Thin-layer interfacial polycondensation using monomer aerosols

Polym~ ScienceU.S.S.R.Vol. 22, 1~'o.12, ]pp.8007-3013,1 9 8 0 Prated in Poland

0082-39501801128006-.07507,5010 O 1981PergamonPreu Ltd.

THIN-LAYER INTERFACIAL POLYCONDENSATION USING MONOMER AEROSOLS* L. B. SOKOLOV and V. B. IooNI~ All-Union Synthetic Resin Research Institute

(Received 1 October 1979) Polyeondensation regularities have been investigated in systems containing an aqueous solution of alipha~ic diarnines and aerosols of iso- and terephthalie acid dichlorides. I t is shown that the process takes place in thin layers of the latter at the air/amine solution interface (thin-layer interracial polycondensation) and results in high-molecular polyamides in good yields of up to 96~o. I t was found t h a t some regularities of thin-layer interfacial polycondensation (e.g. the temperature dependence of the logarithmic viscosity of the polymer) differ markedly from those of ordinary interfaeial polyeondcusation processes.

A novel method of interfacial polycondensation proposed in [1] envisages a process carried out in thin layers of reagents (thin-layer polycondensation). It was shown that some of the regularities observed for this method of polycondensation differ significantly from those associated with traditional iuterfacial polycondensation (in drops, with stirring) and result in higher molecular weight values and higher yields for the polymers obtained. Thin layers of the dichlorides (DIC) used in [1] were prepared under static conditions, utilizing drops of liquid flowing over the air/water interface. This method of thin-layer interfacial polycondensation is laborious and inconvenient, and is unsuitable both from the standpoint of efficient use of the method in question and from the point of view of investigating many of the regularities, of the latter. In this instance we investigated regularities of a dynamic variant (in flow) whereby the foregoing disadvantages are eliminated, and thin-layer interfaciaI polycondensation is carried out with one of the reagents (the carboxylic acid dichloride) in the form of an aerosol [2, 3]. Our investigation was carried out taking as an example the synthesis o f polyhexamethyleneisophthalamide (PHMIA) and polyhexamethylenetrephthalamide (PHMTA). The dynamic method of thin-layer interfacial polycondensation may be carried out by ensuring that drops of one of the monomers spread over the surface of a flowing gas-liquid system (bubbling, foaming conditions). This may be done by introducing small droplets of one of the monomers (the DIC) inta * Vysokomol. soycd. A22: No. 12, 2741-2746, 1980. 3007

3008

L . B . SoxoT.ov and V. B. Ioo~n~

a s t r e a m o f gas (or air) bubbled through an aqueous solution of the o t h e r m o n o m e r

(the diamine); in this way a thin layer of DIC is formed on the air bubble surface at the expense of drops flowing over the latter. I t is best to introduce DIC drops into the system together with air, i.e. in t h e form of an aerosol. I n this case the air flow needed to create an interface (air[ /diamine solution) over which the DIC is flowing m a y at the same time be used to produce small DIC droplets. Small droplets spread more rapidly and form the thinnest layers [4] at the amine solution/air interface. Stages occurring in this variant of thin-layer interfacial polycondensation are depicted in Fig. 1. This experimental method was used in the present instance, and is described in greater detail in the experimental section of the paper.

FIG. 1. Theoretical scheme of stages of thin-layer interfaeial polyeondensation using DIC aerosols: /--aerosol of DIC in diamine solution; 2--system after flow of DIC: 3--final stage of the system (stages 1 and 2 earmolbbe observed visually); a - aqueous solution of diamine, b--air (gas) bubble, c--DIC drops, d--thin layer of DIC, e--thin film of polymer.

Influence of the main factors. It was found that the logarithmic viscosity and the polyamide yields are insignificantly dependent on the monomer concentration (yields calculated on the dichlorides). The experimental results presented in Fig. 2 show that the process under study m a y result in a good yield of high-molecular polymer over a wide range of diamino concentrations in aqueous solutions, and with high diamine concentrations, which is of special importance from a technological standpoint. Some increase in the yield and logarithmic viscosity of PHMIA was noted in the concentration interval from 0.1-0.2 mole/1. However, attention is drawn to the distinctive behaviour of some diamines (e.g. piperazine) in the process under study (see Fig. 2b, curve 3): in the case of piperazine (compared with hexamehtylenediamine HMDA) the diamino concentration in aqueous solution has a more marked influence on the molecular weight of the resulting polyamide. This anomalous behaviour of piperazine is apparently due to anomalous properties of the latter compared with the other diamines under study, and, in particular, to its low surface reactivity. A change in the concentration of dicarbox~lic acid dichloride particles in the aerosol (Fig. 2c, d) leads to some increase in the MW and polymer yield if the concentration of dichloride particles in the aerosol is in the range (0.3-0.7) × × 10 -* mole]l, of gas. On increasing the concentration to 2× 10 -2 mole/1, the specific viscosity and polymer yield are monotonically reduced.

3009

Thin-layer interfacial polycondensation using monomer aerosol8

Similar relations were observed in the synthesis of the other polyamides, viz. polyhexamehtyleneadipamide and polyhezamethylenesebaeamide. The above-specified regularities are preserved on simultaneously changing both the diamine concentration in aqueous phase and the dichloride concentration in the aerosol: a high-molecular polyamide is obtained, with satisfactory yield, in the case of relatively high monomer concentrations (up to 1 mole/].). It should be noted that the molecular weight maximum corresponds to a noJtequimolar monomer ratio (Fig. 3a). The synthesis temperature (temperature of the aqueous diamine solutiun) has a marked effect on the MW and yield of the resulting polymers. ~100

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FIe. 2. Plots of the yield (a, c, e, g) and logarithmic viscosity (b, d, f, h) of P H M T A (1), P H M I A (2) and polypiperazinisophthalamide (3) vs. concentration of diamine in aqueous phase (a, b), vs. concentration of DIC in the aerosol (c, d), versus the synthesis temperature (e, f) and vs. consumption of compressed air in the ejector (g, h).

~010

L.B. SOKOLOVand V. B. IGoNn~

It is seen from the experimental results (Fig. 2e, f) that a marked increase hi the logarithmic viscosity and ,in the polyamide yield accompanies a rise in the synthesis temperature: if the temperature is raised from 20 to 98 ° the logarithmic viscosity of PHMIA is increased from 0.3 to 1.35 dl/g, while the logarithmic viscosity of PHMTA increases from 0.5 to 1.0 ml/g. In the synthesis of PHMIA the temperature influence is more marked than in the case of PHMTA. In the case under review the temperature dependence is related to the thinlayer character of the process: as the temperature rises, the dichloride layer thickness is reduced [1], whereupon the thin-layer character of the process is most clearly manifested. In addition the tempearute dependence could be partially due to increased swelling of the polymer in the aqueous medium: under the synthesis conditions the more swollen polymer remains in a "mobile" state for a longer period of time that apparently suffices for attainment of a high MW. The latter supposition is supported by the following data Wa

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Water absorption of PHMTA, ~o I 1 1I 525

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32

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It should be noted that the temperature dependence of the yield and of the MW of the polymer in the case of thin-layer interracial polycondensation is similar to the dependence reported in [5] for liquid-gas systems. We investigated the polymer yield and the logarithmic viscosity of the polyamides in relation to the gas (air) consumption. It appears from Fig. 2g that the polymer yield and the MW increase with increasing air consumption. Since increased air expenditure is accompanied by a reduction in the size of the concomitantly generated aerosol particles (Fig. 4) of the dichloride, we conclude that the polycondensation process is influenced by the dispersity of aerosol particles of the diearboxylic acid dichloride. r/1 n ,

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Fie. 3. Plots of t/lor-PHMIA (1) and PHMTA (2) vs. initial monomer ratio. Fro. 4. Dispersi~y of aerosol particles of IAD, the consumption of compressed air in the ejector (ma/hr) being: 1--0.5, 2--1.0, 3--2.0, 4--3.0.

Thin-layer interracial polycondonsation using monomer aerosols

3011

Thus it is essential that minimal-sized monomerie aerosols should be used so as to increase the logarithmic viscosity and the polyamide yields in t h o aerosol processes. TABLE

I. C O ~ L R I S O N

Indicators

o~ DIFFERENT TYPES OF POLYCONDENSATIOIq B[ETEROPHASE PROCESSES

Ordinary interracial polycondensation (in drops) [1] 50°

85°

Dynamic thin-layer polycondensation (with a DIC aerosol) 50°

85°

Static thin-layer polycondensation [1] 50°

1

85°

a

J?log, dl/g

Yield, %

0.46

33

0-24

33

0.7

84

1.12

90

0.68

74

i

I

1.02

83

Evidence substantiating the thin-layer character of the process. The most clear-cut evidence of the thin-layer character of the polycondensatioa involving use of a DIC aerosol is soon on comparing different varieties of interfacial polycondensation processes. Table 1 gives the experimental results for the dynamic thin-layer and interfacial as well as for a thin-layer process [1] carried out under identical conditions, including identical solvents. The P H M I A polymer prepared under static conditions with a drop of the isophthalic acid dichloride (IAD) flowing over the surface of an aqueous HMDA solution is characterized by a high yield and by a high logarithmic viscosity. T h e yield and logarithmic viscosity of the PHMIA increase as the synthesis temperature rises. At the same time the thin-layer character of the process is apparent on visual observation. Similar characteristics are typical for a dynamic thin-layer process involving the use of a dichloride aerosol. As may be seen from Table 1, characteristics of t h e latter process do not coincide with those of an ordinary process of interfacial polycondensation in drops (in equipment where provision is made for stirring). Further evidence substantiating the thin-layer character of the process comes to light in peculiarities of the mechanism some curves plotted for the logarithmic viscosity and yield versus various parameters of the process are flatter t h a n those obtained for the interracial process with stirring. This is seen particularly plainly in an analysis of the concentration dependences, owing to the fact t h a t in the case of the various changes (e.g. in the concentration of dichloride particles in the aerosol, or in the ratio of the monomers, etc.) the dichloride concentration at the point of contact with the diamine remains constant (100%). I t is known [61 that in the case of interracial polycondensation processes the most marked changes in the logarithmic viscosity and in the yield are observed on varying the monomer concentrations or monomer ratios, I n regard to the other monomer, the diamine t h a t is in aqueous phase, it was found in [7] t h a t it is adsorbed at the interphase, and thereby influences the polycondensation process. And certainly, as the diamine concentration in water changes during

3012

L. B. SOXOLOVand V. B. Iao~rs

the synthesis, the logarithmic viscosity and the yield remain constant as soon as the diamine concentration increases to the point where there is no longer a n y change in the adsorption of monomer at the interface accompanying a change in the monomer concentration. In the process under study it is seen that if the monomer concentrations are increased above a definite level the monomer ratios remain constant and are related to one monomer (the diearboxylie acid dichloride) spreading over t h e interface, and to adsorption of the other monomer (the diamine) on the interface. The thin-layer character of the process is further attested b y calculations of the dichloride film thickness on the H20 surface: if the concentration of t h e latter is 0.5 × 10 -4 mole/1, of air, it is found to be 500-700 A at a temperature of 85 °, which tallies with the results of direct measurements of DIC film thickness under static conditions (approximately 600 A). I t is evident from the main regularities of thin-layer polycondensation carried out in the manner described under dynamic conditions using monomer aerosols that the method is a general-purpose method that m a y be used for t h e preparation of a variety of polyamides (see Table 2). TABLE

2. M A I N P R O P E R T I E S OF POLYAMIDES P R E P A R E D

BY T H E H E T E R O P H A S E M E T H O I )

U S I N G MONOMERIC AEROSOL

Diamines Ethylenediaxaine Tetramethylenediamine Hcxamethylenediamine

Piperazine 2,2,4-trimethylhexamethylene. diamine

Dicarboxylic acid dichlorides (DIC) Isophthalic acid Terephthalic acid Glutaric acid Adipic acid Sebacic acid Isophthalic acid Terephthalic acid Diphenyloxide-4,4'-dicarboxylic acid Isophthalic acid Terephthalic acid Isophthalic Terephthalic

¥~ld,

Sof~oningpoint,. T,,oC 220 415

1"38 1"12

82 81 80 78 74 97 94

0.81

92

1.83

70 68

300 245 305

~log '

dl/g 1 "00 0"94 1 "00 1"28

0"73

0"98 0.67 0.52

185 260

82

78

The. process is a high-production one using this method under our laboratory conditions the synthesis was carried out under continuous conditions, the productivity being 0-5 kg of polymer per hour using a 0.8 1. reactor (approximately 3"5 t/year). An important feature of the method is the absence of any organic solvent, which means that stages of solvent regeneration are eliminated.

Thin-layer interfacial polycondensation using monomer aerosols

3013

The me~hod of synthesizing the polyamide~ is as follows: an aqueous solution of the alia. mine is fed continuously into a vertical reaction apparatus. The b o t t o m p a r t of the l a t t e r is fitted with an ejector device, whereby feeding of the dichloride into the aerosol into the a p p a r a t u s is effected. The dichloride melt is sucked into the ejector from a calibrated glass tank. Gas (or air), whereby the aerosol is generated, formed gas cavities or bubbles in the aqueous solution of the diamine. The dichloride aerosol located in these cavities reacts with the diamine to form polymer. The mother liquor containing polymer is drawn off continually through an aperture in the top p a r t of the apparatus. The polymer is filtered, washed with water, and dried. Logarithmic viscosities of the polyamides are based on the specific viscosities of 0"5~o polyamide solutions in concentrated sulphuric acid. The monomers used in the investigation. The diamines were ethylene diamine, tetramethylenediamine, hexamethylenediamine, piperazine and 2,2,4-trimethylhexamethylenediamine. These reagents were used without additional purification. The dicarboxylic acid dichlorides (isophthalic, terephthalic, diphenyloxide-4,4'-dicarboxylic, sebacic, adipic, glutaric acids) were of reagent grade and were used without further purification. The authors t h a n k V. Z. N'ikonov for heading the experimental p a r t of the investigation, a n d N. R. Reblzova for carrying out a series of measurements. Translated by R. J. A. HERNDY REFERENCES 1. L. B. SOKOLOV and V. B. IGONIN, Dold. A N SSSR 245: 860, 1979 2. V. Z. NIKONOV, V. B. IGONIN and L. B. SOKOLOV; U.S.S.R. Pat. 448734, 1972; Byull. izob., No. 40, 1974 3. V. B. IGONIN, V. Z. NLKONOV, V. M. SAVINOV, L. B. SOKOLOV and V. A. NIKIFOROV, Pat. 632765, 1976; Byull. izob., 1~o. 42, 1978 4. V. D. SUMM and Yu. V. GORYUNOV, Fiziko-khimicheskiye osnovy smaehivaniya i s r a s t a k a n i y a (Physieochemical Basis of Wetting and Flow). Izd. " K h i m i y a " , 1976 5. L. B. SOKOLOV, L. V. TURETSKII and L. L TUGOVA, Vysokomol. soyed. 4: 1817, 1962 (Not translated in Polymer Sci. U.S.S.R.) 6. L. B. SOKOLOV, Polikondensatsionnyi metod sinteza polimerov (Polycondensatior~ Method of Synthesizing Polymers), Izd. " K h i m y i a " , 1966 7. V. B. IGONIN, V. Z. NIKONOV and L. B. 8OKOLOV, Zh. fiz. khimii 9: 2341, 1978