HCl acceptors in emulsion polyamidation with participation of aromatic reagents

HCI ACCEPTORS IN EMULSION POLYAMIDATION WITH PARTICIPATION OF AROMATIC REAGENTS*t L. B. SOKOLOV a n d T . V. KUDL~ Vladimirsk Research Institute of Synthetic Resins (Received 1 June 1964) F O R the m e t h o d of emulsion p o l y c o n d e n s a t i o n (polycondensation t a k i n g place in a n emulsion s y s t e m t h e phase of one o f t h e c o m p o n e n t s [1, 2]) to be applied t o reactions in which b y - p r o d u c t s such as h y d r o g e n chloride are separated, t h e s y s t e m m u s t include a h y d r o g e n chloride a c c e p t o r (alkali). As in t h e case o f interfacial p o l y c o n d e n s a t i o n , t h e n a t u r e a n d a m o u n t o f a c c e p t o r can be e x p e c t e d t o e x e r t a considerable influenc~ on t h e molecular weight o f t h e p r o d u c t p o l y m e r . B u t w i t h emulsion p o l y c o n d e n s a t i o n s this influence m a y be quite complicated, since t h e a c c e p t o r is n o t o n l y able t o affect t h e r a t e o f t h e side r e a c t i o n o f h y d r o lysis, b u t it also acts as a salting-out agent, altering such characteristics o f t h e emulsion system, as t h e relation o f t h e phases, surface tension a n d so on. W e h a v e studied t h e effect of t h e n a t u r e a n d a m o u n t o f HC1 acceptors on t h e molecular weight o f t h e p r o d u c t POlymer a n d o n certain characteristics o f t h e s y s t e m in t h e emulsion p o l y c o n d e n s a t i o n on m - p h e n y l e n e diamine (mP D A ) a n d isophthalyl dichloride (IDC) in t h e s y s t e m t e t r a h y d r o f u r a n - w a t e r acceptor. PROCEDURE

The experimental study of the nature and amount of aceeptor in emulsion polycondensa~ion was carried out as follows. The IDC was dissolved in tetrahydrofuran and added with constant stirring to an aqueous solution of m-PDA and accepter. Stirring was continued for 10 rain and the product polymer was filtered off, washed three times in hot water and dried. The characteristic viscosity was determined in concentrated HsSO4. Experimental conditions for the synthesis of the polyamide were as follows: IDC concentration in tetrahydrofuran (THF), 0.33 mol/l, m-PDA concentration (CDA)in water, 0"33 tool/1.; initial water : organic phase ratio, 1 : 1. As acceptors we used NasCO s, NaOH and NaOH with NaC1. When these component solutions are added an emulsion is formed and synthesis takes place in the latter. We therefore decided to determine some of the equilibrium characteristics of simulated emulsion systems, since the only difference between these and real ones is the absence of the dichloride. Special experiments had shown that the dichloride did not have any particular effect on the characteristics of the 2-phase system. The experiment with the simulated systems consisted in mixing 37.5 ml solution of diamine (CDA * Vysokomol. soyed. 7: No. 4, 634-637, 1965. t Communication II in the series "Polycondensation in emulsions".

700

HC1 accepters

701

0.33 reel/L) and various eone6ntrations of the different kinds of accepter with the same volume of THF. Layering started after mixing and the following oharacteristies were determined: 1) relation of the phases; 2) water concentration in the organic phase; 3) surface tension at the interface; 4) distribution coefficients of dlamine and accepter as between the organic and aqueous phases. The system was highly labile, which created difficulties in the experiment. The surface tension at the interface was determined by the Rebinder method modified for making measurements on the interface of two liquids [3]. The water content in the organic phase was determined by Fisher titration, and the accepter concentration in the same phase by potentiometrie titration. The m-PDA concentration in the pl~ase~ was determined by nitrogen coupling [4]. RESULTS AND DISCUSSION

The experimental results are set out in the Table and t he Figure.

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Molecular weight (viscosity) of the polymer as a function of the amount of accepter (in values equivalent to the liberated HCL) in the emulsion polyeondensation of m-phenylene diamine and isophthalyl chloride 1--NaOH, 2--NaiCOa, I'--NaOH +NaC1 (1.14 mo]/1.), 2'--NaOH+NaC1 (2.28 mol]l.). A--number of mols of accepter per 1 mol HC1. I t can be seen t h a t the molecular weight of the polymer is very low in systems with a small a m o u n t of accepter. This is probably because the a m o u n t of scceptor in these systems is less t h a n stoichiometric (accepter : HC1 ratio below 1 : 0.125 and is n o t enough completely t o remove bind the HC1. Besides this the phases are completely mixed. To find out the influence of these factors, experiments were performed in which, in one case a v e r y clearly defined interface was produced b y reducing the component concentrations, and in the other case there was none. T h e a m o u n t of accepter was the same in both (referred to the HC1 separated). The results were as follows: [~/]--0.99 in the two-phase systems; [q]=0.32 in the homogeneous system. I t is evident from these results t h a t the molecular weight of the polymer prepared in the two-phase system is considerably higher t h a n for t h a t in the homogenous system. This means t h a t an scceptor is not only necessary to corn-

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bine HC1 but also to act as a salting-out agent in order to create a two-phase emulsion system. We thus have further confirmation of the opinion expressed in [1, 2], namely, that the presence of a 2-phase emulsion system is necessary for successful synthesis of high polymers, since the degree hydrolysis is considerably diminished, both of the original chlorides and of the end chloride groups, due to the clear division of the reaction volume into neutralization and reaction zones. K 1 ~ 1, K ~ 1)*. It is evident from the Table that systems in which a high molecular polymer is formed satisfy the following requirement: K1=6.3 to 55-5, K~--~ 0.0005 to 0.064. As the salt content of the system rises (see Table and Figure), its concentration in the organic phase falls and up to a certain moment the molecular weight of the product polymer rises symbatically. This means that the homogenous hydrolysis of the chlorides in the organic phase has the greatest effect on the magnitude of the molecular weight (apart from the ratio of the components already noted in [1, 2]). For this reason, of course, we were unable to produce a high molecular weight polymer in any case where there was no interface. But it is evident from the results that the molecular weight of the polymer begins to fall when the aceeptor concentration is very high. This, of course, is due to the very high concentration of soda in the aqueous phase. (up to 1.85 mol/l.) and with the ever increasing role of heterogeneous chloride hydrolysis (on the emulsion interface). Attention is drawn to the tabulated data on the close dependence between the molecular weight (viscosity) of the polymer and nature of the acceptor. For exactly the same ~TaOH concentration the molecular weight of the polymer is much lower than with ~a~CO 3. It is evident from the figures, that where ~ a O H is used the diamine does not pass over sufficiently to the organic phase, but with high NaOH concentrations there is a considerable increase in the heterogeneous hydrolysis of the dichloride. Since total transfer of the amine to the organic phase must be a necessary condition for successful emulsion polycondensation, as observed already in [1, 2], it is reasonable to suppose that if the conditions for total transfer of the diamine can be created in systems with l~aOH, high molecular weight products should result. And indeed, the addition of NaC1 to a system with IqaOH (see Fig.) does considerably increase the molecular weight of the polymer. The diamine concentration of the organic phase rises considerably and this leads to a product polymer of high molecular weight. Typically, the polymer yield is 92-96~ in all the cases we studiedt, i.e. • K1

CD/Lin org. solvent "Km~ Csodain org. solvent CD.~in aqueous phase Cs~a in aqueous phase

t Yield 76-80% in some of the experiments was due to losses of low molecular products on separation of the polymer.

704

L. B. SOKOLOVand T. V. KuD~

it approximates t~ the theoretical. This makes a big distinction between the emulsion and interracial modifications of polycondensation, where quite high molecular weight products can be produced at low yield. The difference is due to the difference in mechanism of the two methods. In conclusion we note t h a t in emulsion polyeondensation the conditions in the reaction zone (pH for instance) are reasonably constant during the reaction time, due to the fact that the HC1 is completely withdrawn across the interface to the aqueous phase. This is of quite considerable advantage over the interfacial method, and over polycondensation in solution. CONCLUSIONS

(1) The effect of HC1 aeceptors, 1~a~C08, l~aOH, has been studied in the emulsion polycondensation of m-phenylene diamine and isophthalyl dichloride in the system tetrahydrofuran-water. (2) The nature and concentration of the aceeptor have been found to exert a considerable influence on the characteristics of the emulsion system, and through it, on the molecular weight of the polymer product. (3) It has been found that a condition for the preparation of a high molecular product in emulsion polycondensation is that the components of the reaction, and the acceptor, should be divided up between the emulsion phases, both as a result of the distribution coefficient, and because of the salting-out effect of the inorganic components of the emulsion. (4) Under certain conditions of emulsion polycondensation the molecular weight of the polymer begins to be affected b y the heterogeneous hydrolysis of the chloride on the interface. ~Tra~Zat~ by V. ALFORD REFERENCES

1. L. B. SOKOLOV and T. V. KUDIM, I)okl. Akad. l~auk SSSR 158, 1139, 1964 2. L. B. SOKOLOV, Vysokomol. soyed. 7: 601, 1965 3. L. A. KOZAROVITSKII, Sb. Fiz. -khim. osnovy protsessov pechataniya, Trudy NII OGIZ'a, issue 5, 1937 4. R. P. LASTOVSKII and Yu. I. VAINSHTEIN, Tekhn. analiz v proviz, prom. produktov i krasitelei. (Techn. Analysis in the Production of Dyes and Intermediates.) Goskhimizdat, 204, 1958