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In the presence of water or catalysts giving off water, caprolactam is polymerized by several reaction mechanisms taking place simultaneously. It was investigated whether the formation of polyamide takes place according to a polycondensation or polyaddition mechanism in the presence of phosphoric acid. In order to prove the polycondensation mechanism, the formation at 250°C. of a mixed anhydride from the carboxylic acids and the orthophosphoric acid was studied. N‐phosphoryl aminocaproic acid has also been synthesized. No catalytic effect was exerted by this compound; on the basis of this fact it can be stated that in the case catalysis by orthophosphoric acid, the increase of the polyamide chain does not take place according to a polycondensation mechanism. The adduct of caprolactam and orthophosphoric acid is able to catalyze the polymerization of caprolactam. Polymerizations carried out at temperatures ranging from 170 to 200°C. proved that the acid—amide bond of the caprolactam ring is weakened by the phosphoric acid, thereby rendering possible the polymerization to take place at a lower temperature. At elevated temperatures (exceeding 160°C.), the ammonium salts of phosphoric acid undergo dissociation; thus, free orthophosphoric acid is always present in the mixture undergoing polymerization. Due to the dissociation at higher temperatures, the phosphoric acid yields a product having higher molecular weight than at lower temperatures. It has been established that the rate of polymerization is directly proportional to the square root of the molar concentration of the free orthophosphoric acid. The activation energy of the polymerization catalyzed by phosphoric acid was 46 kcal./mole.

Many investigations have recently been published on the role of crown compounds and cryptates in polymerization processes, but only few of them concerned cyclic siloxanes'*'). Depending on the hole size of these compounds, several metals and metal ions can be complexed by them due to the high polarizability and coordination capability of the oxygen atoms in the ring. The effect of the counter-ion in the polymerization step can well be studied by means of these derivatives.The present paper aims at the investigations of the effect of crown compounds as well as t'lat of the counter-ion in the anionicpolymerization. As a model, activated anionic polymerization of E-caprolactam (CL) was studied.The counter ions of the chosen activator system were Li', Na', and K'; the applied promoter was hexamethylenediisocyanate (HMDI) and octamethylcyclotetrasiloxane (D4) was used as crown compound (bp 175°C at 760 Torr). Experimental PartCL containing 1,5. lo-' M of activator in lactamate form (L) was produced by refluxing the mixture of CL with the calculated amount of sodium or potassium hydroxide at 160°C for 30min under reduced pressure (5 Torr). The system including lithium lactamate was prepared by addition of the indicated amount of metallic lithium to the molten CL at 140°C. The used crown compound was added to the molten mixture of CL and alkali lactamate in concentrations such that the counter-ion content was complexed to 0, 12,5, 25, and 50 percent-supposing a complexing ratio of 1:l. These compositions are marked with a, b, c, and d, respectively, in the Table and in the Figure. Glass vials, fit into the differential scanning calorimetry (DSC) instrument (Unirelax, Tetrahedron Ass., Inc.), were filled with a known amount of HMDI+CL adduct having a mole ratio of activator to promoter of 2: 1 in the ready-to-polymerize system.The mixture of CL with the activator and the crown compound was added very quickly into the above vial in molten form followed by vigorous shaking until the promoter adduct was dissolved. Then the vial was sealed and quenched by liquid nitrogen. This procedure should not take more than 1 min. The sealed vials were stored at -15°C till the DSC recording.DSC curves were recorded at a heating rate of 1 or 1,5"C/min. Results and DiscussionFig . 1 shows the DSC curves of the system containing Li' counter-ion. The thermogram recorded in the absence of D4 (see curve a on Fig. 1) exhibits only a slight effect refemng to the polymerization process. The product is actually a low-molecular-

The polymerization of caprolactam taking place in the presence of water has been investigated by a number of authors. On the basis of 11-ork by Wiloth,' Hermans,2 L I a t h e~,~ and Majury4 it is known that in the presence of water or of catalysts giving off water the polymerization of the caprolactam does not take place with a uniform reaction mechanism but with several reactions proceeding simultaneously. Compounds which give off water at the temperature of the polymerization, that is, at 256°C. are used as catalysts. Thus primarily hexamethylene-diammonium adipate (nylon salt) and aminocaproic acid are used. The acids and bases employed during the polymerizatjon exert only a slight catalytic effect; their role consists primarily of fixing the desired molecular weight.I n our work we investigated whether the phosphoric acid, besides its chain-closing effect, catalyzes the polymerization of the caprolactam. The water formed during the reaction 2H3PO4 HdP207 + H20 t,aking place at 250°C. is primarily expected to exert a catalytic effect. It was doubtful whether the l / l O O -l / 2 O O f l~ phosphoric acid, that is, a quantity sufficient only to stabilize the molecular weight, yields enough water for the polymerization at the velocity desirable for industrial purposes.The polymerizations were carried out in a boiler heated by diphenyl boiling at 256°C. The phosphoric acid was added to carefully distilled and recrystallized caprolactam. The polymerization was carried out under an atmosphere of purified and dried nitrogen gas. The progress of the polymerization was folloived by removing an aliquot from the polymerizing apparatus from time to time. The polymer samples were processed in the n-ay usual in the technicaI literature.The progress of the polymerization is shown in Figure 1. On the basis of the trend and shape of the curve it can be seeii that the phosphoric acid exerts a considerable catalytic effect.The correlation between conversion and time is shown in Table I. Careful examination of the character of the tabulated data and the per-'795

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