Study of branched polyarylates

STUDY OF BRANCHED POLYARYLATES* L. V. DUBROVINA, S. A. PAVLOVA and V. V. KORSI~A~ I n s t i t u t e of Element-Organic Compounds, U.S.S.R. A c a d e m y of Sciences

(Received 13 May 1965)

FLORY [1, 2] and Korshak and coworkers [3, 4] showed that the chain growth reaction under high-temperature conditions is accompanied by exchange reactions on account of hydrolysis, acidolysis, aleoholysis (for polyesters), aminolysis (for polyamides) and interehain exchange. Study of the effect of these reactions on the molecular weight distribution (MWD) of polycondensation products gave rise to several theoretical and experimental papers. The molecular weight distribution of polycondensation products and contemporary viewpoints on this subject are exhaustively dealt with in papers by Flory (1], Korshak [3, 5] Bresler [6], Slonimskii [7] and Howard [8]. The coefficient of polydispersity should increase to a marked extent, according to Flory, with branched products of polycondensation near the gel point. In this case the polydispersity will be increased by

xw

[(1+~) (1-~f/2)]

x~

[1-(f-1)~]

where f is the functionality of the branched component, and a is the value characterizing the degree of branching; moreover, for a linear product a : 0 , and at the beginning of gelling a~0.5. This increase in polydispersity with increase in the degree of branching is always found with polymerization products and also, when there are no reactions causing rearrangement of the units [9], with polycondensation products. It was desired to study how far the molecular weight distribution of branched products of polycondensation is affected by polycondensation equilibrium reactions leading to rearrangement of the units, and to determine the hydrodynamic properties of branched polyarylates. The polyarylates investigated were based on terephthalie acid (Cl--terephthalie acid an_hydride) and phenolphthalein anhydride (2-phenyl-3,3-bis-(4-hydroxyphenyl)phthalimide) [10, 11]. The polycondensation was carried out in a high-boiling solvent m e d i u m under conditions which prevented gelling before equilibrium distribution h a d occurred (6-12 hours is required), i.e. the authors carried out the reaction adding a certain amoun~ * Vysokomol. soyed. 8: No. 4, 752-758, 1966. 827

L. V. DUBROVINA et

828

al.

o f a t r i f u n e t i o n a l ingredient A ~ - p h e n o l p h t h a l e i m i d e (3,3-bis-(4-hydroxyphenyl)-phthalimide) to a n e q u h n o l e c u l a r axnount of t h e b i f u n c t i o n a l m o n o m e r s A - A and B - B . D e p e n d i n g on t h e a m o u n t of t h e A - - A i n g r e d i e n t introduced, p o l y a r y l a t e samples I A w i t h v a r y i n g degrees of b r a n c h i n g were obtained. I t was f o u n d in p r e l i m i n a r y tests t h a t a n insoluble gel is o b t a i n e d b y i n t r o d u c i n g 0"5 tool. of t h e b r i m c h i n g ingredient w i t h an e q u i m o l e c u l a r r a t i o of acid chloride to p h e n o l p h t h a l e i n anilide.

The first qualitative index of the degree of branching is a reduction in [ff] with increase in molecular weight and a rise in Huggin's constant (K') (see Table 1). TABLE 1. BRANCHED POLYARYLATES INVESTIGATED

Sample, No.

A m o u n t of i m i d e (tool. fraction)

[~] in T C E , dl/g

M w light diffusion

K'

1

--

0.422

28,500 34,600 *

1-02

0"05 0"05 0"10 0"20 0'25 0"25 0"25

0.288 0.287 2-284 0.211 0.148 0"225 0.300

1"13 1"24 1 "44 2"06 2"66

23,300

47,500 35,700 28,600

Yield, ~o

91

87"2

74"8 82"6 89"6

measured by light diffusion on "Soflca" (France) photogoniodiffusimeter. t Calculated using Trautman's data on sedimentation in an ultracentrifuge [12]. Amount of A-A ingredient: 7-0"875; 8--0"8125. * M w

~'0

tog M

5.0

0

I-"-I

-1"0 FIG. 1. Viscosity versus molecular w e i g h t for samples 1, 3, 6 in t w o solvents: 1, 2, 3 - samples 1, 3, 6 respectively; a - - s o l v e n t is t e t r a c h l o r o e t h a n e ; b - - s o l v e n t is t e t r a hydrofttran.

Study of branched

polyarylates

829

To obtain curves of molecular weight distribution the authors fractionated samples 1, 3 and 6 b y distribution between two liquid phases [13] (1--20 fractions, 3--20 fractions, 6--16 fractions). The viscosities of the fractions were measured in tetrachloroethane (TCE) and tetrahydrofuran (THF) in a viscometer with a "suspended" level. The molecular weights were measured b y light diffusion on a visual nephelometer at an angle of 90 ° with a wavelength of 5460/~ [14]. (M of some of the samples were measured for purpose of comparison on a "Sofica" device. Satisfactory results were obtained). The results of these measurements were used to determine the constants of the Mark-Houwink equation [tl] = K , × M ~ (Table 2, Fig. 1). The sedimentation constants of five fractions of each sample were obtained b y rapid sedimentation in a G-110 ultracentrifuge (Hungary) in tetrahydrofuran at 20 ° and 50,000 rev/min, and the relations of S=KsM 1-b (Fig. 2, Table 3) were derived. TABLE

2 . PAX=~AMETERS O F M A R K - - I - I o u w I N K REFRACTION

INDEX

EQUATION,

AND FRACTIONAL

SPECIFIC

INCREMENT

OF

VOLUME

An

Sample No.

Solvent TCE THF TCE THF TCE THF

a

K . x 10 -4

0.684 0.488 0-586 0.470 0.412 0.387

4.095 25.85 6.74 19-96 22.75 28.78

-Ac -

Vtt

0.23

0"6772

0.22

0"6823

0.20

0"6271

TABLE 3. PARAMETERS OF RELATION S ~ - K s M 1-b Sample No.

1 --b

Ks

1 --b *

1 3 6

0-356 0'455 0"516

71.85 X10 3 17.41 X 10 -3 5-089 X 10 -3

0.504 0.510 0.538

• Calculated using equation b= ( 1 - a)/3 [15].

The experimental values of 1--b for the branched samples are closer to the calculated values than those for the linear sample. I t follows from these results that the macromolecules of the polyarylates in solution form knots with weak hydrodynamic interaction, and consolidation of the knot on account of branching develops in a w a y that corresponds to increase in the hydrodynamic interact.ion [16].

L. V. DUBI~OVINA et al.

830

As t h e rapid sedimentation method gives a more accurate picture of distribution according to molecular weights, the gradient curves abtained for the unfractionated samples were converted b y Hosting's method into curves of distribution according to mol.ecular weights. Logs 0.(3

1 0"/4

14.0

/

5"0 LogI~I

FIG. 2. Sedimentation constant versus molecular weight: 1, 2, 3 --samples 1, 3, 6 respectively. The weight average and number average molecular weight was cal~'ulated using Flory's equations [1]: -

--

-

1+~

X ~ = [1--(f--1)~]

Mw=M°Xw;

;

Mn=Mo-~,~;

---~n=

1

(1--~f/2)"

Tables 4 and 5 show t h a t instead of a rise in polydispersity near the gel point the coefficient of polydispersity remains low; furthermore, with increase iu the average molecular weight of the polymer the coefficient of polydispersity is reTABLE 4. RESULTS OF A N A L Y S I S OF ~¢[OLECWLAR W E I G H T D I S T R I B U T I O N CWRVES

Sample :No.

Fractionation My) My)

28,500 23,300 47,500

24,800 27,100 51,100

M n

18,800 19,200 35,000

Sedimentation M~

M, 1.319 1"41 1.45

My)

30,400 26,100 76,000

Mn

12,000 13,000 45,500

My)

M~ 2"53 2"0 1"67

duced slightly. This is probably due to the molecular weights becoming uniform on account of the reshuffling of the units of the macromolecules during the time that equilibrium distribution is being established. Certainly when there are polycondensation equilibrium reactions the reshuffling of the units should result, regardless of the degree of branching of the sample, in the same molecular weight distribution as occurs with the linear products, since the redistribution and its degree are determined b y time and b y the number of kinetic weak bonds. The authors believe t h a t the results t h e y obtained confirm the viewpoint previously made known by Korshak, Bresler and Slonimskii.

Study of branched polyarylates

831

TABLE 5. FLORY POLYDISPERSITY VALUES

Sample :No.

Flory

Amount of imide (tool. fraction)

PB

X,

Xw

0-972* 0.932t 0-72st

0-05 0-25 * P=(~,,-1)

Pa 0 0.486 0.429

23 3.6 2.7

45 41 9

X~ X, 1"95 11'3 3"33

x..

t The degree of completeness of the reaction was calculated assuming that only the surplus of --OH groups remains unreaeted.

With regard to the linear and branched polyarylates the changes in Huggin's constant in tetrachloroethane are shown in Fig. 3; judging by the value of exponent a, this seems to be a good solvent. With increase in [~/] of the fractions constant K' is reduced for all four samples, while in sample 6, (the most branched

/4.0

.1

30l 2"0

20[

×Z

~×

o3

K'

x~..'x~ . %.° x ~ . o , ×

o

".~. "~ ~..--L___,

b o

~.o ~x ° × × o x o,a~

o ~ °o ×:.~

oI~

o.G

bT]

0.2

~.

•

°

5''!j / ~i/

FIG. 3. Huggin's constant (K') versus [~/]in two solvents: a--tetrachloroethane; b-tetrahydrofuran; 1, 2, 3--samples 1, 3, 6 respectively. sample) these changes are most marked. I n a "worse" solvent, such as tetrahydrofuran for polyarylates, the values of K ' remain approximately the same for all three samples, and close to 0.5, whereas in the case of the branched samples obtained b y polymerization there is a characteristic increase in K' with increase in [~/] [17], indicating a rise in the degree of branching with increase in the molecular weight. For polycondensation products of epichlorohydrin with bisphenol [9], where exchange reactions do not occur, there was also a rise in the degree of branching with increase in molecular weight.

L. V. DUBROVIlV.~et al.

832

Moreover it is known [18, 9] that with increase in the degree of branching the solubility of polymers is reduced. With the samples investigated, on the other hand, the solubility of the branched polymers increases, as the results of turbidimetric titration show (Fig. 4]. It follows that during fractionation only the high-molecular fractions of polymers 3 and 6 can contain an admixture of the low-molecular fractions of the linear polymer. The coefficients of polydispersity M w / M n for fractions 3--XII, 3--X, 6 - - X I calculated from the gradient curves (ttostings) are 1.26, 1.17, 1.147 and 1.61 respectively, which indicates the relatively small polydispersity of the fractions. Z

o

ooooOO

.~.~.=.. • • / : o . : - - ~ . ~ o I **°~ oO°° L

oo

o

o

3

o

o

oo

ocoo

/ // •J

30

~

~

i

I

/40 50

i

I

6"0

I

I

[

I

!0'0

i'50

'

PpecipitcTn~ , rnL

FIG. 4. Turbidimetrie t i t r a t i o n curves: 1, 2, 3--samples 1, 3, 6 respectively. TXBLE 6.

DEGREE

O F BRAI"~'CHING O F FRACTIO]:~-S O F P O L Y A R Y L A T E S

Sample No. 3

Sample No. 6

mol. weights of fractions

[~] branched [~]linear

mol. weights of fractions

[~]branched [~]linear

17,200 20,700 25,100 28,500 30,800 41,100 71,300

0.626 0"607 0.589 0.577 0.574 0.560 0.509

22,300 27,100 40,000 64,800 151"800

0"367 0.332 0.297 0.268 0.195

Taking into account the above factors and considering the relation [g]branohea/ /[g]l~ear as the degree of branching of the macromolecules [19] (Table 6), and also taking the values of ttuggin's constant in tetrachloroethane (Fig. 3), we may conclude that even when the amount of the branching ingredient is small there are no linear type fractions in the sample, which seems to be a further consequence of regrouping of the units. When there is no such regrouping [9] the lower fractions are linear and the degree of branching is pronocuneed only when the molecular weight of the fractions exceeds 70,000.

Study of branched polyarylatcs

833

The authors attempted to calculate the number of branches m per molecule on the basis of the following suggestions: (1) all the molecules of the trifunctional ingredient went into the polymer, displacing a corresponding amount of bisphenol: from this the polymer yield also was calculated; (2) since, as the data in Table 6 show, no very marked change in the relationship [~]br~nehcd/[~]iinc~r for the fractions occurs, the authors assumed that the degree of branching of all the fractions is equal on average to the degree of branching of the fraction with M~, approximately equal to M~ of the sample as a whole. TABLE 7. R E S U L T S OF ANALYSIS OF BRANCHED POLYARYLATES

Yield Sample No. calculated found

lll~

0.94

20,3001

m

No. of end groups, v*

4

End groups, %

i Ii

[r]]branehed'

calculated found ~ [

i

[rl]lineai:-- i K-Z ?~ :~

0.334 0.3547 i 0-666 1'03 0.7912I 0-269

18 700

i

I

,

m$ Z-Stock.

I

[20]. t Verley titration [21]. :~ K-Z = the number of branches calculated using Kilb-Zimm theory [19]; Z-Stock.- calculated using Zlmm-Stocko mayer theory [22]. * c=m+2

Judging b y the results in Table 7 more accurate values of the degree of branching are obtained in the case under consideration on the basis of the Z i m m Stockmayer theory, i.e. when [~/]branched/[~/]~ncar=g"/'. Similar results were obtained b y Myers and Dagon [9]. The slight divergence in the calculated and experimental number of end groups is p r o b a b l y due to intramolecular ring formation. CONCLUSIONS

(1) Samples of branched polyarylates are obtained. The relations of viscosit y and molecular weight are determined in two solvents: for sample 1--[~]~c~ =4.095 x 10 -4 x M °'6s4, [~]T~F = 25"85 X 10 -4 X M °'4ss; for sample 3--[~/]~CE0"74 X x 10 -4 X M °'5s6, [~]THF= 19.96 × 10 -4 X M°'47°; for sample 6--[~/]TCE-- 22-75 × 10 -4 X X M °'412, [~]TUF=28"78 X 10 -4 X/]/0.387. (2) Comparison is made between molecular weight distribution curves obtained b y fractionation and b y sedimentation on an ultracentrifuge. The sedimentation results show the polydispersity to be slightly higher than in the data for fraetionation, which is explained b y the higher resolving power of the ultracentrifuge. The polydispersity calculated b y Flory's method is considerably higher than that given in the experimental results, thus indicating the effect of interchain exchange and regrouping of the units on molecular weight distribution. (3) The Zimm-Stoekmayer theory regarding the number of branches per molecule agrees with the values calculated using the experimental results.

834

L. V. D U B R O V I N A et al.

(4) In view of the results given here it is suggested that intramolecular rings may be formed in branched samples. Translated by R. J. A. HEND~Y

REFERENCES 1. P. J. FLORY, Chem. Revs. 39: 137, 1946 2. P. J. FLORY, Principles of Polymer Chemistry, N. Y., 1953 3. V. ¥ . KORSHAK and S. V. VINOGRADOVA, Geterotsepnye poliefiry. (Heterochain Polyesters.) Izd. Akad. Nauk SSSR, 79, Moscow, 1958 4. D. N. KURSANOV, V. V. KORSHAK a n d S. V. VINOGRADOVA, Izv. Akad. N a u k SSSR, Otd. khim. n., 140, 1953 5. G. I. TIMOFEYEVA, Dissertatsiya. (Thesis.) 1965 6. S. Ye. BRESLER, V. V. KORSHAK, S. A. PAVLOVA and P. A. FINOGENOV, Izv. Akad. N a u k SSSR, Otd. khim. n., 344, 1954 7. G. L. SLONIMSKII, J. Polymer Sci. 30: 410, 1958 8. G. I. HOWARD, Progress in High Polymers, London, 1961 9. G. E. MYERS and I. R. DAGON, J. Polymer Sci. 2: 2631, 1964 10. ¥ . V. KORSHAK, S. V. VINOGRADOVA and S. N. SALAZKIN, Vysokomol. soyed. 4: 339, 1962 11. S. V. VINOGRADOVA, V. V. KORSHAK, S. N. SALAZKIN and S. V. BEREZA, Vysokomol. soyed. 6: 1403, 1964 12. R. TRAUTMAN, Biochim. et Biophys. Acta 28: 417, 1958 13. G. I. TIMOFEYEVA, L. V. DUBROVINA, V. V. KORSHAK a n d S. A. PAVLOVA, Vysokomol. soyed. 6: 2008, 1964 14. S. A. PAVLOVA a n d S. R. RAFIKOV, Yysokomol. soyed. 1: 387, 1959 15. S. Ya. FRENKEL', Vysokomol. soyed. 2: 731, 1960 16. V. N. TSVETKOV, ¥. Ye. ESKIN and S. Ya. FRENKEL', Struktura makromolekut v rastvore. (Structure of Macromolecules in Solution.) Izd. "Nauka", 405, 1964 17. K. H. CRAGG a n d I. A. MANSON, J. Polymer Sci. 9: 265, 1952 18. I. A. BARANOYSKAYA and V. Ye. ESKIN, Vysokomol. soyed. 6: 339, 1964 19. B. H. Z1MM and R. KILB, J. Polymer Sci. 37: 19, 1959 20. V. N. TSVETKOV, Dokl. Akad. ~ a u k SSSR, 78: 1123, 1951 21. S. R. RAFIKOV, S. A. PAVLOVA a n d I. I. TVERDOKHLEBOYA, Metody opredeleniya molekulyarnykh vesov i polidispersnosti vysokomolekulyarnykh soyedinenii. (Methods of Determining the Molecular Weights a n d Polydispersity of High-molecular Compounds.) Tzd. Akad. N a u k SSSR, 274, 1963 22. B. H. ZIMM a n d W. H. STOCKMAYER, J. Chem. Phys. 17: 1301, 1949