Effect of the nature of organic solvents on polycondensation in emulsion and in solution

Effect of nature of organic solvents on polycon(lensation in emulsion

1271

(2) The effect of temperature, pressure and catalyst on the course of the reaction and on the properties of the polyamidines has been investigated. Translated by R. J. A. HENDRY

REFERENCES 1. E. HICKE, Pharmazie 18: 653, 1963; Chem. Abstrs. 60: 2195, 1964 2. M. HUNT and J. E. KIERBY, U.S. Pat. 2364074, 1944; Chem. Abstrs. 39: 4170, 1945; 2364075, 1944; Chem. Abstrs. 40: 2273, 1946 3. H. E. WINBERG, U.S. Pat. 3121084, 1962; Chem. Abstrs. 60: 13197, 1964 4. G. D. DIANA, R. A. CUTLER, E. S. ZALAY and S. S. SCHALIT, Chem. and Engng. News 45: 53, 1967 5. K. P. KHOMYAKOV, A. D. VIItNIK and Z. A. ItOGOVIN, Uspekhi khimii 33: 1051, 1964 6. It. L. SCHRINER and F. W. NEUMAN, Chem. Revs. 35: 351, 1944 7. F. C. SCHAEFER and A. P. KRAPCHO, J. Organ. Chem. 27: 1255, 1962 8. F. COOPER and M. PARTRIDGE, J. Chem. Soc., 255, 1953 9. R. P. MULL, R. H. MIZZ0NI, M. It. DAPERO and M. E. EGBERT, J. Med. Pharm. Chem. 5: 651, 1962; Chem. Abstrs. 57: 9817, 1962 10. H. BREDERECK and K. BREDERECK, Chem. Ber. 94: 2278, 1961 11. K. MATSUDA, U.S. Pat. 3049499, 1958; Ref. zh. khim. 4S178P, 1964 12. H. C. BROWN, J. Polymer Sci. 44: 9, 1960 13. G. S. GOLDIN, V. G. PODDUBNYI and N. V. NOSENKO, Zh. organ, khim. 3: 15, 1967 14. W. RIED and W. FAKDEN, Liebig's Ann. Chem. 661: 76, 1963 15. It. ROGER and D. G. NIELSON, Chem. Revs. 61: 179, 1961 16. W. KEItMACK and T. WRIGHT, J. Chem. See., 1421, 1935

EFFECT OF THE NATURE OF ORGANIC SOLVENTS ON POLYCONDENSATION IN EMULSION AND IN SOLUTION * n . t~. SOKOLOV, S. S. ~EDVED', •. V. NOVOZItILOVA, T. V. KUDIM, V. D. GERASIMOV, I]). :F. SOKOLOVA a n d G. A. KUZNETSOV

Synthetic Resin Research Institute, Vladimir

(Received 10 June 1968) Relatively little study is being made of processes of polycondensation in solution, particularly when accompanied b y the precipitation of polymer in the synthesis, and the same is true of emulsion polycondensation where the synthesis takes place in the volume of the organic phase. Both methods are particularly useful ways of synthesizing rigid-chain polymers generally possessing lower solubility; moreover, it is possible by means of these methods to * Vysokomol. soyed. A l l : No. 5, 1121-1132, 1969.

L . B . SOKOLOVet al.

1272

produce high molecular weight rigid-chain polymers in media which are not thermodynamic solvents for polymers. However, in this case also, i.e. when the polymer separates from the reaction medium as a precipitate in the synthesis, the nature of the medium will undoubtedly be a major factor influencing various stages in the syr~esis so as to determine the molecular weight of the resulting polymer. The effect of the nature of the organic solvent in processes of polycondensation was studied in reference [2] with regard to polycondensation in true solvents where the molecular weight of the polymer is directly related to the solvent action of the solvent, and also with regard to interracial polycondensation [3] where it was found that the use of a solvent with the "optimum" solvent action facilitates the formation of a high molecular weight product. However, the conclusions in references [2, 3] cannot be transferred to polycondensation accompanied by polymer precipitation, or to emulsion polycondonsation, in view of the very different mechanisms of these processes. This p a p e r describes a s t u d y o f the w a y in which t h e n a t u r e a n d composition o f organic solvents affect the molecular weight o f some a r o m a t i c p o l y a m i d e s in their synthesis b y emulsion p o l y c o n d e n s a t i o n and p o l y e o n d e n s a t i o n in solution (with p o l y m e r precipitation). I n order to elucidate the specific features o f b o t h m e t h o d s a parallel s t u d y was m a d e of the synthesis in emulsion systems a n d solutions, using the same organic solvents. Synthesis of aromatic polyamides in different organic solvents. Samples o f p o l y 3,3'-dimethyl-4,4'-diphenylisophthalamide ( P D D I A ) o b t a i n e d in emulsion a n d in solution in different organic solvents were investigated in reference [4], and differences in the molecular weights of these samples were d e t e c t e d (see T a b l e 1). P D D I A is insoluble in benzonitrile, (BN) cyclohexanone (TsH) a n d m e t h y l c y c l o h e x a n o n e (MTstt) (see T a b l e 1) a n d swells only to a n inconsiderable e x t e n t TABLE

1. MOLECULARWEIGHTS OF PDDIA SAMPLES 0/1o~) SYNTHESIZEDI1~.SOLUTION AND I N EM-U~LSION I ~ D I F F E R E N T ORGANIC SOLVEI~TS

Viscosity in solution Solvent

in emulsion

acco )tots

I pyridino Iethylcyclohehanone (MTsH) Cyclohexanone (TsH) |onzonitrilo (BN)

]

TEDA*

TEA~f

NaHCOs

Na~CO8 I 1NIaOH

0"19

0"43

0.71

0"61

1.11

1"07

0"21 0"77

0'66 0"84

1.09

0"30 0.71

0.43

0"49

2.62

1.07

0.67

* TEDA-- Triethylenediamine. ? T E A - Triethylamine.

in these solvents. I t is therefore impossible to discover which o f these organic solvents m a y be best for P D D I A b y determining t h e degree of swelling, or b y direct dissolution of the polymer: W e a p p r o a c h e d this p r o b l e m with the assump-

Effect of nature of organic solvents on polycondensation in emulsion

1273

tion that a non-solvent having sufficiently strong affinity for the polymer [5] would facilitate the formation of ordered structures in the latter. I t appears that the rate of structural ordering is proportional to the affinity of the medium

r0

Z0

J0

/g

20

J0 20"

Fio. 1. X-ray pictures of PDDIA after swelling for 24 hr: /--initial sample; 2--in MTsH; 3--in TsH; 4--in BN; 5--crystalline sample; a--in pure organic solvents; b--in presence of TEA (0"6 ~ solution). for the polymer. On determining the structural changes arising with different solvents we m a y place the latter in the order of their affinity for the polymer (in respect to solvent action). Figure 1 shows X-ray pictures of the P D D I & samples after swelling for 24 hr in BN, T s H and M:TsH. I t is seen from Fig. la that the degree of structural ordering is highest for the sample swollen in B N and lowest for that swollen in ~/ITsH. I t follows that these organic solvents m a y be placed in the order MTsH ~ T s H < B N in regard to their solvent action with respect to P D D I A . To determine how far the solvent action is affected b y the HCI acceptor, e.g. triethylamine (TEA) used in the synthesis we conducted a similar experiment in the presence of TEA. Figure lb shows the X-ray pictures for P D D I A samples swollen in BN, TsH and ~ T s H in the presence of TEA. A comparison of Figs. la and b shows that T E A in the amount used in the synthesis has no real effect on the solvent action. On comparing these results with the molecular weights (tho~) of P D D I A samples prepared in MTsH, T s H and B N it is seen that in the polycondensation in solution in the presence of the same HC1 acceptor the value of t/lo~ is lowest

1274

L. B. SOKOLOV et a~.

in M~rsH and highest in BN. For example, in the presence of pyridine ~log is: 0.19 (MTsH), 0.21 (TsH) and 0.77 (BN); and in the presence of TEA: 0.71; 1.09 and 2.62 respectively. It follows that in the case of polycondensation in solution accompanied by polymer precipitation the better tl~e solvent the higher the molecular of the polymer obtained in it.

~itog /'5

~x.,_x a x-/ /'0

Ooj

20

¢0

60

lO

20

~#

b"O.

/O

100

Add/t/ve , %

Fro. 2. Plots of t/logfor PDOIA versus composition of mixed solvent of Ts]:[~additive: 1--DMAA; 2--acetone; 3--CC14; 4--cyclohexane; a--polycondensation in solution; b--emulsion polycondensation in system TsH-water-additive-NaaCOs. It was most interesting to make this comparison in cases of emulsion polycondensation in the systems: BN-water-acceptor, TsI-I-water-acceptor and MTsHwater-acceptor. In the emulsion system BN-water-Na~C03 (BN is the best solvent) a polyamide is obtained with ~log-----1.07. However, the molecular weight of the polymer obtained in the system l~TsH-water-Na2CO 3 (1KTsH is the poorest solvent) is approximately the same (~zog=1.11), and in the systems TsH-wateracceptor the molecular weights are low (ylog----0.3---0.49),even though TsH is intermediate between ~ T s H and BN as a solvent. We therefore found no direct relationship between molecular weight and the solvent action of organic solvents. Note that in the case of emulsion polycondensation the effect of the medium on the polycondensation, and so also on the molecular weight, is much more complex than in the polycondensation in solution. Certain difficulties are encountered in comparing the different organic solvents since Several physicochemical characteristics of the process are simultaneously influenced by the nature of the solvent, e.g. the rate of the main reaction, the rates of side reactions and the rate of polymer precipitation. From this standpoint "a better way of following the effect of the nature of the solvent is apparently through the addition of substances affecting its solvent action favourably or unfavourably.

Effect of naturo of organic solvents on polycondensation in emulsion

1275

Synthesis of aromatic ~olyamides in emulsion and in solution using mixed organic solvents. The molecular weight of poly-4-4'-diphenyloxideisophthalamide (PDOIA) in relation to the composition of the organic solvent in emulsion polycondension and in polycondensation in solution accompanied b y polymer precipitation, in solvent systems based on TsH. The results of the experiments are shown in Fig. 2. It is seen from Fig. 2a that in the polycondensation in solution (TEA-HCI acceptor) the molecular weight of the polymer is affected to approximately the same extent when CCI4, acetone and cyclohexane, which are precipitants for PDOIA, are added to TsH. On increasing the content of CC14 or acetone to 20~/o the molecular weight rises slightly, probably owing to some improvement in the solvent action. When the amount of CC14, acetone or cyclohexane in the mixture is further increased to 60%, there is a marked reduction in molecular weight, an4 in pure CCI4, acetone and cyclohexane there is no polymer formation as such, e.g. the product obtained in CC14 has ylog----0.08 in dimethyfformamide containing 5o/o LiC1). This reduction in molecular weight is due to the much weaker action of the solvent in respect to the polymer, and to one of the monomers also: 4,4'diaminodiphenyloxide (DDO) is practically insoluble in CC14 and cyclohexane, while in acetone it is only sparingly soluble. TABLE

2. C H A N G E I N W A T E R CONTENT IN T H E ORGANIC P H A S E OF T H E EMULSION SYSTEMS TsH-ADDITIVE--WATER--Na ,C O a

Water content (% by wt.) with content of additives, %

Additive

I

i

011.33[

Acetone DMAA CCI+ Cyclohexane

5'8

,

.66!5.33

6"0 6"1 --

5"8 -5.8 ~2 5-8

i

10.661 20.0

6"9

8"0

:4.9 9 4"5 4.2 6"7 -- ~ 7"0 2.0 3.5 --

6.6

9"4 7"4

10"9

400

46.6

60.0

12"3

15"2 8"5

32'2

The effect of adding a good solvent, N,N-dimethylacetamide (D~AA) is reflected in much higher molecular weights with a maximum at 5~/o, as a result of the considerable improvement in the solvent. Certainly, when the mixture contains 10% or more of D ~ A A the polymer no longer separates from solution as a precipitate, b u t its molecular weight is slighty reduced, though it remains a lot higher compared with equal additions of CCI4 and the other precipitants. This reduction in molecular m a y possibly be the result of the side reaction of isophthalic acid dichloride (IAD) with DMAA [6]. It is seen that in the emulsion polycondensation (Fig. 2b) the dependence of the molecular weight (~log) on the initial composition of the organic phase is fundamentally different, and moreover the molecular weight is influenced in varying degrees b y precipitants which all had the same effect on the polycondensation in solution. For instance, the addition of about 5°/o of CC14 or cyclohexane

,1276

L . B . SOKOLOVet

aL

~unmixed with water greatly increases the molecular weight, which then remains practically constant on further increasing the amounts added. On the other hand, the molecular weight is slightly increased b y the addition of organic solvents which mix well with water: 1.33% of acetone in the initial organic phase increases the viscosity of P D O I A from 1.60 to 1.73; thereafter the reduction in molecular weight is proportional to the acetone content of the initial organic phase. The presence of a maximum is probably due to some improvement in the solvent action of the organic phase, while the further reduction in viscosity is apparently related to the reduced solubility of both the polymer and the DDO, a further factor being the increased role of termination reactions (hydrolysis). The addition of DMA_£ (a good solvent) also increases the molecular weight (t/Iog=l.85 with 10.66% of D1VIAA in the initial organic phase), after which it falls fairly sharply, apparently owing to the increased role of termination reactions. The fact that the effect of CCI4, cyclohexane and acetone is the same in the polycondensation in solution, b u t different in the emulsion polycondensation is most interesting. With 20-30% contents of CC14 or cyclohexane in the polycondensation in solution a fairly high molecular weight polymer results, and in view of this the sharp reduction in the viscosity observed on adding CC14 or cyclohexane to the organic phase cannot be accounted for on the basis of reduced solvent action: it is probably the result of a different change in the composition of the organic phase accompanying the addition of CCI~ or cyclohexane. I t was found that the introduction of these substances into the 'organic phase affects the water T A B L E 3. E F F E C T OF RATIO OF COMPOIffENTS I N T H E E1KULSIOl~ SYSTEM T s H - A C E T O N I T R I L E - - W A T E R - - ~ a 2 C O 3 O1~ T H E M O L E C U L A R W E I G H T (/]log) OF

PmPIA A~D 75/25 COPOLYMER Initial ratio of components, ml water 40 40 40 40 40 50 60 60 60

acetonitrile

TsH

60 0 10 20 30 13 10 20 30

0 60 50 40 30 37 30 20 10

Content of water in organic phase, %

5"5 11"0 12"2 12"3 9"2 24"7 24"5 23"9

~1log of PmPIA

t / l o g of copolymer

0'23 I '33 1"12 0"74 0"78

0"24 1 "00 0"89 0"69 0"52

1"57

1"57 1"00

0"76 0"64 0"46

0"74 0"36

content of the latter. I t is seen from the data in Table 2 that the water content in the organic phase is increased on adding acetone or DM~_A, while in the c a s e of CC14 or cyclohcxane it is reduced.

Effect of nature of organic solvents orL polyeondensation in emulsion

1277

TABLE 4. CO~TENT OF WATERm THE ORGANm PHASE OF EMVLSION SYSTEMS AFTER EMULSIHCATmN (% BY WT.) Accepters

System MTsH-water TsH-water BN-water

NaHC03

Na~COs

NaOi

no accepter

4.5 5-6 1-0

4.6 5.8 1-0

4.4 5.2 0.9

5.2 6.5 1.2

I t is t h e r e f o r e a p p a r e n t in t h e light of these findings t h a t t h e presence of a cert a i n a m o u n t of w a t e r in t h e organic p h a s e facilitates t h e f o r m a t i o n of high molecular weight polymers. B e c a u s e of this we studied t h e m o l e c u l a r weight of p o l y - m - p h e n y l e n e i s o p h t h a l a m i d e ( P m P I A ) a n d of a c o p o l y m e r b a s e d on 7 5 % of m - p h e n y l e n e d i a m i n e , 25 Yo of p - p h e n y l e n e d i a m i n e a n d I A D in relation to t h e c o m p o s i t i o n of the organic p h a s e of the emulsion s y s t e m T s H - a c e t o n i t r i l e - w a t e r - N a 2 C O S. T h e results obt a i n e d a n d some characteristics of t h e s y s t e m h a v e been t a b u l a t e d (Table 3). T h e role of w a t e r in t h e emulsion p o l y c o n d e n s a t i o n p r e s e n t s one of the m o s t interesting p r o b l e m s . I t is a s s u m e d in reference [1] t h a t w a t e r m a y act as c a t a l y s t for t h e m a i n reaction. Besides this it was shown in [7] t h a t t e t r a h y d r o f u r a n ( T H F ) containing 12% w a t e r is a b e t t e r solvent t h a n a n h y d r o u s T H F for P m P I A . I t is possible t h a t increased w a t e r c o n t e n t s m a y lead to some i m p r o v e m e n t in t h e solvent action of the organic p h a s e in the case n o w u n d e r consideration. T h e presence of a certain a m o u n t of w a t e r in t h e organic p h a s e a p p e a r s to be TABLE

5. D E G R E E

OF HYDROLYSIS

OF lAD

A E D T E R E P n T I I A L I C A C I D DICIILORIDE

(TAD) IN EMULSION SYSTEMS (Time--10 rain, initial ratio of aqueous and organic phases 1 : 1) Degree of hydrolysis, % IAD Aqueous phase

Water 0"5 M solution of NaC1 0.6 M NatICO3 0-3 M Na2CO 3 0.6 M NaOR

TAD I! organic solvent

TsH

MTs]-[

BN

TsH

55

47

1

58

47 84 84 89

38 86 85 92

1 51 63 54

56

82

a n essential condition for success in c o n d u c t i n g t h e emulsion p o l y c o n d e n s a t i o n : it will be seen t h a t each emulsion s y s t e m has a p a r t i c u l a r w a t e r c o n t e n t in t h e organic phase, a n d this a m o u n t is n o t a l w a y s t h e o p t i m u m one for all t h e polymers..

1278

L . B . SOKOLOV e~ a~,

The tabulated data show (Table 4) that the emulsions systems based on MTsH, TsH and BN differ in regard to the water content of the organic phase. The water in the organic phase may prevent the formation of a high molecular weight polymer by reacting with the acid chloride.

Comparison of the rate of hydrolysis of the acid chloride emulsion systems based on different organic solvents. The presence of a relatively high content of water in the organic phase and the aqueous solution of the alkali give grounds for assuming that hydrolysis of the acid chloride may be one of the main factors preventing

/

\\z I

f

!

fJ

2O

2d-

FIG. 3. X-ray pictures of P m P I A samples: /--amorphous unordered sample; 2--amorphous ordered sample; 3--crystalline sample.

the formation of high molecular weight polymers in the emulsion polycondensation. Apart from other factors the molecular weight may be determined by the ratio of the rate of hydrolysis to that of the main reaction. Even the acid chloride groups at the ends of the growing macromolecules may undergo saponification. The main problem therefore lies in determining the role of hydrolysis in the emulsion polycondensation. As a first approximation in approaching this problem we made a comparative study of the hydrolysis of IAD in emulsion systems based on ~TsH, TsH and BN under conditions approximating to those of the emulsion polycondensation. The results are given in Table. 5. It will be seen that the hydrolysis of IAD (in the absence of the diamine and the acceptor) proceeds most rapidly in the system TsH-water, and least rapidly in the system BN-water. At the same time the degree of hydrolysis is proportional to the content of water in the organic phase. The degree of hydrolysis is certainly reduced as the water content is lessened (by adding an agent to salt out NaC1) (the amount of water in the organic phase for the systems solvent-0.5 M solution of NaC1 in water amounts to: TsIt--5.8; I~TsH--4.3 and BN--0.9~o). The lower degree of hydrolysis in the presence of the salting out agent is probably due to the dimin-

Effect of nature of organic solvents on polycondensation in emulsion

1279

ished part played by homogeneous hydrolysis, i.e. the hydrolysis taking place in the volume of the organic phase.

(/

J 6

zb

'

3b

20

302-~"

FIG. 4. X-ray pictures of PDDIA samples obtained by: a--emulsion polycondensation; 1,2--in MTsH; 3,4--in TsH; 5,6--in BN; b--polycondensation in solution: 1,2--in MTsH: 3,4--in TsH; 5--in BN. It is seen from the data in Table 5 that the rate of hydrolysis is higher in the presence of accepters. For example, in the systems based on Tstt there is 84-88% saponification of IAD; the corresponding figures for MTstt and BN are 85-92 and 51-63% respectively. The effect of the nature of the accepter varies according to the system: in systems containing TsH and MTsH the maxim u m degree of hydrolysis is observed in the presence of NaOH (89 and 92% respectively), while in the case of systems based on BN the degree of hydrolysis is highest in the presence of Na~C03. This cannot be accounted for without further investigation, but we m a y assume that the very slight but definite solubility of the accepter in the organic phase could be an important factor in the case in question. Note that the system containing MTsH has the highest degree of hydrolysis, although the content of water in the organic phase is less than in the systems containing TsH. The data in Table 5 show that IAD and TAD are saponified to about the same extent under identical conditions. Comparing the data in Table 5 with the molecular weights (~/log) for P D D I A obtained in emulsion systems based on TsH, ~ T s H and BN (Table 1) we conclude that hydrolysis is not always the main factor determining termination in the

1280

L. B. SOKOLOV et al.

emulsion polycondensation. Certainly the polyamide having the highest molecular weight is obtained under precisely those conditions that are most favourable to hydrolysis, i.e. in the system based on MTsH. From this standpoint it is inter-

I

~g

20

30~"

FIO. 5. X - r a y pictures of P D O I A samples obtained by: 1,2--polycondensation in TsH solution (with T E A as HC1 acceptor); 3,4--emulsion polycondensation in system T s H - w a t e r Na2COs.

esting that in the system TsH-acetone-water-Na2CO ~ (initial content of acetone 60%) PDOIA is obtained with ~iog~0.84, which is a lot higher than the corresponding value of 0.28 for the system TsH-acetone-water-Na2C03, though the degree of IAD hydrolysis for these systems is 54 and 33~/o respectively. It i~ also interesting that the hydrolysis takes place much more rapidly in the emulsion systems than in the interfacial ones. Whereas 55~o of the IAD is hydrolysed in 10 min in the system TsH-water, in the interracial system benzene-water no more than 0.51% is hydrolysed in 15 min [8]. This is in good agreement with the inappreciable amount of water in the organic phase of the interracial systems: it is only 0.008% for the system CC14-water. The rate of hydrolysis in the presence of aeceptors is also much higher in emulsion systems than in interfacial ones: 39.70/0 of the IAD is saponified in 30 rain in the presence of an equimolar amount of KOH in the system benzene-water [8]. Nevertheless the molecular weights of the aromatic polyamides obtained in the emulsion systems are much higher than in the interracial ones. In H2SO 4 the intrinsic viscosity of P m P I A obtained in the system CC14-water is only 0.3, while in the emulsion system THF-water-Na2CO 3 (water content in organic phase--~38%) it is 1.5-2.0 [9]. Taking all these factors into consideration it follows that in two-phase systems hydrolysis is not always responsible for the formation of low molecular weight polymers.

E f f e c t o f n a t u r e o f organic s o l v e n t s o n p o l y c o n d e n s a t i o n in e m u l s i o n

1281

Interrelation between the nature of the organic solvent, processes of precipitation and structural ordering, and the molecular weight of polymers. We know that polymers with one or other type of structure are obtained according to the conTABLE 6.

PROPERTIES

OF

PmPIA

SAMPLES COMPARED

WITH

THE

AMORPHOUS

STRUCTURES

(Curves 1 a n d 2 in Fig. 3) Sample

Properties 1

Solubility in d i m e t h y l f o r m a m i d e , ° o ( t r a n s l u c e n c y o f 5 % solution) H e a t of dissolution, cal/g D e f o r m a t i o n in t h e m o m e c h a n i c a l tests, %; 320 ° * A b i l i t y to flow t h r o u g h capillary 3 m m in dia. a t 320 ° *

~9O 37 # ~50 Flows o u t u n d e r a p r e s s u r e of 100 k g / c m

2

32 ~7 D o e s n o t flow o u t under a pressure of 1000 k g / c m ~

* Taken from [11]

ditions of separation from solution. In the case of slow precipitation the polymer will have a high degree of ordering, and it will be amorphous where there is rapid precipitation [10].When the synthesis is conducted in organic solvents such as 1KTsH, TsH and :BN there is practically no real increase in the molecular weight of the polymer after its precipitation from solution (emulsion) under normal conditions, and in view of this we would assume that the molecular weight of the polymer synthesized in a nonsolvent will be determined by the ratio of the rates of propagation and precipitation vp/Vprec.On the other hand Vprec and the rate of ordering are interrelated, as also is the ordering capacity of the structure. Ordering processes are particularly important when the polyeondensation is accompanied by polymer precipitation, and this is so because even a slight difference in the ordering of polymers such as aromatic polyamides gives rise to marked changes in their properties, including their solubility. Figure 3 shows X-ray pictures of three samples of P m P I A with different degrees of ordering. The difference in samples 1 and 2 is inconsiderable but their properties (Table 6) are very dissimilar. It is interesting to compare the structure of polyamides obtained by polycondensation in emulsion and in solution accompanied by polymer precipitation, as the polymer is formed in a nonsolvent medium. Figure 4a and b shows X-ray pictures of P D D I A samples obtained in emulsion systems based on ~ T s H , TsH, BN (a) and in solution (b), and here samples of approximately equal moleular weight were investigated so that this factor could be neglected, i t is seen from the Figure that generally speaking the degree of ordering increases in the order MTsH, TsIt, BN in emulsion and in solution, and moreover the polyamides obtained in solution have more ordered structures compared with those produced

1282

L . B . SOXOLOVet al.

in an emulsion of the same organic solvent. However the opposite effect is also seen: the P D O I A obtained b y emulsion polycondensation (Fig. 5) has a higher degree of ordering. T A B L E 7. CRYSTALLIZABILITY IN RELATION TO EFFICIENCY OF POLYCONDENSATION IN EMULSION

AND IN SOLUTION

Starting materials diamino

acid chloride

H,N--¢--NH~ IsN-- "/ ~

CIOC--¢--COC1

Ditto CIOC--C~/--COCI

I fllo~ of polymer, Crystalobtained Organic lizabilisolvent' ty* in emul- in solusion tion

++

TsH

1-27"

0.55*

+

TsH

1"98"

1.44"

+++

TsH

0.36*

0"78*

+++

TsH

0.64

0.89

TsH

1"99

0.96

Ditto

oloc-<-o-<-5-coo

H2N--¢--NHz

Ditto

H . N - - ~ - - ~ / 2 ~ _ -NH.

CIOC--[/~ --COCI

+++

TsH

0"49*

1"09"

Ditto

+++

MTsH

1.11"

0.71"

+++

BN

1-07"

2.62*

+++

THF

0.28

+++

THF

0.30

CHs

+

CHa

Ditto

HzN--I~--NHa C10C--<_~/--COCI

I

-

I

Qualitative estimate of crystallizability: + small; -b + medium; + + + high. * According to data in reference [4].

The Vp/Vpree ratio will be higher on changing to a good solvent, and this is seen in the polycondensation in solution accompanied by polymer precipitation, in the order MTsH, TsH, B N (synthesis of PDDIA), since the rate of precipitation Vprce from a good solvent will be lower. I t is to be expected that this ratio will be reduced on increasing the concentration of monomers, since more rapid polymer precipitation is observed in concentrated solutions [10]. The molecular weight (~/log) and the degree of ordering of P D O I A were studied in relation to the monomer concentration in emulsion polycondensation in the system T s H water-Na~COa and in TsH solution. Figure 6 shows plots of %og versus monomer concentration, and the X-ray pictures of the corresponding polyamides are shown in Fig. 7. It will be seen from Fig. 6 that 0.15 mole/1, is the optimum concentration of monomers for both methods of polycondensation. An increase or reduction in this concentration is reflected in lower molecular weight. Figure 7

Effect of nature of organic solvents on polyeondensation in emulsion

1283

shows t h a t polymers with more ordered structures are obtained with a higher concentration of the initial substances, i.e. the growth of the maeromolecules is limited by precipitation through structural ordering. f'T 1"0

°7 I

i

0

I

I

~#

o'3

c, mole/l. FIG. 6. Molecular weight (~log) of PDOIA vs. monomer concentration: 1--polyeondensation in TsH solution (TEA); 2--emulsion polycondensation in system TsH-water-Na=COs. Apparently the rate of precipitation depends not only on the nature of the organic solvent: the nature of the polymer is also quite an important factor in this connection, and the rate is influenced to some extent by the ordering capacity of the polymer.

I

I

ZO

I

I

JO

20 °

FIG. 7. X-ray pictures of PDOIA samples obtained with different concentrations of the initial substances (mole/1.): •,•'--0'07; 2,2'--0.15; 3,3'--0.3; 4,4'--0'6; 1-4--in emulsion system TsH-water-Na=COa; 1'-4"--in TsH solution (TEA). I t was shown in [4] t h a t some high molecular weight aromatic polyamides are obtained by emulsion polycondensation, and others by polycondensation in solution accompanied by polymer precipitation. The data in Table 7 certainly

1284

L.B.

So]~oLov et al.

show that the efficiency of one or other method of polycondensation may be related to the structural ordering capacity of the polymer. All the polyamides possessing crystallizability, i.e. those liable to more rapid precipitation, are obtained with high molecular weights by polycondensation in solution accompanied by polymer precipitation. The exception is PDDIA obtained in MTstt solution, in which case the molecular weight is lower than in the case of emulsion polycondensation. EXPERIMENTAL* Polyamides were synthesized b y the method described in [4]. Determination of ajfinity of solvent for polymer. The initial PDDTA was obtained b y precipitation with water from a 2 % solution of the polyamido (sample with tho~= 1.06) in DMAA containing 5% LiCI, while stirring rapidly. Crystalline P D D I A was obtained b y slowly adding water to the polymer solution [10]. Samples of the initial polymer were kept in the organic solvents under investigation for 24 hr, after which they were filtered, carefully washed with hot water, and dried at 100-110 °. The structural investigations were made with a URS-50IM diffractometer with filtered CuK~-radiation. The water content in th0 organic solvents (organic phase) was determined b y titration using the standard Fischer solution. Pyridine was used as solvent [12] to suppress possible side reactions. The m a x i m u m relative error a m o u n t e d to _+4%. Hydrolysis of acid chlorides. The degree of hydrolysis of acid chlorides in the absence of accepters was determined b y a method similar to the one described in [8]. A solution of the acid chloride (cone. 0.3 mole/1.) in the solvent being investigated was added, with stirring, to the corresponding aqueous solutions. The stirring was discontinued after 10 minutes, and the reaction mixture was transferred to a separating funnel, whereupon the aqueous phase was separated, and the content of I-IC1 in t h e aqueous phase was determined b y titration with 0.1 ~ K O H . I t was found b y means of reference tests t h a t the resulting HC1 is practically all in the aqueous phase. I n a series of experiments with accepters the degree of hydrolysis was determined from the number of C1' ions in the aqueous phase. The ions were t i t r a t e d potentiometrically using a 0.1 ~¢ AgNO3 solution. The solubility and the heats of dissolution were determined for P m P I A following the procedure in [7]. The erystallizability of the polymer samples was determined b y keeping them for 30 min a t a temperature above the softening point, after which the polymer structure was studied b y diffractometry. Initial substances and solvents. Melting point of I A D 43.6°; TAD, 82°; diphenyloxidc4,4'-dicarboxylic acid chloride, 88°; DDO, 189 °, m- and p-phenylenediamines were of analytical purity; MTsH, TsH, BN and T E A were purified as in [4]. Acetonitrile was purified by repeated distillation over P,O 5 until there was no further coloration [13]. Acetone was dried over annealed CaC1, and distilled over IAD; CC14 and cyclohexane were distilled over P205, NaHCO,, Na2CO3 and N a O H of analytical purity.

CONCLUSIONS (1) A s t u d y h a s b e e n m a d e o f t h e e f f e c t o f t h e n a t u r e o f t h e o r g a n i c s o l v e n t on molecular weight in polycondensation in emulsion and in solution accompanied by polymer precipitation. It has been shown that in polycondensation in solution the molecular weight depends on the affinity of the organic solvent for the polymer, but no such relationship was found in the emulsion polycondensation. * S. A. Voronina and G. A. Kirsanova participated in the experimental p a r t of the investigation.

Effect of nature of organic solvents on polycondensation in emulsion

1285

(2) T h e presence of a certain a m o u n t of w a t e r in t h e organic p h a s e is a necess a r y condition for efficient emulsion p o l y c o n d e n s a t i o n . (3) A s t u d y has been m a d e of t h e effect of t h e n a t u r e of the organic s o l v e n t on t h e h y d r o l y s i s of isophthalic acid dichloride in emulsion s y s t e m s b a s e d on m e t h y l c y c l o h e x a n o n e , c y c l o h e x a n o n e a n d benzonitrile. I t has been s h o w n t h a t hydrolysis is n o t t h e reason for the f o r m a t i o n of low m o l e c u l a r weight poly-3,3'd i m e t h y l - 4 , 4 ' - d i p h e n y l i s o p h t h a l a m i d e in t h e s y s t e m s c y c l o h e x a n o n e - w a t e r accepter. (4) I t has been shown t h a t p r e c i p i t a t i o n m a y be the r e a s o n for t h e f o r m a t i o n of low molecular weight p r o d u c t s , p a r t i c u l a r l y w h e n it a c c o m p a n i e d b y s t r u c t u r a l ordering. (5) E m u l s i o n p o l y c o n d e n s a t i o n is a suitable m e t h o d of p r e p a r i n g p o l y a m i d e s t h a t are i n c a p a b l e of s t r u c t u r a l ordering. Translated by R. J. A. HE:~I)I~y REFERENCES

1. L. B. SOKOLOV, Polikondens. meted sint. polim. (Polycondensation as a Method of Synthesizing Polymers). p. 149, Izd. "Khimiya", 1966 2. P. V. MORGAN, Polymer Chemistry and Technology, No. 1, 86, 1964 3. V. V. KORSHAK, S. V. VINOGRADOVA and A. S. LEBEDEVA, Vysokomol. soyed. 2: 64, 1960; L. B. SOKOLOV and L. V. TURETSKII, Vysokomol. soyed. 2: 711, 1960 4. L. B. SOKOLOV and S. S. MEDVED, Vysokomol. soyed. B10: 514, 1968 5. L. MANDEL'KERN, Kristal. polim. (Crystallization of Polymers). p. 110, Izd. "Khimiya", 1966 6. V. M. SAVINOV and L. B. SOKOLOV, Vysokomol. soyed. 7: 772, 1965 7. V. D. GERASIMOV, L. B. SOKOLOV, V. M. SAVINOV, T. V. KUDIM, D. F. SOKOLOVA, A. G. USHAKOVA, G. A. KUZNETSOV and S. S. MEDVED', Vysokomol. soyed. AI0: 1971, 1968 8. V. V. KORSHAK, S. V. VINOGRADOVA, T. M. FRUNZE, A. S. LEBEDEVA and V. V. KURASHEV, Vysokomol. soyed. 3: 984, 1961 9. L. B. SOKOLOV and T. V. KUDIM, Dokl. AN SSSR 158: 113C, 1964 10. V. M. SAVINOV, G. A. KUZNETSOV, V. D. GERASIMOV and L. B. SOKOLOV, Vysokomol. soyed. B9: 590, 1967 11. U.S.S.R. Pat. 208936, 1965; Byull. izobret. No. 4, 93, 1968 12. J. MITCHELL and D. SMITH, Akvametriya (Aquametry). 154, Foreign Lit. Pub. House, 1952 13. A. WAISBERGER, E. PROSKAUER, J. RIDDIK and E. TUPS, Org. rastvor. (Organic Solvents). p. 419, Foreign Lit. Pub. House. 1958