The mechanism of polymerization of ε‐aminocaprolactam catalyzed by phosphoric acid

Abstract

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

Cationic Ring Opening polymerization of ε-caprolactam by a Montmorillonite Clay Catalyst

“…This result shows the effect of Maghnite-H + as a cationic catalyst. Similar results are obtained by Belbachir et al [14,23,29] in the polymerization of ε-caprolactone by Maghnite-H + , which polymerizes only by cationic process [30].…”

“…The cationic polymerization of ε-caprolactam and its reaction mechanism has been studied for many years in the presence of cationic initiators [6][7][8][9][10][11]. Various strong protonic acids able to promote the polymerization of ε-caprolactam have been reported [12][13][14][15][16][17][18]. The separation of the initiators from the polymer is not always possible.…”

“…The novelty of this work is to propose a greener and more sustainable route in order to replace the hazardous acidic catalysts such as: H3PO4 [12,17] and HCl [18] by modified clay of our region (Maghnite-H + ) for the synthesis of polyamide 6, a new, non-toxic cationic catalyst for heterocyclic monomers [23], which is widely available, constitutes low costs and has excellent properties make it the subject of several research. The obtained results will be compared with those obtained previously with strong acids.…”