν Σ Y V (

j-l

( 2 )

J-l

κ- Σ w j ^ Y j=l

3)

Polymerization and Dilute Solution Characterization of Poly

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